Serum cobalt concentrations remain at low levels at a minimum of 20 years following metal-on-metal total hip arthroplasty

Aims Second-generation metal-on-metal (MoM) articulations in total hip arthroplasty (THA) were introduced in order to reduce wear-related complications. The current study reports on the serum cobalt levels and the clinical outcome at a minimum of 20 years following THA with a MoM (Metasul) or a ceramic-on-polyethylene (CoP) bearing. Methods The present study provides an update of a previously published prospective randomized controlled study, evaluating the serum cobalt levels of a consecutive cohort of 100 patients following THA with a MoM or a CoP articulation. A total of 31 patients were available for clinical and radiological follow-up examination. After exclusion of 11 patients because of other cobalt-containing implants, 20 patients (MoM (n = 11); CoP (n = 9)) with a mean age of 69 years (42 to 97) were analyzed. Serum cobalt levels were compared to serum cobalt levels five years out of surgery. Results The median cobalt concentration in the MoM group was 1.04 μg/l (interquartile range (IQR) 0.64 to 1.70) at a mean of 21 years (20 to 24) postoperatively and these values were similar (p = 0.799) to cobalt levels at five years. In the CoP control group, the median cobalt levels were below the detection limit (< 0.3 μg/l; median 0.15 μg/l, IQR 0.15 to 0.75) at 20 years. The mean Harris Hip Score was 91.4 points (61 to 100) in the MoM group and 92.8 points (63 to 100) in the CoP group. Conclusion This study represents the longest follow-up series evaluating the serum cobalt levels after 28 mm head MoM bearing THA and shows that serum cobalt concentrations remain at low levels at a mean of 21 years (20 to 24) after implantation. Cite this article: Bone Joint Res. 2020;9(3):145–150.

269 Attempts to improve equine athletic performance via hypoxia-inducing techniques

Hypoxic conditions encountered at high altitudes result in potential adaptations such as increased hematocrit, hemoglobin, and muscle mitochondrial function. However, living at high altitudes is not practical for many equine athletes. Unfortunately, many trainers have resorted to administering erythropoietin to stimulate red cell production or a large dose of cobalt which reportedly has a hypoxic-inducing effect. Both practices can result in serious health complications (including death) and are typically banned, with a testing threshold of 25 ppb for serum cobalt. Results from Spartan Equine Research confirmed that oral supplementation with 60X the 2007 NRC recommendation of cobalt resulted in serum concentration of 4.7 ppb – far below the testing threshold. These results suggest injectable cobalt, not dietary, is the source of concern. A means of inducing hypoxic effects in humans without living at altitude involves a “tent” covering a bed in which low oxygen concentrations are maintained while sleeping. Similar low-oxygen stalls have been designed for horses. Recent Spartan Equine Research failed to detect any improvement in racing performance in Thoroughbreds housed in such stalls. Challenges not experienced with human athletes were encountered relating to humidity and gases associated with urination and defecation within the airtight chamber – rendering such stalls of limited practicality and safety.

Pseudotumours, cobalt and clinical outcome in small head metal-on-metal versus conventional metal-on-polyethylene total hip arthroplasty

Background: Metal-on-metal total hip arthroplasty (MoM THA) is associated with the formation of pseudotumours. Studies mainly concern pseudotumour formation in large head MoM THA. We performed a long-term follow-up study, comparing pseudotumour incidence in small head metal-on-metal (SHMoM) THA with conventional metal-on-polyethylene (MoP) THA. Predisposing factors to pseudotumour formation were assessed. Methods: From a previous randomised controlled trial comparing SHMoM (28 mm) cemented THA with conventional MoP cemented THA, patients were screened using a standardised CT protocol for the presence of pseudotumours. Serum cobalt levels and functional outcome were assessed. Results: 56 patients (33 MoP and 23 MoM) were recruited after mean follow-up of 13.4 years (SD 0.5). The incidence of pseudotumours was 1 (5%) in the SHMoM THA cohort and 3 (9%) in the MoP THA cohort. Prosthesis survival was 96% for both SHMoM and MoP THAs. Serum cobalt levels did not exceed acceptable clinical values (<5 µg/L) whereas no differences in cobalt levels were detected at follow-up between both groups. Oxford and Harris Hip Scores were good and did not differ between SHMoM and MoP THA. Conclusions: This long-term follow-up study shows a low incidence of pseudotumour formation and good functional outcome in cemented head-taper matched SHMoM and MoP THA.

Abstract 17269: Incidence of Atrial Fibrillation in Patients With Cobalt and Chromium Containing Hip Arthroplasty

Background: Worldwide, approximately one million patients have had total hip arthroplasty with 35% being cobalt and chromium Metal-on-Metal (MoM) or Metal-on-Polythelene (MoP) implants. Animal models have suggested that cobalt and chromium can affect all chambers, but there seems to be an atrial predilection. There are several case reports of metal containing hip arthroplasty causing atrial arrhythmias but the true incidence of atrial fibrillation associated with metal hip arthroplasty remains undefined. Objective: We sought to determine the incidence of atrial fibrillation in patients with metal containing hip arthroplasty. We also examined the association between serum cobalt and chromium levels and arrhythmias in this cohort and all cause mortality. Methods: We retrospectively examined the records of patients from the Mayo Clinic total hip arthroplasty registry (Metal group - Metal-on-Metal: MoM and Metal-on-Polyethylene: MoP, Non-Metal group - Ceramic-on-Ceramic: CoC and Ceramic-on-Polyethylne: CoP) to obtain demographic data, comorbidities, laboratory, ECG, and echocardiographic data. Out of a total of 1756 patients, Cobalt and Chromium levels were available in 138 patients. Results: The mean age of patients with metal containing hip replacement was 50 years and were predominantly male. During a follow up period of 10 years, the incidence of atrial fibrillation in our study population was 8% in metal group compared to 2% (p=0.11) in non-metal group. There was no association between cobalt or chromium levels with the incidence of atrial fibrillation. All-cause mortality was significantly higher in metal group versus non-metal group (p=0.005). Conclusion: The incidence of atrial fibrillation was relatively more in patients with metal versus non-metal hip arthroplasty but there was no association of serum cobalt or chromium levels with incidence of atrial fibrillation in the subset of patients. In addition, all-cause mortality was significantly higher in the metal group suggesting potential toxic effects of metal containing hip arthroplasty.

Trunnion corrosion in metal-on-polyethylene hip arthroplasty

Aims To report our experience with trunnion corrosion following metal-on-polyethylene total hip arthroplasty, in particular to report the spectrum of presentation and determine the mean time to presentation. Patients and Methods We report the presenting symptoms and signs, intraoperative findings, and early results and complications of operative treatment in nine patients with a mean age of 74 years (60 to 86). The onset of symptoms was at a mean of seven years (3 to 18) after index surgery. Results Patients presented with a variety of symptoms including pain, limp and rash. The preoperative mean serum cobalt level was 7.1 ppb (2.2 to 12.8) and mean serum chromium level was 2.2 ppb (0.5 to 5.2). Metal artifact reduction sequence (MARS) MRI showed fluid collection and possible pseudotumour formation in five hips, fluid collection in two hips, and synovitis/debris in one hip, with no MRI in one patient. Acetabular revision was performed in three patients, six patients underwent liner and head exchange only. The postoperative metal levels decreased in all patients: mean cobalt 0.5 ppb (0 to 1.8) and mean chromium 0.9 ppb (0 to 2.6) at a mean of five months (3 to 8) postoperatively. Seven patients had good pain relief and no complications at one year. There were two major complications requiring reoperation: acute infection at six weeks, for which the patient required two-stage reimplantation; and recurrent dislocation, for which the patient was revised to a dual mobility component. Conclusion Trunnion corrosion in metal-on-polyethylene THA has a range of presenting symptoms, and may present later than previously described. A high index of suspicion is warranted, and serum cobalt and chromium levels are recommended for diagnosis. Patients should be counselled about possible postoperative complications. Cite this article: Bone Joint J 2018;100-B:898–902.

Long-term clinical results of the Metasul metal-on-metal total hip arthroplasty: 12.6 years follow-up of 128 primary total hip replacements

Introduction: The purpose of the present study is to report the long-term clinical results of an uncemented total hip arthroplasty (THA) using a Metasul metal-on-metal (MoM) 28-mm bearing and to evaluate the long-term serum cobalt levels. Methods: At an average of 12.6 years following primary THA, we retrospectively reviewed the clinical results of the first 116 consecutive patients (128 THAs) in our institution who underwent 28-mm Metasul MoM THA. Of the 78 patients who were able to visit our outpatient clinic, serum cobalt levels were evaluated. Results: The overall survival rate of the cohort was 96.1% (95% confidence interval [CI], 93.2-99.6), 12.6 years (95% CI, 12.3-12.7 years) following surgery. 3 patients had undergone revision due to aseptic loosening of the stem and 2 patients sustained a periprosthetic fracture. The average modified Harris Hip Score was 90 (72-97) and the average Oxford Hip Score was 56 (48-60), representing both excellent outcome scores. The average serum cobalt of the entire cohort was 20.1 nmol/L (range 8.5-227.7 nmol/L). Serum cobalt levels of patients with a bilateral MoM THA were significantly higher (35.0 nmol/l, p<0.01). No relation between serum cobalt levels, subjective outcome, radiolucent lines on radiographs and survivorship of the implant was noted. Conclusions: Long-term results of the metasul MoM bearing articulation in THA seem to be excellent, although cobalt serum levels should be monitored closely.