Active Shape Models (ASM) have been widely used in the literature for the extraction of the tibial and the femoral bones from MRI. These methods use Statistical Shape Models (SSM) to drive the deformation and make the segmentation more robust. One crucial step for building such SSM is the shape correspondence (SC). Several methods have been described in the literature. The goal of this paper is to compare two SC methods, the 28 MRI of the knee have been used. The validation has been performed by using the leave-one-out cross-validation technique. An ASMMDL and an ASMIMCP-GMMM has been built with the SSMs computed respectively with the MDL and IMCP-GMM methods. The computation time for building both SSMs has been also measured. For 90% of data, the error is inferior to 1.78 mm and 1.85 mm for respectively the ASMIMCP-GMM and the ASMMDL methods. The computation time for building the SSMs is five hours and two days for respectively the IMCP-GMM and the MDL methods. Both methods seem to give, at least, similar results for the femur segmentation in MRI. But (1) IMCP-GMM can be used for all types of shape, this is not the case for the MDL method which only works for closed shape, and (2) IMCP-GMM is much faster than MDL.
Total Shoulder Arthroplasty (TSA) is a solution to fixing shoulder complications and restoring normal shoulder functionality. Shoulder arthritis is one of the common indicators of TSA. Studies suggest that 15% and 7% of the total Rheumatoid Arthritis (RA) and Osteoarthritis (OA) patients respectively, in sub-Saharan Africa, have degenerated shoulders. These patients are implanted with a Total Shoulder Prosthesis (TSP). There are limited literature available on the morphometric features of African shoulders. Previous studies have indicated that differences in shoulder surface geometry of the European and African populations, exists. This study aims at identifying the structural differences of the humeral articulating surfaces between South African and Swiss data sets. The South African data set included the Computerised Tomography (CT) scans of cadavers sourced from the University of Cape Town and the Swiss data set included the cadaver CT scans obtained from the SICAS Medical Image Repository. Sixty reconstructed models of humerus were generated from these scans of 30 (bilateral) healthy cadavers (15 South African and 15 Swiss) using Mimics®. The humeral articulating surfaces were separated from the shaft by performing in-silico surgery using SOLIDWORKS®, according to the guidelines provided orthopaedic surgeons. A Matlab code was generated to determine the superior-inferior (S-I) and the anterior-posterior (A-P) circular diameter and the peak points (PPs) of the articulating surfaces. The PPs were defined as the highest point on the articulating surface, which is most likely to be in contact with the glenoid. The S-I diameter was found to be significantly greater (p<0.01) than the A-P diameter for both the data sets (average difference = 5.02mm). Both the average A-P and S-I diameter for the Swiss data set were significantly larger (p = 0.02 and p = 0.03) than the South African data set by 2.36 mm and 2.70 mm respectively. The PPs were found to lie at an off-set from the origin. in case of the Swiss data set the average PP lie on the superior-posterior (S-P) quadrant and for the South African data set the average PP was found to lie on the anterior-inferior (A-I) quadrant. The A-P variation on the position of PP was highly significant (p = 0.003). The results obtained in this study sheds light on the observed morphological variations between the South African and Swiss data sets. The observed circular diameter values are similar to the literature. The observed results suggest that the average TSP needed for the Swiss data set would have been larger than the ones needed for the South African data set. PP is a novel feature which has not been studied extensively. The fact that the average Swiss data set PP lie in the S-P quadrant might suggest that these humeral heads are more retroverted and superiorly tilted when compared to the South African data set. These morphometric variations can play a major role in post-TSA kinematics. The future scope of this study is to highlight other morphometric variations, if any, for the gleno-humeral articulating surfaces.
The morphology of the proximal part of the humerus varies largely. Morphometric features characterizing the three-dimensional geometry of the proximal humerus have revealed a wide difference within individuals. These parameters include head size, radius of curvature, inclination angle, retroversion angle, offsets and neck-shaft angle. Different implant designs have been adapted so as to make provision for these anatomical variations. However, the optimal design criteria are yet to be established. Implant design is one of the main factors determining the success of Total Shoulder Arthroplasty (TSA) since slight modifications in the implant anatomy could have significant biomechanical effects. Therefore, this study investigates the three-dimensional morphometric parameters of the South African proximal humerus which will serve as a basis for designing a new Total Shoulder Prosthesis for the South African population. Sixteen South African (SA) fresh cadaveric humeri (8 left, 8 right; 8 paired) were used in this study. The data consisted of 6 men and 2 women with ages ranging from 32 to 55 years (43.13 ±8.51). The humeri were scanned using a Computer Tomography (CT) scanner. The Digital Imaging and Communications in Medicine (DICOM) files from the CT data were imported into medical modelling software, MIMICS for reconstruction. The 3D reconstructed model of the humeri as an STL file was used for further processing. The STL data were generated as a cloud of points in a CAD software, SolidWorks. These were then remodeled by defining the detailed Referential Geometric Entities (RGEs) describing the anatomical characteristics. Anatomical reference points were defined for the anatomical neck plane, the epiphyseal sphere and the metaphyseal cylinder. Also, axes were defined which comprises of the humeral head axis and the metaphyseal axis. Thereafter, the posterior offsets medial offsets and the inclination angles were measured based on the RGEs. The posterior offset varied from 0.07 mm to 2.87 mm (mean 1.20 mm), the medial offset varied from 4.40 mm to 8.45 mm (mean 6.50 mm) while the inclination angle varied from 114.00º to 133.87º (mean 121.05º) The outcome of the study showed that the shape and dimensions of the proximal humerus varies distinctively. The articular surface is not a perfect sphere and differs independently with respect to the inclination angles. In addition, variations were noticeable in the medial and lateral offsets. The morphometric data on the African shoulder is very limited and this study will significantly contribute to the shoulder data repository for the SA population. The morphometric parameters measured in this study will be useful in designing a South African shoulder prosthesis that mimics the native shoulder hence eliminating post-surgical complications.
