JSES - 2026-05-20 - Journal Article
Neuromuscular signatures differentiating functional and impaired cases in full-thickness rotator cuff tears.
Weng YH, Wong CK, Chien YT, Liu KY, Weng YC, Chang CH, Lin JJ
Topics
Key Takeaway
In full-thickness rotator cuff tears, shoulder flexor strength (r=0.485) and lower trapezius strength (r=0.376) correlate with functional outcome more strongly than structural parameters such as tear size (r=0.317), which correlates only with pain.
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Summary
This study asked whether structural or neuromuscular factors better differentiate high-functioning from poor-functioning patients with full-thickness rotator cuff tears, comparing the upper and lower quartiles of FLEX-SF scores among 53 patients. Structural parameters (tear size, AHD, CHL thickness) correlated moderately with pain but not with function, while shoulder flexor strength (r=0.485), lower trapezius strength (r=0.376), serratus anterior activation, and reduced teres major compensatory activity (8.0–13.4% lower in good-function group, p=.015–.018) were the primary functional differentiators. The good-function group demonstrated 11.2% greater shoulder flexor strength than the poor-function group (p=.001).
Key Limitation
The cross-sectional design precludes determining whether the identified neuromuscular patterns are adaptive compensatory responses to the tear or pre-existing characteristics that confer functional resilience, making causal inference impossible.
Original Abstract
BACKGROUND
The relationship between structural damage and functional impairment in patients with full-thickness rotator cuff tears (FT-RCTs) remains inconsistent. While some patients maintain high function despite large tears, others experience profound disability, suggesting that compensatory neuromuscular mechanisms may be more closely associated with functional status than with anatomical integrity. This study aims to identify the clinical, structural, and neuromuscular factors that differentiate high-functioning from poor-functioning individuals with FT-RCTs.
METHODS
Fifty-three patients with FT-RCTs were evaluated. Assessments included ultrasonographic measurement (tear size, acromiohumeral distance [AHD], humeral head migration, and coracohumeral ligament [CHL] thickness). Isometric strength (shoulder flexor, upper/lower trapezius, serratus anterior, teres major) was quantified using hand-held dynamometry. Scapular biomechanics, including three-dimensional kinematics and muscle activation, were recorded using an electromagnetic tracking system and electromyography during controlled arm elevation in the scapular plane. Functional levels were determined using the FLEX-SF score. To identify clear differentiators, comparisons were made between the upper quartile (Good-Function) and lower quartile (Poor-Function) groups.
RESULTS
Structural parameters, including larger tear size (r = 0.317, p = .025), thinner CHL (r = -0.365, p = .009), and narrower AHD (r = -0.340, p = .016), showed a statistically significant moderate correlation with pain intensity but not with functional scores. Conversely, superior functional ability was moderately associated with shoulder flexor strength (r = 0.485, p < .001), lower trapezius strength (r = 0.376, p = .007), and reduced superior humeral head migration (r = 0.311, p = .028). Neuromuscularly, better function correlated with increased activation of the serratus anterior (r = -0.338 to -0.335, p = .017) and lower trapezius (r = -0.318 to -0.347, p = 0.014-0.024). The Good-Function group demonstrated significantly greater shoulder flexor strength (11.2% ± 3.2% vs. Poor-Function; p = .001) and significantly lower compensatory activation of the teres major (8.0%-13.4%; p = .015-.018).
CONCLUSIONS
Functional capacity in FT-RCTs appears to be associated with distinct neuromuscular compensatory mechanisms rather than the severity of structural damage. High-functioning individuals exhibit superior strength in the shoulder flexors, while poor function is characterized by excessive teres major activation. Although statistically significant, the moderate effect size indicates that additional unmeasured factors likely influence the functional status of patients with FT-RCTs. Rehabilitation for FT-RCTs may benefit from incorporating a neuromuscular-based perspective alongside the traditional structure-centric model. Given the observed associations, clinicians might consider prioritizing the strengthening of shoulder flexors and the lower trapezius, while monitoring for excessive teres major activity as a potential clinical marker of suboptimal compensation.