Estrogen deposits extra mineral into bones of female rats in puberty, but simultaneously seems to suppress the responsiveness of female skeleton to mechanical loading.

To first test the possible effect of gender on the responsiveness of growing rat skeleton to mechanical loading, 5-week-old littermates of 25 male and 25 female rats were subjected to either free-cage activity or treadmill training for a period of 14 weeks (experiment 1). Using peripheral quantitative computed tomography (pQCT) and mechanical testing of the femoral neck, we observed female rats exhibiting a clearly lower responsiveness to external loading than male rats (+3.0% vs +25% in cross-sectional area (CSA), +4.2% vs +27% in the bone mineral content (BMC), -0.6% vs +10% in volumetric bone mineral density (BMD), and +4.7% vs +28% in fracture strength (F(max)) of the femoral neck). Also, relative to the mechanical demands placed on the skeleton, the bones of the young female rats were considerably denser (>50%) than those of the males. In the subsequent experiment 2, we repeated the above-noted first experiment with 33-week-old rats and observed virtually identical exercise-induced benefits (+2.1% vs +10% in CSA, +3.4% vs +18% in BMC, +2.5% vs +23% in BMD, and -1.1% vs +27% in F(max) in females vs males, respectively) and the growth/puberty-related condensation of mineral into female bones. Finally, in experiment 3, 60 littermates of 3-week-old female rats were first subjected to sham operation or ovariectomy and then further randomized to exercise or control groups, respectively, to study whether the condensation of mineral into female bones and their lower responsiveness to loading were attributable to the effects of estrogen. At the end of the 16-week intervention, our pQCT and mechanical testing analysis showed not only the anticipated effect of reduced bone density in the ovariectomized rats ( approximately -20%) but also the hypothesized better responsiveness to mechanical loading in these estrogen-depleted rats (-3.5% vs +9.1% in CSA, -0.4% vs +12% in BMC, +4.4% vs +9.6% in BMD, and -4.2% vs +16% in F(max) in SHAM vs OVX, respectively). In conclusion, the results of our series of three experiments suggest that as such estrogen seems to have very little primary effect on the sensitivity of female bone to respond to external loading, but rather deposits extra stock of mineral into female bones in puberty. This estrogen-driven extra condensation of the female skeleton seems to persist into adulthood, simultaneously damping the responsiveness of the female skeleton to mechanical loading.

The use of a biodegradable mesh plate to augment grafting of an acetabular defect: Laboratory investigation and clinical pilot study.

We used a biodegradable mesh to convert an acetabular defect into a contained defect in six patients at total hip replacement. Their mean age was 61 years (46 to 69). The mean follow-up was 32 months (19 to 50). Before clinical use, the strength retention and hydrolytic in vitro degradation properties of the implants were studied in the laboratory over a two-year period. A successful clinical outcome was determined by the radiological findings and the Harris hip score. All the patients had a satisfactory outcome and no mechanical failures or other complications were observed. No protrusion of any of the impacted grafts was observed beyond the mesh. According to our preliminary laboratory and clinical results the biodegradable mesh is suitable for augmenting uncontained acetabular defects in which the primary stability of the implanted acetabular component is provided by the host bone. In the case of defects of the acetabular floor this new application provides a safe method of preventing graft material from protruding excessively into the pelvis and the mesh seems to tolerate bone-impaction grafting in selected patients with primary and revision total hip replacement.