QUANTITATIVE ASSESSMENT OF CALLUS DISTRAC TION WITH DUAL-ENERGY X-RAYABSORPTIOMETRY (DEXA)

With dual-energy X-ray absorptiometry (DEXA), bone mineralization duri ng and after limb-lengthening procedures with unilateral fixators can be monitored quantitatively and precisely with low radiation exposure. We measured prospectively the bone mineral density (BMD) in the newly formed callus, in the bone adjacent to the callus and in the proximal femur in 21 patients with leg lengthening of the femur and/or tibia w ith unilateral external fixators. Mineralization showed a typical cour se with a peak value of 0.365 +/- 0.196 g/cm(2) (30.9% of the first va lue) at 6 - 8 weeks after the beginning of distraction and a minimum v alue at the time of maximum distraction. In the consolidation period B MD in the distraction gap increased to 1.020 +/- 0.234 g/cm(2) (87%) a t the time of fixation removal. BMD in the regenerated bone increased faster in regions of interest (ROIs) opposite the fixator compared to ROIs near it. Dynamization of the fixation device led to a 13% increas e in mineralization velocity (V-BMD). On the other hand, dynamization caused more homogeneous regeneration equalizing V-BMD in the different ROIs as well. BMD in the proximal femur of the leg operated on decrea sed to 67% and in the contralateral leg to 87% of the preoperative val ue. We consider DEXA to provide a precise and quantitative assessment of callus and bone mineralization during limb lengthening with unilate ral fixators. Since we are well aware of the limitation of the techniq ue, DEXA helps to understand what is happening in limb-lengthening pro cedures by providing quantitative values.