How Common Is Revision for Adverse Reaction to Metal Debris After Total Hip Replacement with a Metal-on-Polyethylene Bearing Surface?: Commentary on an article by Anders Persson, MD, et al.: "Revision for Symptomatic Pseudotumor Following Primary Total Hip Arthroplasty with a Standard Femoral Stem".

Abstract

Commentary Adverse reaction to metal debris (ARMD) has resulted in a high short-term rate of failure of metal-on-metal (MoM) total hip arthroplasties (THAs)1. ARMD has also been observed after non-MoM THAs. Matharu et al. reported on a retrospective observational study of data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. All 3,340 patients who underwent revision because of ARMD were included. The authors found that 95% of patients who underwent revision due to ARMD had an MoM THA, whereas 7.5% (249 patients) underwent revision of a THA with non-MoM bearing surfaces. The risk of revision due to ARMD was compared among different commonly implanted femoral head sizes and bearing surfaces. The relative risk of revision due to ARMD was 2.80 times (95% confidence interval [CI] = 1.74 to 4.36 times) higher for 36-mm metal-on-polyethylene (MoP) bearings compared with 28-mm and 32-mm MoP bearings (0.058% versus 0.021%; p < 0.001) and 2.35 times (95% CI = 1.76 to 3.11 times) higher for ceramic-on-ceramic bearings compared with hard-on-soft bearings (0.055% versus 0.024%; p < 0.001)1. Persson et al. evaluated 2,102 patients who underwent a total of 2,446 THAs, predominantly for osteoarthritis, from 1999 to 2016 in one center. In this observational cohort study, all patients underwent THA with the same uncemented Bi-Metric femoral stem and MoP (or, in a small number of cases, ceramic-on-polyethylene) articulation. The Bi-Metric femoral stem is a collarless, 3° tapered stem consisting of titanium alloy with its proximal 30% porous-coated (pore size, 100 to 200 μm) and plasma-sprayed with hydroxyapatite. The Morse-type taper consists of titanium alloy (Ti-6Al-4V) with a 4° taper angle, a distal diameter of 12.4 mm, and a contact length of 12.4 mm. The femoral heads were predominantly cobalt-chromium and 28 or 32 mm in diameter. The authors point out that the survival rate of these stems has been reported to be excellent in the literature2. The prevalence of revision for symptomatic ARMD was 0.5% (13 cases) after a mean follow-up of 7 years. The incidence rate was 0.9 case per 1,000 person-years. The strengths of this study include the evaluation of a large cohort of patients in which one well-performing cementless femoral stem was utilized. The data collection was carried out using the Swedish personal identity number and linked to the Swedish Hip Arthroplasty Register. This minimized the risk of the investigators missing additional revisions for ARMD that were carried out in other centers. It provides the incidence of revision for ARMD in one center, in a homogeneous population treated with a well-performing cementless stem with a 28-mm or 32-mm MoP articulation. The authors demonstrated that the rate of revision for symptomatic ARMD is low (0.5%) under these circumstances. They are to be congratulated for their contribution to the literature. The limitation of this study is the extent to which the data can be generalized to all THAs. The incidence of ARMD due to corrosion at the head-neck junction is multifactorial and includes implant factors, surgical factors, and patient factors. Implant factors that influence ARMD include head size, taper geometry, taper tolerances, taper surface finish, flexural rigidity of the neck, and material composition3. The findings in this study should not be applied to cohorts with different femoral head sizes or different tapers. Surgical factors that may impact the occurrence of ARMD include the surgical approach and its effect on the ability to maintain a dry, clean environment for the taper during impaction. In vitro studies have shown the cleanliness of the interface and the assembly forces to be correlated with the performance of the head-neck junction4. The findings presented by Persson et al. may not apply to centers using different surgical approaches or techniques for assembling the head-neck junction, particularly minimally invasive or anterior approaches. Finally, it is accepted that there is a large variation in an individual’s response to wear and corrosion debris generated from THAs. There is little correlation between the amount of wear and corrosion debris and the response to the debris in an individual patient. An individual patient may have substantial debris and exhibit little reaction to it while another may have a modest amount of debris but exhibit a substantial biologic response to it. This variation may be due to genetic polymorphisms, which can vary among different patient cohorts5. In conclusion, this study demonstrated a 0.5% prevalence of revision for ARMD at a mean of 7 years after MoP THAs performed in one center using 28-mm and 32-mm metal heads, a cementless femoral stem with a good long-term survival rate, and a single Morse taper. This finding should not be generalized to other patient cohorts using different femoral stems, femoral head sizes, or tapers implanted using different surgical techniques in different patient populations.