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Methods for In Vivo Biomechanical Testing on Brachial Plexus in Neonatal Piglets
Published on: December 19, 2019
The effect of elbow posture on biceps function at the shoulder in brachial plexus birth injuries: A computational
T R Goins1, Jane E Sullivan2, John Fox3
1Campbell University Doctor of Physical Therapy Program, Buies Creek, NC, United States of America.
Insights
Stabilizing the elbow in a specific position enhances shoulder elevation strength in individuals with brachial plexus birth injuries. This finding offers new therapeutic approaches for improving arm function.
Area of Science:
- Biomechanics
- Human Movement Science
- Rehabilitation Engineering
Background:
- Brachial plexus birth injury alters muscle length and joint motion, affecting shoulder elevation.
- The long head of the biceps is crucial due to its bi-articular nature and reduced optimal length in this population.
- Joint immobilization may enhance the force-generating capacity of bi-articular muscles.
Purpose of the Study:
- To investigate how elbow joint stabilization affects shoulder elevation isometric moment-generating capacity.
- To analyze the impact of altered optimal fiber length on biceps long head active and passive fiber force.
- To explore biomechanical advantages for therapeutic interventions in brachial plexus birth injuries.
Main Methods:
- Musculoskeletal modeling simulations were employed.
- Predicted maximum isometric shoulder elevation moment, active-fiber force, and passive-fiber force.
- Simulated stabilized elbow postures (10°–120°) and varied optimal muscle lengths (0%–30% reduction).
Main Results:
- Optimal shoulder elevation moment was highest with a 30% reduced optimal fiber length for the biceps long head.
- Elbow stabilization at 30° yielded the greatest shoulder elevation moment.
- This specific posture resulted in lower active fiber force but higher passive fiber force.
Conclusions:
- Elbow immobilization in a specific posture can biomechanically enhance shoulder elevation.
- Findings provide a basis for developing targeted therapeutic strategies for brachial plexus birth injuries.
- Understanding these biomechanical principles is key for improving functional outcomes.
Background:
Individuals with a brachial plexus birth injury have changes in optimal muscle length of affected muscles and diminished motion at the elbow and shoulder, impacting active shoulder elevation. The long head of the biceps, a bi-articular muscle, is of particular interest in this population due to its reduced optimal muscle length and simultaneous shortening at the shoulder and elbow during active shoulder elevation. Prior studies have shown immobilization of a joint may improve the moment-generating capacity of a biarticular muscle crossing that joint. The aim of this study was to investigate the impact of joint stabilization on shoulder elevation isometric moment-generating capacity and active and passive fiber force of the long head of the biceps in simulated elbow postures and altered optimal fiber length of the biceps.
Methods:
Simulations, via a musculoskeletal model, were used to predict maximum isometric shoulder elevation moment, active-fiber force, and passive-fiber force versus shoulder elevation in stabilized elbow postures from 10° to 120° with a range of optimal muscle lengths from typical to reduced longitudinal length by 30%, 20%, and 10% to the long head of the biceps.
Findings:
The highest shoulder elevation moment was produced with optimal fiber length reduced 30% for biceps long head and the elbow stabilized in 30°, causing lower active fiber force, but higher passive fiber force.
Interpretation:
Understanding the biomechanical advantage of immobilizing the elbow in a specified posture that improves shoulder elevation in this population, establishes future directions for therapeutic interventions for birth brachial plexus injuries.
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