Association between acromial morphology, scapular control, ultrasonographic impingement and non-surgical treatment outcome in patients with isolated subacromial pain syndrome

The aim of this study was to investigate whether acromial morphology, scapular control, and ultrasonographic impingement were associated with treatment outcome from three months of non-surgical treatment in patients with subacromial pain syndrome (SAPS). Patients were recruited consecutively from an orthopaedic outpatient clinic. All patients were systematically investigated for SAPS and for the presence of concomitant diagnoses by orthopaedic specialists using predefined standardised criteria. All patients diagnosed with SAPS were referred for 3 months physiotherapy. The treatment outcome was defined as the change in the Shoulder Pain and Disability Index (SPADI) from pre- to post-treatment. Acromial morphology was evaluated on standardised outlet view radiographs, scapular control was evaluated with the scapular assistance test and ultrasonographic impingement was evaluated using a reliable method. The association between each of the pathophysiological factors and treatment outcome was investigated with linear regression analyses. A total of 69 patients were included in the analysis for scapular control, 62 patients for ultrasonographic impingement, and 45 patients for the radiographic analysis. Eight patients were lost to follow-up. Acromial morphology was associated with poorer treatment outcome in both the adjusted and unadjusted linear regression models. The adjusted model predicted a change in SPADI of 1.8 points per degree of increased acromial curvature (more hook-shaped acromion). There was no association between scapular control or ultrasonographic impingement and change in SPADI. In patients with isolated SAPS, increasing acromial curvature (more hook-shaped acromion) was associated with poorer non-surgical treatment outcome, while ultrasonographic impingement and scapular control were not. This indicates that acromial morphology may be a prognostic factor for non-surgical treatment outcome, but future research is needed to confirm the findings. Level II, prognostic study.