The relationship of neural structures to arthroscopic posterior portals according to knee positioning.

PURPOSE: The purpose of this study was to investigate the relationship between the proximity of neural structures to standard posterior portals in different knee positions.

METHODS: Ten fresh cadaveric knees were used to establish the standard posteromedial and posterolateral portals using an outside-in technique with arthroscopic transillumination. The distance from each portal site to the adjacent neurovascular structures (infrapatellar branches of the saphenous nerve) and the sartorial branch of saphenous nerve from the posteromedial portal, and the common peroneal nerve from posterolateral portal was measured using a precision caliper. Distances were recorded with the knees in extension, 45° of flexion and 90° of flexion in order to examine the effect of dynamic knee motion on nerve position.

RESULTS: The mean distance between the posteromedial portal and the superior and inferior branches of infrapatellar branches of the saphenous nerve at full extension was significantly greater than at 90° of flexion. However, there was no difference observed between at 45° and at 90° of flexion. The mean distance from the posteromedial portal to the sartorial branch of saphenous nerve at 90° of flexion was significantly greater (26.1 mm, SD: 4.7) than that at 45° of flexion (18.4 mm, SD: 4.6), and at full extension (14 mm, SD: 4.3) (P < 0.0001). The mean distance between the posterolateral portal to the common peroneal nerve at 90° of flexion was also significantly greater (25.4 mm, SD: 9.2) than that at 45° of flexion (22.5 mm, SD: 8.1), and at full extension (20.1 mm, SD: 9.1) (P < 0.0001).

CONCLUSION: In this cadaveric study, it shows that position of 90° knee flexion is reasonably safe, in order to establish a posterior portal in knee arthroscopy using the technique described in the current study, especially to avoid the sartorial branch of saphenous nerve and the common peroneal nerve injuries. Results of this study suggest the establishment of posterior portals, while the knee is flexed at an angle of 90° is recommended to ensure the safety of these structures.