The effects of wrist motion and hand orientation on muscle forces: a physiologic wrist simulator study

Although the orientations of the hand and forearm vary for different wrist rehabilitation protocols, their effect on muscle forces has not been quantified. Physiologic simulators enable a biomechanical evaluation of the joint by recreating functional motions in cadaveric specimens. Control strategies used to actuate joints in 5 physiologic simulators usually employ position or force feedback alone to achieve optimum load distribution across the muscles. After successful tests on a phantom limb, unique combinations of position and force feedback – hybrid control and cascade control – were used to simulate multiple cyclic wrist motions of flexion-extension, radioulnar deviation, dart thrower’s motion, and 10 circumduction using six muscles in ten cadaveric specimens. Low kinematic errors and coefficients of variation of muscle forces were observed for planar and complex wrist motions using both novel control strategies. The effect of gravity was most pronounced when the hand was in the horizontal orientation, resulting in higher extensor forces (p<0.017) and higher out-of-plane kinematic errors (p<0.007), as compared to the vertically 15 upward or downward orientations. Muscle forces were also affected by the direction of rotation during circumduction. The peak force of flexor carpi radialis was higher in clockwise circumduction (p=0.017), while that of flexor carpi ulnaris was higher in anticlockwise circumduction (p=0.013). Thus, the physiologic wrist simulator accurately replicated cyclic planar and complex motions in cadaveric specimens. Moreover, the dependence of muscle 20 forces on the hand orientation and the direction of circumduction could be vital in the specification of such parameters during wrist rehabilitation

The effect of surgical treatments for trapeziometacarpal osteoarthritis on wrist biomechanics: a cadaver study

Purpose: Studies have shown the effects of surgical treatments for trapeziometacarpal osteoarthritis on thumb biomechanics; however, the biomechanical effects on the wrist have not been reported. This study aimed to quantifyalterations in wrist muscle forces following trapeziectomy with or withoutligament reconstruction and replacement. Methods: A validated physiological wrist simulator replicatedcyclic wrist motions in cadaveric specimens by applying tensile loads to six muscles. Muscle forces required to move the intact wrist were compared to those required after performing trapeziectomy, suture suspension arthroplasty, prosthetic replacement and ligament reconstruction with tendon interposition (LRTI). Results: Trapeziectomy requiredhigher abductor pollicis longusforcesinflexion, and higher flex or carpi radialis forces coupled with lower extensor carpi ulnaris forces in radial deviation. Of the three surgical reconstructions tested post-trapeziectomy, wrist muscle forces following LRTI were closest to those observed in the intact case, throughout the range of all simulated motions. Conclusions: This study shows that wrist biomechanics weresignificantly altered following trapeziectomy, and of the reconstructions tested, LRTI most closely resembled the intact biomechanics in this cadaveric model

The importance of abductor pollicis longus in wrist motions: a physiological wrist simulator study

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

Alterations to wrist tendon forces following flexor carpi radialis or ulnaris sacrifice: a cadaveric simulator study

Tenotomies, tendon transfers or nerve injuries can result in partial or complete loss of the flexor carpi radialis (FCR) or flexor carpi ulnaris (FCU) function. The aim of this study was to observe alterations in the distribution of muscle forces at the wrist due to the absence of each of these flexors. Cyclic planar and complex wrist motions were actively simulated in cadaveric specimens by applying tensile loads to six muscle tendons using a validated physiological wrist simulator. The absence of FCR or FCU resulted in higher forces in synergists, coupled with lower forces in antagonists, and an overall decrease in the total force of all tendons. Thus, alterations in wrist tendon forces following reconstructive procedures utilising a tendon may have clinical implications, such as muscle fatigue or reduced strength