The anatomy of the popliteus tendon is well known. The popliteus muscle arises from the proximal posterior surface of the tibia and has insertions into the posterior portion of the lateral meniscus and the femur, both deep and anterior to the lateral collateral ligament. The femoral insertion has a crescent shape, with the superior aspect being concave . The main tendon of the popliteus muscle consists of anterior and posterior fibers. Electromyographic recordings have shown that the muscle acts as a prime medial rotator of the knee joint and in the crouching position is the only muscle in a position to prevent the femoral condyles from gliding forward on the tibia . Some anatomical variants of the popliteus tendon have been described without clinical relevance[12, 13].
Isolated ruptures of the popliteus tendon are rare and few cases are described in the orthopaedic literature. The lesion is more frequently reported as femoral avulsion and only in two cases [6, 8] a complete intrasubstance tear has been identified. Mechanism injury is often misleading and unclear and different mechanisms have been described. Lesions have been reported occurring by a non contact external rotational mechanism: a sudden external rotation to a partially flexed knee [1, 4, 5], a forced external rotation with a varus force application in some cases, or a forced external rotation with femur fixed  have been described. In our case, no specific injury was recalled by the athlete and probably, also considering the type of tear, an overuse or degenerative mechanism could be considered as responsible of the partial tear.
In the avulsion type, an acute haemarthrosis without laxity signs and pain on lateral aspect of knee should lead to suspicion of such a lesion. In the other cases without avulsion, as in our patients, the findings on physical examination are subtle and reveal only discomfort just over the popliteus tendon in an otherwise stable knee. So, the diagnosis is easily overlooked. The diagnosis must be verified by an arthroscopic examination because also the MRI, usually helpful, can be in this pathology unclear. Arthroscopy should be considered an additional step in the process of information gathering  and in case of isolated lesion as reported by previous authors an arthroscopic debridement can be carried out at the same time.
Treatment of isolated rupture of the popliteus tendon is not well defined. Despite the relatively small number of cases presented, different treatments have been reported in literature. Rose and Parisien  presented in the late 80's the first known case of isolated rupture of the popliteus tendon after an indirect trauma, treated with an open repair and full recovery. Gruel , a few years later, presented two cases of rupture of the tendon with an associated bone avulsion treated with an arthroscopic debridment and a bone removal without repair of the torn tendon followed by a complete recovery at two years follow-up. Burstein and Fischer  presented the same outcome after a similar lesion and treatment in a professional football player who sustained a complete rupture. The authors performed a diagnostic arthroscopy and no further surgical treatment was performed. Westrich et al.  presented a case of isolated rupture repaired using two suture anchors, with a complete recover and no signs of lateral/posterolateral instability at its longest follow-up. In this last case it was also associated a partial rupture of the ACL. It is interesting to note that the case of isolated rupture of popliteus reported by Westrich et al.  was the only case that presented a subtle, but clinically detectable, preoperative posterolateral laxity. Mirkopulos et al  reported the case of a young basketball player who underwent surgical reattachment of the avulsed portion of the popliteus tendon using metallic screw and washer.
More recently, Conroy et al.  presented a case of isolated complete rupture in a professional soccer player, with a intra-susbtance tear that was treated by arthroscopic debridment of the stumps with a final return, 6 weeks later, to competitive soccer level. Our case is the first reported case to our knowledge of partial popliteus tendon lesion. On the basis of clinical history this case should be distinguished from the popliteus acute tear and the symptoms were related to mechanical impingement of the torn fibers with the lateral meniscus. Also the arthroscopic findings suggest an overuse disease of the tendon. They are quite similar to that reported by Conroy et al. . For the absence of hemarthrosis and of clear signs of acute injury we did not perform the repair of the tendon. We have only carried out the debridement of the fibers responsible of local symptoms and we have checked the residual mechanical efficiency of the tendon.
The clinical result achieved in this first division professional goalkeeper underlined the uselessness of tendon suture or any posterolateral ligament reinforcement in case of isolated partial rupture of the tendon, with no rotational instability, with an almost complete recovery at medium term follow-up.