Biomechanical study of the initial stability of acetabular cup with different acetabular rim defects for developmental dysplasia of hip / 中华骨科杂志

ABSTRACT

Objective@#To investigate the effects of acetabular coverage on the initial stability of the cup during total hip arthroplasty in developmental dysplasia of hip.@*Methods@#There were 50 fourth-generation synthetic hemi-pelvises. The different cup coverage rate (100% group, 70% group, 60% group, 50% group, 40% group) was created in pelvis with 10 specimens per group. The synthetic hemi-pelvis was fixed rigidly to a customized fixture which was placed on the testing table of the material testing machine. Pull-out and torque test were conducted by computer-control in torsion testing machine.@*Results@#In the acetabular cup pull-out test, the average pull-out force for mode of failure in 100%, 70%, 60%, 50%, and 40% group was 1 560.4±438.7, 1 467.2±349.8, 1 137.8±427.4, 737.4±134.8, 506.6±119.0 N, respectively. The pull-out force was reduced gradually. The pull-out force in 100% group was significantly higher than that in 50% (P=0.004) and 40% (P=0.001) group. The pull-out force in 70% group was significantly higher than that in 50% group (P=0.002) and 40% group (P=0.000). The force in 40% group was significantly lower than that in 60% group (P=0.013) and 50% group (P=0.021). In the acetabular cup torque test, the average torque for mode of failure in 100%, 70%, 60%, 50%, and 40% group was 28.0±3.7, 17.0±2.2, 9.4±1.1, 7.6±1.1, 6.4±1.1 N·m, respectively. The torque was reduced gradually. The torque in 100% group was significantly higher than that in other groups (P<0.05). There was no significant difference between 50% and 40% group (P>0.05). The torque in other groups were similar (P>0.05).@*Conclusion@#The present biomechanical study showed that different acetabular cup coverage rate affected the initial stability of the cup. The highest initial stability was observed in the cup with a 100% of cup coverage rate. The cup could not obtain 100% coverage when with acetabular rim defect. We should try our best to make the cup coverage reach to 70%. The 70% coverage rate has sufficient initial stability to meet daily activities without increasing the cup loosening rate.