Abstract
The abductor pollicis longus (APL) is one of the primary radial deviators of the wrist, owing to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. Although it plays a vital role in surgical reconstructions of the wrist and hand, it is often neglected while simulating wrist motions in vitro. The aim of this study was to observe the effects of the absence of APL on the distribution of muscle forces during wrist motions. A validated physiological wrist simulator was used to replicate cyclic planar and complex wrist motions in cadaveric specimens by applying tensile loads to six wrist muscles – flexor carpi radialis (FCR), flexor carpi ulnaris, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis, extensor carpi ulnaris (ECU) and APL. Resultant muscle forces for active wrist motions with and without actuating the APL were compared. The absence of APL resulted in higher forces in FCR and ECRL – the synergists of APL – and lower forces in ECU – the antagonist of APL. The altered distribution of wrist muscle forces observed in the absence of active APL control could significantly alter the efficacy of in vitro experiments conducted on wrist simulators, in particular when investigating those surgical reconstructions or rehabilitation of the wrist heavily reliant on the APL, such as treatments for basal thumb osteoarthritis.
Highlights
Of the numerous muscles in the forearm that have their tendons crossing the wrist, six muscles insert at the carpals or the base of the metacarpals – flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor carpi ulnaris (ECU) and abductor pollicis longus (APL) – and have larger moment arms about the wrist axes (Brand and Hollister, 1999; Garland et al, 2018)
While simulating FE-5030 in the absence of the APL (Fig. 1), the mean peak FCR force increased by 21% (p = 0.018), while that of FCU, ECRB and ECU decreased by 12% (p = 0.043), 5% (p = 0.018) and 13% (p = 0.028) respectively, as compared to the muscle forces from the intact specimens
Results from multiple cyclic planar and complex wrist motions simulated in this study, with and without the APL, showed that its absence resulted in alterations in the force distribution across the wrist muscles
Summary
Of the numerous muscles in the forearm that have their tendons crossing the wrist, six muscles insert at the carpals or the base of the metacarpals – flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor carpi ulnaris (ECU) and abductor pollicis longus (APL) – and have larger moment arms about the wrist axes (Brand and Hollister, 1999; Garland et al, 2018). Physiological wrist simulators often recreate the kinematic and kinetic conditions of the natural joint in vitro by applying tensile loads to tendons of these muscles (Werner et al, 1996). Some in vitro studies employing wrist simulators neglect the APL, and replicate wrist motions with five actively loaded muscles (Dimitris et al, 2015; Erhart et al, 2012; Farr et al, 2013; Leonard et al, 2002). Since in vitro studies using physiological simulators have direct implications for surgical reconstructions and/or rehabilitation procedures, it is important that these devices are as biofidelic as possible. The aim of this study was to observe the effects of the omission of APL on wrist biomechanics using a physiological wrist simulator. We hypothesised that the absence of APL would result in significant alterations in wrist muscle forces
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
