Analysis of cervical sagittal alignment variations after lumbar pedicle subtraction osteotomy for severe imbalance: study of 59 cases

To evaluate postoperative changes within the cervical alignment following surgical lumbar correction by pedicle subtraction osteotomy (PSO) in patients affected with sagittal global malalignment disease. This was a monocentric, radiographic, and prospective study. 79 patients, who underwent sagittal correction by PSO, performed an EOS imaging pre- and postoperatively between January 2008 and December 2013 at the University Hospital of Bordeaux. Inclusion criteria were a performed pre- and postoperative EOS imaging and a preoperative C7SVA > 5 cm. Were excluded patients who did not allow EOS with a viewable cervical spine due to hyperkyphosis. The study involved the analysis of pelvic, lumbar, thoracic, cervical, and cranial parameters before and after the surgery. 59 patients met the criteria. Mean follow-up was 38 months. The lumbar PSO significantly improved sagittal alignment including L1S1 lordosis, T1T12 kyphosis, and C7SVA (p < 0.001). We did not reported a significant change within cervical parameters after PSO (C2C7 lordosis 22.7A degrees-21.5A degrees p = 0.64, C1C7 lordosis 50.6A degrees-48.8A degrees p = 0.56, C1C2 angle 28.2A degrees-27.9A degrees p = 0.82, C7 slope stayed constant 32.3A degrees-30.5A degrees p = 0.47, OC2 angle 15.54A degrees-15.56A degrees p = 0.99). However, cranial slope decreased significantly (p < 0.05). We did not find correlation between lumbar lordosis and cervical lordosis variations (R = 0.265). Cervical lordosis was highly correlated with the C7 slope (R = 0.597) and with the Spino Cranial Angle (R = - 0.867). Reciprocal changes in cervical spine after PSO are difficult to approach. Maintaining a horizontal gaze involves locoregional mechanisms of compensation adapting to the slope of C7. The cranial system by decreasing the cranial slope allows the gaze alignment and is the first compensation mechanism to get involved after a loss of lumbar lordosis. Restoring optimal C7SVA is necessary to prevent the development of secondary cervical painful symptomatology when the cranial compensation is outdated.