Changes in shoulder muscle size and activity following treatment for breast cancer

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Abstract
Morbidity of the shoulder after breast cancer is a well-known phenomenon. MRI studies have shown muscle morbidity in cervical cancer and prostate cancer. In breast cancer clinical observations and patient reports include muscle morbidity in a number of muscles acting at the shoulder. Several of these muscles lie in the field of surgery and radiotherapy. Timed interaction between muscles that stabilise the shoulder and those acting as prime movers is essential to achieve a smooth scapulohumeral rthythm during functional elevation of the arm. Seventy-four women treated for unilateral carcinoma of the breast were included in the study. All patients filled out the Shoulder Pain and Disability Index (SPADI). EMG activity of four muscles was recorded during scaption on the affected and unaffected side. Muscle cross sectional area and signal intensity was determined from MRI scans. The association between EMG and covariates was determined using multiple linear regression techniques. Three of the 4 muscles on the affected side demonstrated significantly less EMG activity, particularly when lowering the arm. Upper trapezius demonstrated the greatest loss in activity. Decreased activity in both upper trapezius and rhomboid were significantly associated with an increase in SPADI score and increased time since surgery. Pectoralis major and minor were significantly smaller on the affected side. Muscles affected in the long term are the muscles associated with pain and disability yet are not in the direct field of surgery or radiotherapy. Primary muscle shortening and secondary loss of muscle activity may be producing a movement disorder similar to the ‘Dropped Shoulder Syndrome’. Exercise programmes should aim not only for range of movement but also for posture correction and education of potential long-term effects.

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