Biomechanical evaluation of rTSA baseplate designs: implant stability with and without glenoid bone loss.

BACKGROUND

Baseplate fixation is a crucial step in reverse shoulder arthroplasty and presents a challenge when faced with deformities or glenoid bone loss. Utilization of newer baseplates that are augmented to account for bone loss may provide equivalent stability to standard baseplates without bone loss. The purpose of this biomechanical study was to compare modern designs by evaluating 3 baseplates: (1) a one-piece monoblock design (RSP), (2) a two-piece nonlocking baseplate (neutral) without bone loss and (3) a two-piece nonlocking design with a wedge augment (wedge) with asymmetric bone loss.

METHODS

Polyurethane foam block cylinders (n = 6 per group) with a density of 0.48 g/cm were utilized. The 6 foam cylinders for the wedge baseplate were modified to stimulate 50% bone loss and the remaining 12 were left without modification, representing zero bone loss. Samples were mounted into a swing arm attached to the torque motor of a servo-electric test frame equipped with a 5 kN load cell. Samples were cycled through a 55° (from neutral, ±27.5°) arc of motion at 0.5 Hz for 10,000 cycles, while the test frame's actuator applied a constant 750 N compressive. Micromotion (μm) was measured throughout testing.

RESULTS

All samples survived 10,000 cycles of loading without catastrophic failure. None of the constructs exhibited micromotion above the 150 μm threshold. The baseplate micromotions at baseline were observed to be significantly different from one another (P = .001). After 10,000 cycles of loading, similar outcomes were observed where the Neutral had the lowest measured baseplate micromotion compared to RSP and the Wedge. The Wedge baseplate had significantly more micromotion compared to the RSP (P = .0167).

CONCLUSION

The neutral design was found to be the most stable, followed by the RSP and then the wedge design. All designs evaluated remained below the 150-micron threshold. The two-piece nonlocking wedge baseplate design is a viable option for reverse shoulder arthroplasty when dealing with bone loss.