Biometry of thenar muscle origins on the flexor retinaculum

Abstract

The transverse carpal ligament (TCL), the main part of the flexor retinaculum, serves as an anchor for the thenar muscles: abductor pollicis brevis (APB), superficial head of the flexor pollicis brevis (sFPB), and opponens pollicis (OPP). Biomechanically, the thenar muscles rely on their TCL anchoring to transmit muscle contractions distally for thumb force and motion production, and reciprocally, muscle contraction interacts with the TCL at the proximal end through the origins. However, scarce knowledge exists regarding the distribution pattern of the thenar muscle origins. The purpose of this study was to understand the anatomical interface between the thenar muscles and TCL by examining the origin distributions of the individual muscles. Ten cadaveric specimens were dissected for digitization of the muscle origins and TCL volar surface. Digitized data were used for mesh reconstruction and calculation of surface areas and centroids. The origin areas for APB, sFPB, and OPP were 105.8 ± 30.3, 64.6 ± 15.2, and 245.9 ± 70.7 mm 2 , respectively. The surface area of the TCL was 386.2 ± 86.9 mm 2. The origin areas of APB and OPP on the TCL were comparable, 18.4 ± 4.8% and 17.3 ± 9.6% of the TCL area, respectively. The origin locations for APB, sFPB, and OPP were in proximal-radial quadrant of the TCL, on distal aponeurosis outside the TCL, and around the ridge of trapezium, respectively. The knowledge of the anatomical interface provides a foundation for the understanding of biomechanical interactions between the muscles and ligaments and pathomechanical implications.

Palmar Musculature: Does It Affect the Development of Carpal Tunnel Syndrome? A Pilot Study

“…13,15 Loss and Li dissected 10 cadaveric specimens examining the origin of distributions of the individual thenar muscles. 26 It is possible that hypertrophy due to use, and specific anatomical variants, may predispose certain individuals to CTS without any of the background conditions known to be associated with CTS. In this study, the measure of average muscle depth may account for the high anatomical variability seen in the axial plane, but it fails to capture variability between wrists in the coronal plane of the palm.…”

Thenar and Hypothenar Muscle Coverage on the Transverse Carpal Ligament

“…Several studies investigating thenar muscle attachment to the TCL mainly used cadaveric specimens. Loss and Li 9 digitized the footprints of cadaveric muscle origins and reported that 36% of the TCL surface areas was occupied by the thenar muscles. Kung et al 8 quantified that 68% of thenar muscle origin was on the TCL as compared with 24% for hypothenar muscle.…”

“…Previous studies have examined the muscle distribution on the ligament by direct exposure using cadaveric experiments. 8,9 However, there is a lack of in vivo studies on how the ligament is covered by the thenar and hypothenar muscles. Therefore, the purpose of this study was to examine the coverage of thenar and hypothenar muscles on the TCL in the carpal tunnel cross-section at hook of hamate level through in vivo ultrasound imaging.…”