The effect of range of motion after single-level discover cervical artificial disk replacement.

STUDY DESIGN: A biomechanical study of cervical artificial disk replacement (CADR). OBJECTIVE: This study aimed to investigate the range of motion (ROM) of the treated segment, the ROM of the adjacent segments, the global ROM in the sagittal plane, and the total neck ROM in the 3 cardinal planes after single-level Discover CADR. SUMMARY OF BACKGROUND DATA: CADR could theoretically preserve the motion function of the treated segment without affecting the adjacent segments significantly. Although previous studies have reported excellent clinical outcomes and ROM of the treated segment after CADR, few studies have focused on the ROM of the adjacent segments, the global ROM, and the total neck motion. METHODS: C5/6 Discover CADR was performed in 58 patients (37 male and 21 female) between September 2008 and September 2010. Anteroposterior, lateral, and flexion-extension lateral radiographies were performed before operation and at the 1-year follow-up. Clinical parameters, including the Japanese orthopedic association score, the neck disability index, and the visual analogue scale, were evaluated. The ROM of the treated segment (C5/6) and the adjacent segments (C4/5 and C6/7) and the global ROM (C2/7) were measured by radiography. To evaluate the total neck ROM, the cervical ROM device was advocated. Preoperative and postoperative data were compared using the paired t test. RESULTS: The Japanese orthopedic association score was 14.3 at the 1-year follow-up as compared with the preoperative score of 8.7. Other scoring systems had improved postoperatively, including the neck disability index from 85.1 to 68.6 and the visual analogue scale from 7.8 to 3.3. Compared with the preoperative ROM, the postoperative ROM increased by 3.0 degrees (27.0%) in C5/6, 1.3 degrees (13.7%) in C4/5, and 1.8 degrees (17.6%) in C6/7. The postoperative global ROM also increased by 6.7 degrees (15.2%) compared with preoperative global data. Compared with the preoperative total neck motion, the postoperative total neck motion increased by 8.3 degrees (9.3%) in the sagittal plane and 6.1 degrees (7.7%) in the coronal plane. There was an insignificant increase of 0.8 degrees (0.6%) in the horizontal plane. CONCLUSIONS: This study demonstrated that the single-level Discover CADR increased the ROM of the treated segment and the adjacent segments. There was also an increase in the global ROM and the total neck motion in the sagittal and the coronal planes, although there was no significant difference in the horizontal plane before and after operation.