Evaluation of articular cartilage wear against pyrolytic carbon in the context of spherical interposition shoulder arthroplasty

Metal shoulder hemiarthroplasty is known to cause failure due to glenoid cartilage erosion. Pyrolytic carbon (PyC), a non-metallic biomaterial, may be an attractive alternative due to its good general tribological characteristics and biocompatibility. We investigated the in vitro biotribological properties of PyC articulated against living cartilage for use as spherical shoulder interposition implant. The evaluation includes a comparison with the typically used cobalt‑chromium‑molybdenum alloy (CoCrMo) and zirconia toughened alumina (ZTA), a more recent biomaterial for hemiarthroplasty. The rate of cartilage degradation was assessed by means of cartilage wear biomarkers (glycosaminoglycans and hydroxyproline) in lubricant and histological changes of the cartilage superficial zone. In addition, the percentage of cell viability and metabolic activity of chondrocytes was assessed. The data revealed that PyC has similar tribological performance in terms of cell viability, cell metabolic activity, and tissue degradation compared to ZTA. Although not significant, CoCrMo affected chondrocyte metabolism and induced a thinner superficial layer with structural defects. There was a combined adsorption of phospholipids and biomarkers on the biomaterials; sGAGs adsorbed between 23 and 43% of the total concentration, and the adsorption rate of phospholipids increased significantly with friction. Biomaterial analysis is required to obtain the full picture of cartilage biomarker release and lubrication mechanisms. Our results suggest that PyC has good tribological performance and compares well with established biomaterials for hemiarthroplasty. It supports the use of PyC in spherical shoulder interposition implant as a viable alternative to conventional metal hemiarthroplasty. Further evaluation of the clinical performance of PyC is required. •Pyrolytic Carbon (PyC) is a cartilage-friendly biomaterial preserving a thick superficial layer of cartilage and maintaining good biocompatibility.•PyC and Zirconia toughened Alumina (ZTA) show similar cartilage wear characteristics with few differences.•CoCrMo alloy appears to induce tissue degradation with decreased metabolic activity of chondrocytes.•Organic components from the tissue and the media, such as sGAG and phospholipids, adsorb onto biomaterials at various rates.