Abstract
Introduction
Acetabular component loosening has been one of the factors of revision of total hip arthroplasty (THA). Inadequate mechanical fixation or load transfer may contribute to this loosening process. Several reports showed the load transfer in the acetabulum by metal components. However, there is no report about the influence of the joint surface on the load transfer. We developed a novel acetabular cross-linked polyethylene (CLPE) liner with graft biocompatible phospholipid polymer(MPC) on the surface. The MPC polymer surface had high lubricity and low friction. We hypothesized the acetabular component with MPC polymer surface (MPC-CLPE) may reduce load transfer in the acetabulum compared to that of the by CLPE acetabular component without MPC.
Methods
We fixed the three cement cup with MPC-CLPE (Group M; sample No.1–3) and three cement cup with CLPE (Group C; sample No.4–6) placed in the synthetic bone block with bone cement with a 0.10mm thick arc-shaped piezoresistive force sensor, which can measure the dynamic load transfer(Tekscan K-scan 4400; Boston). (Fig 1) A hip simulator (MTS Systems Corp., Eden Prairie, MN) was used for the load transfer test performed according to the ISO Standard 14242-1. Both groups had same inner and outer diameter s of 28 and 50mm, respectively. A Co–Cr alloy femoral head with a diameter of 28 mm (K-MAXs HH-02; KYOCERA Medical Corp.) was used as the femoral component. A biaxial rocking motion was applied to the head/cup interface via an offset bearing assembly with an inclined angle of +20. Both the loading and motion were synchronized at 1 Hz. According to the double-peaked Paul-type physiologic hip load, the applied peak loads were 1793 and 2744 N described in a previous study. The simulator was run 3 cycles. We recorded both the peak of the contact force and the accumulation of the six times load in total. Secondly, we calculated the mean change of the load transfer. We used the Student t-test. P value < 0.05 was used to determine statistical significance. We used EZR for statistical analysis.
Results
The mean of total accumulation of the load transfer in the group M is significantly lower than that of in the group C. (7037±508 N vs 11019±1290 N, P<0.0001). The peak of load in the group M was also significantly lower than that in the group C. (1024±166 N vs 1557±395 N) (Fig 2)The mean of the change of the load transfer in the group M is significantly lower than that of in the group C. (2913±112 N vs 4182±306 N) (Fig 3)
Conclusion
The acetabular component with MPC surface could reduce and prevent the radical load transfer change toward to the acetabulum compared to CLPE acetabular component without MPC.
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