The Relationship Between Preoperative Cervical Muscle Morphology and Reciprocal Cervical Alignment Changes After Lumbar Pedicle Subtraction Osteotomy: A Retrospective Cohort Study

Background: Lumbar sagittal realignment induces compensatory changes throughout the thoracic and cervical spine. Purposes: Given the role of cervical musculature in head posture, we sought to evaluate whether preoperative cervical muscle morphology is associated with immediate cervical alignment changes following lumbar pedicle subtraction osteotomy (PSO). Methods: We conducted a retrospective cohort study in which lumbar PSO patients with preoperative and immediate postoperative (1-30 days) standing whole-spine radiographs were reviewed. C2 to 7 sagittal vertical axis (cSVA) was measured. For muscle analysis, a subset with preoperative cervical MRI was included. At C3, anterior muscle group (AG) and trapezius (TP) functional cross-sectional area (fCSA) and fatty infiltration (FI) were obtained. Results: Ninety-nine patients were included in the initial analysis. Mean cSVA significantly decreased from 30.4 to 26.7 mm. Twenty-two patients had a preoperative cervical MRI available for muscle analysis. Spearman correlation analysis showed that greater TP fCSA correlated with larger postoperative reductions in cSVA, whereas greater TP FI correlated with smaller reductions in cSVA. Larger AG fCSA also correlated with smaller reductions in cSVA. Conclusion: Preoperative cervical muscle morphology was associated with reciprocal cervical alignment changes after PSO. Greater TP fCSA correlated with larger postoperative reductions in cSVA, whereas greater TP FI correlated with smaller reductions. Larger AG fCSA also correlated with smaller immediate cervical alignment changes. Together, these findings suggest that the relative balance between posterior stabilizing and anterior cervical muscle quality may influence the magnitude of acute cervical decompensation following thoracolumbar realignment. Level of Evidence: Level IV, retrospective cohort study.