FIXATION OF HUMERAL PROSTHESES AND AXIAL MICROMOTION

Surgeons often avoid cementing a proximal humeral prosthesis. Occasion ally bony augmentation is needed. This study was undertaken to compare proximal cementation in combination with distal press with fetal ceme ntation or press fit alone. In phase 1 axial micromotion with axial lo ading was measured in 15 pairs of humeri: 5 fully cemented versus prox imally cemented, 5 Fully cemented versus press fit, and 5 proximally c emented versus press fit. X-ray films of the specimens were obtained t o assess canal fill. In phase 2 axial micromotion was measured in 5 pa irs of high mineral density and 5 pairs of low mineral density to comp are proximal cementation with press fit. The 3M modular prosthesis was used in both phases. No difference was found in phase 1 among the 3 f ixation techniques. A strong reverse statistical correlation (P = .007 ) (r = .55) was Seen between axial micromotion and fill of the canal w ith the prosthesis. In the second phase no statistically significant d ifference was found between the techniques of fixation or between the 2 bone densities. Fill of the canal at the distal end of the prosthesi s was the only variable found that affected axial micromotion, but if accounted for only approximately 30% of the variance. Bone qualify and augmentation of the proximal bone with cement did not affect axial mi cromotion in this experiment brit warrant further study.