BACKGROUND:Aspirin after an initial short course of rivaroxaban has been shown to be safe and effective for the prevention of venous thromboembolism after total hip or total knee arthroplasty, but uncertainty remains about the use of aspirin alone. METHODS:In this multicenter, double-blind, randomized, controlled trial, we assigned patients to receive once-daily thromboprophylaxis with either 81 mg of aspirin or 10 mg of oral rivaroxaban for the first 5 days after total hip or total knee arthroplasty. All the patients then received further thromboprophylaxis with 81 mg of aspirin daily for 9 additional days after knee arthroplasty and for 30 additional days after hip arthroplasty. Patients were followed for 90 days for symptomatic venous thromboembolism, which consisted of either proximal deep-vein thrombosis or pulmonary embolism (primary effectiveness outcome), and for bleeding complications (primary safety outcome). The noninferiority margin for aspirin alone as compared with rivaroxaban-aspirin was 0.7 percentage points. RESULTS:A total of 5429 patients underwent randomization. Venous thromboembolism developed in 13 of 2718 patients (0.48%) in the aspirin-alone group and in 12 of 2647 patients (0.45%) in the rivaroxaban-aspirin group (risk difference, 0.02 percentage points; 95% confidence interval [CI], -0.34 to 0.39; P<0.001 for noninferiority). Major bleeding or clinically relevant nonmajor bleeding events occurred in 45 of 2718 patients (1.66%) in the aspirin-alone group and in 54 of 2647 patients (2.04%) in the rivaroxaban-aspirin group (risk difference, -0.38%; 95% CI, -1.11 to 0.34). CONCLUSIONS:After total hip and total knee arthroplasty, the use of aspirin alone was not inferior to a strategy of using rivaroxaban followed by aspirin for the prevention of symptomatic venous thromboembolism, with no clinically relevant difference in bleeding events. (Funded by the Canadian Institutes of Health Research; EPCAT III ClinicalTrials.gov number, NCT04075240.).

Osteoarthritis (OA) is a painful, debilitating disease with no cure or treatments that can predictably stop/reverse its progression. Treatment is particularly difficult since articular cartilage lacks intrinsic repair capacity, despite mesenchymal stem cells (MSCs) being present in the joint with robust chondrogenic potential. While heterogeneity exists among MSC subtypes within human synovium, it remains unclear which populations can regenerate cartilage or impact OA progression. We clonally isolated MSCs from normal and OA patient synovium using indexed flow cytometry, then characterized them through differentiation assays and quantitative proteomics. MSC clones were transplanted into a xenograft rat OA model and evaluated by histology and immunofluorescence. We identified heterogeneity in putative MSCs within and between patient groups and their repair capacity in the rat model. However, traditional cell surface markers could not distinguish these subtypes, highlighting the need for single-cell level understanding. Using unbiased proteomics, we identified CD47 as a novel MSC marker. CD47Hi cells demonstrated robust treatment efficacy in the rat OA model and directly contributed to new articular cartilage formation. Characterizing MSC subtypes is essential for identifying candidates appropriate for clinical investigation and exploiting functional MSCs for cartilage regeneration strategies.

Aims This study aims to determine difference in annual rate of early-onset (≤ 90 days) deep surgical site infection (SSI) following primary total knee arthroplasty (TKA) for osteoarthritis, and to identify risk factors that may be associated with infection. Methods This is a retrospective population-based cohort study using prospectively collected patient-level data between 1 January 2013 and 1 March 2020. The diagnosis of deep SSI was defined as per the Centers for Disease Control/National Healthcare Safety Network criteria. The Mann-Kendall Trend test was used to detect monotonic trends in annual rates of early-onset deep SSI over time. Multiple logistic regression was used to analyze the effect of different patient, surgical, and healthcare setting factors on the risk of developing a deep SSI within 90 days from surgery for patients with complete data. We also report 90-day mortality. Results A total of 39,038 patients underwent primary TKA for osteoarthritis during the study period. Of these, 275 patients developed a deep SSI within 90 days of surgery, representing a cumulative incidence of 0.7%. The annual infection rate did not significantly decrease over the seven-year study period (p = 0.162). Overall, 13,885 (35.5%) cases were excluded from the risk analysis due to missing data. Risk factors associated with early-onset deep SSI included male sex, American Society of Anesthesiologists grade ≥ 3, blood transfusion, acute length of stay, and surgeon volume < 30 TKAs/year. Early-onset deep SSI was not associated with increased 90-day mortality. Conclusion This study establishes a reliable baseline infection rate for early-onset deep SSI after TKA for osteoarthritis using robust Infection Prevention and Control surveillance data, and identifies several potentially modifiable risk factors.

ObjectiveTo determine the relationship between patients' preoperative readiness for total knee arthroplasty (TKA) and surgical outcome at 1 year post‐TKA.MethodsThis prospective cohort study recruited patients with knee osteoarthritis (OA) who were ≥30 years and were referred for TKA at 2 hip/knee surgery centers in Alberta, Canada. Those who underwent primary unilateral TKA completed questionnaires prior to TKA to assess pain using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), physical disability using the Knee Injury and Osteoarthritis Outcome Score physical function short form, perceived arthritis coping efficacy, general self‐efficacy, depressed mood using the Patient Health Questionnaire 8, body mass index, comorbidities, and TKA readiness (patient acceptable symptom state; willingness to undergo TKA); these same individuals also completed the above questionnaires 1 year post‐TKA to assess surgical outcomes. A good TKA outcome was defined as an individual having improved knee symptoms, measured using the Osteoarthritis Research Society International–Outcome Measures in Rheumatology responder criteria, and overall satisfaction with results of the TKA. Poisson regression with robust error estimation was used to estimate the relative risk (RR) of a good outcome for exposures, before and after controlling for covariates.ResultsOf 1,272 TKA recipients assessed at 1 year post‐TKA, 1,053 with data for the outcome assessed in the study were included (mean ± SD age 66.9 ± 8.8 years; 58.6% female). Most patients (87.8%) were definitely willing to undergo TKA and had “unacceptable” knee symptoms (79.7%). Among patients who underwent TKA, 78.1% achieved a good outcome. Controlling for pre‐TKA OA‐related disability, arthritis coping efficacy, comorbid hip symptoms, and depressed mood, definite willingness to undergo TKA and unacceptable knee symptoms were associated with a greater likelihood of a good TKA outcome, with adjusted RRs of 1.18 (95% confidence interval [95% CI] 1.04–1.35) and 1.14 (95% CI 1.02–1.27), respectively.ConclusionAmong patients who underwent TKA for knee OA, patients' psychological readiness for TKA and willingness to undergo TKA were associated with a greater likelihood of a good outcome. Incorporation of these factors in TKA decision‐making may enhance patient outcomes and appropriate the use of TKA.

Proponents of the Sub-Vastus (SV) approach in primary Total Knee Arthroplasty (TKA) claim superior extensor mechanism function which results in earlier recovery after surgery. We performed a meta-analysis of randomized controlled trials comparing the SV and standard Medial Parapatellar (MPP) approaches in primary TKAs. The study was performed using the Cochrane handbook for systematic reviews guidelines. A total of 28 studies with 2171 patients were included and the mean age of the SV group was 68.2 [standard deviation, ±4.4] and of the MPP group was 68.4 (±3.85). The SV approach resulted in a significant improvement in flexion at day 3 postoperatively [mean difference (MD) = 6°; 95% confidence interval (CI), 0.37–11.71; p < 0.01], but this was not sustainable at 6 weeks, 3 months, and 12 months postoperatively. Similarly, despite a significant reduction in the visual analogue scale score at day 1 postoperatively (MD = −1.19; 95% CI, −1.70 to −0.68; p < 0.01), there was not enough evidence to support its superiority after that. The SV approach led to a reduction in days to straight leg raise (MD = −1.88; 95% CI, −2.45 to −1.31; p < 0.01) and lateral releases [relative risk = 0.49; 95% CI, 0.30–0.82; p < 0.01) with no difference in complication rates ( p = 0.64) but at the expense of a prolonged operation (MD = 13 min; 95% CI, 9.41–16.69; p < 0.01). Our conclusion is that the SV approach provides an alternative to the MPP with some advantages in the first 3 days only after primary TKA surgery.

BACKGROUND:The aim of this study is to compare functional outcomes and perioperative complications between patients on a selective serotonin reuptake inhibitor (SSRI) and those who are not on an SSRI preoperatively at the time of total joint arthroplasty. METHODS:A retrospective study was performed on 28,386 patients who received a primary total hip (THA) or knee (TKA) arthroplasty. Patients were compared based on SSRI utilization. We measured patient-reported function and health-related quality of life using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the EuroQol-5 Dimensions (EQ-5D-5L) instruments. Chi-squared test was used to compare categorical variables and t-test was used to compare the continuous variables of 2 study groups. RESULTS:Patients on SSRIs have lower preoperative baseline WOMAC and EQ-5D-5L scores than those not using SSRI (P < .001). Patient-reported outcomes improved significantly following surgery, but functional outcome scores remained inferior in patients using SSRI. After adjusting for baseline variables, SSRI use in TKA predicted lower EQ-5D-5L scores than non-SSRI users (P = .036) while the WOMAC scores were not different (P = .118). For the THA cohort, SSRI use predicted lower EQ-5D-5L (P = .001) and WOMAC scores than non-SSRI users (P = .008). SSRI use was associated with increased transfusion rate, length of stay, readmission rate, and medical events. About 11.3% of TKA and 13.3% of THA patients stopped using SSRI at 12 months after arthroplasty. CONCLUSION:Patients using an SSRI show improvement comparable to patients not on an SSRI, but their 12-month functional scores continue to be inferior. SSRI utilization was associated with increased adverse events including needing a blood transfusion.

First, the authors question our selection of the exposure measure - patients\u0027 pre-operative expectations for total knee arthroplasty (TKA) surgery. In brief, we assessed TKA expectations using the HSS TKA Expectations Questionnaire2 . For each of 17 TKA outcomes, participants are asked, \"How important are these expectations in the treatment of your knee arthritis?\" (5-point Likert scale from \u0027very important\u0027 to \u0027I do not expect this\u0027 or \u0027this does not apply to me\u0027).

Abstract The aim of this study was to determine the incidence, annual trend, and perioperative outcomes and identify risk factors of early-onset ( ≤90  d) deep surgical site infection (SSI) following primary total hip arthroplasty (THA) for osteoarthritis. We performed a retrospective study using prospectively collected patient-level data from January 2013 to March 2020. The diagnosis of deep SSI was based on the published Centre for Disease Control/National Healthcare Safety Network (CDC/NHSN) definition. The Mann–Kendall trend test was used to detect monotonic trends. Secondary outcomes were 90 d mortality and 90 d readmission. A total of 22 685 patients underwent primary THA for osteoarthritis. A total of 46 patients had a confirmed deep SSI within 90 d of surgery representing a cumulative incidence of 0.2 %. The annual infection rate decreased over the 7-year study period ( p=0.026 ). Risk analysis was performed on 15 466 patients. Risk factors associated with early-onset deep SSI included a BMI  >  30 kg m -2 (odds ratio (OR) 3.42 [95 % CI 1.75–7.20]; p<0.001 ), chronic renal disease (OR, 3.52 [95 % CI 1.17–8.59]; p=0.011 ), and cardiac illness (OR, 2.47 [1.30–4.69]; p=0.005 ), as classified by the Canadian Institute for Health Information. Early-onset deep SSI was not associated with 90 d mortality ( p=0.167 ) but was associated with an increased chance of 90 d readmission ( p<0.001 ). This study establishes a reliable baseline infection rate for early-onset deep SSI after THA for osteoarthritis through the use of a robust methodological process. Several risk factors for early-onset deep SSI are potentially modifiable, and therefore targeted preoperative interventions of patients with these risk factors is encouraged.

Aim How reduced femoral neck anteversion alters the distribution of pressure and contact area in Hip Resurfacing Arthroplasty (HRA) remains unclear. The purpose of this study was to quantitatively describe the biomechanical implication of different femoral neck version angles on HRA using a finite element analysis. Materials and methods A total of sixty models were constructed to assess the effect of different femoral neck version angles on three different functional loads: 0°of hip flexion, 45°of hip flexion, and 90° of hip flexion. Femoral version was varied between 30° of anteversion to 30° of retroversion. All models were tested with the acetabular cup in four different positions: (1) 40°/15° (inclination/version), (2) 40°/25°, (3) 50°/15°, and (4) 50°/25°. Differences in range of motion due to presence of impingement, joint contact pressure, and joint contact area with different femoral versions and acetabular cup positions were calculated. Results Impingement was found to be most significant with the femur in 30° of retroversion, regardless of acetabular cup position. Anterior hip impingement occurred earlier during hip flexion as the femur was progressively retroverted. Impingement was reduced in all models by increasing acetabular cup inclination and anteversion, yet this consequentially led to higher contact pressures. At 90° of hip flexion, contact pressures and contact areas were inversely related and showed most notable change with 30° of femoral retroversion. In this model, the contact area migrated towards the anterior implant-bone interface along the femoral neck. Conclusion Femoral retroversion in HRA influences impingement and increases joint contact pressure most when the hip is loaded in flexion. Increasing acetabular inclination decreases the area of impingement but doing so causes a reciprocal increase in joint contact pressure. It may be advisable to study femoral neck version pre-operatively to better choose hip resurfacing arthroplasty candidates.

This chapter presents a case scenario of a 22-year-old female patient who is reporting progressive pain in her right hip over the last six months. The development of new techniques in pelvic osteotomies for hip dysplasia and subsequently the introduction of the concept of femoroacetabular impingement (FAI) have led to an increase in both open and arthroscopic procedures used in the management of hip pathology in young adults. This chapter reviews the available evidence for certain hip-preserving procedures in the orthopedic literature. Both hip arthroscopy and personalized hip therapy are successful methods in the management of FAI; however, hip arthroscopy can result in greater improvements of patients' symptoms in the short term. Periacetabular osteotomy can be used for the treatment of residual acetabular dysplasia in young adults with closed triradiate cartilage. The chapter also provides recommendations for implementing evidence-based practice in the clinical setting.

AIMS Total hip arthroplasty (THA) with dual-mobility components (DM-THA) has been shown to decrease the risk of dislocation in the setting of a displaced neck of femur fracture compared to conventional single-bearing THA (SB-THA). This study assesses if the clinical benefit of a reduced dislocation rate can justify the incremental cost increase of DM-THA compared to SB-THA. METHODS Costs and benefits were established for patients aged 75 to 79 years over a five-year time period in the base case from the Canadian Health Payer's perspective. One-way and probabilistic sensitivity analysis assessed the robustness of the base case model conclusions. RESULTS DM-THA was found to be cost-effective, with an estimated incremental cost-effectiveness ratio (ICER) of CAD $46,556 (£27,074) per quality-adjusted life year (QALY). Sensitivity analysis revealed DM-THA was not cost-effective across all age groups in the first two years. DM-THA becomes cost-effective for those aged under 80 years at time periods from five to 15 years, but was not cost-effective for those aged 80 years and over at any timepoint. To be cost-effective at ten years in the base case, DM-THA must reduce the risk of dislocation compared to SB-THA by at least 62%. Probabilistic sensitivity analysis showed DM-THA was 58% likely to be cost-effective in the base case. CONCLUSION Treating patients with a displaced femoral neck fracture using DM-THA components may be cost-effective compared to SB-THA in patients aged under 80 years. However, future research will help determine if the modelled rates of adverse events hold true. Surgeons should continue to use clinical judgement and consider individual patients' physiological age and risk factors for dislocation. Cite this article: Bone Joint J 2021;103-B(12):1783-1790.

Background: Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are reliable surgical options to treat pain and disability resulting from degenerative conditions around the hip and knee. Obesity is a modifiable risk factor that contributes to significant morbidity. The purpose of this study was to retrospectively compare outcomes in primary hip and knee arthroplasty for patients with increased body mass index (BMI) and those with normal BMI, using data from the registry of the Alberta Bone and Joint Health Institute (ABJHI). Methods: We retrospectively reviewed the data compiled in the ABJHI registry between March 2010 and July 2016. We reviewed outcomes with respect to length of stay, discharge destination, 30-day readmission, postoperative infection, postoperative transfusion requirements, postoperative adverse events and in-hospital postoperative mechanical complications. Results: A total of 10 902 patients (6076 women, 4826 men) who underwent THA and 16 485 patients (10 057 women, 6428 men) who underwent TKA were included in the study. For both THA and TKA, patients with increased BMI had an increased number of in-hospital medical events, had an increased rate of deep infection, were less likely to be discharged home (p < 0.001) and had decreased transfusion requirements (p < 0.001) than patients whose weight was in the normal range. Increased BMI increased the rate of 30-day readmission and length of stay in the THA cohort but not in the TKA cohort. Increased BMI had no effect on acute postoperative dislocation or periprosthetic fractures. Patients with a BMI of 30 kg/m2 or greater required a THA 1.7 years earlier than patients of normal weight, patients whose BMI was 35 kg/m2 or greater required a THA 3.4 years earlier, and patients whose BMI was 40 kg/m2 or greater required a THA 5.8 years earlier. In the TKA cohort, patients with a BMI of 30 kg/m2 or greater required a TKA 2.7 years earlier than patients whose weight was in the normal range, patients with a BMI of 35 kg/m2 or greater required a TKA 4.6 years earlier, and patients whose BMI was 40 kg/m2 or greater required a TKA 7.6 years earlier. Conclusion: Our study quantifies the effects of obesity in primary hip and knee arthroplasty. It provides a greater understanding of the risks in the obese population when contemplating joint arthroplasty.

To assess the relationship between patients’ expectations for total knee arthroplasty (TKA) and satisfaction with surgical outcome.

Synovitis is common in patients with osteoarthritis (OA) and is associated with pain and disease progression. We have previously demonstrated that the chemokine C-C motif chemokine 22 (CCL22) induces chondrocyte apoptosis in vitro; however, the effects of CCL22 on the synovium remain unknown. Therefore, our goal was to investigate the effect of CCL22 on fibroblast-like synoviocytes (FLS). CCL22 treatment suppressed expression of IL-4 and IL-10 and promoted expression of S100A12 in FLS. The response of FLS to CCL22 was not dependent on the disease state of the joint (e.g., normal versus OA), but was instead correlated with the individuals' synovial fluid level of CCL22. CCL22 induction of S100A12 in FLS was attenuated after knockdown of CCR3, yet ligands of CCR3 (CCL7, CCL11) did not induce S100A12 expression. In the presence of CCL22, CCR3-positive FLS upregulate CCL22 and S100A12 driving a potential feedforward pro-inflammatory mechanism distinct from canonical CCL22 and CCR3 pathways.

SummaryPostoperative fever is common following orthopedic trauma surgery. As the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection increases in the community, migration into the acute care hospital setting intensifies, creating confusion when fever develops postoperatively. The transmission dynamics of SARS-CoV-2 make it difficult to adequately gauge and pinpoint risk groups with questionnaires at the time of hospital admission. This is particularly problematic when asymptomatic or presymptomatic patients infected with SARS-CoV-2 require urgent surgery and cannot be screened effectively. One approach is to treat every patient as though they were SARS-CoV-2-positive in preparation for surgery, but doing so could exacerbate shortages of personal protective equipment and staffing limitations. Uncertainty regarding the etiology of postoperative fever could be significantly reduced by universal SARS-CoV-2 testing of all surgical patients at the time of hospital admission in addition to routine screening, but testing capacity and a rapid turnaround time would be required.

AIMS:Dislocation is the most common indication for further surgery following total hip arthroplasty (THA) when undertaken in patients with a femoral neck fracture. This study aimed to assess the complication rates of THA with dual mobility components (THA-DMC) following a femoral neck fracture and to compare outcomes between THA-DMC, conventional THA, and hemiarthroplasty (HA). METHODS:We performed a systematic review of all English language articles on THA-DMC published between 2010 and 2019 in the MEDLINE, EMBASE, and Cochrane databases. After the application of rigorous inclusion and exclusion criteria, 23 studies dealing with patients who underwent treatment for a femoral neck fracture using THA-DMC were analyzed for the rate of dislocation. Secondary outcomes included reoperation, periprosthetic fracture, infection, mortality, and functional outcome. The review included 7,189 patients with a mean age of 77.8 years (66.4 to 87.6) and a mean follow-up of 30.9 months (9.0 to 68.0). RESULTS:THA-DMC was associated with a significantly lower dislocation rate compared with both THA (OR 0.26; 95% CI 0.08 to 0.79) and HA (odds ratio (OR) 0.27; 95% confidence interval (CI) 0.15 to 0.50). The rate of large articulations and of intraprosthetic dislocation was 1.5% (n = 105) and 0.04% (n = 3) respectively. CONCLUSION:THA-DMC when used in patients with a femoral neck fracture is associated with a lower dislocation rate compared with conventional arthroplasty options. There was no increase in the rates of other complication when THA-DMC was used. Future cost analysis and prospective, comparative studies are required to assess the potential benefit of using THA-DMC in these patients. Cite this article: Bone Joint J 2020;102-B(7):811-821.

Osteoarthritis (OA) is the fastest growing global health problem, with a total joint replacement being the only effective treatment for patients with end stage OA. Many groups are examining the use...

Background:Patients with bilateral end-stage hip or knee arthritis want to know if it is safe to have bilateral surgery under a single anesthetic, to restore their quality of life as quickly as possible. The purpose of this study was to assess if there is an increase in the rate of postoperative medical adverse events, length of stay (LOS), blood transfusion rate and 30-day readmission rate among patients who undergo 1-stage bilateral total hip arthroplasty (BTHA) and 1-stage bilateral total knee arthroplasty (BTKA) compared with patients who undergo 2-stage BTHA and BTKA. Methods:Our study cohorts included patients who underwent BTHA and BTKA between Apr. 1, 2009, and Jan. 31, 2016, in Alberta, Canada. To minimize selection bias associated with our retrospective study design, we matched patients who underwent 1-stage BTHA and BTKA with patients with patients who underwent 2-stage BTHA and BTKA, respectively, for age, sex and number of presurgical risk factors using propensity score in a matching ratio of 1:1. Results:Our study included 1645 patients who underwent BTHA and 4125 patients who underwent BTKA. We matched 195 patients who underwent 1-stage BTHA and 302 patients who underwent 1-stage BTKA with patients who underwent 2-stage BTHA and BTKA, respectively. There was no significant difference in postoperative medical adverse events between the 1-stage and 2-stage matched cohort groups for both BTHA (adjusted odds ratio [OR] 1.3, 95% confidence interval [CI] 0.3-4.9) and BTKA (adjusted OR 0.9, 95% CI 0.3-2.6). There was no difference in inpatient, 30- or 90-day mortality between the 2 groups for BTHA or BTKA. Patients who underwent 1-stage BTHA and BTKA had a shorter acute length of stay but increased total length of stay (acute care and rehabilitation unit) and were less likely to be discharged home postoperatively. One-stage BTHA and BTKA were associated with higher odds of blood transfusion than 2-stage BTHA and BTKA. The 30-day readmission rate was significantly lower for 1-stage BTHA than for the 2-stage BTHA matched cohort (adjusted OR 0.3, 95% CI 0.1-0.8), whereas there was no difference in the 30-day readmission rate (adjusted OR 0.6, 95% CI 0.2-1.7) between the 1-stage and 2-stage BTKA matched cohorts. Finally, operating room time was significantly lower for 1-stage BTHA (49.6 min less) and 1-stage BTKA (66.7 min less) than for the 2-stage arthroplasty procedures. Conclusion:Healthy patients who undergo 1-stage BTHA and BTKA have postoperative medical complication rates comparable to those of patients who undergo 2-stage procedures with the additional benefits of a shorter acute length of stay, but they do have a higher risk of blood transfusion and are less likely to be discharged directly home from the acute care hospital. A multicentre randomized controlled trial on this topic is currently being condcuted by the Canadian Arthroplasty Society.

BACKGROUND Testing of whole blood or serum metal ion levels has become an important part of assessing and monitoring the performance of metal-on-metal bearings, both in hip resurfacing arthroplasty and in total hip replacement. The aim of this study was to determine the concordance between 2 laboratories testing cobalt and chromium ion levels in patients with metal-on-metal bearings. METHODS Serum and whole blood samples from patients who had undergone metal-on-metal resurfacing or large-diameter total hip arthroplasty were tested for cobalt and chromium ions in laboratory A (a recognized laboratory) and laboratory B (tasked with testing clinical specimens). Laboratory A performed cobalt and chromium testing on whole blood, and laboratory B performed cobalt testing on whole blood and chromium testing on serum. RESULTS Samples from 104 patients were tested. Laboratory B reported lower whole blood cobalt levels than laboratory A. Furthermore, laboratory A reported that all patients had elevated whole blood cobalt ion levels compared to the normal reference values for the laboratory, whereas laboratory B reported that 46 patients (44.2%) had whole blood cobalt ion levels within the normal reference range for the laboratory. CONCLUSION This comparative study highlights the importance of using a single laboratory for metal ion testing, as values generated from different laboratories may not be directly comparable. With recent literature suggesting that whole blood cobalt levels as low as 1 ppb may be a predictor of adverse reactions to metal debris, accurate clinical measurement needs to be increasingly exact.