RECURRENT DISLOCATION PATELLA

RECURRENT DISLOCATION PATELLA

Factors stabilizing patella

• Static factors
• shape of patella
• shape of femoral condyles (flattening of lateral condyle destabilizes
• normal patellofemoral distance (patella alta)
• normally tensioned medial capsule

• Dynamic factors
  • vastus medialis obliqus
• both dynamic and static forces tend to pull patella laterally

Q angle

• first described by Brattstorm
• angle between line of quadriceps pull and patellar tendon
• line from ASIS to centre of patella and centre of patella to tibial tuberosity
• normal 8-10⁰ males and 15⁰ females
• this valgus angle gives a lateral force vector to patellofemoral joint as knee is extended
• increased Q angle = increased instability
• causes
  • genu valgum
  • increased femoral anteversion
  • external tibial torsion
  • laterally positioned tibial tuberosity
  • tight lateral retinaculum

Causes

• dysplastic patella
• dysplasia of femoral condyle
• patella alta
• change in orientation of the fibres of m
• hypertrophy of vastus lateralis
• generalised ligamentous laxity

Clinical features

• diffuse pain around knee aggravated by going up/down hill
• giving away feel
• patellar crepitus
• knee effusion
• Tests
  • patellar grind test
  • patellar glide test
  • patellar tilt test
  • patellar tracking
    • dynamic
    • active
  • apprehension test
  • quadriceps atrophy
  • generalised ligamentous laxity

Radiographic features

• bipartate patella
• Blumensat line below lower pole of patella (patella alta)
  • 30⁰ flexion- line through intercondylar notch touches the lower pole of patella
• Insall's index (LT/LP >1)
• Blackburne and Peel index
  • ratio of length of articular surface of patella : distance between articular surface of tibial and lower pole of patella
  • Normal .54 to 1.06
• Axial view of patella – shallow sulcus
  • sulcus angle and congruence angle – for diagnosing minimal subluxation
• CT – with full extension of knee – lateral tilt of patella and subluxation more pronounced
• Medial subluxation of patella also described – demonstrated only in Kinetic MRI

Treatment

• Non operative
  • quadriceps strengthening exercise
  • stabilization braces
• Surgical
  • adults
    • lateral retinacular release (open / arthroscopic)
      • for normal Q angle and tight lateral structures
    • proximal extensor realignment
      • for Q angle <20⁰
      • Insall's technique
        • lateral release and advance vastus medialis laterally and distally
      • Madigan's technique
    • distal realignment
      • for Q angle >20⁰
      • Roux Goldthwait surgery
        • in skeletally immature
        • patellar tendon split longitudinally and lateral half transplanted medially
      • Elmslie Trillat operation
        • in skeletally mature
        • lateral release + medial retinacular plication + medial transfer of tibial tuberosity
    • proximal and distal realignment
      • Q angle =~20⁰
      • skeletally mature
      • Hughston, modified Elmslie Trillat
    • patellectomy with extensor realignment
      • as a salvage procedure
        • patellar chondromalacia
        • OA knee
        • >40 yrs of age
      • West and Soto-Hall – patellectomy with plastic repair of Quadriceps
  • in skeletally immature
    • semitenodesis
      • semitendinous tendon is sectioned at musculotendinous junction
      • distal segment of tendon passed through hole in patella and sewn back to itself
    • quadricepsplasty (Green)
      • lateral release with mobilization of vastus lateralis
      • posteromedial portion of vastus medialis advanced distally and laterally

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