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 through the measurement of the 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 2 large, urban, academic medical centers.

Subjects: The included participants had had chronic subacromial pain syndrome for 3 months or longer. Each participant was categorized into 1 of 3 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). Analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were performed for each objective. ANCOVA covariates included age, sex, education level, and pain duration.

Results: The 103 participants included 55 males and had a median age of 55 years, a 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 among imaging groups (F = 1.04, P = .3589). The ANCOVA for secondary hyperalgesia showed no significant difference in log-adjusted TA PPT among imaging groups (F = 0.24, P = .7900).

Conclusions: No significant difference was observed in the analysis of ipsilateral deltoid or contralateral TA PPT among patients with differing structural shoulder pathologies. These findings suggest that the 3 types of structural shoulder abnormalities we examined are not significantly associated with differences in one measure of hyperalgesia.

Trial registration: ClinicalTrials.gov ID NCT03752619.