Pseudarthrosis in long adult spinal deformity instrumentation and fusion to the sacrum: Prevalence and risk factor analysis of 144 cases

Study Design. Retrospective study. Objective. To analyze the incidence of and risk factors for pseudarthrosis in long adult spinal instrumentation and fusion to S1. Summary of Background Data. Few studies on pseudarthrosis in long adult spinal instrumentation and fusion to S1 exist. Methods. A clinical and radiographic assessment of 144 adult patients with spinal deformity (average age 52.0 years; range 21.1-77.6) who underwent long (5-17 vertebrae, average 11.9) spinal instrumentation and fusion to the sacrum at a single institution between 1985 and 2002, with a minimum 2- year follow- up (average 3.9; range 2-14) was performed. Results. Of 144 patients, 34 (24%) had pseudarthroses. There were 17 patients who had pseudarthroses at T10-L2 and 15 at L5-S1. A total of 24 patients (71%) presented with multiple levels involved (2-6). Pseudarthrosis was most commonly detected within 4 years postoperatively (31 patients; 94%). Factors that statistically increased the risk of pseudarthrosis were: thoracolumbar kyphosis (T10-L2 >= 20 degrees vs. < 20 degrees, P < 0.0001); osteoarthritis of the hip joint (P = 0.002); thoracoabdominal approach (vs. paramedian approach, P = 0.009); positive sagittal balance >= 5 cm at 8 weeks postoperatively (vs. <= 5 cm, P = 0.012); age at surgery older than 55 years (vs. 55 years or younger, P = 0.019); and incomplete sacropelvic fixation (vs. complete sacropelvic fixation, P = 0.020). Fusion from upper thoracic spine (T2-T5) did not statistically increase the pseudarthrosis rate compared to lower thoracic spine (T9-T12) (P = 0.20). Patients with pseudarthrosis had significantly lower Scoliosis Research Society 24 outcome scores (average score 71/120) than those without (average score 90/ 120; P < 0.0001) at ultimate follow- up. Conclusion. The overall prevalence of pseudarthrosis following long adult spinal deformity instrumentation and fusion to S1 was 24%. Thoracolumbar kyphosis, osteoarthritis of the hip joint, thoracoabdominal approach (vs. paramedian approach), positive sagittal balance >= 5 cm at 8 weeks postoperatively, older age at surgery (older than 55 years), and incomplete sacropelvic fixation significantly increased the risks of pseudarthrosis to an extent that was statistically significant. Scoliosis Research Society 24 outcomes scores at ultimate follow- up were adversely affected when pseudarthrosis developed.