Donald W. Howie

The differences in toxicity and release of bone-resorbing mediators induced by titanium and cobalt-chromium-alloy wear particles.

We investigated the relationship between the toxic effects of metal wear particles and their ability to stimulate the release of inflammatory mediators implicated in bone resorption. In vitro studies were carried out with use of rat peritoneal macrophages, which were exposed to either cobalt-chromium-alloy or titanium-aluminum-vanadium particles, milled from the metal components of hip prostheses. The particles were in the size-range of, and at concentrations similar to, those found in the tissues surrounding failed prostheses in humans. The titanium-aluminum-vanadium particles showed little toxicity even at high concentrations, while the cobalt-chromium particles were very toxic. The titanium-aluminum-vanadium particles induced significantly more release of prostaglandin E2 than did the cobalt-chromium particles, and this was true for a wide range of concentrations. Exposure to titanium-aluminum-vanadium increased the release of prostaglandin E2, interleukin-1, tumor necrosis factor, and interleukin-6. In contrast, exposure to cobalt-chromium particles was associated with a decreased release of prostaglandin E2 and interleukin-6, and it had little effect on the release of interleukin-1 and tumor necrosis factor.

A rat model of resorption of bone at the cement-bone interface in the presence of polyethylene wear particles

Resorption of bone and the formation of a membrane at the interface between acrylic cement and bone were induced by particles of high-density polyethylene that were similar in size to those that are present in the tissues surrounding a human joint prosthesis. A non-weight-bearing plug of methylmethacrylate was inserted through the knee joint into the distal part of the femur of the rat. The plug rapidly became surrounded by a shell of bone. After repeated injections of particles of high-density polyethylene into the knee joint, resorption of bone occurred at this stable interface. No resorption of bone occurred after the opposite knee was injected with a control preparation that did not contain particles. The resorption of bone that occurred around the plug after the injection of particles of polyethylene took place in the absence of mechanical causes for loosening and in the absence of infection.

The osteoclastogenic molecules RANKL and RANK are associated with periprosthetic osteolysis

Extensive osteolysis adjacent to implants is often associated with wear particles of prosthetic material. We have investigated if RANKL, also known as osteoprotegerin ligand, osteoclast differentiation factor or TRANCE, and its natural inhibitor, osteoprotegerin (OPG), may be important in controlling this bone loss. Cells isolated from periprosthetic tissues containing wear particles expressed mRNA encoding for the pro-osteoclastogenic molecules, RANKL, its receptor RANK, monocyte colony-stimulating factor (M-CSF), interleukin (IL)-1beta, tumour necrosis factor (TNF)alpha, IL-6, and soluble IL-6 receptor, as well as OPG. Osteoclasts formed from cells isolated from periprosthetic tissues in the presence and absence of human osteoblastic cells. When osteoclasts formed in the absence of osteoblastic cells, markedly higher levels of RANKL mRNA relative to OPG mRNA were expressed. Particles of prosthetic materials also stimulated human monocytes to express osteoclastogenic molecules in vitro. Our results suggest that ingestion of prosthetic wear particles by macrophages results in expression of osteoclast-differentiating molecules and the stimulation of macrophage differentiation into osteoclasts.

Tissue response in relation to type of wear particles around failed hip arthroplasties

To establish the types of wear particles and associated tissue response around human prostheses the periprosthetic tissues around 50 hip arthroplasties revised for aseptic loosening of one or more components were examined by light microscopy, transmission electron microscopy, and energy-dispersing x-ray microanalysis. The tissues around cementless metal-on-bone and ceramic-on-ceramic prostheses contained few or no prosthesis wear particles. The tissues around metal-on-metal prostheses contained large numbers of metal particles and large numbers of macrophages, and occasional multinucleate giant cells. The tissues around cemented metal-on-polyethylene prostheses often contained large numbers of small and large polyethylene particles, variable numbers of cement particles, and occasional metal particles. Large numbers of macrophages and multinucleate giant cells were frequently seen in these tissues. Lymphocytes were occasionally seen in association with metal particles. Ultrastructural studies of the periprosthetic tissues confirmed the phagocytosis of submicroscopic wear particles by macrophages. Varying degrees of degenerative change in macrophages were seen in association with phagocytosis of metal particles. Large numbers of cytolysosomes were seen in cells in association with the accumulation of wear particles.

Large femoral heads decrease the incidence of dislocation after total hip arthroplasty: a randomized controlled trial.

BACKGROUND The use of larger femoral heads has been proposed to reduce the risk of dislocation after total hip arthroplasty, but there is a lack of evidence to support this proposal. The aim of this multicenter randomized controlled trial was to determine whether the incidence of dislocation one year after total hip arthroplasty is significantly lower in association with the use of a 36-mm femoral head articulation as compared with a 28-mm articulation. METHODS Six hundred and forty-four middle-aged and elderly patients undergoing primary or revision arthroplasty were randomized intraoperatively to receive either a 36 or 28-mm metal femoral head on highly cross-linked polyethylene. Patients who were at high risk of dislocation (including those with dementia and neuromuscular disease) and those undergoing revision for the treatment of recurrent hip dislocation or infection were excluded. Patients were stratified according to other potential risk factors for dislocation, including diagnosis and age. Diagnosis of hip dislocation required confirmation by a physician and radiographic evidence of a dislocation. RESULTS Overall, at one year of follow-up, hips with a 36-mm femoral head articulation had a significantly lower incidence of dislocation than did those with a 28-mm articulation (1.3% [four of 299] compared with 5.4% [seventeen of 316]; difference, 4.1% [95% confidence interval, 1.2% to 7.2%]) when controlling for the type of procedure (primary or revision) (p = 0.012). The incidence of dislocation following primary arthroplasty was also significantly lower for hips with a 36-mm femoral head articulation than for those with a 28-mm articulation (0.8% [two of 258] compared with 4.4% [twelve of 275]; difference, 3.6% [95% confidence interval, 0.9% to 6.8%]) (p = 0.024). The incidence of dislocation following revision arthroplasty was 4.9% (two of forty-one) for hips with a 36-mm articulation and 12.2% (five of forty-one) for hips with a 28-mm articulation; this difference was not significant with the relatively small sample size of the revision group (difference, 7.3% [95% confidence interval, -5.9% to 21.1%]) (p = 0.273). CONCLUSIONS Compared with a 28-mm femoral head articulation, a larger 36-mm articulation resulted in a significantly decreased incidence of dislocation in the first year following primary total hip arthroplasty. However, before a 36-mm metal-on-highly cross-linked polyethylene articulation is widely recommended, the incidence of late dislocation, wear, periprosthetic osteolysis, and liner fracture should be established.

Loosening of matt and polished cemented femoral stems

We have compared prospectively the incidence of loosening of 20 femoral stems with a matt surface with that of 20 polished stems of an otherwise identical tapered, non-modular design of Exeter hip replacement. The stems were inserted using the same technique at operation and radiographs showed no difference in the adequacy of the cement mantle or of fixation. All the patients were reviewed regularly and none was lost to follow-up. After a minimum follow-up of nine years, four matt but no polished stems had been revised for aseptic loosening. Polished stems subsided slightly within the cement mantle early, but did not loosen.

Metal on metal total hip replacement workshop consensus document.

The objective of this workshop was to provide a forum to discuss the reintroduction of metal on metal bearings for clinical use in total hip arthroplasty. Approximately 100 researchers clinicians, and industry representatives presented the state of the art interpretation of the metal on metal total hip replacements past performance, and the clinical, tribologic, and biologic considerations of all metal bearings. Based on the scientific presentations at the symposium, the extant literature, the clinical experience of the panelists, and the current regulatory, legal, and economic environment, consensus statements were developed.

A comparison of different surgical approaches for the periacetabular osteotomy.

The periacetabular osteotomy is a well established surgical procedure for the preventative treatment of degenerative joint disease caused by symptomatic acetabular dysplasia. Surgeons on several continents use varying surgical approaches to achieve the same effective osteotomy. Individual surgical approaches must provide accurate and adequate exposure for the osteotomy and the reorientation of the acetabular fragment. The aim of the surgical approach for such complex and expansive surgery is to minimize morbidity related to the approach. This article compares experiences among three common approaches including the modified Smith-Petersen, ilioinguinal, and direct anterior approaches and describes the double approach.

Wagner resurfacing hip arthroplasty. The results of one hundred consecutive arthroplasties after eight to ten years.

In a prospective study of 100 consecutive Wagner resurfacing hip arthroplasties in ninety-three patients, the outcomes for all hips were determined for an eight to ten-year follow-up period. By survivorship analysis, the rate of survival of the arthroplasty was calculated to be 70 per cent at five years, but only 40 per cent at eight years. The major cause of failure was aseptic loosening of the acetabular or femoral component, or both. Fracture of the neck of the femur occurred in three hips. Although the medium-term results (at fifty-six to eighty-three months) were better than those in most comparable studies of resurfacing arthroplasty, the poor long-term results (at ninety-one to 118 months) show that meaningful studies of new prosthetic designs must continue for at least eight years, and, if at all possible, must include 100 per cent follow-up. The survival curve for the resurfacing arthroplasties in this study can serve as the basis for comparison of the early, medium, and long-term results of future designs of resurfacing hip prostheses.

Biologic effects of cobalt chrome in cell and animal models.

The literature on animal and cellular models used to study the response to cobalt chrome alloy implants and wear and corrosion products is reviewed. Animal studies show that in solid form cobalt chrome alloy is relatively well tolerated. Injections of large numbers of particles in a single bolus lead to acute inflammation and necrosis, followed by a chronic inflammatory response. Macrophages are the predominant cell type and may persist in the tissues for years. Long term studies have failed to confirm the induction of tumors. In vitro studies confirm the toxic effects of cobalt chrome alloy corrosion products and wear particles, especially cobalt, and show that intracellular corrosion is an important mechanism for early release of cobalt ions. In vitro studies show that cobalt chrome alloy particles induce the release of inflammatory mediators from macrophages before causing cell death. These mediators have significant effects on osteoblastlike cells, as well as inducing bone resorption. Variations in the cell types, implantation site, and characteristics of the particles used in experimental models make interpretation of the results difficult. Standardized methods to control for size, shape, and number of particles for testing are proposed. It is important that in vitro and in vivo findings not be taken in isolation, but be compared with the results of human studies.