Can metal-on-metal bearings improve the longevity of total hip prostheses?

PURPOSE OF THE STUDY: In total hip arthroplasty (THA), inter-series comparative clinical results cannot be considered worthy before at least 10 years of average follow-up, as shown in the Swedish Arthroplasty Register experience (1978-1993). Last generation metal-on-metal bearings were introduced in France only nine years ago (1995). To date, using mid term information, data from the literature, and our experience, one could assume that this bearing material has the capacity to improve THA longevity. Three types of information were analyzed: 1) comparative radiographic and EBRA studies published on early migration (<2 years) of acetabular implants; 2) preliminary comparative data on wear and osteolysis at the 8-year maximum follow-up; 3) clinical data on dislocation frequency and in vitro and in vivo observations of bearing separation and sliding. Study no 1: primary stability of these metal-on-metal acetabular cups was better than for polyethylene (PE) cups or alumina liners; study no 2: no detectable wear and less osteolysis were observed to date with metal-on-metal bearings versus their alumina-on-PE counterparts. Study no 3: less dislocation and less head sliding were measured with the metal-on-metal versus alumina-on-PR bearings possibly due to the interfacial forces provided by lubricating fluid (suction fit). CONCLUSION: According to current knowledge, this metal-on-metal bearing still represent, with alumina-on-alumina and highly crosslinked PE, a competitive and comprehensive option to improve THA longevity. The real pending problem concerns the frequency and above all the intensity of metal delayed hypersensitivity reaction and their potential effect on implant loosening.     

Changes in blood ion levels after removal of metal-on-metal hip replacements: 16 patients followed for 0–12 months

Background and purpose

In patients with metal-on-metal (MoM) hip prostheses, pain and joint effusions may be associated with elevated blood levels of cobalt and chromium ions. Since little is known about the kinetics of metal ion clearance from the body and the rate of resolution of elevated blood ion levels, we examined the time course of cobalt and chromium ion levels after revision of MoM hip replacements.

Patients and methods

We included 16 patients (13 female) who underwent revision of a painful MoM hip (large diameter, modern bearing) without fracture or infection, and who had a minimum of 4 blood metal ion measurements over an average period of 6.1 (0–12) months after revision.

Results

Average blood ion concentrations at the time of revision were 22 ppb for chromium and 43 ppb for cobalt. The change in ion levels after revision surgery varied extensively between patients. In many cases, over the second and third months after revision surgery ion levels decreased to 50% of the values measured at revision. Decay of chromium levels occurred more slowly than decay of cobalt levels, with a 9% lag in return to normal levels. The rate of decay of both metals followed second-order (exponential) kinetics more closely than first-order (linear) kinetics.

Interpretation

The elimination of cobalt and chromium from the blood of patients who have undergone revision of painful MoM hip arthroplasties follows an exponential decay curve with a half-life of approximately 50 days. Elevated blood levels of cobalt and chromium ions can persist for at least 1 year after revision, especially in patients with high levels of exposure.After a dramatic rise in initial popularity, the use of metal-on-metal (MoM) hip arthroplasties has declined precipitously, both in hip resurfacings and conventional hip replacement, due to an alarming incidence of adverse inflammatory reactions (van der Weegen et al. 2011, NJR 2012).There are now serious concerns about potential adverse biological effects, both local and systemic, arising from wear debris generated by MoM articulations (Matthies et al. 2011). The nano-scale particles generated through wear of MoM bearings can enter the reticulo-endothelial system and cross over into the circulation as early as 5 days after implantation (Daniel et al. 2007). The specific surface area (surface area to mass ratio) of these particles makes them susceptible to corrosion in vivo (Hart et al. 2010), leading to elevated levels of cobalt and chromium ions in the blood, usually ranging from 5 to 10 times normal values (Jacobs et al. 1996, Brodner et al. 1997, Skipor et al. 2002, Dunstan et al. 2005, Daniel et al. 2009, Hart et al. 2009, van der Weegen et al. 2011). Possible complications from long-term elevated metal ion levels include immune reactions (Pandit et al. 2008), necrosis (Campbell et al. 2010), toxicity (Keegan et al. 2007, Tower et al. 2010, Corradi et al. 2011), chromosomal aberrations (Ladon et al. 2004), and carcinogenicity (Case et al. 1994). However, the most common short-term complication is joint pain associated with inflammatory reactions (Milosev et al. 2005). In many cases where there is pain with soft-tissue masses, often in association with elevated levels of cobalt and chromium ions, removal of the implanted components is necessary. This form of failure is more common in female patients than in male patients, and it has been reported in 1–20% of cases at 5 years (Schmidt et al. 1996) depending on the design of the prosthesis.Although revision is performed in the hope that the elevation of ion levels and symptoms will resolve, little is known about the kinetics of storage and turnover of these ions in the body. We examined the kinetics of cobalt and chromium ion decay after revision of MoM hip replacements. Our principal goals were to characterize the decay curves of cobalt and chromium ions after revision procedures and to determine when blood concentrations return to levels below the MHRA action level of 7 ppb, in order to determine exposure risk (MHRA 2010). We hypothesized that: (1) removal of MoM components results in a rapid drop in the level of metal ions in the blood followed by a slow steady-state decline; (2) chromium concentrations will decrease more slowly than cobalt concentrations; (3) the total body exposure to ions is orders of magnitude higher with poorly functioning or loose implants than with well-functioning components.     

Does hip implant positioning affect the peak external adduction moments of the healthy knees of subjects with total hip replacements?

After unilateral total hip replacement (THR) for hip osteoarthritis (OA), knee OA incidence or progression is common. The contralateral knee is at particular risk, and some have speculated that abnormal THR‐hip biomechanics contributes to this asymmetry. We investigated the relationships between operated‐hip joint geometry or gait variables and the peak external knee adduction moments—an indicator of knee OA risk—in 21 subjects with unilateral THRs. We found that the peak adduction moment was 14% higher on the contralateral versus the ipsilateral knee (p = 0.131). The best predictors of ipsilateral knee adduction moments were superior‐inferior joint center position and operated‐hip peak adduction moment (adj R² = 0.291, p = 0.017). The sole predictor of the contralateral knee adduction moment was the medial‐lateral hip center position (adj R² = 0.266, p = 0.010). A postoperative medial shift of the hip center was significantly correlated with a lower postoperative contralateral/ipsilateral knee adduction moment ratio (R = 0.462, p = 0.035). Based on these relationships, we concluded that implant positioning could influence the biomechanical risk of knee OA progression after THR. Although implant positioning decisions are necessarily driven by other factors, it may be appropriate to assess individual THR candidate's knee OA risk and adjust perioperative management accordingly. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1187–1194, 2013     

The absence of a metal-on-metal bearing does not preclude the formation of a destructive pseudotumor in the hip—a case report

4 patients with a mean age of 20 years and isolated congenital radial head dislocation (1 unilateral anterior, 1 unilateral posterior and 2 bilateral anterior dislocations) were all pain-free and had almost normal elbow function.     

Does bone quality predict loosening of cemented total hip replacements?

We matched 78 patients with a loose cemented Charnley Elite Plus total hip replacement (THR) by age, gender, race, prosthesis and time from surgery with 49 patients with a well-fixed stable hip replacement, to determine if poor bone quality predisposes to loosening. Clinical, radiological, biomechanical and bone mineral density indicators of bone quality were assessed. Patients with loose replacements had more pain, were more likely to have presented with atrophic arthritis and to have a history of fragility fracture, narrower femoral cortices and lower peri-prosthetic or lumbar spine bone mineral density (all t-test, p < 0.01). They also tended to be smokers (chi-squared test, p = 0.08). Vitamin-D deficiency was common, but not significantly different between the two groups (t-test, p = 0.31) In this series of cemented hip replacements performed between 1994 and 1998, aseptic loosening was associated with poor bone quality. Patients with a THR should be screened for osteoporosis and have regular radiological surveillance.     

Pseudotumor formation following large-diameter metal-on-metal total hip arthroplasty—Report of two cases and literature review

Pseudotumor after metal-on-metal total hip arthroplasty is an increasingly frequent complication in Taiwan. Orthopedic surgeons should be aware of this complication and follow up their patients regularly so that the disease can be detected early and properly managed. We report two cases of this complication. Case 1 exhibited cystic change with fluid accumulation, and in Case 2 a semisolid mass was found. In Case 1, a high inclination angle of the cup (at 65°) was noted. In Case 2, the cup was placed at a normal inclination angle, but it was too anteverted (31°). The histopathological studies revealed that the cystic pseudotumor had more diffuse lymphocyte infiltration and perivascular lymphocyte cuffing with eosinophil and plasma cells. The semisolid mass of Case 2 had less lymphocyte infiltration. Both cases had metal debris with foreign body granuloma. In patients with residual groin pain and a palpable mass after surgery, the possibility of pseudotumor formation should be considered. Various imaging techniques, such as ultrasound, computed tomography scan, and magnetic resonance imaging, can be used to confirm the presence of such lesions. Revision with nonmetal-on-metal articulation is suggested to relieve the symptoms.     

Results of metal-on-metal hip resurfacing in patients 40 years old and younger

The prevalence of total hip arthroplasty in young patients is small but increasing. We analyzed the results of metal-on-metal hip resurfacing (MMHR) in patients aged 40 years or less. In total 74 operations were performed on 64 patients. Mean age at operation was 33.2 years. HHS averaged 92.3 points at latest follow-up, mean UCLA activity was 8.2. Patients with comorbidity evinced lower scores in HHS, in UCLA activity and in quality of life than patients without comorbidities. Eight revisions (10.8 %) were performed, of which seven due to adverse reaction to metal debris. Seven-year survival was 90.5 %. The functional outcome of hip resurfacing in this cohort was excellent, but overall survival was unsatisfactory. Further analysis is required to verify the role of hip resurfacing among young and active patients.     

Femoral head diameter affects the revision rate in total hip arthroplasty: An analysis of 1,720 hip replacements with 9–21 years of follow-up

Background?In a previous study concerning 1,660 ScanHip THAs that were followed for up to 12 years, the cumulative revision rate was not found to be dependent on whether a 22-mm or a 32-mm head size had been used. We have re-examined these patients to see whether a longer follow-up time (9–21 years) would disclose an effect of head size on the revision rate.

Patients and methods?We analyzed the cumulative revision rate for 1,720 Scan Hip arthroplasties with either 22-mm or 32-mm femoral heads. The patients were followed for 9–21 years.

Results?Arthroplasties with 32-mm head had 2.8-times higher cumulative revision rate than those with a 22-mm head. Older age reduced the risk of revision while male sex increased the risk.

Interpretation?We found that head size affects revision risk, but that even in a reasonably large material a long follow-up time is required to disclose the effects of head size—and thus wear—on survival.     

What is appropriate surveillance for metal-on-metal hip arthroplasty patients?

The unexpected high revision rates of large-diameter (femoral head sizes of 36?mm or greater) metal-on-metal hip arthroplasties (MoMHAs) have led to worldwide regulatory authorities recommending regular surveillance, even for asymptomatic individuals. However, these recommendations are not evidence-based and are very costly. The rapidly evolving evidence base requires an update regarding the investigation and management of MoMHA patients. This article is the first of 2 (the second article in this series will consider the threshold for performing revision, and the outcomes following ARMD revision surgery: Matharu et al., Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris: A clinical update. Acta Orthop 2018; in press), and considers the various investigative modalities used during surveillance, with specific focus on blood metal ion sampling and cross-sectional imaging. No single investigation can universally be used during MoMHA patient surveillance. Recent studies have now provided important information on interpreting blood metal ions (effective in identifying patients at low risk of problems), clarifying the roles of cross-sectional imaging (reserve combined ultrasound and MARS-MRI for complex cases), and providing parameters to safely exclude many asymptomatic patients from regular surveillance. This information will be useful when designing future surveillance protocols for MoMHA patients     

What is the evidence for viscosupplementation in the treatment of patients with hip osteoarthritis? Systematic review of the literature

Introduction

Osteoarthritis (OA) is a disease of the synovial joints and is the most common cause of chronic pain in the elderly. One of the treatment modalities for OA of the hip is viscosupplementation (VS). Today there are several different formulations of viscosupplements produced by different manufactures of different molecular weights. The objective of this review is to asses the efficacy of VS treatment of hip OA osteoarthritis in the current literature.

Material and methods

The following databases were searched: Medline (period 1966 to November 2006), Cochrane Database of Systematic Reviews (1988 to November 2006), Cochrane Clinical Trial Register (1988 to November 2006), Database of Abstracts on Reviews and Effectiveness, Current Controlled Trials, National Research Register and Embase (January 1988 to November 2006). The search terms [osteoarthritis, hip (joint), viscosupplementation, hyaluronic acid, hyaluronan, sodium hyaluronate and trade names] were applied to identify all studies relating to the use of VS therapy for OA of the hip joint.

Results

Sixteen articles concerning the efficacy of a total of 509 patients undergoing VS treatment for hip OA were included. Twelve European studies, three Turkish studies and one American study with Levels of Evidence ranging from I to IV evaluated the following products: Hylan G-F 20, Hyalgan^®, Ostenil^®, Durolane^®, Fermatron^® and Orthovisc^®. Heterogeneity of included studies did not allow pooled analysis of data.

Discussion

Despite the relatively low Level of Evidence of the included studies, VS performed under fluoroscopic or ultrasound guidance seems an effective treatment and may be an alternative treatment of hip OA. Intra-articular injection of (derivatives of) HA into the hip joint appears to be safe and well tolerated. However, VS cannot be recommended as standard therapy in hip OA for wider populations, and therefore the indications remain a highly individualised matter.

     

Survivorship of Conserve® Plus monoblock metal-on-metal hip resurfacing sockets: radiographic midterm results of 580 patients

Resurfacing systems use press-fit, monoblock, cobalt chrome alloy acetabular sockets because of the material's ability to withstand stresses while accommodating a large femoral head. Despite the widespread use of these types of sockets for both hip resurfacing and total hip replacement, there is a paucity of literature assessing the outcomes of these cups in particular. The 10 year survivorship of the Conserve? Plus monoblock acetabular component used in this study was 98.3% with small pelvic osteolytic lesions suspected in only 2.3%. This study highlights the excellent radiographic survivorship profile of the Conserve? Plus socket.     

In vivo wear of bilateral total hip replacements: conventional versus crosslinked polyethylene

Crosslinked polyethylene (PE) was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results but there is as yet limited clinical data. We identified three patients with bilateral total hip replacements who received a crosslinked PE liner (Marathon^TM, DePuy, Warsaw, IN, USA) on one side and a conventional PE insert (Enduron^TM, DePuy) on the contralateral side. As an assessment of in vivo PE wear, linear head penetration was measured on standardized radiographs using a validated computer-assisted technique. In all the three cases, a marked reduction of more than 70% in volumetric wear was found in association with Marathon crosslinked PE. These case reports support the efficacy of this type of crosslinked PE in a selected group that allows direct comparison of the two different materials without the influence of patient-related factors such as activity, gender, weight, or others.     

Management of metal-on-metal hip implant patients: Who,when and how to revise?

The debate on how best to manage patients with metal-on-metal(MOM) hip implants continues. With over 1 million patients affected worldwide, the impact is far reaching. The majority of the aggressive failures of MOM hip implants have been dealt with by revision hip surgery, leaving patients with a much more indolent pattern of failure of devices that have been in situ for more than 10 years. The longer-term outcome for such patients remains unknown, and much debate exists on how best to manage these patients. Regulatory guidance is available but remains open to interpretation due to the lack of current evidence and long-term studies. Metal ion thresholds for concern have been suggested at 7 ppb for hip resurfacing arthroplasty and below this level for large diameter total hip arthroplasties. Soft tissue changes including pseudotumours and muscle atrophy have been shown to progress, but this is not consistent. New advanced imaging techniques are helping to diagnose complications with metal hips and the reasons for failure, however these are not widely available. This has led to some centres to tackle difficult cases through multidisciplinary collaboration, for both surgical management decisions and also follow-up decisions. We summarise current evidence and consider who is at risk, when revision should be undertaken and how patients should be managed.     

Cross-sectional imaging of metal-on-metal hip arthroplasties: Can we substitute MARS MRI with CT?

Background and purpose —

Metal artifact reduction sequence (MARS) MRI is widely advocated for surveillance of metal-on-metal hip arthroplasties (MOM-HAs). However, its use is limited by susceptibility artifact at the prosthesis-bone interface, local availability, patient compliance, and cost (Hayter et al. 2011a). We wanted to determine whether CT is a suitable substitute for MARS MRI in evaluation of the painful MOM-HA.

Patients and methods —

50 MOM-HA patients (30 female) with unexplained painful prostheses underwent MARS MRI and CT imaging. 2 observers who were blind regarding the clinical data objectively reported the following outcomes: soft tissue lesions (pseudotumors), muscle atrophy, and acetabular and femoral osteolysis. Diagnostic test characteristics were calculated.

Results —

Pseudotumor was diagnosed in 25 of 50 hips by MARS MRI and in 11 of 50 by CT. Pseudotumors were classified as type 1 (n = 2), type 2A (n = 17), type 2B (n = 4), and type 3 (n = 2) by MARS MRI. CT did not permit pseudotumor classification. The sensitivity of CT for diagnosis of pseudotumor was 44% (95% CI: 25–65). CT had “slight” agreement with MARS MRI for quantification of muscle atrophy (κ = 0.23, CI: 0.16–0.29; p < 0.01). Osteolysis was identified in 15 of 50 patients by CT. 4 of these lesions were identified by MARS MRI.

Interpretation —

CT was found to be superior to MRI for detection of osteolysis adjacent to MOM-HA, and should be incorporated into diagnostic algorithms. CT was unable to classify and failed to detect many pseudotumors, and it was unreliable for assessment of muscle atrophy. Where MARS MRI is contraindicated or unavailable, CT would be an unsuitable substitute and other modalities such as ultrasound should be consideredIt is estimated that over 500,000 metal-on-metal (MOM) hip arthroplasties, including both hip resurfacing and total hip replacements (THRs), have been carried out worldwide in the last 15 years (Skinner et al. 2010). There are increasing reports of progressive soft tissue changes in response to metal debris including: solid or cystic, non-malignant masses around the prostheses (termed pseudotumors) (Pandit et al. 2008), perivascular lymphocytic infiltration (Davies et al. 2005), musculotendinous pathology (in particular, wasting of the hip abductors) (Sabah et al. 2011), and periprosthetic osteolysis (Park et al. 2005, Milosev et al. 2006, Korovessis et al. 2006).There is international agreement that the high failure rate of MOM hip arthroplasties (MOM-HAs) has created the need for surveillance of these devices with cross-sectional imaging (MHRA. 2012). Both pseudotumors and muscle atrophy have been associated with high rates of major complications and poorer outcomes after revision surgery (Grammatopolous et al. 2009). To this end, sensitive detection of periprosthetic changes is vital in order to provide the best outcome for MOM-HA patients with early detection and revision.Cross-sectional imaging has been shown to be useful for providing a diagnosis in cases of unexplained pain and in planning of revision surgery (Hayter et al. 2011b). A recent European multidisciplinary consensus statement recommended the use of cross-sectional imaging using any of US, MARS MRI, or CT (Hannemann et al. 2013). The gold standard modality is not clear, which has resulted in a variety of diagnostic algorithms being used in different referral centers.Both CT and MARS MRI similarly offer multi-planar and complete cross-sectional images from which the extent of disease and relationship of the abnormality to normal anatomy can readily be appreciated. MARS MRI has been reliably and extensively used to investigate MOM hip complications (Sabah et al. 2011, Hayter et al. 2012a, Thomas et al. 2013, Nawabi et al. 2013) and has been shown to permit early diagnosis of pseudotumor and other soft tissue pathologies (Toms et al. 2008) associated with pain, loss of function, and higher revision rates. However, the use of MARS MRI is limited by susceptibility artifact at the prosthesis-bone interface, local availability, patient compliance, and cost.CT is more widely available than MARS MRI (Anderson et al. 2011) and has been used routinely at some centers for the screening of periarticular masses (Bosker et al. 2012). It has been proposed as an alternative to it, for example in cases of claustrophobia, pacemaker, and where there are loose metal implants. CT has been shown to be useful in cases of suspected impingement, acetabular osteolysis (Cahir et al. 2007, Roth et al. 2012), and in identification of prostheses at risk of elevated wear (Hart et al. 2009). The notable success in detecting common complications of hip arthroplasty coupled with widespread accessibility has meant that some centers rely entirely on CT (McMinn. 2012) to follow up patients with suspected MOM-associated bony and soft tissue changes, but to date there have been no published studies comparing CT with MRI.We investigated whether CT is a suitable substitute for MARS MRI in the evaluation of the painful MOM-HA. We wanted to provide measures of diagnostic accuracy of CT compared to the current gold standard (MARS MRI) for the detection of common periprosthetic complications. The primary outcome measure focused on the detection of pseudotumors, owing to their high prevalence and strong association with adverse outcomes (Hart et al. 2009), with secondary outcome measures for the detection of muscle atrophy and osteolysis.     

No clinical difference between large metal-on-metal total hip arthroplasty and 28-mm-head total hip arthroplasty?

Purpose  

We aimed to test the claim of greater range of motion (ROM) with large femoral head metal-on-metal total hip arthroplasty.     

Treatment of transient bone marrow oedema of the hip—a comparative study

Between 1990 and 2000, we treated 43 patients with transient bone marrow oedema of the hip. Five were treated with nonsteroidal antiinflammatory drugs (NSAIDs) and limited weight bearing, and 38 by core decompression followed by limited weight bearing. At follow-up 2-10 years later, all patients were assessed by a structured interview as well as the Harris hip score (HHS) and the Western Ontario and MacMaster Universities Osteoarthritis Index (WOMAC). Both groups reached the same clinical outcome (HHS and WOMAC). Core decompression enabled a significantly faster recovery. There were no complications, but progression to avascular necrosis was seen in both groups. Core decompression induced fast pain relief, making it the preferable treatment.     

Cancer incidence and cause-specific mortality in patients with metal-on-metal hip replacements in Finland: A population-based study with a mean follow-up of 4.6 (1–11) years

Background and purpose

Metal-on-metal hip implants have been widely used, especially in the USA, Australia, England and Wales, and Finland. We assessed risk of death and updated data on the risk of cancer related to metal-on-metal hip replacements.

Patients and methods

A cohort of 10,728 metal-on-metal hip replacement patients and a reference cohort of 18,235 conventional total hip replacement patients were extracted from the Finnish Arthroplasty Register for the years 2001–2010. Data on incident cancer cases and causes of death until 2011 were obtained from the Finnish Cancer Registry and Statistics Finland. The relative risk of cancer and death were expressed as standardized incidence ratio (SIR) and standardized mortality ratio (SMR). SIR/SIR ratios and SMR/SMR ratios, and Poisson regression were used to compare the cancer risk and the risk of death between cohorts.

Results

The overall risk of cancer in the metal-on-metal cohort was not higher than that in the non-metal-on-metal cohort (RR = 0.91, 95% CI: 0.82–1.02). The risk of soft-tissue sarcoma and basalioma in the metal-on-metal cohort was higher than in the non-metal-on-metal cohort (SIR/SIR ratio = 2.6, CI: 1.02–6.4 for soft-tissue sarcoma; SIR/SIR ratio = 1.3, CI: 1.1–1.5 for basalioma). The overall risk of death in the metal-on-metal cohort was less than that in the non-metal-on-metal cohort (RR = 0.78, CI: 0.69–0.88).

Interpretation

The overall risk of cancer or risk of death because of cancer is not increased after metal-on-metal hip replacement. The well-patient effect and selection bias contribute substantially to the findings concerning mortality. Arthrocobaltism does not increase mortality in patients with metal-on-metal hip implants in the short term. However, metal-on-metal hip implants should not be considered safe until data with longer follow-up time are available.Metal-on-metal hip implants have been widely used, especially in the USA, Australia, England and Wales, and Finland (AOANJRR 2010, NJR 2011, Cohen 2012, Seppänen et al. 2012). The theoretical health risks related to chronically elevated blood metal ion concentrations induced by abnormal wear and corrosion of the metal-on-metal implants—apart from local symptoms around the failing implant—include systemic symptoms of poisoning (Steens et al. 2006, Oldenburg et al. 2009, Rizzetti et al. 2009, Tower 2010, 2012, Mao et al. 2011, Sotos and Tower 2013, Zyviel et al. 2013) and carcinogenesis (Mäkelä et al. 2012, Smith et al. 2012, Brewster et al. 2013). Systemic metal ion toxicity cases due to a failed hip replacement are rare. However, there have been several recent reports of systemic cobalt toxicity following revision of fractured ceramic components, and also in patients with a failed metal-on-metal hip replacement (Steens et al. 2006, Oldenburg et al. 2009, Rizzetti et al. 2009, Tower 2010, 2012, Mao et al. 2011, Sotos and Tower 2013, Zyviel et al. 2013). Possible clinical findings include fatigue, weakness, hypothyroidism, cardiomyopathy, polycythemia, visual and hearing impairment, cognitive dysfunction, and neuropathy. Fatal cardiomyopathy due to systemic cobalt toxicity after hip replacement has been reported (Zyviel et al. 2013).Metal debris from hip replacement may be associated with chromosomal aberrations and DNA damage (Case et al. 1996, Bonassi et al. 2000, Daley et al. 2004). However, the risk of cancer is not increased after conventional metal-on-polyethylene total hip replacement or after first-generation metal-on-metal total hip arthroplasty (Visuri et al. 1996, 2010a). The short-term overall cancer risk after modern metal-on-metal hip arthroplasty is not increased either (Mäkelä et al. 2012, Smith et al. 2012, Brewster et al. 2013). However, recent linkage studies of overall cancer risk are based on hospital episode statistics, which may have less quality assurance than cancer registry data (Smith et al. 2012, Brewster et al. 2013). Annual updating of cancer registry data concerning the metal-on-metal issue is advisable.In this paper, we update our earlier published results on risk of cancer (Mäkelä et al. 2012) and give an assessment of the overall and cause-specific mortality in primary metal-on-metal and non-metal-on-metal hip replacement patients who were operated on from 2001 to 2010, by combining data from the Finnish Arthroplasty Register, the Population Register Centre, and the Finnish Cancer Registry. The reason for this early updating of the cancer data was to be able to detect a cancerogenic effect of metal-on-metal implants as early as possible.     

Corrosion in modular total hip replacements: An analysis of the head–neck and stem–sleeve taper connections

In this retrieval study, modular junctions of retrieved S-ROM^® implants were examined to determine the extent of corrosion at the head–neck and stem–sleeve junctions. Corrosion severity was graded in relation to the bearing surface material over time. It was found that the corrosion at the head–neck taper is greater for cobalt–chrome femoral heads compared to ceramic femoral heads. The stem–sleeve junction had significantly more corrosion damage (p < 0.05) in implants that had hard-on-hard bearing surfaces compared to hard-on-soft bearings. This study suggests that bearing surface materials and head size affect the amount of corrosion that is present at the modular junctions.