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Assessing the regenerate strength in distraction osteogenesis is crucial for clinical treatment. Several methods have been used to achieve this, including plain radiography, digital radiography, quantitative computed tomography, dual energy xray absorptiometry, and ultrasound. The aim of the current study was to investigate the use of ultrasound in monitoring regenerate formation and to correlate this to biomechanical testing results. An osteotomy was done on the tibia of 30 Yucatan micropigs and an Ilizarov-type half-ring external fixator was mounted. After a 5-day latency period, the tibias were distracted for 10 days and then left to consolidate for 10 days. Seven ultrasound examinations were done during Day 15 through Day 25. After sacrifice, the bone mineral density was measured using quantitative computed tomography. Maximum load and torsional stiffness were measured and correlated with ultrasound measurements and bone mineral density. The ultrasound penetration depth and the bone mineral density correlated closely with torsional stiffness. Ultrasound can be a noninvasive predictor of bone regenerate strength in the early phase of distraction osteogenesis, which may reduce the need for radiographs.

The newly formed regenerate bone during limb lengthening usually is assessed by observing standard plain radiographs. However, no objective data correlate the radiographic appearance with the quantitative strength of the newly formed bone. A noninvasive method was developed to assess the regenerate bone using digital radiography. The investigations were performed in a micropig animal model. The right tibia was distracted for 10 days at 2 mm per day. Digital radiography was performed after the distraction during a 10-day consolidation period. For quantitative analysis, an aluminum step wedge was placed on all images, and a region of interest was outlined in the regenerate bone. A calibration curve was calculated by measuring the corresponding gray values of the aluminum phantom. The calibration equation was used for determining the mean density in the region of interest. This method was sensitive in assessing day to day healing progress. The measurements taken the day before sacrifice were compared with torsional mechanical data using a material testing machine. The high correlation between the densimetric evaluations and the biomechanical data suggests this method is a useful tool for in vivo assessment of the regenerate bone during the consolidation period in distraction osteogenesis.

Bone injuries have a systemic influence on the remodeling of bone. This effect has not been examined concerning its extent and duration. We measured the systemic effect of distraction osteogenesis on the remodeling of bones of the axial skeleton by means of the mineral apposition rate and bone formation rate in an animal experiment. Distraction osteogenesis was performed on the tibiae of 24 mature Yucatan minipigs. After a 4-day latency period, the tibiae were distracted 2 mm/day for 10 days. The ensuing consolidation phase lasted 10 days. Three fluorescent labeling substances were applied intravenously: calcein green at the second postoperative day, tetracycline 1 day after the end of the distraction phase, and xylene orange 2 days before sacrifice. We prepared ground sections from the ninth right ribs. The mineral apposition rate and bone formation rate were measured histomorphometrically on labeled osteons. The median mineral apposition rate during distraction was 2.39 microm/day (2.12-2.62 microm/day), which was higher than the rate during consolidation (median, 1.62 microm/day; 1.54-1.84 microm/day). The median bone formation rate confirmed this result and was 840.51 microm(2)/day (744.20-1148.26 microm(2)/day) during distraction and 384.25 microm(2)/day (330.84-467.71 microm(2)/day) during consolidation. Thus, a short period of distraction osteogenesis appears to have an anabolic effect on the mineral apposition rate of remote cortical bone.

To determine histomorphometric and bone strength distribution of the proximal humerus, analyses were done on 24 freshly harvested human cadaveric humeri. Median ages of 46 and 69 years were recorded respectively for the male group (n = 11; minimum, 34 years; maximum, 76 years) and the female group (n = 13; minimum, 46 years; maximum, 90 years). The humeral head was sliced into four equal horizontal levels (Levels 1-4). Five regions of interest were defined in each cutting plane: anterior, posterior, lateral, medial, and central. Histomorphometric analyses evaluated structural parameters (tissue volume to bone volume ratio, trabecular thickness), connectivity (number of nodes, node to node length), and trabecular orientation (mean bone length). The peak values of histomorphometric parameters and bone strength were identified for the cranial section and decreased caudally. The medial and dorsal aspects of the proximal humeral head were found to be the areas of highest bone strength. The trabecular network formed a pattern that connected the center of the gleaned cavity. The structural and connectivity parameters, bone strength, and trabecular orientation showed region- and level-related characteristics. Knowledge of distribution, microstructure, and quality of bone in the humeral head allows the remaining bone stock to be used effectively, even in elderly patients, with a minimally invasive approach and maximum mechanical stability.

After replacement of the anterior cruciate ligament with a free tendon graft, the substitute initially is avascular and without a synovial surface. To ensure long-term survival, the graft must become revascularized. Despite numerous studies on the topic, there still is discussion regarding revascularization. The goal of the current study was to investigate the endoligamentous microcapillary revascularization of the free tendon graft after anterior cruciate ligament replacement with time. Thirty-six mature sheep had an anterior cruciate ligament reconstruction with an ipsilateral flexor tendon split graft. Midsubstance tissue samples were immunostained for von Willebrand factor (Factor VIII) at 6, 9, 12, 24, 52, and 104 weeks to detect the endothelial cells of capillaries. Cross sections of vessels were determined in three zones (subsynovial, intermediate, and center of the graft) and were evaluated by means of histomorphometry using a digital imaging analysis system. The observations showed that capillary vessels, which originate from the synovial envelope, invaded the avascular graft tissue from the surface toward the center zone. The highest level of vascular density was found after 6 weeks, reaching the vascular status of the native anterior cruciate ligament after 24 weeks. These findings are in contrast to the findings of previous studies in animals. The current study showed, for the first time, the kinetics of an endoligamentous revascularization of a free tendon graft at the capillary level. In the current model, the process of revascularization terminated earlier than previously described.

New composite hybrid fixators for fracture stabilization using single or multiple rings with monolateral bars and half-pin fixation may provide clinical advantages such as reduced bulk and easier skin access. However, the mechanical properties of these fixators are difficult to estimate from numerous design parameters. Addressing this problem the following research questions were asked: (1) Do composite hybrid fixators have similar stiffness properties to clinically proven triple-ring fixators; (2) How does the fixation mechanism affect the stiffness properties of external fixators, and, (3) Are there interferences between ring number and fixation method? An experimental study was done on simulated metaphyseal tibial fractures and stiffness of 12 fixators was measured for different loading conditions. The results showed that triple-ring fixators provide approximately 20% stiffer properties than double-ring and single-ring fixators. No influence of ring number on the AP bending properties was found and different fixation methods were associated with large differences in fixator stiffness, whereas significant interferences were found between ring number and fixation method. Although the mechanical properties investigated in the current study cannot predict directly the clinical performance of these fixators, the stiffness data provide useful information for making decisions regarding the treatment of fractures using external fixation.