A 12-year-old male player presented two days following an acute injury to his knee. He describes experiencing a relatively innocuous twisting injury followed by immediate pain and rapid swelling. He has been unable to move his knee since the injury and is unable to weight bear. On examination he was clearly distressed. His knee moved between 30 and 50 degrees of flexion. There was a tense effusion. The extensor mechanism was intact. Within the limitations of his examination there did not appear to be any ligamentous laxity.
X-ray images showed an effusion but no bony injury. An MRI scan was arranged. This shows an extensive chondral fracture involving most of the medial trochlear surface. The fracture has separated a fragment which measures 18 x 26 mm in transverse and long axis dimension. The separated fragment is sitting in the suprapatellar recess medially. No cortical bony component is identified.
The significance of the injury was emphasised to both the player and his parents. The lesion was fixed in place using bio-absorbable screws. At three-month follow up he has made good progress. He is able to walk comfortably, is able to ride a stationary bike and has a near normal knee examination.
Acute osteochondral injuries like this are relatively rare. They should be suspected whenever a child or adolescent presents with acute knee pain and a history suggestive of a haemarthrosis. Obtaining an early MRI should be considered.
Similar to osteochondral injuries that develop more chronically (‘osteochondritis dissecans’), children and adolescents with extensive osteochondral injuries require specialised orthopaedic treatment. Outcomes are dictated by the location and extent of the osseous and cartilage lesion (fragment size, stability, location, and separation). The age of the patient, and whether the physes are open or closed, are important considerations. It is important to emphasise to the player that returning to change-of-direction sports like football, may not be good for the health of the knee in the longer term.
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