Short-term Comparison of Cervical Fusion With Static and Dynamic Plating Using Computerized Motion Analysis

Abstract

This study is a retrospective review of fusion rates for cervical plates, analyzed by means of computerized analysis. This study compares the fusion rates for two-level anterior cervical discectomy and fusion between patients with static versus dynamic plates. Anterior cervical plating has been shown to decrease the pseudarthrosis rate. However, static plates, which have been successful in reducing nonunion rates, may be "too rigid" in certain situations, leading to pseudarthrosis in some patients. Recently, some surgeons have begun using dynamic plate constructs to avoid this problem. A retrospective review was performed of patients having a two-level anterior cervical discectomy and fusion performed either with a static or dynamic plate. A computerized method for evaluating the presence of a solid fusion was used with a criterion of <2 degrees of motion considered a solid fusion. The follow-up time period averaged 10 months (range, 5.8-13 months) for the static plate group and 9.5 months (range, 5.8-13 months) for the dynamic plate group. Based on a motion threshold of 2 degrees, the rate of fusion per level for patients in the static plate/autograft group was 87.8%, resulting in an overall fusion rate of 76.2%. The rate for fusion per level for patients treated with a dynamic plate and allograft was 89.8%, with an overall fusion rate of 81.8%. There was no statistically significant difference between the two groups (P = 0.469). The fusion rate increased during the follow-up period: In the 6- to 9-month interval, the static plate/autograft group had a 62.5% fusion rate, versus 75% for the dynamic plate/allograft group. In the 10- to 13-month interval, the fusion rate had increased to 84.7% for the static plate/autograft group and 90% for the dynamic plate/allograft group. Computerized evaluation of digitized films can improve the accuracy and reproducibility of the analysis of anterior cervical fusion. An angular threshold of 2 degrees was selected for this purpose. This study showed that the rate of fusion with a dynamic plate was similar to that of the static plate despite the use of allograft bone with the dynamic plate. In addition, this study found that successful fusions continued to evolve throughout the first year following surgery.