Introduction: Reconstruction of ruptured anterior cruciate ligament is a commonly performed orthopaedic procedure. There are many ways of reconstructing this ligament. One method of doing so is to harvest a tendon graft from the hamstring muscles and use it as part of the reconstruction. The tendon is usually harvested by passing a tendon stripper along the length of the tendon from an anterior knee incision. The semitendinosus and the gracilis are the hamstring muscles whose tendons are used for this. A recent case study reported injury to the sciatic nerve during the harvest of semitendinosus graft. Although morbidity arising from iatrogenic injury to nerves at the anterior aspect of the knee has been well documented, little has been written about the relationship of the sciatic nerve to the semitendinosus and gracilis in the posterior thigh. This study proposes to look at this anatomical relationship.

Method: 20 legs on ten cadavers underwent the same dissection to expose the semitendinosus tendon, gracilis tendon and the sciatic nerve while maintaining their anatomical relationships. In all cases the gracilis lay further away from the sciatic nerve than the semiten-dinosus tendon. As the semitendinosus tendon was in between the semitendinosus and the sciatic nerve in all instances it was decided not to measure the distance between gracilis and the sciatic nerve. The distance between the closest point of the sciatic nerve to the tendon of semitendinosus was measured at the joint line and at intervals of 20 mm from the joint line.

Results: In 45 % of the subjects the sciatic nerve and the semitendinosus tendon gradually moved further apart as the measurements were taken more proximally in the leg. In 10 % they consistently moved apart from 6 cm from the joint line onwards. In another 10% they moved consistently apart from the 8cm from the joint line measurement and in 15 % they moved apart consistently from 12 cm from the joint line. In the remaining 20 % the sciatic nerve and the semitendinosus tendon did not consistently move apart from each other until after 14 cm from the joint line. In one subject (a female of small stature) it was noted that the semitendinosus muscle lay almost directly upon the sciatic nerve. In 6 subjects the minimum distance between the sciatic nerve and the semitendinosus tendon was less than 18mm. In one subject the distance between the sciatic nerve and the semitendinosus tendon was found to be 10 mm at the closest point and remained in close proximity for a further 4 cm.

Conclusion: In 55 % of our patients the sciatic nerve did not consistently move further away from the semi-tendinosus tendon as it was measured more proximally. In some subjects the minimum distance between the nerve and the tendon was less than 2 cm. Both these facts would put the sciatic nerve at risk during tendon harvesting if the tendon stripper were to move outside of the tendon during the procedure.