Biomechanical Simulations Informed by Multimodal Measurements Link Symptoms to Glenohumeral Joint Forces Across Healthy and Pathological Rotator Cuffs.

Purpose: Rotator cuff tears pose a biomechanical challenge to glenohumeral joint stability and present with varied clinical symptoms. This study aimed to characterize glenohumeral joint contact force, a key indicator of mechanical stability, and its relationship to rotator cuff tear status and symptom severity.

Methods: Twenty older adults, including six with full-thickness supraspinatus tears, performed eight tasks. Joint contact forces were estimated using a biomechanical shoulder model with four scapular degrees-of-freedom, driven by measured muscle activations and kinematics. Forces were characterized by compressive magnitude, direction, and path length to assess group differences and discriminate by tear status and symptom severity.

Results: Participants with rotator cuff tears exhibited reduced compressive forces and more anteriorly situated joint contact forces than age-matched controls. The estimated force magnitudes were closer to instrumented implant data than prior modeling studies. Group differences were task-dependent and temporally dynamic; differences were largest at initiation and conclusion but converged during the task. Path lengths were significantly longer in the tear group. Compressive force magnitude provided the strongest classification for both tear status and symptom severity.

Conclusion: This study advances understanding of the biomechanical consequences of rotator cuff tears, establishing a link between glenohumeral joint loading, structural pathology, and symptom severity. Joint force characteristics discriminated individuals by pathology and symptom severity, supporting their utility as objective markers of dysfunction. Our findings highlighted that mechanical consequences were most pronounced in the absence of passive restraint, implicating preparatory muscle activation and underscoring the importance of temporally resolved joint force characterizations in biomechanical assessments.