A 13-year-old boy presented with lateral knee pain following a twisting injury at football. Plain radiographs revealed an avulsion fracture at the popliteal sulcus (Fig. 1, arrow). MRI confirmed avulsion of the popliteal tendon (Fig. 2, arrowhead) deep to the fibular collateral ligament (Fig. 2, arrow), with no other injury identified.

Fig. 1
figure 1

Plain radiograph

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Fig. 2
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MR image

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The popliteal tendon originates primarily from the popliteal sulcus of the lateral femoral condyle. It then courses inferiorly, between the lateral meniscus and the joint capsule, to join its muscle belly posterior to the proximal tibia. Along with the fibular collateral and biceps femoris ligaments, the popliteal tendon is a major stabilizer of the posterolateral corner of the knee [1].

Injury to the popliteal tendon is usually seen in conjunction with injuries to other structures at the posterolateral corner of the knee. However, isolated avulsion of the popliteal tendon has been reported [2]. The presence of an avulsed bone fragment at the popliteal sulcus should lead one to the diagnosis of popliteal tendon avulsion.