The factors that influence the postoperative segmental range of motion after cervical artificial disc replacement.

Background Context: Advantages of cervical artificial disc replacement (ADR) are to preserve segmental range of motion (ROM) and avoid adjacent segmental disease. To achieve successful outcome after cervical ADR, ROM maintenance is important, but few authors have investigated the factors that influence the postoperative segmental ROM.

Purpose: To evaluate the factors that influence the postoperative segmental ROM after cervical ADR.

Study Design/setting: A retrospective clinical study.

Patient Sample: Forty-one consecutive cervical ADR cases were analyzed.

Outcome Measures: Disc height, segmental and overall ROM, and clinical parameters checked with Neck Disability Index (NDI) and visual analog scale (VAS) in neck and arm pain were assessed.

Methods: There were 21 men and 20 women with a mean age of 45 years (range, 27-61 years). All cases were followed up for more than 2 years (range, 24-54 months; average, 31 months). Angles of the inserted implant on the immediate postoperative lateral radiographs, segmental and overall ROM (full flexion angle-full extension angle), disc height increment (immediate postoperative disc height-preoperative disc height), and adjacent segment changes at cephalad and caudal disc space were measured. Correlations between the factors and segmental ROM at last follow-up were analyzed.

Results: Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 at last follow-up, and mean VAS in the neck pain decreased from 56.8 preoperatively to 11.8 postoperatively and arm pain decreased from 68.1 to 18.0. The mean preoperative segmental ROM changed from 7.4+/-3.2 degrees preoperatively to 10.4+/-5.9 degrees at last follow-up, and mean preoperative disc height increased from 6.4+/-1.0 (4.1-8.4) mm preoperatively to 7.9+/-1.0 (6.3-9.9) mm postoperatively. The segmental ROM at last follow-up was not significantly correlated with preoperative segmental and overall ROM, angle of inserted implant, VAS, or age (p>.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p=.046, r=0.374) and preoperative NDI (p=.026, r=0.412). The patient group with the postoperative segmental ROM greater than 10 degrees had a significantly lower mean preoperative disc height than the group with the segmental ROM less than 10 degrees (p=.050).

Conclusions: At a minimum of 2 years after cervical ADR, clinical outcomes were satisfactory in terms of function and pain scores. Within our results, the segmental ROM was not affected by preoperative ROM but postoperative disc height increment positively and preoperative disc height negatively.