Changes in cervical range of motion and sagittal alignment in early and late phases after total disc replacement: radiographic follow-up exceeding 2 years.

OBJECT: This was a retrospective clinical study in which the follow-up period exceeded 2 years. The authors investigated the time course of radiographic changes in the cervical range of motion (ROM) and sagittal alignment after cervical total disc replacement involving the ProDisc-C artificial disc.
METHODS: Eighteen patients who underwent C5-6 total disc replacement were followed for an average of 27 months. Cervical neutral and flexion-extension lateral radiographs were obtained before and at 1 and 3 months after surgery for early-phase observations and at the last follow-up for late-phase observation. Segmental ROM values in the treated, superior, and inferior adjacent segments were measured. For whole-neck motion, C2-7 ROM was also measured. The percentage contributions of ROM at functional and adjacent segments to whole-neck motion were calculated. For evaluating sagittal alignment, C2-7 and C5-6 Cobb angles were measured. All data from ProDisc-C arthroplasty were compared with the results obtained in 22 patients who underwent C5-6 interbody fusion in which a Solis cage was used and who were followed for an average of 25 months.
RESULTS: In the ProDisc-C group, C2-7 and C5-6 ROM significantly decreased in the early phase after surgery and returned to preoperative levels in the late phase. Both superior and inferior adjacent segments showed significantly decreased ROM in the acute phase after surgery and returned to the preoperative values in the late phase. In terms of contributions to whole-neck motion, the ROM of the functional and adjacent segments did not change significantly compared with the preoperative ROM. In the cage group, C2-7 ROM was also significantly decreased in the early phase after surgery and returned to preoperative levels at the late phase. Both superior and inferior adjacent segments exhibited significantly increased ROM and percentage contributions to whole-neck motion in the early and late phases. Sagittal alignment of the whole cervical spine became significantly more lordotic in the late phase in the ProDisc-C group. The C5-6 Cobb angle became significantly lordotic in the ProDisc-C group, whereas there was no significant change in C5-6 Cobb angle in the cage group.
CONCLUSIONS: In the early phase after ProDisc-C replacement, the ROM of the entire neck as well as functional and adjacent segments decreased but, at the late phase, they returned to the preoperative state. Contributions of functional and adjacent segments to whole-neck motion were not changed after ProDisc-C replacement. Adjacent-segmental motion could be saved by ProDisc-C replacement instead of interbody cage fusion. Segmental degenerative kyphosis was significantly corrected in patients who underwent ProDisc-C replacement.