Comparison of Hybrid Constructs with 2-Level Artificial Disc Replacement and 2-Level Anterior Cervical Discectomy and Fusion for Surgical Reconstruction of the Cervical Spine: A Kinematic Study in Whole Cadavers

BACKGROUND Multi-level cervical degeneration of the spine is a common clinical pathology that is often repaired by anterior cervical discectomy and fusion (ACDF). The aim of this study was to investigate the kinematics of the cervical spine after hybrid surgery compared with 2-level ACDF. MATERIAL AND METHODS Five freshly frozen, unembalmed whole human cadavers were used including 3 males and 2 females with a mean age of 51 ± 8 years. After evaluating the intact spine for range of motion (ROM), sagittal alignment and instantaneous center of rotation (ICR), each cadaver underwent 4 consecutive surgeries: 2-level artificial disc replacement (ADR) from C4 to C6 (ADR surgery); 2-level ACDF from C4 to C6 (ACDF surgery); hybrid C4-5 ACDF and C5-6 ADR (ACDF+ADR surgery); and hybrid C4-5 ADR and C5-6 ACDF (ADR+ACDF surgery). The ROM and ICR of adjacent intact segments (C3-4; C6-7), and whole sagittal alignment were revaluated. RESULTS Two-level ACDF resulted in increased ROM at C3-4 and C6-7 compared with intact spine. ROM was significantly different to intact spine using ACDF surgery at C3-C4 and C6-C7 and ROM was increased with ACDF+ADR surgery at C6-C7 (all P<0.05). No improvement in sagittal alignment was observed with any approach. The localization of the ICR shifted upwards and anteriorly at C3-C4 after reconstruction. ICR changes at C3-C4 were greatest for ADR+ACDF surgery and were significantly different to ACDF surgery (P<0.05), but not between ADR surgery and ACDF+ADR surgery. At C6-C7, the ICR was more posterior and superior than in the intact condition. The greatest change in ICR was observed in ACDF surgery at the C6-C7 level, significantly different from the other groups (P<0.05). CONCLUSIONS For 2-level reconstruction, hybrid surgery and ADR did not alter ROM and minimally changed ICR at the adjacent-level. The type of surgery had a significant impact on the ICR location. This suggests that hybrid surgery may be a viable option for 2-level cervical surgery.