Association between body mass index, body height, and the prevalence of spinal deformities.

Background Context: The most common spinal deformities among adolescents are adolescent idiopathic scoliosis (AIS; 2%-3% prevalence) and Scheuermann kyphosis (SK; 1%-8% prevalence). Both are believed to have a genetic influence in their etiology. The association between body mass index (BMI) and body stature and their possible association to spinal deformities is uncertain.

Study Design: A cross-sectional prevalence study.

Purpose: To examine the prevalence of all adolescent spinal deformities according to the extent of their severity as well as their possible association to BMI and body height.

Outcome Measures: Subjects diagnosed as having spinal deformities were classified into one of three severity groups; "Mild," "Intermediate," or "Severe," according to their curve scoliosis or kyphosis measurement with a standing X-ray.

Methods: The data for this study were derived from a medical database containing records of 17-year-old male and female patients before their recruitment into mandatory military service. Information on the disability codes associated with spinal deformities according to the Regulations of Medical Fitness Determination was retrieved. Logistic regression models were used to assess the association between the BMI and body height to various degrees of spinal deformities by severity.

Results: The study cohort included 829,791 consecutive subjects, of whom 103,249 were diagnosed with spinal deformities (76% were mild in degree). The prevalence of spinal deformities was significantly greater among the underweight male and female patients (p<.001). Increased BMI had a protective effect for developing spinal deformities. The odds ratios for severe spinal deformities were greater compared with mild spinal deformities in the underweight groups. The risk for developing spinal deformities increased significantly with height for both genders (p<.001).

Conclusions: An association between height and the risk for spinal deformities by severity was found for all height groups. Below normal BMI is associated with severity of spinal deformities, whereas above-normal BMI apparently has a protective effect. Body height is also positively associated with the severity of spinal deformities.