The cause of unexplained pain among metal-on-metal hip implant patients is more likely to be tissue damage than wear of the implant, Hospital for Special Surgery researchers have found. The study, performed by Dr. Danyal Nawabi, orthopedic surgery fellow, and research collaborators at HSS, will be reported at the upcoming annual meeting of the American Academy of Orthopaedic Surgeons, March 19-23, in Chicago.
Researchers set out to determine causes of unexplained pain among patients with metal-on-metal hip implants (in which the ball and socket are both made of metal) who came to the hospital for revision surgery. Metal-on-metal implants have potential advantages, said Timothy Wright, Ph.D., Kirby Chair of Orthopedic Biomechanics at Hospital for Special Surgery (HSS): "If they remain well lubricated, as happens with the oil in your car, it minimizes wear." In addition, surgeons can implant a bigger head, or ball, making the hip joint more stable. But nationwide, failure of metal-on-metal hip devices due to unexplained pain is rising.
The research group, which did not have any ties to hip implant manufacturers, was led by Dr. Douglas Padgett, chief of the Adult Reconstruction and Joint Replacement Division and chief of the Hip Service at HSS, and Dr. Hollis Potter, chief of the Division of Magnetic Resonance imaging (MRI). They compared 50 patients (33 with total hip arthroplasties and 17 with hip resurfacing arthroplasties) who came to HSS for revision surgery because of unexplained pain, to a control group of 48 patients (23 with total hip arthroplasties and 25 with hip resurfacing arthroplasties) who came to HSS for revision surgery because of loosening, malalignment, infection or fracture. The investigators combined results from clinical examinations of the patients, magnetic resonance imaging, wear analysis studies on the removed implants, and pathology studies of tissues removed at surgery, including the degree of aseptic lymphocytic vasculitis-associated lesions (ALVAL), a sign of adverse tissue reactions to metal debris.