Study Design: Prospective cohort study.

Objective: To study the relationship between scoliosis and Chiari I malformation, with reference to the possible role of cranio-vertebral decompression in preventing the need for scoliosis correction.

Methods: Prospective data collection on all Chiari I patients referred to a single paediatric neurosurgeon with an interest in Chiari malformation.

Subjects: From a total of 35 patients with symptomatic Chiari I who underwent primary cranio-vertebral decompression, 13 had clinically detected scoliosis. Of these 13, 10 (7 males) had no other structural spine abnormality, which could influence the natural history of scoliosis and were included in this study. Mean age at diagnosis was 11.5 years (range 8.8– 15.9 years).

Results: Of the 10 patients, 8 had left-sided curves and two had right sided curves. Six patients did not require corrective scoliosis surgery following cranio-vertebral decompression. The mean Cobb angle for those not requiring scoliosis correction was 29 degrees compared to 76 degrees for those requiring correction (p=0.001, one way ANOVA). The mean age of patients requiring corrective surgery was 12.75 years versus 10.33 years for those not requiring correction (p=0.084, one way ANOVA). These findings were confirmed by multivariate analysis, which also confirmed that symptom duration, syrinx length and site were not significant in predicting the need for corrective surgery following cranio-vertebral decompression.

Conclusion: Cranio-vertebral decompression for Chiari I may prevent the need for corrective scoliosis surgery when performed before the age of ten and below a Cobb angle of 30 degrees.