The impact of lymphedema severity on shoulder joint function and muscle activation patterns in breast cancer survivors: a cross-sectional study.

Purpose: This study aimed to investigate the impacts of breast cancer-related lymphedema (BCRL) severity on shoulder function including range of motion, strength, muscle activation patterns, and patient-reported disability.

Methods: A cross-sectional, observational study design was utilized. Seventy-five women with unilateral BCRL were recruited and categorized into mild, moderate, and severe groups based on limb swelling severity. Outcomes included shoulder range of motion, isometric strength, Disabilities of Arm Shoulder and Hand (DASH) scores for disability, and surface electromyography (EMG) of shoulder muscles. Data were analyzed using parametric and nonparametric tests.

Results: Increasing lymphedema severity was associated with progressive declines in shoulder mobility, strength, and function. Severe cases showed markedly reduced shoulder flexion, abduction, rotation, and extension range of motion along with decreased isometric flexor and abductor strength versus mild cases (p < 0.001). Higher pain levels (p < 0.001) and DASH disability scores (p < 0.001) were noted in severe BCRL. Surface EMG revealed impaired activation patterns including reduced amplitudes (p < 0.001) and delayed onsets (p < 0.001) in the deltoids, rotator cuff, and scapular muscles with greater impairment.

Conclusions: Advancing BCRL severity was associated with substantial declines in shoulder mobility, strength, neuromuscular activation, pain threshold, and upper limb functionality. These quantitative results demonstrate impaired shoulder joint control underlying disability in arm elevation and daily tasks. The progressive nature of these deficits highlights the relationship between lymphedema severity and shoulder dysfunction in breast cancer survivors.