A Novel Mini-Prosthesis with a Nano-Multilayer Film-Coated Surface and 3D-Printed Porous Stem for Focal Cartilage Lesions

Background: Focal cartilage lesions (FCLs) of the knee can cause pain and dysfunction. Focal resurfacing with mini-prostheses offers an alternative to biological treatments, yet current clinical options remain limited. This preliminary study investigated a novel mini-prosthesis in a porcine model. Methods: A Ti6Al4V mini-prosthesis with a carbon-based nano-multilayer film (NMF)-coated articular surface and a 3D-printed porous stem was developed (NMF@3D-Ti). Two comparators were included in the study: an NMF-coated Ti articular surface with a hydroxyapatite (HA)-coated stem (NMF@HA-Ti) and a cobalt-chromium (CoCr) prosthesis with a polished articular surface and an HA-coated stem (HA-CoCr). Twenty-five Bama pigs underwent bilateral medial femoral condyle surgery and were divided into 5 treatment groups: NMF@3D-Ti, NMF@HA-Ti, HA-CoCr, microfracture (MF), and sham. All animals were killed at 24 weeks. Evaluations included radiography, biocompatibility, overall joint condition, gross and histological analysis of opposing and adjacent cartilage, gene expression analysis in opposing cartilage, synovial inflammatory cytokines, and osseointegration. Results: Radiographs revealed no implant-related complications, and biocompatibility was confirmed. The HA-CoCr group had the most severe opposing-cartilage damage, with significantly worse macroscopic and microscopic scores, upregulated catabolic gene expression, and elevated synovial inflammatory cytokines compared with all other groups (all p < 0.05), along with disrupted collagen organization. The NMF@3D-Ti and NMF@HA-Ti groups were comparable with the sham group across all cartilage assessments. The MF group showed intermediate histological and gene expression changes in the opposing cartilage. Furthermore, the NMF@3D-Ti group demonstrated superior osseointegration, with significantly greater bone volume/total volume, bone mineral density, and bone-implant contact than the other implant groups (all p < 0.05), and no evidence of stress-shielding in the comparison with the sham group. Conclusions: At 24 weeks, the NMF@3D-Ti mini-prosthesis exhibited favorable biocompatibility and robust osseointegration, and achieved superior cartilage protection compared with both the CoCr mini-prosthesis and MF. Clinical Relevance: This mini-prosthesis provides a joint-preserving approach that may be a valuable addition to the current armamentarium, enriching the stepped-care algorithm for osteoarthritis.