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Updated: May 4, 2026
Methods for In Vivo Biomechanical Testing on Brachial Plexus in Neonatal Piglets
Published on: December 19, 2019
Computational sensitivity analysis to identify muscles that can mechanically contribute to shoulder deformity
Dustin L Crouch1, Johannes F Plate1, Zhongyu Li1
1Virginia Tech-Wake Forest School of Biomedical Engineering and Sciences; the Department of Biomedical Engineering and the Department of Orthopaedic Surgery, Wake Forest School of Medicine; the Neuroscience Program, Wake Forest Graduate School of Arts and Sciences, Winston-Salem; and the Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina.
Insights
Certain shoulder muscles can cause deformity in children with brachial plexus birth palsy through strength imbalance or impaired growth. Identifying these muscles is key for understanding and treating shoulder deformities.
Area of Science:
- Biomechanics
- Pediatric Orthopedics
- Musculoskeletal Modeling
Background:
- Brachial plexus birth palsy (BPBP) can lead to shoulder deformities.
- Two primary mechanisms are implicated: muscle strength imbalance and impaired longitudinal muscle growth.
- Understanding the specific muscles involved is crucial for effective treatment.
Purpose of the Study:
- To identify specific shoulder muscles capable of producing forces that promote osseous and postural deformity in BPBP.
- To differentiate the roles of strength imbalance versus impaired muscle growth in causing these deformities.
Main Methods:
- A computational musculoskeletal model of the upper limb was utilized.
- Simulated strength imbalance by setting individual muscle forces to 30% of maximum.
- Simulated impaired longitudinal muscle growth by reducing muscle functional length by 30%.
Main Results:
- Strength imbalance in subscapularis, latissimus dorsi, and infraspinatus increased posterior glenohumeral joint force.
- Impaired growth of infraspinatus, subscapularis, and biceps long head most increased posterior glenohumeral joint force.
- Strength imbalance in subscapularis, anterior deltoid, and pectoralis major reduced external rotation; impaired growth of anterior deltoid, subscapularis, and triceps long head reduced shoulder motion.
Conclusions:
- Infraspinatus, subscapularis, latissimus dorsi, biceps long head, anterior deltoid, pectoralis major, and triceps long head are implicated in BPBP-related shoulder deformity.
- These muscles are mechanically capable of generating deforming forces.
- Targeting these muscles is recommended for experimental studies and therapeutic interventions in BPBP.
Purpose:
Two mechanisms, strength imbalance or impaired longitudinal muscle growth, potentially cause osseous and postural shoulder deformity in children with brachial plexus birth palsy. Our objective was to determine which muscles, via either deformity mechanism, were mechanically capable of producing forces that could promote shoulder deformity.
Methods:
In an upper limb computational musculoskeletal model, we simulated strength imbalance by allowing each muscle crossing the shoulder to produce 30% of its maximum force. To simulate impaired longitudinal muscle growth, the functional length of each muscle crossing the shoulder was reduced by 30%. We performed a sensitivity analysis to identify muscles that, through either simulated deformity mechanism, increased the posteriorly directed, compressive glenohumeral joint force consistent with osseous deformity or reduced the shoulder external rotation or abduction range of motion consistent with postural deformity.
Results:
Most of the increase in the posterior glenohumeral joint force by the strength imbalance mechanism was caused by the subscapularis, latissimus dorsi, and infraspinatus. Posterior glenohumeral joint force increased the most owing to impaired growth of the infraspinatus, subscapularis, and long head of biceps. Through the strength imbalance mechanism, the subscapularis, anterior deltoid, and pectoralis major muscles reduced external shoulder rotation by 28°, 17°, and 10°, respectively. Shoulder motion was reduced by 40° to 56° owing to impaired growth of the anterior deltoid, subscapularis, and long head of triceps.
Conclusions:
The infraspinatus, subscapularis, latissimus dorsi, long head of biceps, anterior deltoid, pectoralis major, and long head of triceps were identified in this computational study as being the most capable of producing shoulder forces that may contribute to shoulder deformity following brachial plexus birth palsy.
Clinical Relevance:
The muscles mechanically capable of producing deforming shoulder forces should be the focus of experimental studies investigating the musculoskeletal consequences of brachial plexus birth palsy and are potentially critical targets for treating shoulder deformity.
