Robotic reaming, multiple screw fixation results in significantly improved initial acetabular cup stability

This study aimed to compare the biomechanical performance of cups implanted with manual versus robotic reaming, single versus sequential reaming, as well as no screws, 1 screw and 2 screws.

A total of 48, 56-mm diameter 3D-printed porous acetabular cups were impacted into separate polyurethane foam bone models reamed with either manual or robotic arm reaming, and either single or sequential reaming techniques. Simultaneous torsion-compression loading yielded torque at failure, angular displacement at failure and torsional stiffness of acetabular cups fixed with either 0, 1 or 2 acetabular screws.

Overall, torsional stiffness for robotically-reamed cups (both sequential and single) was 45% higher than those reamed via manual instrumentation (3609.0 vs. 2484.6 N·m/rad; p < 0.0001). With increasing number of acetabular screws, the torque at failure (zero screws: 60.1 N·m vs. 1 screw 67.0 N·m vs. 2 screws 97.9 N·m; p < 0.001) and angular displacement at failure (0 screws: 2.0° vs. 1 screw 1.7° vs. 2 screws 5.3°; p < 0.001) increased. There was no difference in the torque, angular displacement at failure or torsional stiffness observed between cups reamed via single or sequential reaming (all p > 0.05). Neither torque nor angular displacement showed differences at failure (all p > 0.05).

Robotically-reamed cups demonstrated nearly 50% greater torsional stiffness than those reamed manually, suggesting that robotic reaming results in fewer deviations in sphericity, thereby optimising the congruency of the acetabulum-cup interface.