An athletic 14-year-old Asian-American female with no significant past medical history presented 4 weeks after a basketball injury with right knee pain. She was playing in a high school competition when she dove for the ball and fell to the ground. She struck her right knee with the contralateral knee and twisted her right knee as she fell. The right knee was swollen for several days. There was an audible "pop" at the time of the injury. She continued to have pain on the medial and lateral aspects of the right knee which gradually improved. She was able to bear full weight, and she wore a compression knee sleeve.
On examination the patient did not have an antalgic gait. The right knee had no bruising and there was no residual effusion. Bilateral knee range of motion was 0  to 145  and painless. There was no tenderness to palpation along the right medial or lateral joint lines and McMurray's test (evaluates for meniscal injury) was normal. The right knee demonstrated normal stability with anterior and posterior drawer tests and with varus and valgus stress (respective tests for anterior, posterior, lateral, and medial ligamentous injuries). The patella was stable without apprehension and painless with the patellar grind test (evaluates for patellar chondral injury). The Dial test was symmetric and normal at 30  and 90  bilaterally without pain (evaluates for posterolateral corner injuries). The neurovascular exam was normal. The patient had no other significant physical exam findings but she was unable to run, jump or twist. Due to her history and her inability to return to sports an MRI was ordered.
A six-sequence, closed, 3.0T MRI was completed. A high grade-to-complete rupture of the popliteus tendon was seen at the level of the popliteal hiatus, with retracted tendon distal and medial to the tibiofibular articulation. This tear can be visualized in Figure 1 (axial MRI) as an enlarged cross section of the popliteus resulting from retraction and scarring of the muscle. The posterior compartment of the knee is visualized in Figure 2 (Sagittal MRI), however, the popliteus is not seen in the popliteal hiatus due to the tear (green arrow). It would normally be seen at the posterior horn of the lateral meniscus. There is edema adjacent to the soleus muscle posterior to the popliteal hiatus, deep to the lateral head of the gastrocnemius (blue arrow). This resulted from the popliteus injury. The distal popliteus is visualized (blue arrows) in Figure 3 (Coronal MRI) however a gap is seen where the tendon should attach proximally at the fibular head and lateral femoral condyle (yellow circle). A few proximal tendinous fibers remain.
Bone contusions were seen in the posterolateral corner on the tibial plateau and adjacent fibular head. There was no further injury to the posterolateral corner including the lateral collateral ligament (LCL) and biceps femoris. There was no tear of the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), or menisci. The medial collateral ligament (MCL) and iliotibial (IT) band and were intact. There was no damage to the articular cartilage.