No safe zone: The anatomy of the saphenous nerve and its posteromedial branches.

BACKGROUND

Following a case of medial meniscal repair via an inside-out repair, a patient developed acute postoperative electric shock-like paresthesias of the proximal medial calf with any knee flexion beyond 80°. Open saphenous nerve exploration revealed entrapment by suture material of an unnamed branch off the sartorial branch of the saphenous nerve. Symptoms resolved immediately with release. The objective of the study was to perform a cadaveric study to examine the existence and frequency of these previously under-reported branches of the sartorial branch of the saphenous nerve.

METHODS

In 16 knees from eight fresh, matched whole cadavers, the medial structures of the knee were exposed, reproducible anatomical structures were identified, and previously under-described posteromedial branches of the sartorial nerve were identified and measured in relation to surrounding structures and the joint line.

RESULTS

The saphenous nerve, its sartorial and infrapatellar branches, and its posteromedial branches were identified in all specimens. The sartorial nerve divided from the saphenous nerve an average of 4.8 cm proximal to the medial femoral epicondyle. Between one and four further posteromedial branches off the sartorial nerve were identified. These branches formed at a range of 5.3 cm proximal to 3.0 cm distal to the joint line.

CONCLUSIONS

This cadaveric study establishes the consistent presence of a posteromedial branch off the sartorial nerve. It was consistently located near the posteromedial joint line. These branches are at risk for injury during medial meniscus repairs due to entrapment by suture materials, or during other surgical procedures near the posteromedial aspect of the knee.