Modern metal-on-metal (MoM) hip resurfacing arthroplasty (HRA), while achieving good results with well-orientated, well-designed components in ideal patients, is contraindicated in women, men with head size under 50 mm, or metal hypersensitivity. These patients currently have no access to the benefits of HRA. Highly crosslinked polyethylene (XLPE) has demonstrated clinical success in total hip arthroplasty (THA) and, when used in HRA, potentially reduces metal ion-related sequelae. We report the early performance of HRA using a direct-to-bone cementless mono-bloc XLPE component coupled with a cobalt-chrome femoral head, in the patient group for whom HRA is currently contraindicated. This is a cross-sectional, observational assessment of 88 consecutive metal-on-XLPE HRAs performed in 84 patients between 2015 and 2018 in three centres (three surgeons, including the designer surgeon). Mean follow-up is 1.6 years (0.7 to 3.9). Mean age at operation was 56 years (Objectives
Methods
Blood metal ion sampling can help detect poorly functioning metal-on-metal hip arthroplasties (MoMHA's) requiring revision. Little is known about the variation in these levels following bearing exchange. This study aimed to determine the changes that occur in blood and urine metal ion concentrations following MoMHA revision. A single-centre prospective cohort study was undertaken between 2005 and 2012 of patients with failing large-diameter MoMHA's and high blood metal ions requiring revision to non-metal-on-metal articulations. All patients had normal renal function. Whole blood and urine were collected for metal ion analysis preoperatively and regularly following revision. Twenty-three MoMHAs (21 hip resurfacings and 2 total hip arthroplasties; mean age 56.0 years and 65% female) were revised at a mean time of 7.9 years (range 2.0–14.5 years) from primary surgery. All revisions were performed by the senior author using primary total hip implants (12 ceramic-on-polyethylene bearings, 10 oxinium-on-polyethylene bearings, and 1 metal-on-polyethylene bearing implanted). Mean (range) metal ion concentrations pre-revision were: blood cobalt 13.9µg/l (1.32–74.7µg/l), blood chromium 8.9µg/l (1.29–57.3µg/l), urine cobalt 104.6µg/24 hours (4.35–747.3µg/24 hours), urine chromium 33.2µg/24 hours (4.39–235.4µg/24 hours). After revision the mean metal ion concentrations (percentage of pre-revision values) were: blood cobalt at 2 days=10.7µg/l (77%), 6 days=7.7µg/l (55%), 2 months=3.4µg/l (24%), 1 year=1.0µg/l (7%), 2 years=0.42µg/l (3%); blood chromium at 2 days=8.7µg/l (98%), 6 days=5.5µg/l (62%), 2 months=2.2µg/l (25%), 1 year=1.5µg/l (16%), 2 years=0.97µg/l (11%); urine cobalt at 2 days=31.9µg/24 hours (30%), 6 days=21.5µg/24 hours (21%), 2 months=6.1µg/24 hours (6%), 1 year=0.99µg/24 hours (1%), 2 years=0.61µg/24 hours (1%); urine chromium at 2 days=34.4µg/24 hours (103%), 6 days=15.8µg/24 hours (48%), 2 months=9.3µg/24 hours (28%), 1 year=2.8µg/24 hours (8%), 2 years=1.9µg/24 hours (6%). Following MoM revision cobalt levels decline rapidly in an exponential pattern with a single rate of decay through the 2 year period, reaching reference levels within the first year. Chromium follows a similar pattern but starts lower and takes longer. Renal response to cobalt returns to reference level within days of revision.
The use of modular systems adds versatility to the implant system, better restoration of hip biomechanics and lower inventory to the hospital. There have been reports of high metal ions, ARMD reactions and high implant failure rates due to potential problems from taper failures. These are more common in metal-on-metal hip replacements, but are being also reported in other bearings. Between 2001 and 2010, we performed 383 consecutive metal-on-metal (MoM) THRs through a posterior approach, using a BHR cup and Birmingham modular head with one of three different stems, all with 12/14 tapers. The earliest 104 hips employed a cemented MS30 stem (Zimmer GmbH, Winterthur, Switzerland). Subsequent 256 were Synergy and then 23 Anthology (both uncemented and both Smith and Nephew Orthopaedics, Memphis TN USA). There was no significant difference in the average age at surgery (65.4 years cemented vs 65.6 uncemented, There were 3 deep infections and 11 debris-related failures (overall revision rate 4.9%). The revision rate from aseptic failures (ALTR, effusion, osteolysis or component loosening) is 2.87%. Kaplan-Meier analysis of the entire cohort showed a 10-year implant survival of 96.8% with revision for any reason as the end-point. Cemented stems had a 100% survival at 10 years and 98.6% at 12 years. The uncemented stems had a 93.8% survival at 10 years. Within the uncemented group, the monoblocks had a 5 and 10-year survival of 99.0% and 96.4% respectively while the sleeved had 98.7% (5 years) and 96.3% (7 years) and 82.5% at 8 years. Retreival analysis showed clear evidence of taper failure. Our experience suggests taper failure leading to ALTRs and its sequelae. Others have reported ALTR type reactions in metal on polyethylene and ceramic on polyethylene bearing types as well in bearing diameters ranging from 28mm to 40mm. There is a need to improve taper design especially for use with large heads, and in high demand patients.
The natural knee allows multi-planar freedoms of rotation and translation, while retaining stability in the antero-posterior direction. It allows flexion with roll back, and medial, lateral and central rotation movements. The natural femoral condyles of the knee are spiral, therefore inducing a side to side translatory movement during flexion and extension. Incorporating all these features is vital in successful knee replacement design. The different knee designs currently in use demonstrate different deficiencies in knee function. A study of 150 Posterior Cruciate (PCL) Retaining Total Knee Replacements [1] has shown that in 72% of knees direct impingement of the tibial insert posteriorly against the back of the femur was responsible for blocking further flexion. The mean pre-operative range of flexion was 105° and post-operative was 105.9°. For every 2mm decrease in posterior condylar offset, the maximum flexion was reduced by 12.2°. The major disadvantage of the Posterior Stabilised (PS) Total Knee Replacement is gross anterior to posterior mid-flexion instability [2]. The Medial Rotation Total Knee Replacement is good in mid-flexion but not in high flexion where the femur slides forward on the tibia leading to impingement. The Birmingham Knee Replacement (BKR) is a rotating platform knee design which is stable throughout the range of flexion. In high flexion, the BKR brings the femur to the back of the tibia. The BKR also has spiral femoral condyles, matching the natural kinematics of the knee. The combined static and dynamic effect is 10mm lateral translation of the femur in flexion and vice versa in extension. Results for seventy nine BKRs (in seventy two patients) show the best Oxford Knee Score of 12 at follow up – excluding ten patients whose inferior scores were due to other pathologies. Knee flexion results show a 21° post-operative improvement in range of flexion. On objective independent testing, maximum walking speed is slower for patients with a standard knee replacement (6.5km/h) and the loading through the replaced side does not match the normal side. Comparatively, patients with a BKR have a faster maximum walking speed of 11km/h and the loading closely matches that of the normal knee. Studies based on the National Joint Register PROMs data [2] show that nearly thirty percent of Total Knee Replacement patients are not much better since their operation. A lot of improvement is needed in the design of knee replacements in order to achieve better function for knee replacement patients.
To examine mortality and revision rates among patients with osteoarthritis undergoing hip arthroplasty and to compare these rates between patients undergoing cemented or uncemented procedures and to compare outcomes between men undergoing stemmed total hip replacements and Birmingham hip resurfacing. Hip arthroplasty procedures were linked to the time to any subsequent mortality or revision (implant failure). Flexible parametric survival analysis methods were used to analyse time to mortality and also time to revision. Comparisons between procedure groups were adjusted for age, sex, American Society of Anesthesiologists (ASA) grade, and complexity.Objectives
Main outcome measures
High short-term failure rates have been observed with a number of metal-on-metal (MoM) hip designs. Most patients require follow-up with blood metal ions, whichprovide a surrogate marker of in-vivo bearing wear. Given these results are used in clinical decision making it is important values obtained within and between laboratories are reproducible. To assess the intra-laboratory and inter-laboratory variability of blood metal ion concentrations analysed by four accredited laboratories. Whole blood was taken from two participants in this prospective study. The study specimen was obtained from a 42 year-old female with ceramic-on-ceramic hip arthroplasty failure resulting in unintended metal-on-ceramic wear and excessively high systemic metal ion levels. The control specimen was from a 52 year-old healthy male with no metal exposure. The two specimens were serially diluted to produce a total of 25 samples with different metal ion concentrations in two different anticoagulants each. Thus 50 samples were sent blinded in duplicate (total 100) to four accredited laboratories (A, B, C, D) to independently analyse blood metal ion concentrations. Ten commercially available reference specimens spiked with different amounts of metal ions were also obtained with known blood metal ion concentrations (range for cobalt 0.15µg/l-11.30µg/l and chromium 0.80µg/l to 37.00µg/l) and analysed by the four laboratories. The intra-laboratory coefficients of variation for repeat analysis of identical patient specimens were 7.32% (laboratory A), 4.64% (B), 7.50% (C), and 20.0% (D). The inter-laboratory variability for the analysis of all 25 samples was substantial. For the unmixed study specimen the laboratory results ranged from a cobalt of 263.7µg/l (D) to 525.1µg/l (D) and a chromium of 13.3µg/l (D) to 36.9µg/l (A). For the unmixed control specimen the laboratory results ranged from a cobalt of 0.13µg/l (B) to 0.77µg/l (D) and a chromium of 0.13µg/l (D) to 7.1µg/l (A). For one of the mixed specimens the laboratory results ranged from a cobalt of 12.50µg/l (A) to 20.47µg/l (D) and a chromium of 0.73µg/l (D) to 5.60µg/l (A). Similar inter-laboratory variation was observed for the other mixed samples. The true mean (standard deviation) of the 10 commercial samples was 4.48µg/l (4.20) for cobalt and 8.97µg/l (10.98) for chromium. This was similar to the values obtained by all four laboratories: mean (standard deviation) cobalt ranged from 3.54µg/l (3.17) in laboratory A to 4.35µg/l (4.13) in laboratory D, and chromium ranged from 7.76µg/l (9.50) in laboratory B to 9.55µg/l (9.16) in laboratory A. When testing patient samples, large variations existed both between and within four laboratories accredited to perform analysis of blood metal ion concentrations. However, this was not the case when assessing commercially spiked samples which are regularly used to validate laboratory testing. This is of great clinical concern and could lead clinicians to either recommend unnecessary revision or delay surgery, with both having the potential to adversely affect patient outcomes. It is recommended that laboratories use patient samples to assess the accuracy and reproducibility of the analyses performed. This may also assist in explaining the variations observed in this study.
Metal-metal surface replacement (MoMSRA) is increasingly used in the young. Systemic metal ion release and its effects cause concern. Do metal ions cross the placenta in pregnant women with potential mutagenic effects? The hypothesis is that metal ions pass freely through the placenta and there is no difference in maternal and cord metal levels. This is a controlled cross-sectional study of women with MoMSRA. (n=25, mean age 32years, implantation 60months, 3 bilateral). The control group were 24 subjects with no metallic implant and not receiving cobalt/chromium supplements, mean age 31years. No patient was known to have renal failure. Whole blood specimens were obtained before delivery/ fluid-infusion and Cord blood specimens immediately after delivery. Cobalt and chromium were detectable in all specimens in both cohorts. In the control group, the difference between maternal and cord levels was only 5 to 7% indicating free passage. Study group cord levels were significantly lower than maternal cobalt, p<0.05 and chromium p<0.0001 thus rejecting the null hypothesis. The differences between maternal and cord metal ions in the controls indicate that normally the placenta allows an almost free passage of metal ions. The relative levels of metal ions in the maternal and cord blood in the study group reveal that the placenta exerts a modulatory effect on metal transfer.
Kinematics of the knee change during the full range of flexion [1]. The lateral femoral condyle (LFC) rolls back progressively through the entire range of flexion. The medial femoral condyle (MFC) does not move back during the first 110 degrees, but from 110 to 160 degrees it moves back by 10mm. This dual arc makes anatomical knee design a challenging task. In medial rotation, during flexion, the MFC stays in place, but the LFC moves forward in extension and backward in flexion. In lateral rotation the LFC stays still while the MFC moves back and forward in flexion and extension. During central rotation both condyles move reciprocally. However the knee is stable against an anteriorly or posteriorly directed force. It is important that all these degrees of freedom and stability are reproduced in total knee replacement (TKR) design. Furthermore, the two femoral condyles together form a spiral. Like the threads of a screw in a nut they allow medio-lateral translation of the femur [2] in the tibial reference frame. During flexion the knee centre moves laterally nearly 20% of the width of the tibial plateau and in extension the femur translates medially. This medio-lateral translation occurs in the natural normal knee joint. This has special significance in knee design because the natural femur (along with the trochlea) moves laterally in flexion, allowing the patella to be sited laterally, while most regular TKRs drive the patella medially. In order to test this anomaly we studied patellar maltracking in vivo and in cadavers.
This has application to total knee replacement design. Unless the spiral design is incorporated in the condyles, patellar maltracking is inevitable and is likely to cause lateral knee pain and stiffness post-operatively.
The modern era of hip resurfacing was initiated over two decades ago to address the poor results of existing hip replacement devices in young patients. High failure rates have been reported with certain resurfacings. This is a 1 to 17-year review of a single surgeon series of resurfacings in patients under the age of 50 years. Between July 1997 and June 2014, 3627 hip resurfacing arthroplasties were implanted at our Centre in 2878 patients using a posterior approach. Of these 863 patients (1063 hips, 754 in men and 309 in women) were under the age of 50 years at the time of operation. They were followed up with postal questionnaires for up to 10 years through independent Outcomes Centres initially and are currently followed up by our own Centre. 18 patients (24 hips) died 5.9 (0.02 – 11) years after surgery due to unrelated causes, including one patient (1 hip) who was revised and died 5 years after revision. Mean follow-up is 11.9 years (0.8 to 17.8 years). There were 22 revisions altogether (2.1%) at a mean of 6.2 years (0.01 to 14.6 years) including one malpositioned cup in a female patient with developmental dysplasia who dislocated post-operatively and had to be repositioned. 9 hips failed from collapse of the femoral-head and 3 hips from femoral-neck fractures, giving rise to 12 femoral failures in all. There were six deep infections and three bearing-related failures including one pseudotumour, one for osteolysis and one for unexplained pain with neither metallosis nor pseudotumour. With revision for any reason as the end-point Kaplan-Meier survival analysis showed 98.9%, 98.6% and 97.2% implant survival at 5, 10 and 17 years. Men had better survival (99.1% and 98.1% at 10 and 17 years respectively) than women (97.3% and 95.3%). 17-year cumulative revision rates were higher in patients with a pre-operative diagnosis of dysplasia (6.1%) and AVN (7.6%) compared to all other diagnoses combined (1.5%). Patients with osteoarthritis had the best results (99.5%, 99.3%, 98.4% at 5, 10 and 17 years respectively). Our study shows that resurfacing arthroplasty is a viable option for hip arthritis in the young with a low incidence of wear-related failures in the long-term.
Little is known about variations in blood metal ions following bearing exchange for poorly functioning metal-on-metal hip replacements (MoMHRs). This study aimed to determine the changes that occur in blood and urine metal ion concentrations following MoMHR revision. Between 2005–2012, a single-centre prospective cohort study was undertaken of patients with large-diameter MoMHRs and high blood metal ions requiring revision. Whole blood and urine were collected both pre-revision and post-revision for metal ion analysis.Introduction
Methods
We report a 12- to 15-year implant survival assessment
of a prospective single-surgeon series of Birmingham Hip Resurfacings
(BHRs). The earliest 1000 consecutive BHRs including 288 women (335
hips) and 598 men (665 hips) of all ages and diagnoses with no exclusions
were prospectively followed-up with postal questionnaires, of whom
the first 402 BHRs (350 patients) also had clinical and radiological
review. Mean follow-up was 13.7 years (12.3 to 15.3). In total, 59 patients
(68 hips) died 0.7 to 12.6 years following surgery from unrelated
causes. There were 38 revisions, 0.1 to 13.9 years (median 8.7)
following operation, including 17 femoral failures (1.7%) and seven
each of infections, soft-tissue reactions and other causes. With
revision for any reason as the end-point Kaplan–Meier survival analysis
showed 97.4% (95% confidence interval (CI) 96.9 to 97.9) and 95.8%
(95% CI 95.1 to 96.5) survival at ten and 15 years, respectively.
Radiological assessment showed 11 (3.5%) femoral and 13 (4.1%) acetabular
radiolucencies which were not deemed failures and one radiological
femoral failure (0.3%). Our study shows that the performance of the BHR continues to
be good at 12- to 15-year follow-up. Men have better implant survival
(98.0%; 95% CI 97.4 to 98.6) at 15 years than women (91.5%; 95%
CI 89.8 to 93.2), and women <
60 years (90.5%; 95% CI 88.3 to
92.7) fare worse than others. Hip dysplasia and osteonecrosis are
risk factors for failure. Patients under 50 years with osteoarthritis
fare best (99.4%; 95% CI 98.8 to 100 survival at 15 years), with
no failures in men in this group. Cite this article:
Metal-metal surface replacement (MoMSRA) continues to be used in young women. Systemic metal ion release and its effects cause concern. Do metal ions crossing the placenta in pregnant women have potential mutagenic effects? The hypothesis is that metal ions pass freely through the placenta and there is no difference in maternal and cord metal levels. This is a controlled cross-sectional study of women with MoMSRA. (n = 25, 3 bilateral, mean age 32 years, time from implantation to delivery 60 months). The control group consisted of 24 subjects, mean age 31 years, with no metallic implant and not receiving cobalt/chromium supplements. No patient was known to have renal failure. Whole blood specimens were obtained before delivery and before any infusion or transfusion, and cord blood specimens immediately after delivery.Introduction
Methods
Large diameter metal-on-metal hip arthroplasty (LDMMTHA) provides benefits of reduced dislocation rates and low wear. The use of modular systems allows better restoration of hip biomechanics. There have been reports of modular LDMMTHAs with tapered sleeves generating excessively high metal ions, due to possible mismatch between the titanium stem and the cobalt-chrome sleeve and the dual Morse tapers involved. We evaluated metal ion levels in LDMMTHA patients with and without a cobalt-chrome (CoCr) tapered sleeve. A cross-sectional series of 91 patients with proximal porous titanium alloy stem LDMMTHA with identical design CoCr bearings, attending a 1 to 2-year review were assessed with routine clinical and radiographic examinations, hip scores and metal ion analysis. Of these 65 had a single Morse taper between monoblock CoCr heads and the stems. Twentysix had a tapered cobalt-chrome sleeve in addition, with the resultant dual taper. Mean bearing diameter was 46 mm in both groups and mean age was 58 years in the monoblocks and 66 years in the tapered sleeve group.Introduction
Methods
Modern metal-on-metal bearing resurfacings have been in use for nearly two decades. Local and systemic metal ion exposure continues to cause concern. We could not find a prospective metal ion study in such patients with a 10-year follow-up. This is the first ten year prospective study of metal ion levels in blood and their release in urine following hybrid fixed metal-on-metal surface arthroplasty. Twenty six patients were included in an ongoing longitudinal metal ion study of patients with unilateral metal-on-metal hip resurfacings. Three of them were excluded due to subsequent contralateral resurfacing and one has relocated abroad. Cobalt and chromium levels were assessed in 12 hour urine collections before and periodically after operation (5 days to 10 years) using high resolution plasma mass spectrometry. Mean age at operation was 53 years and mean BMI 27.9.Introduction
Methods
This is a retrospective review of the incidence of deep venous thrombosis (DVT) in 679 consecutive unilateral primary hip arthroplasty procedures performed between January 2007 and December 2010 managed with no anticoagulants. Mean age at operation was 58 years. Mean BMI was 26. The prophylaxis regimen included hypotensive epidural anesthesia, compression stockings, intermittent calf compression, early mobilization and an antiplatelet agent. 562 hybrid hip resurfacing procedures and 117 uncemented THRs, all performed through a posterior incision were included. Doppler ultrasound screening for DVT was performed in all patients between the fourth and sixth post-operative days. Patients were reviewed clinicoradiologically 6 to 10 weeks after operation and with a postal questionnaire at the end of 12 weeks to detect symptomatic VTE incidence following discharge. 14 patients with pre-existent VTE, coagulation disorders or cardiac problems requiring anticoagulant usage were excluded.Introduction
Methods
High early failure rates have been reported with certain metal-metal surface arthroplasties and good results have been reported with others. This is a minimum 10-year review of the first 1000 consecutive resurfacings including all ages and diagnoses from one centre. The first 1000 surface arthroplasties (892 patients) were followed-up with postal questionnaires. Of these the first 402 hips (350 patients) were also invited for a clinico-radiological review. 54 patients (63 hips) died 6.7 years (0.7–12.6) later due to unrelated causes. Mean follow-up is 12.2 years (range 10.8–13.7). Radiographs were assessed independently by a senior musculoskeletal radiologist.Introduction
Methods
Wear and corrosion of metal-on-metal (MM) bearings releases (a) soluble metal ions which collect locally and pass into the systemic circulation and (b) insoluble particles which undergo local deposition and lymphoreticular dissemination. Debris-related failures from osteolysis, metallosis and pseudotumours warrants revision of these MM bearing devices to non-MM bearing arthroplasties with the expectation that both the systemic and local effects will be reversed with time since the source of metal ion release is removed. The purpose of the present study is to determine (a) whether metal ion levels in blood and urine decrease after revision of a MM bearing arthroplasty to a non-MM bearing device and (b) the rate at which this decrease is effected. Blood and urine levels of cobalt and chromium ions are studied prospectively over two years in 15 patients whose MM resurfacings were revised to cross-linked polyethylene containing total hip replacements (THRs). Specimen collection was started before and periodically after the revision at 2, 4 and 6 days and 2 months, 6, 12 and 24 months after operation. None of the patients had other MM devices or compromised renal function.Introduction
Methods
Hip simulator studies show that metal-on-metal bearing wear can be reduced by reducing the diametral clearance of the bearing. We present the six-year follow-up results of a prospective clinico-radiological and metal ion study in patients with a low clearance metal-metal surface arthroplasty. The results are compared to published results of similar design bearings with conventional clearance. Twentysix male patients (mean age 55 years, mean BMI 26) who received a 50 mm bearing resurfacing (radial clearance 50μm) were included in an ongoing clinico-radiological and metal ion study. Urine/blood specimens were obtained before and periodically after hip resurfacing. Patients were also assessed with Oxford Hip Scores and Harris Hip Score questionnaires. Two hips were excluded during follow-up, one for revision and another for contralateral hip arthroplasty.Introduction
Methods
The results of the Birmingham Hip Resurfacing (BHR) device in several series reveal that the predominant mode of failure is femoral neck fracture or femoral head collapse and that careful patient selection and precise operative technique are vital to the success of this procedure. In this report we consider the results of BHR in patients with severe arthritis secondary to femoral head AVN. This was a single-surgeon consecutive series of BHRs with a minimum follow-up of 5 years. Fifty-nine patients with Ficat-Arlet grade III or IV femoral head AVN (66 hips) and treated with BHRs at a mean age of 43.9 years (range 19 to 67.7 years) were followed up for 5.4 to 9.6 years (mean 7.1 years). No patient died and none was lost to follow-up. Revision for any reason was the end-point and unrevised patients were assessed with Oxford hip scores. They were also reviewed clinically and with AP and lateral radiographs.Introduction
Methods
Large diameter metal-metal total hip replacements (MM THRs) offer the advantages of low wear and low dislocation risk and are being increasingly used in high-demand patients whose bone quality rules out the possibility of a hip resurfacing. However suggests that large headed MM devices may result in greater systemic metal exposure compared to small diameter bearings. This raises fresh concerns of elevated systemic metal levels. Whole blood concentrations and daily output of cobalt and chromium in 28 patients with unilateral large diameter MM THRs (42 to 54mm bearings) were studied at 1-year follow-up. These were compared with the whole blood levels in 20 patients at 1 year and daily output of metal ions in 28 patients with 28mm MM THRs at 1 to 3 years. Both bearings are made of high carbon cobalt-chrome alloy, the larger bearing is as-cast alloy and the smaller is wrought alloy. High resolution inductively coupled plasma mass spectrometry was used for analysis. None of the patients had other metal devices or compromised renal function. They had either a cemented polished tapered stainless steel stem or a cementless porous ingrowth titanium alloy stem.Introduction
Methods
Secondary osteoarthritis in a dysplastic hip is a surgical challenge. Severe leg length discrepancies and torsional deformities add to the problem of inadequate bony support available for the socket. Furthermore, many of these patients are young and wish to remain active, thereby jeopardising the long-term survival of any arthroplasty device. For such severely dysplastic hips, the Birmingham Hip Resurfacing (BHR) device provides the option of a dysplasia component, a hydroxyapatite-coated porous uncemented socket with two lugs to engage neutralisation screws for supplementary fixation into the solid bone of the ilium more medially. The gap between the superolateral surface of the socket component and the false acetabulum is filled with impacted bone graft. One hundred and thirteen consecutive dysplasia BHRs performed by the senior author (DJWM) for the treatment of severely arthritic hips with Crowe grade II and III dysplasia between 1997 and 2000 have been reviewed at a minimum five year follow-up. There were 106 patients (59M and 47F). Eighty of the 113 hips were old CDH or DDH, 29 were destructive primary or secondary arthritis with wandering acetabulae and four were old fracture dislocations of the hip. Mean age at operation was 47.5 years (range 21 to 68 years – thirty-six men and forty-four women were below the age of 55 years). There were two failures (1.8%) out of the 113 hips at a mean follow-up of 6.5 years (range 5 to 8.3 years). One hip failed with a femoral neck fracture nine days after the operation and another failed due to deep infection at 3.3 years.Introduction
Methods and results
Evidence with respect to conventional hip arthroplasties suggests that device wear is related to patient activity rather than duration of usage. Activity level questionnaires appear to suggest that subjects with resurfacing arthroplasties continue to remain active after the procedure. However there is a paucity of objective evidence relating to the step rates of these patients in their daily lives and its effect on metal ions generated. The aim of this investigation is to assess
the activity levels of hip resurfacing patients as follow up progresses and if there is any correlation between activity and metal ions generated. Twenty-five consecutive male patients (average age 56 years) who underwent a unilateral 50 mm diameter hip resurfacing carried out by a single surgeon (DJWM) were recruited after informed consent. Patient step activity (Step Activity Monitor, SAM, Cymatech. Seattle WA, USA) was recorded at 1, 2, and 4-year follow-up stages and at the same time patient whole blood samples were collected and analysed using High Resolution Inductively Coupled Mass Spectroscopy (HR-ICPMS). All patients in this study had well functioning hips at the four year follow up stage. All femoral components implanted were within the desired range of neutral to 10°. The mean acetabular component inclination angle was 42° (33° – 55°). Patient overall step activity remains unchanged up to the 4-year follow-up period. At one year follow up, the whole blood cobalt and chromium concentrations show no correlation to mean number of steps taken per day by each patient (r2=0.02). The correlation between whole blood cobalt and chromium concentration versus a function of body weight and peak index is not significant (r2=0.11). This study provides objective evidence of the activity rates of patients at different stages of follow-up after a MoM surface replacement arthroplasty. It should be emphasised that the walking speeds of these patients on average was significantly slower than 1 Hz, which is generally used in laboratory hip simulator studies.
This is the first six-year report of a prospective longitudinal study of daily output of cobalt and chromium in urine and their levels in blood following hybrid metal-on-metal surface arthroplasty. Urine and whole blood specimens were analyzed before and periodically after hip resurfacing in 26 male patients after informed consent (mean age 52.9 years, mean BMI 27.9). Two of these patients have undergone contralateral hip resurfacings for progressive pain from end-stage arthritis and had to be excluded. All patients were found to have well-functioning resurfacings at 6-year follow-up. No patient complained of persistent pain or disability. The median 6-year Oxford hip score was 12. Urine chromium and cobalt at six years were 3.9 and 7.8 μg/24 hrs and blood levels were 1.11 and 1.17μg/l respectively. Both urine and blood levels show a statistically significant early increase reaching a peak six months to one year postoperatively followed by a steady decrease over the following five years, although the individual reductions are not statistically significant, except for blood chromium where the 4 and 6 year levels were significantly lower than the 1-year level. Elevated systemic metal exposure following MM bearing arthroplasty continues to cause concern. Our results show that metal release in these bearings shows a reducing trend after an initial peak dispelling the fear that a steady build-up of in vivo metal occurs with progressively increasing blood levels. However, as long as the significance of these elevated levels remains unknown, the need for continued vigilance persists.
It has been suggested that metal ion level elevations in certain bilateral MM bearing arthroplasties were overwhelming the renal threshold for metal excretion leading to systemic build-up of metal ions above the expected levels. In order to investigate this we studied renal concentrating efficacy through concurrent specimens of urine and whole blood over a range of metal levels. Concurrent specimens from 305 unselected patients were obtained. They include preoperative patients (76) and those with unilateral and bilateral hip arthroplasties (229) through to ten years after operation. 39 pre-operative specimens and 4 follow-up specimens had blood levels at or below the detection limit for cobalt or chromium and were excluded. The ratio of urine to whole blood concentration was 0.78 in the pre-operative patients. In patients with MM arthroplasties the different ratios in patients increased (from 3.1 to 9.2) with increasing urine concentrations. The ratio of urine cobalt concentration to blood cobalt concentration is a measure of renal concentrating efficacy. Amongst pre-operative controls, this ratio is 0.78, indicating that there is renal conservation of cobalt. In terms of cobalt, these patients’ urine was dilute in comparison to whole blood. In patients with MM bearings, the ratio went up to 4.8 indicating that the kidneys were now actively excreting against a concentration gradient in an attempt to maintain internal milieu. If renal threshold was being breached at higher levels, then the ratio should progressively fall at higher concentrations. The trend in this experiment shows quite the contrary effect and the ratio reached 9.2 in those with urine cobalt >
15 μg/l, demonstrating that renal clearance efficiency holds up even against this steep gradient and that the threshold is not breached within clinically relevant levels.
The mean difference in cord chromium between the study and control groups is not statistically significant (p >
0.05), although cord cobalt in the study group is significantly higher (p <
0.01) than that in controls. Whilst there is a four-fold elevation of maternal cobalt in the study patients and an almost 7-fold increase in maternal chromium levels as compared to the control group, the elevation in the cord cobalt and chromium in the study group are smaller.
Some authors have suggested that metal wear in patients with well-functioning MM bearings occurs only during the run-in wear phase and that continued corrosion of metal particles released during that period is responsible for metal level elevation later on. However the reducing trend in the later phase following revision in this study suggests that metal ion elevation from corrosion is not sustained indefinitely and therefore cannot by itself account for the persistent elevation of systemic metal levels throughout. Bearing wear continues to occur throughout bearing life.
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.
Second-generation metal-on-metal bearings were introduced as a response to the considerable incidence of wear-induced failures associated with conventional replacements, especially in young patients. We present the results at ten years of a consecutive series of patients treated using a metal-on-metal hip resurfacing. A distinct feature of the bearings used in our series was that they had been subjected to double-heat treatments during the post-casting phase of their manufacture. In the past these bearings had not been subjected to thermal treatments, making this a unique metal-on-metal bearing which had not been used before in clinical practice. We report the outcome of 184 consecutive hips (160 patients) treated using a hybrid-fixed metal-on-metal hip resurfacing during 1996. Patients were invited for a clinicoradiological follow-up at a minimum of ten years. The Oxford hip score and anteroposterior and lateral radiographs were obtained. The mean age at operation was 54 years (21 to 75). A series of 107 consecutive hips (99 patients) who received the same prosthesis, but subjected to a single thermal treatment after being cast, between March 1994 and December 1995, were used as a control group for comparison. In the 1994 to 1995 group seven patients (seven hips) died from unrelated causes and there were four revisions (4%) for osteolysis and aseptic loosening. In the 1996 group nine patients died at a mean of 6.9 years after operation because of unrelated causes. There were 30 revisions (16%) at a mean of 7.3 years (1.2 to 10.9), one for infection at 1.2 years and 29 for osteolysis and aseptic loosening. Furthermore, in the latter group there were radiological signs of failure in 27 (24%) of the 111 surviving hips. The magnitude of the problem of osteolysis and aseptic loosening in the 1996 cohort did not become obvious until five years after the operation. Our results indicate that double-heat treatments of metal-on-metal bearings can lead to an increased incidence of wear-induced osteolysis.
We describe the findings at six years in an ongoing prospective clinicoradiological and metal ion study in a cohort of 26 consecutive male patients with unilateral Birmingham Hip Resurfacing arthroplasties with one of two femoral head sizes (50 mm and 54 mm). Their mean age was 52.9 years (29 to 67). We have previously shown an early increase in the 24-hour urinary excretion of metal ions, reaching a peak at six months (cobalt) and one year (chromium) after operation. Subsequently there is a decreasing trend in excretion of both cobalt and chromium. The levels of cobalt and chromium in whole blood also show a significant increase at one year, followed by a decreasing trend until the sixth year.
If run-in wear is the only source of sustained metal release, then replacing the bearing with a non-MM bearing should not make a difference to metal release in patients and elevated levels should continue to persist even after such a revision. In order to verify this we studied metal release in patients who underwent revision of a MM bearing to a non-MM bearing after revision.
An earlier study (Clarke et al JBJS(Br) 2003) suggests that smaller bearings generate less wear. In that study bearings with different metallurgy and wear properties were grouped together, a potential confounding factor. The present study does not suffer from that error and our findings do not support the view that a larger bearing diameter leads to either an increase or decrease in metal ion generation.
Dislocation rates in large headed metal-on-metal resurfacings are extremely low. However, many patients are unsuitable for resurfacing and need a replacement. In such cases, it is attractive to transfer the large-headed metal-metal bearing advantage to replacement arthroplasty in order to reduce wear and dislocation rates. Does large diameter metal-metal total hip replacement really reduce the early dislocation rate?
Age at operation ranged from 37 to 83 years. Thirty patients were 55 years or under, eighty one were 56 – 65 years and ninety five were over 65 years. There were 122 females and 67 males. Posterior approach was used in all.
The extremely low failure rate in the medium term proves the suitability of resurfacing in young active patients. However, caution needs to be exercised until long term results are available.
There is sufficient evidence in this study to prove that metal ions do cross the placenta. There is therefore a continuing need for vigilance on the possible effects on the offspring born to patients with metal-metal devices.
Old age, osteopaenia, alcohol abuse, and large cysts are risk factors for fractures. It has been suggested that performing a bilateral resurfacing puts the first side at risk of fracture from the force used in implanting the second resurfacing. Is this a true risk or a sampling error?
The low incidence of fractures (2/382, 0.5%) in this bilateral resurfacing series does not support the view that there is an increased risk of fracture from a bilateral procedure.
Bland-Altman analysis (Figure 1A) shows the limits of agreement between serum and WB are unacceptably wide (1.7 to -5.1 for chromium) suggesting poor agreement.
The dysplasia cup, which was devised as an adjunct to the Birmingham Hip Resurfacing system, has a hydroxyapatite-coated porous surface and two supplementary neutralisation screws to provide stable primary fixation, permit early weight-bearing, and allow incorporation of morcellised autograft without the need for structural bone grafting. A total of 110 consecutive dysplasia resurfacing arthroplasties in 103 patients (55 men and 48 women) performed between 1997 and 2000 was reviewed with a minimum follow-up of six years. The mean age at operation was 47.2 years (21 to 62) and 104 hips (94%) were Crowe grade II or III. During the mean follow-up of 7.8 years (6 to 9.6), three hips (2.7%) were converted to a total hip replacement at a mean of 3.9 years (2 months to 8.1 years), giving a cumulative survival of 95.2% at nine years (95% confidence interval 89 to 100). The revisions were due to a fracture of the femoral neck, a collapse of the femoral head and a deep infection. There was no aseptic loosening or osteolysis of the acetabular component associated with either of the revisions performed for failure of the femoral component. No patient is awaiting a revision. The median Oxford hip score in 98 patients with surviving hips at the final review was 13 and the 10th and the 90th percentiles were 12 and 23, respectively.
We report a retrospective review of the incidence of venous thromboembolism in 463 consecutive patients who underwent primary total hip arthroplasty (487 procedures). Treatment included both total hip replacement and hip resurfacing, and the patients were managed without anticoagulants. The thromboprophylaxis regimen included an antiplatelet agent, generally aspirin, hypotensive epidural anaesthesia, elastic compression stockings and early mobilisation. In 258 of these procedures (244 patients) performed in 2005 (cohort A) mechanical compression devices were not used, whereas in 229 (219 patients) performed during 2006 (cohort B) bilateral intermittent pneumatic calf compression was used. All operations were performed through a posterior mini-incision approach. Patients who required anticoagulation for pre-existing medical problems and those undergoing revision arthroplasty were excluded. Doppler ultrasonographic screening for deep-vein thrombosis was performed in all patients between the fourth and sixth post-operative days. All patients were reviewed at a follow-up clinic six to ten weeks after the operation. In addition, reponse to a questionnaire was obtained at the end of 12 weeks post-operatively. No symptomatic calf or above-knee deep-vein thrombosis or pulmonary embolism occurred. In 25 patients in cohort A (10.2%) and in ten patients in cohort B (4.6%) asymptomatic calf deep-vein thromboses were detected ultrasonographically. This difference was statistically significant (p = 0.03). The regimen followed by cohort B offers the prospect of a low incidence of venous thromboembolism without subjecting patients to the higher risk of bleeding associated with anticoagulant use.
Metal ions generated from joint replacements are a cause for concern. There is no consensus on the best surrogate measure of metal ion exposure. This study investigates whether serum and whole blood concentrations can be used interchangeably to report results of cobalt and chromium ion concentrations. Concentrations of serum and whole blood were analysed in 262 concurrent specimens using high resolution inductively-coupled plasma mass-spectrometry. The agreement was assessed with normalised scatterplots, mean difference and the Bland and Altman limits of agreement. The wide variability seen in the normalised scatterplots, in the Bland and Altman plots and the statistically significant mean differences between serum and whole blood concentrations suggest that they cannot be used interchangeably. A bias was demonstrated for both ions in the Bland-Altman plots. Regression analysis provided a possible conversion factor of 0.71 for cobalt and 0.48 for chromium. However, even when the correction factors were applied, the limits of agreement were greater than ±67% for cobalt and greater than ±85% for chromium, suggesting that serum and whole blood cannot be used interconvertibly. This suggests that serum metal concentrations are not useful as a surrogate measure of systemic metal ion exposure.
Metal-on-metal bearings are being increasingly used in young patients. The potential adverse effects of systemic metal ion elevation are the subject of ongoing investigation. The purpose of this study was to investigate whether cobalt and chromium ions cross the placenta of pregnant women with a metal-on-metal hip resurfacing and reach the developing fetus. Whole blood levels were estimated using high-resolution inductively-coupled plasma mass spectrometry. Our findings showed that cobalt and chromium are able to cross the placenta in the study patients with metal-on-metal hip resurfacings and in control subjects without any metal implants. In the study group the mean concentrations of cobalt and chromium in the maternal blood were 1.39 μg/l (0.55 to 2.55) and 1.28 μg/l (0.52 to 2.39), respectively. The mean umbilical cord blood concentrations of cobalt and chromium were comparatively lower, at 0.839 μg/l (0.42 to 1.75) and 0.378 μg/l (0.14 to 1.03), respectively, and this difference was significant with respect to chromium (p <
0.05). In the control group, the mean concentrations of cobalt and chromium in the maternal blood were 0.341 μg/l (0.18 to 0.54) and 0.199 μg/l (0.12 to 0.33), and in the umbilical cord blood they were 0.336 μg/l (0.17 to 0.5) and 0.194 μg/l (0.11 to 0.56), respectively. The differences between the maternal and umbilical cord blood levels in the controls were marginal, and not statistically significant (p >
0.05). The mean cord blood level of cobalt in the study patients was significantly greater than that in the control group (p <
0.01). Although the mean umbilical cord blood chromium level was nearly twice as high in the study patients (0.378 μg/l) as in the controls (0.1934 μg/l), this difference was not statistically significant. (p >
0.05) The transplacental transfer rate was in excess of 95% in the controls for both metals, but only 29% for chromium and 60% for cobalt in study patients, suggesting that the placenta exerts a modulatory effect on the rate of metal ion transfer.
This is a longitudinal study of the daily urinary output and the concentrations in whole blood of cobalt and chromium in patients with metal-on-metal resurfacings over a period of four years. Twelve-hour urine collections and whole blood specimens were collected before and periodically after a Birmingham hip resurfacing in 26 patients. All ion analyses were carried out using a high-resolution inductively-coupled plasma mass spectrometer. Clinical and radiological assessment, hip function scoring and activity level assessment revealed excellent hip function. There was a significant early increase in urinary metal output, reaching a peak at six months for cobalt and one year for chromium post-operatively. There was thereafter a steady decrease in the median urinary output of cobalt over the following three years, although the differences are not statistically significant. The mean whole blood levels of cobalt and chromium also showed a significant increase between the pre-operative and one-year post-operative periods. The blood levels then decreased to a lower level at four years, compared with the one-year levels. This late reduction was statistically significant for chromium but not for cobalt. The effects of systemic metal ion exposure in patients with metal-on-metal resurfacing arthroplasties continue to be a matter of concern. The levels in this study provide a baseline against which the
The recent resurgence in the use of metal-on-metal bearings has led to fresh concerns over metal wear and elevated systemic levels of metal ions. In order to establish if bearing diameter influences the release of metal ions, we compared the whole blood levels of cobalt and chromium (at one year) and the urinary cobalt and chromium output (at one to three and four to six years) following either a 50 mm or 54 mm Birmingham hip resurfacing or a 28 mm Metasul total hip replacement. The whole blood concentrations and daily output of cobalt and chromium in these time periods for both bearings were in the same range and without significant difference.
Hip Resurfacing has always been an attractive concept for the treatment of hip arthritis in younger patients. Introduction of modern metal-on-metal hip resurfacing in 1991 in Birmingham, UK made this concept a reality. In the early years, resurfacings were used only by a few experienced surgeons. From 1997, Birmingham Hip Resurfacings (BHRs) are being widely used in younger and more active patients. A breakdown of the ages at operation in the regional NHS hospital in Birmingham during the period April 1999 to March 2004 show that the mean age of metal-metal resurfacings is 51 years and the mean age of total hip replacements is 70 years. At a 3.7 to 10.8 year follow-up (mean follow-up 5.8 years), the cumulative survival rate of metal-metal resurfacing in young active patients with osteoarthritis is 99.8%. In the long term, none of these patients were constrained to change their occupational or leisure activities as a result of the procedure. The overall revision rate of BHRs in all ages and all diagnoses is also very low (19 out of 2167 [0.88%] with a maximum follow-up of 7.5 years). Improvements in instrumentation and a minimally invasive approach developed by the senior author have made this successful device even more attractive. Although objective evidence does not support the fact that the longer approach was any more invasive than the minimal route, patient feedback shows that it is very popular with them. While minimal approach is indeed appealing, it has a steep learning curve. In the early phase of this curve, care should be taken to avoid the potential risk of suboptimal component placement which can adversely affect long-term outcome. It is true that metal-metal bearings are associated with elevated metal ion levels. In vitro studies of BHRs show that they have a period of early run-in wear. This is not sustained in the longer term. These findings are found to hold true in vivo as well, in our studies of 24- hour cobalt output and whole blood metal ion levels. Epidemiological studies show that historic metal-metal bearings are not associated with carcinogenic effects in the long-term. Metal ion levels in patients with BHRs are in the same range as the levels found in those with historic metal-metal total hip replacements.