Does disc distraction after cervical total disc arthroplasty impact range of motion and patient-reported outcomes?

OBJECTIVE Total disc arthroplasty (TDA) has been established as a safe and effective alternative to anterior cervical discectomy and fusion for the treatment of cervical spine pathology. However, there remains a paucity of studies in the literature regarding the amount of disc height distraction that can be tolerated, as well as its impact on kinematic and clinical outcomes. METHODS Patients who underwent 1- or 2-level cervical TDA with a minimum follow-up of 1 year with lateral flexion/extension and patient-reported outcome measures (PROMs) were included. Middle disc space height was measured on preoperative and 6-week postoperative lateral radiographs to quantify the magnitude of disc space distraction, and patients were grouped into < 2-mm distraction and > 2-mm distraction groups. Radiographic outcomes included operative segment lordosis, segmental range of motion (ROM) on flexion/extension, cervical (C2-7) ROM on flexion/extension, and heterotopic ossification (HO). General health and disease-specific PROMs were compared at the preoperative, 6-week, and final postoperative time points. The independent-samples t-test and chi-square test were used to compare outcomes between groups, while multivariate linear regression was used to adjust for baseline differences. RESULTS Fifty patients who underwent cervical TDA at 59 levels were included in the analysis. Distraction < 2 mm was seen at 30 levels (50.85%), while distraction > 2 mm was observed at 29 levels (49.15%). Radiographically, after adjustment for baseline differences, C2-7 ROM was significantly greater in the patients who underwent TDA with < 2-mm disc space distraction at final follow- up (51.35 degrees +/- 13.76 degrees vs 39.19 degrees +/- 10.52 degrees, p = 0.002), with a trend toward significance in the early postoperative period. There were no significant postoperative differences in segmental lordosis, segmental ROM, or HO grades. After the authors controlled for baseline differences, < 2-mm distraction of the disc space led to significantly greater improvement in visual analog scale (VAS)-neck scores at 6 weeks (-3.68 +/- 3.12 vs -2.24 +/- 2.70, p = 0.031) and final follow-up (-4.59 +/- 2.74 vs -1.70 +/- 3.03, p = 0.008). CONCLUSIONS Patients with < 2-mm disc height difference had increased C2-7 ROM at final follow-up and significantly greater improvement in neck pain after controlling for baseline differences. Limiting differences in disc space height to < 2 mm affected C2-7 ROM but not segmental ROM, suggesting that less distraction may result in more harmonious kinematics between all cervical levels.