Introduction: Low-intensity pulsed ultrasound stimulation (LIPUS) can enhance bone regeneration and callus healing during fracture repair. However, whether a certain phase of the healing process in fracture repair in particular is infiuenced by LIPUS treatment remains unclear. In this investigation, the effect of LIPUS on callus remodeling in a gap healing model was evaluated by bone morphometric analyses using 3-dimensional (3D) quantitative micro computed tomography (μCT) at the healing site, providing information on the temporal sequence of mineralized remodeling events that characterize the gap healing.

Materials and Methods: The rabbit osteotomy model with 2-mm gap for the right tibia was immobilized with four pins fixed to an external fixator with double side bars. LIPUS was continued for both the treatment group (n=7/group/time point) and the control group (n=7/group/time point), for 20 min, six times/week, for 4, 6, or 8 weeks. The control group also received a sham inactive transducer under exactly the same condition as the LIPUS group. After the harvested tibia was scanned by μCT, region of interest was set at the callus healing area. It defined as a center of the osteotomy gap with a width of 1 mm. Morphometric parameters used for evaluation were mineralized callus volume (BV, cm³) and volumetric bone mineral density of mineralized tissue comprising the callus (mBMD, mBMD = BMC/ BV, mgHA/cm³). The whole ROI was measured and was subdivided into three zones. The periosteal callus zone (External), the medullary callus zone (Endosteal) and the remaining zone was the cortical gap zone (Intercortical). For each zone, BV and mBMD were measured. Data of the μCT evaluations were analyzed using a one-way ANOVA test. Statistically significant difference was set at p < 0.05.

Results: In the LIPUS groups, BV for the Endosteal zone was significantly lower for the 8-week group than for the 4-week group. Comparing results at the same time point, the LIPUS group at 8 weeks was significantly higher than that of the control group in the Intercortical zone. As for mBMD, in the LIPUS group, the 8-week group was significantly higher than the 4-week group for Total, External, Internal, and Endosteal zones, respectively. Comparing results at the same time point, mBMD was significantly higher for the LIPUS group at 8 weeks than for the control group in both External and Intercortical zones.

Discussion: The most striking finding in our study was that LIPUS accelerated bone formation in the Intercortical zone and callus resorption in the Endosteal zone. This suggests that LIPUS could shorten the time required for remodeling. However, the results of this study do not clarify whether an early phase in callus formation in particular is infiuenced by LIPUS.

Introduction: Low-intensity pulsed ultrasound stimulation (LIPUS) reportedly enhances restoration of strength at fracture healing sites. However, evaluation of strength by mechanical testing was limited to only one direction, with either bending or torsion. Quantitative micro computed tomography (μCT) scans allow us to calculate strength-related parameters such as cross-sectional moment (CSM) and cross-sectional moment of inertia (CSMI). Previous studies have performed 2-dimensional (2D) analyses, and 3-dimensional (3D) evaluations have not been described. The purpose of this study was thus to investigate the effects of LIPUS on osteotomy healing using 3D analyses of CSM and CSMI.

Materials and Methods: Bilateral, transverse, mid-tibial osteotomies with a 2-mm gap were performed in 42 rabbits. LIPUS was continued for both the treatment group (n=7/group/time point) and the control group (n=7/ group/time point), for 20 min, six times/week, for 4, 6, or 8 weeks. The control group also received a sham inactive transducer under the same condition as the LIPUS group. After the tibia was scanned by μCT, region of interest (ROI) was set at the center of the osteotomy gap with a width of 1 mm. Center of gravity for the ROI and the XYZ coordinate was calculated. An optional line (I) can be drawn in this coordinate. The angle of the Z axis (𝛉) was measured, and also the degree of angle of the X axis (φ) was measured. The 3D CSM [I (φ, 𝛉)] around this line was calculated using the following equation: I (φ, 𝛉) = ∫ r²dV (mm5), where r is the distance of a voxel to the center of gravity (mm) and dV is the area of a voxel (mm3). The axial CSM was defined as CSMx: I (0, 90), CSMy: I (90, 90), whereas the polar CSM was also defined as CSMp: I (any, 0). 3D CSMI weighted by density distribution was calculated using the following equation: I’ (φ, 𝛉) = ∫ r²dm = ∫ ρr²dV (mg.mm²), ρ is the measured volumetric callus mineral density. Likewise CSMIx, CSMIy and CSMIp were calculated. These data of the μCT evaluations were analyzed using a one-way ANOVA test (p< 0.05).

Results: When 3D CSMs at the same time point were compared, values for the LIPUS groups were significantly higher than those for control groups for CSMx at 6 weeks and CSMp at 8 weeks. As for comparison of 3D CSMIs at the same time point, values for the LIPUS groups were significantly higher than those of the control groups for CSMIx, CSMIy, and CSMIp at 6 and 8 weeks.

Discussion: Bone healing by 3D CSM and CSMI has not been described before. Our results demonstrate that these bone strength parameters improved with LIPUS during the early phases. However, whether the late phase of callus formation is infiuenced remains unclear.

Ring frames have the advantage of allowing progressive correction. However, the available frames for complex deformities are heavy and bulky leading to poor compliance by patients. Also, the mounting procedure requires considerable expertise and skill. On the other hand, a unilateral external fixator has the advantages of less bulk and a lighter weight. Thus, it causes less disability and can achieve better patient compliance even with bilateral application. However, previous unilateral fixators have had various limitations with respect to deformity correction, such as restricted placement of hinges, restricted correction planes, and a limited range of correction angles. In addition, it was impossible to achieve progressive correction while fixation was maintained. To overcome these disadvantages of existing unilateral fixators, we developed a new fixator for gradual correction of multi-plane deformities including translational and rotation deformities. This unilateral external fixator is equipped with a universal bar link system. The link is constructed from three dials and two splines that are connecting the dials. The pin clamps are able to vary the direction of a pin cluster in the three dimensional planes. The system allows us to correct angulation, translation, rotation, and the combination of the above. In addition, open or closed hinge technique is available because the correction hinge can be placed right on the center of rotational angulation (CORA), or at any desired location, by adjusting the length of the link spline. By increasing the spline length, the virtual hinge can also be set far from the fixator. Gradual correction can be performed by rotating the three dials using a worm gear goniometer that is temporarily attached. A 3D reconstructed image of the bone is generated preoperatively. Preoperative planning can be done using this image. Mounting parameters are determined by postoperative AP and lateral computed radiography images. These postoperative images are matched with the pre-operative 3D CT image by 2D and 3D image registration. Then, the fixator can be virtually fixed to the bone. By performing virtual correction, it is possible to plan the correction procedure. The fixator is manipulated by rotating each of the three dials to the predetermined angles calculated by the software. Static load testing disclosed that the fixator could bear a load of 1700 N. No breakage or deformation of the fixator itself was recognized. Mechanical testing demonstrated that this new fixator has sufficient strength for full weight bearing, as well as sufficient fatigue resistance for repeated or prolonged use. The results of clinical application in patients with multi-plane femoral deformities were excellent, and correction with very small residual deformity was achieved in each plane.

The most important issue in the assessment of fracture healing is to acquire information on the restoration of mechanical integrity of the bone. To measure bending stiffness at the healing fracture site, we focused on the use of echo tracking (ET) that was a technique measuring minute displacement of bone surface by detecting a wave pattern in a radiofrequency echo signal with an accuracy of 2.6 μ. The purpose of this study was to assure that the ET system could quantitatively assess the progress, retardation or arrest of healing by detecting bending stiffness at the fracture site.

With the ET system, eight tibial fractures in 7 patients with an average age of 37 years (range: 24–69) were measured. Two tibiae in 2 patients were treated conservatively with a cast, and 6 tibiae in 5 patients were treated with internal fixation (intramedullary nailing: 4, plating: 1, screw 1). Patients assumed supine position, and the affected lower leg was held horizontally with the antero-medial aspect faced upwards. The fibula head and the lateral malleolus were supported and held tight by a Vacufix ®. A 7.5 Hz ultrasound probe was placed on each antero-medial aspect of the proximal and distal fragments along its long axis. Each probe was equipped with a multi-ET system with 5 tracking points with each span of 10 mm. A load of 25 N was applied at a rate of 5 N/second using a force gauge parallel to the direction of the probe and these probes detected the bending angle between the proximal and distal fragments. An ET angle was defined as the sum of the inclinations of both fragments. In the patients treated with a cast, the contralateral side was also measured and served as a control. Fracture healing was assessed time sequentially with an interval of 2 or 3 weeks during the treatment.

None of the patients complained of pain, or no other complication related to this measurement occurred. In the patient (patient:M) treated with a cast, the ET angle exponentially decreased as time elapsed (y = 1.4035e-0.1053x, R = 0.9754) and the radiographic appearance showed normal healing. Including this case, in all patients with radiographic normal healing, the ET angle exponentially decreased. However, in patients with retarded healing (patient:N), the decrease of the angle was extremely slow(y = 0.2769e-0.0096x, R = 0.815). In patients with non union (patient:T), the angle stayed at the same level.

With this method, noninvasive assessment of bending stiffness at the healing site was achieved. Bending angle measured by ET diminished over time exponentially in patients with normal healing. On the contrary, in patients with healing arrest, no significant decrease of the bending angle was recognized. It was demonstrated that the echo tracking method could be applicable clinically to evaluate fracture healing as a versatile, quantitative and noninvasive technique.