Biological responses to individualized small titanium implants for the treatment of focal full-thickness knee cartilage defects in a sheep model

The present study aimed to evaluate the functional, radiological and histological outcome of a customized focal implant for the treatment of focal full-thickness cartilage defects in sheep. The study used magnetic resonance imaging data as the basis for construction of the titanium implant using a three-dimensional printing technique. This was then placed on the medial condyle of the knee joint in eight sheep and left in place in vivo over a period of six months. Following euthanasia, the local biological response was analyzed using micro-computed tomography, light microscopy and histological evaluation (International Cartilage Repair Society (ICRS) score). The variables were analyzed using a generalized linear mixed model. Odds ratios were given with 95% confidence intervals. The osseointegration rate was 62.1% (SD 3.9%). All implants were prone to the neighboring cartilage bed (4.4–1096.1 μm). Using the IRCS score, the elements ‘surface’, ‘matrix’, ‘cell distribution’ and ‘cell population’ all showed pathological changes on the operated side, although these did not correlate with implant elevation. On average, a difference of 0.7 mm (±2 mm) was found between the digitally planned implant and the real implant. As a result of imprecise segmentation and difficult preparation conditions at the prosthesis bed, as well as changes at the surface of the implant over the operational lifetime of the prosthesis, it must be stated that the approach implemented here of using a customized implant for the treatment of focal full-thickness cartilage defects at the knee did not meet our expectations.