Is bone mineral mass truly decreased in teenagers with a first episode of forearm fracture? A prospective longitudinal study.

BACKGROUND: Forearm fractures are common in the pediatric population and are mostly treated by cast immobilization. The purposes of this study were first to determine whether forearm fractures in adolescents are associated with abnormal bone mineral density (BMD) or content (BMC) at the time of fracture, and second, to quantify the bone mineral loss at various sites due to cast-mediated immobilization.

METHODS: This longitudinal case-control study recruited 50 adolescents (age, 12.8 ± 1.8 y) who underwent cast-mediated immobilization for a forearm fracture and 50 healthy controls (13.0 ± 1.8 y). Using 2 dual-energy x-ray absorptiometries, BMD and BMC were measured at various skeletal sites (total body, lumbar spine, total upper limb, and forearm) at fracture time and at cast removal.

RESULTS: At the fracture time, BMD/BMC Z-scores at the lumbar spine and areal BMD at the peripheral wrist were not different among the injured and the healthy subjects. At cast removal, significant BMD decreases were observed in adolescents with fracture at the level of the radial and the ulnar diaphyses (-5.6% and -3.8%, respectively) and the total upper limb (-5.6%) compared with the noninjured side. Significant decreases in the BMC values were observed at the level of the radial diaphysis (-6.4%), ultradistal ulna (-10.2%), total upper limb, and total ulna (-8.2% and -4.9%, respectively).

CONCLUSIONS: These data demonstrate that total body, lumbar spine, or wrist bone mineral mass and density (BMC and BMD) are not reduced at the fracture time in adolescents sustaining a first episode of upper limb fracture when compared with healthy subjects. These findings suggest that forearm fractures are not related to osteopenia in youth. In addition, cast-mediated immobilization results in a significant bone mineral loss at the upper limb, which may explain the increased risk of sustaining a second fracture. Finally, bone callus formation may interfere when assessing bone mineral mass after cast removal and may lead to an erroneous underestimation of bone mineral mass decrease.

LEVEL OF EVIDENCE: Level IV.