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The effects of wear mechanisms on the long-term survivorship of artificial hip implants emphasized the importance of determining the 3D volumetric wear in retrieved hip replacements. Traditional methods for determining the volumetric wear on acetabular cups require reference surface from a pre-worn model, which is not feasible for clinical retrieved implants. In this study, a methodology based on co-ordinate measuring machine (CMM) measurement is proposed to reconstruct the reference surface by applying a mathematical model on those selected unworn regions of the acetabular liners. For validation purposes, three polyethylene liners from 5-million-cycle hip simulator testing were employed, whose wear volume at different measurement points was determined by applying the developed method and the results were compared to those determined via traditional approaches. Volumetric loss estimated by the developed method was found to correlate well with the results estimated by the traditional methods ([Formula: see text]). Moreover, two surgically retrieved inserts were analyzed using the developed methodology. The wear volume estimated from the two retrieved liners was also found to agree well with the observation from X-ray photograph. Results demonstrated that the proposed method is effective in determining the volumetric wear for retrieved components providing viable unworn regions on the liner.

The high-precision phase extraction method directly determines the final measurement performance of the heterodyne laser interferometer. This paper proposes a digital quadrature phase-locked (DQPL) method with sub-nanometer precision based on FPGA hardware and compiled on the LABVIEW FPGA platform. DQPL method can accurately extract the phase difference of the two optical signals in the heterodyne laser interferometer. The validity and stability of the method have been verified by simulations and experiments. The experimentally obtained measurement resolution is 0.074 nm, and the measurement standard deviation obtained by the Monte Carlo method is 0.22 nm.

Asphericity and out-of-roundness are generally used to evaluate the manufacturing quality of ultra-high molecular weight polyethylene (UHMWPE) cup inner surfaces, which can potentially affect initial clinical wear and contribute to osteolysis of total hip arthroplasty. This study measured the location and magnitude of asphericity and the out-of-roundness value for four UHMWPE cups in a single set, and then investigated the effects of the asphericity on the contact mechanics of UHMWPE cups. A co-ordinate measuring machine (CMM) was used for the surface measurement and finite element analysis (FEA) was adopted for contact mechanics study. The results demonstrated that the asphericity varied between cups with the maximum value as 0.088[Formula: see text][Formula: see text][Formula: see text]0.004[Formula: see text]mm. Although such a value met the ISO specification, large difference of volume appeared for the asphericity above 0.060[Formula: see text]mm. Actual surface profile accounting for the asphericity was found to affect the value of contact pressure and contact area by around 12%. The inferior asphericity resulted in a nonsmoothly distributed contact pressure, which had a negative effect on the contact mechanics of UHMWPE cups and the edge loading was predicted to occur for the sample with a large asphericity. In conclusion, the asphericity of UHMWPE cup could affect the contact mechanics of the articular bearings and may subsequently contribute to initial wear during bedding-in phase.