Inferior Patella Dislocation due to Impaction in the Femoral Trochlea

Abstract

Acute inferior dislocation of the patella is a rare presentation in trauma and orthopaedics. Type II is caused by direct upward force on the inferior pole of the patella when the knee is flexed impacting the superior pole osteophyte into the intercondylar notch. Impaction in the femoral trochlea is rarely reported. A 92-year-old lady presented with locked knee held in 85° of flexion with an abnormal knee contour. Radiographs demonstrated that the upper pole of the patella was impacted in the femoral trochlea with a fracture of a superior pole osteophyte. The extensor mechanism was intact. Closed reduction is achieved under strong opioid pain relief. The patient returned to her baseline knee function within 6 weeks. Closed reduction of an inferior patellar dislocation in elderly patients is aided by superior pole osteophyte fracture and facilitates early mobilization, and avoidance of general anaesthesia.