The influence of radiographic viewing perspective and demographics on the critical shoulder angle

Abstract

Background Accurate assessment of the critical shoulder angle (CSA) is important in clinical evaluation of degenerative rotator cuff tears. This study analyzed the influence of radiographic viewing perspective on the CSA, developed a classification system to identify malpositioned radiographs, and assessed the relationship between the CSA and demographic factors. Methods Glenoid height, width and retroversion were measured on 3D CT reconstructions of 68 cadaver scapulae. A digitally reconstructed radiograph was aligned perpendicular to the scapular plane, and retroversion was corrected to obtain a true antero-posterior (AP) view. In 10 scapulae, incremental anteversion/retroversion and flexion/extension views were generated. The CSA was measured and a clinically applicable classification system was developed to detect views with >2° change in CSA versus true AP. Results The average CSA was 33±4°. Intra- and inter-observer reliability was high (ICC≥0.81) but decreased with increasing viewing angle. Views beyond 5° anteversion, 8° retroversion, 15° flexion and 26° extension resulted in >2° deviation of the CSA compared to true AP. The classification system was capable of detecting aberrant viewing perspectives with sensitivity of 95% and specificity of 53%. Correlations between glenoid size and CSA were small (R≤0.3), and CSA did not vary by gender (p=0.426) or side (p=0.821). Conclusions The CSA was most susceptible to malposition in ante/retroversion. Deviations as little as 5° in anteversion resulted in a CSA >2° from true AP. A new classification system refines the ability to collect true AP radiographs of the scapula. The CSA was unaffected by demographic factors.

Age-dependent variation of glenohumeral anatomy: a radiological study

“…Due to improvements in the resolution, a b c e d radiation exposure and length of examination of CT scans as well as the availability of 3D reconstruction software, preoperative planning for surgical procedures involving the reconstruction of glenohumeral osseous structures has been significantly facilitated [15,16].…”

Critical shoulder angle is an effective radiographic parameter that is associated with rotator cuff tears and osteoarthritis: a systematic review

“…In the original study first introducing the concept of the CSA, authors reported variability of ≤2° in measuring the CSA with malrotations of the scapula of up to 20° of internal rotation or extension and 20° of external rotation or flexion 8. However, in a biomechanical study of 68 non-pathological cadaver shoulders, the authors found that the radiographic alignment of the scapula in anteversion and retroversion can yield highly inaccurate measurements of the CSA 39. More specifically, a 5°–8° change in viewing perspective can result in a 2° change in CSA 39.…”

“…However, in a biomechanical study of 68 non-pathological cadaver shoulders, the authors found that the radiographic alignment of the scapula in anteversion and retroversion can yield highly inaccurate measurements of the CSA 39. More specifically, a 5°–8° change in viewing perspective can result in a 2° change in CSA 39. Henceforth, given the small range of non-pathological CSA values (30°–35°),8 clinicians must be careful to have appropriate shoulder/scapula positioning in order to avoid significant miscalculations of the CSA.…”

Natural History of Degenerative Rotator Cuff Tears

“…A second group of 119 patients diagnosed with adhesive capsulitis and normal radiographs served as controls. Only 326 (21%) of 1552 radiographs were of sufficient quality to measure the CSA due to the influence of scapular position on boney landmarks as defined by Suter et al [10]. Patients with cuff tears had a slightly higher (mean of 2°) CSA, but the CSA was not different between enlarging and stable tears, it did not change over time, and it did not correlate with baseline tear length.…”