Subacromial injection failure in shoulder impingement: is somatic amplification the missing link?

Abstract

Objectives: To investigate whether somatosensory amplification - a heightened sensitivity to normal bodily sensations - affects the clinical response to corticosteroid injection in shoulder impingement syndrome (SIS) patients who did not respond to conservative treatment.

Methods: This prospective observational study included 70 patients with SIS and persistent pain despite at least four weeks of physical therapy and non-steroidal anti-inflammatory drugs (NSAIDs). All patients received a standardized corticosteroid injection into the subacromial space under ultrasound guidance. Pain intensity was measured using the Visual Analog Scale (VAS) at rest (VAS-rest) and during movement (VAS-movement), while shoulder-related disability was assessed with the Shoulder Pain and Disability Index (SPADI) at baseline and one month after the injection. Somatosensory amplification - referring to increased sensitivity to normal bodily sensations—was evaluated using the Somatosensory Amplification Scale (SSAS), a brief self-report questionnaire administered at the one-month follow-up by a psychiatrist blinded to clinical outcomes. Treatment response was defined as a ≥30% reduction in VAS-movement, based on the minimal clinically important difference (MCID). Patients were categorized as responders or non-responders accordingly.

Results: Thirty (42.9%) patients were classified as responders and 40 (57.1%) as non-responders. At 1-month, non-responders had significantly higher SSAS scores than responders (30.7 [27.4-32.6] vs. 21.5 [19.4-23.4], P<0.001). Compared to non-responders, the responder group demonstrated more significant improvements in VAS-rest, VAS-movement, and SPADI scores (P<0.001 for all). Spearman correlation analysis revealed strong positive correlations between SAS and VAS-rest (r=0.732), VAS-movement (r=0.748), and SPADI (r=0.734); P<0.001 for all.

Conclusions: Higher levels of somatosensory amplification were linked to a lower likelihood of benefiting from subacromial injection in SIS. These findings support the importance of including psychosomatic assessment in routine care to improve treatment outcomes and guide more personalized management.

Keywords

• Shoulder impingement
• ultrasound
• subacromial injection
• somatosensory amplification
• minimal clinically important difference (MCID)
• chronic pain

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