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Chondromalacia Patellae and Patellofemoral OA

  • Chondromalacia is a pathological description and means cartilage softening
  • Patellofemoral OA may be seen as the end result of progression of chondromalacia

Aetiology

  • Trauma (or repeated microtrauma) may initiate cartilage degeneration by initiating the release of PGE2, causing increased synthesis of proteases, which break up matrix proteins. This creates a vicious cycle, where more destruction and inflammation ensue.
  • 50% idiopathic
  • 20% secondary to maltracking; lateral patellar compression syndrome
  • 15% post traumatic
  • 15% due to unstable patella (recurrent dislocation)
  • Wiberg described 3 types of patella morphology, but found no association between patellar shape and chondromalacia
    • Type I : Equal medial and lateral facets, which are both slightly concave (normal anatomy)
    • Type II : Smaller medial than lateral facet, medial facet is flat or slightly convex
    • Type III : Very small medial facet, which is convex
    • Type IV : Without a medial ridge or medial facet (described by Baumgartl, 1944)

ref: Chrisman " The role of articular cartilage in patellofemoral pain" OCNA 17:231, 1986
ref: Wiberg G. Roentgenographic and anatomic studies of the patellofemoral joint, with special reference to chondromalacia patella. Acta Orthop Scand 12:319, 1941

Classification (Outerbridge)

  • Stage I : Localised softening of the cartilage with minimal or no break in the surface
  • Stage II : Fissuring within the softened area
    • Often longitudinal 'shark gill' type
    • Area < 1.25 cm
  • Stage III : Breakdown of the surface and fibrillation, extending down to subchondral bone
    • 'Crab meat' type
    • Area > 1.25 cm
  • Stage IV : Early osteoarthritis; erosive changes and exposure of subchondral bone, usually involves the opposite articular surface (more often the lateral than the medial femoral surface)

ref: Outerbridge "The aetiology of Chondromalacia Patellae" JBJS 46B: 179, 1961

Pathology

  • Cartilage becomes soft, swollen and spongy
  • Surface looses its lustre and becomes fissured and fibrillated
  • Superficial cartilage damage is painless, but does not heal
  • Deep cartilage damage is painful and may attempt to heal by the formation of fibro-cartilage
  • Patient is usually female and reports diffuse pain in the front (anterior knee pain) of the knee, especially after bent knee activities (stairs, sitting, etc.)

Treatment

Conservative

  • Rest
  • Activity modification
  • Quadriceps training, esp. VMO
    • SLR type are best ( are isometric), after some strength has been achieved can start short arc isotonic exercises in last 30o of extension
    • Knee exercise from 90o to full extension with weight on the ankle is contraindicated as applies high load on patellofemoral joint
  • NSAID : may have protective role in articular cartilage by decreasing prostagladin synthesis
  • McConnell program
    • Stretching of tight lateral restraints
    • Taping of patella to maintain stretch
    • VMO training This program will help in 60% of cases

ref: McConnell J "The management of chondromalacia patellae- along term solution" Aust J Physiother 32: 215, 1986

Operative

  • Patellar shaving : unstable flaps of cartilage are removed
  • Subchondral bone drilling, cortical abrasion, and spongialisation : all aim to encourage fibrocartilage ingrowth from the underlying cancellous bone
  • Lateral release
    • Useful in patients with lateral patellar tilt, without subluxation
    • If subluxed, needs either proximal or distal alignment
    • Effective in 60%
  • Elevation of the tibial tubercle
    • Aims to reduce contact pressures
    • Maquet calculated that a 2 cm advancement of the tibial tuberosity would reduce contact forces by 50%
    • Most of the force reduction occurs in the initial 1 - 1.5 cm of elevation. This is now the recommended distance for advancement
    • Results
      • Maquet procedure (Rozbruk etal Orthop Trans 3:291, 1979)
        • 60% satisfactory results in 30 knees at 1-5 years
        • Complications : skin necrosis, infection
      • Fulkerson procedure (Fulkerson etal " Anteromedial tibial tubercle transfer without bone graft" Am J Sports Med 18: 490, 1990)
        • 89% satisfactory results in 30 knees, more than 2 years follow up
        • No skin sloughs or infections
  • Patellar resurfacing
    • Not indicated
    • Poor long term results
  • Patellectomy
    • Last resort 
    • Patella increases the moment arm of the quadriceps mechanism
    • Patellectomised knees have a decreased torque compared to normal side of 50%
    • Leads to difficulties in stair climbing and rising from chairs
    • Excellent or good in 75% of patients (50% in patello-femoral OA)
    • Poorer results with weakness / instability
    • Must rehabilitate patients aggressively

Ref : Fulkerson and Shea " Disorders of patellofemoral alignment" JBJS 72A: 1424-1429, 1990
Ref: Kelly and Insall " patellectomy" OCNA 17:289, 1986. Lewis etal " Patellectomy- an analysis of 100 cases" JBJS 58A: 736, 1976. Lennox etal "Knee function after patellectomy" JBJS 76B:485-487, 1994



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