The effectiveness of blood metal ions in identifying bilateral metal-on-metal total hip arthroplasty patients at risk of adverse reactions to metal debris.

We investigated whether blood metal ions could effectively identify bilateral metal-on-metal total hip arthroplasty (THA) patients at risk of adverse reactions to metal debris (ARMD). Whole blood metal ions were sampled in 50 patients with bilateral 36mm Corail-Pinnacle THAs. Patients were divided into ARMD (n=10) and non-ARMD groups (n=40), with optimal ion thresholds for identifying ARMD determined using receiver operating characteristic analysis. Maximum cobalt or chromium produced the highest area under the curve (71.8%). The optimal ion threshold for distinguishing between patients with and without ARMD was 4.0µg/l (90.0%=sensitivity, 65.0%=specificity, 39.1%=positive predictive value, 96.3%=negative predictive value). Fixed regulatory authority thresholds missed more patients with ARMD (10%-12% missed) compared to our threshold (2% missed). Bilateral THA patients with blood metal ions below our threshold were at low-risk of ARMD. Compared to currently recommended fixed authority thresholds, our threshold appears preferable for managing patients with these particular implants.

Birmingham Hip Resurfacing: A Single Surgeon Series Reported at a Minimum of 10 Years Follow-Up.

We report outcomes on 120 Birmingham Hip Resurfacings (BHRs) (mean age 50 years) at a minimum of ten-years follow-up. Cases were performed by one surgeon and included his learning curve. Six hips were revised, with no revisions for infection, dislocation, or adverse reaction to metal debris. Ten-year survival was 94.2% (95% confidence interval (CI) 88.8%-98.7%) for all revisions and 96.1% (95% CI 91.5%-99.8%) for revisions for aseptic loosening. Gender (P = 0.463) and head size (P = 0.114) did not affect revision risk. Mean post-operative Harris hip score was 84.0. Contrary to previous independent reports, good outcomes into the second decade were achieved with the BHR in both men and women. Longer term follow-up will confirm whether these promising outcomes in women continue.

Influence of implant design on blood metal ion concentrations in metal-on-metal total hip replacement patients.

PURPOSE: Most factors considered to affect blood metal ions following metal-on-metal hip replacement are based on hip resurfacing patients. The study aims were to determine which factors affect blood metal ion concentrations following metal-on-metal total hip replacement (MoM THR). METHODS: All unilateral MoM THR patients at one centre with whole-blood cobalt (Co) and chromium (Cr) concentrations measured up to May 2013 were included. Blood sampling was at a mean of 4.5 years (range 1.1-11.8 years) postoperatively. RESULTS: Of 496 patients (mean age 59.1 years; 52.8% male), blood metal ions >7 µg/l were observed in 9.7% (n = 48). Large femoral head sizes (≥38 mm) had significantly higher (p < 0.0001) blood metal ions than smaller sizes (28/36 mm). Corail-Pinnacle implants produced significantly lower blood metal ions compared to other implant designs (p < 0.01 Co and Cr). Univariate linear regression demonstrated the only significant predictors of both blood Co and Cr concentrations were femoral head size (R(2) = 8.6% Co and R(2) = 3.3% Cr, both p < 0.0001) and implant design (R(2) = 8.8%, p = 0.005 Co and R(2) = 5.1%, p = 0.003 Cr). When the three THR implant design groups (Corail-Pinnacle, Synergy, Other) were analysed separately, femoral head size no longer significantly affected blood metal ions in any of the three implant design groups. CONCLUSIONS: Implant design was the most important factor affecting blood metal ion concentrations. We recommend the regularity of follow-up be tailored to survival rates of various MoM THR designs rather than according to femoral head size.

Survival and functional outcome of the Birmingham Hip Resurfacing system in patients aged 65 and older at up to ten years of follow-up.

PURPOSE: Limited evidence exists regarding the outcomes of hip resurfacing in elderly patients. The primary study aims were to determine the survival and functional outcome following Birmingham Hip Resurfacing (BHR) in patients ≥65 years at up to ten years of follow-up. Secondary aims were to explore factors affecting survival and functional outcome. METHODS: Between 1997 and 2012, data were prospectively collected on 180 BHR (162 patients; mean age 69.2 years; 62 % male) implanted by one designing surgeon. Mean follow-up was six (range one to 14.4) years with no loss to follow-up. Outcomes of interest were implant survival, functional outcome [Oxford Hip Score (OHS)] and radiological evidence of implant failure. RESULTS: Three hips were revised, giving an overall cumulative survival of 96.4 % [95 % confidence interval (CI) 90.3-100] at ten years. Survival of 111 male BHR was 98.9 % (95 % CI 94.8-100) at ten years (one revision) compared with 91.9 % (95 % CI 77.0-100) in 69 female BHR (two revisions). Survival was affected by age (p = 0.014) and femoral head size (p = 0.024) but not by gender (p = 0.079). Median pre-operative OHS was 50.0 % [interquartile range (IQR) 37.5-68.8], improving to 4.4 % (IQR 0-10.4) postoperatively. Men had significantly better postoperative OHSs compared with women (median male OHS 2.1 % versus 6.3 % female OHS; p = 0.021). CONCLUSIONS: Good survival and functional outcomes were achieved with the BHR at ten years in men and women ≥65 years. Despite registry findings to the contrary, age alone should not be a contraindication for hip resurfacing in centres with expertise in this procedure.

Femoral neck fracture after Birmingham Hip Resurfacing Arthroplasty: prevalence, time to fracture, and outcome after revision.

A consecutive cohort of 3076 Birmingham Hip Resurfacings from a single institution was analyzed. The prevalence of femoral neck fracture, the time to fracture, and the outcome after revision were investigated. Fractures occurred in 34 hips (prevalence, 1.1%). Median time to fracture was 0.27 year (range, 0.014-11.2 years). Mean operation time for revision was 59 minutes, and 71% underwent isolated femoral component revision. At a mean follow-up of 5.5 years since revision, 3 patients required re-revision (2 aseptic loosening, 1 for sepsis) giving a survival of 95.7% (confidence interval, 86.9%-100%) at 5 years for the revision. Median Oxford Hip Score was 12.5% (interquartile range, 3.2%-32.3%). There were no cases of radiologic failure during follow-up. Most fractures occur early after hip resurfacing and were straightforward to revise.

Revision surgery for failed unicompartmental knee replacement: technical aspects and clinical outcome.

The aims of this study were to determine the complexity of surgery required to revise failed unicompartmental knee replacements and to evaluate the outcome following revision. Between 2000 and 2009, 494 cemented Oxford phase 3 medial unicompartmental knee replacements were implanted, with 24 (4.9%) requiring revision (mean age: 63.5 years; 58% male). Mean time to revision was 3.0 years. All cases were revised to a cemented total knee replacement, with primary components used in 67% and revision components in 33%. At a mean follow-up of 3.2 years the median Oxford knee score was 333% with one knee requiring re-revision (5-year survival 933%). Most failed unicompartmental knee replacements could be revised without the need for stemmed implants, augmentation, or bone allograft. When bone loss occured it was commonly on the tibial side. Good functional outcome for the revised unicompartmental knee replacement was achieved and was comparable to primary knee replacement.

Metal-on-metal hip resurfacing in osteonecrosis of the femoral head.

BACKGROUND: The treatment of end-stage osteonecrosis of the femoral head remains a challenge to the orthopaedic surgeon. Historically, total hip arthroplasty for this condition has been associated with poor rates of survival and function when compared with total hip arthroplasty for the treatment of osteoarthritis. The purpose of this study was to determine the medium-term clinical and radiographic results of metal-on-metal hip resurfacing arthroplasty in patients with end-stage osteonecrosis of the femoral head. METHODS: From June 1994 to March 2004, a consecutive single-surgeon series of seventy-three hip resurfacing procedures were performed in sixty patients for the treatment of end-stage osteonecrosis of the femoral head. The cohort included forty-two men (ten of whom had a bilateral resurfacing) and eighteen women (three of whom had a bilateral resurfacing). The mean age was forty-three years (range, seventeen to sixty-nine years). A clinical and radiographic review was performed. RESULTS: There were four revision operations and one planned revision of the seventy-three hips during the follow-up period. Two of these revisions were necessitated by aseptic failure of the femoral component. This represents an overall survival rate of 93.2% at a mean of 6.1 years of follow-up (range, two to twelve years). CONCLUSIONS: On the basis of this study, metal-on-metal resurfacing of the hip for osteonecrosis can be considered a safe and effective form of surgery for this group of patients. Longer-term follow-up is required to confirm the expected continued success of this form of arthroplasty in this difficult-to-treat population. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

The Effectiveness of Blood Metal Ions in Identifying Patients with Unilateral Birmingham Hip Resurfacing and Corail-Pinnacle Metal-on-Metal Hip Implants at Risk of Adverse Reactions to Metal Debris.

BACKGROUND: We investigated whether blood metal ions could effectively identify patients with metal-on-metal hip implants with two common designs (Birmingham Hip Resurfacing [BHR] and Corail-Pinnacle) who were at risk of adverse reactions to metal debris. METHODS: This single-center, prospective study involved 598 patients with unilateral hip implants (309 patients with the BHR implant and 289 patients with the Corail-Pinnacle implant) undergoing whole blood metal ion sampling at a mean time of 6.9 years. Patients were classified into two groups, one that had adverse reactions to metal debris (those who had to undergo revision for adverse reactions to metal debris or those with adverse reactions to metal debris on imaging; n = 46) and one that did not (n = 552). Three metal ion parameters (cobalt, chromium, and cobalt-chromium ratio) were compared between groups. Optimal metal ion thresholds for identifying patients with adverse reactions to metal debris were determined using receiver operating characteristic analysis. RESULTS: All ion parameters were significantly higher (p < 0.0001) in the patients who had adverse reactions to metal debris compared with those who did not. Cobalt maximized the area under the curve for patients with the BHR implant (90.5%) and those with the Corail-Pinnacle implant (79.6%). For patients with the BHR implant, the area under the curve for cobalt was significantly greater than that for the cobalt-chromium ratio (p = 0.0005), but it was not significantly greater than that for chromium (p = 0.8483). For the patients with the Corail-Pinnacle implant, the area under the curve for cobalt was significantly greater than that for chromium (p = 0.0004), but it was similar to that for the cobalt-chromium ratio (p = 0.8139). Optimal blood metal ion thresholds for identifying adverse reactions to metal debris varied between the two different implants. When using cobalt, the optimal threshold for identifying adverse reactions to metal debris was 2.15 µg/L for the BHR group and 3.57 µg/L for the Corail-Pinnacle group. These thresholds had good sensitivities (88.5% for the BHR group and 80.0% for the Corail-Pinnacle group) and specificities (84.5% for the BHR group and 76.2% for the Corail-Pinnacle group), high negative predictive values (98.8% for the BHR group and 98.1% for the Corail-Pinnacle group), and low positive predictive values (34.3% for the BHR group and 20.0% for the Corail-Pinnacle group). The authority thresholds proposed by the United States (3 µg/L and 10 µg/L) and the United Kingdom (7 µg/L) missed more patients with adverse reactions to metal debris at 2.0% to 4.7% (twelve to twenty-eight patients) compared with our implant-specific thresholds at 1.2% (seven patients missed). CONCLUSIONS: Patients who underwent metal-on-metal hip arthroplasty performed with unilateral BHR or Corail-Pinnacle implants and who had blood metal ions below our implant-specific thresholds were at low risk of adverse reactions to metal debris. These thresholds could be used to rationalize follow-up resources in asymptomatic patients. Analysis of cobalt alone is acceptable. Implant-specific thresholds were more effective than currently recommended fixed authority thresholds for identifying patients at risk of adverse reactions to metal debris requiring further investigation. LEVEL OF EVIDENCE: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Predicting high blood metal ion concentrations following hip resurfacing.

PURPOSE: To determine whether gender, femoral head size, acetabular inclination, and time since surgery predicted high blood metal ion concentrations following Birmingham Hip Resurfacing (BHR). METHODS: BHR patients with unilateral bearings at one specialist centre with blood cobalt and chromium concentrations measured up to May 2013 were included. This comprised a mixed (at-risk) group including symptomatic patients and asymptomatic individuals with specific clinical and/or radiological findings. Blood sampling was at a mean of 7.5 years (range 1-15.4 years) postoperatively. RESULTS: Of 319 patients (mean age 49.3 years; 53% male), blood metal ions greater than 7 µg/l were observed in 9% (n = 28). Blood metal ions were significantly higher in females (p<0.001), femoral head sizes ≤48 mm (p<0.01), and cup inclinations >55° (p<0.001). Linear regression demonstrated femoral head size was responsible for the highest proportion of variance in blood metal ions (cobalt p<0.001, R2 = 8%; chromium p<0.001, R2 = 11%). Analysis of femoral head size and inclination together demonstrated 36% of BHRs with head sizes of 38-44 mm and inclination >55° had blood metal ions >7 µg/l. BHR 10-year survival for this at-risk group was 91% (95% confidence intervals 86.0%-95.0%) with 30 hips revised. CONCLUSIONS: If blood metal ions are used to screen hip resurfacing patients for adverse reactions to metal debris it is recommended those with small femoral head sizes (38-44 mm) and high acetabular inclinations (>55°) are targeted. These findings require validation in other cohorts as they may not be applicable to all hip resurfacing devices given the differences in radial clearance, coverage arc, and metallurgy.

Revision of metal-on-metal hip replacements and resurfacings for adverse reaction to metal debris: a systematic review of outcomes.

PURPOSE: This systematic review assessed evidence on outcomes following revision of MoM hip resurfacings (HRs) and total hip replacements (THRs) for adverse reaction to metal debris (ARMD). METHODS: Four electronic databases were searched between January 2009 and July 2013 to identify studies reporting clinical outcomes following revision of MoM HRs and THRs for ARMD. Only studies reporting cohorts with more than 10 metal-on-metal (MoM) hips revised for ARMD were included. Outcomes of interest following ARMD revision were: (1) complication rates; (2) re-revision rates; (3) surgical intervention other than re-revision; (4) functional outcome. RESULTS: Of 148 unique studies identified, six studies were eligible for inclusion containing 216 MoM hips (197 HRs and 19 THRs) revised for ARMD. Mean follow-up time from ARMD revision ranged between 21-61 months. Complication rates were 4%-50% for HR and 68% for THR. Re-revision rates were 3%-38% for HR and 21% for THR. Dislocation (n = 14), ARMD recurrence (n = 11), and acetabular loosening (n = 9) were the three commonest complications and indications for re-revision. All six studies reported between one and three cases of ARMD recurrence during follow-up. One study specifically reported on performing procedures other than re-revision with 26% requiring closed reductions for dislocated THRs. Functional outcomes following ARMD revision were good or satisfactory in all but two studies. CONCLUSIONS: Limited evidence exists regarding outcomes following revision of MoM hips for ARMD, especially for THRs. This should be addressed in future studies and may be important when counselling asymptomatic individuals in whom revision is considered for raised blood metal ions.

Impact of active patient follow-up on worst-case implant survival analysis.

BACKGROUND: Patients lost to follow-up pose problems when performing implant survival analysis. We are unaware of any report detailing how implant survival is affected by the sequential capture of patients.
 AIMS: To assess the logistics of long-term follow-up of patients undergoing Birmingham Hip Resurfacing (BHR), and to determine what impact this had on implant survival with time.
 METHODS: Between 1997 and 2006 data was prospectively collected on consecutive BHR's implanted by a single surgeon in patients under 50 years of age. Survival analysis was performed at monthly intervals during this study with all patients lost to follow-up at any point in time considered to have failed. 
 RESULTS: There were 447 BHR's implanted in 393 patients. At study commencement cumulative 10-year survival was 42% (95% CI 36% to 48%) calculated on the confirmed knowledge of the outcome at that time of 275 BHR's, with the remaining 172 lost to follow-up and considered to have been revised. As patients were actively followed-up there was gradual improvement in survival and narrowing of confidence intervals with a final 10-year BHR survival of 96.3% (95% CI 93.7% to 98.3%) with no loss to follow-up. 
 CONCLUSIONS: The findings demonstrate improvement in long-term implant survival with the sequential capture of young and active patients undergoing BHR who were initially considered lost to follow-up. The results reiterate the recommendation that every effort should be made to follow all patients up after joint replacement. This will improve the accuracy of survival reporting and assist comparison between different prostheses.

A review of hip resurfacings revised for unexplained pain.

BACKGROUND: Adverse reaction to metal debris (ARMD) has come to prominence as a mode of failure for metal-on-metal hip resurfacings. These patients frequently present with unexplained groin pain. AIMS: 1) To review all metal-on-metal hip resurfacings revised for unexplained pain seeking evidence for ARMD; 2) To determine the clinical outcome following revision arthroplasty. METHODS: The hospital database was searched (1997-2009) to identify all cases of Birmingham Hip Resurfacings (BHRs) revised for unexplained pain. ARMD was diagnosed using specific clinical, radiological, and histopathological criteria. Postoperatively all patients were assessed in clinic and completed an Oxford Hip Score (OHS) questionnaire. RESULTS: Of 3076 BHRs implanted 149 were revised. Of these, 20 BHRs in 17 patients were revised for unexplained pain (mean age at BHR 50.5 yr; 55% female). Unexplained pain requiring revision had a prevalence of 0.65% of all hip resurfacings performed (20/3076). ARMD was the mode of failure in 50% (n = 10). Common features observed in ARMD patients included hip-joint effusions, femoral neck thinning, intraoperative macroscopic granulomas, and lymphocytic infiltrates on histopathological examination. No ARMD patients had macroscopic soft-tissue destruction. A range of mechanical causes were responsible for the remaining failures. At a mean 3.6 year follow-up (range 1.1-8.0) one ARMD patient experienced a dislocation. There were no further complications or need for surgical re-intervention. Median OHS for the cohort was 25.0%. CONCLUSIONS: Hip resurfacings revised for unexplained pain comprise a diverse group of conditions with ARMD being the commonest. ARMD probably contains subgroups yet to be defined, some of which may be related to mechanical rather than immunological factors.

Clinical outcome following surgical intervention for periprosthetic hip fractures at a tertiary referral centre.

Complications following surgical intervention for periprosthetic hip fractures are not uncommon. We report the clinical outcome following definitive surgical intervention for this indication at a single tertiary referral centre. All patients admitted between 2003 and 2009 undergoing such treatment were included. Patient demographics, all surgical interventions, complications following definitive fracture treatment, and postoperative mortality were recorded. Radiographs were reviewed to determine the Vancouver classification for each fracture. There were 67 patients (mean age at revision 76.7 years; 61% female). Fractures occurred around primary total hip arthroplasties (43%), revision arthroplasties (34%), and hip hemiarthroplasties (23%). Mean time to fracture from the most recent arthroplasty performed was 7.0 years. Most fractures were Vancouver type B2 (49%). The majority of patients underwent revision total hip arthroplasty (96%), using long-stemmed prostheses or proximal femoral endoprostheses, with cables for fracture fixation. Wound infection and systemic complications were seen in 16% and 13% respectively. One or more further surgical interventions were performed in 12%. There were no deaths in-hospital or at 30-days, with 10 fatalities (15%) at a mean 2-year follow-up. Lower rates of re-intervention and mortality were observed when surgery for acute periprosthetic hip fractures was performed at a tertiary centre. Revision hip arthroplasty with or without fracture fixation proved an effective and safe treatment of periprosthetic hip fractures in a high-risk patient population.

Perioperative bridging anticoagulation therapy in at-risk patients undergoing elective arthroplasty surgery.

We investigated the efficacy and safety of a standardized periprocedural anticoagulation bridging regimen that was instituted for patients who were on long-term oral anticoagulation therapy and were admitted for elective lower limb arthroplasty. Over a 3-month period, from March to June 2007, 15 inpatients who required temporary interruption of oral anticoagulation therapy in order to undergo elective orthopedic surgery were included in the study. All patients had bridging anticoagulation therapy instituted as per a standardized hospital protocol adapted from a British Orthopaedic Association publication. Patients were followed up prospectively during their inpatient stay. One operation was canceled, and 1 operating theatre list was rescheduled to delay a procedure because of nonadherence to the protocol. There were 2 cases of excessive surgical wound bruising, which caused additional morbidity and delayed discharge. One patient died from a cause unrelated to anticoagulation. Lack of proper knowledge of the bridging therapy protocol and improper communication between the medication prescribing and dispensing staff were the most important areas of concern. Given our study results, we believe that patient information and staff education are the key elements in successful implementation of a perioperative bridging anticoagulation protocol in elective arthroplasty.

A comparison of subsidence of Exeter standard and long stems.

The survivorship of the polished, double taper Exeter stem is related to subsidence within the cement mantle. Long Exeter stems have altered geometry which may influence subsidence characteristics. Using digitised x-rays and appropriate computer software we measured the subsidence of 35 standard and 40 long stem Exeter implants. Measurements were taken from initial postoperative radiographs and repeated at intervals up to 5 years. Long stem implants were used in cemented revisions without the use of impaction bone grafting. Subsidence rates of the standard length stems in our study were comparable to that in published literature. Long stems did not replicate this subsidence pattern and had subsided less at 6, 12 and 24 months. However, the 205mm long stem, which has a fully tapered design, did follow the subsidence characteristics of the standard stem. Subsidence of long stem Exeter implants does not mirror that of the standard length stem. Loss of the fully tapered geometry of the longer stem implants may account for this finding. We suggest that whenever possible, the 205mm long stem should be used if the biomechanical principles of the standard Exeter stem are to be utilised.

The influence of head size and sex on the outcome of Birmingham hip resurfacing.

BACKGROUND: Hip resurfacing has gained popularity for the treatment of young and active patients who have arthritis. Recent literature has demonstrated an increased rate of revision among female patients as compared with male patients who have undergone hip resurfacing. The aim of the present study was to identify any differences in survival or functional outcome between male and female patients with osteoarthritis who were managed with metal-on-metal hip resurfacing. METHODS: A prospective collection of data on all patients undergoing Birmingham Hip Resurfacing at a single institution was commenced in July 1997. On the basis of the inclusion and exclusion criteria, 1826 patients (2123 hips, including 799 hips in female patients and 1324 hips in male patients) with a diagnosis of osteoarthritis who had undergone the procedure between July 1997 and December 2008 were identified. The variables of age, sex, preoperative Oxford Hip Score, component size used, surgical approach, lead surgeon, and surgeon experience were analyzed. A multivariate Cox proportional hazard survival model was used to identify which variables were most influential for determining revision. RESULTS: The mean duration of follow-up was 3.46 years (range, 0.03 to 10.9 years). The five-year cumulative survival rate for the 655 hips that were followed for a minimum of five years was 97.5% (95% confidence interval, 96.3% to 98.3%). There were forty-eight revisions. Revision was significantly associated with female sex (hazard rate, 2.03 [95% confidence interval, 1.15 to 3.58]; p = 0.014) and decreasing femoral component size (hazard rate per 4-mm decrease in size, 4.68 [95% confidence interval, 4.36 to 5.05]; p < 0.001). Revision was not associated with age (p = 0.88), surgeon (p = 0.41), surgeon experience (p = 0.30), or surgical approach (p = 0.21). A multivariate analysis including the covariates of sex, age, surgeon, surgeon experience, surgical approach, and femoral component size demonstrated that sex was no longer significantly associated with revision when femoral component size was included in the model (p = 0.37). Femoral component size alone was the best predictor of revision when all covariates were analyzed (hazard rate per 4-mm decrease in size, 4.87 [95% confidence interval, 4.37 to 5.42]; p < 0.001). CONCLUSIONS: The present study demonstrates that although female patients initially may appear to have a greater risk of revision, this increased risk is related to differences in the femoral component size and thus is only indirectly related to sex. Patient selection for hip resurfacing is best made on the basis of femoral head size rather than sex.

Renal clearance of cobalt in relation to the use of metal-on-metal bearings in hip arthroplasty.

BACKGROUND: A concern regarding the use of metal-on-metal bearings in hip arthroplasty has been that the high levels of metal ions that are released overwhelm the renal threshold for metal excretion, leading to systemic buildup of metals. The purpose of this investigation was to determine if the physiological renal capacity for cobalt clearance and cobalt concentrating efficiency is overwhelmed by the elevation in metal ion levels seen in patients with metal-on-metal-bearing hip devices. METHODS: Concurrent specimens of urine and plasma were obtained from a group of 461 patients (346 men and 115 women) at various intervals after either a unilateral (296) or a bilateral (130) metal-on-metal hip arthroplasty or preoperatively (thirty-five patients; the control specimens). Metal ion analyses were performed with high-resolution inductively coupled mass spectrometry. Renal efficiency was measured as the ratio of urine cobalt concentration to plasma cobalt concentration. Cobalt clearance was calculated by dividing the urine cobalt output in twenty-four hours by the plasma cobalt concentration. Dividing the quotient by 1440 adjusts it to clearance per minute. RESULTS: The median renal efficiency was found to be 0.9 in the analysis of the preoperative specimens, indicating that there was renal conservation of cobalt. In patients with metal-on-metal bearings, the median renal efficiency was 3.2, indicating that, as a result of cobalt excretion, the cobalt concentration in urine was threefold higher than the concentration in plasma. Linear regression analysis showed that renal efficiency progressively increased at a rate of 9% for every microg/24 hr increase in cobalt release. Cobalt clearance showed a similar trend, increasing from 1.3 mL/min in the preoperative group to 3.7 mL/min in the follow-up group. In the follow-up group, renal cobalt clearance progressively increased from 1.9 to 7.1 mL/min with increasing daily cobalt output, which indicates that with increasing in vivo metal ion release there was a progressive increase in the rate at which the kidneys cleared the plasma of cobalt. CONCLUSIONS: In subjects with no prosthetic device, the kidneys tend to conserve cobalt in the body. We found that, in patients with a metal-on-metal hip prosthesis, there is a progressive increase in cobalt clearance with increasing in vivo wear at the levels of cobalt release expected in patients with an array of metal-on-metal-bearing total joint arthroplasties. We found no threshold beyond which renal capacity to excrete these ions is overwhelmed.

The influence of surgical approach on outcome in Birmingham hip resurfacing.

UNLABELLED: Various approaches have been described for metal-on-metal hip resurfacing. We compared the posterolateral and direct lateral approaches for complications, pain, function, and implant survival in the short and medium term for two surgeons in a consecutive series of 790 patients (909 hips; July 1997 to July 2004) followed until July 2007. The direct lateral approach group included 135 resurfacing procedures and the posterolateral group included 774 procedures. There was no difference between the two groups for age or gender. The minimum followup for the anterolateral group was 2 years (mean, 5.1 years; range, 2.0-9.4 years) and for the posterolateral group 2 years (mean, 5.5 years; range, 2.0-9.6 years). There were no differences between the two approaches for complications, additional surgery, implant survival, or Oxford hip scores. The 8-year survival rate was 97.9% (95% confidence interval, 89.9-100) for the direct lateral approach and 97.2% (95% confidence interval, 93.9-99.3) for the posterolateral approach. This study indicates both approaches offer excellent pain reduction and return to function after Birmingham hip resurfacing with no difference in survival or in the incidence of complications. An 8-year survival rate of 97% can be achieved using either the posterolateral approach or the direct lateral approach. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Guidelines for authors for a complete description of levels of evidence.

Mini-incision resurfacing arthroplasty of hip through the posterior approach.

UNLABELLED: The success of metal-on-metal hip resurfacing in the medium term in young and active patients is becoming evident. The procedure now can be done using a minimal approach developed by the senior author using a single posterior incision. This mini-incision resurfacing arthroplasty of the hip has made resurfacing more attractive to surgeons and patients. But does a mini incision approach allow reliable component placement? The results of 232 consecutive Birmingham Hip Resurfacings done using this approach between January and December 2004 are presented. Mean incision length was 11.8 cm. Seventy-seven percent of the incisions were between 9 and 12 cm long. Body mass index of the patients studied ranged from 17.6 to 46.7. Comparing the traditional approach with the mini-incision resurfacing arthroplasty of hip did not show a difference between the two groups in terms of operating time. The mean hospital stay was reduced by a day in the mini-incision group. The mean inclination of the acetabular components was within the target range in the two groups. Patient feedback shows that reduced postoperative pain, faster recovery rate, and better cosmesis make the mini-incision approach very popular. Although the mini incision is indeed appealing, it has a steep learning curve. In the early phase of the learning curve, care should be taken to avoid suboptimal component placement, which has the potential to affect long-term outcome adversely. LEVEL OF EVIDENCE: Therapeutic study, Level III (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.