Anteromedial instability masquerading as extensor weakness.

Presenting Author - Jayendra Subbaraman
Rupture of the extensor mechanism of the knee is a devastating complication after total knee arthroplasty (TKA). Decreased extension strength may be seen following injury to extensor mechanism of normal knee or post operatively following TKA, ACL reconstruction and other knee surgeries. We had a patient who underwent TKA 3 months ago, his post op knee range of motion was good and he had no extensor lag. However the patient had a fall following which he presented with an 80* extensor lag. On trying to actively extend the knee, we found an attitude of external rotation. On passively extending the knee he was able to sustain extension without support. On examination there was valgus opening of the knee. On investigating the patient we found the radiograph was normal. Ultrasound scan reported a quadriceps tear. Intra operatively we found an intact quadriceps. There was disruption of medial capsular attachment and medial collateral ligament. This anteromedial instability presented as extensor lag. We reconstructed the MCL with hamstring autograft and repaired the capsule. Post operatively he was able to completely extend the knee.