Case controlled study.
To explore the relative effects of body mass index (BMI) and the presence or absence of adolescent idiopathic scoliosis (AIS) on bone mineral density (BMD) as evidenced by Z-scores in adolescents.
Prior studies have identified adolescents with idiopathic scoliosis as having “osteoporosis” or “osteopenia,” when only a small percentage of subjects in these studies actually had bone density that was clinically abnormal. The terms osteoporosis and osteopenia as used in adults cannot be applied to adolescents and children, as fracture risk has not been well correlated to Z-scores. As we had noted that our scoliosis patients of normal and heavy weight had normal Z-scores, this study was undertaken to explore the relationship of bone mineral density to body mass index in adolescents with and without scoliosis.
Dual energy x-ray absorptiometry (DXA) scans of 49 adolescents with adolescent idiopathic scoliosis were compared to 40 normal control adolescents. Z-scores were compared to reduce variability when comparing subjects of varying age and genders. Student t test or simple linear regression was used to explore relationships between Z-scores and clinical and demographic variables.
In both groups of subjects, Z-score was most strongly correlated with BMI (P < 0.001). The presence of scoliosis had the effect of lowering the Z-score as if the individual had “lost” 3.4 BMI units.
Z-scores in subjects with and without scoliosis were most strongly correlated to BMI: thin patients had lower bone density, heavy patients had higher. The presence of scoliosis had an effect similar to subtracting 3.4 “BMI units,” lowering the Z-score from what might otherwise be predicted. The “scoliosis effect” may be noticeable in thin individuals, pushing them to the “low for age” level, whereas in heavier individuals, the effect is negligible. No subjects in either group met the ISCD definition for osteoporosis.
From the Departments of *Orthopaedics and Rehabilitation, †Pediatrics, and ‡Emergency Medicine, ¶University of New Mexico School of Medicine, Albuquerque, New Mexico; and §Department of Orthopaedics, University of Missouri, Kansas City, Missouri.
The device(s) and drug(s) is/are FDA approved or approved by corresponding national agency for this indication.
Institutional and Foundation funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
Supported by institutional and foundations funds and by the George E. Omer Research Fund. A student research scholarship was provided by Carrie Tingley Hospital Foundation.
Acknowledgment date: August 22, 2007. Revision date: October 9, 2007. Acceptance date: October 10, 2007.
Address correspondence and reprint requests to Elizabeth A. Szalay, MD, UNM Carrie Tingley Hospital, 1127 University Blvd. NE, Albuquerque, NM 87102; E-mail: ESzalay@salud.unm.edu