The initiation of failure in cemented femoral components of hip arthroplasties

TLDR

The study aimed to delineate the initial mechanisms of loosening in cemented femoral components of hip arthroplasties. Researchers retrieved 16 femora post‑mortem from symptomless patients with cemented total hip arthroplasties ranging from two weeks to 17 years in situ to examine early loosening processes. Only one of 16 specimens showed radiographic loosening, but all had intact cement‑bone interfaces; however, most exhibited cement‑prosthesis debonding and fractures—often originating at sharp metal corners, thin mantle areas, or voids—indicating that long‑term failure is primarily mechanical, beginning with interface debonding and progressing through gradual cement fractures.

Abstract

We studied 16 femora retrieved at post-mortem from symptomless patients who had a satisfactory cemented total hip arthroplasty from two weeks to 17 years earlier, with the aim of delineating the initial mechanisms involved in loosening. Only one specimen showed radiographic evidence of loosening; the other 15 were stable to mechanical testing at 17.0 Nm of torque. In all 16 specimens, the cement-bone interface was intact with little fibrous tissue formation. By contrast, separation at the cement-prosthesis interface and fractures in the cement mantle were frequent. The most common early feature was debonding of the cement from the metal, seen at the proximal and distal ends of the prosthesis. Specimens which had been in place for longer also showed circumferential fractures in the cement, near the cement-metal interface, and radial fractures extending from this interface into the cement and sometimes to the bony interface. The most extensive cement fractures appeared to have started at or near sharp corners in the metal, or where the cement mantle was thin or incomplete. Fractures were also related to voids in the cement. The time relationship in this series suggested that long-term failure of the fixation of cemented femoral components was primarily mechanical, starting with debonding at the interface between the cement and the prosthesis, and continuing as slowly developing fractures in the cement mantle.