Thursday, September 27, 2018 3:35 PM–5:05 PM Section on Motion Technology Abstract Presentations: 139. Artificial disc replacement adjacent to a multilevel fusion in the cervical spine: a biomechanical study

Abstract

BACKGROUND CONTEXT Cervical total disc replacement (TDR) has emerged as a motion-preserving alternative to anterior cervical discectomy fusion. Biomechanical studies have demonstrated that the TDR preserves motion at the diseased segment and minimizes motion and stress at adjacent segments compared to fusion. There has been growing interest in performing a TDR adjacent to a cervical fusion. The kinematics of a cervical TDR adjacent to a multilevel fusion construct (>2 levels) has not been investigated. PURPOSE The purpose of this study was to evaluate the motion of a cervical total disc replacement after fusing adjacent cervical segments both caudal and cranial to the implant. OUTCOME MEASURES The primary outcome measure was the segmental flexion-extension range of motion at the level of a cervical total disc repalcement. The secondary outcome measures were the overall cervical range of motion and the segemental motion of the remaining cervical segments. METHODS Seven fresh-frozen human cadaveric cervical spine specimens from C1-T1 were used (average age 56.2±7.3 years). A C6-7 TDR was tested adjacent to a C5-6, C4-6 and C3-6 fusion. A C2-3 TDR was tested adjacent to a C3-4, C3-5 and C3-6 fusion. The protocol consisted of taking lateral radiographs of each construct at maximal angular displacement in flexion and extension. Cobb angles were measured on the digital radiographs to determine flexion-extension range of motion. RESULTS The segmental ROM of the C6-7 TDR in the unfused spine was 11.3±1.9°. After performing a three-level fusion (C3-6) the segmental motion of the C6-7 TDR increased to 12.9±1.3°(p=.33). The difference between the motion of the C6-7 TDR and the C6-7 native segment caudal to a three-level fusion was not statistically significant; 12.9±1.3° versus 11.3±1.9°, respectively (p=.30).The segmental ROM of the C2-3 TDR in the unfused spine was 5.0 ±1.1. After performing a three-level fusion (C3-6), the C2-3 TDR segmental motion was 6.1±1.3° (p=.09). The difference in motion of the TDR cranial to a three-level fusion and the native disc cranial to a three-level fusion was not statistically significant; 6.1± 1.3° versus 6.4± 0.8°, respectively (p=.15). CONCLUSIONS The TDR had similar flexion extension motion to the native segment when instrumented either caudal or cranial to the single, two and three level fusions. The TDR had a trend toward increased motion as additional fusion levels were added adjacent to the implant. Biomechanically, performing a TDR adjacent to a long fusion construct did not subject the implant to greater motion than when instrumented alone. This result suggests that a TDR adjacent to a long segment fusion may not necessarily be subjected to greater mechanical stress. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.