Follow-up of Metal-on-Metal Hip Replacements at a Large District Hospital and the Implementation of Medicines and Healthcare Products Regulatory Agency Guidelines: A Review of 297 Patients

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.