High frequency of adverse local tissue reactions in asymptomatic patients with metal-on-metal THA
The key to successful management of patients with metal-on-metal (MOM) THAs is to diagnose adverse local tissue reactions (ALTRs) early. ALTRs have been described in asymptomatic patients with resurfacing arthroplasties. Whether this concerning finding applies to modular MOM THAs is unknown.
We (1) determined the prevalence of ALTRs in asymptomatic patients with modular MOM THAs, (2) described any differences in the appearance of these lesions between symptomatic and asymptomatic patients, and (3) analyzed potential predictive factors for any associations with ALTR prevalence.
We evaluated 114 patients with modular MOM THAs who had MRI with metal artifact reduction sequence software and metal ion laboratory results at a mean of 57 months postoperatively. There were 83 asymptomatic and 31 symptomatic patients. We defined ALTRs as abnormal fluid collections, solid or semisolid pseudotumors, or muscle or bone damage. Ion levels, lesion size, and cup abduction angles were analyzed.
Twenty-six (31%) asymptomatic patients had ALTR lesions, all of which were in the greater trochanteric area. Most lesions in symptomatic patients also were in that location, but there was more diversity of location in this group. The cup position among patients with ALTRs was generally good; the average abduction angle for the asymptomatic patients with ALTRs was 40°. In 24 (92%) and 22 (85%) of 26 asymptomatic patients with ALTRs, respectively, chromium and cobalt levels were below the 7-ppb threshold.
A 31% incidence of periarticular fluid collections in asymptomatic patients with modular MOM THAs is alarming and calls into question any algorithmic approach dependent on symptomatology. The presence of pain was insufficient to identify patients at risk for ALTRs. To determine whether routine cross-sectional imaging of all asymptomatic patients with MOM implants is necessary will require a larger study cohort, longer followup, and clearer understanding of the natural history of periarticular lesions in these patients.