Glenohumeral and scapulothoracic strength impairments exists in patients with subacromial impingement, but these are not reflected in the shoulder pain and disability index

Background:Pain and loss of function are cardinal symptoms associated with Subacromial impingement syndrome(SIS), while the presence and magnitude of deficits in strength and range of motion (ROM) are largely undescribed innon-athletic patients with SIS. Moreover, the relevance of impairments in strength and ROM to patient-reportedshoulder function is not well described, even though testing of strength is recommended in clinical guidelines.The purpose of this study was, first, to investigate impairments in glenohumeral and scapulothoracic strength and inabduction and internal rotation ROM in patients with SIS. Secondly, to investigate the influence of these impairmentson patient-reported shoulder function.Methods:Cross-sectional study based on a consecutive cohort of 157 patients referred to specialist examination anddiagnosed with shoulder impingement (SIS) using predefined validated diagnostic criteria. Prior to specialistexamination, questionnaires regarding shoulder function (Shoulder Pain And Disability Index, SPADI) demographicsand kinesiophobia (TSK-11) were collected, and shoulder strength and ROM was measured by trained testers, with thepatient reporting pain levels during testing and for the last week. Impairments in strength (abduction, external-rotation,(protraction and horizontal-extension) and ROM (abduction and internal rotation) were investigated in patients withunilateral shoulder pain, using one-sample t-tests. SPADI total score (SPADI) and SPADI function score (SPADI-F), werechosen as dependent variables in multiple regressions to investigate the influence of impairments on patient-reportedshoulder function. Independent variables of interest were; strength in abduction and external rotation, abduction ROM,pain-during-tests, pain-last-week and kinesiophobia.Results:Significant impairments were found for all impairment tests, but most pronounced for glenohumeral strengthand abduction ROM (29–33% deficits), and less for scapulothoracic strength and internal rotation ROM (8–18% deficits).Pain variables influenced SPADI and SPADI-F score to a high degree (R2=23.4–31.6%,p< 0.001), while strength andROM did not.