Improving primary care management of musculoskeletal (MSK) pain is a priority. A pilot cluster RCT tested prognostic stratified care for patients with common MSK pain presentations, including low back pain, in 8 UK general practices (4 stratified care; 4 usual care) with 524 patients. GPs in stratified care practices were asked to use i) the Keele STarT MSK tool for risk-stratification and ii) matched treatment options for patients at low-, medium- and high-risk of persistent pain. A linked qualitative process evaluation explored patients' and GPs' views and experiences of stratified care. Individual ‘stimulated-recall’ interviews with patients and GPs in the stratified care arm (Background
Methods
Distal femoral replacements (DFR) are used in children for limb-salvage procedures after bone tumor surgery. These are typically modular devices involving a hinged knee axle that has peripheral metal-on-polyethylene (MoP) and central metal-on-metal (M-M) articulations. While modular connections and M-M surfaces in hip devices have been extensively studied, little is known about long-term wear or corrosion mechanisms of DFRs. Retrieved axles were examined to identify common features and patterns of surface damage, wear and corrosion. The cobalt chromium alloy axle components from 13 retrieved DFRs were cleaned and examined by eye and with a stereo microscope up to 1000× magnification. Each axle was marked into 6 zones for visual inspection: the proximal and distal views, and the middle (M-M) and 2 peripheral (MoP) zones. The approximate percentage of the following features were recorded per zone: polishing, abrasion or scratching, gouges or detectable wear, impingement wear (i.e. from non- intentional articulation), discoloration and pitting.Background
Methods
In 2010, a widely used metal-on-metal hip implant was voluntarily recalled from the market by the manufacturer. Our lab performed detailed retrieval analysis of 548 of the explanted devices and 165 periprosthetic tissue specimens. We reported a high degree of variability in the multiple measurements that we performed on the components, including volumetric wear. Other studies using semi-quantitative tissue grading methods to describe the histology of the periprosthetic tissues from metal-on-metal hips have looked for relationships between component wear and histological features. Grammatopoulos et al found higher ALVAL scores in 45 hip resurfacing patients with pseudotumors compared to 11 without pseudotumors and a moderately positive correlation between wear and the histological rankings for tissue necrosis and lymphocytic response. We examined correlations between the component wear measurements from retrieval analysis and the tissue features in this large group of one metal-on-metal hip design. Tissues were processed routinely into paraffin sections, stained with H&E and characterized with light microscopic semi-quantitative scores for ALVAL features and for the number of macrophages and lymphocytes, extent of metal debris and the estimated percentage of necrosis per slide. Spearman correlation analysis was conducted to evaluate any correlations between retrieval wear measurements and histological findings.Introduction
Materials and Methods
Low back pain (LBP) is a major health challenge globally. Research has identified common trajectories of pain over time. We aimed to investigate whether trajectories described in one primary care cohort can be confirmed in another, and to determine the prognostic value of factors collected 5 years prior to the identification of the trajectory. The study was carried out on 281 patients who had consulted primary care for LBP, at that point completed a baseline questionnaire, and then returned a questionnaire at 5-years follow-up plus at least 3 (of 6) subsequent monthly questionnaires. Baseline factors were measured using validated tools. Pain intensity scores from the 5-year follow-up and monthly questionnaires were used to cluster participants into 4 previously derived pain trajectories (no or occasional mild, persistent mild, fluctuating, persistent severe), using latent class analysis. Posterior probabilities of belonging to each cluster were estimated for each participant. The posterior probabilities for the assigned clusters were very high (>0.90) for each cluster except for the smallest ‘fluctuating’ cluster (0.74). Lower social class (OR 2.9; 95% CI 1.2, 7.0), higher pain intensity (1.6 per unit; 1.2, 2.2), and pain duration greater than 3 years (2.7; 1.0, 7.3), were significantly associated with a more severe trajectory 5-years later, as were higher physical disability, emotional impact of pain, and perception pain will last a long time.Background and objectives
Methods and results
Recently, a special type of surface pitting found on metal implants was proposed to arise from “inflammatory cell-induced” corrosion (ICI, Figure 1) (1, 2). The actual mechanism of this was unknown, but similar features were suggested to be artefacts of electrocautery damage from revision surgery (3). Under lab conditions and without the influence of any cells, we aimed to reproduce the same surface pits and structures with electrocautery. A polished cobalt-chromium disk (40 mm diameter, 8 mm thick) was marked into 8 sections for various testing conditions (Figure 2a). A stainless steel Bovie tip with a unipolar electrocautery machine (SYSTEM 5000, ConMed, USA) was used at typical surgical coagulation conditions: (70 volt, 120 watts, 562 KHz frequency). We mimicked three types of surgical techniques with the electrocautery: “Dotting” was repeated, on and off, direct surface contact; “Dragging” was constant, direct surface contact; “Hovering” was pausing several millimeters above the surface. We also examined the interplay of these practices on diamond-tip-induced scratches and either dry or wet (normal saline) conditions. High magnification images (Keyence VHX-2000E) were taken after the disk was cleaned with laboratory soap, light mechanical scrubbing, and formalin soak. Coagulation mode generated electrical sparks when dotting/dragging and electrical arcs when hovering. These left seared marks that persisted even after cleaning (Figure 2b). At higher magnification, the surface features were comparable in size and shape to those attributed to ICI (1, 2). Areas wet with saline (Figure 3a) showed an abundance of ringed pits with raised edges that closely resembled those observed in Figure 1. Furthermore we obtained images similar to the phenomenon of “cellular tracks” (Figure 3b) (1). Premade scratches did not influence the pit arrangement but scratches made by the Bovie tip produced the characteristic scratch-associated ICI features as observed on implant retrievals in the past (Figure 3c) (4).Methods
Results
Young osteoarthritic male patients have been considered the ideal candidates for Metal-on-Metal (MoM) hip resurfacing arthroplasty (HRA), based on generally good long term results. In contrast, hip resurfacing in young female patients has become controversial. Recently, one implant manufacturer withdrew 46mm and smaller components, citing poorer than expected 10 year outcomes in females with smaller HRAs. Whether this difference is related to gender or to component size is still debated. Possible reasons for higher failure rates reported in females include higher rates of hip dysplasia, poorer bone quality and the risk of higher wear in some smaller sized implants with low cup coverage angles. We reviewed HRA revision specimens with the aim of comparing mode of failure, time to revision, femoral cement characteristics and acetabular bone attachment in specimens larger and smaller than 46mm and from male versus female patients. The study included all of the MoM HRA devices in our collection. Of the 284 hip resurfacing devices with complete clinical information, 131 were from male and 153 from female patients. Femoral sizes ranged from 36 – 58mm, median and mode 46mm; median size in females was 44 and 50mm in males. Time to failure ranged from 1 to 178 months, median 24 mos. Seven designs were represented but the majority were Conserve Plus (n=105 WMT, USA) and BHR (n=78 Smith & Nephew, USA) which differ in cementing technique. 131 femoral components were sectioned and the width of the cement mantle and the amount of cement in the head were measured. Where available, the amount of bone attached to the cup porous surface (n=91), tissue ALVAL scores (n=75) and bearing wear depth (n=138) were included in the multivariate analysis. As a function of gender, there were no significant differences in time to revision, cement measurements or ALVAL scores. Wear depth was significantly higher in females (femoral 41um vs 21um; cup 50um vs 16um, p=0.05). As a function of size (46 and less = small), the <46mm group had a slightly shorter time to revision, 30 vs 38 months, p=0.04). Bone ingrowth ranged from 0 to 60% (Figure 1) and significantly less bone attachment was noted in both the smaller and larger components (p = 0.001). Other characteristics were similar in both groups. When wear-related failure modes (cup malposition, lysis, high ions) were compared, no differences between male and female or large vs small were found. The amount of cement in the femoral heads covered a wide range but femoral loosening or fracture rates were not different as a function of size or gender.Methods
Results
Bone ingrowth fixation of large diameter, beaded cobalt chromium cups is generally considered to be reliable but this is typically judged radiographically. To date, implant retrieval data of attached bone has been limited. This study evaluated correlations between the pre-revision radiographic appearance and the measured amount of bone attachment on one design of porous coated cup. Twenty-six monoblock, CoCr Birmingham Hip Resurfacing (BHR, Smith and Nephew, TN, USA) cups with macroscopic beads and hydroxyapatite coating were studied. Seventeen were revised for acetabular malposition with the remainder revised for femoral loosening (4), pain (1), infection (1), dislocation (1) or lysis (2). Median time to revision was 35 months (10 – 70 months). Ten patients were female; the median age of all patients was 54 years. The pre-revision radiographs were visually ranked for cup-bone integration as follows: 0 = none, 1 = < 50%, 2 = 50 – 75%, 3 = 76 – 95%, 4 = > 96% integration. Rankings were made for the superior and inferior aspects, without knowledge of the appearance of bone on the retrievals. The revised cups were photographed at an angle so the dome and the cup periphery were visualized. The area of bone in four equal segments in each of the superior and inferior aspects was measured with image analysis software. A probe was used to differentiate bone from soft tissue. Only bone that covered the beads was counted. Correlation coefficients were calculated for the radiographic and image analysis data. Radiographically, most cups were assessed as having more than 50% of bone attachment and 7 cups were ranked as having almost total integration with bone. Only 2 cups were assessed radiographically as fully loose. Measured total bone attachment ranged from none to 55%. Superior and inferior percent ingrowth were highly correlated (corr=0.68, p<0.001) but there was no correlation between percent bone and x-ray rank (inferior corr=0.01, p=0.96; superior corr=0.23, p=0.26). There was no correlation between cup malpositioning as a reason for revision and x-ray integration ranking (superior p=0.34; inferior p=0.80).Methods
Results
Avascular necrosis of the femoral head (AVN) is associated with collapse of the femoral head and arthritic degeneration of the joint. The combination of an implant inserted into the femoral head that provides mechanical support and bone grafting to promote bone formation may offer a possible joint-preserving solution1. Seventeen such procedures were performed between November 2012 and March 2014 during an IRB approved clinical trial. Thirteen out of 18 patients remained unrevised at a minimum of 12 months; the results of radiographic and histological analysis of four revisions are presented. The investigational device (Figure 1) was developed as a joint preserving treatment for AVN with a clinical grade of IIC or less according to the ARCO grading system2. The device consisted of a braided spherical Nitinol cage with a Titanium / Nitinol orientation feature. It was implanted using fluoroscopic navigation into a spherical cavity cut into the femoral head via an 11mm diameter access tunnel. Once deployed, the implant was filled with a lightly impacted mixture of autologous bone graft and bone marrow soaked Conduit TCP (DePuy CMW, Blackpool, UK). The implant's purpose was to provide mechanical support to the weakened subchondral surface while the bone graft mixture re-integrated with the host bone. The retrieved femoral heads were trimmed to leave approximately 3mm of bone around the implant, dehydrated, embedded in methacrylate resin, sectioned and thinned into 50–70µm coronal slices for histological analysis. The following observations were made (Figure 2): Case 1 (Female, age 70, ARCO IIB, revised after 2 days): The patient was revised for spontaneous sub-trochanteric fracture secondary to osteoporosis. Contact between the native bone and bone graft was observed. Marrow elements and repair tissue were visible within the pores in the graft (Figure 2a). Case 2 (Male, age 67, ARCO IIIC, revised after 82 days): Two wires were broken but retained within the braided structure. A radiolucent gap caused by the presence of fibrous tissue between the graft mixture and native bone was evident suggesting that the implant was unable to prevent progression in this case. Case 3 (Female, age 70, ARCO IIC, revised after 482 days): The cavity penetrated the subchondral surface; at revision the implant was found to have breached the articular cartilage. There was partial separation of the proximal osteonecrotic fragment and no evidence of graft revascularisation or remodelling within the implant. Case 4 (Male, age 42, ARCO IIC, revised after 469 days): There was no indication of bone graft re-integration. Collapse of the necrotic bone and deformation of the implant was diagnosed from 1 year follow-up x-rays. This treatment has preserved the joints of fourteen patients. Of the four revised, two patients had clinical grades or bone quality contra-indicated for the device and three had lesions occupying more than 30% of the femoral head: Improved criteria for patient selection may be required. The device is only partially load-bearing and incapable of stabilising fractures: The radiolucent band associated with fibrous tissue formation may be an early indication of failure.Conclusion
The histopathology of periprosthetic tissues has been important to understanding the relationship between wear debris and arthroplasty outcome. In a landmark 1977paper, Willert and Semlitsch (1) used a semiquantitative rating to show that tissue reactions largely reflected the extent of particulate debris. Notably, small amounts of debris, including metal, could be eliminated without “overstraining the tissues” but excess debris led to deleterious changes. Currently, a plethora of terms is used to describe tissues from metal-on-metal (M-M) hips and corroded modular connections. We reviewed the evaluation and reporting of local tissue reactions over time, and asked if a dose response has been found between metal and tissue features, and how the use of more standardized terms and quantitative methodologies could reduce the current confusion in terminology. The PubMed database was searchedbetween 2000 and 2015 for papers using “metal sensitivity /allergy /hypersensitivity, Adverse Local Tissue Reaction (ALTR): osteolysis, metallosis, lymphocytic infiltration, Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL), Adverse Reaction to Metal Debris (ARMD) or pseudotumor/ pseudotumour” as well as metal-on-metal / metal-metal AND hip arthroplasty/replacement. Reports lacking soft tissue histological analysis were excluded. 131 articles describing M-M tissue histology were found. In earlier studies, the terms metal sensitivity / hypersensitivity /allergy implied or stated the potential for a Type IV delayed type hypersensitivity response as a reason for revision. More recently those terms have largely been replaced by broader terms such as ALTR, ALVAL and ARMD. ALVAL and metal hypersensitivity were often used interchangeably, both as failure modes and histological findings. Several histology scoring systems have been published but were only used in a limited number of studies. Correlations of histological features with metal levels or component wear were inconclusive, typically because of a high degree of variability. Interestingly, there were very few descriptions that concluded that the observed reactions were benign / normal or anticipated i.e. regardless of the histological features, extent of debris or failure mode, the histology was interpreted as showing an adverse reaction.Methods
Results
To identify treatment effect modifiers within the STarT Back Trial which demonstrated prognostic stratified care was effective in comparison to standard care for patients with low back pain. Secondary analysis of the STarT Back Trial using 688 patients with available 4-month follow-up data. Disability (baseline and 4 months) was assessed using the Roland Morris Disability Questionnaire (RMDQ) using continuous and dichotomized (>7) outcome scores. Potential treatment effect modifiers were evaluated with group x predictor interaction terms using linear and logistic regression models. Modifiers included: age, gender, education, socio-economic status (SES), employment status, work satisfaction, episode duration, general health (SF-12), number of pain medications, and treatment expectations.Purpose and Background:
Methods:
A wide array of measures has been developed to assess the role of psychological factors in the development and persistence of pain. Yet there is likely to be considerable conceptual overlap between such measures, and consequently a lack of clarity about the importance of psychological factors. To investigate whether conceptual overlap exists within psychological measures used in back pain research.Background
Purpose
People with back pain often experience long-term pain with recurrences and fluctuations. However, few studies have considered which factors predict long-term outcomes. To determine the prognostic factors, measured around the time of a primary care back pain consultation, that predict clinically significant pain in both the short (6 months) and long-term (5 years).Background
Purpose
It has been suggested that metal ion levels are indicative of 182 patients (73 females and 109 males)with a unilateral Conserve Plus (WMT, TN USA) MMHRA and had who had provided blood for metal ion analysis data from December 2000 to June 2011 were retrospectively studied. Only measurements made more than 12 months after surgery were included in order to exclude hips that had yet to reach steady-state wear. For patients with multiple draws, the most recent qualifying draw was used. Activity level was assessed by the UCLA activity score. The mean age was 51.5 years (20.0 to 77.5 years). The mean follow-up time for the last blood draw was 70 months (range, 12 to 165). Serum cobalt (CoS) and chromium (CrS) levels were analyzed using inductively coupled plasma mass spectrometry in a specialized trace element lab. Using acetabular abduction and anteversion measured by EBRA, component size, and reported coverage angle of the acetabular component, the CPR distance was calculated as previously described. Multiple logistic regression was performed to identify significant relationships between high metal ion levels (7 μg/L or greater) and gender, activity and CPR distance. The median CoS level for the entire cohort was 1.13 μg/L (range, 0.15 to 175.30), and the median CrS level was 1.49 μg/L (range, 0.06 to 88.70). The average CPR distance was 13.8 mm (range, 3.2 to 22.1). There was a significant association between low CPR values and CoS and CrS. There was a 37-fold increase in the risk of CoS >7μg/L (p=0.005) and 11-fold increase in the risk of CrS > 7μg/L (p=0.003) when CPR distance was 10 mm or less. No associations were shown for gender and UCLA activity scores. CPR distance was found to be a reliable predictor of ion levels > 7μg/L and appears to be a useful indicator to evaluate the multi-factorial process of edge-loading and wear. Patients with a low CPR distance should be monitored for increased metal ion levels.
The Conserve® Plus (Wright Medical Technology Inc., Arlington, TN) was introduced clinically in the United States in 1996. A study of the serum cobalt and chromium ion levels was started in 2000 in our center to monitor the metal ion levels over time as part of an FDA clinical trial. Thirteen male and five female patients received this resurfacing for idiopathic osteoarthritis (14), post-traumatic degenerative changes (3) or developmental dysplasia (1). Fourteen received a unilateral implant but four subsequently received a contralateral device from 52 to 86 months post-op. Four patients had bilateral resurfacings done in a one-stage procedure. All surgeries were performed by the senior author. None of these patients had known exposure to cobalt or chromium, kidney disease or other metal implants elsewhere in their bodies. Each prospectively provided blood samples and then yearly thereafter to measure cobalt and chromium levels for up to 11 years. Metal levels were measured using atomic absorption spectrophotometry and inductively coupled plasma mass spectrometry by a specialized trace element analysis laboratory. Acetabular component position was evaluated using Einzel-Bild-Röentgen-Analysis (EBRA) software. Contact patch to rim (CPR) distance was computed as described by Langton et al JBJS Br 91: 2009. A mixed model linear regression analysis was performed to evaluate long term trends, and multivariate analysis was performed to examine effects of implant and patient covariates on the metal ion levels. One bilateral patient underwent revision for femoral loosening, all other patients were clinically well-functioning at the time of last follow-up (ave 89 mos). The median pre-operative Co was below the detection limit (d.l) of 0.3μg/L and the median pre-operative Cr was 0.069μg/L (d.l. 03μg/L). Metal levels increased within the first year then decreased and stabilized (fig 1). For unilaterals over all time intervals, the median Co was 1.06 μg/L, while the median Cr was 1.58 μg/L. For bilaterals, the mean post-operative Co was 2.80 μg/L, while the mean Cr was 5.80 μg/L. Generally, Cr levels were higher at all time points than Co. Bilateral patients had Co values 1.96 times greater on average than the unilateral patients (p<0.001). None of the possible covariates studied (femoral size, cup abduction angle, cup anteversion, CPR distance, activity, BMI and testing method) were related to the assay values. The results of this study have shown that serum metal levels in well functioning implants can be low and do not increase over time. These are among the lowest levels reported for resurfacing devices and comparable to levels reported for well functioning small diameter metal-on-metal total hips. The study is limited due to the relatively small sample size and limited range of values for the covariates studied. However, it included patients who were active, female or bilateral and we collected ion levels up to 11 years. We now recommend that patients who have well-oriented Conserve Plus components with stable radiographic interfaces and no incidences of unexplained pain or hip noises be scheduled for follow-up every 2–3 years, rather than annually.
In patients with conventional metal-on-Polyethylene (MoP) hip replacements, osteolysis can occur in response to wear debris. During revision hip surgery, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the inflammatory granulomatous tissues in the joint. We used a human/rat xenograft model to evaluate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic (nude) rats. The tissues were assessed before and after implantation and the bone response to the tissues was evaluated after 1 week and 3 weeks using micro-computed tomography, histology, and immunohistochemistry. After 3 weeks, the majority (70%) of defects filled with osteoarthritic tissues healed, while only 21% of defects with polyethylene granuloma tissues healed. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Surgeons should remove polyethylene granuloma tissues during revision surgery when possible, since these tissues may slow bone healing around a newly implanted prosthesis. This model provides a method for delivering clinically relevant sized particles into an
Pseudotumours have been associated with metal-on-metal (MoM) hip replacements. We define it as a solid mass which may have cystic components that is neither neoplastic nor infectious in aetiology. The cause of a pseudotumour is not fully understood but could be due to excessive wear, metal hypersensitivity or due to an as-yet unknown cause. We present the retrieval analysis of early failure MoM hips revised for pain, loosening or a symptomatic mass. Tissues and implants were examined for the possible causes of failure and pseudotumour formation. Corrosion as a potential new cause for pseudotumour formation will be presented.Background
Aim
To compare a variety of commercially available bone graft substitutes (BGS) in terms of promoting adherence, proliferation and differentiation of osteoprogenitor cells. A fixed number of porcine mononuclear cells obtained from cancellous bone of the proximal femur was mixed with a standard volume of BGS and then cultured for one week in media followed by two weeks in osteogenic media. BGS included commercially available β-Tricalcium Phosphate (□-TCP), highly porous β-TCP, Hydroxyapatite/Tricalcium phosphate composite, calcium sulphate (CS), Hydroxyapatite (HA), Demineralised bone matrix (DBM), polygraft, and polymers (PGA, PLGA). Staining for live/dead cells as well as scanning electron microscopy (SEM) were carried out on all samples to determine viability and cellular binding. Further outcome measures included alkaline phosphatase assays with normalisation for DNA content to quantify osteogenic potential. Negative (BGS without cells) and positive (culture expanded osteoprogenitors) control experiments were carried out in parallel to validate the results.Aim
Materials and methods
Clinical proteomics is an exciting new sub-discipline of proteomics that involves the application of proteomic technologies at the bedside to identify new biomarkers, associated with specific diseases. In this study to compare serum protein profiles between identical age-matched groups of fracture and non-fracture controls, we looked at the initial proteomic profile of 10 patients who had fractures and compared them to age-matched controls to see if there was any specific difference indicative of fracture. 10 patients with single fractures of the long bones, wrist or ankle gave a blood sample upon presentation at the fracture clinic. 10 healthy, age-matched, non-fracture volunteers also donated blood. Plasma was isolated and the albumin and IgG fractions removed before loading equal amounts of each sample onto 2 dimensional polyacrylamide gels for analysis by isoelectric point in the first dimension and molecular mass in the second dimension. Protein profiles between fracture patients and non-fracture controls were contrasted using Phoretix 2D analysis software. Data analysis differentiated between the average gel of the patient group and the average gel of the control group. More than 300 protein spots were observed in both the control and patient group. Seven protein spots were identified which showed a statistically significant (p<0.05) difference between the control and patient samples. Of these, three spots (X, Y, Z) were clear, distinct and present in at least 80% of these gels. All the three spots were up regulated in the patient group as opposed to the control group. These proteins are currently being investigated further by MALDI-TOF TOF for specific protein identification. Proteomic analysis is already a powerful tool in the identification of disease markers. We aim to show here that there are differences seen in blood plasma profiles in fracture patients compared to non-fracture healthy controls. The differences seen may help us to understand the fracture repair process better.Materials and Methods
Discussion
Social context may be important in chronic pain. One focus is reactions to pain between persons with LBP and their partners. Researchers have investigated partner reactions and found influences on pain levels and psychological outcomes, but little is known about factors underpinning these reactions. To investigate the associations of relationship quality and perceived partner responses with LBP intensity and disability.Background
Aim
There have been many reports of metal ion levels measured in the bloodstream of patients after metal-on-metal hip replacement, and it is generally accepted that levels of cobalt (Co) and chromium (Cr) are elevated after these types of devices are implanted. However, it is not clear how to interpret these elevated levels; in particular what are the acceptable levels and what levels indicate that close monitoring of the patient is needed. Our aim was to establish the differences in metal ion levels between well functioning patients and those with clinical problems. We measured serum Co and Cr levels (microgram’s per litre or μg/l) using inductively coupled plasma mass spectrometry with a well established collection protocol of all patients attending follow-up clinics. Our inclusion criteria for this study were all patients unilaterally implanted with a metal-on-metal hip resurfacing with no other metallic implant; patients were categorized as either A. Well Functioning or B. Clinically Problematic (pain, reduced function, reduced ROM, negative x-ray findings) and differences in ion levels between these two groups were examined. Well functioning patient data was only included if measurements were made more than 12 months post-operatively to avoid run-in wear levels. Abduction angle was also measured from x-rays of the pelvis, and the frontal plane coverage arc of each implanted cup calculated (De Haan JBJS[Br] 2008;90(10):1291–7). There were a total of 519 patients, with 358 in Group A and 161 in Group B; patients had a variety of devices with Birmingham Hip Resurfacing (64%) and Conserve Plus (29%) being the most commonly implanted. To establish a guideline upper ion level value for well functioning implants the upper 75th percentile values for Co and Cr levels for Group A patients having 15 mm or more coverage arc were calculated. The risk of having clinical problems was calculated as function of metal ion levels higher or lower than these upper limits. The ion levels were significantly (Mann Whitney U p<
0.001) higher in Group B (mean [95% confidence intervals], Co 10.2 μg/l [5.9 to 14.5], Cr 10.3 μg/l [6.7 to 14.0]) compared to Group A (Co 2.3 μg/l [1.7 to 2.4], Cr 2.8 μg/l [2.3 to 3.4]). The well functioning upper limit for Co was 4.1 μg/l and for Cr was 5.2 μg/l. Metal ion levels greater than these upper limits were significantly (Chi-square p<
0.001) associated with the presence of clinical problems. The odds ratio for Co greater than 4.1 μg/l was 11.2 [95%CI 5.7 to 22.3] and that for Cr greater than 5.2 μg/l was 4.3 [95%CI 2.6 to 7.0]. There were significantly higher metal ion levels measured in patients with clinical problems after metal-on-metal hip resurfacing than those with well functioning hips. We have proposed upper acceptable limits for Co (4.1 μg/l) and Cr (5.2 μg/l) serum levels. Cobalt levels appear to be more reliable in predicting risk of clinical problems; levels greater than our proposed upper limit have 11 times the odds of developing clinical problems and patients with such levels should be followed closely.
