Background

We have previously described the relationship between wear rates of MOM components and soft tissue necrosis. In this study we investigated the link between wear rates, metal ion concentrations and osteolysis.

Hip resurfacing may be a useful surgical procedure when patient selection is correct and only implants with superior performance are used. In order to establish a body of evidence in relation to hip resurfacing, pseudotumour formation and its genetic predisposition, we performed a case-control study investigating the role of HLA genotype in the development of pseudotumour around MoM hip resurfacings. All metal-on-metal (MoM) hip resurfacings performed in the history of the institution were assessed. A total of 392 hip resurfacings were performed by 12 surgeons between February 1st 2005 and October 31st 2007. In all cases, pseudotumour was confirmed in the preoperative setting on Metal Artefact Reduction Sequencing (MARS) MRI. Controls were matched by implant (ASR or BHR) and absence of pseudotumour was confirmed on MRI. Blood samples from all cases and controls underwent genetic analysis using Next Generation Sequencing (NGS) assessing for the following alleles of 11 HLA loci (A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPB1, DPA1). Statistical significance was determined using a Fisher's exact test or Chi-Squared test given the small sample size to quantify the clinical association between HLA genotype and the need for revision surgery due to pseudotumour. Both groups were matched for implant type (55% ASR, 45% BHR in both the case and control groups). According to the ALVAL histological classification described by Kurmis et al., the majority of cases (63%, n=10) were found to have group 2 histological findings. Four cases (25%) had group 3 histological findings and 2 (12%) patients had group 4 findings. Of the 11 HLA loci analysed, 2 were significantly associated with a higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) and 4 were noted to be protective against pseudotumour formation (DQA1*03:01:01, DRB1*04:04:01, C*01:02:01, B*27:05:02). These findings further develop the knowledge base around specific HLA genotypes and their role in the development of pseudotumour formation in MoM hip resurfacing. Specifically, the two alleles at higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) in MoM hip resurfacing should be noted, particularly as patient-specific genotype-dependent surgical treatments continue to develop in the future

Metal-on-metal hip arthroplasty has fallen out of favor because of complications arising from the articulation, namely metal sensitivity and accelerated wear. These complications can lead to early/mid-term failures from pain, osteolysis, implant loosening, and pseudotumor formation. However, it has become clearer that MOM total hip arthroplasty behaves differently from MOM hip resurfacing, due to the additional junctions present in the total hip arthroplasty setting. Garbuz et al have demonstrated in a randomised controlled trial that MOM THA has significantly higher metal ion levels than MOM hip resurfacing. Clinical results of a MOM THA compared with a MOM HR using the same articulation also demonstrate significantly poorer results with the THA. Newer literature has also shown that corrosion occurs at the taper junction of a THA due to the dissimilar metals. These corrosion products are likely what are causing a higher incidence of adverse local tissue reactions. Because a hip resurfacing implant is a monoblock ball, there is no taper junction of dissimilar metals that has the potential for corrosion. National registry studies have also demonstrated a difference in the survival curves of MOM THA vs. hip resurfacing. MOM HR, in select patient groups, has a lower revision rate at 10 years than traditional metal-on-poly THA. Thus, to eliminate MOM hip resurfacing as a treatment option is akin to “throwing the baby out with the bathwater”, which the presenter deeply opposes

Introduction. Edge loading is a common wear mechanism in Metal-on-Metal (MOM) hip resurfacing and is associated with higher wear rates and the incidence of pseudotumour. The purpose of this study was to develop a method to investigate the contributions of patient, surgical and implant design variables on the risk of edge loading. Method. We created a mathematical model to calculate the distance from the head-cup contact patch to the rim of the cup and used this to investigate the effect of component position, specific design features and patient activity on the risk of edge loading. We then used this method to calculate the contact patch to rim distance (CPRD) for 160 patients having undergone revision of their MOM hip resurfacing in order to identify any possible associations. Results. We identified several variables that reduce the CPRD and increase the risk of edge loading, including; increased cup anteversion and inclination, activities involving increased hip flexion, reduced clearance, reduced hip diameter and reduced cup arc angle. We also determined the threshold cup orientation for edge loading for five resurfacing designs (Figure 1). In patients with failed MOM hip resurfacings, there was a significant correlation between CPRD and both component wear rates (Figure 2) and blood metal ion levels (all p < 0.005). The ASR was associated with increased wear, reduced CPRD, and increased prevalence of edge loading (all p < 0.05). Conclusions. Edge loading is common and difficult to avoid in MOM hip resurfacing. Whilst some designs, such as the ASR, are more susceptible to edge loading, all are unforgiving of suboptimal cup position. Furthermore, common activities involving flexion of the hip result in edge loading even in patients with a well-positioned cup

Soft tissue reactions following metal-on-metal arthroplasty of the hip have been under discussion in recent times. The phenomenon has been observed since the advent of arthroplasty, but the particular nature of metal-on-metal (MoM) resurfacing or total hip arthroplasty (THA), and the associated shedding of metal particles in high wear states, appears to excite a more aggressive response. Recent reports suggest involvement of muscle groups on a wide scale, and some cases of neurovascular involvement. It is not known which reactions require widespread muscle excision, and which cases may be adequately addressed by bearing exchange alone. We report three cases of soft tissue reaction (pseudotumour) following MoM hip resurfacing all managed with revision to ceramic-on-ceramic (CoC) THA with minimal soft tissue excision. All patients were female with ages at original operation of 49, 52 and 58 years. Time to revision surgery was 85, 28 and 66 months respectively. Prosthesis revision resulted in progressive and satisfactory resolution of the pseudotumour. We propose that in the early stages, pseudotumour following MoM hip resurfacing can be adequately managed with revision to ceramic-bearing THA with minimal soft tissue excision, rather than revision with extensive soft tissue debridement that has been recently described

Background:. Failed metal-on-metal (MOM) bearings and corrosion reactions are being increasingly encountered with little to guide evaluation for periprosthetic joint infection (PJI). Our purpose was to determine the utility of the erythrocyte sedimentation rate (ESR), C-Reactive Protein (CRP), synovial fluid white blood cell (WBC) count and differential (%PMN) in diagnosing PJI in failed hips with a MOM bearing or corrosion. Methods:. 150 revision hips (92 MOM total hip arthroplasties, 19 MOM hip resurfacings, 30 non-MOM bearings with corrosion and 9 full-thickness bearing surface wear with metallosis) were retrospectively evaluated. Nineteen patients were diagnosed as infected using MSIS criteria. Mean laboratory values were compared between groups and receiver operator characteristic curves (ROC) generated with an area under the curve (AUC) to determine test performance and optimal cutoffs. Results:. The synovial fluid WBC count was judged to be inaccurate secondary to cellular debris in 47 of the 141 patients where one was obtained (33.3%); a WBC count was still reported, however, in 35 hips, 11 of which were falsely positive. Infected patients had significantly higher mean serum ESR, CRP, synovial fluid WBC count, and differential (p < 0.0001, all). The best tests for diagnosis of PJI were the synovial fluid WBC count (AUC=98%, optimal cutoff 4350 WBC/μL), and differential (AUC = 90%, optimal cutoff 85% PMN). Diagnostic performance of the synovial fluid WBC count and differential improved with fewer false positives after excluding inaccurate samples. The ESR and CRP both had good sensitivity. Conclusions:. The diagnosis of PJI is extremely difficult in patients with MOM bearings or corrosion and the synovial fluid WBC count can frequently be falsely positive and should be relied upon only if a manual count is done and if a differential can be performed. A more aggressive approach to preoperative evaluation for PJI is recommended in these patients to allow for careful evaluation of the synovial fluid specimen, the integration of synovial fluid culture results, and repeat aspiration if necessary

The purpose of this study was to evaluate early results of a new as yet not described minimal invasive posterior gluteus maximus splitting approach for total hip arthroplasty (THA) and also metal on metal hip resurfacing. A new minimal invasive gluteus maximus splitting posterior approach is described backed up with intra-operative videos. This single incision approach allowed THA to be carried out through an incision ranging from 5.5 cm. to 9 cm. and metal on metal (MOM) resurfacing through an incision ranging from 7.5 cm. to 10 cm. Intra-operative fluoroscopy is not needed. The patients were not selected according to body mass index (BMI). All patients are suitable for this approach except for severely obese patients. 30 patients underwent THA (both cemented and uncemented) and 20 underwent MOM resurfacing. Early results at average 6 months indicate low post-operative pain scores, low blood loss (less than 5% needing transfusion), early mobilisation and discharge from hospital. Patients also returned to normal activities early with excellent cosmetic results and high patient satisfaction scores. There were no complications. THA and MOM hip resurfacing can safely be done through a minimally invasive gluteus maximus splitting approach with excellent early results without any complication

Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation. Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis. Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated. Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty

Introduction. Solid or cystic pseudotumour is a potentially destructive complication of metal on metal (MoM) couples, usually needing revision surgery. However, complete clearance of the pseudotumour is unlikely at times. This prospective case-controlled study reports cases which had recurrence after revision surgery for pseudotumour related to metal on metal hip couples. Methods. A total of 37 hips (33 MoM hip resurfacing and four big head MoM total hip arthroplasty (THA)) were revised for pseudotumour during the last 10 years. The patient demographics, time to revision, cup orientation, operative and histological findings were recorded for this cohort. Patients were divided into two groups - group R (needing re-revision for disease progression) and group C (control - no evidence of disease progression). Oxford hip scores (OHS, 0–48, 48 best outcome) were used to assess clinical outcome. The diagnosis of disease progression was based on recurrence of clinical symptoms, cross-sectional imaging, operative and histological findings. Results. Nine of 37 (24%) patients identified with worsening symptoms, eight underwent further re-revision surgery while one is awaiting revision surgery (group R). All patients were females and the mean time to initial revision in group R was 34 months (SD 21.8) and 60.5 months in group C (SD 27.5, p< 0.01). The mean cup abduction angle and anteversion in group R were 480 (SD 9.3) and 5.10 (SD 5.0), and 500 (SD 8.7) and 14.50 (SD 8.5) respectively. Re-revision surgery confirmed disease progression in all cases. Oxford hip score was significantly worse in group R 19 (SD 8.0) as compared to group C 33 (SD14.2) (p=0.03). Discussion. This study demonstrates that solid pseudotumour can progress following initial revision. This is likely to be an ongoing reaction to retained metal debris despite adequate clearance. All patients revised for pseudotumour should be monitored using early ultrasound or MRI

Purpose. There are concerns of soft-tissue reactions such as metal hypersensitivity or pseudotumors for metal-on-metal (MoM) bearings in hip arthroplasty, however, such reactions around ceramic or polyethylene bearings are incompletely understood. The present study was conducted to examine the capabilities of ultrasound screening and to compare the prevalence of periarticular soft-tissue lesions among various types of bearings. Methods. Ultrasound examinations were conducted in 163 hips (153 patients) with arthroplasty after mean a follow-up of 8.1 years (range, 1–22 years). This included 39 MoM hip resurfacings (M-HR) including 30 Birmingham hip resurfacings (BHR) and 9 ADEPT resurfacings; 36 MoM total hip arthroplasties (M-THA) with a large femoral head including 26 BHR and 10 ADEPT bearings; 21 ceramic-on-ceramic THAs (C-THA) of Biolox forte alumina bearings; 24 THAs with a conventional polyethylene liner (cPE-THA) including 19 Lubeck and 5 Omnifit systems; and 43 THAs with a highly cross-linked polyethylene liner (hxPE-THA) including 28 Crossfire and 15 Longevity liners. All procedures were performed in the lateral position through the posterior approach without trochanteric osteotomy. The M-HR group had a significantly higher frequency of male patients than the C-THA, cPE-THA, and hxPE-THA groups, and the patients in the M-HR group were younger than those in the other four groups. Ultrasound images were acquired as a still picture and in video format as the hip moved in flexion and rotation, and 4 qualitative classifications for periarticular soft-tissue reactions were determined as normal pattern, joint-expansion pattern (marked hypoechoic space between the anterior capsule and the anterior surface of the femoral component), cystic pattern (irregularly shaped hypoechoic lesions), and mass pattern (a large mass extending anterior to the femoral component). Magnetic resonance imaging (MRI) was subsequently performed in 45 hips with high-frequency encoding bandwidths. For the reliability of ultrasound screening, positive predictive value, negative predictive value, and the accuracy of the presence of abnormal patterns on ultrasound were calculated using the abnormal lesions on MRI as a reference. Results. Among the 45 hips that underwent MRI, periarticular abnormal lesions were detected in 26 hips (58%). Using MRI findings as reference, positive predictive value, negative predictive value, and the accuracy of ultrasound examination for the detection of soft-tissue lesions were 83%, 71%, and 78%, respectively. Abnormal ultrasound lesions with joint expansion, cystic, or mass patterns were most frequently observed in the cPE-THA group (50%), followed by the M-THA (25%), hxPE-THA (23%), M-HR (18%), and C-THA groups (14%). Compared to the hxPE-THA group, the frequency of abnormal patterns did not differ significantly in the two MoM groups. A mass pattern was detected in 3 hips of the M-THA group and 1 hip of the C-THA group (Figure 1). Abnormal ultrasound lesions were significantly associated with the presence of symptoms. Conclusion: Various soft-tissue reactions could be observed other than those for MoM bearings, and pseudotumors may not be a specific feature of MoM bearings. Ultrasound examination may be a suitable screening tool for further large prospective investigations of soft-tissue reactions around various types of bearings