HA particles can be released from well-fixed HA-coated stems: histopathology of biopsies from 20 hips 2-8 years after implantation.

20 hip arthroplasties with a Landos Corail Ti6Al4V stem entirely plasma-sprayed with a 155+/-35 microm thick HA coating were reoperated on after median 6 (2-8) years because of polyethylene wear (10), acetabular loosening (7), instability (2), or infection (1). We took biopsies from the proximal femurs adjacent to the well-fixed stems. Undecalcifled sections were prepared and examined with a light microscope. The biopsies contained median 5 (1.3-16 ) mm metal interface with 54% HA, 32% bone, and 14% soft tissue. The median thickness of the remaining HA coating was 137 (6-380) microm, and the HA-tissue interface included 89% bone and 11% soft tissue. All HA coatings showed partial degradation and replacement by soft tissue, osteoid-like tissue, or bone. 6 hips had tissue ingrowth between HA and metal consistent with delamination. 14 hips showed bone resorptive areas containing some HA particles and large amounts of polyethylene and metal particles, partly internalized in multinucleated giant cells and macrophages. Bone resorption was associated with metal and polyethylene particles, but not with HA particles. The HA coatings were undermined, resulting in release of large flakes of HA with free access to the articulation. We believe this mechanism may be responsible for third-body wear.