Background Accurate assessment of the critical shoulder angle (CSA) is important in clinical evaluation of degenerative rotator cuff tears. 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 Flavopiridol HCl 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 Flavopiridol HCl 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. scapular orientation. Alterations in the projection of the glenoid margin and the lateral extension of the acromion may consequently lead to errors in CSA measurement. Moor et al documented a reproducible assessment of the CSA yielding variability ≤ 2° for malrotations up to 20° of scapular internal rotation or extension and 20° of external rotation or Rabbit polyclonal to Transmembrane protein 57 flexion.28 However most hospitals do not routinely take AP radiographs of the glenohumeral joint under fluoroscopic control. Therefore precise radiographic criteria which technicians radiologists and orthopaedic surgeons could use to detect malpositioned scapula that will result in an inaccurate CSA are lacking. Digitally reconstructed radiographs (DRR) generated from 3D computed tomography (CT) reconstructions of the scapula allow the study of these positional errors and their influence on the CSA. The DRR has recently been validated as a surrogate for clinical radiographs that can be generated from controlled perspectives with respect to the CT image stack.15 Furthermore little is known about how the CSA varies in populations with otherwise healthy shoulders as a function of demographic factors like glenoid size gender or side. Therefore the purpose of this study was to analyze the influence of non-AP viewing perspectives on the magnitude and reproducibility of the CSA as compared to the true AP view and to develop and validate a clinical classification system to identify a malpositioned scapula that will result in an inaccurate CSA. In addition we assessed the relationship between the CSA and glenoid size gender and side. We hypothesized that the non-AP viewing perspectives would significantly alter the reproducibility and absolute values of the CSA as compared to true AP views and that the CSA would increase with glenoid size. We also hypothesized that the CSA would be larger in males than in females but would not differ between left and right shoulders. Materials and Methods Analysis of cadaveric scapulae Glenohumeral joints were selected from a database of cadaver specimens with both 3D CT data and documentation of specimen dissection/condition. Shoulders were excluded if any pathology was detected during dissection. Glenoid cartilage was visually screened for degenerative changes consistent with OA and the RC was visually assessed for degenerative full-thickness tears. All dissections were performed by a board certified orthopaedic surgeon (R.T.). A total of 68 non-pathologic cadaver shoulders were included in this study (25 pairs + 18 individual). CT data acquisition and three-dimensional reconstruction Each cadaver shoulder was placed in a supine anatomic position and axial CT images were acquired using a Siemens Sensation 16 CT Scanner (130 kV tube voltage 512 × 512 acquisition matrix 1 mm slice thickness 0.75 pitch 170 baseline tube current). CT scans were stored in DICOM (Digital Imaging and Communications in Flavopiridol HCl Medicine) format for later processing. Scapulae were then semi-automatically segmented from the CT image data using Amira (v5.4 Visage Imaging San Diego CA) and 3D reconstructions of the bony surfaces were generated.15 16 Previous validation studies verified that accurate and reproducible 3D models of excised and scapulae can be created from Flavopiridol HCl segmentation of CT scans.5 17 22 Morphometric measurements on 3D reconstructions The 3D reconstructions of the scapulae were imported into.