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Higher than expected adverse event rates with metal/metal THA
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The rate of adverse events, such as pseudotumor formation, high metal ion levels and metallosis, relative to metal-on-metal total hip arthroplasties exceeds that reported previously in the literature.
“Our study shows a substantially higher incidence of pseudotumor formation and subsequent revisions in patients with metal-on-metal total hip arthroplasties than previously reported,” Bart H. Bosker, MD, a researcher in the department of orthopaedic surgery and traumatology at the Isala Clinics, The Netherlands, said at the 12th EFORT Congress 2011.
For their study, Bosker and colleagues evaluated a prospective cohort of asymptomatic patients to determine the incidence of symptomatic pseudotumors after large-diameter femoral head metal/metal total hip arthroplasty (THA) and to identify potential risk factors for this condition.
Bosker noted these results came after an April 2010 alert issued by the British Orthopaedic Association regarding adverse events after metal/metal THA.
From January 2005 through November 2007, Bosker and colleagues studied 108 patients who had metal/metal THAs with large diameter femoral heads performed at a single center. They collected data on pain and mechanical symptoms, hip outcome scores, SF-36 scores and measured metal-ion levels. Investigators also performed physical examinations and obtained conventional hip and pelvis radiographs and CT scans. Patients whose CT scans showed possible peri-articular masses were evaluated via MRI, ultrasound biopsies and histological tests.
Overall, the study group was followed up for 3.6 years, average.
The investigators diagnosed 42 patients with pseudotumors and 13 patients with a symptomatic pseudotumor underwent revision THAs that included polyethylene acetabular components and small diameter metal heads. The total revision rate was 12%.
“We did not anticipate the high incidence of pseudotumor formation. Most revision cases were identified only after applying an intensive screening protocol,” Bosker told Orthopaedics Today Europe. “We recommend close monitoring of patients with a metal-on-metal hip arthroplasty.” – by Tara Grassia
Reference:
- Bosker BH, Ettema HB, Boomsma MF, et al. Incidence of pseudotumors in patients after metal-on-metal large-diameter femoral head total hip arthroplasty: A prospective cohort study. Presented at the 12th EFORT Congress 2011. June 1-4. Copenhagen, Denmark.
- Bart H. Bosker, MD, can be reached at P.O. Box 10500, 800GM, Zwolle, The Netherlands; +31-6-24866058; email: b.h.bosker@isala.nl.
- Disclosure: Bosker has no relevant financial disclosures.
The results of this study add to the growing concerns of unacceptable rates of serious complications following large diameter total hip arthroplasty. There are a number of interesting points in the article which are consistent with our experience and those of others.
Large diameter total hip arthroplasty (LDMOMTHRs) should be regarded as a separate entity, distinct from metal-on-metal (MoM) resurfacings. There is accumulating evidence to show that the modular junction of large diameter total hip repalcement is an important source of metallic debris. In fact, it is our own experience at our center that debris generated from taper junctions appears to more readily stimulate a negative cascade of events culminating in adverse tissue reactions. In other words, an amount of debris released from tapers appears to be more significant than an equivalent amount released from bearing surfaces. For this reason, blood cobalt concentrations in a total hip replacement (THR) patient should be interpreted differently from a concentration in a resurfacing patient. Certainly the suggested Medicines and Healthcare Products Regulatory Agency threshold value of 7 mg/L appears to equate to advanced damage of the taper junction and is likely too high for THRs.
Because it appears that the modular junction of the THR is the significant issue, there is not the clear relationship between component size/orientation and increased metal ion concentrations/rates of failure which has been observed in hip resurfacing arthroplasty. For example in resurfacing devices, as components become larger, median metal ion concentrations decrease and this is mirrored in a decrease in metal reaction rates. These relationships have not been demonstrated with LDMoMTHRs and, in fact, a trend towards increasing ion levels and increasing bearing size has been reported.
The key points here are:
- All MoM devices are not the same.
- Symptoms in the presence of “normal” blood metal ion concentrations must not be ignored.
- Symptomatology does not appear to correlate well with extent of tissue lesions.
- All patients with LDMoMTHR should be followed closely until the scale of the problem has been fully elucidated with regard to different manufacturers’ devices.
Finally, we must at least consider the possibility that this is not truly a MoM problem per se, but rather a large diameter problem.
— David J. Langton, MRCS
Joint Replacement
Unit
University Hospital of North Tees
Stockton, England
Disclosure: Langton receives
consulting/instructional course fees from DePuy, Finsbury and Wright Medical
and travel reimbursement from DePuy, Wright Medical, Smith & Nephew and
Zimmer.
References:
- Bolland BJ, Culliford DJ, Langton DJ, et al. High failure rate with a large-diameter hybrid metal-on-metal total hip replacement: clinical, radiological and retrieval analysis. J Bone Joint Surg Br. 2011;93:608-615.
- Garbuz DS, Tanzer M, Greidanus NV, et al. Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial. Clin Orthop. 2010;468:318-325.
- Langton DJ, Jameson SS, Joyce TJ, et al. Accelerating failure rate of the ASR total hip replacement. J Bone Joint Surg Br. 2011;93:1011-1016.
- Medicines and Healthcare products Regulatory Agency. Medical device alert: all metal-on-metal (MoM) hip replacements (MDA/2010/033). http://www.mhra.gov.uk/Publications/Safetywarnings/MedicalDeviceAlerts/CON079157.
- Wynn-Jones H, Macnair R, Wimhurst J, et al. Silent soft tissue pathology is common with a modern metal-on-metal hip arthroplasty. Acta Orthop. 2011;82:301-307.