Abstract
The aim of this paper is to investigate mechanical functioning of a single skeletal muscle, active within a group of (previously) synergistic muscles. For this purpose, we assessed wrist angle-active moment characteristics exerted by a group of wrist flexion muscles in the rat for three conditions: (i) after resection of the upper arm skin; (ii) after subsequent distal tenotomy of flexor carpi ulnaris muscle (FCU); and (iii) after subsequent freeing of FCU distal tendon and muscle belly from surrounding tissues (MT dissection). Measurements were performed for a control group and for an experimental group after recovery (5 weeks) from tendon transfer of FCU to extensor carpi radialis (ECR) insertion. To assess if FCU tenotomy and MT dissection affects FCU contributions to wrist moments exclusively or also those of neighboring wrist flexion muscles, these data were compared to wrist angle-moment characteristics of selectively activated FCU. FCU tenotomy and MT dissection decreased wrist moments of the control group at all wrist angles tested, including also angles for which no or minimal wrist moments were measured when activating FCU exclusively. For the tendon transfer group, wrist flexion moment increased after FCU tenotomy, but to a greater extent than can be expected based on wrist extension moments exerted by selectively excited transferred FCU. We conclude that dissection of a single muscle in any surgical treatment does not only affect mechanical characteristics of the target muscle, but also those of other muscles within the same compartment. Our results demonstrate also that even after agonistic-to-antagonistic tendon transfer, mechanical interactions with previously synergistic muscles do remain present.
Highlights
IntroductionTransferring the tendon of insertion of a selected muscle to the insertion of another muscle is a surgical intervention performed frequently in a number of clinical conditions (e.g., cerebral palsy, obstetric brachial plexus palsy, stroke, and spinal cord injury), both in the lower extremity [1], and in the upper extremity [2,3]
Transferring the tendon of insertion of a selected muscle to the insertion of another muscle is a surgical intervention performed frequently in a number of clinical conditions, both in the lower extremity [1], and in the upper extremity [2,3]
As there are severe limitations of studying tendon transfers in humans, we recently presented a rat model to study effects of transferring flexor carpi ulnaris muscle (FCU) muscle to the distal tendons of extensor carpi radialis brevis and longus muscles (ECR) [24,25,26]
Summary
Transferring the tendon of insertion of a selected muscle to the insertion of another muscle is a surgical intervention performed frequently in a number of clinical conditions (e.g., cerebral palsy, obstetric brachial plexus palsy, stroke, and spinal cord injury), both in the lower extremity [1], and in the upper extremity [2,3]. A presumed problematic imbalance of muscle forces at a joint, thought to be caused by the hyperactive and uncontrollable muscle overpowering its antagonistic muscles, is corrected [5]. Gait or upper extremity function improves after recovery from such surgery and patients report satisfaction with this improvement [6,7,8]. The actual mechanical effects of the (to be) transferred muscle at the joint is seldom evaluated in human patients. Acute effects of disrupting connective tissues on muscular mechanical properties have been reported [5,11,12], indicating effects of epimuscular myofascial force transmission (for reviews, see 13,14). Epimuscular myofascial force transmission is defined as force transmission between a muscle and its immediate surroundings via pathways other than the origin and insertion
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