Humeral Tissue Remodeling in Contact with Pyrocarbon Interposition Implant

Abstract

The interactions between pyrocarbon (PyC) interposition implants and human humeral cancellous bone leads to the formation of a new interpositional tissue made a dense layer of cortical bone and a cartilage-like tissue. A sample of the tissue in contact with the PyC interposition implant was harvested on the humeral bone side from 6 patients undergoing a re-operation for implant removal due to staged surgery or clinical failure related to pain. The samples where then prepared for histology to evaluate the tissue morphology and immunohistology to assess for the presence of collagen I and collagen II within the matrix. For all the cases, a layer of dense cortical bone and a layer of soft tissue was observed between the PyC interpositional implant and the humeral cancellous bone. The nature of the interpositional soft tissue was different between the cases. While the hypothesis that a new tissue was modeled at PyC - humeral cancellous bone interface was confirmed, the nature of the soft interpositional tissue evolved from a fibrocellular to a cartilage-like tissue depending on the cases. The hypotheses for the different nature of the soft interpositional tissue observed between the different cases was based on humeral bone mechanobiological remodeling. The influence of the degree of attachment between the soft and bony interpositional-tissues and on the PISA geometry on the soft interpositional tissue nature are discussed. Further investigations on the role of humeral bone and on the PISA biomechanics should be performed to better understand this tissue remodeling.