METHODS OF ASSESSING NEW BONE-FORMATION DURING LIMB LENGTHENING - ULTRASONOGRAPHY, DUAL-ENERGY X-RAY ABSORPTIOMETRY AND RADIOGRAPHY COMPARED

We studied the quantity and rate of formation of new bone during lengt hening of 17 limb segments in 10 patients using dual-energy X-ray abso rptiometry (DEXA), ultrasonography and radiography. Whereas new bone w as detected by both DEXA and ultrasonography within 1 to 2 weeks of di straction, it was not visible on the radiographs until 4 to 8 weeks. L imb alignment and gap measurement were accurately assessed by DEXA wit hout the need for standard radiographs or scanograms. With ultrasound the distraction gap appeared as an echolucent window which narrowed pr ogressively producing a hyper-reflecting line after which further cons olidation could not be assessed. As measured by DEXA the density of th e new bone at this stage was approximately 45% of control values and d id not represent normal cortication. Whereas ultrasound could be used to identify defects in mineralisation and to determine when to dynamis e the fixator system, DEXA could measure the quantity and rate of form ation of bone throughout lengthening. We conclude that if ultrasound i s used to complement DEXA the need for radiography can be greatly redu ced.