Abstract
Subject-specific musculoskeletal models require accurate values of muscle moment arms. The aim of this study was to compare moment arms of wrist tendons obtained from non-invasive magnetic resonance imaging (MRI) to those obtained from an in vitro experimental approach. MRI was performed on ten upper limb cadaveric specimens to obtain the centrelines for the 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) tendons. From these, the anatomical moment arms about each of the flexion-extension (FE) and radioulnar deviation (RUD) axes of the wrist were calculated. Specimens were mounted on a physiologic wrist simulator to obtain functional measurements of the moment arms using the tendon excursion method. No differences were observed between anatomical and functional values of the FE and RUD moment arms of FCR, ECRL and ECRB, and the RUD moment arm of ECU (p > .075). Scaling the anatomical moment arms relative to ECRB in FE and ECU in RUD reduced differences in the FE moment arm of FCU and the RUD moment arm of APL to less than 15% (p > .139). However, differences persisted in moment arms of FCU in RUD, and ECU and APL in FE (p < .008). This study shows that while measurements of moment arms of wrist tendons using imaging do not always conform to values obtained using in vitro experimental approaches, a stricter protocol could result in the acquisition of subject-specific moment arms to personalise musculoskeletal models.
Highlights
The accurate measurement of tendon moment arms is important for the development of musculoskeletal models
Functional moment arms differed from the anatomical values for flexor carpi ulnaris (FCU) in FE (23.8%) and radioulnar deviation (RUD) (41.1%), extensor carpi ulnaris (ECU) in FE (60.9%), and abductor pollicis longus (APL) in FE (36.5%) and RUD (16.3%) (p < .023)
Functional moment arms were within two standard deviations of those reported in other experimental studies on the wrist (Brand and Hollister, 1999; Horii et al, 1993; Loren et al, 1996) (Fig. 2)
Summary
The accurate measurement of tendon moment arms is important for the development of musculoskeletal models. While generic models may utilise values obtained from the literature, the recent rise in subject-specific modelling necessitates quantification on an individual basis. Imaging techniques, such as magnetic resonance imaging (MRI), could enable non-invasive estimation of such parameters. ⇑ Corresponding author at: Department of Bioengineering, Imperial College technique (An et al, 1983) that cannot be performed in vivo The accuracy of such measurements from imaging has not been determined for the wrist, possibly because the wrist has two degrees of rotation – flexion-extension (FE) and radioulnar deviation (RUD) – and two moment arms for each tendon
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