Abstract
[Introduction]
In 1995, Muller reported on the improvement of metal-on-metal (MOM) bearing over the existing metal-on-polyethylene (MOP) articulations which demonstrated more rapid wear together with granulomatous foreign body reactions, damage of periarticular bony and soft tissues and associated expansile psoas bursal masses. He suggested that adequate lubrication together with improved material properties and manufacturing technologies would bring to the market a superior device with greater longevity. We wish to present our experience with a modern version of a MOM bearing.
[Material and Methods]
Between April 2008 and February 2012, we implanted 160 MOM THA with head diameters of 38–50 mm in 139 patients (21 males and 118 females). Their ages were 40–86 years (avg. 63.6 yrs). Follow up was 9 to 53 months post implantation (avg. 28 months). All implants were manufactured by one company (Wright Medical Technology, Arlington, TN, USA). The stems were of a standard titanium-aluminum alloy, either 45 ANCA-FIT or 115 PROFEMUR Z non-cemented stems. Acetabular components were all CONSERVE PLUS cobalt-chromium monoblock shells. Heads were also fabricated out of cobalt-chromium alloy, with modular junctions. Patients with complaints of groin pain and/or swelling or hip instability underwent MRI examination in order to detect the presence of fluid collections or soft tissue masses (Fig. 1 and 2). The statistical correlation between abnormal findings on MRI and age, gender, head diameter, component position and duration post-surgery was performed.
[Results]
27 hips in 23 patients (16.9%) were found to have either a fluid collection or “pseudotumor”. These were in 2 males and 21 female patients. There were 19 males and 97 females without complaints who did not undergo MRI examination. There was no difference in age between these two groups of patients (63.1 vs. 63.7 yrs). There was no difference in duration from the time of implantation, but there was an early presentation of symptomatic pseudotumor. There appeared to be a significant difference between the mean head diameter of the two groups, 41.8 mm and 44.2 mm respectively. There was no statistical difference between the two groups with regard to implant orientation: cup inclination 18–70 degrees (40.4 vs. 43.8 degrees); cup anteversion −13−49 degrees (14.0 vs. 15.0 degrees); stem anteversion 2–48 degrees (20.2 vs. 23.1 degrees); and stem offset 17.5–56.2 mm (38.2 vs. 37.8 mm).
[Discussion]
In this study, it is important to emphasize that the appearance of symptoms and development of a pseudotumor occurred early after a MOM THA in some patients. It may represent a hypersensitivity to materials implanted. However, the possibility that this may represent a foreign body reaction to particulate debris produced by articulating surfaces much like that seen with alternative material such as MOP, reflective of wear, insufficient lubrication or other causes. In this regard, our study suffers from the limitation that serum levels of chromium and cobalt were not obtained from symptomatic patients. Nor were these patients skin tested for hypersensitivity to these materials. Also it will be important to subject all patients to MRI examination to evaluate the possibility of “silent” fluid collections and pseudotumors.
