Pelvic tilt and trunk inclination: new predictive factors in curve progression during the Milwaukee bracing for adolescent idiopathic scoliosis

Abstract

Introduction: Previous studies had shown that sagittal spinal and pelvic morphology may be associated with the development and progression of adolescent idiopathic scoliosis, but the predictive value of initial spinal and pelvic morphology on the curve progression during brace treatment is unknown. The objective of this study was to evaluate the relation between initial spinopelvic morphology and the risk of curve progression of adolescent idiopathic scoliosis with the Milwaukee brace.

Materials and methods: From 2002 to 2007, adolescent idiopathic scoliosis (single thoracic curve with apex at or above T8) was treated with the Milwaukee brace in 60 girls. Initial standing, full-length lateral radiographs were made and seven sagittal radiographic parameters of spinal and pelvic alignment were measured. Patients were followed until skeletal maturity or progression of Cobb angle >45°. The progression of curve was defined as an increase of Cobb angle ≥6° at final follow-up or progression to surgery during brace treatment.

Results: The 45 patients (75.0 %) who had successful control of curve progression were initially significantly more skeletally mature (higher mean Risser sign) than the 15 patients (25.0 %) who had curve progression. The initial mean Cobb angle was similar between the stable and progressed groups. The mean pelvic tilt, T1-spinopelvic inclination and T9-spinopelvic inclination angles were significantly greater in the stable group than in the progressed group and these three angles were independent predictors for curve progression during brace treatment. There were no significant differences between the stable and progressed groups in initial mean pelvic incidence, sacral slope, thoracic kyphosis or lumbar lordosis angles. Pre-bracing pelvic tilt ≤-0.5° was strongly predictive and T1-spinopelvic inclination ≤3.5° was moderately predictive of curve progression during the Milwaukee brace treatment.

Conclusions: Initial pelvic tilt and spinopelvic inclination angles may predict the curve progression and treatment outcome of adolescent idiopathic scoliosis with the Milwaukee brace.

Fig. 1

a Posteroanterior radiograph of a 13-year-old girl with adolescent idiopathic scoliosis at presentation: Risser grade 0, primary thoracic Cobb angle 31°. b, c Lateral radiographs of the same patient at presentation: T1-spinopelvic inclination (T1-SPI) 5°, pelvic tilt (PT) 16°. d Posteroanterior radiograph of the patient after Milwaukee brace treatment (3 years) shows decreased thoracic Cobb angle (21°)

Fig. 2

a Posteroanterior radiograph of a 12-year-old girl with adolescent idiopathic scoliosis at presentation: Risser grade 0, primary thoracic Cobb angle 27°. b, c Lateral radiographs of the same patient at presentation: T1-spinopelvic inclination (T1-SPI) 3°, pelvic tilt (PT) −7°. d Posteroanterior radiograph after Milwaukee brace treatment (1.5 years) shows increased thoracic Cobb angle (43°) and failure of brace treatment

Fig. 3

Receiver operator characteristic curve for pre-bracing pelvic tilt. Each point is a cut point for pelvic tilt at which the sensitivity and specificity for predicting the failure of bracing is evaluated

Fig. 4

Receiver operator characteristic curve for pre-bracing T1-spinopelvic inclination. Each point is a cut point for T1-spinopelvic inclination at which the sensitivity and specificity for predicting the failure of bracing is evaluated

Fig. 5

Receiver operator characteristic curve for pre-bracing T9-spinopelvic inclination. Each point is a cut point for T9-spinopelvic inclination at which the sensitivity and specificity for predicting the failure of bracing is evaluated