Overall wear rates for heads and liners for the 5MC of normal gait and the 2MC of distraction testing and for the whole 7MC. 95% confidence intervals are plotted for each set of six heads and liners. Weight changes were converted to volumetric wear using a density of 3,800kgm-3. Even after extended drying, the liners all showed small weight gains. The heads apparently wore slightly during the normal walking cycle but gained weight during the distraction cycle. Overall, the heads showed a small wear rate of 0.17±0.09mm3/MC and the liners showed a small ‘negative’ wear rate of −0.11±0.07mm3/MC. Due to the uncertainties involved in the drying procedure, it is concluded that DoD wear rates were unmeasurably low for this test. Distraction is known to increase wear rates for CoC systems [ However, the 2MC of distraction testing produced only small weight gains. The heads showed no evidence of ‘stripe wear’ as reported for CoC systems.
A prospective study of displaced femoral neck fractures was conducted, using the Corail® stem, a non cemented HA-coated device, provided with a bipolar head. 293 consecutive patients were included. Our reasons to shift to an uncemented implant were:
the existence of intraoperative deaths during cementation; Cardiac failures consecutive to overhydration during cementation (to prevent drop of blood pressure); As life expectancy increases, concerns about skeletal fixation of cemented devices in osteoporotic patients, when the cortico-medullary index decreases. Follow-up was extended up to 5 years, unless the patient died before. 7 patients were lost from FU. Function was assessed every year using various clinical scores (Parker’s mobility score, Qureshi’s mental status, Jensen’s autonomy index,). An X-Ray was obtained at each visit when possible, with a special insistence at completion of the follow up (136 out of the 144 still alive patients). Intraoperatively, 11 isolated calcar cracks and 1 fracture of the major trochanter were seen. In three cases, it was impossible to obtain a stable implantation. In two of these, a cemented implant was used. In the third patient, instability was not seen, leading to an 8 mm subsidence, along with thigh pain and distal hypertrophy of the femur. The 278 other patients had no intra-operative complications. Late complications were:
1) 14 patients had a secondary subsidence of their device (1–4 mm), with a subsequent good stability and unaltered fixation to the skeletal tissue; 2) No loosening; 3) One femoral fracture, due to a second fall (at M4) requiring ORIF; 4) 14 small radiolucent line of less than 1 cm in the major trochanter area, whose the meaning remains obscure, as no adverse reactions are seen thereafter; 4) no stress shielding, despite a full coating of HA.
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:
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. 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. 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.
We examined specimens of hydroxyapatite-coated femoral prostheses from four patients who had died within nine months of implantation for fractured neck of femur. Histology showed newly formed immature bone overlying the hydroxyapatite coating with new trabeculae bridging to the endosteal bone layer. In the diaphysis, where there had been contact between the hydroxyapatite and the cortex, there was dense, firmly anchored bone with an haversian architecture. In other places the newly formed bone had a trabecular structure, containing bone marrow tissue with normal cellularity. It appeared that biological osseointegration had taken place.
