An Unusual Source of Knee Pain in a Competitive Breaststroke Swimmer

Aims: The purpose of this case report is to present an unusual source of knee pain in a competitive breaststroke swimmer and review the clinical, etiologic, and radiographic features of the disease process.
Presentation of Case: A 20-year-old collegiate swimmer presented with complaints of left knee pain and weakness. Physical findings of tenderness in a lateral condylar location, measurable thigh atrophy, and pain on a resisted knee extension test were present. Plain radiographs demonstrated osteochondritis dissecans of the lateral femoral trochlear groove and evidence of moderate trochlear dysplasia. Surgical findings confirmed a 3 cm by 1 cm loose osteochondritis dissecans fragment.
Discussion: The knee is forcefully extended against the resistance of the water during the propulsive phase of the whip kick used by breaststroke swimmers. This movement results in high lateral patellofemoral contact loads and increased lateral patellar displacement forces. In a knee with trochlear dysplasia there are additional increases in patellar displacement and contact pressures. Osteochondritis dissecans involving the lateral trochlear groove has been associated with repetitive tangential type shear stresses.
Conclusion: The findings in the present case report would suggest a very unique situation in which high lateral trochlear shear stresses were created by the repetitive whip kick activity in the knee of a breaststroker swimmer and that these unusual stresses were further magnified by underlying trochlear dysplasia. With continued intense training efforts, the shear stresses eventually exceeded a critical threshold of the subchondral bone of this region and failure occurred, resulting in osteochondritis dissecans of the lateral trochlea.