Morphological and mechanical analysis of the glenoid trabecular bone

Bone quality is an important factor in glenoid component fixation and ultimately the long-term outcome of shoulder replacement. The aims of this study were to explore the relationship between bone morphology and mechanical properties, to develop an experimental fixation model to explore the properties of cemented glenoid fixation, and to investigate the strength of the bone anchors as a function of bone density. Nineteen embalmed and six fresh frozen human glenoids were acquired for testing. In order to determine basic morphological and mechanical properties, specimens were tested using a flat cylindrical indentor at eleven pre¬selected grid points from which the strength and elastic modulus were acquired from the resulting load-deformation output. The subchondral thickness and bone volume to total volume ratio (BV/TV) were determined by scanning the whole glenoid using a MicroCT in the vicinity of the indentations. The thickness measurements were validated by sectioning the specimens post scanning. Multiple regression analysis found a significant correlation between strength and both BV/TV and subchondral thickness data derived across all of the indentation sites. Similar results were found for the elastic modulus. MicroCT provided to be a powerful tool for elucidating these relationships. Several previous studies have been undertaken on component fixation, but there are none that have investigated the differences between the peg and keel design, the cement mantle thickness and initial fixation strength. In this study Sawbones (open cell foam) were used to represent cancellous bone and these enabled the cement to flow within the surrogate bone structure and provide a more suitable morphological model. From this study, it was clear that open cell Sawbones are not applicable for mechanical testing of glenoid fixation. They may, however, be useful for looking at different cementing techniques and the interdigitation of cement for different cement formulations, designs of prostheses or surgical procedures. This study investigated the relationship between pullout strength and BMD when using suture anchors loaded with Orthocord™ (Depuy, USA) sutures. It is likely that the rank order and, therefore, the correlation between BMD and strength remain valid and that tissue quality is an important determinant of anchor strength.