Peripheral nerve lengthening by controlled isolated distraction: a new animal model.

We have developed a simple and effective animal model to study the distraction neurogenesis utilizing the sciatic nerve-lengthening technique in rats. The model allows macroscopic, physiological, and histological evaluation of the distraction site. Fourteen adult Harlan Sprague Dawley rats (300-350 g) were used in this study. A 10 mm segment of the right sciatic nerve of each animal in the nerve-lengthening group was resected. Gradual nerve lengthening was performed by advancing the proximal nerve stump at a rate of 1 mm/day. The proximal stump neuroma was then resected and a direct nerve anastomosis was performed. On the left side a standard autogenous nerve-grafting procedure was performed with a 10 mm segment of sciatic nerve used as an in situ nerve graft. Three months after the second surgery, the sciatic nerves were exposed and investigated by gross observation and EMG followed by histological processing and tissue analysis. Neomicrovascularization was observed surrounding the sciatic nerve anastomosis in all five specimens of the nerve-lengthening group as compared to the more white-colored scar tissue that was observed in the nerve-grafting group. The EMG results were similar for both groups. Histological studies of the lengthened nerves showed axon morphology equivalent to the grafted nerves. This study demonstrated a clear evidence of the successful nerve regeneration within a segmental nerve gap by nerve lengthening.

Tibial plateau fracture as a measure of early estrogen-dependent bone fragility in rats.

The goals of this study were to develop a protocol to induce a compressive fracture at the tibial plateau of the rat knee in vitro and to determine if the biomechanical parameters provided a sensitive assessment of the early skeletal changes induced by estrogen deficiency. Sixty-one rats underwent an ovariectomy (n = 36) or sham operation (n = 25) and were maintained for 50 days after the procedure. Just before death, the proximal tibia of each animal was scanned with high-resolution x-ray tomography. From the three-dimensional images, the mean trabecular bone volume, thickness, and separation and the number of trabeculae were calculated. The knees were then harvested and mounted into a servohydraulic materials testing system so that the distal femoral condyle could be forced into the proximal tibial plateau until fracture. The fracture load of the ovariectomized rats was 24% less than that of the rats that had the sham operation. Similarly, the structural stiffness of the ovariectomized knees was decreased by 22%. Both of these differences were statistically significant (p < 0.01) and were explained by differences in trabecular bone volume (r = 0.56, p < 0.0001 and r = 0.42, p < 0.005, respectively). The other measures of trabecular bone structure were correlated with the volume and did not improve the prediction by the biomechanical parameters. These data demonstrate that biomechanical testing of the tibial plateau in rats can quantify the structural consequences of estrogen deficiency at an early time point before they become apparent at other bone sites, such as the lumbar spine.