Critical shoulder angle combined with age predict five shoulder pathologies: a retrospective analysis of 1000 cases

Abstract

Background: Acromial morphology has previously been defined as a risk factor for some shoulder pathologies. Yet, study results are inconclusive and not all major shoulder diseases have been sufficiently investigated. Thus, the aim of the present study was to analyze predictive value of three radiological parameters including the critical shoulder angle, acromion index, and lateral acromion angle in relationship to symptomatic patients with either cuff tear arthropathy, glenohumeral osteoarthritis, rotator cuff tear, impingement, and tendinitis calcarea.

Methods: A total of 1000 patients' standardized true-anteroposterior radiographs were retrospectively assessed. Receiver-operating curve analyses and multinomial logistic regression were used to examine the association between shoulder pathologies and acromion morphology. The prediction model was derived from a development cohort and applied to a validation cohort. Prediction model's performance was statistically evaluated.

Results: The majority of radiological measurements were significantly different between shoulder pathologies, but the critical shoulder angle was an overall better parameter to predict and distinguish between the different pathologies than the acromion index or lateral acromion angle. Typical critical shoulder angle-age patterns for the different shoulder pathologies could be detected. Patients diagnosed with rotator cuff tears had the highest, whereas patients with osteoarthritis had the lowest critical shoulder angle. The youngest patients were in the tendinitis calcarea and the oldest in the cuff tear arthropathy group.

Conclusions: The present study showed that critical shoulder angle and age, two easily assessable variables, adequately predict different shoulder pathologies in patients with shoulder complaints.

Keywords: Critical shoulder angle; Cuff tear arthropathy; Glenohumeral osteoarthritis; Impingement; Rotator cuff tear.

Fig. 1

True-anteroposterior radiographs of a patient diagnosed with rotator cuff tear (RCT) of the right shoulder. a The critical shoulder angle (CSA of 38.8°), which was measured by drawing one line connecting the superior and inferior osseous margins of the glenoid cavity and then another line from the inferolateral border of the acromion and intersected the first line at the inferior glenoid margin. The angle between the two lines results in the CSA. b The acromion index (AI of 0.72) was calculated by dividing the distance of the glenoid plane to the lateral acromion border (GA) by the distance of the glenoid plane to the lateral margin of the humeral head (GH). c The lateral acromion angle (LAA of 76.05°) was assessed at the intersection of two lines representing the glenoid cavity and the acromion’s undersurface

Fig. 2

Scatterplots showing critical shoulder angles (CSA). CSA and age grouped according to actual (a, c) and predicted (b, d) shoulder pathologies including cuff tear arthropathy (CTA, black circles), osteoarthritis (OA, green circles), rotator cuff tear (RCT, purple circles), impingement (IM, orange circles), and tendinitis calcarea (TC, blue circles) of the development (a, b) and external validation (c, d) cohort

Fig. 3

Scatterplots showing critical shoulder angles (CSA). CSA and age grouped according to predicted shoulder pathologies including cuff tear arthropathy (CTA, black circles), osteoarthritis (OA, green circles), rotator cuff tear (RCT, purple circles), impingement (IM, orange circles), and tendinitis calcarea (TC, blue circles) of both the development and the external validation cohort. The red lines mark a 58 year old patient with a CSA of 38° and the yellow lines mark a 67 year old patient with a CSA of 28°