Estimated muscle forces during running and cutting for ACL deficient, ACL reconstructed, and healthy subjects using a two-joint EMG-driven model

Date
2011
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University of Delaware
Abstract
The purpose of this study was to extend an EMG-Driven Model to two joints in order to compare predicted joint moments and estimated muscle forces during dynamic movements between healthy subjects and those who had injured their anterior cruciate ligaments (ACL) and were either ACL-deficient (ACL-D) or had their ACL reconstructed (ACL-R). Eight subjects volunteered for this study, with one subject as both ACL-D and ACL-R since data were collected both pre-surgery and post-surgery. The forces of 12 muscles of the thigh and shank were estimated for both straight-ahead running and running with a side cut at 45̊. Comparisons were made for estimated muscle forces at their peak force during gait. In order to be compared between different subjects, the muscle forces were normalized to the theoretical maximum muscle force as computed by the model. Motion capture data were acquired for each subject for walking, running, and run-cut tasks. Additionally, maximum voluntary isometric and isokinetic contractions were collected using a dynamometer. The collected data were processed and combined with a musculoskeletal model in order to be input into the EMG-Driven Model. Normalized muscle force for the biceps femoris long-head were observed to be decreased for the ACL-D and ACL-R groups compared to the healthy group, while normalized muscle force for the biceps femoris short-head was increased for the ACL-D group over the healthy and ACL-R groups. Normalized muscle force for all vastii muscles were decreased for the ACL-D group only for running tasks compared to all other groups and to cutting trials. These findings suggest that the force of the biceps femoris short-head increases for ACL-D patients in order to resist anterior tibial translation during dynamic tasks. The decrease in force of the biceps femoris long-head coincides with the increase in force of the biceps femoris short-head in order to maintain proper force and moment contribution from the lateral hamstrings as a whole. The decrease in vastii force for the ACL-D subjects agrees with previous studies that have reported quadriceps weakness for ACL-D patients. This result could be related to pain prevention, a lack of confidence in the injured leg, and decreased joint proprioception for the ACL-D subjects. The subject with pre and post surgery data underwent a quadruple semitendinosus-gracilis graft and exhibits two major differences from the previous results: the forces of the biceps femoris long-head and the semimembranosus increase post surgery. Five of the eight muscles crossing the knee show an increase in peak force post-surgery during running, indicating that joint contact forces also increase post-surgery. In summary, we have presented an application of an EMG-Driven Model expanded to two-joints in order to successfully predict joint moments and estimate muscle forces for dynamic movements between healthy subjects and those with ACL injury. It is hoped that this model will be applied to investigate altered muscle force patterns between healthy subjects and pathological subject groups.
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