Mild Changes in Sternocleidomastoid Muscle Quality Predict Pseudarthrosis after Anterior Cervical Discectomy and Fusion

Study Design. Retrospective cohort Objective. To investigate the impact of cervical paraspinal muscle mass and quality on the rate of pseudarthrosis and patient-reported outcome measures (PROMs) after anterior cervical discectomy and fusion (ACDF). Summary of Background Data. Poor muscle quality has been shown to correlate with inferior outcomes in spine surgery. However, few studies have investigated the impact of paraspinal sarcopenia on pseudoarthrosis following cervical spine surgery. Methods. Adult patients who underwent primary, elective one-to-four level ACDF with preoperative magnetic resonance imaging (MRI) and postoperative radiographs were included. MRIs were reviewed to assess sternocleidomastoid (SCM) cross-sectional area (CSA) and Goutallier grade at the C5-C6 disc space. Pseudarthrosis was diagnosed on 1-year postoperative flexion-extension radiographs as greater than 1 millimeter of interspinous motion between each instrumented level. Patient demographic and surgical variables and 1-year patient-reported outcome measures (PROMs) were compared between those with and without pseudoarthrosis on bivariate and multivariate analyses. Results. 205 patients were included (33.7% with pseudoarthrosis). The pseudoarthrosis group had a higher percentage of patients with 4-level (7.25% vs. 1.47%) and 3-level (30.4% vs. 17.6%, P =0.01) ACDF. The groups were similar in terms of demographics, surgical variables, and SCM area normalized to BMI. After controlling for SCM CSA group, age, sex, BMI, and number of levels fused, higher Goutallier grade independently increased the odds of pseudoarthrosis (odds ratio (OR): 3.46, P =0.009). Patients with greater SCM fatty infiltration experienced greater improvement in PCS scores ( P =0.023), but there were no other differences in PROM scores between groups. Conclusion. Although this analysis did not show an association between SCM muscle size and pseudoarthrosis, even mild fatty infiltration appears to be independently predictive of pseudoarthrosis. In contrast, PROMs were not associated with SCM size or fatty infiltration. Further work is needed to confirm these findings and explore their clinical implications.