Acute injuries to the posterolateral corner of the knee in children: a case series of 6 patients.

BACKGROUND: Isolated avulsion fractures of the posterolateral structures (the popliteus tendon, the lateral collateral ligament, and the popliteofibular ligament) of the knee are rare.

PURPOSE: To describe the outcome after an isolated avulsion fracture at the femoral attachment of the posterolateral structures in skeletally immature patients and to communicate our clinical experience concerning diagnosis and treatment.

STUDY DESIGN: Case series; Level of evidence, 4.

METHODS: Six skeletally immature patients (mean age, 13.3 years; range, 12.6-13.7 years; 5 boys, 1 girl) with an avulsion fracture of the femoral attachment of the posterolateral structures were evaluated on average 5.1 years (range, 2.7-8.3 years) after the injury. Five patients were treated with open reduction and fixation of the fragment. The sixth patient was treated nonoperatively with cast immobilization. The evaluation was based on reassessment of radiographs and magnetic resonance imaging (MRI scans), registration of activity level, and examination of objective and subjective knee function.

RESULTS: The injury involved both the popliteus tendon and the lateral collateral ligament in 5 of the 6 cases. In the operated patients, the mean Lysholm knee score was 98 (range, 94-100) (0-100, with higher scores indicating a better outcome). The mean Knee injury and Osteoarthritis Outcome Score (KOOS) quality of life (QOL) was 80 (range, 50-100) (0-100, with higher scores indicating a better outcome). The range of motion and the KT-1000 arthrometer anterior laxity measurements were normal. The nonoperatively treated patient with involvement of both the popliteus tendon and the lateral collateral ligament suffered a bone bridge in the periphery of the femoral physis, causing a valgus deformity of the knee. An open wedge femoral osteotomy was performed. The Lysholm knee score was 80, and KOOS QOL was 25 at follow-up. The patient also had an extension deficit of 5° and a flexion deficit of 10°.

CONCLUSION: An avulsion of the femoral attachment of the posterolateral structures in skeletally immature patients may involve both the popliteus tendon and the lateral collateral ligament. Open reduction and fixation of the fragment gave a satisfactory outcome.