Identifying the Relative Contributions of Shoulder Dysfunction in Patients with Subacromial Pain Syndrome.

Objective: To identify and quantify the factors associated with shoulder dysfunction in patients with subacromial pain syndrome (SAPS).

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

Setting: Two large, urban, academic medical centers in the United States.

Subjects: Participants included those with chronic SAPS for three months or longer.

Methods: Shoulder function was evaluated using both the Functional Impairment Test-Hand and Neck/Shoulder/Arm (FIT-HaNSA) and Shoulder Pain and Disability Index-Disability (SPADI-D). First, 12 demographic and clinical variables were independently assessed for an association with FIT-HaNSA and SPADI-D score. Next, two separate multivariable linear regression analyses, one for each outcome measure, were created to examine the association of each with all variables.

Results: The 113 participants had a median age of 55 years, a median pain duration of 14 months, and a median composite SPADI score of 43.85%. In univariate analysis, four variables were associated with FIT-HaNSA and five were associated with SPADI-D. The FIT-HaNSA multivariable linear regression model (F = 4.01, p < 0.0001) had an overall R2 of 38.27% (n = 98). This identified the worst pain in the past week (F = 10.86, p = 0.0014), and deltoid pressure pain threshold (F = 14.94, p = 0.0002) with significant associations. The SPADI-D model (F = 4.20, p < 0.0001) had an overall R2 of 39.38% (n = 98). This identified the worst pain in the past week (F = 21.04, p > 0.001) and Pain Catastrophizing Scale score (F = 5.32, p = 0.235) with significant associations.

Conclusions: Six variables were associated with shoulder function in univariate analyses and three associated in a multivariable analysis. Future research is necessary to determine if these variables are appropriate targets for clinical intervention to improve shoulder function, and to identify the other factors explaining the remaining outcome measure variability.