anatomical study of the sartorial branch of the saphenous nerve: its surgical relevance in anterior cruciate ligament reconstruction

ABSTRACT

Reports on nerve injury after arthroscopic anterior cruciate ligament [ACL] reconstruction using hamstring tendon autograft had mainly focused on injury to the infrapatellar branch of the saphenous nerve [IPBSN], with few reports on injury of the sartorial branch of the saphenous nerve [SBSN]. Was to calculate the prevalence of injury to the SBSN after arthroscopic ACL reconstruction using hamstring tendon grafts, and to define the level of anatomical termination of the saphenous nerve in relation to the level of the knee joint line and the relation of its sartorial branch to the surrounding tendons so that it could be avoided during hamstring tendon harvesting. The clinical study included 56 patients with a complete tear of the ACL who had arthroscopic ACL reconstruction using hamstring tendon autograft. Patients were followed up for a mean period of 28.3 months after surgery. Postoperative evaluation included neurologic examination for any post-surgical numbness and/or hyposthesia at the distribution of IPBSN, SBSN, or both nerves. The anatomical study included cadaveric dissection of the medial aspect of the knee joint of 25 preserved knees. The saphenous nerve was dissected proximal to the knee joint and followed distally till it was divided into its two terminal branches. At 3 months post surgery, numbness and hyposthesia were present at the distribution of the SBSN in 21.4%, at the distribution of the IPBSN in 19.6%, and at the distribution of both nerves in 30.4%. At final follow up, numbness and hyposthesia were present at the distribution of the SBSN in 18.4%, at the distribution of the IPBSN in 10.2%, at the distribution of both nerves in 32.6%. In 68% of the dissected knees, the saphenous nerve gave its two terminal branches at a mean distance of 8 +/- 4.1 [range 3.5-21.5cm] above the knee joint line. In 32%, the level of termination of the saphenous nerve was below the knee joint line by a mean distance of 3 +/- 1.2 [range 1-4cm]. In 92% the saphenous nerve or the SBSN was passing posterior to the sartorius tendon, while in 8% the nerve was anterior to the tendon at the knee joint line. In 68% the saphenous nerve or the SBSN continued distally anterior to the gracilis tendon, while in 16% the SBSN continued distally posterior to it. In 12% the saphenous nerve or the SBSN was lying directly on the gracilis tendon and in 4%, the SBSN was lying deep to the tendon at the knee joint line. In 24% the distance between the saphenous nerve or the SBSN and gracilis tendon was 5 mm or less. In all the knees the saphenous nerve or the SBSN was passing distally anterior to the semitendinosus tendon. The saphenous nerve or its terminal branch the SBSN, are liable to be injured during arthroscopic ACL reconstruction using hamstring tendon auto graft. The nerve is at a close anatomical relation with the gracilis tendon. This might predispose the nerve to be damaged during passage of the tendon stripper over the tendon. Injury of the saphenous nerve or its terminal branch [SBSN] might be an intrinsic problem associated with the technique itself