HISTORY -A 40-year old professional mascot, was evaluated by the trainer and presented to the sports medicine clinic 8 days after a right knee injury. The patient was performing an air guitar routine for the home team with an adolescent participant. He jumped in the air and landed on his knees, as is his usual routine. This time, however, he was momentarily distracted and his full weight fell on his right proximal tibia. His pain caused him to limp off of the court. This posterior knee pain persisted but he was able to finish the game. His knee swelled over the next 24 hours. He noted decreased ROM, a “popping & bunching” and pain exacerbated by any axial load. His knee does not lock or catch but he had a sense of giving way and looseness. It had awakened him from sleep but this was relieved with Naproxen. PHYSICAL EXAMINATION -The patient had a slightly antalgic gait. He was unable to fully extend his right knee while standing. There was mild quad atrophy and a 1+ effusion. ROM was 0/5/125 compared with his left knee 0/0/145. He was tender to palpation in the mid-portion of his right politcal fossa. The anterior knee was not tender. The tibial sag sign was absent. The quadriceps active drawer test and Lachman were negative. The posterior drawer was slightly increase on the right with an equivocal end point when compared with the left. The pivot shift and reverse pivot shift were negative, although he was noted to have some guarding. The posterolateral drawer sign was negative. He had no meniscal signs. DIFFERENTIAL DIAGNOSIS: PCL tear Posterior lateral meniscal tear Lateral collateral ligament sprain and posterolateral corner injury Baker's cyst TESTS AND RESULTS: Right knee anterior-posterior, notch, lateral and sunrise radiographs - normal. Right knee MRI - Tear of the PCL.- No meniscal injury. - Joint effusion and Baker's cyst. FINAL/WORKING DIAGNOSIS: Posterior Cruciate Ligament Tear. TREATMENT: Cryotherapy, Ibuprofen 800 mg QD to BID PRN Rehabilitation quadriceps strengthening program. PCL stabilizing brace Return to full activity in 7–14 days.