Feasibility of Nerve Transfer to Palmaris Longus in Forearm-Level TMR: Anatomic Study and Clinical Series

Targeted muscle re-innervation (TMR) is increasingly being used for treatment of postamputation pain and myoelectric prosthesis (MYP) control. Palmaris longus (PL) is a potential target following transradial amputation. The purpose of this study was to determine the branching pattern of the median nerve (MN) as it pertains to the PL motor branch entry point (MEP) and to present clinical results of patients who had PL used as a target. Eight cadaveric arms were dissected and branching patterns of the MN were documented. Additionally, we reviewed adult patients from a prospectively collected database who underwent TMR using PL. We recorded patient-reported outcomes and signal strength generated by the PL. The average distance from the medial epicondyle to PL MEP was 53 mm. All palmaris motor branches passed through a chiasm within the flexor digitorum superficialis muscle belly, which was a mean of 18 mm away from the MN proper. Patients with long-term follow-up reported an average Pain visual analog scale of 3.3 and Disabilities of the Arm, Shoulder and Hand of 46.2. All but one patient were using an MYP, and all generated at least 10 mV of signal from the PL, which is ample signal for surface electrode detection and MYP control. There were no postoperative neuromas and only one patient-reported postoperative phantom limb pain. Palmaris longus is a suitable target for TMR. Our objective measurements and anatomic relationships may help surgeons consistently find the PL’s motor branch. Our series of patients reveal sufficient signal strength and acceptable clinical outcomes following TMR using the PL.