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Ortho FRACS > Knee > Flashcards

Knee Flashcards

1
Q

Define Patellofemoral instability

A

Encompasses a broad spectrum of instability from frank dislocation to subluxation

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2
Q

Factors predisposing to PFJ instability

A

BONY

  • Patella Alta
  • Trochlea dysplasia
  • Lateral Femoral condyle dysplasia
  • Patealla dysplasia

SOFT TISSUE

  • Ligamentous Laxity
  • MPFL Injury
  • VMO atrophy / high insertion
  • VL hypertrophy
  • Tight Lateral Structures (ITB, VL, Capsule)

ALIGNMENT

  • Femoral Anteversion
  • External Tibial Torsion
  • Lateral Tibial Tuberosity
  • Genu Valgum
  • Pes Planus
  • Increased Q Angle
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3
Q

Define Q Angle

A

Angle Subtended by a line drawn from the ASIS to centre of patella and the centre of the patella to the tibial tuberosity

Male = 10, Female = 15

Pathological Male >15, Female >20

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4
Q

Schottle’s Point

A

Anatomic isometric insertion of the MPFL Defined at the point 1mm anterosuperior to the intersection of two lines

  • a line extending from the posterior cortex and another
  • perpendicular to the first, just proximal to the most posterior point of Blumensaat’s Line
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5
Q

MPFL

A

Medial Patellofemoral Ligament

  • Primary Stabiliser of the Patella
  • Extrasynovial ligament that runs transversely from the MFC to the patella in Layer II
  • Most often injured on the femoral side
  • Femoral Insertion - MFC midway between adductor tubercle and medial epicondyle
  • Patella Insertion - Proximal 1/2 medial border of patella
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6
Q

Algorithm of Tx for PFJ Instability

A

o Patella Alta: - TTT Distalisation

o ↑ TTTG: - TTT Medialisation

o MPFL Tear: - MPFL Reconstruction

o Patellar Tilt: - Lateral Release

o Severe Trochlear Dysplasia: - Trochleoplasty (uncommonly performed)

o ↑ Femoral Anteversion: - Femoral Derotation Osteotomy

o External Tibial Torsion: - Tibial Derotation Osteotomy

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7
Q

Patella Height Measurements

A

Insall- Salvati Method

  • Insall-Salvati method measures the greatest diagonal longitudinal length of the patella (usually from superoposterior corner to inferior pole) and the length of the inferior pole of patella to the tibial tuberosity (the posterior border of the patella tendon)
  • This ratio is A/B, with patella tendon (A) and patella height (B).
  • Normal ratio is 1.0 + 0.2.
  • Patella alta has a high ratio >1.2.
  • Patella infera (baja) has a low ratio <0.8.

Blackburne-Peele Method

  • Blackburne-Peele method measures the longitudinal length of the patella articular surface and the length of the inferior patellar articular surface to the perpendicular joint line.
  • This ratio is A/B, with inferior articular surface to joint line (A) and patella articular surface (B).
  • Normal ratio is 0.8 + 0.2.
  • Patella alta has a high ratio >1.0.
  • Patella infera (baja) has a low ratio <0.8.

Caton Deschamps Method

  • Caton-Deschamps Index is similar to ISI and BPI.
  • It is a ratio of the posterior articular length of the patella and the length from the inferior pole to the superoanterior tip of the tibia.
  • Normal is 1.0 +/-0.2.
  • Patella alta is > 1.2
  • Patella infera is <0.8.
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8
Q

Trochlear Morphology

A

Trochlear Depth = < 8mm = shallow

Bump Sign

  • If line of floor where it joins the ant cortex has a bump Patella will not engage properly
  • Bump >3mm is abnormal

The Crossing Sign

  • A primary radiographic indication of trochlear dysplasia and is visualized when the line representing the trochlear floor crosses the anterior border of the femoral condyles
  • Can be combined with a TROCHLEAR SPUR
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9
Q

Radiologic Trochlear Angles

A

Sulcus Angle

  • Sulcus Angle is the depth of convexity of the trochlear groove.
  • Angle made with lines from centre of trochlear groove to highest point of medial and lateral femoral condyles.
  • Normal angle is 136° + 6.
  • > 145 = dysplasia

Subluxation (Patellofemoral congruence angle of Merchant)

  • Angular difference between
    • line bisecting the sulcus angle &
    • line from sulcus apex to the lowest point on patella
  • Medial direction is –ve
  • Merchant (JBJS Am 1974)
    • 100 Normal subjects - Normal = –6 ± SD11°
    • 25 recurrent dislocators - +23°
    • AbN = greater than 16o

Lateral tilt - Laurin’s lines

  • Line along lateral patellar facet
  • Line b/w most prominent ant points of trochlea
  • Normal = Lines should diverge laterally
  • Laurin 1978
    • 100 Normal - 97% opened laterally
    • 30 Recurrent subluxators - 80% parallel & 20% opened medially
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10
Q

Patella Radiologic Investigations

A
  • All patients post an acute dislocation should have XRAYS & MRI (look for concomitant osteochondral lesions which occur in 30%)
  • Radiological investigations include
    • XRAYS (AP WEIGHT BEARING / LATERAL [30° FLEXION] / SKYLINE [MERCHANT 45°])
      • Coronal Plane Deformity – 3 FOOT STANDING FILMS
      • Patella Height (Insall-Salvati / Blackburne Peele / Blumensaats/Caton-Deschamps)
      • Trochlear Morphology
        • Crossing Sign (Lateral)
        • Sulcus Angle (Skyline)
      • Patella Tilt
    • CT (TTTG)
      • Lower Limb Version – PERTH PROTOCOL/SCANNOGRAM
      • TTTG
      • Patella Tilt
      • Sulcus Angle
    • MRI
      • Bone Bruising
      • Chondral Injury
      • MPFL Injury
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11
Q

Tibial Tubercle Trochlear Groove Angle

A
  • TTTG angle represents relationship of centre of deepest part of trochlear sulcus & tibial tuberosity.
  • Assessment of TTTG by superimposing the trochlear groove and tibial tuberosity on axial CT.
  • Horizontal line is drawn from the posterior femoral condyles.
  • Perpendicular line is drawn to the deepest part of the trochlear groove and the anterior part of the tibial tubercle.
  • The distance between the 2 lines is the TTTG.
  • Normal TTTG is 10-12mm.
  • TTTG > 20mm is an indication for TTT.
  • TTTG b/w 12-20mm is the grey area for TTT treatment.
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12
Q

Medial Knee Layers

A

Layer 1

  • Fascia
  • Sartorius

Layer 2

  • Superficial MCL
  • POL (Posterior Oblique Ligament)
  • MPFL
  • Semimembranosus

Layer 3

  • Deep MCL
  • Capsule
  • Coronary Ligament
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13
Q

Lateral Knee Layers

A

Layer 1

  • ITB
  • Biceps

Layer 2

  • PF retinaculum
  • LPFL

Layer 3 Superficial

  • LCL
  • Fabellofibular Ligament

Layer 3 Deep

  • Popliteus tendon
  • Popliteofibular ligament
  • Arcuate Ligament
  • Coronary Ligament
  • Capsule
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14
Q

Covertry Criteria for HTO

A

COVENTRY (Long Term Results of Upper Tibial Osteotomy for Degenerative Arthritis of the Knee – Acta Orthopaedic Belgium 1982) published results of his criteria for HTO. There are 7 criteria:

  • Age <65 Years / Physically Active
  • Pain Correlated with Radiological Changes (Medial)
  • Radiologically Normal Lateral Compartment
  • Varus Deformity < 15°
  • FFD < 15° / ROM > 90°
  • Stable Knee (Cruciate Intact)
  • Internal Derangements Excluded
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15
Q

Indications for HTO

A
  • 3/12 failed NON-OT Mx
  • Age < 55 years
  • Physically Active
  • Unicompartmental OA (Clinically & Radiologically [MRI])
  • Asymptomatic Mild PFJ OA
  • FFD <15°
  • Varus Deformity <10
  • SUBLUXATION < 1CM
  • ROM > 90°
  • Stable Knee (Cruciate Intact)
  • Weight < 90 kg
  • Non-Inflammatory Arthritis
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16
Q

Contra-indications for HTO

A
  • Age > 55 years
  • Physically Inactive
  • BICOMPARTMENTAL / TRICOMPARTMENTAL OA
  • INFLAMMATORY ARTHRITIS
  • Symptomatic PFJ OA
  • FFD > 15°
  • ROM < 90°
  • Unstable Knee
  • Weight > 90 kg
  • VARUS / VALGUS THRUST
  • Subluxation > 10MM
17
Q

Pre-op Planning of HTO

A

Dugdale Technique

  • Osteotomy plan as per DUGDALE (Preoperative Planning for HTOL: The Effect of Lateral Tibiofemoral Separation and Tibiofemoral Length – CORR 1992) involves preoperative templating and planning degree of correction and osteotomy cuts.
  • Line A is a longitudinal line drawn from centre of ankle to the lateral 62.5% of the tibial plateau as measured from the medial edge of the proximal tibia.

This point lies lateral to the lateral tibial spine and equates to 3-5° of overcorrection.

  • Line B is a longitudinal line drawn from centre of femoral head to the lateral 62.5% of the tibial plateau as measured from the medial edge of the proximal tibia.
  • The size of the wedge = the distance BC
  • The angle formed is the α ANGLE and the amount of correction required.

(Either opening requiring structural bone graft or closing requiring resection)

  • For medial opening wedge, osteotomy is performed 4cm below the medial joint line aimed at the tip of the fibular head.
  • For lateral closing wedge, osteotomy is performed 2.5cm below the lateral joint line horizontally, with the wedge removed corresponding with the α angle.
18
Q

Goals to TKR

A

Restore mechanical Axis

Restore Joint Line

Ligamentous Balance

Restore Normal Q angle

19
Q

Goals of Revision TKR

A

Extraction with minimal bone loss

Replacement of bone deficiences

Revision Implant Stability

Restore Mechanical axis

Restore Joint Line

Ligamentous Balance

Restore Normal Q angle

20
Q

Principles of Revision TKR

A

Use Old Incisions

Clear medial and lateral gutters

Difficult access – Quads snip or TTO

Implant Removal – maintain bone stock

Recut surfaces to fit new prosthesis

Establish tibial joint line

Coronoal balancing

Sagittal balancing

Patellofemoral tracking

21
Q

Causes of Valgus Knee

A
  • CONGENITAL (SKELETAL DYSPLASIAS)
  • ACQUIRED
    • MALUNION (FEMUR / TIBIA - COZEN)
    • PHYSEAL INJURY (FEMUR / TIBIA)
    • TRAUMA (FRACTURES)
    • MENISECTECTOMY
    • SONK
    • LATERAL COMPARTMENT OA
22
Q

Anatomy of ACL

A
  • ACL average length is 38MM and width is 11MM
  • Femoral insertion: POSTERIOR ASPECT OF MEDIAL SURFACE OF LATERAL FEMORAL CONDYLE.
  • Tibia insertion: INTERCONDYLAR EMINENCE OF TIBIAL PLATEAU.
  • It passes DEEP to the TRANSVERSE MENSICAL LIGAMENT.
  • Few fibres blend with the ANTERIOR HORN of LATERAL MENSICUS.
  • There are 2 BANDS of the ACL, named after their tibial insertion orientation:
    • ANTEROMEDIAL BAND (Tight in Flexion / Larger / AP STABILITY) AMF
    • POSTEROLATERAL BAND (Tight in Extension / Smaller / ROTATORY STABILITY) PLE
23
Q

Screw Home Mechanism

A
  • During ROM, the femur ROTATES on the tibia.
  • During extension, femur IR (EIR – EXTENSION with INTERNAL ROTATION).
  • During flexion, femur ER (FER – FLEXION with EXTERNAL ROTATION)
  • The screw home mechanism leads to the terminal IR during the last 15° extension.
24
Q

Compensation for Loss of ACL

A

Other anatomical structures can compensate for the loss of ACL:

  • POSTERIOR HORN MEDIAL MENISCUS (principally)
  • POSTEROLATERAL COMPLEX
  • POSTEROMEDIAL COMPLEX
  • HAMSTRINGS
25
Q

Function of ACL

A
  • PREVENT ANTERIOR TIBIAL TRANSLATION
  • SECONDARY STABILISATION AGAINST VARUS / VALGUS
  • SECONDARY STABILISATION AGAINST ER
  • PROPRIOCEPTION
  • It acts as a guide rope during the SCREW HOME MECHANISM of knee extension.
  • It also acts as a guide for PHYSIOLOGICAL FEMORAL ROLLBACK during ROM.
  • During normal walking, ACL only carries small loads of 20% of ultimate load.
26
Q

ACL Technical Factors

A
  • GRAFT TYPE
  • TUNNELS PLACEMENT
  • FIXATION TYPE (weakest component on reconstruction)
  • TENSION GRAFT
27
Q

Natural History of ACL Injury

A
  • Recurrent instability is the main complication ACL ruptures that are not treated with reconstruction and occurs in 15-90%
  • Meniscal tears are classically dependent on the stage of injury.
    • Acute ACL ruptures are associated with LATERAL MENISCAL TEARS.
    • Chronic ACL ruptures are associated with MEDIAL MENISCAL TEARS (less mobility and higher risk of injury

INDELLICATO (Clinical Orthopaedics 1985) demonstrated ACL injuries result in:

  • ACUTE ACL RUPTURES ASSOCIATED WITH MENISCAL TEARS IN 70%
  • CHRONIC ACL RUPTURES ASSOCIATED WITH MENISCAL TEARS IN 90%
  • NON-OPERATIVE TREATMENT ASSOCIATED WITH 60% RATE MENISECTOMY AT 5 YEARS
  • Posttraumatic OA of the knee develops INDIRECTLY to an ACL rupture and progression to OA is variable.
    • A chronically unstable knee will undergo meniscal injury, which ↓ hoop stress absorption from the damaged meniscus, which results in ↑ loading forces on the articular surface.
28
Q

ACL Graft Type

A
  • There are several types of grafts available, divided into 3 categories
    • AUTOLOGOUS (Ipsilateral or Contralateral)
      • AUTOLOGOUS HAMSTRINGS (2400 N)
      • AUTOLOGOUS BONE-PATELLA TENDON-BONE (BPTB) (3000 N)
    • ALLOGRAFT
    • SYNTHETIC
  • All grafts have an ULTIMATE LOAD TO FAILURE > 2000 N (normal ACL is 1725 N).
  • NO GOLD STANDARD à LARGELY PRACTITIONER CHOICE
  • Graft ultimate load to failure depends on the type of graft as well as the thickness & width.

(↑ Thickness / Width = ↑ Ultimate Load to Failure)

  • In general, autologous grafts and allografts have similar long term outcomes.
  • GRAFT INCORPORATION depends on the type of graft used.
    • For hamstrings and quadriceps tendons, healing is via ligament to bone (10-12/52)

For BPTB, healing is via bone to bone and QUICKER (6-8/52)

29
Q

ACL Tension of Graft

A
  • Graft needs to be inserted under tension to perform primary function.
  • Ideal tension is unknown.
  • Most suggest tension to 40N.
  • Ideal position of tension is KNEE FLEXION 30°, which is shown to be better than in full extension.
  • Tension of graft will ↓ with time as grafts are VISCOELASTIC MATERIALS and hence undergo STRESS RELAXATION, CREEP and FATIGUE.
  • Creep is the time dependent deformation that of a material under a constant load
  • Stress relaxation is the time dependent change in stress that occurs under a constant strain (deforming force).
  • Therefore all grafts will lengthen and ↓ tension with time.
30
Q

ACL Tunnel Placement

A
  • TUNNEL PLACEMENT is a critical aspect of ACL reconstruction.
  • Ideal position is unknown
    • Isometric, Direct Fibres, Eccentric and Equidistant, Anatomic, Low Tension
  • FEMORAL TUNNEL PLACEMENT = POSTERIOR RIDGE OF MEDIAL ASPECT LFC AT 1030HRS OR 1330HRS
  • Too vertical femoral tunnel will results in PCL IMPINGEMENT.
  • TIBIAL TUNNEL PLACEMENT is referenced off several points:
    • ACL STUMP
    • HALFWAY BETWEEN ANTERIOR HORN LATERAL MENISCUS & MEDIAL TIBIAL SPINE
    • 7MM ANTERIOR TO PCL
31
Q

ACL Fixation Type

A
  • This is the weakest component of ACL reconstruction.
  • Tibial fixation is the weakest (weaker than femoral) due to cancellous bone in tibial metaphysis.
  • Forces acting on ACL graft during early rehabilitation are 450-500 N.
  • As Initial fixation is provided by mechanical devices they need to be strong enough to allow stability in rehabilitation.
  • There are three main types of fixation methods for ACL reconstruction:
  • APERTURE FIXATION
    • Advantages
      • Provides anatomical and direct fixation
      • No slippage under cyclical loading
      • Neutralises graft motion and tunnel widening
      • Nil bungee effect or synovial tunnel inflow
    • Disadvantages
      • Laceration
      • Eccentric graft placement
      • Reproducibility and technical variables
      • Biogradable – cystic changes
  • SUSPENSORY FIXATION (ENDOBUTTON)
    • Advantages
      • Reproducibility
      • Biomechanical properties
      • Bigger graft sizes
      • Tibia
    • Disadvantages
      • Bungee effect
      • Tunnel widening
  • TRANSCONDYLAR/CROSS PINS
    • Advantages
      • Biomechanical Properties
      • Less Tunnel Widening and Bungee Effect
    • Disadvantages
      • Technically Demanding
      • Higher intra and post operative complications
      • Expensive 3 x cost Endobutton
  • In the RCT clinical trials NO DIFFERENCE IN PATIENT OUTCOME SCORES

Ortho FRACS (3 decks)

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