Snapping knee syndrome in an athlete caused by the semitendinosus and gracilis tendons. A case report.

We report a case of symptomatic subluxation of the semitendinosus and gracilis over the posteromedial corner of the tibia manifesting with snapping. This is the first such case recorded in non-Asian population and in a high-demand athlete. Snapping was reproduced on active extension of the knee and at initiation of flexion and could be readily palpated over the posteromedial aspect of the tibia. Dynamic ultrasound, a key diagnostic tool in such conditions, revealed abrupt anterior subluxation of the semitendinosus and gracilis tendons during active terminal extension over the insertion of the semimembranosus as well as areas of tendinopathy corresponding with the site of subluxation. Due to failure of conservative treatment, surgery was undertaken, involving tenotomy and resection of a 10-12 cm segment of the semitendinosus and gracilis. The patient returned to the same level of sporting activities within 4 months and remained symptom-free 18 months post-operatively. The role of eccentric loading of the knee joint, as well as the "protective" role of the accessory tendinous bands and aponeurotic expansions of the semitendinosus and gracilis is discussed.