General Session: MIS-3
Presented by: M. Gornet - View Audio/Video Presentation (Members Only)
M. Gornet(1), J.A. Hipp(2), N.D. Wharton(2), F.W. Schranck(3), A.G. Copay(3), K. Wymore(4)
(1) The Orthopedic Center of St. Louis, St Louis, MO, United States
(2) Medical Metrics, Houston, TX, United States
(3) SPIRITT Research, St Louis, MO, United States
(4) University of Missouri, School of Medicine, Columbia, MO, United States
Purpose: Heterotopic ossification (HO) following cervical disc arthroplasty (CDA) can compromise the ability of a CDA to provide motion at the treated level. It is important to understand the factors that may lead to HO, as this can help to identify strategies to avoid HO. With this goal an analysis was performed to identify risk factors for HO following CDA.
Materials and Methods: Multiple assessments were performed using prospectively collected PreOp through 24 month radiographs and MRI exams for 266 CDA patients. CDA had been completed at between one and three levels. Three FDA approved CDA devices were used. Disc height loss was measured using previously validated software, and imaging assessments were made by two radiologists with a 3rd radiologist adjudicating discrepancies. Statistical analyses were completed to identify risk factors for the development of moderate to severe HO.
Results: Based on logistic regression analyses, the type of CDA implanted, the level implanted, the severity of disc degeneration observed on MRI at PreOp, and the presence of endplate Modic changes at PreOp were not significant (P>0.2). The risk for HO increased with number of levels implanted, the radiographic severity of disc degeneration at PreOp, and placing the CDA so the resulting center-of-rotation was too posterior. The results support that the features of disc degeneration observed on PreOp radiographs may influence subsequent development of HO whereas the features of disc degeneration observed in MRI exams do not. However, a reduction in disc height relative to PreOp was the most significant risk factor for HO (Figure 1). The odds ratio for moderate to severe HO at 24 months was 10 when the disc height was reduced by > 1 mm after CDA . However, it should be noted that there were some patients with a > 1 mm loss in disc height who did not develop HO and some with an increase in disc height that did develop HO.
Conclusion: The data support that multiple factors may be associated with development of HO following CDA. Avoiding a posterior center-of-rotation and avoiding implantation of a CDA such that the disc height is reduced relative to PreOp may help to reduce the risk of HO in some CDA patients.