Robert K. Whittaker

The Reliability of a Scoring System for Corrosion and Fretting, and Its Relationship to Material Loss of Tapered, Modular Junctions of Retrieved Hip Implants

It has been suggested that corrosion and fretting at the tapered, modular junctions of hip arthroplasties may contribute to implant failure. In this study the reliability of a commonly used peer-reviewed scoring system for visual assessment of corrosion and fretting at these junctions was evaluated. Volumetric material loss at the tapered head surface was measured and associations with the visual scores were investigated. We found that the inter-observer reproducibility and single-observer repeatability of the corrosion scores were substantial using Cohens weighted Kappa statistic (k = 0.64-0.71). The reproducibility and repeatability of the fretting scores however were slight to fair (k = 0.18-0.31). Taper corrosion scores were significantly and moderately correlated with the volume of material loss measured (Spearmans r = 0.59; P < 0.001). We recommend the continued use of this scoring system but it should not be a substitute for measurement of material loss.

Validation of primary metal-on-metal hip arthroplasties on the National Joint Registry for England, Wales and Northern Ireland using data from the London Implant Retrieval Centre: A study using the NJR dataset

Arthroplasty registries are important for the surveillance of joint replacements and the evaluation of outcome. Independent validation of registry data ensures high quality. The ability for orthopaedic implant retrieval centres to validate registry data is not known. We analysed data from the National Joint Registry for England, Wales and Northern Ireland (NJR) for primary metal-on-metal hip arthroplasties performed between 2003 and 2013. Records were linked to the London Implant Retrieval Centre (RC) for validation. A total of 67 045 procedures on the NJR and 782 revised pairs of components from the RC were included. We were able to link 476 procedures (60.9%) recorded with the RC to the NJR successfully. However, 306 procedures (39.1%) could not be linked. The outcome recorded by the NJR (as either revised, unrevised or death) for a primary procedure was incorrect in 79 linked cases (16.6%). The rate of registry-retrieval linkage and correct assignment of outcome code improved over time. The rates of error for component reference numbers on the NJR were as follows: femoral head category number 14/229 (5.0%); femoral head batch number 13/232 (5.3%); acetabular component category number 2/293 (0.7%) and acetabular component batch number 24/347 (6.5%). Registry-retrieval linkage provided a novel means for the validation of data, particularly for component fields. This study suggests that NJR reports may underestimate rates of revision for many types of metal-on-metal hip replacement. This is topical given the increasing scope for NJR data. We recommend a system for continuous independent evaluation of the quality and validity of NJR data. Cite this article: Bone Joint J 2015;97-B:10–18.

Influence of stem type on material loss at the metal-on-metal pinnacle taper junction

The clinical importance of material loss at the head–stem junction is unknown. Comparison of retrievals with different stem types can provide the opportunity to understand the importance of the taper junction. This was a case–control study involving 20 retrieved 36 mm metal-on-metal Pinnacle (DePuy) hips that were paired with either a Corail (n = 10) or S-ROM (n = 10) stem. The median head taper material loss rate for the Corail group was 0.238 (0.0002–2.178) mm3/year and was significantly greater than the S-ROM group (p = 0.042), which had a median material loss rate of 0.132 (0.015–0.518) mm3/year. The only significant difference between the groups was the stem taper roughness and length: this was rougher and shorter for the Corails. Long and smooth stem taper designs are preferred when used in conjunction with metal heads.

Clinical relevance of corrosion patterns attributed to inflammatory cell-induced corrosion: A retrieval study

In vitro studies have shown that human osteoclasts can corrode stainless steel and titanium leading to the production of metal ions responsible for inflammatory reactions. Moreover, traces of cellular activities on metal orthopaedic explants have recently been reported as inflammatory cell-induced (ICI) corrosion being the result of the cells sealing on the metal surfaces and releasing reactive oxygen species (ROS) through Fenton-like reactions. The extent and clinical relevance of this phenomenon has yet to be understood. We analysed a cohort of 100 CoCr alloy hips collected at our retrieval centre; we performed macroscopic and microscopic screening and used statistical analysis to correlate our findings with implant and clinical variables. We found that 59% of our implants had evidence of surface damage consistent with what has previously been described as cell-induced corrosion. There was a significant association between the patterns and aseptic loosening for the ASR modular (r = -0.488, p = 0.016) and the Durom modular (r = 0.454, p = 0.026). This is the largest implant retrieval study to examine the phenomena of so-called ICI corrosion and is the first to investigate its clinical relevance. We recommend further work to determine the role of cells in the damage patterns observed.

The effect of using components from different manufacturers on the rate of wear and corrosion of the head–stem taper junction of metal-on-metal hip arthroplasties

AIMS Surgeons have commonly used modular femoral heads and stems from different manufacturers, although this is not recommended by orthopaedic companies due to the different manufacturing processes. We compared the rate of corrosion and rate of wear at the trunnion/head taper junction in two groups of retrieved hips; those with mixed manufacturers (MM) and those from the same manufacturer (SM). MATERIALS AND METHODS We identified 151 retrieved hips with large-diameter cobalt-chromium heads; 51 of two designs that had been paired with stems from different manufacturers (MM) and 100 of seven designs paired with stems from the same manufacturer (SM). We determined the severity of corrosion with the Goldberg corrosion score and the volume of material loss at the head/stem junction. We used multivariable statistical analysis to determine if there was a significant difference between the two groups. RESULTS We found no significant difference in the corrosion scores of the two groups. The median rate of material loss at the head/stem junction for the MM and SM groups were 0.39 mm(3)/year (0.00 to 4.73) and 0.46 mm(3)/year (0.00 to 6.71) respectively; this difference was not significant after controlling for confounding factors (p = 0.06). CONCLUSION The use of stems with heads of another manufacturer does not appear to affect the amount of metal lost from the surfaces between these two components at total hip arthroplasty. Other surgical, implant and patient factors should be considered when determining the mechanisms of failure of large diameter metal-on-metal hip arthroplasties. Cite this article: Bone Joint J 2016;98-B:917-24.

Corrosion of Metal Modular Cup Liners

Numerous studies have reported on corrosion at the modular head taper, however less is known about the interface between the metal shell and liner of modular cups. This study examined the backside of a series of metal modular cup liners of two designs (DePuy Pinnacle and Smith & Nephew R3), retrieved from 67 patients. Visual inspection found evidence of corrosion in virtually all liners, with the engaging rim surface significantly more corroded than the polar regions (P<0.001). EDX confirmed that black surface deposits were chromium rich corrosion debris, while SEM analysis revealed considerable pitting in the vicinity of the black debris. The R3 liners were significantly more corroded that the Pinnacles (P<0.001); this may help to explain the higher revision rates of this design.

Clinical significance of corrosion of cemented femoral stems in metal-on-metal hips: a retrieval study

PurposeThe clinical significance of corrosion of cemented femoral stems is unclear. The purpose of this retrieval study was to: (1) report on corrosion at the stem-cement interface and (2) correlate these findings with clinical data.MethodsWe analysed cemented stems (n = 36) composed of cobalt-chromium (CoCr) and stainless steel (SS) in a series of revised metal-on-metal hips. We performed detailed inspection of each stem to assess the severity of corrosion at the stem-cement interface using a scale of 1 (low) to 5 (severe). We assessed the severity of corrosion at each stem trunnion and measured wear rates at the head taper and bearing surfaces. We used non-parametric tests to determine the significance of differences between the CoCr and SS stems in relation to: (1) pre-revision whole blood Co and Cr metal ion levels, (2) trunnion corrosion, (3) bearing surface wear and (4) taper material loss.ResultsThe corrosion scores of CoCr stems were significantly greater than SS stems (p < 0.01). Virtually all stem trunnions in both alloy groups had minimal evidence of corrosion. The median pre-revision Co levels of implants with CoCr stems were significantly greater than the SS stems (p < 0.01). There was no significant difference in relation to pre-revision Cr levels (p = 0.521). There was no significant difference between the two stem types in relation to bearing wear (p = 0.926) or taper wear (p = 0.148).ConclusionsSevere corrosion of cemented femoral stems is a common finding at our retrieval centre; surgeons should consider corrosion of CoCr stems as a potential source of metal ions when revising a hip.

Detailed inspection of metal implants.

Detailed visual inspection of metal hips is the first step in retrieval analysis. In this study a systematic visual inspection protocol was developed to quantify bearing surface changes and their associations with material loss was investigated. Simple and multiple linear regression models found that moderate surface scratching, discolouration, haziness and the size of visible wear scars were all significantly associated with material loss (R2 = 5%-73%, p<0.05). Visual inspection is not a substitute for measurement of material loss but an understanding of bearing surface changes may offer unique clues as to the mechanisms of failure of retrieved hips.

Variation in taper surface roughness for a single design effects the wear rate in total hip arthroplasty

Material loss from the head‐stem taper junction of total hip arthroplasty (THA) is implicated in adverse reactions to metal debris (ARMD); the mechanisms for this are multi‐factorial. We investigated the relationship between the roughness of the “as manufactured” taper surface and the wear rate from this junction. Fifty retrieved Pinnacle metal‐on‐metal (MOM) bearings paired with a Corail stem were included in the study. Multivariable statistical analysis was performed to determine the influence of taper roughness on material loss rate after controlling for other confounding surgical, implant, and patient factors. The surface roughness of the “as manufactured” head taper surface was associated with the rate of material loss from this surface. Four of eighteen roughness variables taken from ISO 4,287 and ISO 13,565‐2 were significant: The Reduced Peak Height (Rpk, the protruding peaks above the core) (p = 0.004), Material Ratio 1 (Mr1, the ratio of the protruding peaks above the core) (p = 0.002), Area of the Peak Region (A1, the area of the Abbott‐Curve that contains the peaks from the profile) (p = 0.003) and the Skewness (Rsk, the asymmetry of the height distribution corresponding to the height or depth of surface features) (p = 0.03). We found a large variability in the measured values with a median (range) of 0.50 (0.05–2.98), 11.98 (0.46–39.98), 30.89 (0.15–581.00), and 0.04 (−0.73–0.84), respectively. A 1‐unit increase in Rpk was associated with a 73% increase in the taper wear rate. The variability of “as manufactured” surface roughness has a significant effect on taper material loss.

Fretting and Corrosion Between a Metal Shell and Metal Liner May Explain the High Rate of Failure of R3 Modular Metal-on-Metal Hips

BACKGROUND The R3 acetabular system used with its metal liner has higher revision rates when compared to its ceramic and polyethylene liner. In June 2012, the medical and healthcare products regulatory agency issued an alert regarding the metal liner of the R3 acetabular system. METHODS Six retrieved R3 acetabular systems with metal liners underwent detailed visual analysis using macroscopic and microscopic techniques. RESULTS Visual analysis discovered corrosion on the backside of the metal liners. There was a distinct border to the areas of corrosion that conformed to antirotation tab insertions on the inner surface of the acetabular shell, which are for the polyethylene liner. Scanning electron microscopy indicated evidence of crevice corrosion, and energy-dispersive X-ray analysis confirmed corrosion debris rich in titanium. CONCLUSION The high failure rate of the metal liner option of the R3 acetabular system may be attributed to corrosion on the backside of the liner which appear to result from geometry and design characteristics of the acetabular shell.