The Lateral Distal Femoral DEXA Scan in Children: A Chronology of Growing Bone?

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abstractDual energy x-ray absorptiometry (DEXA) is the current standard for measuring bone mineral density (BMD) in children. The International Society for Clinical Densitometry recommends scanning the total body and spine in children. However, in orthopedics, the total-body and spine DEXA scans are often rendered useless by the presence of metallic hardware and/or contractures.The lateral distal femoral DEXA scan was developed as a scan mode for children such as those with cerebral palsy who have contractures or metallic implants, which make it impossible to do total-body or spine scans. Unlike other DEXA scans, a single scan of the lateral distal femoral illustrates the density of the metaphyseal cancellous (newer) bone, the transitional, and the cortical (older) bone in 1 image. Because of this, we hypothesized that an individual lateral distal femoral scan could provide a map of bone health over time.The lateral distal femoral scans of 40 children whose bone growth was tainted by distant chemotherapy (chemotherapy group) were compared to the LDF scans of 40 children whose bone environment had remained relatively stable over time (control group).The hypothesis was not confirmed by the data. The “Z-score difference,” the difference between the Z-scores of the cancellous and cortical bone, for the chemotherapy group (0.16) and the control group (0.32) were not statistically different.While these results did not confirm the hypothesis, the lateral distal femoral scan remains a reproducible and useful DEXA scan in pediatric orthopedic clinical practice.

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