Short summary

Concerns related to the use of metal-on-metal (MoM) hip arthroplasty (HA) include side effects from chromium and cobalt particles released due to implant wear. Systemic complications are described in patients with malfunctioning MoM HA. No larger nation-wide study describing fluctuation in metal ion levels since surgery in patients with MoM HA and its association with cardiomyopathy and heart fail-ure has been performed.

Rationale

Background: Total hip arthroplasty (THA) is a cost-effective and safe intervention for end-stage osteoarthri-tis. Different bearing components have been used to improve THA survival. Metal-on-metal (MoM) THA was introduced in the early 1960s and in the 1990s, MoM hip resurfacing arthro-plasty was introduced. These implants were assumed to have lower wear and long-term fail-ure rates and lower risk of dislocation due to the larger femoral head sizes. They were espe-cially used in young patients, who had poor results with other more commonly used bearings such as metal-on-polyethylene (MoP). 1,400 MoM hip resurfacing arthroplasties and 2,100 MoM total hip arthroplasties have been implanted in Denmark from 2000 to 2012 and 1,5 million MoM implants are inserted worldwide.

MoM hip implants have shown to have higher revision rates than MoP hip implants. In addi-tion, concerns have been raised regarding the side effects from the metal particles mainly consisting of chromium and cobalt, that are released from the bearing surface due to implant wear. The chromium and cobalt released from MoM hip implants may cause local and systemic complications. The local complications affect bone and soft tissue around the MoM hip implant, including darkening of the soft tissues (metallosis) and the formation of pseudotumours. Systemic complications have been described in patients with malfunctioning MoM hip implants causing cardiomyopathy or heart failure. Further, carcinogenicity was one of the early concerns related to elevated chromium and cobalt levels. Other systemic complications include impaired vision and hearing, tinnitus, hypothyroidism, peripheral neu-ropathy, anxiety, depression, fatigue, anorexia and changes in the lymphocytes chromosomes. Due to the above-mentioned concerns, all patients with a MoM hip implant in Denmark were, from 2012, offered to participate in a follow-up program including a clinical examination, measurement of chromium and cobalt blood levels and x-ray of the hip after 1, 2, 5, 7-8, 10 years and hereafter every 5th year.

Development of heart disease, as a result of a MoM hip implants, is a severe and very serious complication. Some studies have demonstrated an increased risk of developing heart disease in patients with a MoM hip implant, compared to patients with a MoP hip implant and they therefore recommend regular monitoring of cardiac function. Other studies have not found a correlation. Heart disease due to high metal-ion levels occurs in few patients, but it has se-vere consequences for those affected, and for society, due to the increased morbidity and mortality, as well as increased healthcare costs associated with this.

Overall aim The overall aim is to 1) investigate the association between MoM hip implants and risk of heart disease, 2) describe fluctuation of metal ion levels in patients having MoM hip implant, 3) in-vestigate the prevalence of heart failure and cardiomyopathy in patients with MoM hip implants compared to patients with other bearings and to the background population, and 4) investigate the cardiac function by Cardiac Magnetic Resonance Imaging in patients with MoM hip im-plants and elevated metal ion levels.

Description of the cohort

Study population: 50 patients with unilateral MoM THA or HRA and increased levels of Cr and Co over the 7 µg/L limit during the latest 2 samples from the follow-up program. Control group consisting of 50 participants, who do not have an artificial hip. The groups will be randomly selected.

Data and biological material

Data will be collected from - The Danish Civil Registration System (CRS) - The Danish Hip Arthroplasty Register (DHR) - The Danish National Patient Registry (DNPR) The participants of the study will undergo an MRI of the heart, a clinical examination of the hip, blood sample with metal ion levels and they have to answer following questionaires: - Oxford Hip Score, - Forgotten joint score (FJS-12) - EQ-5D-5L59, and - Modified Kansas City question-naire (KCCQ)

Collaborating researchers and departments

Department of Cardiology, Odense University Hospital

Department of Clinical Epidemiology, Aarhus University Hospital

Department of orthopedic surgery, and Traumatology, Copenhagen University Hospital