Lateral epicondylar femoral avulsion fracture combined with tibial fracture: a counterpart to the arcuate sign.

We present a case of femoral avulsion of the lateral collateral ligament (LCL) with complete tear of the posterior cruciate ligament (PCL) and popliteus tendon accompanied by demonstrable posterolateral rotary instability (PLRI) of the knee. A 55-year-old man was involved in a road traffic accident. Radiographs revealed an avulsion fracture of the lateral epicondyle of the femur and a fracture of the tibial shaft. An MRI scan showed the lateral epicondyle was avulsed by the LCL and the popliteus tendon. The PCL signal was absent. The tibial shaft fracture was fixed with an intra medullary nail. Sagging of the tibia, with loss of prominence of tibial tuberosity and a positive posterior drawer test, demonstrated a complete tear of the PCL. The avulsion fracture of the lateral epicondyle was treated by an open reduction and internal fixation with two staples. A ligament can be avulsed at either end, and to our knowledge, this pattern of injury as a counterpart to arcuate sign has never been documented in the literature. It is important not to dismiss a small avulsion fracture around the knee joint as insignificant, as it could indicate the presence of a major ligamentous injury.