Bone mineralization gradient at the callotasis site.

Thirteen patients (18 lengthenings; mean age at operation, 11.0 years) underwent dual-energy X-ray absorptiometry (DEXA) scanning weekly during the distraction phase, at 2-week intervals until removal of the fixator, and at the time of each outpatient visit after removal of the apparatus for a median of 353 days. The three transverse regions remained significantly different in the 7 achondroplastic patients throughout the study, but the difference among these regions became nonsignificant by fixator removal in the 11 limb length discrepancy (LLD) patients. The most proximal region was significantly more mineralized throughout the study in the achondroplastic patients. The central region became the region of highest mineralization in the LLD patients by week 16 after removal of the fixator. The three longitudinal regions showed significantly different mineralization at all time points except at fixator removal. The central and medial regions always showed the highest mineralization. The mechanical characteristics of the fixator and the biomechanical features of the lengthening site may account for the mineralization gradient reported in this study and should probably be taken into account when planning removal of the fixator and subsequent weight-bearing.