| Summary: | Background: The use of partial articular resurfacing surgery with a mini-implant has been gradually increasing; the implant is mainly made of cobalt–chromium metal material, and cartilage changes cannot be monitored after implantation. Thus, we aimed to develop a novel local articular resurfacing polyetheretherketone (PEEK) mini-implant and investigate its feasibility for postoperative magnetic resonance imaging (MRI) monitoring of implant location, bone changes, and cartilage degeneration without artefacts. Methods: Nine skeletally mature female standardised goats were used and divided into the sham, PEEK, and cobalt–chromium–molybdenum alloy (Co–Cr–Mo) groups. The animals underwent local articular resurfacing operation with Co–Cr–Mo alloy (Co–Cr–Mo group) and PEEK (PEEK group) mini-implants. X-ray, computed tomography, and MRI examinations were performed at 12 weeks postoperatively. The sham group underwent a similar surgical procedure to expose the femoral head but without implantation. Gross necropsy and surface topography measurement of the articular cartilage of the acetabulum were performed after sacrificing the animals. Imaging artefacts and opposing cartilage degeneration in the acetabulum were also examined. Results: Cartilage damage occurred in both the Co–Cr–Mo and PEEK groups, and the damaged cartilage area was markedly larger in the Co–Cr–Mo group than in the PEEK group, as assessed by gross necropsy and histological staining. The mean surface roughness of the opposing cartilage was approximately 65.3, 117.4, and 188.4 μm at 12 weeks in the sham, PEEK, and Co–Cr–Mo groups, respectively. The Co–Cr–Mo mini-implant was visualised on radiographs, but computed tomography and MR images were markedly affected by artefacts, whereas the opposing cartilage and surrounding tissue were clear on MR images in the PEEK group. Opposing cartilage damage and subchondral bone marrow oedema could be detected by MRI in the PEEK group. Conclusions: The PEEK mini-implant can be a novel alternative to the Co–Cr–Mo mini-implant in articular resurfacing to treat focal osteochondral defects with less cartilage damage. It is feasible to postoperatively monitor the PEEK implant location, surrounding bone changes, and opposing cartilage degeneration by MRI without artefacts. The translational potential of this article: The use of MRI to monitor changes in the opposing cartilage after prosthesis implantation has not been widely applied because MR images are generally affected by artefacts generated by the metal prosthesis. This study revealed that the PEEK mini-implant can be a novel alternative to the Co–Cr–Mo mini-implant in articular resurfacing to treat focal osteochondral defects, and it is feasible to monitor the PEEK implant location, surrounding bone changes, and opposing cartilage damage/degeneration by MRI without artefacts postoperatively.
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