Establishing Relationships Among Shoulder Joint Dynamics and Rotator Cuff Tendon Health in Youth Manual Wheelchair Users with Pediatric-Onset Spinal Cord Injury or Disorder

Abstract

IntroductionCumulative duration of manual wheelchair use places approximately 250,000 children in the United States with pediatric-onset spinal cord injury or disorder (SCI/D) at risk for early-onset rotator cuff tendon pathology, such as tendinosis or tendon tears. Rotator cuff pathology impairs shoulder function and causes pain, hindering mobility, participation and reducing quality of life. Unfortunately, there are no guidelines for preservation of shoulder health specific to youth manual wheelchair users. Further, the development of clinical assessment and intervention tailored to the youth wheelchair user is limited due to poor understanding of the typically developing shoulder joint complex, especially the rotator cuff soft tissues. The purpose of this dissertation was to establish relationships among shoulder joint biomechanics and rotator cuff health outcomes in youth manual wheelchair users with pediatric-onset SCI/D. The central hypothesis, that modifiable manual wheelchair biomechanics among youth with pediatric-onset SCI/D are related to specific patterns of diagnostic and quantitative musculoskeletal ultrasound findings for the rotator cuff, was tested using three specific aims. Aim 1: Establish associations between manual wheelchair handrim kinetics and rotator cuff quantitative macroscale morphology in youth with pediatric-onset SCI/D.Methods: In the first aim, the correlations of wheelchair handrim biomechanics with rotator cuff quantitative macroscale morphology parameters including tendon thickness and subacromial impingement risk were determined using B-mode musculoskeletal shoulder ultrasound, and wheelchair handrim kinetics in in 11 youth manual wheelchair users. Results: Increasing acromiohumeral distance was associated with increasing handrim peak resultant force, and with decreasing variability of handrim force effectiveness. Supraspinatus tendon thickness was associated with decreasing handrim force effectiveness and decreasing variability of handrim force effectiveness. Supraspinatus tendon thickness was also associated with increasing peak resultant force variability and increasing variability of rate of rise of handrim resultant force. Increasing subacromial occupation ratio was associated with decreasing peak rate of rise of resultant force, and with decreasing variability of handrim force effectiveness. Discussion: This was the first study to investigate relationships among handrim kinetics and rotator cuff morphology in youth manual wheelchair users with pediatric-onset SCI/D. Associations were identified between subacromial impingement risk factors and magnitude and variability of wheelchair handrim kinetics. Because handrim kinetics are directly related to shoulder joint kinematics and kinetics, this results indicated the critical need to further explore the relationships among wheelchair biomechanics, rotator cuff pathology, and rotator cuff morphology in youth manual wheelchair users. Aim 2: Establish relationships among glenohumeral joint dynamics, rotator cuff tendon pathology, and rotator cuff quantitative morphology in youth with pediatric-onset SCI/D.Methods: In the second aim, this dissertation determined correlations of glenohumeral joint dynamics with rotator cuff tendon pathology and rotator cuff quantitative morphology in 34 youth manual wheelchair users with pediatric-onset SCI/D. A physiatrist performed B-mode shoulder ultrasound, and quantitative morphology parameters including rotator cuff tendon thickness and the subacromial occupation ratio were determined using ultrasound images. Rotator cuff tendon pathology was assessed qualitatively by a musculoskeletal radiologist. Manual wheelchair handrim kinetics and motion capture marker trajectories were acquired during propulsion at a self-selected speed on a smooth, level surface, and an inverse dynamics model computed glenohumeral joint kinematics and kinetics (dynamics). A conservative approach was utilized first, with Spearman correlation coefficients used to determine relationships between glenohumeral joint dynamics and rotator cuff quantitative morphology, and Mann-Whitney U tests used to determine relationships between glenohumeral joint dynamics and rotator cuff tendon pathology, and between quantitative morphology and tendon pathology. A second, broad approach was used to define potential relationships among rotator cuff tendon pathology, quantitative morphology, and glenohumeral joint dynamics. An iterative data transformation process was developed, with log transformations performed on non-normal variables, and Box-Cox transformations performed for data remaining non-normal. Results: A single relationship was identified using the conservative approach: glenohumeral anterior force was lower with supraspinatus tendon pathology. The second approach revealed many distinct potential associations among glenohumeral joint dynamics magnitude and variability, rotator cuff pathology, and rotator cuff quantitative morphology. Discussion: The potential correlations identified in this study indicate complex relationships of glenohumeral joint dynamics to rotator cuff health outcomes in youth manual wheelchair users. The bi-directionality inherent in the relationship of some quantitative morphology features to pathology, such as rotator cuff tendon thickness and acromiohumeral distance, rendered full clinical interpretation of these data difficult. Aim 3: Determine patterns in wheelchair propulsion glenohumeral joint biomechanics and quantitative morphology underlying rotator cuff pathology and shoulder pain in youth manual wheelchair users with pediatric-onset SCI/D.Methods: In the third aim, this dissertation addressed a critical gap in knowledge by defining rotator cuff tendon pathology and quantitative macroscale morphology using bilateral B-mode shoulder ultrasound in a cohort of 25 typically developing, non-wheelchair user youth. Bilateral shoulder ultrasound was also performed in 34 youth manual wheelchair users. Glenohumeral joint dynamics were computed for the wheelchair users by an inverse dynamics model using optical motion capture and wheelchair handrim kinetics data as in the second aim. An innovative machine learning approach was employed to elucidate the relationships of glenohumeral joint dynamics to rotator cuff health. A bilayer clustering method employing k-means clustering followed by agglomerative hierarchical clustering determined latent youth rotator cuff health phenotypes using key quantitative macroscale morphology parameters and two common self-reported measures of pain and satisfaction. Glenohumeral joint dynamics potentially related to rotator cuff tendon health, selected based on the findings from the second aim, were used to develop logistic regression prediction models to determine glenohumeral joint dynamics underlying rotator cuff phenotype and tendon pathology. Results: There was substantial overlap in rotator cuff health between youth manual wheelchair users and typically developing youth. Four distinct phenotypes emerged. One phenotype, composed almost entirely of wheelchair user shoulders, had minimal pathology. Phenotypes were distinguishable by tendon morphology, pain, and satisfaction. Glenohumeral joint dynamics predicted phenotype and pathology in youth manual wheelchair users with 91.2% and 94.1% accuracy, respectively. Discussion: Complex patterns in glenohumeral joint dynamics were identified which appeared related to rotator cuff morphology and rotator cuff tendon pathology in youth manual wheelchair users. One phenotype indicates that the interaction of glenohumeral joint dynamics and rotator cuff morphology may be leveraged to minimize the risk of tendon pathology in youth wheelchair users. Conclusion:The three studies in this dissertation provide insights about the role of pediatric manual wheelchair use in rotator cuff health that will inform musculoskeletal care for youth with SCI/D. The results of this dissertation indicate that there is substantial overlap in rotator cuff health between youth manual wheelchair users and non-wheelchair users, but suggest the presence of a phenotype specific to youth with SCI/D who are at lower risk for rotator cuff tendon pathology than their peers, despite similar age and cumulative duration of wheelchair use. This dissertation determined that patterns in glenohumeral joint dynamics are highly predictive of rotator cuff phenotype and tendon pathology. The comprehensive understanding of ”he n’ture of glenohumeral joint dynamics patterns differentiating rotator cuff phenotype and the presence and severity of rotator cuff tendon pathology establishes the framework for individualized assessments of rotator cuff health and biomechanical targets for rotator cuff injury prevention in youth manual wheelchair users. The findings from this dissertation could also facilitate the development of objective, individualized recommendations for manual wheelchair propulsion technique training and wheelchair fit or design parameters. These results constitute important considerations in the design of future generations of manual wheelchairs. The knowledge gained from this dissertation could inform personalized wheelchair fit to promote beneficial shoulder biomechanics, or the development of clinical guidelines for shoulder exercise for injury prevention or rehabilitation. As a general recommendation for wheelchair users, the results of this dissertation suggest that decreasing superior force and internal rotation moment loading of the glenohumeral joint in wheelchair propulsion may decrease risk for rotator cuff tendon pathology. The relationships of modifiable wheelchair propulsion factors to rotator cuff morphology and pathology identified in this dissertation provide directions for future research focused on the development of clinical interventions to prevent or treat early-onset rotator cuff pathology and understand the progression of rotator cuff health and relationships to changes in wheelchair biomechanics, pain, and quality of life.