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Special treatment, detection needed for complications from metal-on-metal hips
Complications from metal-on-metal hip arthroplasty call for individualized treatments, according to an orthopedic surgeon researcher from Rush University Medical Center in Chicago.
“Clinical decision making must be based on the constellation of symptoms and signs in the individual patient, as well as the findings on imaging tests and laboratory studies,” Joshua J. Jacobs, MD, said during his presentation at the Current Concepts in Joint Replacement 2011 Winter Meeting.
Serum and urine metal ion level testing may allow surgeons to monitor wear of the bearing surfaces; however, metal levels also reflect metal release from corrosion of modular metal/metal connections, Jacobs said. Orthopedists should proceed with caution when performing routine clinical measurements unless they have a reliable and validated lab.
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Adverse local tissue reactions (ALTR) as the cause of painful metal-on-metal (MoM) total hip arthroplasties are getting considerable attention in the media, Jacobs said. ALTRs include osteolysis, delayed type hypersensitivity-like responses (aseptic lymphocyte-dominated vasculitis-associated lesion or ALVAL), and soft tissue masses or pseudotumors. Metal artifact reduction sequence MRI (MARS MRI) is an important diagnostic test to evaluate the soft tissue envelope around the hip. “The adaptive immune response or hypersensitivity may play an important role in the pathogenesis of these ALTRs, in a subset of patients, but currently diagnostic tools for metal hypersensitivity have yet to be clinically validated,” Jacobs said.
Key diagnostic tools
The best diagnostic tool for patients with MoM hip implants, is a history and physical “to rule out spinal pathology or local soft tissue inflammation Orthopedic surgeons should also inquire about patients’ general health and the new onset of any systemic symptoms, Jacobs said. Plain X-rays can determine whether the implants demonstrate signs of loosening. An infection work-up is essential. MARS MRI and ultrasound can be used to image periprosthetic soft tissues.
Serum cobalt (Co) and chromium (Cr) levels may also be useful to monitor wear of the bearing surface and/or corrosion of metal/metal modular connections, Jacobs said.
“When Co levels are elevated out of proportion to the Cr levels, corrosion of modular connections is suspected,” Jacobs observed.
Using metal levels to measure wear could be “tricky” unless the orthopedist has an extensive database, Jacobs said. A laboratory network that enables reproducible and reliable results does not currently exist in the United States, and there may be variability in analyses if the orthopedist uses different labs. Some labs perform whole blood, erythrocytes, plasma or serum testing. The specimen collection may vary and contamination must be avoided, Jacobs warned. Most labs use inductively coupled plasma mass spectrometry, but some may still use atomic absorption spectrometry.
“It may be premature at this time to recommend routine surveillance, despite the fact that some regulatory agencies, for example, the [Medicines and Healthcare products Regulatory Agency] MHRA in the United Kingdom, have already done so,” Jacobs said.
Toxicity and pseudotumors
In vitro studies have shown the effects of metal ions on cells, Jacobs said. High concentrations of cobalt in particular can be toxic to cells. The cobalt will be distributed both locally and systemically from wear and corrosion of MoM bearings. He noted that systemic end organ damage is rare and cited four case reports that had fractured ceramic heads that lead to excessive trunion wear and severely toxic situations.
Metal hypersensitivity to orthopedic implants has been described and is generally a delayed type IV cell-mediated response, Jacobs said. This is based on numerous case reports in the literature, which demonstrate “a temporal association between the implantation of a device and the development of, for example, a cutaneous reaction,” he said.
“Why might metal allergy occur?” Jacobs asked. “Because metal ions or particles generated from wear and/or may form complexes with serum proteins changing their conformation so that they are recognized as non-self proteins. This initiates a delayed-type hypersensitivity response.”
Patch testing is a helpful test to determine the presence or absence of contact dermatitis, but it is not necessarily a good test for determining deep tissue allergy, Jacobs said. Lymphocyte transformation testing (LTT) may be a better alternative. LTT testing may be most helpful in the work-up of patients who are symptomatic and do not demonstrate substantial elevations in serum or whole blood metal levels.
“Since there is cross talk between the adaptive and innate immune responses, metal allergy can lead to periprosthetic osteolysis,” Jacobs said. “This process is mechanistically distinct from particulate polyethylene-induced osteolysis in metal-on-polyethylene bearings.”
Higher levels of cobalt and chromium in the blood have been shown to be associated with the occurrence of pseudotumors, Jacobs said. In a study by Langton and colleagues, Jacobs said, that researchers found that serum cobalt and chromium levels correlated with volumetric wear. However, the wear “did not correlate with the extent of deep tissue damage, which suggested that there was variability in to the host response to debris,” Jacobs said.
“The management of patients with metal on metal bearings will continue to evolve as more clinical research findings are reported. Periodic and long-term surveillance is highly recommended,” Jacobs said. – by Renee Blisard
References:For more information:
- Jacobs JJ. Metal-metal hip arthroplasty: What are the indications for intervention? Paper #58. Presented at the Current Concepts in Joint Replacement Winter Meeting. Dec. 7-10, 2011. Orlando, Fla.
- Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, et al. Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: A consequence of excess wear. J Bone Joint Surg Br. 2010; 92(1):38-46. doi:10.1302/0301-620X.92B1.22770.
- Joshua J. Jacobs, MD, can be reached at Rush University Medical Center, 1725 Harrison St., No. 1063, Chicago, IL 60612; 312-432-2344; email: joshua.jacobs@rushortho.com.
- Disclosure: Jacobs receives consulting fees from Depuy, Medtronic, Smith & Nephew Orthopaedics, Spinal Motion, Advanced Spine Technology and Zimmer. He receives research grants from Medtronic, Advanced Spine Technology and Zimmer. He also receives stock options as a consultant for Implant Protection.