Pressure Pain Sensitivity is Independent of Structural Pathology in Patients with Subacromial Pain Syndrome: A Cross-Sectional Analysis

Objective: To compare localized (primary) and widespread (secondary) hyperalgesia using pressure pain threshold (PPT) of patients with normal imaging findings, rotator cuff tear, or other pathologies.

Design: This was a cross-sectional design with data collected at a single time point.

Setting: This study was performed at two large, urban, academic medical centers.

Subjects: Participants included had chronic subacromial pain syndrome for three months or longer. Each participant was categorized into one of three imaging groups: normal imaging, rotator cuff tear, or other structural pathology.

Methods: Primary hyperalgesia was assessed with PPT at the midsection of the painful shoulder's lateral deltoid. Secondary hyperalgesia was assessed with PPT at the contralateral tibialis anterior muscle (TA). An ANOVA and ANCOVA was performed for each objective. ANCOVA covariates included age, sex, education level, and pain duration.

Results: The 103 participants included 55 males, had a median age of 55 years, median pain duration of 14.0 months, and a median composite Shoulder Pain and Disability Index (SPADI) score of 43.1%. The ANCOVA for primary hyperalgesia showed no significant difference in square-root adjusted deltoid PPT between imaging groups (F = 1.04, p = 0.3589). The ANCOVA for secondary hyperalgesia showed no significant difference in log-adjusted TA PPT between imaging groups (F = 0.24, p = 0.7900).

Conclusions: No significant difference was observed in the analysis of ipsilateral deltoid or contralateral TA PPT between patients with differing structural shoulder pathologies. These findings suggest that the three types of structural shoulder abnormalities we examined are not significantly associated with differences in one measure of hyperalgesia.