MECHANICAL PROPERTIES OF GLENOID CANCELLOUS BONE

Abstract

Total shoulder arthroplasty is a well-established and widely accepted method of treatment for a variety of shoulder disorders, loosening of the glenoid prosthesis is the main complication in total shoulder arthroplasty, it is highly dependent on the quality of the glenoid cancellous bone. Very little is known about mechanical properties of this cancellous bone. The objectives of this study were to determine the mechanical properties (elastic modulus and strength) of glenoid cancellous bone in the axial, coronal and sagittal planes including regional variation using a uniaxial compression test. To our knowledge, this kind of study was not done before.

Eleven scapulas were obtained from six fresh-frozen, unembalmed human cadavers (mean age eighty-eight years). Eighty-two cubic cancellous bone specimens of 6×6×6mm3 were used for mechanical testing in the three planes. The test was a uniaxial compression along each direction, Elastic modulus and strength were determined from the stress-strain curve. Apparent density was also calculated.

The study showed significant differences in the mechanical properties with anatomic location and directions of loading. Young modulus and strength were found to be significantly higher at the posterior part of the glenoid with the weakest properties at the antero-inferior part. Cancellous bone was found to be anisotropic with higher mechanical properties in the latero-medial direction (perpendicular to the articular surface of the glenoid). The apparent density was on average equal to 0.29 g/cm3 with the higher values at the posterior and superior part of the glenoid. Good correlation between apparent density and elastic modulus was found only in the sagittal plane but not in the coronal and axial plane, the overall correlation was low (r2 = 0.22, p< 0.0001) which emphasizes the role of trabecular bone architecture in predicting mechanical properties.

The mechanical properties determined in this study provide input data for finite element method analyses and may help to assist in uncemented shoulder prosthesis design.