Adverse local tissue reactions (ALTRs) were initially reported as complications associated with metal-on-metal (MoM) bearings; however, there is increasing concern regarding the occurrence of adverse local tissue reactions from mechanically assisted crevice corrosion (MACC) at the femoral head-neck junction or between other modular junctions of the implant containing cobalt chromium parts in patients with metal-on-polyethylene (MoP) bearings. ALTR due to MACC at the head-neck junction has primarily been reported in association with cobalt chromium alloy femoral heads. As pain following total hip arthroplasty may have various intrinsic and extrinsic causes, a systematic approach to evaluation (risk stratification algorithm) based on the currently available data is recommended to optimize patient management. Evaluation should begin by ruling out common causes of pain, including component loosening and periprosthetic joint infection. While specialized tests such as blood metal analysis and metal artifact reduction sequence magnetic resonance imaging (MARS MRI) are useful modalities in evaluating for ALTRs, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. There should be a low threshold to perform a systematic evaluation for ALTR due to MACC in patients with metal-on-polyethylene total hip arthroplasty as early recognition and diagnosis is critical, as delays in appropriate treatment initiation may result in soft-tissue damage, which complicates surgical treatment and is associated with a higher risk of complications and poorer patient outcomes.

BACKGROUND: Medicines and Healthcare products Regulatory Agency (MHRA) guidance for patients with metal-on-metal (MoM) hip replacements was provided in 2012 and updated in 2017 to assist in the early detection of soft-tissue reactions due to metal wear debris. A large number of MoM hip replacements were undertaken at our hospital trust. A program of recall for all patients with MoM hip replacements was undertaken and MHRA guidelines were implemented. In this study, we aimed to investigate the effectiveness of the revised MHRA guidelines in the detection of early adverse reactions to metal debris and to re-evaluate the indications for metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) and revision surgery.
METHODS: Identification and recall of all patients with MoM hip replacements from 2001 were conducted by using theatre logs, patient records, clinical coding information, and consultant logbooks. Two senior arthroplasty consultants reviewed X-rays and patient records. Postal questionnaires were forwarded to patients, together with requests for general practitioners to complete cobalt and chromium blood tests. The two consultant-led review of MOM replacements was undertaken with further radiological investigations (X-rays, MARS-MRI) performed according to the 2017 guidance with support of consultant radiologists.
RESULTS: Of 674 identified patients, 297 were available for review: 26 patients did not have MoM implants, 36 were untraceable, 59 refused follow-up, 87 moved out of area, 147 had died, and 22 already had revision. Of 297 patients, 126 were women and 171 were men; age range was 39 to 95 years (mean age, 69 years); 126 had resurfacing and 171 had MoM replacements. Twenty-six patients had elevated metal ions. Thirty-three patients underwent MARS-MRI: MARS-MRI results were positive in 17 and negative in 16. Of 17 patients with positive MARS-MRI, 10 patients were asymptomatic and seven were waiting revision.
CONCLUSIONS: Positive MARS-MRI can often occur in the absence of elevated metal ion levels; elevated blood metal ion levels do not mean MARS-MRI will be positive. All patients with MoM replacements were at risk. It is imperative to assess patients regularly for symptoms that may raise clinical suspicion and maintain a low threshold to performing MARS-MRI.

BACKGROUND: In the follow-up evaluation of patients with metal-on-metal (MoM) hip replacements, current evidence suggests that orthopaedic surgeons should avoid reliance on any single investigative tool. Current risk stratification guidelines can be difficult to interpret because they do not provide guidance when there are several risk factors in different groups (high and low risk). To improve the clinical utility of risk stratification guidelines, we designed a scoring system to assess the risk of revision.
METHODS: The study population consisted of 1,709 patients (1,912 hips) enrolled in a multicenter follow-up study of a recalled MoM hip replacement. Eleven scoring criteria were determined on the basis of existing follow-up algorithm recommendations and consisted of patient-related factors, symptoms, clinical status, implant type, metal ion levels, and radiographic imaging results. Forward stepwise logistic regression was conducted to determine the minimum set of predictive variables for the risk of revision and to assign variable weights. The MoM risk score for each hip was then created by averaging the weighted values of each predictive variable.
RESULTS: Receiver operating characteristic curve analysis yielded good discrimination between all revised and unrevised hips, with an area under the curve of 0.82 (p < 0.001). The odds of revision for the group with a high MoM risk score were increased by 5.8-fold (95% confidence interval [CI], 3.1 to 11.0) relative to the moderate risk group and by 21.8-fold (95% CI, 9.9 to 48.0) compared with the low risk group.
CONCLUSIONS: Although the use of MoM hip arthroplasty has been limited since 2010, we continue to be faced with the follow-up and risk assessment of thousands of patients who have not had a revision. As more knowledge about risk stratification is gained, the complexity of the algorithms is expected to increase. We propose the use of the MoM risk score as a tool to aid in the clinical decision-making process.
METHODS: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

This paper reports the consensus of an international faculty of expert metal-on-metal (MoM) hip resurfacing surgeons, with a combined experience of over 40,000 cases, on the current status of hip resurfacing arthroplasty. Indications, design and metallurgy issues, release of metal ions and adverse soft tissue reactions to particles, management of problematic cases and revisions, as well as required experience and training are covered. The overall consensus is that MoM hip resurfacing should not be banned and should be viewed separately from MoM total hip arthroplasty (THA) with a large diameter head because of the different design and wear behaviour related to the taper/trunnion connection. The use of hip resurfacing has decreased worldwide but specialist centres continue to advocate hip resurfacing in young and active male patients. Regarding age the general recommendation is to avoid hip resurfacing in men older than 65 and in women older than 55, depending on the patient activity and bone quality. Female gender is considered a relative contraindication. Most surgeons would not implant a MoM hip in women who would still like a child. Regardless of gender, there is a consensus not to perform hip resurfacing in case of a femoral head size smaller than 46 mm and in patients with renal insufficiency or with a known metal allergy. Regarding follow-up of hip resurfacing and detection of adverse local tissue reactions, metal ion measurements, MRI and ultrasound are advocated depending on the local expertise. The consensus is that hip resurfacing should be limited to high volume hip surgeons, who are experienced in hip resurfacing or trained to perform hip resurfacing in a specialist centre.

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There should be a low threshold to perform a systematic evaluation of patients with MoM hip arthroplasty as early recognition and diagnosis will facilitate the initiation of appropriate treatment prior to significant adverse biological reactions. A painful MoM hip arthroplasty has various intrinsic and extrinsic causes, and a systematic treatment approach based on the currently available data is presented to optimize management of MoM patients. The risk stratification algorithm presented will continue to develop as further evidence becomes available providing additional insights. While specialized tests such as metal ion analysis are useful modalities for assessing MoM hip arthroplasty, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. Future research focusing on validation of the current diagnostic tools for detecting adverse local tissue reactions as well as optimization of MoM bearings and modular connections to further diminish wear and corrosion is warranted.

BACKGROUND: There is an ongoing debate about the optimal use of metal-on-metal (MoM) bearings in total hip replacement, since there are uncertainties about local and systemic adverse effects due to wear and corrosion of these bearings. Despite various national recommendations, efforts to achieve international harmonization of specific evidence-based recommendations for best practice are still lacking.
OBJECTIVE: An international consensus study group should be able to develop recommendations on the use and monitoring of MoM bearings, preferably at the European level, through a multidisciplinary approach, by integrating the perspectives of various stakeholders.
METHODS: Twenty-one experts representing three stakeholder groups and eight countries participated in this European consensus study, which consisted of a consensus meeting, subsequent structured discussion, and consensus voting.
RESULTS: The current statement defines first of all benefits, local and systemic risks, as well as uncertain issues related to MoM bearings. Safety assessment after implantation of MoM comprises all patients. A closer follow-up is recommended for large head MoM (≥36mm) and resurfacing. In these implants basic follow-up should consist of x-rays and metal ion measurement of cobalt in whole blood, performed with GF-AAS or ICP-MS. Clinical and/or radiographic abnormality as well as elevated ion levels needs additional imaging (ultrasound, CT-scan and/or MARS-MRI). Cobalt values less than 2 μg/L are probably devoid of clinical concern, the threshold value for clinical concern is expected to be within the range of 2-7 μg/L.
CONCLUSIONS: This is the first multinational, interdisciplinary, and multiprofessional approach for developing a recommendation for the use and monitoring of MoM bearings in total hip replacement. The current recommendations are in partial agreement with previous statements regarding the extent of follow-up and imaging techniques. They however differ from previous communications regarding measurement of metal ions and especially the investigated medium, technique, and eventual threshold levels.
METHODS: Level V, expert opinion/agreement conference.

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