Introduction The role of apoptosis in the progression of rotator cuff tendinopathy is poorly understood. The primary aim of this study was to quantify the amount of apoptosis in supraspinatus tendons presenting partial-thickness tears and matched intact subscapularis tendons.

Methods 9 partially torn supraspinatus tendons and matched intact subscapularis tendons were biopsied and compared to 10 reference subscapularis tendon samples. Immunohistochemistry was used to assess apoptotic cells (activated caspase-3; Asp175), proliferation (Ki67) and p53 (M7001), a key protein involved in regulating cell death. The Bonar scale was used to evaluate tendon degeneration.

Results The partially torn supraspinatus tendons and matched subscapularis tendons demonstrated a significant increase in the density of apoptotic cells and p53 expression. The Bonar score revealed significant tendon degeneration in the partially torn supraspinatus tendon compared to both matched and reference subscapularis tendon. The number of proliferating tendon cells was higher in the partially torn supraspinatus than in the matched or reference subscapularis tendons.

Discussion The presence of increased apoptosis and p53 in partial-thickness tears of the supraspinatus tendon is accompanied by features of both degeneration as well as ongoing repair. Apoptosis may be a relatively early feature in the continuum of rotator cuff tendinopathy.