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An Anatomical Study of the Innervation Patterns of the Palmaris Longus Muscle and Clinical Results of its Utilization in Targeted Muscle Reinnervation
Matthew R. Delarosa, MD1, R. Glenn Glenn Gaston, MD1, Bryan J. Loeffler, MD1, Dane N. Daley, MD1, Eitan Melamed, MD2 and Neil Vranis, MD3, (1)OrthoCarolina, Charlotte, NC, (2)Orthopedic Surgery, NYU Hospital for Joint Diseases, New York, NY, (3)NYU Langone Health, New York, NY

INTRODUCTION

The purpose of this study is two-fold. First to further elucidate the anatomical branching pattern of the median nerve as it pertains to the palmaris longus motor branch for TMR. Secondly, this paper is a retrospective review of a series of patients who underwent Targeted Muscle Reinnervation (TMR) and palmaris longus (PL) was utilized as a target.

MATERIALS AND METHODS

8 cadaveric arms were dissected to document the branching pattern of the median nerve. Additionally, we present the 8 transradial amputee patients that underwent targeted muscle reinnervation in which PL was utilized as a target.

RESULTS

From our cadaveric dissections the average length of the forearms from medial epicondyle to ulnar styloid was 24.8 cm (22-29 cm), and the average length from medial epicondyle to palmaris muscle motor entry point was 5.3 cm (3.0-7.7 cm). Additionally, all palmaris motor branches passed through a tunnel within the FDS muscle belly, the average distance of which was 1.8 cm away from the median nerve proper (.7-3.6 cm).

We also report our postoperative subjective and objective outcome data. The 8 patients reported an average pain VAS of 2 and DASH of 45.7. All 8 transradial amputees (100%) are utilizing a prosthesis, with 7 out of 8 utilizing a myoelectric prosthesis (88%). Additionally, only 33% of patients report phantom sensation and only one (12.5%) of these patients reports having phantom pain.

CONCLUSIONS

The anatomy of the palmaris longus motor branch, when present, is a reliable target for TMR surgery. The branching pattern of the median nerve was highly variable, however, the PL motor branch consistently ran through a tunnel in the FDS muscle and entered the muscle belly an average of 5.3 cm distal to the medial epicondyle. This has implications for surgery as the PL motor branch is reliably identified along the undersurface of the FDS fascia as it pierces the FDS to innervate the PL. The superficial location and distinct muscle belly make palmaris longus an ideal target in the setting when performing TMR for transradial amputations. Patients in this series with PL used as a TMR target are doing well in regards to their clinical outcomes, PROs, and prosthetic utilization.


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