Background. There is no consensus on which glenoid plane should be used in total shoulder arthroplasty. Nevertheless, anatomical reconstruction of this plane is imperative for the success of a total shoulder arthroplasty. Methods. Three-dimensional reconstruction CT-scans were performed on 152 healthy shoulders. Four different glenoid planes, each determined by three surgical accessible bony reference points, are determined. The first two are triangular planes, defined by the most anterior and posterior point of the glenoid and respectively the most inferior point for the Saller's Inferior plane and the most superior point for the Saller's Superior plane. The third plane is formed by the best fitting circle of the superior tubercle and the most anterior and posterior point at the distal third of the glenoid (Circular Max). The fourth plane is formed by the best fitting circle of three points at the rim of the inferior quadrants of the glenoid (Circular Inferior). We hypothesized that the plane with normally distributed parameters, narrowest variability and best reproducibility would be the most suitable surgical glenoid plane. Results. No difference in position of the mean humeral center of rotation is found between the Circular Max and Circular Inferior plane (X=91.71degrees/X=91.66degrees p=0.907 and Y=90.83degrees /Y=91.7degrees p=0.054 respectively), while clear deviations are found for the Saller's Inferior and Saller's Superior plane (p < 0.001). The Circular Inferior plane has the lowest variability to the coronal scapular plane (p<0.001). Conclusion. This study provides arguments to use the Circular Inferior glenoid plane as preferred surgical plane of the glenoid. Level of evidence: Level II, Basic Science Study, Anatomical Survey

Introduction:. The complex 3D geometry of the scapula and the variability among individuals makes it difficult to precisely quantify its morphometric features. Recently, the scapular neck has been recognized as an important morphometric parameter particularly due to the role it plays in scapular notching, which occurs when the humeral component of a reverse shoulder arthroplasty (RSA) prosthesis engages the posterior column of the scapula causing mechanical impingement and osseous wear. Prosthetic design and positioning of the glenoid component have been accepted as two major factors associated with the onset of notching in the RSA patient population. The present image-based study aimed to develop an objective 3D approach of measuring scapular neck, which when measured pre-operatively, may identify individuals at risk for notching. Materials and Methods:. A group of 81 subjects (41 M, 69.7 ± 8.9 yrs.; 40 F, 70.9 ± 8.1 yrs.) treated with RSA were evaluated in this study. The 3D point-cloud of the scapular geometry was obtained from pre-operative computed tomography (CT) scans and rendered in Mimics. Subsequently, a subject-specific glenoid coordinate system was established, using the extracted glenoid surface of each scapula as a coordinate reference. The principal component analysis approach was used to establish three orthogonal coordinate axes in the geometric center of the glenoid. Utilization of glenoid-specific reference planes (glenoid, major axis, and minor axis plane) were selected in order to remove subjectivity in assessing “true” anterior/posterior and profile views of the scapula. The scapular neck length was defined as the orthogonal distance between the glenoid surface and the point on the posterior column with the significant change of curvature (Fig. 1). In addition, the angle between the glenoid plane, area center of the glenoid, and the point of significant change of the curvature were assessed (Fig. 2). This new parameter was developed to serve as a predictive critical value for the occurrence of notching. The incidence of notching increases as the value of the notching angle decreases. In order to evaluate relationships between glenoid and scapular neck, the glenoid width and height was also measured at the glenoid plane. Results:. Glenoid neck length and notching angle within the population were normally distributed with mean values of 7.8 ± 2.3 mm and 19.6 ± 4.8°, respectively (Fig. 3). No gender difference was found (p = 0.676). In one subject, a glenoid neck length of less than 1 mm was measured with the notching angle less than 2.5°. No association between glenoid neck length and glenoid size were identified (vs. glen. height r. 2. = 0.001, and vs. glen. width r. 2. = 0.05). Conclusion:. The present study reported on the scapular neck length and notching angle as measureable morphometric parameters that follow a normal distribution throughout the population and that are not correlated to the subject's glenoid size. Pre-operative acquisition of these novel and unique CT-based measurements may promote more appropriate RSA prosthesis selection to account for subject-specific anatomy in an effort to avoid scapular notching. Inferior placement of a baseplate or lateralization of glenoid component center of rotation (either biologically or mechanically) both serves to theoretically increase the notching angle

Introduction. Patient Specific Guides (PSGs) are used to increase the accuracy of arthroplasty. PSGs achieve this by incorporating geometry that fits in one unique position and orientation on a patient's bone. Sufficient docking rigidity ensures PSGs do not shift before being fixed by pins. Despite the importance of PSG docking rigidity, minimal research has been conducted on this issue. This study aims to determine whether commercially available PSGs, in their equilibrium position, provide sufficient stability for reliable surgical use. Materials and Methods. A commercially available PSG (Glenoid PSG, BLUEPRINT™, Wright Medical) was analyzed and tested in this study; the mechanical performance of this guide was assessed using a custom testing apparatus mounted to a universal testing machine (UTM) (MTI-10k, Materials Testing Inc), assembled with a high-precision load cell (MiniDyn Type 9256C, Kistler). The apparatus accepts an additively manufactured glenoid surrogate and was designed to transform vertical crosshead forces from the UTM into PSG-applied forces transverse to the glenoid plane along anterior-posterior and superior-inferior axes and PSG-applied torques about lateral, anterior, and superior axes. Three trials were recorded for each force and torque application. Prior to each test, the glenoid surrogate and PSG were articulated together with a constant 27N compressive force — equivalent to the normal force exerted by a surgeon using the guide — applied using springs. Forces were recorded when the guide was displaced 2mm by transverse loads or 5° by torque application; if the guide visibly dislodged from the glenoid surrogate before either criterion was met, force was recorded at the time of dislodgement. If no PSG movement occurred, testing ceased at 75N or 1.19N⋅m, depending on the test type. Results. The lowest and highest torques to displace the PSG by 5° were around the lateral (−0.08±0.02 N⋅m) and superior axes (0.87±0.23 N⋅m), respectively. The lowest and highest forces to displace the PSG by 2mm were along the inferior (31.77± 6.30N) and posterior axes (64.80±0.79N), respectively. Although it yielded at a higher torque than about the lateral axis, CCW rotation about the posterior axis produced the earliest PSG dislodgement at 3.76° while the PSG dislodged after only 1.05mm in the anterior direction. Discussion. The above results demonstrate that the tested PSG design produces similar docking rigidity for all tested rotations except rotations about the lateral axis, which provided 4 times less stability than the next lowest result. This indicates that the PSG may not provide sufficient resistance in this direction to prevent inadvertent mal-rotation. The relatively low rigidity in anterior and superior translation indicate that this PSG design may be prone to mal-positioning errors in these directions. With these data in mind, PSG docking rigidity is not equal in all loading directions which could play a role in the clinical accuracy. Furthermore, this indicates that a systematic, objective method for PSG design optimization may be warranted. For any figures or tables, please contact authors directly

INTRODUCTION. The glenoid version assessment is crucial step for any Total Shoulder Arthroplasty (TSA) procedure. New methods to compute 3D version angle of the glenoid have been proposed. These methods proposed different definitions of the glenoid plane and only used 3 points to define each plane on the 3D model of the scapula. In practice, patients often come to consultation with their CT-scans. In order to reduce the x-ray dose, the scapulae are often truncated on the inferior part. In these cases, the traditional scapula plane cannot be calculated. We hypothesised that a new plane definition, of the scapula and the glenoid, that takes into account all the 3D points, would have the least variation and provide more reliable measures whatever the scapula is truncated or not. The purpose of the study is to introduce new fully automatic method to compute 3D glenoid version for TSA preoperating planning and test its results on artificially truncated scapulae. MATERIAL AND METHODS. Volumetric preoperative CT datasets have been used to derive a surface model shape of the shoulder. The glenoid surface is detected and a 3D version and inclination angle of the glenoid surface are computed. We propose a new reference plane of the scapula without picking points on the 3D model. The method is based on the mathematical skeleton of the scapula and the least squares plane fitting. Specific software has been developed to apply the plane fitting in addition the automatic segmentation process. An orthopedic surgeon defined the traditional scapular plane based on 3 points and applied the measures on 12 patients. The manual process has been repeated 3 times and the intra-class correlation coefficient (ICC) was calculated to compare the results with our automatic method. To validate the reliability of the new plane relating to truncated scapulae, we have measured the 3D orientation variation on 37 scapulae. Nine iterations have been applied on each scapula by cutting 5mm of the scapular inferior part. RESULTS. The ICC of the scapula plane orientation for the three orientation components (x, y, z) were 0.98, 0.99 and 0.89 respectively. The reliability results applied by cutting the inferior side show good results with means: 0.01±0.01 mm, 0.01±0.01 mm and 0.02±0.02 mm for X, Y, Z respectively. CONCLUSION. New referential scapular plane has been proposed to compute 3D glenoid version. The method is fully automatic and doesn't need manual positioning of points on the 3D points. The orientation of the new plane is correlated with the standard scapular plane. The study showed that plane orientation is reasonably constant while truncating the scapula body till 45mm of cut on the inferior and the medial side. This is the only study that proposes a reference plane for truncated scapula