Quantifying wear depth in hip prostheses using a 3D optical scanner.

The visualization of wear depth in hip prostheses can assist the evaluation of new bearing materials and implant designs. The goal of this study was to develop an accurate, fast, and economical methodology to generate colorimetric maps of wear depth in hip implants using a structured light 3D optical scanning system. The accuracy and precision of this novel technique were determined using reference blocks with known wear depths. This technique was then used to measure the in vitro wear of a hip resurfacing device for canines that incorporates a highly cross-linked polyethylene liner. The 3D optical scanner had an average accuracy of 2.1 µm and an average precision of 1.4 µm, which corresponded to errors less than 10% when measuring wear depths of 20 µm or greater. The scanner was able to repeatedly generate 3D colorimetric maps of wear depth in highly cross-linked polyethylene liners in 20 min or less. These colorimetric maps identified localized regions with 3-fold greater wear than the average wear depth, and revealed liners with asymmetric wear patterns. For the first time, this study has validated the use of 3D optical scanning to quantify in vitro surface wear in a hip replacement device.

Wear testing of a canine hip resurfacing implant that uses highly cross-linked polyethylene.

Hip resurfacing offers advantages for young, active patients afflicted with hip osteoarthritis and may also be a beneficial treatment for adult canines. Conventional hip resurfacing uses metal-on-metal bearings to preserve bone stock, but it may be feasible to use metal-on-polyethylene bearings to reduce metal wear debris while still preserving bone. This study characterized the short-term wear behavior of a novel hip resurfacing implant for canines that uses a 1.5 mm thick liner of highly cross-linked polyethylene in the acetabular component. This implant was tested in an orbital bearing machine that simulated canine gait for 1.1 million cycles. Wear of the liner was evaluated using gravimetric analysis and by measuring wear depth with an optical scanner. The liners had a steady-state mass wear rate of 0.99 ± 0.17 mg per million cycles and an average wear depth in the central liner region of 0.028 mm. No liners, shells, or femoral heads had any catastrophic failure due to yielding or fracture. These results suggest that the thin liners will not prematurely crack after implantation in canines. This is the first hip resurfacing device developed for canines, and this study is the first to characterize the in vitro wear of highly cross-linked polyethylene liners in a hip resurfacing implant. The canine implant developed in this study may be an attractive treatment option for canines afflicted with hip osteoarthritis, and since canines are the preferred animal model for human hip replacement, this implant can support the development of metal-on-polyethylene hip resurfacing technology for human patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1196-1205, 2018.