Quantifying postoperative bone loss in children.

Abstract

Postoperative bone density loss is an accepted phenomenon that has not been objectively quantified. The extent of this bone loss is documented using preoperative and postoperative dual energy x-ray absorptiometry scans to demonstrate the magnitude of the problem and to underline the need for prevention and treatment. Children undergoing lower extremity surgery who required a minimum of 4 weeks of either non-weight bearing or cast immobilization postoperatively were recruited to undergo preoperative and postoperative dual energy x-ray absorptiometry scans of lumbar spine and both distal femora. Percent change in bone mineral density (BMD) as well as Z-scores in preoperative and postoperative scans were compared, as were operated and nonoperated limbs, using paired t tests. Fifteen of 18 subjects completed the second scan. Children lost up to 34% BMD in the cancellous region of the operated leg (average, 16.5%), up to 28% in transitional bone (average, 11.5%), and up to 16% (average, 4.8%) in the cortical region (P < 0.05). The Z-scores fell 1.0 SD for cancellous, 0.75 transitional, and 0.45 cortical. That children can lose up to 34% of BMD in 4 to 6 weeks is sobering. A 1 SD drop in T score, in adults, can infer a 2-fold increase in fracture risk. This may be insignificant in a healthy child with good BMD, but to a chronically ill child, a doubling of fracture risk may lead to insufficiency fracture. Avoiding the problem and proactive treatment are the goals. Level I, prospective diagnostic study.