Abstract
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.
