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Imaging for patellar instability?


  • Anatomy
    • Passive stability
      • medial patellofemoral ligament (MPFL) is primary restraint in first 20 degrees of knee flexion
      • usually avulses from medial epicondyle of femur
      • patellar-femoral bony structures account for stability in deeper knee flexion
    • Dynamic stability
      • vastus medialis (attaches to MPFL)​
  • Radiographs - AP, lateral, skyline, oblique
    • rule out fracture or loose body
      • medial patellar facet (most common)  
      • lateral femoral condyle (usually occurs when patella is reduced)
    • AP views 
      • best to evaluate overall lower extremity alignment and version
    • lateral views
      • best to assess for trochlear dysplasia
      • Trochlea >145  = dysplasia
      • Crossover sign = dysplasia = trochlea crrosses the supracondylar prominence
    • Evaluate for patellar height (patella alta vs baja)
      • Blumensatts line should be inferior to patella
      • Insall-Salvati method
      • Blackburne-Peel method
      • Caton-Deschamps
      • Plateau-Patella Angle (20-30 deg)
    • axial views
      • best assess for lateral patellar tilt
      • lateral patellofemoral angle  
  • MRI 
    • help further rule out suspected loose bodies
    • osteochondral lesion and/or bone bruising 
    • medial patellar facet (most common)
    • lateral femoral condyle
    • tear of MPFL
      • tear usually at medial femoral epicondyle
  • CT 
    • TT-TG > 20 shows excessive varus
      • Torsional assessment
    • Assess trochlear anatomy



You are concerned about patellar tendon rupture.  Give 4 ways to assess patellar height

  • Blumensatts line should be inferior to patella
  • Insall-Salvati method
    • ​length patella/length tendon = 1
  • Blackburne-Peel method
    • length articular surface/distance from line drawn parallel to tibial plateau = 0.8
  • Caton-Deschamps
    • length articular surface/distance to tibial plateau = 1.0
  • Plateau-Patella Angle (20-30 deg)
    • line drawn along tibial plateau, then line drawn from posterior plateau to inferior patella


Treatment options for patellar instability?


  • NSAIDS, activity modification, and physical therapy
    • indications
      • mainstay of treatment for first time patellar dislocation
      • without any loose bodies or intraarticular damage
      • habitual dislocator
    • techniques
      • short-term immobilization for comfort followed by 6 weeks of controlled motion
      • emphasis on strengthening 
        • closed chain short arc quadriceps exercises
        • VMO strengthening
        • core strengthening of hip abductors, gluteals, and abdominals 
      • patellar stabilizing sleeve or "J" brace
      • consider knee aspiration for tense effusion
        • positive fat globules indicates fracture
  • Operatvie Approach
    • Address all deformities (Osseous, static, dynamic)
    • Options for Osseus
      • Dysplasia - groove deepening
      • TT-TG or patella alta - tibia osteotomy
    • Static
      • MPFL reconstruction
  • Not all need to be addressed; sometimes an osteotomy with MPFL reconstruction will comprensatate for trochlear dysplasa
  • arthroscopic debridement vs ORIF
    • indications
      • displaced osteochondral fractures or loose bodies
      • chronic patellofemoral instability
    • techniques
      • arthroscopic vs open 
  • MPFL repair 
    • indications
      • acute first time dislocation
    • techniques
      • direct repair when surgery can be done within first few days
      • no clinical studies support this over nonoperative treatment
  • MPFL reconstruction with autograft vs allograft 
    • Has good outcomes and can improve stability even with associated boney abnormalities, however the ideal situation is below
      • TT-TG <20
      • Caton-dechamps < 1.2
      • Apprehension at 30 deg of flexion
      • Grade A trochlear dysplasia
    • indications
      • recurrent instability (>2)
  • medial tibial tubercle transfer
    • Indications
      • may be used in addition to MPFL or in isolation for significant malignment
      • TT-TG >20mm on CT
    • Techniques
      • anteromedialized displacement of osteotomy and fixation
      • correct TT-TG to 10-15mm (never less than 10mm)
  • lateral release
    • islolated release no longer indicated for instability
    • only indicated if there is excessive lateral tilt or tighness after medialization 
    • To help offload the patella in times of painful PF syndrome refractory to PT
    • technique
      • arthroscopic
  • trochleoplasty
    • Poor outcomes with high rates of OA and limited improvement in pain (despite some reports of improved outcomes)
    • Indications
      • rarely addressed (in the USA) even if trochlear dysplasia present
      • may consider in severe or revision cases
      • May consider if there is no other pathology
      • *Contra-indicated if there is evidence of arthritis
      • Often patients will get increased pain post-op, even though risk of dislocation is dramatically reduced
    • techniques
      • arthroscopic or open trochlear deepening procedure
  • osteochondral defect repair
    • indications
      • large osteochondral loose body
    • techniques
      •  primary repair vs allograft depending on size



Complications associated with patellar instability

  • Recurrent dislocation
    • redislocation rates of 15-44% have directed interest more towards surgical treatment
  • Medial patellar dislocation and medial patellofemoral arthritis
    • almost exclusively iatrogenic as a result of prior patellar stabilization surgery 


Where is Schottle's point

  • 1 mm anterior to the posterior cortex extension line
  • 2.5 mm distal to the posterior origin of the medial femoral condyle
  • proximal to the level of the posterior point of the Blumensaat line
  • on a lateral radiograph with both posterior condyles projected in the same plane


Ideal situation and indications for MPFL repair

  • Ideal situation
    • TT-TG <20
    • Caton-dechamps < 1.2
      • Apprehension at 30 deg of flexion
    • Grade A trochlear dysplasia
  • indications
    • recurrent instability (>2)

Doesn't mean that it can't be done with boney abnormalities, but it just makes it less likely to suceed



Types of muscle contractions

  • Isotonic 
    • Force remains constant through range of motion 
    • improves motor performance
    • Biceps curls using free weights
  • Isometric 
    • Constant muscle length and tension that is proportional to the external load
    • Causes muscle hypertrophy
    • Pushing against an immovable object
  • Concentric 
    • Shortened muscle and tension that is proportional to the external load
    • Biceps curl with elbow flexing
  • Eccentric
    • Force remains constant as muscle lengthens.
    • Most efficient method of strengthening muscle 
    • Biceps curl with elbow extending 
  • Isokinetic 
    • Muscle contracts at a constant velocity or constant external load.      
    •  often used to objectively evaluate muscle strength during injury rehabilitation.
    • Require special machines (e.g, Cybex).
  • Plyometric
    • Rapid eccentric-concentric shortening
    • Good training for sports the require power
    • Box jumps
  • Open chain 
    • Distal end of extremity moves freely
    • Seated leg extensions and curls
  • Closed chain 
    • Distal end of extremity is fixed
    • Squats with planted foot


How does dynamic exercise training improve cardiac output?

increasing stroke volume


Changes that occue during aerobic training

  • contractile muscle adapts by increasing energy efficiency
    • increases in mitochondrial size, number, and density
    • increases in enzymes involved in Krebs cycle, fatty acid processing, and respiratory chain
    • over time, increased use of fatty acids > glycogen
    • over time, oxidative capacity of Type I, IIA, and IIB fibers increase
    • percentage of more highly oxygenated IIA fibers increases
  • Aerobic Threshold: level of effort at which anaerobic energy pathways become significant energy producer
  • Anaerobic (lactate) Threshold: level of effort at which lactate production > lactate removal


How does is strength training assoicated with strength gains?

  • typically high-load, low-repetition activities
  • results in increased cross-sectional area of muscle due to muscle hypertrophy
    • hyperplasia (increased number of fibers) less likely
  • results in increased motor unit recruitment +/- improved synchronization of muscule activity
  • maximal force production is proportional to muscle physiologic cross-sectional area


how does weight traing change muscle composition

  • Effects on muscles
    • increased cross-sectional area
    • increased strength
    • increased mitochondria
    • increased capillary density
    • thickened connective tissue
  • Adult strength gains are associated with muscle hypertrophy
  • Adolescent strength gains occur more from increased muscle firing efficiency and coordination


What are 4 kinds of muscle injury?

  • Muscles soreness
    • caused by edema and inflammation in the connective tissue
      • leads to increased intramuscular pressure
      • occurs primarily in Type IIB fibers
    • worse with unaccustomed eccentric exercise
    • often with delayed onset: Delayed-Onset Muscle Soreness (DOMS) 
      • peaks at 24-72 hours
    • elevated CK levels seen in serum
  • Muscles strain
    • occurs commonly at myotendinous junction (off during eccentric contraction which produces highest forces in skeletal muscle)
    • pathoanatomy in inflammation followed by fibrosis
  • Muscle contusion
    • non-penetrating blunt injury
    • leads to hematoma and inflammation
    • extracellular connective tissue forms within 2 days, peaks between 5-21 days
    • healing characterized by late scar formation, variable muscle regeneration
    • myositis ossificans (bone formation within the muscle tissue) 
      • most apparent 4 weeks post-injury
  • Muscle laceration (complete tear)
    • typically occur near myotendinous junction
    • characterized by abnormal muscle countour
    • fragments heal by dense connective scar tissue
      • this process is mediated by myofibroblasts
      • TGF-Beta stimulates differentiation and proliferation of myofibroblasts 
    • regeneration and renervation: unpredictable and likely incomplete


Treatment of muscle injury

  • Goals of treatment
    • decrease inflammation
    • increase local blood flow
    • increase tissue compliance
  • Modalities include
    • cryo or heat treatments
    • massage
    • ultrasound
    • electrical stimulation
    • Iontophoresis 
      • use of an electrical current to drive charged molecules of medicine through the skin to the deep tissues
      • medications including steroids, local anesthetics, salicylates, and non-steroidal anti-inflammatory drugs


Approach to chondral defect in the knee

  • <2 = drilling
  • 2-4 = mosaiplasty
  • >4 = allograft
    • not enough donor to fill in the defect
    • becomes too irregular
  • HTO
    • If it’s more degenerative
    • Or to augment any procedure
    • Always look at your alignment
  • ACI
    • Not used in Canada
    • Cost – 25K
    • Similar outcomes to microfracture
  • Allograft
    • Fresh, matched
    • Preserved, not frozen
    • Needs to be implanted with-in 21 days
    • 15K


Risk factors for patellar instability


  • ligamentous laxity (Ehlers-Danlos syndrome)
  • dysplastic vastus medialis oblique (VMO) muscle
  • lateral displacement of patella
  • patella alta
  • causes patella to not articulate with sulcus, losing its constraint effects
  • trochlear dysplasia
  • excessive lateral patellar tilt (measured in extension)
  • lateral femoral condyle hypoplasia
  • increased quadriceps angle (Q angle)
  • average for women 15 degrees
  • average for men 10 degrees
  • previous patellar instability event 
  • "miserable malalignment syndrome" 
  • femoral anteversion
  • genu valgum
  • external tibial torsion / pronated feet


Pertient physical exam findings of patellar instablity


  • large hemarthrosis  
  • absence of swelling supports ligamentous laxity and habitual dislocation mechanism
  • medial sided tenderness (over MPFL) 
  • increase in passive patellar translation
    • measured in quadrants of translation (midline of patella is considered "0"), and also should be compared to contralateral side
    • normal motion is <2 quadrants of patellar translation
    • lateral translation of medial border of patella to lateral edge of trochlear groove is considered "2" quadrants and is considered abnormal amount of translation
  • <1cm at 30 deg of flexion
  • patellar apprehension 
  • increased Q angle
  • J sign 
    • excessive lateral translation in extension which "pops" into groove as the patella engages the trochlea early in flexion
  • associated with patella alta


Technique for MPFL Repair

  • Diagnostic arthroscopy
  • ST is harvested
    • the graft is prepare with sutures at both ends
  • Superomedial patella is exposed, two drill holes are made
  • femoral origin can be reliably found radiographically (Schottle point)  
  • check isometry of the graft
  • Drill your hole
  • Secure the graft with an interference screw in the femur
    • Be careful not to overtension the graft if there is trochlear dysplasia
    • Controversial where to tighten the graft
  • pull the graft threw the drill holes in the patella and sutured onto themselves


Differential diagnosis for painful cartilage lesion in the knee

  • Secondary osteonecrosis
    • older woman
    • think risk of AVN
  • Spontaneous osteonecrsis of the knee
    • middle age female
    • releived by arthroscopy
  • Osteochondritis dissecans (OCD)
    • more commonly found at lateral aspect of medial femoral condyle of 15 to 20-year-old males
  • Transient osteoporosis
    • more common in young to middle-aged men
    • multiple joint involvement found in 40% of patients (transient migratory osteoporosis)
  • Occult fractures and bone bruises
    • associated with trauma, weak bones, or overuse


What is the outerbridge classification

Grade 0: Normal cartilage
I: Softening and swelling
II: Partial thickness defect, fissures < 1.5cm diameter
III: Fissures down to subchondral bone, diameter > 1.5cm
IV: Exposed subchondral bone


Factors that will affect your decision making in articular cartilage defect


  • patient factors
    • age
    • skeletal maturity
    • low vs. high demand activities
    • ability to tolerate extended rehabilitation
  • defect factors
    • size of defect
    • location
    • contained vs. uncontained
    • presence or absence of subchondral bone involvement



Surgical options to address cartilage lesions in the knee


  • Address concominant injuries
    • Soft tissue
      • Meniscus
        • Meniscetomy is a relative contraindication to cartilage salvage procedures
        • Young patients may warrant a meniscal transplant
      • Cruciate deficiency
      • MFPL or patellar stabilization
    • Boney (unloading or alignment)
      • High tibial osteotomy
      • Tibial tubercle osteotomy
  • ORIF
    • acute injury
    • sufficient osseous portion
  • Microfracture <2X2
    • can do retrograde if articular surface is intact
    • single procedure
    • does not address bone loss
    • Best results
      • <2X2cm
      • contained
      • acute
  • Moscaoplasty <2X2
    • limited by irregular surface and harvest
    • medial and lateral NWB trochlea
    • cost effective, single stage
    • requires 3 month NWB
  • ACI
    • 2 stage, expensive
    • requires contained defect
    • comparable to microfracture
  • Allograft
    • large, uncontained defect
    • lots of processing, expensive, but works 

For older patients can consider UKA, TKA


What are two patellar unloading procedures

  • Maquet (tibia tubercle anteriorization)
    • indicated only for distal pole lesions
    • only elevate 1 cm or else risk of skin necrosis
    • contraindications
      • superior patellar arthrosis (scope before you perform the surgery)
  • Fulkerson alignment surgery (tibia tubercle anteriorization and medialization)   
    • indications (controversial)
      • lateral and distal pole lesions 
      • increased Q angle
    • contraindications
      • superior medial patellar arthrosis (scope before you perform the surgery) 
      • skeletal immaturity


technique for allochondral graft for the knee

  • overview 
    • goal is to replace cartilage defect with live chondrocytes in mature matrix along with underlying bone
    • fresh, refrigerated grafts are used which retain chondrocyte viability
    • Max 28 days
    • may be performed as a bulk graft (fixed with screws) or shell (dowels) grafts
  • technique
    • match the size and radius of curvature of articular cartilage with donor tissue - based on the plain AP
    • MRI can be used but will underestimate the size of the lesion
    • Small subvastus can be used vs more extended medial or lateral parapatellar for improved exposure
    • a recipient socket is drilled at the site of the defect 
    • an osteochondral dowel of the appropriate size is cored out of the donor 
    • Thinner is better to reduce amount of implanted bone
    • the dowel is press-fit into place
  • Clinical pearls
    • Lots of irrigation to reduce thermal injury
    • Light impaction of the graft so you don't injury the condrocytes
  • benefits 
    • include ability to address larger defects, can correct significant bone loss, useful in revision of other techniques
  • limitations
    • limited availability and high cost of donor tissue
    • live allograft tissue carries potential risk of infection
  • Post-op
    • Avoid shear or compressive stress for 6 weeks
    • Limited WB
    • Full ROM
    • Brace is controversial
    • 6-12 weeks
      • ADL, progress strength
    • 3 months
      • Strength, core, proprioceptive with gradual return to sports
    • Avoid impact activities (6-12months) 


Options for cartilage regeneration

  • Chondrocytes
    • ACI: autologous chondrocyte implantation
    • chondrocytes harvested from non-wt bearing surface & expanded ex-vivo
    • in separate procedure, periosteal flap harvested and sewn over defect; chondrocytes in collagen suspension are squirted underneath & sealed with fibrin
    • problem → does not regenerate hyaline cartilage
  • Pluripotent Stem Cells
    • embryonic stem cells (ESC) & induced pluripotent stem cells (iPSC)
    • may lead to the development of tumor; teratoma formation in vivo is well recognized
    • no current studies underway
  • Mesenchymal Stem Cells
    • ability to differentiate along various cell lineages, including chondrocytes, adipocytes, osteoblasts, and myocytes
    • ideal option for cartilage regeneration because they represent a readily available and accessible supply of cells, and they have the capacity for considerable expansion and differentiation
    • TGFβ & BMPs used to induce chondrogenesis
    • bone marrow stem cells (BMSC) have been used in some studies with promising results


What are the main factors stimulating cartilage growth

TGFβ family, including BMP-2 & BMP-7

chondrogenic differentiation

stimulating production of cartilage ECM


FGF, IGF-1, PDGF, and, of course, PRP!


What predisposes females to ACL tears

Neuromuscluar, quads dominant
Landing biomechanics - higher valgus, more extension (see below)
Smaller notches
Smaller ligaments
Hormone levels (arises at puberty, poor understanding)
Valgus leg alignment
Higher tibial slope


Anatomy of the ACL


  • 85% of anterior stability
    • 1100N to tear
    • 90% type 1 collagen
    • Secondary restraint to rotation
  • Anatomy
    • 33X11mm
    • LFC
    • Anterior to PCL, at level of anterior horn of lateral meniscus
  • Bundles
    • Anteromedial - isometric
    • Posteriolateral - tight in extension, contributes to rotational stability
  • Blood supply - middle geniculate artery
  • Innervation - posterior articular nerve (from tibial nerve)



Injuries associated with ACL tear

  • Often associated with a meniscal tear
    • lateral meniscal tears in up to 50% of acute ACL tears 
  • Bone bruising (50%)
    • LFC in sulcus terminalis
    • Posterior tib plateau
  • Chronic ACL deficient knees associated with 
    • chondral injuries
    • complex unrepairable meniscal tears
    • medial meniscal tears
    • relation with arthritis is controversial


what degree of slope is at risk for ACL tear

>12 deg


What are key factors to include in an acl prevention program

  • 30 min, 3 times/wk for approximately 8 wk
  • Preseason implementation for neuromuscular adaptation
  • Perform as a warm-up to avoid neuromuscular fatigue
  • Maintenance recommended to avoid deconditioning, which can occur at 2 to 8 wk
  • Must include neuromuscular and proprioceptive training, plyometrics, agility drills, func-tional balance, and core strengthening
  • Low cost and easy to implement
  • Identify at-risk players who need more intensive intervention (eg, drop vertical test)
  • Encourage compliance (eg, varied workouts, correlate training with improved sport/ muscular performance, risk awareness education/training)