Quantification of metaphyseal modeling in children treated with bisphosphonates

There has been recent concern in the literature that the treatment with bisphosphonates in children can have an adverse effect on metaphyseal modeling leading to "drug-induced osteopetrosis". We created a normal database called metaphyseal index in the distal femur so that we could quantify the inwasting modeling process in children on bisphosphonates. Radiographs of the distal femur of 468 normal children who had presented to our institution for orthopedic trauma were examined. A measurement of the distal femoral growth plate width (GPW) was recorded. The femoral width at an interval of 0.5 GPW proximal to the distal femoral growth plate was also recorded (0.5 W). The metaphyseal index was defined as a ratio of 0.5 W/GPW. A graph of the means, one and two standard deviations from the mean, was constructed using the data obtained from this cohort. We found this ratio to be constant with minimal variability regardless of the age or sex of the child. We plotted 20 patients at our institution given bisphosphonates for localized orthopedic complaints. Z scores for girls averaged 0.68 and boys 0.13. Three patients had Z scores >2.0, with values of 2.2, 2.9, and 3.2. Metaphyseal modeling in the distal femur is constant, with slight variation between sexes, resulting in a similar shape of the distal femur throughout childhood. Clinically relevant doses of bisphosphonates given for appropriate indications do not necessarily disturb this process, while the beneficial clinical effect is maintained.