**3. Conclusion**

**2.1. Ionizing radiation**

86 Advanced Techniques in Bone Regeneration

**2.2. Ultrasonography**

complications like cysts and collections.

penetration of the ultrasonographic beam [11]. (see **Figure 1**)

methods.

X-ray, dual energy X-ray absorptiometry (DEXA) and computed tomography can be utilized for the evaluation of the bone callus. However, the necessity for a serialized evaluation, exposure to ionizing radiation, metallic artifacts susceptibility, and the high cost and more restricted availability of computed tomography and DEXA limit the utilization of these

The X-ray is the most used, because it allows proper evaluation of the bone extremities and distraction distance (gap). Using the "three cortical rule," where the visualization of at least three corticals with 2 mm thickness on orthogonal views is necessary, the removal of the external fixator is indicated [6, 7]. Yet, it was observed that this method is subject to great observer variation, not being more accurate than random chance [8]. Other limitations are

Studies valued the role of DEXA in the evaluation of the regenerated tissue, from the length‐ ening stages until its attempt to objectively define the best moment to remove the external fixator. Some research parameters include the relation between the regenerated bone mineral density and contralateral limb, and also the percentage of the weekly increase of bone mineral density [9, 10]. Despite promising results, there is still no standardization of these parameters.

The quantitative computed tomography (QCT) sums the quantitative evaluation with highresolution images of regenerating bones, presenting better correlation than the DEXA and allowing a global evaluation to the assistant doctor. However, high cost, little availability, and

Recently, the role of ultrasonography in the monitoring and distraction has been target of several studies. Several characteristics make this a method of interest, as it does not use ionizing radiation, it is widespread, and it is not subject to artifacts related to external fixators. The top advantage is the possibility of characterization of soft tissue and precocious detection of

For the ultrasonographic evaluation, linear transducers for high resolution must be used (5– 12 MHz). The osteotomy is evaluated with beams perpendicular to the bone corticals, longi‐ tudinally and transversely along the bone axis. In the initial evaluation, the ultrasonography identifies the osteotomy corticals as hyperechoic surfaces, with posterior acoustic shadow and acute margins. Between them is located the soft callus, defined as a hypoechoic area with great

In the first weeks, the appearance of echogenic outbreaks longitudinally oriented in the interior of the "gap" is noticed. In the cross-sectional assessment, there is a "cut wire" aspect. Between 2 and 4 weeks, the first individualized ossification center starts to be identified. Over time, there is an increase in number and size of those centers with the tendency to confluence on the longitudinal axis. Gradually, there is loss of penetration power in the callus and rounding of

related to the initial stages where radiography is incapable of evaluating soft tissue.

great exposure to radiation (more than the other methods) limit its application [1].

The monitoring of the osteogenesis distraction is fundamental to avoid complications and reduce the time of use of the external fixator. Several methods are available, each one present‐ ing advantages and disadvantages. The ultrasound seems like an excellent method in the initial evaluation of distraction; however, it is incapable of orienting objectively the moment of removal of the external fixator. The methods using ionizing radiation present several possi‐ bilities, but lack in objective and standard data limits its application. Considering these factors, a multimodal evaluation of the progression of the treatment, conciliating clinical expertise, and the rational use of the available complimentary exams for the optimization of the treatment must be used.
