Anatomical Variation of Infrapatellar Innervation Determines Clinical Risk of Infrapatellar Neuropathy.

BACKGROUND: Infrapatellar neuropathy arises from traumatic, iatrogenic, or compression injury to the infrapatellar branch (IB) of the saphenous nerve. The risk of infrapatellar neuropathy has been shown to depend on the IB's anatomical course. The infrapatellar branch of the saphenous nerve (ISBN) has been discovered to take varying courses, and the IB can emerge directly from the femoral nerve. The variety of the IBSN's courses and the prevalence of cases involving the infrapatellar branch of the femoral nerve (IBFN) call the uniform IB course described in textbooks into question.

OBJECTIVES: In this study, we aim to identify sites of IB emergence and their anatomical relations and evaluate them for their risk of neuropathy.

STUDY DESIGN: The study is an anatomical prospective pilot study.

SETTING: The setting is a single-center cadaveric study performed at the anatomical institute of the Medical University of Vienna.

METHODS: Twenty-two anatomical specimens were evaluated for the relationship of their IBs to anatomical risk sites. The subsartorial course, distal sartorial penetration, and the crossing of the medial femoral epicondyle were assessed. The measurements and relations of the IB were determined with callipers and assessed by computational modelling.

RESULTS: Nine IBs originated from the saphenous nerve, 11 originated from the femoral nerve, and 2 originated from both. The subsartorial course was most frequent in IBs of saphenous origin. Penetrating and profound distal sartorial relations correlated moderately with emergence type and were highest in the saphenous group. The crossing of the medial femoral epicondyle was the most common relation of IBs that emerged femorally.

LIMITATIONS: The study's limitations were the low number of cadavers to examine and the confining of the exploration of knee extension to anatomical specimens that restricted an inferential analysis.

CONCLUSION: Infrapatellar innervation can emerge from the saphenous nerve, the femoral nerve, or a combination of both, and the origin of the innervation determines the clinical risk for infrapatellar neuropathy. While innervation from the IBSN may lead to compression at the subsartorial course, distal sartorial penetration, and the crossing of the medial femoral epicondyle, innervation from the IBFN carries reduced anatomical risk for infrapatellar neuropathy.