Ultrasound Anatomic Demonstration of the Infrapatellar Nerve Branches

Purpose: To (1) confirm the correct identification of the infrapatellar branches of the saphenous nerve (IPBSNs) by high-resolution ultrasound (HRUS) with ink marking and consecutive dissection in anatomic specimens; (2) evaluate the origin, course, and end-branch distribution in healthy volunteers; and (3) visualize the variable anatomic course of the IPBSN by HRUS.

Methods: HRUS with high-frequency probes (15-22 MHz) was used to locate the IPBSN in 14 fresh anatomic specimens at 4 different locations. The correct identification of the IPBSN was verified by ink marking and consecutive dissection. Moreover, the IPBSNs were located in both knees of 20 healthy volunteers (n = 40). Their courses were marked on the volunteers' skin in a flexed-knee position. Distances were measured from the IPBSN branch closest to the median of the patella base (D1), center (D2), and apex (D3) and in a 45° (D4) and 0° (D5) relation to the median patella apex. Standardized photographs of all knees were mapped on 1 typically shaped knee.

Results: Dissection confirmed the correct identification of the IPBSN in 86% to 100% of branches, depending on their location. Intraindividual differences for distance measurements were observed for D1 (P < .001) and D2 (P = .002). The coefficient of variation was highest for D5 (0.86) and lowest for D1 (0.14). Mapping of the nerve branches on a typical knee showed a highly variable course for the IPBSN.

Conclusions: This study confirmed the reliable ability to visualize the IPBSN and its variations with HRUS in anatomic specimens and in healthy volunteers; such visualization may therefore enhance the diagnostic and therapeutic management of patients with anteromedial knee pain.

Clinical relevance: Ultrasound successfully pinpoints the variable course of the IPBSN from the origin to the most distal point and, therefore, may enable the correct identification of (iatrogenic) nerve damage in every location.