Osteochondritis Dissecans of the Knee

Patients describe an insidious onset of vague anterior or medial knee pain, worse with running, jumping, and stair descent. Symptoms are often misattributed to growing pains, patellofemoral pain, or a previous sprain. Recurrent effusion after activity is typical. Younger children may present with a limp, activity avoidance, or reduced sports participation. Bilateral symptoms are common in juvenile cases - always examine the opposite knee.

Mechanical symptoms - catching, locking, giving way - are red flags for an unstable or displaced fragment with a loose body and warrant urgent orthopaedic assessment with MRI.

Examination: focal tenderness over the affected condyle (knee flexed to 90 degrees exposes the classic medial femoral condyle lesion). Wilson's test reproduces pain on internal rotation of the tibia during knee extension from 90 to 30 degrees, relieved by external rotation - the tibial spine contacts the classic lesion. Sensitivity is modest; a positive test supports the diagnosis but a negative does not exclude it. Quadriceps wasting is common in chronic cases. Range of motion may be limited if a loose body is present. Always assess gait, patellar tracking, meniscal signs, and ligamentous stability.

Differentials: meniscal injury, patellofemoral pain, patellar tendinopathy, Sinding-Larsen-Johansson, Osgood-Schlatter, discoid lateral meniscus (commonly coexists with lateral femoral condyle OCD), and juvenile idiopathic arthritis.

A high index of suspicion in adolescent athletes with persistent knee pain is essential; OCD is frequently missed on initial imaging.

Standard plain-film workup is AP, lateral, tunnel (notch), and skyline views. The tunnel view specifically exposes the posterior medial femoral condyle where the classic lesion sits and is often the diagnostic film when AP and lateral are normal. The skyline view (Merchant or Laurin) catches the under-10% of lesions on the patella that AP, lateral, and tunnel miss. A Rosenberg view (PA weight-bearing at 45 degrees flexion) is a useful adjunct for posterior condylar assessment. Bilateral views are appropriate in juvenile cases given the frequency of bilateral disease.

MRI is the best non-invasive test for lesion characterisation and stability staging. Features that suggest instability include a high-signal fluid line between the fragment and donor bed on T2, subchondral cysts beneath the lesion, articular cartilage disruption over the lesion, and a displaced fragment. In juvenile OCD, MRI instability criteria are less reliable than in adults and must be correlated with the clinical picture.

CT has a limited role beyond defining bony anatomy for surgical planning. Arthroscopy remains the reference standard for direct stability assessment and can be combined with definitive surgical management.

UK practice is informed by NICE knee-pain assessment principles, BSCOS pathways, and specialist cartilage surgery guidance including NICE TA477 for autologous chondrocyte implantation. Skeletal maturity and lesion stability drive management.

Juvenile (open physes) - stable lesion (ICRS I-II): non-operative trial with activity modification (stop running, jumping, and high-impact sport), limited or protected weight-bearing, and a knee immobiliser, hinged brace, or cast in highly symptomatic cases (practice varies). Physiotherapy for quadriceps strengthening and proprioception once symptoms settle. Serial clinical review with repeat imaging assesses healing. Non-operative treatment is usually trialled for at least 3-6 months; healing is variable, with failure rates up to 50%. Return to sport is criteria-based after evidence of healing.

Juvenile - unstable or displaced (ICRS III-IV) or failed non-operative trial: orthopaedic referral for surgical management. Options depend on stability, size, fragment viability, and surgeon judgement - retrograde or antegrade drilling for stable but non-healing lesions, internal fixation for unstable but viable in-situ fragments (metallic, bioabsorbable, or biological/suture-based constructs), or fragment excision with cartilage restoration (microfracture, OATS, ACI/MACI per NICE TA477 for symptomatic defects typically over 2 cm squared and not previously treated).

Adult OCD: less likely to heal non-operatively, with a lower surgical threshold. Displaced lesions almost always need surgery.

Simple analgesia (paracetamol, NSAIDs per NICE CKS) for symptomatic control. Avoid intra-articular corticosteroid. Refer urgently for true locking, a displaced fragment on imaging, loose body, or a large effusion with mechanical symptoms.

Protocols vary by lesion stability, healing trajectory, and procedure. Broad principles:

Non-operative rehabilitation (stable juvenile lesion): Phase 1 - activity modification, cessation of impact loading, maintaining range of motion, isometric quadriceps and gluteal activation. Phase 2 - progressive closed-chain strengthening, proprioception, stationary cycling, swimming. Phase 3 - graduated return to running, cutting, and jumping guided by imaging and clinical progress. Phase 4 - criteria-based return to sport once healing is established.

Post-operative rehabilitation (drilling, fixation, or cartilage restoration): protocols vary significantly by procedure. Most involve initial protected weight-bearing (non-weight-bearing to toe-touch) for 6-8 weeks, early range-of-motion to protect the articular cartilage, and progressive weight-bearing and strengthening thereafter. Return to high-impact sport is typically 6-12 months and highly variable.

Return-to-sport criteria for both pathways: imaging evidence of healing or sound post-surgical appearance, pain-free weight-bearing and stair navigation, symmetrical quadriceps strength (LSI over 90%), symmetrical single-leg hop mechanics, sport-specific drill completion without symptoms, and psychological readiness.

• •NICE TA477 - Autologous chondrocyte implantation (ACI/MACI) is recommended for symptomatic articular cartilage defects of the knee, typically over 2 cm squared and not previously treated.
• •BSCOS knee-preservation guidance - paediatric orthopaedic referral pathways for confirmed juvenile OCD, with surgery for unstable, displaced, or non-healing lesions.
• •ICRS classification (International Cartilage Regeneration & Joint Preservation Society) - the standard arthroscopic stability classification guiding intra-operative surgical decisions.
• •Andriolo et al. (2014, KSSTA) - Juvenile OCD with stable lesions heals in around half of cases with non-operative management; non-operative failure is common and warrants monitoring.
• •Pascual-Garrido et al. (2009, AJSM) - Adult OCD demonstrates substantially worse healing potential than juvenile OCD, supporting earlier surgical intervention in skeletally mature patients.

• •The classic OCD lesion sits on the lateral aspect of the medial femoral condyle (mnemonic LAME) and accounts for 70-85% of knee OCD - the standard X-ray workup must include a tunnel (notch) view to catch it.
• •Juvenile OCD (open physes) has far better prognosis than adult OCD (closed physes); always consider OCD in adolescent athletes with persistent knee pain and an effusion.
• •Mechanical symptoms (true locking, catching, persistent giving way) suggest an unstable or displaced fragment - urgent orthopaedic referral with MRI.
• •ICRS is primarily an arthroscopic stability classification; MRI features inform pre-operative likelihood of instability but arthroscopy remains the reference standard.
• •NICE TA477 supports ACI/MACI for symptomatic cartilage defects typically over 2 cm squared that have not been previously treated.
• •Discoid lateral meniscus is associated with lateral femoral condyle OCD and should be considered on examination of the affected side.