Understanding end plate changes associated with disc surgery

Abstract

Purpose of study: As disc arthroplasty for the treatment of degenerative disc disease becomes more prevalent, questions are beginning to arise as to the possible effects that these devices may have on the vertebral end plates. The end plate changes seen on magnetic resonance imaging (MRI) films after disc surgery usually come in two forms: they can either appear as anatomical changes to the configuration to the cartilage/vertebral body, or the changes can manifest themselves through differential signal intensities on MRIs. These latter types of abnormalities, Modic changes, represent an alteration in the vascularity and fat content of the bone marrow. End plate remodeling and Modic changes are thought to occur in the response to a number of factors, including natural degeneration of the disc or bone, infection within or around the disc or adjustments of the vertebrae in response to changes in load pressures. Both end plate remodeling and Modic changes typically occur after most types of surgical procedures to the disc, such as decompression, discectomy and fusion. Although end plate remodeling and Modic changes are common, their long-term clinical significance is not well understood. The intent of this study is to document the short- and long-term effects of prosthetic nucleus devices on the vertebral end plates.Methods used: In this retrospective study we followed 60 patients implanted with PDN prosthetic disc-nucleus devices (Raymedica, Inc.) for a period of 12 months. Preoperative MRI films were compared with 6-week through 12-month follow-up images.of findings: Of the 60 patients examined, 67% showed some degree of postoperative end plate remodeling and/or Modic change. Early in the follow-up process, none of the changes could be correlated with any clinical symptoms, and MRI done at the 12-month follow-up showed that for the most patients the changes had stabilized. There were three cases where end plate remodeling continued to a degree that resulted in significant disc-height narrowing.Relationship between findings and existing knowledge: The presence of end plate remodeling and Modic changes in patients implanted with prosthetic nucleus devices is not unexpected given that this type of change is commonly seen after surgical procedures affecting the disc. The results are also in agreement with the concept that bone will remodel in response to changes in stress (Wolff's law).Overall significance of findings: Although vertebral body and end plate radiographic changes do occur in some patients implanted with PDN devices, these changes usually stabilize over time and rarely lead to clinical sequelae. Therefore, treatment decisions based on the presence of postoperative radiographic changes should not be made unless the changes can be correlated to clinical signs and symptoms.Disclosures: Device or drug: PDN prosthetic disc-nucleus device. Status: investigational.Conflict of interest: Rick Vazquez, employee of Raymedica Inc.; Mark Myers, consultant, Raymedica Inc.