Preoperative Patient-Specific Factors Predict the Change in Adjacent Segment Range of Motion Three Years After Anterior Cervical Discectomy and Fusion

STUDY DESIGN: Prospective cohort study. OBJECTIVE: To identify patient factors that predict changes in adjacent segment kinematics three years after ACDF. SUMMARY OF BACKGROUND DATA: Approximately 25% of patients who undergo anterior cervical discectomy and fusion (ACDF) develop symptomatic adjacent segment disease (ASD) requiring reoperation within 10 years. Studies have found associations between ASD and patient genetics, age, BMI, psychiatric history, and preoperative disc degeneration. Few studies have linked these factors to mechanical changes to explain ASD. METHODS: Patients performed flexion/extension and axial rotation captured by biplane radiography before, one year after, and three years after ACDF (3YR-POST). Digitally reconstructed cervical radiographs were matched to the biplane radiographs to calculate intervertebral kinematics and preoperative disc height. Patient age, sex, BMI, smoking, diabetes, psychiatric history, inciting event, length of symptoms, preoperative disc bulge, and NDI were collected. Multivariate linear regression identified patient factors associated with changes in adjacent segment kinematics and NDI 3YR-POST. RESULTS: Sixty-two patients completed testing. Younger age (1.1° per 10 yr, 95% CI: 0.04-1.8, P =0.011), female sex (1.8°, 95% CI: 0.5-3.1, P =0.016), lower BMI (1.4° per 10 kg/m², 95% CI: 0.4-2.5, P =0.019), and no superior adjacent disc bulge (1.4°, 95% CI: 0.0-2.7, P =0.035) predicted a larger increase in superior adjacent segment flexion/extension range of motion (ROM) 3YR-POST. Lack of superior adjacent disc bulge (1.2°, 95% CI: 0.2-2.2, P =0.025) predicted a larger increase in superior adjacent segment axial rotation ROM. No patient factors were associated with changes in inferior adjacent segment ROM. CONCLUSION: A greater increase in superior adjacent segment motion 3YR-POST is predicted in younger, lower BMI, female patients with healthier preoperative discs. These results support the theory that disc degeneration progresses from early instability in younger, healthier discs to stabilization in older, less healthy discs.