2.1.1 History of metal-on-metal hip replacement
The first attempts to treat osteoarthritis with a prosthesis by the French surgeon Pierre Delbet date back to between 1910 and 1920. He performed hemiarthroplasty of the hip using a rubber femoral head to replace the osteoarthritic caput of the femoral bone. During the following three decades, a variety of materials, such as ivory and acryl, were used as a hemiarthroplasty with varying degrees of success. The first total hip arthroplasty (THA), and simultaneously the first metal-on-metal (MoM) hip arthroplasty, was described by Philip Wiles in 1938. He used components made of stainless steel but, unfortunately, with poor results. The first widely used prostheses were developed by Thompson in 1950 and by Böhlman and Moore in 1952. The first person to develop a successful MoM THA was George McKee in the 1950s. Another successful MoM THA was developed by Peter Ring in the 1960s. The MoM hip replacements of this era form the first generation of MoM THA. (Gomez and Morcuende 2005). The use of these MoM implants had ceased by 1970s after John Charnley developed the steel-on-polyethylene THA, which performed better. In the 1980s, interest in MoM arthroplasty grew again when second generation MoM THAs were introduced by Maurice Muller, Bernard Weber and the Sulzer brothers.
(Amstutz and Grigoris 1996)
At the same time, first generation MoM hip resurfacings were being developed by Derek McMinn in England and Heinz Wagner in Germany. MoM hip resurfacings were developed based on the hypothesis that the failure of previous hip resurfacing attempts using metal-on-polyethylene (MoP) bearings was due to excessive friction. This led to a myriad of polyethylene wear particles being generated and resulted in osteolysis. The MoP THA had proved to be well-suited for older people, but in young and active people the excessive wear of the
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polyethylene was a problem. The proposed benefits of hip resurfacings included preservation of femoral bone, normal joint biomechanics and stability of the joint due to the ability to use large heads. (Amstutz and Grigoris 1996). Early clinical reports of the McMinn resurfacing devices were encouraging (McMinn, Treacy, Lin 1996) and led to the development of the Birmingham hip resurfacing (BHR) (second generation resurfacing) by McMinn (McMinn 2003). Early clinical reports of BHR resurfacings also showed excellent results (Daniel et al. 2004, Back et al.
2005). These MoM resurfacings were targeted at young and active people due to their wear resistance and preservation of bone (Amstutz and Le Duff 2006). As MoM hip resurfacings provided promising results, interest in MoM bearings in THA also grew (third generation) and MoM bearings quickly gained popularity. In 2009, MoM bearings were used in approximately 35% of all THA surgeries performed in the United States (Bozic et al. 2009). In 2012, it was estimated that more than one million patients had received a MoM hip replacement (Lombardi Jr et al. 2012). However, the rapidly increasing use of MoM bearings, especially the Articular Surface Replacement (ASR) (by DePuy Orthopaedics) hip resurfacing and the ASR XL (by DePuy Orthopaedics) THA, was not supported by sufficient evidence from clinical trials (Reito et al. 2017).
Despite the promising early results of MoM bearings, concerns began to be raised some years later when the first reports describing adverse soft tissue reactions around MoM bearings were published (Boardman et al. 2006, Gruber et al. 2007, Pandit et al. 2008a, Toms et al. 2008). Histopathological studies revealed that the majority of the periarticular tissues obtained from patients with failed MoM hip replacements consisted of lymphocyte and macrophage infiltrates and varying amounts of necrosis (Davies et al. 2005, Willert et al. 2005, Pandit et al.
2008b, Mahendra et al. 2009, Campbell et al. 2010). In 2007, the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) stated that the ASR (by DePuy Orthopaedics) and Durom (by Zimmer, Warsaw, IN, USA) hip resurfacings had unexpectedly high revision rates (AOANJRR 2007).
The real extent of problem came to light in 2010 when the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK published a medical device alert regarding adverse soft tissue reactions in patients with MoM hips (MHRA 2010). Four months later, in August 2010, DePuy voluntarily recalled the ASR XL and ASR hip resurfacings from the market (DePuy Orthopaedics 2010). It was later shown from internal documents that the marketing and research conducted by DePuy were gravely fraudulent and that the company was aware of the severe problems long before the public and the authorities (Steffen et al. 2018).
Numerous other MoM systems have since been recalled as well: Durom by Zimmer in 2008, R3 by Smith & Nephew in 2012, Rejuvenate and ABG II by Stryker in 2012, and Modular SMF and Modular Readapt Femoral System by Smith
& Nephew in 2016 (FDA 2008, 2012b, 2012a, 2016a, 2016b, Smith & Nephew Orthopaedics 2012). As a result of the recalls and high revision rates, the use of MoM bearings in both THA and hip resurfacing surgeries has almost completely ceased (AOANJRR 2017, NJR 2017).
2.1.2 Reasons for revision surgery in MoM hips
MoM hip replacements have both traditional modes of implant failure as seen with conventional THA but also failure modes that are more specific to MoM bearings.
Traditional failure modes include dislocation, aseptic component loosening, infection, periprosthetic fracture and osteolysis (Carrothers et al. 2010, Reito et al.
2014, Matharu et al. 2016, Seppänen et al. 2016, NJR 2017). However, failures related to metal wear debris resulting from wear of the implant have been of the most concern. Adverse Reaction to Metal Debris (ARMD) is among the most frequent causes of failure in MoM hip replacements. ARMD is an umbrella term and refers to the harmful tissue responses caused by metal wear debris, such as pseudotumors, inflammatory responses, necrosis and metallosis (Langton et al.
2010). In data from the National Joint Registry of England and Wales (NJR), ARMD is the most frequent cause of failure in MoM THA and the second most frequent cause in MoM resurfacings (NJR 2017). In the majority of studies reporting the outcomes of patient cohorts from single centers, ARMD has been the most frequent cause of failure in both THA and hip resurfacings (Ollivere et al.
2009, Langton et al. 2010, 2011b, Reito et al. 2013, Lainiala et al. 2014, Reito et al.
2015a, Matharu et al. 2016, Sidaginamale et al. 2016, Matharu et al. 2017, Lainiala et al. 2019). Moreover, it has been suggested that data from registries underestimate the prevalence of ARMD due to reasons such as the underreporting of MoM failures and the delayed introduction of ARMD as a revision indication (Matharu 2017).
On very rare occasions, the accumulation of cobalt and chromium ions in the bloodstream may lead to systemic consequences. For example, neurotoxicity, cardiomyopathy and thyroid toxicity have all been reported (Bradberry et al. 2014).
In their systematic review, Bradberry et al. found 18 case reports of MoM patients with evidence of symptoms caused by the systemic dissemination of metal ions.
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Neurological symptoms included peripheral neuropathy, hearing loss and cognitive impairment. Complete or partial resolution of the symptoms were seen in most patients after removal of the metal-containing prostheses.