There is a general perception that adverse local tissue reactions in metal-on-metal hip arthroplasties are caused by wear, but the degree to which this is the case remains controversial. To what extent is the magnitude of wear associated with (1) the histological changes; (2) presence of metallosis; and (3) likelihood of pseudotumor formation in the periprosthetic tissues? One hundred nineteen metal-on-metal total hip arthroplasties and hip resurfacings were selected from a retrieval collection of over 500 implants (collected between 2004 and 2012) based on the availability of periprosthetic tissues collected during revision, clinical data including presence or absence of pseudotumor or metallosis observed intraoperatively, and wear depth measured using a coordinate measurement machine. Histological features of tissues were scored for aseptic lymphocytic vasculitis-associated lesions (ALVAL). Correlation analysis was performed on the three endpoints of interest. With the sample size available, no association was found between wear magnitude and ALVAL score (ρ = −0.092, p = 0.423). Median wear depth (ball and cup) was greater in hips with metallosis (137 μm; range, 8–873 μm) than in those without (18 μm; range, 8–174 μm; p < 0.0001). With the numbers available, no statistically significant association between wear depth and pseudotumor formation could be identified; median wear depth was 74 μm in hips with pseudotumors and 26 μm in those without (p = 0.741). Wear alone did not explain the histopathological changes in the periprosthetic tissues. A larger sample size and more sensitive outcome variable assessments may have revealed a correlation. However, wear depth has been inconsistently associated with pseudotumor formation, perhaps because some patients with hypersensitivity may develop pseudotumors despite low wear. Metal wear alone may not explain the histological reactions and pseudotumors around metal-on-metal hip implants.

Metal-on-metal (MoM) total hip arthroplasties (THAs) and the head-neck and neck-body junctions in modular THA are associated with a variety of local and systemic reactions to their related wear and corrosion products. Although laboratory testing is available, the relationship between laboratory values—including serum metal ion levels—and adverse local tissue reactions (ALTRs) remains controversial and incompletely characterized. (1) What is the range of serum metal levels associated with ALTR in patients who have MoM THAs or corrosion at the head-neck and neck-body junctions in metal-on-polyethylene (or ceramic-on-polyethylene) THAs? (2) How much wear occurs in patients with MoM total hips? (3) Is there evidence of a dose-response relationship between wear and ALTR? PubMed and Embase databases were reviewed for English-language studies assessing serum metal levels in the presence of ALTR and papers describing the results of wear measurements from revised MoM implants and ALTR histopathology were systematically reviewed. Reported linear wear data were separated into groups with ALTR and without ALTR as listed in individual papers and graphed to determine whether a dose-response relationship was present between wear and ALTR. Overall, 15 studies including 338 hips with ALTR with corresponding serum metal levels were identified and analyzed. Twelve studies reported the wear depth or volume of MoM components from patients with a variety of local reactions. Two studies investigated corrosion at the head-neck and neck-body junctions in metal-on-polyethylene THA. There was a high level of variability and study heterogeneity, and so data pooling (meta-analysis) could not be performed. Average reported metal concentrations were elevated above established normal values in patients with ALTR (cobalt concentrations ranged from 5 to 40 ppb, and chromium levels ranged from 5 to 54 ppb). Whereas several studies demonstrated that patients with ALTR had higher average linear wear of the bearing surfaces, this finding was not made in all studies that we identified in this systematic review. Because of this high degree of variability, no clear dose-response relationship between wear and ALTR could be established. Serum metal level analysis and implant retrieval analysis both contribute to the understanding of ALTR. Serum metal levels generally are elevated in the presence of ALTR but should not be used in isolation for clinical decision-making. Many but not all patients with ALTR, including those with pseudotumors, demonstrate high wear, but more data and more systematic descriptions of the histopathology are needed to define the amount of wear that induces adverse reactions.

The lubrication of the cartilaginous structures in human joints is provided by a fluid from a specialized layer of cells at the surface of a delicate tissue called the synovial lining. Little is known about the characteristics of the fluids produced after a joint arthroplasty procedure. A literature review was carried out to identify papers that characterized the synovial lining and the synovial fluids formed after total hip or knee arthroplasty. Five papers about synovial lining histology and six papers about the lubricating properties of the fluids were identified. The cells making up the re-formed synovial lining, as well as the lining of interface membranes, were similar to the typical Type A and B synoviocytes of normal joints. The synovial fluids around joint replacement devices were typically lower in viscosity than pre-arthroplasty fluids but the protein concentration and phospholipid concentrations tended to be comparable, suggesting that the lining tissue function was preserved after arthroplasty. The widespread, long-term success of joint arthroplasty suggests that the lubricant formed from implanted joint synovium is adequate for good clinical performance in the majority of joints. The role the fluid plays in component wear or failure is a topic for future study.

Hip resurfacing arthroplasty (HRA) has a long clinical history and has utilized a variety of bearing material combinations with mixed clinical success. This paper reviews the local and systemic consequences of metal-on-metal hip resurfacing implants. Local tissue reactions cover a spectrum from no clinically adverse effects to adverse complications leading to revision associated with pain, osteolysis, or pseudotumor formation. Factors affecting the local tissue response to any implant include surgical, implant and patient factors. Metal particle size, shape and volume are important to the response around metal-on-metal implants. Surgical placement, particularly of the acetabular component, is important to the generation of wear debris. The number of patients with a sensitivity to the cobalt or chromium constituents of metal-on-metal implants is thought to be low and the cause and effect between patient sensitivity and implant failure is considered to be uncertain. Systemic toxicity from chronic exposure to the ions from metal-on-metal implants is still extremely rare although studies into potential cardiac or neurologic effects have suggested that subtle changes may be present that warrant continued and larger follow-up studies of longer-term cohorts.

Numerous studies have examined the histology of metal‐on‐metal hip tissues for evidence of a dose response to metal wear but have often reported inconclusive or contradictory findings. The aim of the present study was to address these discrepancies using multiple histological scoring methods to characterize the tissue features of one large group of revised metal‐on‐metal total hips. Periprosthetic tissues from 165 metal‐on‐metal hip revisions were examined for features of aseptic lymphocytic vasculitis associated lesions (ALVAL) as rated using two scoring systems as well as rankings for macrophage and lymphocyte numbers, intracellular wear debris and necrosis. Correlations between histological features and clinical variables including gender and time to revision and implant variables including articular surface wear volume or visual taper corrosion scores were examined. Both ALVAL scores reflected the macrophage dominated histology with average scores of 5.9/10 and 1.5/3. There was a statistically significant correlation between the original ALVAL score and wear rate per year (correlation coefficient = 0.17, p = .05) and a moderate correlation between the number of macrophages and wear particles and wear volume. There was no statistically significant correlation between wear and any other feature including lymphocytic inflammation or necrosis. Strong correlations between combined cup and ball wear volume and histological characteristics were not observed, although the number of macrophages was more closely correlated with wear than lymphocytes or necrosis.