Failure of a novel ceramic-on-ceramic hip resurfacing prosthesis.

We report the early failure of five ceramic-on-ceramic hip resurfacings (CoCHRs). The ceramic used for the acetabular liner was a novel ceramic-composite (two thirds polyurethane and one third alumina ceramic). All cases were revised for increasing metal ion levels (blood cobalt 3.93-208.0 µg/l and chromium 1.57-17.5 µg/l) due to ceramic liner fracture and/or accelerated wear of the ceramic femoral head coating. Patients underwent bearing exchange and revision using primary hip arthroplasty implants at a mean of 3.0 years following CoCHR. Intraoperatively all patients had metallosis. At 1 to 2 years of follow-up blood metal ions normalized with no complications. We do not recommend this particular type of ceramic-on-ceramic bearing for hip resurfacing.

What are the risks accompanying the reduced wear benefit of low-clearance hip resurfacing?

BACKGROUND: Clearance is an important determinant of metal-metal bearing function. Tribologic theory and laboratory evidence suggest low clearance (LC) reduces wear but with a potential to increase friction and clinical reports show LC resurfacings have high implant failure rates. Thus, the role of LC is unclear. QUESTIONS/PURPOSES: We asked: is in vivo wear as reflected by cobalt (Co) and chromium (Cr) levels reduced in LC bearings, and if so, is this benefit offset by increased friction as assessed by implant-bone interface changes? METHODS: We retrospectively reviewed 26 patients with LC resurfacings. We assessed Co and Cr levels in blood and urine, hip function, and radiographic adverse features. These data were compared with those from 26 patients with a similar resurfacing but with conventional clearance (CC) from a previous study. Minimum followup was 4.0 years (mean, 4.1 years; range, 4.0-4.7 years). RESULTS: Co and Cr ion comparisons showed three phases: in the first 2 months, there was no difference between the cohorts; at 2 to 24 months, the CC group showed higher levels; and subsequently, levels in the two groups converged. A mean Oxford hip score of 13 and step activity of 1.9 million cycles per year in the LC group were similar to those of the CC group. Cup radiolucencies were seen in three patients in the LC group and none in the CC group. CONCLUSIONS: Lower Co and Cr levels suggest lower wear in the LC resurfacings in the intermediate term, but the presence of radiolucencies raises the concern that higher bearing friction is affecting implant fixation. A larger clearance than the theoretically predicted ideal may be required to allow for minor manufacturing imperfections, component deformation, and progressive changes in the in vivo lubricant. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Is mid-head resection a durable conservative option in the presence of poor femoral bone quality and distorted anatomy?

BACKGROUND: High medium-term survivorship of hip resurfacing arthroplasty in young patients has led to its increased usage. To achieve high survival rates, selecting patients with appropriate proximal femoral morphology and bone quality is important. For patients with poor bone quality or abnormal morphology, the mid-head resection technique is an alternative, bone-conserving procedure but whether this technique results in acceptable complications and survival is unknown. QUESTIONS/PURPOSES: We therefore assessed (1) implant survivorship of a mid-head resection device during short- and medium-term followup, (2) hip function, (3) adverse radiographic features emphasizing proximal stress shielding, and (4) complications. METHODS: We retrospectively reviewed 164 patients (171 hips) who underwent reconstruction with the Birmingham Mid-Head Resection device (Smith and Nephew Orthopaedics Ltd, Warwick, UK) between 2003 and 2008. Patients were reviewed with hip outcome questionnaires, clinical examination, and radiographs. We report findings in 156 of these 171 hips with a minimum followup of 2 years (mean, 3.5 years, range, 2-7.5 years). They include three successive iterations based on the same design rationale. RESULTS: There were four revisions during this period, including two femoral failures, giving 3.5-year survivorships of 97.4% and 98.7% with revision or reoperation for any reason and femoral failure as the end points, respectively. No patient is currently awaiting revision. Average hip function was 98%, as assessed by Oxford hip score. Five of the 87 intermediate-iteration (V1) stems showed proximal femoral stress shielding, a phenomenon not observed in the other two iterations. Four patients had asymptomatic below-knee deep venous thrombosis and one had nonfatal pulmonary embolism, all of which resolved uneventfully. CONCLUSIONS: The mid-head resection technique can circumvent the need for a more invasive procedure such as standard THA in patients who would benefit from a conservative arthroplasty but do not possess good femoral head bone quality or morphology.

Early markers of nephrotoxicity in patients with metal-on-metal hip arthroplasty.

BACKGROUND: Metal ions released from arthroplasty devices are largely cleared in urine, leading to high exposure in renal tissues. Validated early markers of renal damage are routinely used to monitor workers in heavy metal industries, and renal risk can be quantified in these industries. It is unclear if the ion levels in patients with metal-on-metal hips are sufficient to cause renal damage. QUESTION: Does metal-on-metal (MOM) bearing use over a 10-year period lead to elevation of early renal markers compared with the levels expected in subjects with no metal exposure? METHODS: We retrospectively reviewed 31 patients who underwent MOM hip resurfacings 10 years earlier. Whole blood specimens were collected for metal ion analysis, serum for creatinine estimation, and urine for timed metal ion output and renal markers. The renal marker levels of 30 age- and gender-matched subjects with no metal exposure and no known renal problems or diabetes mellitus were used as controls for renal markers. RESULTS: Median serum creatinine level in the MOM group was 1.1 mg/dL (interquartile range, 1.0-1.2 mg/dL) and median creatinine clearance was 79.2 mL/min. In this cohort, the number of patients with markers of renal damage above the reference range was comparable to the controls. None of the renal markers were associated with metal levels. CONCLUSION: The absence of elevation of renal markers in this cohort 10 years after MOM bearing implantation is reassuring. However, we believe surveillance through further longer-term, large-scale controlled trials are needed to monitor this arthroplasty-induced low-intensity (but long-term) trace element exposure to rule out potential nephrotoxicity.

Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing.

OBJECTIVES: 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. METHODS: 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 (sd 11; 21 to 82), and 73% of implantations were in female patients. All patients were individually counselled, and a detailed informed consent was obtained prior to operation. Primary resurfacing was carried out in 85 hips, and three cases involved revision of previous MoM HRA. Clinical, radiological, and Oxford Hip Score (OHS) assessments were studied, along with implant survival. RESULTS: There was no loss to follow-up and no actual or impending revision or reoperation. Median OHS increased from 24 (interquartile range (IQR) 20 to 28) preoperatively to 48 (IQR 46 to 48) at the latest follow-up (48 being the best possible score). Radiographs showed one patient had a head-neck junction lucency. No other radiolucency, osteolysis, component migration, or femoral neck thinning was noted. CONCLUSION: The results in this small consecutive cohort suggest that metal-on-monobloc-XLPE HRA is successful in the short term and merits further investigation as a conservative alternative to the current accepted standard of stemmed THA. However, we would stress that survival data with longer-term follow-up are needed prior to widespread adoption.Cite this article: R. B. C. Treacy, J. P. Holland, J. Daniel, H. Ziaee, D. J. W. McMinn. Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing. Bone Joint Res 2019;8:443-450. DOI: 10.1302/2046-3758.810.BJR-2019-0060.R1.

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.

Systemic metal exposure in large- and small-diameter metal-on-metal total hip replacements.

Large-diameter metal-metal total hip replacement (THR) offers the advantages of low wear and low dislocation risk. the aim of this investigation was to compare metal levels in large and small-diameter metal-metal hip replacements. Whole blood concentrations and daily output of cobalt and chromium in 28 patients with unilateral large diameter (42- to 54-mm) metal on metal hip replacements at 1-year follow-up were compared with levels in patients with 28-mm metal-on-metal THRs. Both bearings were made of high-carbon cobalt-chrome alloy. The larger bearing is as-cast and the smaller wrought alloy. High-resolution inductively coupled plasma mass spectrometry was used for analysis. The patients had either a cemented polished tapered stainless steel stem or a cementless porous ingrowth titanium alloy stem. Mean whole blood levels in the small- and large-diameter THRs are not significantly different at 1 year (cobalt, 1.7 vs 2.3 microg/L and chromium 1.7 vs 1.4 microg/L). Daily urinary output of cobalt and chromium was also in the same range and without a significant mean difference (cobalt 11.6 microg/24 h in large-diameter and 12.3 microg/24 h in small-diameter THRs and chromium 3.7 and 4.1 microg/24 h, respectively).

A clinicoradiologic study of the Birmingham Mid-Head Resection device.

This is a 1.2- to 5.3-year survival and clinicoradiologic study of patients with the Birmingham Mid-Head Resection (BMHR) device (Smith & Nephew Orthopaedics, Warwick, United Kingdom). Sixty consecutive hips implanted with this device between 2003 and 2007 were reviewed with hip outcome questionnaires, clinical examination, and radiographs at a minimum follow-up of 1 year. There were no revisions, mechanical failures, or signs of femoral neck stress shielding. All hips were functioning well and showed no significant adverse clinical or radiographic features. Birmingham Mid-Head Replacement offers the prospect of circumventing the need for a more invasive procedure such as hip replacement in patients who would benefit from a conservative arthroplasty but lack femoral head bone quality, which is a prerequisite for a successful hip resurfacing.