Topographical pressure pain sensitivity maps of the shoulder region in individuals with subacromial pain syndrome

BACKGROUND: Topographical pain maps (TPM) are useful tools to assess deep tissue sensitivity in musculoskeletal pain conditions. There is evidence suggesting bilateral sensitivity in subacromial pain syndrome (SAPS), although it is not widely accepted. No previous study has investigated TPM of the shoulder in SAPS.

OBJECTIVE: To investigate whether differences for TPM of the shoulder are evident among patients with unilateral SAPS and controls.

METHODS: Pressure pain thresholds (PPTs) were assessed 3 times at each point and there was a 20 s rest period between each one. The TPM were calculated using 29 pre-determined points on both shoulders in all groups by inverse distance weighted interpolation of PPT data. Multivariate Analysis of Covariance was applied to detect differences in PPTs between groups, sides, points (gender as covariate).

RESULTS: The results revealed significant differences between points and genders (both, P < 0.001), but not between groups (P = 0.243) and sides (P = 0.812). Heterogeneous distribution of mechanical pain sensitivity was found in both groups as the PPTs were lower on the root spine of the scapula and the posterior border of the acromion (points 5-8, P < 0.05), glenohumeral joint (points 17-20, P < 0.01) and the anterior deltoid muscle (points 21-25, P < 0.001) compared to the average of the other sites on the shoulder. Women exhibited bilateral lower PPTs in all points than men in both groups (all, P < 0.01).

CONCLUSIONS: This study revealed no differences for mechanical pain sensitivity in patients with SAPS experiencing lower levels of pain compared with matched controls, but showed heterogeneous distribution of PPTs in the shoulder.