The anterior branch of the medial femoral cutaneous nerve innervates the anterior knee: a randomized volunteer trial

BACKGROUND: The midline skin incision for total knee arthroplasty may be an important generator of chronic neuro-pathic pain. The incision is innervated by the medial femoral cutaneous nerve (MFCN), the intermediate femoral cutane-ous nerves (IFCN) and the infrapatellar branch from the saphenous nerve. The MFCN divides into an anterior (MFCN-A) and a posterior branch (MFCN-P). The primary aim was to compare the areas anesthesized by MFCN-A versus MFCN-P block for coverage of the incision.METHODS: Nineteen healthy volunteers had IFCN and saphenous nerve blocks. The subgroup of volunteers with a non -anesthetized gap between the areas anesthetized by the saphenous and the IFCN blocks was defined as the study group for the primary outcome. Subsequently selective MFCN-A block and MFCN block (MFCN-A + MFCN-P) were performed to investigate the contributions from MFCN-A and MFCN-P to the innervation of the midline incision. All assessments were performed blinded.RESULTS: Ten out of 19 volunteers had a non-anesthetized gap. Nine out of these 10 volunteers had coverage of the non-anesthetized gap after selective anesthesia of the MFCN-A, whereas anesthesia of the MFCN-P did not contribute to coverage of the gap in any of the 10 volunteers.CONCLUSIONS: In half of the cases, a gap of non-anesthetized skin was present on the surgical midline incision after anesthesia of the saphenous nerve and the IFCN. This gap was covered by selective anesthesia of the MFCN-A without contribution from MFCN-P. The selective MFCN-A block may be relevant for diagnosis and interventional management of neuropathic pain due to injury of MFCN-A.

Automated summary

The midline skin incision for total knee arthroplasty may cause chronic neuro-pathic pain. The MFCN-A block can effectively cover the incision, while the MFCN-P does not contribute to coverage.