Early Failure of Metal-on-Metal Artificial Disc Prostheses Associated with Lymphocytic Reaction Diagnosis and Treatment Experience in Four Cases

Study Design. Report of four collected cases. Objective. The purpose of this report is to describe the presentation, diagnostic workup, treatment, and pathologic findings in four cases of lymphocytic reaction in patients receiving a metal-on-metal total disc replacement (TDR). Summary of Background Data. Metal-on-metal designs in hip arthroplasty have gained popularity because of decreased volumetric wear rates and theoretically increased implant longevity. Systemic metal ions produced have not been associated with adverse clinical sequelae, although there have been reports of local soft-tissue reactions leading to early prosthetic failure. Histologic evaluation in these cases suggested a cell-mediated delayed-type hypersensitivity reaction. Metal-on-metal bearings have also emerged in lumbar and cervical TDR. Methods. This report is on four patients, from three centers, who underwent TDR, using a metal-on-metal implant, and later presented with symptoms that were determined to be due to lymphocytic reaction. Details of their symptoms, diagnostic work-up, treatment, and outcomes were compiled. Results. All four patients initially had a good surgical outcome, followed by the onset and worsening of axial pain, and/or radicular symptoms months later. All patients had imaging findings of a mass lesion with neurologic impingement. All three of the lumbar patients underwent a decompressive posterior procedure before the eventual device removal and fusion. Intraoperatively, in all the lumbar cases, a thick, yellowish, avascular soft-tissue mass was found to be responsible for an epidural-mass effect on the thecal sac. In the cervical case, there was a gray-tinged soft-tissue response around the implant, suggestive of metallosis. Independent laboratory analysis confirmed a lymphocytic reaction to the implant. Three of the patients had a good outcome after the explant and revision surgery. The remaining patient continued to have residual symptoms related to the neural compression caused by the mass. Conclusions. In this group of patients from three centers, a metal-on-metal TDR resulted in a lymphocytic reaction causing subsequent failure of the surgery. This phenomenon has previously been recognized with metal bearings in hip arthroplasty. Surgeons using metal-on-metal TDRs should be aware of this possible occurrence.