Large-head metal-on-metal total hip replacement has a failure rate of almost 8% at five years, three times the revision rate of conventional hip replacement. Unexplained pain remains a feature of this type of arthroplasty. All designs of the femoral component of large-head metal-on-metal total hip replacements share a unique characteristic: a subtended angle of 120° defining the proportion of a sphere that the head represents. Using MRI, we measured the contact area of the iliopsoas tendon on the femoral head in sagittal reconstruction of 20 hips of patients with symptomatic femoroacetabular impingement. We also measured the articular extent of the femoral head on 40 normal hips and ten with cam-type deformities. Finally, we performed virtual hip resurfacing on normal and cam-type hips, avoiding overhang of the metal rim inferomedially. The articular surface of the femoral head has a subtended angle of 120° anteriorly and posteriorly, but only 100° medially. Virtual surgery in a normally shaped femoral head showed a 20° skirt of metal protruding medially where iliopsoas articulates. The excessive extent of the large-diameter femoral components may cause iliopsoas impingement independently of the acetabular component. This may be the cause of postoperative pain with these implants

Aims. Large-diameter metal-on-metal (MoM) total hip arthroplasty (THA) has demonstrated unexpected high failure rates and pseudotumour formation. The purpose of this prospective cohort study is to report ten-year results in order to establish revision rate, prevalence of pseudotumour formation, and relation with whole blood cobalt levels. Methods. All patients were recalled according to the guidelines of the Dutch Orthopaedic Association. They underwent clinical and radiographical assessments (radiograph and CT scan) of the hip prosthesis and whole blood cobalt ion measurements. Overall, 94 patients (95 hips) fulfilled our requirements for a minimum ten-year follow-up. Results. Mean follow-up was 10.9 years (10 to 12), with a cumulative survival rate of 82.4%. Reason for revision was predominantly pseudotumour formation (68%), apart from loosening, pain, infection, and osteolysis. The prevalence of pseudotumour formation around the prostheses was 41%, while our previous report of this cohort (with a mean follow-up of 3.6 years) revealed a 39% prevalence. The ten-year revision-free survival with pseudotumour was 66.7% and without pseudotumour 92.4% (p < 0.05). There was poor discriminatory ability for cobalt for pseudotumour formation. Conclusion. This prospective study reports a minimum ten-year follow-up of large-head MoM THA. Revision rates are high, with the main reason being the sequelae of pseudotumour formation, which were rarely observed after five years of implantation. Blood ion measurements show limited discriminatory capacity in diagnosing pseudotumour formation. Our results evidence that an early comprehensive follow-up strategy is essential for MoM THA to promptly identify and manage early complications and revise on time. After ten years follow-up, we do not recommend continuing routine CT scanning or whole cobalt blood measurements, but instead enrolling these patients in routine follow-up protocols for THA. Cite this article: Bone Jt Open 2022;3(1):61–67

Summary. Five year migration results of 49 large-head metal-metal (MoM) total hip arthroplasties show good implant stability and no association between implant migration and metal-ions levels, stem and cup position, or femoral bone mineral density. Introduction. The failure mechanism of metal-metal (MoM) total hip arthroplasty has been related to metal wear-debris and pseudotumor, but it is unknown whether implant fixation is affected by metal wear-debris. Patients and Methods. In July-August 2012 41 patients (10 women) at a mean age of 47 (23–63) years with a total of 49 MoM hip arthroplasties (ReCap Shell/M2a-Magnum head/Bi-Metric stem; Biomet Inc.) participated in a 5–7 year follow-up with blood tests (chrome and cobalt serum ions), questionnaires (Oxford Hip Score (OHS) and Harris Hip Score (HHS), measurement of cup and stem position and periprosthetic BMD. Further the patients had been followed with stereo-radiographs post-operative and at 1, 2 and 5 years for analysis of implant migration (Model-Based RSA 3.32). Results. 4 patients (6 hips) had elevated metal-ion levels (>7ug/l). The mean cup inclination was 45°(sd 6), the mean cup anteversion was 17°(sd7), and the mean stem anteversion was 19°(sd7). The difference between genders was statistically insignificant (p>0.09). At 5 years follow-up total translation (TT) for the stems (n=39 hips) was a mean 0.79mm (sd 0.53) and total rotation (TR) was a mean 1.99° (sd 1.53). Between 1–2 years there was no significant difference in mean TT (p=0.49)for the stems and between 2–5 years TT was mean 0.13 mm (sd 0.35) which was significant (p=0.03) but clinically very small and within the precision limits of the method. We found no significant migration along the 3 separate axes. There was no significant association between stem migration and metal ion levels >7ug/l (p=0.55), female gender (p=0.86), stem anteversion > 25° (p=0.29), T-scores < −1 (p=0.23), total OHS < 40 (p=0.19) or total HHS < 90 (p=0.68). Between 1–5 years there was no significant change in neither subsidence (p=0.14) nor in version (p=0.91) of the stems. At 5 years TT for the cups (n=36) was mean 1.21 mm (sd 0.74) and TR was mean 2.63° (sd 1.71). Between 1–2 years cup migration along the z-axis was mean 0.29 (sd 0.73) (p=0.03), which was also within precision limits of the method. There was a positive association between total OHS below 40 (n=4) and cup migration (p=0.04), but no association between cup migration and metal ion levels >7ug/l (p=0.80), female gender (p=0.74), cup inclination > 50° (p=0.93), cup anteversion > 25° (p=0.88) or HHS < 90 (p=0.93). Proximal cup migration at 5 years was mean 0.46 mm (sd 0.47), which was similar to the cup migration at 1 year (p=0.91) and 2 years (p=0.80) follow-up. No patients were revised before the final 5–7 year follow-up. Patient satisfaction was high (94%). Conclusion. All cups and stems were well-fixed between 1–5 years. We found no statistical significant correlation between implant migration and other factors that have been associated with failure of MoM hip arthroplasty such as elevated metal ion levels, component position, and female gender. Cup migration was higher in patients with a total OHS below 40. In conclusion, metal wear-debris does not seem to influence fixation of hip components in large-head MoM articulations at mid-term follow-up

High complication rates and poor outcomes have been widely reported in patients undergoing revision of large head metal-on-metal arthroplasty. A previous study from our centre showed high rates of dislocation, nerve injury, early cup loosening and pseudotumor recurrence. After noting these issues, we implemented the following changes in surgical protocol in all large head MOM revisions: One: Use of highly porous shells in all cases. Two: Use of largest femoral head possible. Three: Low threshold for use of dual mobility and constrained liners when abductors affected or absent posterior capsule. Four: Use of ceramic head with titanium sleeve in all cases. Five: Partial resection of pseudotumor adjacent to sciatic and femoral nerves.

The purpose of the present study is to compare the new surgical protocol above to our previously reported early complications in this group of patients

We specifically looked at (1) complications including reoperations, (2) radiologic outcomes, and (3) functional outcomes. Complication rates after (Group 1), and before (Group 2) modified surgical protocol were compared using Chi-square test, assuming statistical significance p < 0 .05.

Major complications occurred in 4 (8.3%) of 48 patients who had modified surgical technique, compared to 12 (38%) of 32 revisions prior to modification (p < 0 .05). Two hips of 48 (4.17%) endured dislocations in Group 1, compared to 9 of 32 (28%) in Group 2 (p < 0 .05). Four patients of 48 had repeat revision in Group 1: 2 for recurrence of pseudotumor, 1 for dislocation, and 1 for infection, compared to 6 patients who had 7 repeat revisions of 32 patients in Group 2: 3 for acetabular loosening, 3 for dislocation, and 1 for recurrence of pseudotumor (p=0.1). None of 48 revisions in Group 1 had acetabular loosening, compared to 4 of 32 in Group 2 (p=0.02). Two patients had nerve injury in Group 2, compared to none in Group 1 (p=0.16). The mean WOMAC pain score was 87.1 of 100 and the function score was 88.4 of 100 in Group 1, compared to a mean WOMAC pain score of 78 of 100 (p=0.6) and a function score of 83 of 100 in Group 2 (p=0.8).

Modification of the surgical techniques described in the introduction has resulted in a significant decrease in complications in revision of large head MOM total hips. We continue to use this protocol and recommend it for these difficult cases.

Background

High complication rates and poor outcomes have been widely reported in patients undergoing revision of large head metal-on-metal arthroplasty. A previous study from our center showed high rates of dislocation, nerve injury, early cup loosening and pseudotumor recurrence. After noting these issues, we implemented the following changes in surgical protocol in all large head MOM revisions: 1. Use of highly porous shells in all cases 2. Use of largest femoral head possible 3. Low threshold for use of dual mobility and constrained liners when abductors affected or absent posterior capsule 4. Use of ceramic head with titanium sleeve in all cases 5. Partial resection of pseudotumor adjacent to sciatic and femoral nerves.

There has been a significant decline in the use of metal-on-metal (MoM) bearings due to concerns regarding adverse reaction to metal debris (ARMD). The Medicines and Healthcare products Regulatory Agency (MHRA) recommends annual follow-up for life with blood Cobalt (Co) and Chromium (Cr) ion level measurement in all MoM THRs with femoral head size greater than or equal to 36mm. We present the serial ten year serum Co and Cr levels in a cohort of large head MoM THRs and analyse the utility of measuring serum ions levels annually.

All patients who underwent unilateral large head MoM THR between January 2004 and December 2006 were included in this prospective study. Annual serum Co and Cr measurements were measured. Clinical case notes and radiographs were reviewed for failure, revision surgery and the occurrence of ARMD. Mann Whitney test was used to analyse changes in serum Co and Cr levels. Receiver Operating Characteristic (ROC) curve was plotted based on their sensitivity and specificity to detect ARMD.

256 patients were included. There was a significant increase in serum ion values in the first two years. After 7 years, there was no significant change in Co values(p=0.78) and there was a decline in Cr value after 9 years(p<0.001). With 7 µg/l as the cut-off value, the sensitivity and specificity of Co was 82.1% and 65.5% and of Cr was 53.5% and 91.3%.

Annual follow-up of patients with MoM THR based on the MHRA guideline to obtain serum metal ion levels can cost about £9 million/year. Our study noted poor discriminatory ability for both Co and Cr values in the ROC curve. There is poor correlation between serum metal ion levels and the occurrence of ARMD on MARS MRI. Based on our results we find limited utility in doing ion levels after 7 years in asymptomatic patients.

Peri-articular soft-tissue masses or ‘pseudotumours’ can occur after large-diameter metal-on-metal (MoM) resurfacing of the hip and conventional total hip replacement (THR). Our aim was to assess the incidence of pseudotumour formation and to identify risk factors for their formation in a prospective cohort study.

A total of 119 patients who underwent 120 MoM THRs with large-diameter femoral heads between January 2005 and November 2007 were included in the study. Outcome scores, serum metal ion levels, radiographs and CT scans were obtained. Patients with symptoms or an identified pseudotumour were offered MRI and an ultrasound-guided biopsy.

There were 108 patients (109 hips) eligible for evaluation by CT scan at a mean follow-up of 3.6 years (2.5 to 4.5); 42 patients (39%) were diagnosed with a pseudotumour. The hips of 13 patients (12%) were revised to a polyethylene acetabular component with small-diameter metal head. Patients with elevated serum metal ion levels had a four times increased risk of developing a pseudotumour.

This study shows a substantially higher incidence of pseudotumour formation and subsequent revisions in patients with MoM THRs than previously reported. Because most revision cases were identified only after an intensive screening protocol, we recommend close monitoring of patients with MoM THR.

The prevalence of pseudotumours in patients with large-head metal-on-metal (MOM) THA has been the subject of implant recalls and warnings from various regulatory agencies. To date, there is no consensus on whether ultrasound or MRI is superior for the detection and following the progression of pseudotumours. Ultrasound is relatively cheap but can be operator dependent. MARS MRI has the advantage of excellent visibility of the soft tissue. However, MRI comes at a marked increase cost and takes about twice as long to perform. At our institution, we prospectively compared ultrasound to MRI for pseudotumour detection in an asymptomatic cohort of patients with MOM THAs. We enrolled 40 patients with large-head MOM THAs in the study. The mean age was 54 years (range, 34–76 years). The mean time from surgery was 54 months (range, 40–81 months). There were 28 men and 12 women. All patients underwent ultrasound and MRI using slice encoding for metal artifact correction. The gold standard was defined as follows: if both ultrasound and MRI agreed, this was interpreted as concordant and the result was considered accurate. Ultrasound and MRI agreed in 37 of 40 patients (93%). The prevalence of pseudotumours was 31% (12 of 39) in our cohort. Twenty-three of 39 patients (59%) had completely normal tests and four (10%) had simple fluid collections. Ultrasound had a sensitivity of 100% and specificity of 96% while MRI had a sensitivity of 92% and specificity of 100%. Conclusions: A negative ultrasound rules out pseudotumour in asymptomatic patients as this test is 100% sensitive. Given its lower cost, we recommend ultrasound as the initial screening tool for pseudotumours. More recently, Kwon et al have compared ultrasound to MARS MRI for following the progression of pseudotumours. They found a strong agreement between the 2 modalities for assessing change in size and consistency of pseudotumours

Large-head metal-on-metal (MoM) total hip replacements (THR) have given rise to concern. Comparative studies of small-head MoM THRs over a longer follow-up period are lacking. Our objective was to compare the incidence of complications such as infection, dislocation, revision, adverse local tissue reactions, mortality and radiological and clinical outcomes in small-head (28 mm) MoM and ceramic-on-polyethylene (CoP) THRs up to 12 years post-operatively. A prospective cohort study included 3341 THRs in 2714 patients. The mean age was 69.1 years (range 24 to 98) and 1848 (55.3%) were performed in women, with a mean follow-up of 115 months (18 to 201). There were 883 MoM and 2458 CoP bearings. Crude incidence rates (cases/1000 person-years) were: infection 1.3 vs 0.8; dislocation 3.3 vs 3.1 and all-cause revision 4.3 vs 2.2, respectively. There was a significantly higher revision rate after ten years (adjusted hazard ratio 9.4; 95% CI 2.6 to 33.6) in the MoM group, and ten of 26 patients presented with an adverse local tissue reaction at revision. No differences in mortality, osteolysis or clinical outcome were seen. In conclusion, we found similar results for small-head MoM and CoP bearings up to ten years post-operatively, but after ten years MoM THRs had a higher risk of all-cause revision. Furthermore, the presence of an adverse response to metal debris seen in the small-head MOM group at revision is a cause for concern. Cite this article: Bone Joint J 2014; 96-B:868–75

The prevalence of pseudotumours in patients with large-head metal-on-metal (MOM) THA has been the subject of implant recalls and warnings from various regulatory agencies. To date, there is no consensus on whether ultrasound or MRI is superior for the detection of pseudotumours. Ultrasound is relatively cheap but can be operator dependent. MARS MRI has the advantage of excellent visibility of the soft tissue. However MRI comes at a marked increase cost and takes about twice as long to perform. At our institution we prospectively compared ultrasound to MRI for pseudotumour detection in an asymptomatic cohort of patients with MOM THAs. Methods. We enrolled 40 patients with large-head MOM THAs in the study. The mean age was 54 years (range, 34–76 years). The mean time from surgery was 54 months (range, 40–81 months). There were 28 men and 12 women. All patients underwent ultrasound and MRI using slice encoding for metal artifact correction. The gold standard was defined as follows: if both ultrasound and MRI agreed, this was interpreted as concordant and the result was considered accurate. Results. Ultrasound and MRI agreed in 37 of 40 patients (93%). The prevalence of pseudotumours was 31% (12 of 39) in our cohort. Twenty-three of 39 patients (59%) had completely normal tests and four (10%) had simple fluid collections. Ultrasound had a sensitivity of 100% and specificity of 96% while MRI had a sensitivity of 92% and specificity of 100%

Background. Previous studies have indicated poor outcomes and high complication rate in patients having revision of metal-on-metal (MoM) hip implants resulting from adverse local tissue reactions. Metal ions released by MoM bearings may potentially increase infection occurrence in patients with failed implants. Questions/purposes. We reviewed all patients at our institution who sustained revision of a failed large-head metal-on-metal hip implant to determine if infection-related complications are associated with the elevation of serum metal ions concentration. Methods. From December 2005 to April 2013, we performed 44 revisions of large-head MoM total hip arthroplasty (THA) and resurfacing in 44 patients. In all revision procedures MoM couplings (ASR XL Acetabular System and DePuy ASR Hip Resurfacing System) were explanted. Preoperative diagnosis were: aseptic loosening in 21 hips, hip pain with high serum metal ions levels in 7 hips, high serum metal ions levels without hip pain in 9 hips, deep infections in 4 hips, unexplained hip pain in 2 hips and periprosthetic fracture in 1 hip. Serum cobalt and chromium analysis were preoperatively conducted in 25 patients. Intraoperative fluid aspiration was performed in all cases to determine the presence or absence of periprosthetic joint infection. Results. Fluid analysis for bacteria reported that 35 of 45 cases were culture negative and 10 of 45 cases (22%) were culture positive to Staphylococcus (St) Aureus (4), St Capitis (2), St Epidermidis (2), St Hominis (1), Streptococcus Mitis (1). All preoperative diagnoses of deep infection were confirmed. Within patients evaluated with serum metal ions analysis (mean Co and Cr, 78 μg/l and 39 μg/l, respectively), five cultures resulted positive (20%). The infection rate within patients with higher (> 20 μg/l) metal ions levels (4 positive cultures of 18, 22%) was not significantly higher than infection rate within patients with lower (≤ 20 μg/l) metal ions levels (1 positive culture of 7, 14%). Conclusions. We observed a high rate of periprosthetic joint infection among our revision cases. High metal ions concentrations released by MoM bearings might promote bacterial infections in patients with MoM THA and resurfacing. When evaluating patients with failed MoM hip devices, there may be an increased incidence of co-infection in these patients

The aim of this study was to investigate the possible benefit of large-head metal-on-metal bearing on a stem for primary hip replacement compared with a 28 mm diameter conventional metal-on-polyethylene bearing in a prospective randomised controlled trial. We investigated cemented stem behaviour between these two different bearings using Einzel-Bild-Röntgen-Analyse, clinical and patient reported measures (Harris hip score, Western Ontario and McMaster Universities osteoarthritis index, Short Form-36 and satisfaction) and whole blood metal ion levels at two years. A power study indicated that 50 hips were needed in each group to detect subsidence of > 5 mm at two years with a p-value of < 0.05. . Significant improvement (p < 0.001) was found in the mean clinical and patient reported outcomes at two years for both groups. Comparison of outcomes between the groups at two years showed no statistically significant difference for mean stem migration, clinical and patient reported outcomes; except overall patient satisfaction which was higher for metal-on-metal group (p = 0.05). Metal ion levels were raised above the Medicines and Healthcare products Regulatory Agency advised safety level (7 µg per litre) in 20% of the metal-on-metal group and in one patient in metal-on-polyethylene group (who had a metal-on-metal implant on the contralateral side). Two patients in the metal-on-metal group were revised, one for pseudotumour and one for peri-prosthetic fracture. . Use of large modular heads is associated with a risk of raised whole blood metal ion levels despite using a proven bearing from resurfacing. The head-neck junction or excess stem micromotion are possibly the weak links warranting further research

Background. The second generation metal-on-metal (MoM) prosthesis of the hip became a worldwide success in the 90s. However, after the placement of a MoM prosthesis the cobalt ion concentrations raise significantly. This may lead to systemic complaints and even cobalt toxicity. Methods. Sixty-one patients (26F/35M) with both an unilateral and bilateral resurfacing or large-head MoM (LHMoM) hip prosthesis were included. At last follow-up (5.77 ± 1.57 yrs) cobalt concentrations in the blood were determined by ICP-MS. Based on the known cobalt toxicity symptoms we developed a non-validated questionnaire. Analysis was done on two groups; a low cobalt concentration group and a high cobalt concentration group. We used 170 nmol/L as the upper limit of well functioning prosthesis as defined by the Dutch Orthopaedic Society (NOV). Independent samples T test and Pearson correlation coefficient were done. Results. In 61 patients, 70 prosthesis were implanted: 44 resurfacings and 26 LHMoM. Mean cobalt and chromium ion concentrations were 110 ± 138 (9 – 833) and 104 ± 138 (6 – 592) nmol/L. The low cobalt concentration group consisted of 52 patients, while the high cobalt concentration group consisted of 9 hips. With respect to the systemic complaints, the subjects in the high or low group reported no significant differences. A trend towards more complaints with visual problems (75% vs 51.9%, P = .089) and dizziness (62.5% vs 38.9%, P = .098) was notable in the high cobalt concentration group. Conclusions. Metal on metal hip arthroplasty stays controversial for the possible side-effects. This study shows trends, but no significance, in systemic complaints from high cobalt ion concentrations. Complaints of neuro-ocular toxicity are most common. This is in correspondence with other literature, although the upper limit for cobalt ion concentrations remains uncertain. Level of Evidence. 2b. Disclosure. no financial or nonfinancial relationships to disclose

Hip simulators have been used for ten years to determine the tribological performance of large-head metal-on-metal devices using traditional test conditions. However, the hip simulator protocols were originally developed to test metal-on-polyethylene devices. We have used patient activity data to develop a more physiologically relevant test protocol for metal-on-metal devices. This includes stop/start motion, a more appropriate walking frequency, and alternating kinetic and kinematic profiles. There has been considerable discussion about the effect of heat treatments on the wear of metal-on-metal cobalt chromium molybdenum (CoCrMo) devices. Clinical studies have shown a higher rate of wear, levels of metal ions and rates of failure for the heat-treated metal compared to the as-cast metal CoCrMo devices. However, hip simulator studies in vitro under traditional testing conditions have thus far not been able to demonstrate a difference between the wear performance of these implants. Using a physiologically relevant test protocol, we have shown that heat treatment of metal-on-metal CoCrMo devices adversely affects their wear performance and generates significantly higher wear rates and levels of metal ions than in as-cast metal implants

Aims

The present study investigated the five-year interval changes in pseudotumours and measured serum metal ions at long-term follow-up of a previous report of 28 mm diameter metal-on-metal (MoM) total hip arthroplasty (THA).