Unusual presentation of a Hoffa fracture

Clinical History

Driver of a car involved in a road traffic accident presenting with an open knee fracture and dislocated patella.

Imaging Findings

A 23 year old man, driver of a car was involved in a head-on collision with an articulated lorry. He presented to casualty with a dislocated right patella associated with an open wound of his right knee. Initial clinical examination revealed a tense haemarthrosis of the knee with an opened distal femoral fracture presenting as a tranverse wound across the distal right thigh. There was no distal neurovascular deficit. Radiograph of the knee and showed a hoffa fracture which involved a fracture of the lateral femoral condyle which has displaced laterally taking along the patella with it. The patient was taken to theatre immediately ( 2 hours following the injury). Thorough washout of the knee was performed and the fracture was fixed temporarily with k-wires followed by 3 cannulated lag screws to fix the lateral condyle. The patient was started on anticoagulant and intravenous antibiotics. Mobilization was started after 48 hours. He was discharged 4 days following the surgery. Full weight-bearing was allowed after six weeks. Three months after surgery the patient has full range of knee movements with no ligamentous laxity. Radiograph showed good bony healing with no avascular necrosis of the condyle.

Discussion

Unicondylar fractures of the femur in the coranal plane was first described by Hoffa in 1904. These are rare injuries. They are usually isolated injury to the involved femur and lateral condyle fractures are more common than medial fractures. Axial loading on the lateral remoral condyle with the knee in 90 degrees or more of flexion produces the tangential fracture patterns. This fracture essentially separates the patellofemoral joint from the tibiofemoral joint causing high shear forces on weight bearing. In addition, hoffa fractures are intraarticular fractures and therefore anatomical reduction and internal fixation is essential. Examination usually reveals an effusion and the neurovascular status should be assessed as these are high-energy injuries. AP and lateral radiographs can be unimpressive in the undisplaced fractures. Appearance of varus and valgus malalignment on the AP view is associated with the shortened femoral condyle. The femoral condyles are not superimposed on the true lateral view. Holmes et al used a standardized surgical approach and used optimally positioned screws placed perpendicularly to the fracture plane with good outcome.

Differential Diagnosis List

Final Diagnosis

Hoffa fracture

URL:	https://www.eurorad.org/case/5661
DOI:	10.1594/EURORAD/CASE.5661
ISSN:	1563-4086