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Abstract
Background and Aims Chronic neuropathic pain affects one in ten patients after total knee arthroplasty (TKA).1 The midline skin incision is the main generator of iatrogenic nerve injury and neuropathic pain.The incision area is innervated by the medial femoral cutaneous nerve (MFCN), the intermediate femoral cutaneous nerves (IFCN) and the infrapatellar branch from the saphenous nerve (SN).2,3It is not known whether the anterior (MFCN-A) or posterior branch (MFCN-P) of the MFCN innervates the skin incision, and this knowledge is clinically important to precisely diagnose and treat chronic neuropathic pain using interventional techniques such as cryoneurolysis, radiofrequency ablation or peripheral nerve modulation.4The primary aim was to assess the contributions from the MFCN-A and MFCN-P to the innervation of the skin incision for TKA.
Methods Twenty healthy volunteers were enrolled in this randomized, double-blind trial (fig 1). Volunteers had active SN block (distal femoral triangle block, FTB) and active IFCN block (IFCNB) bilaterally. Selective MFCN-A block (fig 2) and subsequently MFCN block were then added to investigate the contributions from MFCN-A and MFCN-P to the innervation of the midline skin incision.
Results In 90% of the cases, selective MFCN-A block completely anesthetized the non-anesthetized gap following combined IFCNB and distal FTB completely, whereas MFCN-P did not contribute (p=0.004) (fig 3).
Conclusions In the majority of cases, the skin incision was not anesthetized by the combination of IFCNB and distal FTB. The remaining gap was consistently anesthetized by our new selective MFCN-A block, which may be relevant for diagnosis and interventional management of chronic neuropathic pain.