Osteochondritis Dissecans of the Capitellum

MRI is the gold standard for staging capitellar OCD. The critical finding is whether there is fluid signal between the fragment and the underlying bone on T2 sequences. If the cartilage is intact and there is no fluid behind the fragment, the lesion is likely stable and may heal with rest. If fluid tracks behind the fragment or cartilage is disrupted, the lesion is unstable and surgery is generally indicated. Plain radiographs alone may underestimate lesion severity.

Beyond the generic stable/unstable staging, two named systems are worth quoting. The Minami radiographic classification grades the plain film: Grade I - a translucent cystic shadow in the middle or lateral capitellum (early, stable); Grade II - a clear split line or zone of demarcation between the fragment and the adjacent subchondral bone; Grade III - a loose body with a defect in the capitellum. The arthroscopic ICRS-OCD classification grades what is seen and probed at surgery: ICRS-OCD I - intact but softened (stable) cartilage over the lesion; II - partial cartilage discontinuity, fragment stable on probing; III - complete discontinuity, a "dead in situ" but undisplaced fragment; IV - a displaced fragment or empty crater (loose body). The exam logic mirrors the MRI: a higher Minami or ICRS grade means a less stable, less healable lesion that moves you from rest toward fixation or cartilage restoration.

Q: A 12-year-old baseball pitcher has lateral elbow pain. Radiographs show a radiolucent lesion in the capitellum. What is the next most appropriate investigation? A: MRI of the elbow. MRI is the gold standard for staging capitellar OCD. It determines whether the lesion is stable (intact cartilage, no fluid behind fragment) or unstable (disrupted cartilage, fluid behind fragment), which directly guides management.

Q: A 7-year-old presents with lateral elbow pain. Radiographs show flattening and fragmentation of the entire capitulum. No loose bodies are seen. What is the diagnosis? A: Panner disease. Age under 10, involvement of the entire capitulum, and absence of loose bodies are characteristic. Panner disease is an osteochondrosis (analogous to Perthes disease of the hip) and is self-limiting with rest. No surgery is indicated.

Q: What is the most important conservative measure for stable capitellar OCD? A: Complete cessation of the offending activity (throwing, gymnastics, weight-bearing). Partial rest (reducing but not stopping activity) often fails. A minimum of 3 months of complete activity restriction is required, with repeat MRI to assess healing before gradual return.

Q: What MRI finding indicates that a capitellar OCD lesion is unstable and likely requires surgery? A: Fluid signal (high T2 intensity) between the fragment and the underlying bone, indicating disruption of the articular cartilage and fragment mobility. This is the most reliable MRI sign of instability. Other signs include displaced fragments and loose bodies.

Q: Why is the capitellum vulnerable to OCD in young athletes? A: The capitellum has limited end-arterial blood supply and is almost entirely covered by articular cartilage, restricting vessel access. In skeletally immature athletes, the ossification centre is still developing. Repetitive compressive loading at the radiocapitellar joint (valgus stress in throwing, axial loading in gymnastics) causes microtrauma and ischaemia in the vulnerable subchondral bone.

Q: What is the typical timeline for return to sport after surgical fixation of an unstable capitellar OCD lesion? A: 6-9 months after confirmation of fragment union on imaging. Rehabilitation involves 6 weeks of protected motion, followed by progressive strengthening and gradual return to throwing or gymnastics over months. Return to the same competitive level is not guaranteed.