Yet another new study is pointing to the serious dangers posed by metal-on-metal hip replacement devices, including a risk of aseptic acetabular loosening, metallosis and pseudotumor formation. Most importantly, the new study, published in the journal Orthopedics, found that when metal-on-metal hip implants do fail, such failures generally occur within a few years of initial surgery.
The study reviewed information on 80 metal-on-metal hip replacement patients who underwent revision surgeries for failing implants at two institutions were a high volume of such procedures are performed. The main reason for the revisions – 56% or 45 patients – was aseptic acetabular loosening. Of those patients who suffered loosening, most had received either Zimmer’s Durom Cup (78% or 35/45 patients), or DePuy Orthopaedic’s ASR cup (9% or 4/35 patients). The rest had been fitted with Biomet Magnum cups (2), Depuy Pinnacle cups (1), Wright Conserve cup (1) and 1 un¬known cup.
Other reasons for failures included:
• Infection, 12.5%
• Metal hypersensitivity, 6.25%
• Failed resurfacing, 6.25%
• Fracture, 5%
• Loose stem, 3.75%
• Dislodged liner, 3.75%
• Seizing, 1.25%
• Cup malposi¬tion, 1.25%
• Femoral stem fracture, 1.25%
A total of 10 patients experienced significant metallosis or significantly involved lo¬cal tissue changes due to the metal debris seen during revision surgery. Most of these patients – 4 – had been fitted with DePuy ASR cups. The Pinnacle and Magnum were each used in two cases, while the Birmingham Hip Resurfacing cup and an unknown cup were each used in once case. Two patients with the ASR and Birmingham cups experienced pseudotumor formation.
Overall, 78% of the revisions were being performed within 2 years of the initial operation and 92.5% within 3 years. Like other metal-on-metal hip implant studies published previously, the Orthopedic study points to a need for close follow-up of all patients with all-metal devices.