LAUSR

A 10-year-old male was presented to the emergency department with complaints of right knee pain. He fell from a swing set and noted immediate pain and deformity of his right lower extremity. He was unable to extend his knee or bear weight on the affected leg. Upon examination, he had obvious deformity and effusion of the right knee. He had limited range of motion and was reluctant to fully extend his knee. He had intact skin, motor and sensory function, and palpable distal pulses in the right lower extremity symmetric with the contralateral extremity. Compartments were soft and compressible. He underwent sedation in the emergency room for closed reduction of the knee. Examination was grossly unstable with questionable anterior drawer laxity, Positive Posterior Drawer Test, and increased laxity with varus stress. Plain radiographs demonstrated a skeletally immature individual with lateral subluxation of the tibia relative to the femur without obvious fracture (Fig. 1a, b). Magnetic resonance imaging (MRI) demonstrated intact ACL, disruption of the PCL with femoral avulsion, concern for disruption of PLC structures LCL and posterolateral capsule, and a horizontal, anterior horn lateral meniscal tear (Fig. 2a–f). The patient underwent surgery 2 days later. Examination under anesthesia demonstrated recurvatum deformity of the knee, positive posterior drawer, and varus laxity at 0° and 30° of flexion. Arthroscopically, articular cartilage was intact in all compartments. The ACL was intact, however, the PCL was avulsed from its femoral origin. Significant widening was noted within the lateral compartment consistent with a positive drive thru sign as well as an anterolateral meniscal tear. An open approach to the lateral knee was undertaken where the LCL was avulsed from its femoral origin and posterolateral capsular injury was evident. Popliteus Introduction