Use of thermography to monitor the bone regenerate during limb lengthening--preliminary communication.

BACKGROUND Bone regenerate is routinely assessed on X-ray images obtained every 7 to 14 days in the distraction period and every 14 to 28 days during the stabilisation period. Tissue reconstruction during new bone formation and increased metabolism in the tissues being lengthened are associated with an increase in the temperature of the limb. The aim of this study was to establish a correlation between the bone regenerate, assessed on the basis of X-ray evidence, and thermographic images of the limb registered in a non-invasive manner with a thermographic camera. A positive correlation would enable a reduction in the number of X-ray studies in the future. MATERIALS AND METHODS Bone lengthening using the Ilizarov technique of distraction osteogenesis was performed in 18 patients (9 men and 9 women) aged 12-74. The lengthened segments included the crus in 13 patients, the thigh in 4 patients and lower arm in 1 patient. Assessments of the bone regenerate were made during periodic follow-up visits on the basis of X-ray images and compared to thermographic images, on the basis of which thermal indices were established. The indices comprised the difference in the temperatures between the lengthened limb at the lengthening site and the contralateral limb at the same level, as well as the difference in the temperature of the lengthened limb at the lengthening site and at selected nearby points. RESULTS A statistical analysis of the results of the monitoring of distraction osteogenesis established a statistically significant correlation between the regenerate status and thermal indices. The strongest correlation between X-ray and thermographic images was obtained in the frontal view for the crural bones. Mean values of Spearman's correlation coefficient for the tibia and femur were rS = 0.925 (p < 0.01) and 0.724 (p < 0.05), respectively. CONCLUSIONS As a non-invasive method of measuring temperature thermography is a valuable adjunct to the traditional diagnostic methods and can be used successfully to monitor and evaluate the formation and remodelling of the regenerate at all stages of the treatment. It is particularly useful for the assessment of the bone regenerate in the tibia. The robust correlation between the regenerate and thermal indices measured with Spearman's correlation index enables a reduction in the number of radiographic studies of up to 50% in most cases. Moreover, thermography enables early detection of soft tissue inflammation around Kirschner wires.