OSTEOINTEGRATION OF CORAIL STEMS. HISTOLOGY OF 49 HUMAN RETRIEVALS IN A TEN-YEAR PERIOD.

Abstract

Osteointegration of HA coated devices is well demonstrated. An abundant experimental material exists, allowing to describe the various properties of HA (early osteointegration, sealing effect, gap healing effect, etc…). Various side-effects have been described (third body wear of HA debris, delamination of the proximal coating etc…). Thus controversy still exists, despite a more and more convincing clinical experience. The role of human retrievals is therefore crucial to determine the exact role of all these parameters in the natural life of the implant throughout the years.

49 human well-functioning explants have been retrieved during systemic autopsies in elderly patients previously operated for a displaced fracture of the neck with a Corail® implant. Delays of implantation vary from 5 days to 10 years. All these specimens have been processed for optical microscopy, electronic microscopy with backscattering. This constitutes the longest report on one single implant and the retrievals are evenly distributed over this ten-year period. Several histomorphometric parameters were measured in the different Gruen’s zones: cortical bone density, cortical bone thickness, density of endosteal bone

3 steps are recognized:

1. Bone formation around the implant appears early after surgery. Multiple units of bone formation go to coalescence as soon as 6 weeks and develop thereafter, leading to osteointegration.

2. Bone remodelling reorganizes the architecture of connecting trabeculae according to the mechanical stresses resulting from the presence of the implant. Compression areas are generally the seat of broad and interconnected trabeculae, whereas tensile stresses areas display the presence of long, thin, unconnected and often parallel trabeculae. Very broad and short trabeculae are often seen at the level of the corners.

3. Coating resorption is seen in every specimen beyond one year of implantation, predominantly in the areas with less bone coverage.

Release of HA particles in the joint cavities was never encountered. Some metallic particles, originating from the femoral ball are commonly seen in the polyethylene. HA particles (presumably scratched off the prosthesis during insertion?...) have never been identified in the heterotopic ossifications.

We conclude that the osteointegration of the Corail stems is a reliable phenomenon with a reproducible sequence of events. It lasts even after the disappearance of the coating in a 5–10 years period. The presence of the stem provokes a remodelling of the cortices but the presence of a total coating and its longer duration at the level of the tip does not induce a disappearance of the proximal bone or a loose of the proximal fixation.