Noninvasive monitoring techniques for quantitative description of callus mineral content and mechanical properties

The noninvasive evaluation of fracture healing may allow more precise timing of fixation device removal, quantitative recommendations for weight bearing, and the prediction of abnormal fracture healing patterns. Techniques used for the evaluation of intact bone and of healing fractures include resonance frequency and impedance methods, the measurement of sound speed using ultrasound, computed tomography of ultrasonic energy, roentgenographic photodensitometry, quantitative computed tomography (QCT), single-photon absorptiometry (SPA), and dual-energy x-ray absorptiometry (DEXA). A study comparing QCT, SPA, and DEXA showed that all three techniques had strong correlations with the torsional properties of healing canine tibial osteotomies. Quantitative computed tomography and SPA had stronger correlations with local gap tissue properties than DEXA. The relatively poor performance of DEXA may have been related to the relatively large resolution (2 mm) of the device used in the study. Current DEXA devices have resolutions as low as 0.5 mm, perhaps enhancing its capabilities. Computed tomography of ultrasonic energy, QCT, SPA, and DEXA each appear to have great potential for future use in the evaluation of fracture healing.