Postmenopausal osteoporosis leads to a significant increase in bone fragility. In this study we used the rat tibia plateau fracture model to investigate the efficiency of estrogen replacement therapy (ERT) to mitigate the post-ovariectomy decrease in fracture load. A total of 73 virgin Sprague Dawley rats had been ovariectomized and 26 animals underwent sham operation. The ovariectomized animals were either untreated (n = 35) or treated with estrogen injections (10 micrograms/kg per day 3 days a week until sacrifice), starting treatment at either 0, 5, 8, or 13 days post surgery. Before starting ERT and at 50 days post surgery, the trabecular structure of the right proximal tibial metaphysis of each animal was imaged non-invasively using high resolution X-ray topography. The animals were then sacrificed and the right knee from each animal was harvested and mounted into a servo-hydraulic materials testing system so that the distal femoral condyle could be forced into the proximal tibial plateau until fracture occurred. The failure load (F) of the ovariectomized group without estrogen administration was significantly less than that for the sham group. The mean stiffness (K) of the ovariectomized group was 22 percent less than that of the sham group, though this difference did not reach statistical significance. Across all groups, the failure load and stiffness were significantly correlated with the trabecular bone volume. Our data suggest that prompt ERT can increase the fracture load and stiffness of trabecular bone by allowing bone formation to continue in previously activated bone remodeling units while suppressing the production of new remodeling units. This may be the mechanism by which estrogen and other antiresorptive agents increase bone mass, and thereby reduce the risk of osteoporotic fractures in postmenopausal women.
No abstract
In a previous paper in this Journal, the case for laparoscopic inguinal hernia repair by the transabdominal preperitoneal (TAPP) approach was made, in terms of superiority of outcomes in both recurrence rate and long-term symptoms. This approach has been used by many people, but not always with such good outcomes. This may be due to inattention to detail. The technique used by the author is described, as if following the patient through his surgical pathway. Instrumentation, materials (including composition, configuration and placement) are delineated, suggesting that tailoring the mesh to the individual patient and his hernia are justified, after looking at the outcomes for different mesh sizes.
The purpose of this study was to characterize the effects of cyclic mechanical loading at different frequencies on the intervertebral disc and vertebral endplates. Static, 0.5 Hz or 5 Hz loading at 5 x BW was applied to the rabbit lumbar spine in vivo 2 hours/day, 5 days/week for up to 30 weeks. Following the loading period, MRI, μCT and histology analyses were performed. Results indicate an increase in subchondral bone density in cyclically loaded animals which was loading ratedependent. There was also a decrease in trans-endplate diffusion at the loaded levels in animals exposed to high frequency loading. The trend of increased bone density at the loaded level was not seen in statically loaded animals. The extent of disc degeneration was also dependent on the frequency of loading, with decreases in disc height, fibrosis and matrix disorganization occurring at high frequency and static loading. The differences observed between loading frequencies may be related to the rate dependant, viscoelastic mechanical properties of the intervertebral disc.
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