Objective: To explore the natural history of scoliosis after posterior fossa decompression (PFD) in patients with Chiari malformation/syringomyelia and examine the risk factors associated with curve progression.
Methods: A retrospective radiographic study was performed at our scoliosis center for 26 patients undergoing PFD for Chiari malformation between January 2002 and December 2007. Their clinical and radiological parameters, including age, curve magnitude, curve pattern, extent of cerebellar tonsil herniation, maximal syrinx/cord ratio, syrinx size and length, were evaluated pre- and postoperatively. Curve progression was defined as an increment of Cobb angle over 5° compared with that of initial curve (progression group); whereas an increment of Cobb angle equal to or under 5° was considered curve stabilization or improvement (non-progression group). All aforementioned parameters at the time of PFD were compared between two groups with Student t and Fisher exact tests.
Results: Their average initial age, curve magnitude and follow-up duration were 10.3 ± 2.4 (6.5-14.7) years, 33.5° ± 7.7° (20°-45°) and 57.5 ± 26.9 (24-118) months respectively. At the final follow-up, curve improvement or stabilization occurred in 11 (42%) patients. Compared with the non-progression group, significantly greater initial age was observed in the progression group (11.1 ± 2.2 vs 9.2 ± 2.2 years, P = 0.041). In addition, the percentage of double major curve was significantly higher in the progression group than that in the non-progression group (26.7% vs 9.1%, P = 0.037). With regards to Cobb angle, Risser sign, extent of cerebellar tonsil herniation, maximal syrinx/cord ratio, syrinx length, sagittal parameters and percentage of patients with preoperative neurological signs or symptoms, no significant differences existed between two groups (P > 0.05).
Conclusion: PFD may halt curve progression in 42% of patients with Chiari malformation/syringomyelia. And those with older age or double major curves are more likely to experience the progression of scoliosis during the post-PFD course.