Optimization of Cemented Glenoid Peg Geometry. A Comparison of Resistance to Axial Distraction

Glenoid loosening is one of the most common complications of anatomic total shoulder arthroplasty (aTSA). Numerous glenoid pegged designs exist within the market place; however, little effort has been made to optimize peg geometry, and as a result, there is no consensus regarding the superiority of one design over another. The aim of this study was to determine the impact of peg design on the fixation strength by comparing the force and displacement associated with five different geometries of cemented glenoid components when each is axially displaced from two different densities of polyurethane bone substitute substrates.

An axial pull-out test was conducted on five different cemented peg geometries in both low- and high- density polyurethane bone-substitute blocks. All substrates were prepared utilizing a drill, which created a 7.3 mm diameter hole to a depth of 26.8 mm. Cemex ® brand bone cement was prepared and used to cement all pegs. After cementation of each peg, an electromechanical load frame applied a linear ramp displacement of 10 mm/minute axially to each peg while the polyurethane block was fully con strained. Load and displacement of each peg was sampled at 100 Hz until failure and axial distraction of each peg where the peak pull-out force and associated displacement were recorded. The average load to failure and associated displacement for each peg geometry were compared utilizing the Student's t-test where a p-value < 0.05 determined significance.

Cemented peg design #3 was associated with the greatest axial load to failure (675.3 N ± 18.8 N in low density and 707.3 N ± 11.7 N in high density) for both densities of bone-substitute blocks. Peg designs #5 and #2 were associated with the next highest axial loads to failure in both low and high density blocks. Finally, peg designs #1 and #4 were associated with the lowest axial loads to failure in both low and high density blocks. Only design #3 had a statistically significant difference between peak pull-out forces between the low- and high-density bone substitute blocks, as compared to all other designs.

The results of this study demonstrate that glenoid peg geometry can significantly influence the resistance to axial distraction where the continuous threaded geometry exemplified by peg design #3 demonstrated significantly superior cemented fixation relative to the other peg designs. It can be concluded that overall macrostructure and design of the peg itself plays a key role in pull-out force; however, performance in a clinical setting is required to confirm these biomechanical results.