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Flashcards in Arthroplasty Deck (106):

Options for this young (<50yo) patient with a painful right knee

  • Exhaust concervative treatment
    • PT, NSAIDS
    • off loading brace
    • Cortisone injections
  • Valgus producing tibial ostotomy 
    • Contraindications
      • Inflammatory arthritis
      • Less than 90 deg flexion
      • Flexion contracture > 10 deg
      • Ligament instability (varus thrust)
      • Lateral tibial subluxation > 1cm
      • Medial compartment bone loss
      • Lateral compartment joint space narrowing
    • Predictors of failure
      • Smoking
      • > 60
      • Varus > 10
      • Other arthritides
  • Closing wedge problems
    • Patella baja
    • Loss of posterior slope
  • Opening wedge
    • Nonunion
    • Loss of valgus correction


Contraindications to HTO

Inflammatory arthritis
Less than 90 deg flexion
Flexion contracture > 10 deg
Ligament instability (varus thrust)
Lateral tibial subluxation > 1cm
Medial compartment bone loss
Lateral compartment joint space narrowing


Predictors of failure of HTO

> 60
Varus > 10
Other arthritides


Options for this 65yo male with painful right knee?

  • Exhuast non-operative
    • ​PT, NSAIDS
    • cortisone injection
    • offloading brace
    • Cane, mobility aids
  • UKA vs HTO vs TKA
  • UKA benefit over HTO and TKA
    • Smaller incision
    • Better knee function
    • Shorter stay with less pain

  • Technique
    • Do not overcorrect - can cause early failure
    • Varus - correct to 1-5 deg of valgus
  • Contraindications
    • ACL deficiency (strongest)
    • fixed varus or valgus deformity > 10 degrees
    • restricted motion
      • < 90° of flexion
      • fixed flexion contracture of > 10°
    • joint subluxation of 5 mm or greater
    • arthrosis of the additional compartment
      • modest Outerbridge Stage II chondromalcia of patella is acceptable
    • non-osteoarthritis arthritis
    • younger high activity patients and heavy laborers
    • overweight patients (> 90 kg)
  • Selection criteria
    • Pain must be localized to the compartment being replaced
    • Anterior knee pain means patellofemoral disease
    • Global pain means tricompartmental disease
  • Complications
    • Stress fractures
      • best visualized on bone scan
      • Usually on the tibial side
    • Tibial component collapse
      • poor mechanical properties of the bone
    • Failure
      • Overcorreciton
  • Undercorrection
  • Fixed-bearing (loosening)
  • Mobile bearing (diseae progression)
  • Patellar impingment (requires revision to TKA)


Normal alignment of the knee

Lateral proximal femoral angle: 90 degrees

Mechanical Lateral distal femoral angle: 88 degrees

Anatomic Lateral distal femoral angle: 81 degrees

Medial proximal tibial angle: 87 degrees
Lateral distal tibial angle: 89 degrees



What is this depicting and what are your considerations when measuring the deformity?

CORA - center of rotation of angulation

  • Draw a line threw the axis of the distal and proximal end
  • If there is only angulation - will occur at the apex of deformity
  • If there is combined translation - will occur at a distance equal to the amount of translation deformity
  • If angulation is seen on both AP and lateral, the true angulation will be larger than that seen on either XR
  • When you don't see angulation in one plane, but you do on the other - this is the true angular deformity


What is your appraoch to this patient?

  • History
    • Take a complete and ample history
    • Pain, functional issues, issues in other joints
    • Previous surgeries, trauma
    • PMHx, meds, all
  • Physical
    • Look
      • Gait, measure alignment and deformity
    • Feel
      • Assess stability of the hip, knee, ankle/foot
    • Move
      • ROM, contractures
    • Full NV exam
  • Imaging
    • Radiographs - full length standing AP/Lat
  • Indications for surgery
    • Ligamentous laxity on the concave side
    • LLD > 2cm
    • Uniconylar OA of the knee
    • Inability to place the foot in a plantigrade position
  • Conservative
    • Unloading brace
    • Shoe lift/orthoses
    • Appropriate analgesia
  • Considerations
    • Healing potential
      • Should be done in an area with better healing potential
      • Can accept some translation as long as the deformity is anticipated
    • Leg length discrepancy - affected by both closing/opening and varus/valgus, the affect is combined
    • Closing wedge can relatively lengthen ligaments and tendons
    • Opening wedge with lengthen = half the base of the triangle
  • Varus correction will produce lengthening
    • This will decrease as you go more distal
  • Valgus produces shortening​


Technical goals of TKA

  • restore mechanical alignment (mechanical alignment of 0°)
  • restore joint line ( allows proper function of preserved ligaments. e.g., pcl)
  • balanced ligaments (correct flexion and extension gaps)
  • maintain normal Q angle (ensures proper patellar femoral tacking)


You are planning a TKA for this patient. What are the order of releases

  • osteophytes
  • deep MCL  (usually osteophytes and deep MCL is sufficient release)
  • Posteromedial corner
    • Semimembranosus
    • capsule
    • superfical MCL
      • can find as it blends into pes anserine complex
      • can not completely release or will have valgus instability (requires constrained prosthesis). Therefore perform subperiosteal elevation only
      • Differential release: performed with two component of superficial MCL
        • posterior oblique portion is tight in extension (release if tight in extension)
        • anterior portion is tight in flexion (release if tight in flexion)
  • PCL


Order of release for a flexion contracture

  • Order of posterior release
    • osteophytes
    • posterior capsule
    • gastronemius muscles (medial and lateral)
  • You do not want to address by removing too much tibia
  • will change joint line and lead to patella alta
  • Performed with the knee flexed so there is less risk to the popliteal artery


Important considerations for planning your TKA cuts


  • uses intramedullary guide, if can't get this then use CT guided (post DFVO, trauma etc)
  • Distal femur valgus cut (5-7° from AAF )
    • jig measures 6 degrees from femoral guide (anatomic axis)
    • will vary if people are very tall (VCA < 5°) or very short (VCA > 7°)
  • Posterior referencing with femoral cut
    • 3 deg ER (normal DR is 3 deg IR)
    • otherwise will internally rotate your component
    • should be parallel to interchondylar axis 
    • be careful with hypoplasia of the lateral femoral condyle, you can put the prosthesis into IR with a posterior reference system


  • Cut should be perpendicular to mechanical axis
  • Can use intramedullary, unless there is deformity then need to use extramedullary


This patient comes in with knee pain. What is the most common complications of TKA?  How can you prevent it?

  • Abnormal patellar tracking, although not the most serious, is the most common complication of TKA.
  • The most important variable in proper patellar tracking is preservation of a normal Q angle (11 +/- 7°)
    • the Q angle is defined as angle between axis of extensor mechanism (ASIS to center of patella) and axis of patellar tendon(center of patella to tibial tuberosity)
  • Any increase in the Q angle will lead to increased lateral subluxation forces on the patella relative to the trochlear groove, which can lead to pain and mechanical symptoms, accelerated wear, and even dislocation.
  • Common errors include:
    • internal rotation of the femoral prosthesis
    • medialization of the femoral component
    • internal rotation of the tibial prosthesis
    • placing the patellar prosthesis lateral on the patella


Where should the joint line be in TKA?   What problems can you run into if you move it

  • Normal joint line
    • 1 cm above fibula
    • ​​2 fingerbreaths about tibial tuberosity
  • elevating the joint line (> 8mm leads to motion problems) and can lead to
    • mid-flexion instability
    • patellofemoral tracking problems
    • an "equivalent" to patella baja
  • lowering joint line
    • lack of full extension
    • flexion instability


Saggital balancing.  Go. All of it. You have 30 sec.


You are planning a TKA on this patient.  What is your order of release.  What are some important considerations?

  • Classification
    • Stage 1 - not correctable
    • Stage 2 - > 10 deg, not correctable
    • Stage 3 - severe deformity, possibly incompetent MCL, severe bone loss
  • Order of Release
    • osteophytes
    • lateral capsule
    • iliotibial band if tight in extension (release if tight in extension)
      • with Z-plasy or release off Gerdy's tubercle
    • popliteus if tight in flexion (release if tight in flexion
    • for severe deformities release both the iliotibial band and the popliteus
    • LCL  
      • some authors prefer to release this structure first if tight in both flexion and extension
      • others prefer this should be the last structure to release, if you need to release it consider of constrained prosthesis
  • Considerations
    • ​Coronal balancing - older patient can use CCK, younger patient want to take less bone, but still want to do a primary knee
    • peroneal nerve palsy


You do a TKA on this patient and surprise! He gets a peronal nerve palsy.  What are some risk factors? How do you treat?


  • Prognosis
    • most resovle in 3 months
  • Risk Factors
    •  use of epidural anesthesia; 
    •  previous spinal surgery (double crush); 
    •  valgus knee deformity 
    •  flexion contracture more than 20 deg
    • abarent retractors
    • pre-op neuropathy
  • Immediate
    • take of dressing
    • flex the knee
    • throrough documentation of physical exam
  • Post-op
    • AFO
    • PT for ROM
    • EMG with-in one month
  • At 3 months
    • Repeat EMG for improvement
    • Decompression with neuroloysis
      • 4 cm proximal 
      • adherence to fibular head
      • 7-15 cm distal to fibular head


Amount of antibiotics to put in antibiotic cement

  • Need to keep under 2g/40g of cement to preserve mechanical function
  • Safe loading dose
    • Vanco - 10.5g
    • Gent - 12.5g (although some report lower - 2g)
  • Masri recommends 3.6g tobra and 1g vanc per 40 mg
  • Powder is poured into liquid cement, vacum is not used - keeps porosity high to help with elution of cement


What's the most important factor in post-op TKA ROM?

Pre-op ROM


Pros and Cons of a CR knee 

  • Most common, relies on native PCL
  • Bone conserving
  • More consistent joint line preservation
  • Proprioceptive feedback
  • Disadvantages
    • Loss of PCL will lead to instability and failure
      • Tight PCL will cause tightness in flexion and cause lift-off of component
      • Excessive resection will cause failure from repetitive subluxation
      • Instability, pain, buckling
    • Harder to balance
      • Avoid in varus > 10, valgus > 15
    • PCL Rupture
      • Trauma
      • Osteolysis
    • Paradoxical movement - due to loss of ACL
      • Tibia slides forward under the femur instead of posteriorly
        Modern implants move center of rotation more posterior


Pros and cons of anteriorly stabilized knee

  • Anterior lip prevents femor from rolling forward
  • PE is highly congruent, there is no cam
  • Advantage
    • Bone conserving
    • Easier balancing
    • Operative versatility
    • Regulated kinematics
  • Disadvantage
    • Increased PE surface
    • Minimal rollback
    • Flexion gap laxity = instability and pain - requires treatment to assess this


Indications, pros and cons of a PS knee

  • Outcomes are the same for PS and CR knee
  • Indications
    • Previous patellectomy - weak extensor mechanism can lead to anterior dislocation
    • Inflammatory arthritis - leads to PCL rupture
    • varus >10
    • valgus >15
  • Advantages
    • Easier balancing
    • No sliding
    • better flexion
  • Disadvantages
    • Cam jump - if flexion gap is loose, knee will hyperextend, rotate and jump over post and dislocate
      • Reduce with sedation, 90 deg of flexion and anterior drawer maneuver
      • Avoid in knees with >130 flexion
      • Ultimately needs to be revised to address loose flexion gap
        • Overreleased poplitues with saw blade
        • Overrelease anterior MCL
        • Anterior translation femoral component
    • Patella Clunk
      • Scar tissue superior to patella gets cause in box
      • Flexion - Ex at 45 deg
      • Treatment - arthroscopic or mini open debridement
    • PE Wear from tibial post
      • Causes aseptic loosening
      • If need if hyperextended will cause impingement anteriorly and increase wear rate
      • Flexed femoral component, excess tibial slope, anterior translation
    • Additional bone removed
      • For post
      • Large flexion gap
        • Due to PCL removable
        • Need to take more distal femur to account for this
  • Beware joint line elevation with patella baja** Max 8mm 


Indications for the use of this prosthesis?

  • LCL/MCL attenuation or deficiency
  • Flexion gap laxity
  • *Can be used more in revision TKA, but consider at times for primary
    • ie; severe valgus knee

the patient depicted had instability following CR knee and PCL rupture



Indications for the following prosthesis

Constrained hinge with rotating platform

  • Tibia rotates with-in yoke to allow rotation during gait
    • Without rotation there was a high loosening rate
    • Intramedullary stem for high rotational loads
  • Indications
    • Global ligament deficiency
    • Hyperextension instability (polio or tumor resection)
    • Knee resection for tumor
    • Complete MCL (controversial)


Why was this prosthesis choosen?

Tumour Prosthesis

  • tumour
  • significant bone loss


You do this procedure on a healthy 65 yo male.  What are all the complications?

  • Femoral Notching
    • Jig is placed too low on the femur
    • Lowers load to failure (fracture)
    • In bending the fracture extend from the notch creating an oblique fracture
  • Peroneal Nerve Palsy
  • PCL deficiency  (in a CR knee)
    • Will become loose in flexion, knee will feel unstable and femur will start to slide forward
    • Will get anterior knee pain
    • Treat with revision to PC or CCK
  • Lateral Retinacular Release
  • Patella Fracture
  • Intra-operative MCL injury
    • Primary repair with 6 weeks NWB with full ROM (if young)
    • Recommended treatment is to covert to highly constrained prosthesis
  • Arthrofibrosis
  • Post-op Flexion Contracture
    • The most important factor of post-op range of motion is pre-op ROM
    • In a well balanced knee the gastroc is the cause of the flexion contracture
  • Severe extra-articular femoral deformity
    • Can do a combined osteotomy with TKA with long stem that goes past the osteotomy site
  • Osteolysis
    • Usually around 8-10 years
    • Gradual increase in effusion with mild warmth but no erythema
    • Normal lab results and aspiration
    • Most common place is the posterior femoral condyle


What is usually causing a flexion contracture post-op TKA



When do you usually see osteolysis in TKA and where do you get it?

8-10 years

posterior femoral condyle


You do the following procedure.  They come back at 6 weeks and a stiff knee.  How do you approach this?

  • Functional ROM
    • 90 degrees needed to go down stairs
    • 95 to get up from a chair
  • Factors to assess
    • Boney resection
    • patella baja/elevation of joint line
    • tibial slope (not enought)
    • posterior osteophytes
    • patient factors
  • Radiography
    • Assess joint line based on fibula and patella
    • Assess alignment of implants
    • presence of osteophytes
  • Treatment
    • depends on the surgeon, some will take them back if not to 90 by 6 weeks, can be done up to a year
    • Manipulation
      • usually at 6 weeks
      • Later manipulation as high rate of fracture
    • Scope
      • release adhesions, cement/loose bodies
    • Arthrotomy 
      • poly exchange, patellar exchange, posterior release, tuberosity transfer, quads snip
      • Not highly recommended, often fails with recurrent pain and stiffness
    • Revision TKA
      • tibial tuberosity osteotomy, V-Y plasty
      • address tibial slope, patellar height


TKA.  Patient can no longer extend their knee.  How do you approach this?

  • Can also occur with lowering of the joint line
  • Overview
    • patellar tendon rupture is a rare and devastating complication after TKA with an incidence reported ranging from 0.17% to 2.5%
    • Quadriceps tendon rupture extremely rare ~1%.
      • Higher risk with infection, multiple surgeries, hinged prosthesis
    • Patellar Fracture
      • Thickness <12mm
      • Lateral retinacular release (osteonecrosis)
        • Due to transection of superior genicular artery
      • Osteonecrosis
        • Theoretical risk with removal of fat pad, lateral release, quads turndown
        • Blood supply comes from the medial to lateral part of the knee
    • Can also be caused by maltracking or direct trauma
  • Quads or patellar tendon rupture
    • Overall very poor outcome
  • Treatment
    • Can treat conservatively if the component is solid and there is no extensor lag
    • Quads
      • Drill holes if no patella resurfacing
      • Suture anchors if there is less bone stalk
    • Patellar
      • Primary repair with drill holes or suture anchor does not do well
      • Component revision if there is enough bone, component resection if not
      • Allograft or autograft if there is significant extensor lag
      • Fresh frozen is the prefered choice
    • Use a detensioning wire (or mersiline tape) for 3 months


Considerations when deciding whether to resurface the patella

  • High clinical variability in practice
  • Complications 
    • patellar fracture
    • malailignment
  • Consequences
    • Anterior knee pain with higher revision rate
    • 50% re-operation rates and higher complication rates with no patellar resurfacing - at about 5 years outcomes become the same
  • Earlier designs had a high failure rate, newer designs have longer survivorship
  • Technique
    • Indicaitons to resurface
      • maliagnmnet
      • minimal wear
      • inflammatory disease
    • If you're not resurfacing use a more anatomic design
    • Patellar cut
      • Use the caliper before and after
      • Under resection leads to pain and a tight compartment
    • Over resection leads to fracture - max thinness is 12mm
    • Medial-superior placement is ideal
      • Helps to restore Q angle with fewer tracking complications
    • Lateral Release
    • complications
      • fracture
      • component dislocation
      • wear
      • infection


Diagnosis?  Causes? Treatment considerations in TKA?

Patella Baja

  • Introduction
    • A condition manifested by a shortened patellar tendon
    • Leads to limited flexion due to patellar impingement on the tibia in extremes of flexion
  • Causes
    • proximal tibial osteotomy   
    • tibial tubercle shift or transfer
    • proximal tibia previous trauma
  • Presentation
    • mechanical block to full flexion 
  • Management
    • Operative with TKA
      • lowering joint line
        • distal femoral augmentation and cutting off more proximal tibia
        • avoid bone cuts that raise the joint line (raising the joint line will effectively increase the patella baja deformity)
      • elevating patella 
        • use small patellar component and place superiorly
        • trim bone or polyethylene to reduce impingement
    • one option in severe deformity is to cut the patella but not to resurface it (this will reduce patellar impingement allowing for more knee flexion)


This patient comes into your clinic with a painful knee.  What is your approach and general priniciples?


  • take a complete history around the pain, duration, time pain free, instability, PMHx, smoking
    • assess for knee stability, contractures, neurological issues, vascular issues
    • previous inctions
    • patellar tracking
  • Get all previous OR notes
  • ESR, CRP, possible aspiration
  • Bone scan - fracture, infection
  • Imaging - AP, lateral WB views, full length standing
    • compare to previous, assess for further lysis
    • assess opposite knee
    • Look at lysis around each component
    • component alignment, shift
      • posterior sag tibia = PCL
    • full alignment of knee
  • Goals of revison surgery
    • extraction of components with minimal bone loss and destruction
    • restoration of bone deficiencies
    • restoration of joint line 
    • balance knee ligaments
    • stable revision implants
    • address patellar malalignment
    • soft tissue coverage
  • Exposure
    • Use most lateral incision with multiple incisions
    • Try to leave skin bridge 6cm if you can't use old incision
    • Release all adhesions and scar tissue
      • do not pull off the patellar tendon
    • If the patella cannot be everted safely
      • Quads snip - snip across the quads
        • No need to protect WB
        • 45 deg angle to arthrotomy
      • Patellar turndown - V-Y
        • Associated with weakness
        • Protect WB with extension brace for 6 weeks
      • Tubercle ostotomy
        • Less weakness but can't do if there is patellar baha
        • 2cm wide, 1cm thick, 6 cm long
        • start 1cm medial to tubercle with an osillating saw
        • finish laterally with an osteotome
        • stemed revision must bipass osteotomy
        • WBAT with ROMAT
  • Prothesis Extraction
    • Do with as little damage as possible
    • Contact rep for specific implant removal
      • ostotomes, punchs, slap hammer, clamps, saw, burr
    • Take poly out
    • Free femur with saw and osteotome
      • don't lever
      • remove with punch or slaphammer
    • Similar technique with the tibia
      • may need to cut the stem
      • osteotomy for exposure
    • Patella
      • can leave, or cut the pegs off and then drill them out
    • Clear cement, if you are re-cementing you can leave the cement
  • ​​Bone Loss
    • Cause
      • abrasion, infection, osetolysis, extraction
    • load sharing to the diaphysis (stem)
      • stem is cement often, unless you have such sever bone loss you need to go up to the diaphysis (not like a hip)
    • cavity defect filling
      • cement
        • for cavitary defect is < 1 cm
      • structural bone grafts
        • includes metal augments, or modular endoprosthetic devices 
        • indicated for segmental defect > 1cm​​​
  • ​​Appropriate implants
    • Tibia first, establish joint line
      • use contralateral films
      • 2cm above fibular head
    • hinged 
      • ​no ligamentous support
      • multiply revised
      • hyperextension seen in polio
      • tumor, infection
      • charcot (relative)
    • CCK/stem (constrained condylar knee)
      • ​MCL/LCL laxity
      • flexion gap
    • CR to PS or CCK
  • Soft tissue
    • Medial gastroc is the most reliable
    • Do not delay closure, should be done at the same time as revision


Complications associated with Revision TKA?

  • Pain
    • pain scores less favorable than primary TKR 
    • activity related pain can be expected for 6 months
  • Stiffness
  • Neurovascular problems
    • peroneal nerve subject to injury with correction of valgus and flexion deformity
  • Infection
  • Skin necrosis
    • prior scars should be incorporated into skin incision whenever possible
    • bloody supply to anterior knee is medially based, so lateral skin edge is more hypoxic 
    • if multiple previous incisions, use most lateral skin incision 
    • can use wound care, skin grafting, or muscle flap coverage (gastroc) for full thickness defects
  • Extensor mechanism disruption
    • can use extensor mechanism allograft using achilles tendon
    • Semi-T graft can be used to help augment
    • Can use this intra-op if you loose the tendon


Indicaitons, contraindications and optimal position


  • Indications
    • painful ankylosis after infection or trauma
    • neuropathic arthropathy
    • tumor resection
    • salvage for failed TKA (most common)
    • loss of extensor mechanism
  • Contraindications
    • absolute
      • active infection
    • relative
      • bilateral knee arthrodesis
      • contralateral leg amputation
      • significant bone loss
      • ipsilateral hip or ankle DJD
  • Optimal Position
    • 5-8° valgus
    • 0-10° of external rotation (match other leg)
    • 0-15° of flexion
    • some limb shortening advantageous for patient self-care


Options for fixation for the following?  Complications?

  • Fixation
    • Intramedullary rod fixation 
      • can be one long antegrade device or a two part device connected at the knee
      • patella can be left alone or incorporated into arthrodesis
    • External fixation 
      • must allow compression of arthrodesis site
      • done with unilateral external fixation, Ilizarov, or Taylor Spatial Frame
    • Plate fixation 
      • can be done alone in combination with intramedullary nailing
  • Complications
    • Nonunion
    • Infection
    • Low back pain
    • Ipsilateral hip degenerative changes
    • Contralateral knee degenerative changes
    • Fracture
    • supracondylar femur or proximal tibial metaphysis fractures


Indications and contraindications; Advantages and disadvantages

  • Indications
    • patients with advanced arthritis and good proximal femoral bone stock
    • three types of patients for whom hip resurfacing is indicated (Amstutz, et al)
      • patients with proximal femoral deformity making total hip arthroplasty difficult
      • patients with high risk of sepsis due to prior infection or immunosuppression
      • patients with a neuromuscular diagnosis
  • Contraindications
    • absolute
      • bone stock deficiency of the femoral head or neck (e.g., cystic degeneration of the femoral head)
        • >75% femoral head
      • abnormal acetabular anatomy (small)
        • Associated with acetabular loosening
    • relative
      • coxa vara
      • increased risk for neck fractures
      • significant leg length discrepencies (resurfacing does not allow for leg length corrections)
      • female gender (controversial)
  • Advantages
    • preservation of femoral bone stock
    • improved restoration of hip biomechanics with lower risk of limb length discrepancy
    • lower dislocation rate
    • rapid recovery
    • revision is easier than an intremedullary THA
    • better stability compared to standard small head (22- to 32-mm) THA
    • ability to engage in high demand activities
  • Disadvantages
    • lack of modularity with inability to adjust length or correct offset
    • requires larger exposure than conventional THA


Outcomes of hip resurfacing

  • variable outcome findings in the literature (79% to 98% success rate)
  • better results
    • young
    • larger males
    • excellent bone stock treated
    • osteoarthritis  better than for dysplasia or osteonecrosis
  • some case series have shown survival comparable to conventional THA, while others have reported higher rates of early revision
  • some products have been removed from the market due to early failure
  • more recent prospective trials have shown few differences between resurfacing and THA


Patient comes in one year following hip resurfacing for OA. Differential for associated complications.

  • Periprosthetic femoral neck fracture 
    • incidence of 0% to 4% (more common than in THA)
    • frequent cause for revision in acute post-operative period (<20 weeks)
    • mechanism thought to be related to osteonecrosis
    • risk factors:
      • notching of the femoral neck
      • osteoporotic bone
      • large areas of pre-existing osteonecrosis
      • femoral neck impingement (from malaligned acetabular component)
      • female sex
      • varus positioning of femoral component
      • presents as groin pain
    • treatment
      • convert to a THA
  • Implant loosening (aseptic)
    • early loosening of the cemented femoral resurfacing component
  • Heterotopic ossification
    • higher incidence of heterotopic ossification (from wider exposure)
  • Elevated metal ion levels in blood and urine from metal debris (unknown significance)
    • Metallosis
    • pseudotumour
    • ALVAL (Aseptic Lymphocytic Vasculitis Associated Lesions)
      • Can see this on biopsy
    • Treatment is to replace with a THA metal on poly


What are three ways to assess the rotation of your femoral component?

  • anteroposterior axis 
    • defined as a line running from the center of the trochlear groove to the top of the intercondylar notch
    • a line perpendicular to this defines the neutral rotational axis
  • transepicondylar axis 
    • defined as a line running from the medial and lateral epicondyles
    • the epicondylar axis is parallel to the tibial surface
    • A posterior femoral cut parallel to the epicondylar axis will create the appropriate rectangular flexion gap
  • posterior condylar axis   
    • defined as a line running across the tips of the two posterior condyles
    • this line is in ~ 3 degrees of internal rotation from the transepicondylar axis, the femoral prosthesis should be externally rotated 3 degrees from this axis to produce a rectangular flexion gap
    • if the lateral femoral condyle is hypoplastic, use of the posterior condylar axis may lead to internal rotation of the femoral component  


Deformities associated with CAM (clinical/anatomical - not radiographic)

decreased head-to-neck ratio
aspherical femoral head
decreased femoral offset
femoral neck retroversion 


Deformities associated with Pincer (clinical/anatomical - not radiographic)

anterosuperior acetabular rim overhang
acetabular retroversion
acetabular protrusio
coxa profunda (deep socket)


Radiological features of FAI

  • Technique
    • Hips in 15 deg IR with beam centered between symphysis and ASIS
    • Assess symmetry of obturator, tear drops; symphysis should be 1-2 cm from the coccyx
  • Findings
    • Overall
      • Tonnis grade - OA
      • Joint space < 2mm is a poor prognostic factor
      • Shenton's line
    • Acetabulum
      • CEA > 40, Tonnis angle < 0
      • Version; cross over sign,  ischial spine sign
      • Retroversion index > 33-50% are significant
      • Assess protrusio, coxa profunda
      • Posterior wall sign
    • Femoral side
      • Assess coxa vara
      • Sphericity and contour of femoral head - 'pistol grip deformity'
  • Dunn view
    • Alpha angle >50 (cam)
  • Cross-table lateral
    • Head neck off-set >8mm (cam)
  • false profile view 
    • to assess anterior coverage of the femoral head
    • standing position at an angle of 65° between the pelvis and the film 


What is the tonnis grade for arthritis

  • Grade 0 - no signs of OA
  • Grade 1 - sclerosis with minimal joint space narrowing
  • Grade 2 - small cysts in head or acetabulum with joint space narrowing
  • Grade 3 - large cysts in the head with obliteration of joint space and severe head deformation


Radiographic investigations for FAI or young hip


  • Differential
    • DDH (+/-cam)
    • FAI 
      • cam
      • pincer/retroversion
    • Residual deformity
      • SCFE
      • LCP
  • AP View
    • Technique
      • Hips in 15 deg IR with beam centered between symphysis and ASIS
      • Assess symmetry of obturator, tear drops; symphysis should be 1-2 cm from the coccyx
    • Findings
      • Tonnis grade - OA
      • Joint space < 2mm is a poor prognostic factor
      • Shenton's line
      • Acetabulum
        • CEA = 25-40
        • Tonnis angle 1-10
        • Version; cross over sign, ischial spine sign
          • Retroversion index > 33-50% are significant
        • Assess protrusio, coxa profunda
        • Posterior wall sign
      • Femoral side
        • Assess coxa vara/valgus
        • Sphericity and contour of femoral head - 'pistol grip deformity'
  • Dunn view at 45deg
    • Alpha angle >50 (cam)
  • Cross-table lateral
    • Head neck off-set >8mm (cam)
  • false profile view 
    • to assess anterior coverage of the femoral head
    • standing position at an angle of 65° between the pelvis and the film 
  • Von Rosen
    • Flexion, abduction, IR
    • Helps to assess femoral version
    • Mimics a true PAO
  • Adduction or abduction views
    • Can help assess the congruency of the joint
    • mimics a valgus osteotomy
  • CT
    • can be used as adjunct to assess for structural abnormalities
    • Drawback is radiation in a young population
  • MRI
    • best modality to evaluate for articular cartilage, and labral degeneration and tears
      • 63% sensitive, 71% specific
    • can assess anatomy of femoral head/neck junction abnormalities
    • More accurate to assess the alpha angle
    • Cam - debonding anterior superior lesion in the cartilage
      • "outside-in"
    • Pincer - anterior superior as well, but can be more global
      • Posterior rim lesions, or 'contrecoup' lesions, should be assessed
    • Used to look at the integrity of the cartilage
    • Not commonly used
  • Flouroscopic guide hip injection
    • 4-6ml of anesthetic under flouro guidance can help
    • Have patient assess pain before and after injection
    • Can be very helpful to determine if pain in intra-articular


Diagnosis?  Treatment Options?


  • Conservative
    • first line of treatment
    • NSAIDS, activity modification
  • arthroscopic osteochondroplasty of acetabular rim and/or femoral head reshaping
    • reserved for mild to moderate lesions without posterior involvement of the femoral head or neck
    • Can be done via scope or surgical dislocation (trochanteric slide)
      • Risk of osteotomy non-union
  • periacetabular osteotomy +/- a femoral osteotomy
    • Salter osteotomy (Ganz/Bernese)
      • Most commonly used, allows medialization of the hip joint that reduces hip reaction forces
      • Lateral rotatation, anterior rotation, with medialization of femoral head
      • indications
        • Pain or progressive limp
        • Adequate ROM
          • >90 deg flexion
          • >30 deg abduction
        • concentrically reduces hip/congruent joint
        • good joint space (tonnis < 2)
      • advantages
        • provides hyaline cartilage coverage
        • posterior column remains intact and patients can weight bear
        • Does not change pelvic shape in women of weight bearing age
        • preserves hip abductors
    • salvage pelvic osteotomy (chiari, shelf)
      • Not used as frequently due to improvements in THA
      • indications
        • unreduced hip
        • incongruous joint with obliterated joint space
        • Can confirm with an abduction view whether the hip is reducible
      • major goal of procedure
        • cover femoral head with fibrocartilage (NOT articular cartilage)
        • Will often need a graft to cover the head anteriorly
      • Drawback of shelf is that you are not medializing the joint
  • Femoral Osteotomy
    • Often needed when you don't get enough coverage of the head
    • Need to use flouro to decide where optimal position is
    • Don’t close the canal too much because it makes future THA difficult
  • Arthrodesis or resection arthroplasty
    • Options but not good ones for DDH
    • Resection arthroplasty might be better for patients with neuromuscular conditions
  • total hip arthroplasty (THA)
    • indications
      • treatment of last resort for those with severe arthritis
      • preferred treatment for older patients (>50) and those with advanced structural changes
      • in a patient with bilateral hip dysplasia, there are significant technical challenges that need to be addressed to ensure a successful total hip arthroplasty.


Indications and Contraindcations to doing a PAO?

  • Indications - For DDH
    • Pain or progressive limp
    • Adequate ROM
      • >90 deg flexion
      • >30 deg abduction
    • concentrically reduces hip/congruent joint
    • good joint space (tonnis < 2)
  • Contraindicaitons for FAI (reverse PAO)
    • Posterior-wall overcoverage
    • Tonnis > 2
    • Combined pincer/cam


Technique of a PAO

  • Smith-peterson
  • 4 cuts
    • anterior ischium below the acetabulum
    • superior pubic ramus
    • supra-acetabular ilium
    • posterior column (joining cut number one)
  • Re-approximate (for DDH)
    • Tilt laterally and anteriorly
      • Avoid excessive extension and retroversion
    • Rotate inwardly
    • Medialize
  • Fix with k-wires, assess ROM and position with flouro
  • Secrure with 4.5 cannulated screws
  • Arthrotomy
    • Assess head-neck junction and perform osteochondroplasty as necessary


Complications associated with PAO

  • Most important factor affecting complications is the surgeons experience
  • Nerve dysfunction - most common
    • LFCN
    • Less commonly femoral, pudendal and sciatic
  • Vascular - related to ilioiguinal appraoch
  • Non-union
    • Usually the pubis, less commonly the ilium/ishium
    • Can be treated with bone grafting
  • Impingement
  • High incidence of HO
    • Give indomethecin
  • Femoral instability
    • If you don't do associated femoral ostotomy can get recurrence of instability
  • Osteolysis
    • Can get osteolysis with excessive stripping
  • Inferior gluteal artery is the one to be concerned about, comes out below the piriformis


Technique for a femoral osteotomy

  • PFO can be altered as per what you need
    • DDH - varus +/- ER
    • SCFE (Southwick) - flexion, abduction, IR
    • Femoral neck nonunion - southwick
  • Place a k-wire at the level of the ostotomy site
  • Place a k-wire where the blade should go
    • This will depend on the angle of the plate
    • Can also assess whether you will need flex or ex at this time
    • This should be at least 1.5cm away from k-wire1 
  • 3rd kwire or chisel is used to determine the length of the blade
  • Use a chisel to make the blade cut along wire number 2
  • Mark your version with a k-wire
  • Osteotomize the femur at Kwire 1
  • Remove a wedge if you need to
  • Remove the chisel
  • Place the balde, watch this under flouro
  • Secure the blade to the proximal fragment
  • Secure the plate to the distal fragement
  • Check the position on flouro
  • Post-op
    • Start abduction at 6 weeks
    • TTWB until 8-12 weeks
    • Plate may be removed at 1-2 years
  • Complications are technical
    • Blade protrusion into joint
    • Fragmentation of distal fragment
    • Nonunion
  • Outcome
    • 25% conversion to THA at 15 years
    • Improved outcomes with less OA


Young hip physical exam

  • ROM
    • Test in IR (20) ER (45) in seated position
    • Test AD (20), AB (45) and flexion (120) in supine
  • Gait
    • LLD
    • Trendelenberg
    • Weak adductors
      • DDH, anything that medializes the head
    • Pelvic obliquity
  • Arthritis
    • Anterior impingement
    • Roll test - tight and stiff
    • Patrick test - same as FABER with pain anteriorly
    • Stinchfeild test - Pain with resisted flexion
  • Trendelenberg Test
  • Hip contracture
    • Hyperextension of the lumbar spine
    • During gait lumbar will extend to compensate
  • Tompson test
    • Flex up both hips to neutralize spine
    • Then extend each hip indivicually
  • Rotation of hip is more accurately tested in prone
  • FADIR - anterior impingement
    • Flexion, adduction and IR
    • Will cause pain with anterior impingment
    • Look for SI pain
  • Anterior Apprehension
    • Extension with ER
  • Psoas snapping
    • Passive flexion to 90
    • ER with abduction extend the leg, the tendon will snap
  • Ober test
    • Patient in lateral
    • Abduct the hip with the knee flexed extend the hip
    • Pulls the IT band behind the GT
    • Tight IT - hip won't adduct past neutral
    • Tight glut med - delay with hip in neutral


Approach to residual LCP

  • Residual deformity
    • Coxa magna
    • Asphericity
    • Coxa plana
    • Short neck
    • Acetabulum remodels and becomes dysplastic
  • Usually requires
    • Osteochondroplasty, neck lengthening, distal trochanteric transfer
  • Approaches
    • Anterior approach combined with lateral for PFO
      • Can be extended up to do an acetabular osteotomy if they have instability
    • Surgical dislocation to do everything
  • If they need both POA and PFO you can stage it or do it at the same time


Indications and contraindications to hip arthroscopy

  • Indications
    • FAI
    • labral tears
    • AVN (diagnosis and staging)
    • loose bodies
    • synovial disease
    • chondral injuries
    • ligamentum teres injuries
    • snapping hip
    • mechanical symptoms
    • impinging osteophytes
  • Contraindications
    • advanced DJD
    • hip ankylosis
    • joint contracture
    • severe osteoporotic bone
    • significant protrusio acetabuli


Portals for hip arthroscopy

  • Anterolateral portal 
    • function
      • primary viewing portal
      • anterolateral hip joint access
    • location and technique
      • located 2 cm anterior and 2cm superior to anterosuperior border of greater trochanter
      • typically established first under flouroscopic guidance
  • Posterolateral portal
    • function
      • posterior hip joint access
    • location and technique
      • located 2cm posterior to the tip of the greater trochanter
  • Anterior portal
    • function
      • anterior hip joint access
    • location and technique
      • located at intersection between
        • superior ridge of greater trochanter
        • ASIS
      • flexion and internal rotation of hip loosens capsule and assists scope insertion


Complications of hip arthroscopy

  • Direct injuries
    • can occur from scope or cannula placement
    • most commonly reported complication
      • chondral injuries
  • Neurovascular injury
    • traction related
    • pudendal nerve injury
      • most common neurovascular complication
      • due to traction post in groin for traction
      • neuropraxia or compression injury
    • peroneal nerve injury
      • traction neuropraxia
    • may prevent traction injuries with
      • intermittent release of traction
      • adequate anesthesia
  • anterolateral portal
    • risks superior gluteal nerve
  • posterolateral portal
    • risks sciatic nerve
      • increased risk with external rotation of hip
  • anterior portal
    • risks lateral femoral cutaneous nerve injury
    • risks femoral neurovascular bundle
    • risks ascending branch of lateral femoral circumflex artery


Most common complication of hip arthroscopy

chondral damage


Risk factors


  • Alcoholism
  • steroids (either endogenous or exogenous)
    • High the dose the higher the risk
  • dysbaric disorders (decompression sickness, "the bends")
  • marrow-replacing diseases (e.g. Gaucher's disease)
  • sickle cell disease
  • hypercoagulable states
    • May explain idiopathic disease
  • SLE
  • Inflammatory Bowel Disease
  • transplant patient
  • virus (CMV, hepatitis, HIV, rubella, rubeola, varicella)
  • protease inhibitors (type of HIV medication)
  • AVN associated with trauma
    • due to injury of femoral head blood supply (medial femoral circumflex)
    • AVN rates of specific injuries
      • femoral head fracture: 75-100%
      • basicervical fracture: 50%
      • cervicotrochanteric fracture: 25%
      • hip dislocation: 2-40% (2-10% if reduced within 6 hours of injury)
      • intertrochanteric fracture: rare


Radiographic work-up for AVN

  • Think to get imaging of both hips,  50% of the time is a bilateral disease
  • Radiographs
    • AP hip
      • Double line sign associated with crescent sign
      • Present in 80% of cases
    • frog-lateral of the hip - more sensitive
      • classification systems based largely on radiographic findings (see below)
    • Size of lesion - % head on AP X % head on lateral
      • Small - < 15%
      • Medium - 15-30%
      • Large - > 30%
  • MRI - Gold standard
    • highest sensitivity and specificity
    • T1: dark
    • T2: bright (marrow edema)
      • Will have evidence of high signal from edema as well as low signal changes
    • Extent of femoral head involvement
    • Kerboul Angle
      • Combine necrotic angles on saggital and coronal 
      • >200 associated with poorer outcomes


Diagnosis?  How do you know?  Prognosis?

Transient Osteoporosis of the Hip

  • Classic picture is low signal on T1 and high signal on T2 with no evidence of low signal in T2
  • All the way threw the head, neck and trochanteric region
  • If there are risk factors or concerns of AVN you can do serial progression, TOH will resolve


Ficat classification

  • stage 0:
    • plain film: normal
    • MRI: normal
    • clinical symptoms: nil
  • stage I:
    • plain film: normal or minor osteopaenia
    • MRI: edema
    • clinical symptoms: pain typically in the groin
  • stage II:
    • plain film: mixed osteopenia &/or sclerosis &/or subchondral cysts, without any subchondral lucency (crescent sign: see below)
    • MRI: geographic defect
    • clinical symptoms: pain and stiffness
  • stage III:
    • plain film: crescent sign & eventual cortical collapse
    • MRI: same as plain film
    • clinical symptoms: pain and stiffness+/- radiation to knee and limp
  • stage IV:
    • plain film: end stage with evidence of secondary degenerative change
    • MRI: same as plain film
    • clinical symptoms: pain and limp


Options for treatment


  • Prognosis
    • 80% will collapse
  • Bisphosphonates
    • indicated for precollapse AVN (Ficat stages 0-II)
    • trials have shown that alendronate prevents femoral head collapse in osteonecrosis with subchondral lucency
  • Shock-wave, hyperbaric has been tried, but hasn't been showed to work and there is no evidence behind it
  • Tantalum rod is an old procedure that was thought to provide support and perhaps revascularization but the outcomes have been shown to be poor
  • Core decompression  with bone grafting 
    • indications
      • for early AVN (FICAT 1, 2), before subchondral collapse occurs
      • Small lesions (<15%)
      • Reversible cause
    • Now will just do multiple tracks with a smaller drill bit
      • **Just don’t drill below the less troch region
    • Not very good results
  • Rotational osteotomy
    • indications
      • only for small lesions (<50%) in which the lesion can be rotated away from a weight bearing surface
      • Beaule paper
        • <45 deg
        • Kerboul < 200
        • off steroids
    • technique
      • typically performed through intertrochanteric region
      • Japan does a trans-trochanteric that has not become common in NA
      • Need to be careful because can make conversion to THA more difficult
  • vascularized free-fibula transfer
    • indications
      • pre-collapse in patients young and over 40
      • Moderate to large lesion
      • collapsed AVN in young patient
      • Reversible cause
    • technique
      • fibular strut is placed under subchondral bone to help prevent collapse or tamp up small areas of collapse
      • complications  - are related to donor site morbidity
        • sensory deficit
        • motor weakness
        • FHL contracture
        • tibial stress fracture from side graft is taken
  • total hip replacement
    • indications
      • femoral head collapse
      • acetabular DJD
      • Advanced collapse in younger patients
    • Technique
      • Remember that the bone quality is poor - be gentle with acetabular reaming
      • Evaluate the femur for previous surgery - core decompression, osteotomy
      • Use a large head, use a lateral approach
      • Consider ceramic in younger patients
    • Outcomes
      • in young patients with osteonecrosis  there is a higher rate of linear wear of the polyethylene liner and a higher rate of osteolysis than when compared to older patients who have THA for osteoarthritis
      • Should be using uncemented components so they can in-grow
  • total hip resurfacing
    • indications
      • in advanced DJD with small, isolated focus of AVN
    • contraindicated in underlying disease process or chronic steroid use causing AVN (poor bone quality) and renal disease (metal ions from metal-on-metal implant)
  • hip arthrodesis
    • indications
      • only consider in the very young patient in a labor intensive occupation


Increased risk of progression with AVN

  • > 5mm less chance of progression
  • Lateral lesion in the weight bearing zone more chance of progression
  • Keboul angle > 200deg has increased chance of progression
  • Risk of contralateral hip (50%)


Considerations for THA in patients with AVN


  • Use a large head, use a lateral approach
  • Consider ceramic in younger patients
  • Remember that the bone quality is poor - be gentle with acetabular reaming
  • Evaluate the femur for previous surgery - core decompression, osteotomy


Steinberg classification AVN

  • 0 - normal  
  • I  - normal XR, abnormal MRI
  • II - cystic or sclerosis change
  • III - crescent sign (subchondral collapse)
  • IV - flattening of femoral head
  • V  - narrowing of joint abnormal 
  • VI - advanced degenerative changes 


Two classifications for DDH when considering THA?

  • Crowe
    • I
      • Less than 10% Proximal
      • Less than 50% lateral
    • II
      • 10-15% proximal 
      • 50-75% lateral
    • III
      • 15-20% proximal
      • 75-100% lateral
    • IV
      • Greater than 20%
      • Greater than 100%
  • Hardofilakidis
    • Dysplasia (Type A)
      • Femoral head within acetabulum despite some subluxation. Segmental deficiency of the superior wall. Inadequate true acetabulum depth.
    • Low dislocation (Type B)
      • Femoral head creates a false acetabulum superior to the true acetabulum. There is complete absence of the superior wall. Inadequate depth of the true acetabulum.
    • High dislocation (Type C)
      • Femoral head is completely uncovered by the true acetabulum and has migrated superiorly and posteriorly. There is a complete deficiency of the acetabulum and excessive anteversion of the true acetabulum.


What are you consderations for THA

  • Acetabulum
    • smaller cup, superior migration, false acetabulum
    • loss of anterior/superior and lateral coverage
      • Augment with screw fixation
      • Augment with implant augments
    • Small cup mean a small femoral head to accommodate sufficient poly
    • Offset-bore components are available that change the position of the head in the poly to reduce risk of instability
  • Femur
    • Previous surgeries
      • Loss of canal
    • Posterior GT
      • GT osteotomy or ETO
    • May need to shorten
      • 2-4 cm is max without shortening
    • Soft tissue changes associated with superior migration
      • Abductors become transverse
      • Psoas and capsule hypertrophy
      • Adductor, rectus and hamstring shortening


Technical approach for each crowe classification

  • Technique for I
    • Acetabulum
      • can usually use the native acetabulum
      • size less of an issue
      • Just consider degree of bone loss
    • Femur - no need to shorten
      • Try to go cementless because these patients are young
      • Minimal deformity - metaphyseal fitting proximally coated stem
      • Larger deformity - small, DDH stem with minimal flare
        • Diaphyseal fitting, long coating
        • Allows correction of version
  • Technique for II/III and Hardofilikas B
    • Acetabulum
      • 1) Leave the cup superior (high hip center)
        • Means you will have a very small cup
        • May need less shortening
        • increased stress with early failure
      • 2) Medialize the cup (acetabuloplasty) at native hip center
        • Reduces joint reaction forces
      • 3) Augment with bone graft which is available from the femoral head
      • Poor results have been published when > 30% of head is uncovered requiring graft/augment (this is when you would consider leaving the cup more superior)
    • Femur
      • Will need a diaphyesal fitting stem with modular components to assess verion
        • fully porous coated
        • fluted?
      • May need to be shortened
        • >2-4 cm
        • GT osteotomy with sequential femoral resection
        • Canal that is left is poor quality
        • Need to use a small DDH cemented stem
      • Subtroch osteotomy is better but harder to do - do this from a posterior approach
        • make subtroch osteotomy and leave hip in pseudoacetab
        • prepare the acetab
        • shorten your femur as necessary, release the head and soft tissues
        • size your stem
        • reduce secure the stem with k-wires/allograft as necessary
      • Risk of nonunion
  • Technique IV
    • Put in the native acetabulum
      • Extra-small cup
      • The bone will be soft, don't over ream
      • Do the last reamer on reverse
    • ​Posterior approach for femoral shortening osteotomy via GT or subtroch osteotomy


Indications and contraindications to hip arthrodesis

  • Indications
    • salvage for failed THA (most common)
    • young active laborers with painful unilateral ankylosis after infection or trauma
    • neuropathic arthropathy
    • tumor resection
  • Contraindications
    • active infection
      • delay until no active sinus and normal lab values
    • severe limb-length discrepancy greater than 2.0 cm. 
    • bilateral hip arthritits
    • adjacent joint degenerative changes 
      • lumbar spine
      • contralateral hip
      • ipsilateral knee
    • severe osteoporosis
    • degenerative changes in lumbar spine
    • contralateral THA
  • increased failure rate (40%)  in THA when there is a contralateral hip arthrodesis


What is true about the biomechanics and pathology of this patient?

Hip Arthrodesis

  • Pathomechanics
    • reduces efficiency of gait by ~50%
    • increases pelvic rotation of contralateral hip
    • increases stress at adjacent joints
  • Biochemistry
    • increases oxygen consumption
    • requires 30% more energy expenditure for ambulation
  • Prognosis
    • provides pain relief and reasonable clinical results in most patients
    • success may be limited by adjacent joint degeneration in 60% of patients
      • lumbar spine, ipsilateral knee or contralateral hip may be affected
      • low back pain and arthritic ipsilateral knee pain are the most common symptoms
      • may start within 25 years of hip arthrodesis


This is a 16yo male with a combined pelvis and femoral neck fracture.  He developed infection post-op.  After I&D, 6 weeks IV abx and 6 weeks PO abx, he has resolving ESR/CRP with an abx holiday.  What is your plan now?  Explain your technical approach.

Hip arthrodesis

  • goals
    • achieve apposition of arthrodesis surfaces, obtain rigid internal fixation and promote early mobilization
  • plan for future THA
    • preserve the abductors
    • preserve bone stalk; address missing bone stalk
  • optimal position
    • 20-35° of flexion
      • Appropriate flexion for sitting, reduce lumbar strain
      • Too much can exaccerbate LLD
    • 0°-5° adduction
      • avoid abduction as it creates pelvic obliquity and increased back pain
      • Too much adduction can  make sexual activity and toileting difficult in women
    • 5-10° external rotation
      • Facilitates putting on shoes and foot care
    • Leg length
      • < 2cm difference is acceptable
        • Can use abduction to correct 2cm (cannot abduct further than that)
        • Do not abduct > 6 deg
      • >4 cm stage the procedure and do a second lengthening procedure
  • Approach
    • lateral approach with trochanteric osteotomy is preferred 
      • important to preserve the abductor complex (used to strip the abductors off the pelvis, now elevate them)
      • avoid injury to the superior gluteal nerve
    • anterior approach to hip is also popular 
      • Less risk to the abductors
      • supine on the operative table makes positioning hip easier
      • Screw augments the plate - lag screw done first, the plate onto crest up near SI 
  • Address bone deficiet
  • Instrumentation
    • cobra plating
    • anterior plating
    • double plating
      • trochanteric approach
      • better with excessive bone loss, provides more support
      • 2 stage - first prepare the joint, second fix the GT back down
        • improves fusion rates


This patient comes back to you at 25yo with low back pain.  What is you assessment/approach now?


  • Prognosis
    • provides pain relief and reasonable clinical results in most patients
    • success may be limited by adjacent joint degeneration in 60% of patients
      • lumbar spine, ipsilateral knee or contralateral hip may be affected
      • low back pain and arthritic ipsilateral knee pain are the most common symptoms
      • may start within 25 years of hip arthrodesis
  • ​Conservative treatment
    • Consider other causes of low back pain
    • Do a full hx and neurological exam
    • ask about progression of the pain and any attempt at conservative treatment
    • ask about pain in other joints
    • try to prolong take-down
  • Conversion of fusion to THA
    • Indications - pain in adjacent joints
      • severely debilitating back pain (most common - 70%)
      • severe ipsilateral knee pain with instability
      • severe contralateral hip pain
      • Relative:
        • LLD > 3 cm
        • previous nonunion of arthrodesis
    • ​Contraindications
      • unable to cope with large procedure (relative)
      • active infection - stage procedure)
  • Pre-op
    • Full History
      • Pain
      • Indications and age at initial procedure
      • Spontaneous vs surgical
      • Complications following the procedure
    • Exam
      • Incisions, palpate abductors
      • Assess hip position, LLD
      • Lumbar spine, contralateral hip, ipsilateral knee
      • Full NV exam
    • Rule out infection
      • ESR, CRP
      • Neutrophil count intra-op
      • If concerns, take down with prostalac with staged procedure
    • Imaging
      • AP/lateral pelvis, full length standing (LLD), judet views
      • Assess for position of the plate and bone stalk
    • CT for bone, and alignment
    • MRI or ECG to access abductors
  • Outcomes
    • clinical outcome is dependent on abductor complex function
    • Good outcome patient can expect
      • Improved back/joint pain
      • Increased mobility
      • Resolved leg length discrepancy
    • the presence of hip abductor complex weakness or dysfunction
      • requires prolonged rehabilitation (2years)
      • severe lurching gait may develop


Technique and considerations to perform THA on these patients

Hip Arthrodesis conversion to THA

  • Goals
    • (1) identify and preserve the hip abductor muscles
    • (2) accurately identify the hip rotation center of the acetabulum
    • (3) perform concentric reaming of the acetabular bone bed to achieve medialization and sizing of the component
    • (4) avoid placement of the acetabular cup in an excessively cephalic position
    • (5) optimize leg length equalization
    • (6) restore ideal femoral offset to avoid impingement and instability
  • Supine on a radiolucent table
    • supine easier assessment of acetabulum
    • will need flouro guidence
  • Approach
    • GT osteotomy (more common)
      • Fix with circlage wires or claw plate for weaker bone
    • Posteroateral
      • Avoid issues with nonunion of osteotomy site
  • Take down osteotomy
    • Junction between the ilium and femoral neck is the osteotomy site
    • Use flouro
    • Anterior acetabular rim and sciatic notch can also be used
    • Transverse acetabular ligament if present
  • Have allograft or augments available in case of poor bone stalk or deficiency
  • Acetabulum
    • Define the acetabulum
    • Be cognicent of the position of the other hip
      • Flexion and adduction of the other hip might cause pelvic obliquity and you may antevert the cup
    • Cup
      • Porous coated, multi-hole cup or porous metal (TM)
      • Large cup to allow for a larger poly/head
  • Femur
    • Want more offset to improve abductor function
    • Large head (>36)
      • Increase ROM, decrease instability
    • Proximal stem usually ok
      • Have a revision stem on hand if required
  • Post-op
    • PWB for 6-8 weeks
    • Will require can for excessive period of time
    • Hip precautions or abduction splint
      • Because poor soft tissue/abductors
      • At risk of dislocation
  • Complications
    • Intra-op
      • pelvic discontinuity
      • greater trochanteric fracture
      • femoral perforation
      • calcar fracture
    • Post-operative
      • trochanteric osteotomy nonunion
      • infection
      • dislocation
      • nerve palsy
      • HO​
  • Outcomes
    • clinical outcome is dependent on abductor complex function
    • Good outcome patient can expect
      • Improved back/joint pain
      • Increased mobility
      • Resolved leg length discrepancy
    • the presence of hip abductor complex weakness or dysfunction
      • requires prolonged rehabilitation (2years)
      • severe lurching gait may develop



Indications and contraindications to convert hip arthrodesis to THA

  • Indications
    • severely debilitating back pain (most common - 70%)
    • severe ipsilateral knee pain with instability
    • severe contralateral hip pain
    • Relative:
      • LLD > 3 cm
      • previous nonunion of arthrodesis
  • ​Contraindications
    • unable to cope with large procedure (relative)
    • active infection - (stage procedure)


Hip Biomechanics and joint reaction force

  • Center of rotation is the center of the femoral head
  • Forces threw the hip
    • 2.5 X in single leg stance
    • 3 X with walking
    • 6 X with running
  • Cane - takes weight away from the hip
  • Decrease joint reaction force - increase in ratio of A/B (shift center of rotation medially) 
    • moving the acetabular component as far medial, inferior, and anterior 
    • shifting body weight over affected hip   
      • this results in Trendelenburg gait 
      • reduces abductor pull
    • increasing offset of femoral component 
    • long stem prosthesis
    • lateralization of greater trochanter
    • varus neck-shaft angulation 
      • increases shear across joint
    • cane in contralateral hand 
      • reduces abductor muscle pull and decreases the moment arm between the center of gravity and the femoral head 
    • carrying load in ipsilateral hand 
      • produces additional downward moment on same side of rotational point
  • increase joint reaction force 
    • valgus neck-shaft angulation 
      • decreases shear across joint
    • Lateralize cup/liner
    • decreased offset


THA Press Fit Stem Design and Complications

  • Design
    • Pressfit 
      • Usually taper with proximal fit
      • .5-1mm smaller than stem
      • Fractures due to underreaming
      • Don't need screws for acetab
    • Line to line
      • long cylindrical stem, isn't really used except for revision
        • Fails distally due to modulus mismatch
      • Ream to same size
      • Depends on scratch fit for stem
      • Need to use screws for acetabulum
  • Fixation
    • Bone ingrowth - porous coating
      • Poor size - 50-150 um
      • Poor depth - deeper is better
      • Porosity 40-50%
      • Circumferential coating
    • Bone ongrowth - grit blasted
      • Micro-divots created by blasting the surface
      • Define by surface roughness (depth of pores created)
      • Bone growth in valleys, microinterdigitation
      • Always with a press-fit technique, usually with a wedge taper
  • Optimizing fixation
    • Minimal Gap
      • <50um - osteoblast jumping distance
    • HA coated
      • Will get ingrowth, but this helps
      • Osteoconductive
      • Decreases time to stability
  • Complications
    • Intra-op fracture if underreamed
    • High loosening in irradiated bone due to lack of ingrowth
      • Will last for about 2 years if you don't have ingrowth
    • Stress sheilding
      • Can be due to distal fixation and long porous coating
      • More related to different in modulus
        • Hoek's law - stiff spring sees more load
        • Better to have a less stiff component so you get less sheilding
      • Increased stiffness
        • Stem diamter (Large stem)
        • Geometry (Solid stem)
        • Metallury (cobalt)


THA Cementing design and complications

  • Cement interdigitates into metaphyseal bone, not diaphyseal bone
  • Indications
    • Better interdigitation into OP bone - mantal should be >2mm
    • Limited remodeling potential
    • Better for irradiated bone
    • Type C femur - hard to get a tight fit with the pressfit (DORR)
  • Technical aspects leading to poor results
    • Reduce porosity
    • Pulse lavage canal
    • Pressurization
    • Centralization
    • Stiff Stem
  • Complications
    • Cement mantel fracture
    • Loosening - a stiff stem is better because it will bend less in the cement mantel
  • Smooth vs rough
    • Smooth will slide threw the cement as the cement undergoes creep and will remain stable over time
    • Rough although seems like it would be stable at first, will not slide as the cement creeps and can act as sandpaper


Cement generations

  • First
    • hand mixed
    • hand packed
  • Second
    • ​Canal lavage/preparation
    • cement plug
    • cement gun
  • Third
    • vacuum-mixing to reduce cement porosity
    • cement pressurization
    • femoral canal preparation 
      • pulsatile lavage


Optimization of cement fixation

  • limited porosity of cement
    • leads to reduced stress points in cement
  • cement mantle > 2mm 
    • increased risk of mantle fractures if < 2mm mantle
  • stiff femoral stem
    • flexible stems place stress on cement mantle
  • stem centralization
    • avoid malpositioning of stem to decrease stress on cement mantle
  • smooth femoral stem 
    • sharp edges produce sites of stress concentration
  • absence of mantle defects
    • defined as any area where the prosthesis touches cortical bone with no cement between
    • creates an area of higher concentrated stress and is associated with higher loosening rates
  • proper component positioning within femoral canal 
    • varus or valgus stem positioning increases stress on cement mantle


Radiographic signs a stem has ingrown (cement vs biologic)

  • Barrack and Harris grading system - Cement 
    • grade A 
      • complete filling of medullary canal
      • "white-out" of cement-bone interface
    • grade B 
      • slight radiolucency of cement-bone interface
    • grade C 
      • radiolucencies > 50% of bone-cement interface or incomplete cement mantles
    • grade D 
      • gross radiolucencies and/or failure of cement to surround tip of stem
  • signs of a well-fixed cementless femoral component 
    • spot-welds 
      • new endosteal bone that contacts porous surface of implant 
    • absence of radiolucent lines around porous portion of femoral stem
    • proximal stress shielding in extensively-coated stems 
    • absence of stem subsidence on serial radiographs
  • signs of a well-fixed cementless acetabular component 
    • lack of migration on serial radiographs
    • lack of progressive radiolucent lines
    • intact acetabular screws


Complications of THA component fixation

  • Aseptic loosening
    • causes 
      • poor initial fixation
      • mechanical loss of fixation over time
      • particle-induced osteolysis
    • clinical presentation 
      • acetabular loosening 
        • groin/buttock pain
      • femoral loosening 
        • thigh pain 
        • start-up pain
    • evaluation 
      • sequential radiographs
      • bone scan
    • treatment 
      • revision of loose components 
  • Stress shielding 
    • definition 
      • proximal femoral bone loss in the setting of a well-fixed stem 
    • risk factors 
      • stiff femoral stem 
        • most important risk factor
      • large diameter stem
      • extensively porous coated stem
      • greater preoperative osteopenia
    • clinical implications 
      • clinical implications of proximal stress shielding unknown
  • Intraoperative fracture 
    • risk factors 
      • use of press fit technique
    • treatment 
      • acetabular fracture 
        • stable cup 
          • add screws for additional fixation
        • unstable cup 
          • remove cup, stabilize fracture, and reinsert cup with screws
      • femur fracture  
        • stable prosthesis
          • consider cerclage cables/wires
          • limit weight-bearing
        • unstable prosthesis 
          • remove prosthesis, stabilize fracture, reinsert new stem that bypasses fracture by two cortical diameters


Stages of osteolysis and types of wear

  1. particulate debris formation

  2. macrophage activated osteolysis 
  3. prosthesis micromotion
    • ​micromotion leads to more wear
    • elevated N-telopeptide
  4. particulate debris dissemination
    • ​moves to effective joint space
    • hydrostatic pressure increases with inflammation
  • Radiostereometric analysis is the most accurate way to assess wear
  • particulate size < 1micron


  • Adhesive wear
    • most important in osteolytic process
    • microscopically PE sticks to prosthesis and debris gets pulled off
  • abrasive wear
    • cheese grater effect of prosthesis scraping off particles
  • third body wear
    • particles in joint space cause abrasion and wear
  • volumetric wear
    • main determinant of number of particles created
    • directly related to square of the radius of the head
    • volumetric wear more or less creates a cylinder 
      • V=3.14rsquaredw
      • V is volumetric wear, r is the radius of head, w is linear head wear
    • head size is most important factor in predicting particles generated
  • Linear wear 
    • is measured by the distance the prosthesis has penetrated into the liner


Wear characteristics by material

  • polyethylene
    • non-cross linked UHMWPE wear rate is 0.1-0.2 mm/yr
      • linear wear rates greater than 0.1 mm/yr has been associated with osteolysis and subsequent component loosening   
    • highly-cross linked UHMWPE generates smaller wear particles and is more resistant to wear (but has reduced mechanical properties compared to conventional non-highly cross-linked)     
    • factors increasing wear in THA
      • thickness < 6mm
      • malalignment of components
      • patients < 50 yo
      • men
      • higher activity level
      • femoral head size between 22 and 46mm in diameter does not influence wear rates of UHMWPE 
  • Ceramics 
    • ceramic bearings have the lowest wear rates of any bearing combination (0.5 to 2.5 µ per component per year)  
    • ceramic-on-polyethylene bearings have varied, ranging from 0 to 150 µ.
    • has a unique complication of stripe wear occurring from lift-off separation of the head gait 
      • recurrent dislocations or incidental contact of femoral head with metallic shell can cause "lead pencil-like" markings that lead to increased femoral head roughness and polyethylene wear rates.
  • Metals 
    • metal-on-metal produces smaller wear particles as well as lower wear rates  than those for metal-on-polyethylene bearings (ranging from 2.5 to 5.0 µ per year) 
    • titanium used for bearing surfaces has a high failure rate because of a poor resistance to wear and notch sensitivity. 
    • metal-on-metal wear stimulates lymphocytes 
    • metal-on-metal serum ion levels greater with cup abduction angle >55 degrees and smaller component size 


Factors increasing wear in THA

  • thickness < 6mm
  • malalignment of components
  • patients < 50 yo
  • men
  • higher activity level
  • femoral head size between 22 and 46mm in diameter DOES NOT influence wear rates of UHMWPE 


Describe macrophage activation by particulate debris (<1micron)

  • Macrophage activation 
    • results in macrophage activation and further macrophage recruitment 
    • macrophage releases osteolytic factors (cytokines) including  
      • TNF- alpha
      • TGF-beta
      • osteoclast activating factor
      • oxide radicals
      • hydrogen peroxide
      • acid phosphatase
      • interleukins (Il-1, IL-6) 
      • prostaglandins
  • Osteoclast activation and osteolysis 
    • increase of TNF-alpha increases RANK
    • increase of VEGF with UHMWPE  inhances RANK and RANKL activation
      • RANKL mediated bone resorption 
        • an increase in production of RANK and RANKL gene transcripts leads to osteolysis 


Factors contributing to periprothetic fracture of the knee

  • poor bone quality 
    • age
    • steroid use
    • rheumatoid arthritis
    • stress-shielding
  • mechanical stress-risers 
    • screw holes
    • local osteolysis
    • stiffness
  • neurological disorders 
    • epilepsy
    • Parkinson's disease
    • cerebellar ataxia
    • myasthenia gravis
    • polio
    • cerebral palsy


Su classfication of periprosthetic fractures

  • Type I
    • Fracture is proximal to the femoral component     
  • Type II
    • Fracture originates at the proximal aspect of the  femoral component and extends proximally      
  • Type III
    • Any part of the fracture line is distal to the upper edge  of anterior flange of the femoral component


options for fixation of periprosthetic fracture around femoral compoent of TKA?

  • antegrade intramedullary nail
    • supracondylar fracture proximal to the femoral component (Su Type I)
  • retrograde intramedullary nail 
    • intact/stable prosthesis with open-box design to accommodate nail
    • fracture proximal to femoral component (Su Type I)
    • fracture that originates at the proximal femoral component and extends proximally (Su Type II)
  • ORIF with fixed angle device
    • intact/stable prosthesis
    • Su Types I or II (described above) unable to accommodate intramedullary device
    • fracture distal to flange of anterior femoral component (Su Type III) 
    • techniques 
      • condylar buttress plate (non-locking)
      • locking supracondylar plate   
      • blade plate
      • dynamic compression screw
    • complications 
      • nonunion   
        • increased risk in plating via extensile lateral approach compared with submuscular approach 
  • revision to a long stem prosthesis 
    • indications 
      • loose femoral component
      • Su Type III (described above) with poor bone stock
  • distal femoral replacement   
    • indications 
      • elderly patients with loose or malpositioned components and poor bone stock
    • advantages 
      • immediate weight-bearing
      • decreased operative time of procedure


risk factors for tibial TKA fracture

prior tibial tubercle osteotomy
component loosening
component malposition
insertion of long-stemmed tibial components 


Risk factors for patella fracture TKA

  • patellar osteonecrosis   
  • asymmetric resection of patella
  • inappropriate thickness of patella
  • implant related
    • central single peg implant   
    • uncemented fixation
    • metal backing on patella   
    • inset patellar component


Options for treatment of patella fracture following TKA

  • Casting in extension
    • stable component
    • intact extensor mechanism
  • Operative
    • indications
      • loose patellar component   
      • extensor mechanism disruption   
    • techniques (indications for each have not been clearly defined)
      • ORIF with or without component revision   
      • partial patellectomy with tendon repair
      • patellar resection arthroplasty and fixation
      • total patellectomy


variables that lead to catastrophic poly wear

  • PE thickness
    • <8mm
  • articular surface design
    • flat PE increases contact load 
    • solution
      • high congruency with less roll back is less anatomic but more load sharing
  • kinematics
    • excessive femoral rollback
    • solution
      • less femoral rollback
      • nadir has been move more posterior in most knees
  • PE sterilization
    • Oxygen rich environment
      • subsurface delamination
      • pitting
      • fatigue cracking
    • Solution
      • sterilize in nitrogen gas or vacum
  • PE machining
    • Ram bar extrusion = machine shear forces = stretched PE bands
      • delamination and fatigue
    • Solution
      • direct compression moulding


What are the 4 important variables that determine THA stability

component design
component position
soft-tissue tensioning
soft tissue function


How can you improve stability in THA

  • Component design
    • large femoral heads
      • head-neck ratio increased
        • allow greater arc range of motion prior to impingement   
      • skirts can be avoided 
        • ​decrease the head-neck ratio 
      • jump-distance is increased 
        • amount of translation prior to dislocation
    • femoral offset 
    • elevated rim liner 
      • a posteriorly placed elevated rim liner may increase joint stability   
    • lateralized liner 
      • increasing offset
  • Component Postition
    • Acetabular position 
      • ​anteversion - 20° ± 10°
      • abduction - 45° ± 10°
    • Femoral stem position
      • ​10°- 15° of anteversion
  • Restore offsett   
    • increasing length of femoral neck
    • decreasing neck-shaft angle
    • medializing the femoral neck while increasing femoral neck length
    • trochanteric advancement   
    • alteration of the acetabular liner (see "component design" above)


What is the consequence of a malpositioned component

  • excessive retroversion   
    • posterior dislocation
  • excessive anteversion 
    • anterior dislocation
  • excessive abduction (high theta angle, vertical cup) 
    • posterior superior dislocation   
    • eccentric polyethylene wear and late instability
  • excessive adduction (low theta angle, horizontal cup) 
    • impingement in flexion
    • inferior dislocation


How does offset affect THA

  • increased offset leads to 
    • increased soft-tissue tension
    • decreased impingement
    • decreased joint reaction force 
  • deceased offset may lead to 
    • instability
    • abductor weakness
    • gluteus medius lurch
    • increasing offset improves hip stability


What are contraindications to hip joint preserving surgery

  • >50
  • >1 Tonnis
  • inflammatory arthritis; 
  • bipolar lesions
  • uncontained lesion; 
  • inability to perform rigorous postoperative physical therapy regimen


What are the indications and advantages of mosaicplasty in the hip

  • unipolar lesion on the femur < 2cm
  • pros
    • elimination of the need for a second procedure (as in ACI)
    • contains hyaline cartilage
    • near-immediate weight bearing
  • cons
    • requires hip dislocation
    • donor site morbidity


What are you options for cartilage replacement of the hip

  • Femur
    • <2cm = "apple bite" following cam resection
      • microfracture
      • mosciacplasty
      • allograft
    • 2-6cm
      • micorfracture if found 
      • allograft if known
    • >8cm 
      • THA
  • Acetabulum
    • <6cm
      • microfracture
    • >6cm
      • THA


complications of a constrained liner

  • Acetabular loosening
  • Dissociation of the constrained liner from the shell
  • Material failure
  • Disengagment of the constraining ring
  • Excessive wear due to thin liner 


What are the pros and cons of ceramic bearings

  • Pros
    • best wear characteristics
    • particles are non-oncogenics
  • Cons
    • risk of fracture
      • 1/5000-1/12000
      • 70% with-in 12 months
      • higher with small, neutral offset heads
    • Chipping 1.2%
    • Squeak 0.45%
    • Stripe wear with edge loading
    • Fewer prosthetic options 
    • More technically demanding


What is the treatment of fractured ceramic on ceramic

  • complete synovecotmy
  • can't but ceramic head on damaged trunion
    • some options are available
  • best option is ceramic on ceramic
  • Metal on poly most commonly used but carries risk of accelerated wear from 3rd body debris


What are good prognostic factors following PPJI

  • THA rather than a TKA
  • causative bacteria is known 
  • gram-positive
  • antibiotic therapy tailored to the causative bacterium is administered for 12 weeks
  • infection is not polymicrobial ie. single bug
  • patient factors are optimal (ie. no comorbidities, no immunosuppression)


4 necessary criteria when choosing antibiotic cement for spacer

  • water soluble 
  • thermodynamically stable
  • must have a bactericidal effect
  • released gradually over an appropriate period of time
  • evoke minimal local inflammatory reaction


Benefits of a spacer over beads for treatment of PPJI

  • substantially shorter surgical time 
  • shorter hospital stay 
  • reduced blood loss (during 2nd stage)
  • decreased transfusion requirements (during 2nd stage)
  • better interim hip function 


Paprosky acetabulum

Type I - Minimal deformity, intact rim

Type IIA - Superior bone lysis with intact superior rim
Type IIB -  Absent superior rim, superolateral migration
Type IIC -  Localized destruction of medial wall
Type IIIA - Bone loss from 10am-2pm around rim, superolateral cup migration
Type IIIB - Bone loss from 9am-5pm around rim, superomedial cup migration


Paprosky Femur

  • Components
    • ischial bone loss
    • tear drop lysis
    • femoral head center migration
    • kohlers line (ilioischial line)
  • Type I Minimal metaphyseal bone loss
    • proximal fitting wedge taper stem
  • Type II Extensive metaphyseal bone loss with intact diaphysis  
    • fully porous coated diaphyseal stem
  • Type IIIa Extensive metadiaphyseal bone loss, minimum of 4 cm of intact cortical bone in the diaphysis  
    • fully porous coated dephyseal stem
  • Type IIIb Extensive metadiaphyseal bone loss, less than 4 cm of intact cortical bone in the diaphysis  
    • fully porous coated modular tapered stem with derotational spines
  • Type IV Extensive metadiaphyseal bone loss and a nonsupportive diaphysis
    • APC
      • step cut into native femur reinforced with circlage wires to help creeping subsitution
      • risk of disease transmission, benefit is bone in young patients
    • impaction grafting
      • clean canal of cement and fibrous tissue, reinforce with mesh
      • morsalized allograft then cement in revision stem
    • proximal femoral replacement
      • instability, loosening, can't reattach soft tissues


Options for acetabulum reconstruction in revision THA

  • Paprosky 1/2
    • porous metal, hemispherical, multi-hole revision cup
    • can use metal augmets to bolster the cup if there is significant bone loss
    • allograft is no longer recommended
  • Paprosk 2c/3a/3b
    • porous metal cup with metal augments
    • antiprotrusio cage with cemented liner
      • if you think the acetabulum won't heal (cancer, pagets) then you don't need to put a cup in because you'll never get ingrowth
      • does not have good long term outcomes
      • advantages of cementing liner
        • can cement liner in proper position
        • can use antibiotic cement
    • Distraction cup
      • jumbo cup is used to distract the disontinuity, need to be careful in poor quality bone
      • only really good results from paprosky
    • cup-cage construct
      • cage has a phalange that goes into the ishium and then secured with screws onto the ilium
    • custom triphlange cup
      • made to bridge the defect 
      • porous titanium, HA coated
      • phalange for ischium, ilium and pubis
      • expensive, stiff, question of whether it can incorperate