Hip protectors: recommendations for biomechanical testing--an international consensus statement (part I).

INTRODUCTION: Hip protectors represent a promising strategy for preventing fall-related hip fractures. However, clinical trials have yielded conflicting results due, in part, to lack of agreement on techniques for measuring and optimizing the biomechanical performance of hip protectors as a prerequisite to clinical trials. METHODS: In November 2007, the International Hip Protector Research Group met in Copenhagen to address barriers to the clinical effectiveness of hip protectors. This paper represents an evidence-based consensus statement from the group on recommended methods for evaluating the biomechanical performance of hip protectors. RESULTS AND CONCLUSIONS: The primary outcome of testing should be the percent reduction (compared with the unpadded condition) in peak value of the axial compressive force applied to the femoral neck during a simulated fall on the greater trochanter. To provide reasonable results, the test system should accurately simulate the pelvic anatomy, and the impact velocity (3.4 m/s), pelvic stiffness (acceptable range: 39-55 kN/m), and effective mass of the body (acceptable range: 22-33 kg) during impact. Given the current lack of clear evidence regarding the clinical efficacy of specific hip protectors, the primary value of biomechanical testing at present is to compare the protective value of different products, as opposed to rejecting or accepting specific devices for market use.

Intestinal calcium transport: the role of sodium.

The role of sodium in intestinal calcium transport was investigated in everted rat intestine. Ethacrynic acid, but not ouabain, inhibited calcium transport. However, ouabain did inhibit net water transport and, therefore, sodium transport, establishing the dissociation of the two transport processes. In addition to a magnesium-dependent adenosine triphosphatase (activated by sodium and potassium), a phosphatase dependent on sodium and calcium was localized to the lateral and basal membrane fractions of the mucosal cell. Activity of the latter phosphatase, similar to calcium transport in intact tissue, was inhibited by ethacrynic acid and not by ouabain. Sodium, therefore, may participate in the calcium transport process by activating an enzyme complex, dependent on adenosine triphosphate, that mediates calcium transport.

The role of phosphate in the action of vitamin D on the intestine.

The response of chick intestine to vitamin D and its metabolites was studied in an organ culture preparation of chick ileum explants. Both 25-hydroxycholecalciferol (25-OHD(3)) at a concentration of 20 ng/ml or greater and 1,25-dihydroxycholecalciferol [1,25-(OH)(2)D(3)] at a concentration of 50 pg/ml or greater stimulated the rate of accumulation of [(32)P]phosphate and (45)Ca by the explants and the incorporation of [(3)H]thymidine into DNA. The accumulation of [(32)P]phosphate by the explants was against a concentration gradient and inhibited by ouabain and dinitrophenol. Two saturable mechanisms appeared to mediate the cellular accumulation of phosphate with K(a) of 0.0047 and 0.125 mM, respectively. The V(max) of the lower affinity transport mechanism was accelerated by 1,25-(OH)(2)D(3). Actinomycin D (5.0 mug/ml) did not block the intestinal response to 1,25-(OH)(2)D(3) stimulation of both [(32)p]phosphate and (45)Ca accumulation. Significant stimulation of [(32)P]phosphate accumulation was observed 30 min after the addition of 1,25-(OH)(2)D(3), preceding the sterol-induced increase in the rate of (45)Ca uptake by 30 min and the sterol-induced increase in [(3)H]thymidine incorporation into DNA by 150 min. Increasing extracellular phosphate concentration to 3.0 mM increased [(3)H]thymidine incorporation into DNA and the rate of (45)Ca uptake by the explants. Reducing extracellular phosphate concentration to 0.05 mM attenuated the response of the explants to 1,25-(OH)(2)D(3). From these observations it is postulated that the primary action of vitamin D sterols in the intestine is to enhance the ability of the mucosal cell to accumulate phosphate. The data suggest that restoration of intracellular phosphate levels may then permit expression of the cells' response to vitamin D sterols.

Indentification of an intestinal sodium and calcium-dependent phosphatase stimulated by parathyroid hormone.

Previous reports suggest that the site of the energy-dependent intestinal calcium transport against an electropotential and concentration gradient is located along the basal-lateral membrane of the mucosal cell. Accordingly, basal-lateral membranes were prepared from rat intestinal homogenates in order to identify the enzyme mediating this step in the transport process. An alkaline phosphatase was delineated which utilized ATP as a substrate and was dependent on both Na(-) and Ca(++) with optimum enzyme activity at 200 mM and 0.04 mM, respectively. Furthermore, the activity of the enzyme was demonstrated to decrease with the advance in age of the animal and to decrease with removal of the parathyroid glands, consistent with a decreased rate of (45)Ca release from mucosal cells under the same experimental conditions. Calcium binding to basal-lateral membrane fragments was also sodium dependent and enhanced by the prior administration of parathyroid extract. The consistent correlation between the rate of calcium transport across the basal-lateral membrane of the mucosal cell and the activity of this Na, Ca-dependent phosphatase under a variety of experimental conditions suggest that this enzyme may mediate the parathyroid hormone-sensitive active transport of calcium across the intestine.

25-hydroxycholecalciferol stimulation of muscle metabolism.

Intact diaphragms from vitamin D-deficient rats were incubated in vitro with [3H]leucine. Oral administration of 10 mug (400 U) of cholecalciferol 7 h before incubation increased leucine incorporation into diaphragm muscle protein by 136% (P less than 0.001) of the preparation from untreated animals. Nephrectomy did not obliterate this response. ATP content of the diaphragm muscle was also enhanced 7 h after administration of the vitamin. At 4 h after administration of cholecalciferol, serum phosphorus concentration was reduced by 0.7 mg/100 ml (P less than 0.025) and the rate of inorganic 32PO4 accumulation by diaphragm muscle was increased by 18% (P less than 0.025) over the untreated animals. Increasing serum phosphate concentration of the vitamin D-deficient animals by dietary supplementation with phosphate for 3 days failed to significantly enhance leucine incorporation into protein. However, supplementation of the rachitogenic, vitamin D-deficient diet with phosphorus for 3 wk stimulated the growth of the animal and muscle ATP levels. This increase in growth and muscle ATP content attributed to the addition of phosphorus to the diet was less than the increase in growth and muscle ATP levels achieved by the addition of both phosphorus and vitamin D to the diet. To eliminate systemic effects of the vitamin, the epitrochlear muscle of the rat foreleg of vitamin D-depleted rats was maintained in tissue culture. Addition of 20 ng/ml of 25-hydroxycholecalciferol (25-OHD3) to the medium enhanced ATP content of the muscle and increased leucine incorporation into protein. Vitamin D3 at a concentration of 20 mug/ml and 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) at a concentration of 500 pg/ml were without effect. Analysis of muscle cytosol in sucrose density gradients revealed a protein fraction which specifically bound 25-OHD3 and which demonstrated a lesser affinity for 1,25-(OH)2D3. These studies suggest that 25-OHD3 may influence directly the intracellular accumulation of phosphate by muscle and thereby play an important role in the maintenance of muscle metabolism and function.

Influence of sodium and parathyroid hormone on calcium release from intestinal mucosal cells.

The uptake and release of (45)Ca from the intestinal mucosal epithelium were investigated under a variety of conditions. The initial rate of uptake characterized a calcium pool with a half-time of saturation of less than 2 min. The entry of (45)Ca into this pool was inhibited by NaCN and ethacrynic acid and was stimulated by the removal of Cl(-) from the incubation. The initial rate of (45)Ca release was also inhibited by NaCN and removal of Na(+) from the incubation. Parathyroid hormone administration enhanced the release of (45)Ca from cells prepared from parathyroid-ectomized animals. These observations suggest that calcium transport across the brush border and basallateral membranes are identifiable components of the kinetics of (45)Ca uptake and release and that parathyroid hormone stimulates a sodium-dependent mechanism of calcium transport across the basal-lateral membranes.

Study of calcium absorption in man: a kinetic analysis and physiologic model.

A physical model of calcium absorption was developed from analysis of data obtained on 23 subjects, including 13 patients having a variety of abnormalities of calcium metabolism. The model was tested and found consistent in all subjects studied. This technique provides a quantitative description of the rate of entry of oral dose of (47)Ca into the circulation as a function of time by analysis of serum or forearm radioactivity in response to intravenous and oral administration of (47)Ca. The kinetics of the absorption process as proposed by the model are characterized by an initial delay phase of 15-20 min, by a maximal rate of absorption at 40-60 min after ingestion, and by 95% completion of the absorption within 2(1/2) hr. Partial identification of the physiological counterparts of the model was possible by introduction of the isotope at various levels of the gut. Although the region of the duodenum was found to have the greatest rate of absorption per unit length in normal subjects, it was least responsive to stimulation by parathyroid hormone and suppression by calcium loading. Furthermore, the response of the gut to parathyroid hormone was delayed, whereas the suppression of absorption by intravenous or oral calcium loading was rapid and dramatic. The implications of these observations are discussed.

Phenobarbital-induced alterations in vitamin D metabolism.

The metabolic fate of intravenously injected vitamin D(3)-1,2-(3)H (D(3)-(3)H) was studied in two normal individuals on chronic phenobarbital therapy. Silicic acid column chromatography of lipid-soluble plasma extracts obtained serially for 96 hr after D(3)-(3)H injection demonstrated a decreased plasma D(3)-(3)H half-life and increased conversion to more polar metabolites. The polar metabolites formed included several with chromatographic mobility similar to known biologically inactive vitamin D metabolites and one with chromatographic mobility identical to 25-hydroxycholecalciferol. Disappearance of this latter material was also accelerated. A child with rickets and a normal volunteer studied before and after a 2 wk course of phenobarbital therapy demonstrated similar alterations in D(3)-(3)H metabolism. When liver microsomes from 3-wk-old Sprague-Dawley rats treated with phenobarbital were incubated with D(3)-(3)H, polar metabolites were produced with chromatographic mobility similar to the plasma D(3)-(3)H metabolites from phenobarbital-treated humans. Similar incubations employing 25-hydroxy-cholecalciferol-26-27-(3)H as the substrate also demonstrated an increased conversion to polar metabolites. The data suggest that the reported increased incidence of osteomalacia observed in patients on chronic anticonvulsant therapy may be the result of an accelerated conversion of vitamin D and its active metabolite, 25-hydroxycholecalciferol, to polar metabolites by druginduced liver microsomal enzymes.

Prolactin-secreting pituitary tumor associated with von Recklinghausen's disease.

A prolactin-secreting pituitary tumor, manifesting as galactorrhea and amenorrhea, was detected in association with multiple neurofibromatosis (von Recklinghausen's disease) in a young woman. The patient showed an excellent symptomatic response to bromocriptine mesylate treatment. To our knowledge, this association has never before been reported and may represent a new endocrine tumor association.

Diltiazem-induced psychosis and a possible diltiazem-lithium interaction.

Calcium channel blockers are being used increasingly for a variety of cardiovascular problems. Diltiazem hydrochloride, a benzothiazepine derivative, has been reported to have a low incidence of adverse side effects. We report a case of acute psychosis associated with the use of diltiazem in a patient receiving lithium carbonate therapy. Both diltiazem hydrochloride and lithium carbonate have calcium antagonist effects in the central nervous system, and we review their mechanisms of action. A possible synergistic drug interaction between diltiazem and lithium is reported.

Additive effects of weight-bearing exercise and estrogen on bone mineral density in older women.

The separate and combined effects of weight-bearing exercise and hormone replacement therapy (HRT) on bone mineral density (BMD) were studied in 32 women, 60 to 72 years of age. HRT consisted of continuous conjugated estrogens 0.625 mg/day and trimonthly medroxyprogesterone acetate 5 mg/day for 13 days. Exercise consisted of 2 months of low-intensity exercise followed by 9 months of more vigorous weight-bearing exercise approximately 45 minutes/day, > or = 3 days/week, at 65-85% of maximal heart rate. Lumbar spine and proximal femur BMD were significantly increased in response to exercise and to HRT, and total body BMD was significantly increased in response to HRT; neither exercise nor HRT had an effect on wrist BMD. The combination of exercise + HRT resulted in increased BMD at all sites except the wrist, with effects being additive for the lumbar spine and Ward's triangle and synergistic for the total body. Based on reductions in serum osteocalcin levels, it appears that increases in BMD in response to HRT and exercise + HRT were due to decreased bone turnover. The lack of change in serum osteocalcin and IGF-I in response to exercise alone suggests that increases in BMD were due to decreased bone resorption and not increased formation. Results indicate that weight-bearing exercise + HRT may be effective in preventing and/or treating osteoporosis. It is likely that the additive effects of weight-bearing exercise and HRT on bone mineral accretion, coupled with other adaptations to the exercise (i.e., increased strength and functional capacity), could effectively reduce the incidence of falls and osteoporotic fractures.

Effects of exercise involving predominantly either joint-reaction or ground-reaction forces on bone mineral density in older women.

This study compared the effects of two exercise training programs, 11 months in duration, on bone mineral density (BMD) in older, sedentary women. Thirty-nine women, aged 60-74 years, were assigned to the following groups: (a) a group that performed exercises that introduced stress to the skeleton through ground-reaction forces (GRF) (i.e., walking, jogging, stairs); (b) a group that performed exercises that introduced stress to the skeleton through joint-reaction forces (JRF) (i.e., weight lifting, rowing); or (c) a no-exercise control group. BMD of the whole body, lumbar spine, proximal femur, and distal forearm was assessed five times at approximately 3-month intervals. The GRF and JRF exercise programs resulted in significant and similar increases in BMD of the whole body (2.0 +/- 0.8% and 1.6 +/- 0.4%, respectively), lumbar spine (1.8 +/- 0.7% and 1.5 +/- 0.5%, respectively), and Ward's triangle region of the proximal femur (6.1 +/- 1.5% and 5.1 +/- 2.1%, respectively). There was a significant in BMD of the femoral neck only in response to the GRF exercise program (GRF, 3.5 +/- 0.8%; JRF, -0.2 +/- 0.7%). There were no significant changes in BMD in control subjects. Among all exercisers, there was a significant inverse (r = -0.52, p < 0.01) relationship between increases in whole body BMD and reductions in fat mass, suggesting a dose response effect of exercise on bone mass. Although femoral neck BMD was responsive only to the GRF exercise program, some adaptations (i.e., increase in lean body mass and strength) that were specific to the JRF exercise program may be important in preventing osteoporotic fractures by reducing the risk for falls. It remains to be determined whether all of these benefits can be gained through a training program that combines the different types of exercises employed in this study.

Effects of age and estrogen on calcium absorption in the rat.

In order to differentiate the relative effects of age and estrogen on rates of calcium absorption and serum levels of parathyroid hormone and calcitonin, the effect of oophorectomy with and without estrogen replacement (2 weeks) was studied in rats for 30- or 120-day periods. Whereas oophorectomy for 30 days resulted in a significant decrease in serum calcium and an increase in serum phosphate, no change in either calcium or phosphate was observed in the 120-day oophorectomized animals. iPTH decreased in both the 30- and 120-day oophorectomized animals although these changes were not significant at the .05 level. Whereas no significant change in basal circulating calcitonin occurred in the 30-day oophorectomized rats, it decreased significantly in the older animals following the ablative procedure. Forty-five days following estrogen deprivation, calcitonin release to a calcium secretagogue was significantly blunted. Intestinal calcium absorption decreased with age, and unlike the increments in calcium absorption observed in the younger estrogen-repleted, 30-day oophorectomized rat, no change in calcium absorption was observed when estrogens were administered to the older, 120-day oophorectomized rat. The accumulated data suggest that the effects of estrogen loss on the hormonal control of bone metabolism and calcium absorption are age dependent, and that estrogen contributes significantly to changes in calcium homeostasis observed in the maturing rat.

Abnormal regulation of 25-hydroxyvitamin D3-1 alpha-hydroxylase activity by calcium and calcitonin in renal cortex from hypophosphatemic (Hyp) mice.

25-Hydroxyvitamin D3-1 alpha-hydroxylase activity was assayed in primary serum-free monolayer tissue culture of renal cortical cells from hypophosphatemic (Hyp) mice and normal litter mates. Morphological and growth characteristics of cells from the two genotypes were indistinguishable. Basal enzyme activity was not significantly different in either type of cell over a wide range of substrate concentration. The enzyme from both genotypes was stimulated by PTH and suppressed by increased phosphate concentration in the culture medium. Whereas 1 alpha-hydroxylase activity in cells from normal mice was increased in low calcium medium and suppressed in high calcium medium, the enzyme in cells from Hyp mice was not altered by similar changes in the medium calcium concentration. Salmon calcitonin caused a significant increase in 1 alpha-hydroxylase in cells from normal mice, but did not stimulate enzyme activity in cells from Hyp mice. These studies indicate that control of 1 alpha-hydroxylase activity is abnormal in renal cortical cells from Hyp mice. Impaired control of this enzyme could result in the inappropriately low circulating concentrations of 1,25-dihydroxyvitamin D3 that have been observed in humans with hypophosphatemic rickets and in the relatively low activity of 1 alpha-hydroxylase in renal cortical homogenates of Hyp mice compared to that in normal mice on a low phosphate diet.

Inhibition of calcitonin secretion by exogenous calcitonin in the rat.

The effect of synthetic salmon calcitonin (CT) on calcium- and pentagastrin-stimulated plasma CT was investigated in male Sprague-Dawley rats. Plasma samples were obtained before and 3 and 6 min after calcium (1 mg/100 g BW, iv) or pentagastrin (5 micrograms/100 g BW, iv) infusion. Although salmon CT at the dose of 0.4 MRC U/100 g BW administered 15 min before either the calcium or pentagastrin infusion did not influence circulating endogenous CT levels, salmon CT in doses of 4 and 20 U/100 g BW administered 15 min before the injection of secretogogues significantly reduced the response of CT to either calcium or pentagastrin without significantly changing plasma calcium levels from those of control animals. Salmon CT (20 U/100 g BW) given 5 min before pentagastrin infusion again significantly suppressed the response of plasma CT to this stimulus. Similarly, salmon CT administered chronically in a dose of 2 U/100 g BW for 28 days significantly reduced the response of CT to the calcium infusion. These data suggest that in the rat, at least pharmacological dosage of CT modulates the production and/or secretion of glandular CT itself.

The duodenal 1 alpha,25-dihydroxyvitamin D3 receptor in rats with experimentally induced diabetes.

Studies in the rat with streptozotocin-induced diabetes of short and long duration revealed decreased circulating 1 alpha,25-dihydroxyvitamin D [1,25-(OH)2D] levels and an intact 1,25-(OH)2D3 duodenal cytosolic receptor with a sedimentation coefficient of 3.3S. Whereas no significant alterations in the equilibrium dissociation constant (Kd) were observed in the diabetic animals, the number of 1,25-(OH)2D3-binding sites was increased in the animals with short term (235 +/- 48 vs. 100 +/- 15 fmol/mg protein) and long term (521 +/- 60 vs. 119 +/- 15 fmol/mg protein) diabetes. The data are consistent with the hypothesis that alterations in intestinal calcium absorption previously observed in the diabetic state are due, at least in part, to dynamic relationships between circulating 1,25-(OH)2D concentrations and the number of intestinal 1,25(OH)2D3-binding sites.

Regulation of 25 hydroxyvitamin D3 1-hydroxylase in serum-free monolayer culture of mouse kidney.

Primary monolayer cultures of cells from normal mouse kidney were initiated and maintained in serum-free medium supplemented with insulin, transferrin and prostaglandin E1. Renal epithelial cells grow to confluence without detectable growth of fibroblasts. These cells contain an active 25(OH)D3 1-hydroxylase with half-maximal formation of 1,25(OH)2D3 achieved at a substrate concentration of 13.3 nM. Activity of this enzyme is increased by low calcium medium or parathyroid hormone and decreased by high calcium medium, high phosphate medium or 1,25(OH)2D3.

Vitamin D metabolism in the chronic streptozotocin-induced diabetic rat.

Alterations in circulating vitamin D3 metabolites have been documented in both experimental and human diabetes mellitus. Using a recirculating hepatic perfusion system and in vitro kidney mitochondrial assays, we studied vitamin D3 hydroxylation in control and insulin-deficient rats 6 weeks after the induction of streptozotocin-diabetes. Vitamin D3-25-hydroxylase activity, assessed by hepatic conversion of [3H]vitamin D3 to [3H]25-hydroxyvitamin D3 during a 4-h perfusion, was similar in diabetic and control animals. The hepatic degradation of 25-hydroxyvitamin D3 to more polar metabolites was also normal, as was glucuronide conjugation and biliary excretion of vitamin D3 metabolites. The chronic insulin-deficient state resulted in a significantly (P less than 0.01) decreased 1 alpha-hydroxylase activity and enhanced (P less than 0.001) renal 24-hydroxylase activity. These alterations in vitamin D metabolism may relate to the deranged mineral homeostasis and skeletal morphology observed in rats and humans with chronic insulin deficiency.

Serum leptin levels are reduced in response to exercise training, but not hormone replacement therapy, in older women.

The aim of this study was to evaluate the effects of exercise training and hormone replacement therapy (HRT) on serum leptin levels in older women. Previously sedentary, healthy women, aged 60-72 yr, were assigned to control (n = 16), exercise (n = 17), HRT (n = 15), or exercise + HRT (n = 13) groups. Exercise training consisted of a 2-month flexibility-exercise program followed by a 9-month exercise program that included walking, jogging, and stair climbing. HRT consisted of 11 months of continuous conjugated estrogens (0.625 mg/day) and medroxyprogesterone acetate (5 mg/day) for 13 days every third month. Body composition was assessed by dual-energy x-ray absorptiometry, and serum insulin levels were measured in the fasted state and in response to a glucose challenge. Leptin levels were reduced by 23 +/- 25% and 22 +/- 27% (both P < 0.01) in response to exercise and exercise + HRT, respectively. There was no effect of HRT on leptin. Fat mass was the strongest predictor of serum leptin concentration, both before (r = 0.81; P < 0.001) and after (r = 0.85; P < 0.001) the study period, and the change in fat mass in the exercisers was significantly correlated with the change in leptin (r = 0.55; P < 0.01). There did not seem to be an effect of exercise, independent of the reduction in fat mass, on leptin. Insulin levels were significantly correlated with leptin levels, but this was not independent of the association with adiposity. The curvilinear relationship between leptin level and fat mass and the finding that the ratio of leptin mass to fat mass decreased after weight loss suggest that fat cell size is an important determinant of circulating leptin levels.

Single and dual energy tomographic analysis of spinal trabecular bone: a comparative study in normal and osteoporotic women.

To investigate the effects of age on rates of bone loss and the relationship between amount of trabecular bone and clinical severity of osteoporosis, trabecular mineral density of the lumbar spine (VMD) was measured in 55 osteoporotic women and 133 healthy women with both single energy (SE) and dual energy (DE) quantitative computed tomography (QCT). The amount of marrow fat was indirectly estimated by the difference (delta) between DE and SE VMD values. The rate of bone loss in the normal women was 1.14%/yr with SE and 1.03%/yr with DE QCT. Osteoporotic patients had a VMD decline of 1.62%/yr with SE and 1.17%/yr with DE QCT. Osteoporotic patients had significantly lower (P less than 0.0001) mean SE and DE VMD at any age, but VMD was not significantly different among groups characterized by different number of fractures or different radiographic severity of fractures. The threshold values of VMD below which the risk of having fractures was increased were 99.8 and 118.7 mg/cm3, respectively, for SE and DE QCT. Dispersion around the mean, overlap between osteoporotic and healthy women, and the incidence of asymptomatic osteoporosis were greater with DE than SE QCT. Osteoporotic women had higher delta values (P less than 0.05) compared to normal women, but delta did not correlate with clinical severity of osteoporosis. The results indicate that factors in addition to the amount of spinal trabecular bone determine the number and severity of fractures in osteoporotic women; DE QCT reduce the VMD underestimation due to intravertebral fat content, but not the overlap between osteoporotic and normal women; and further anatomical studies of osteoporotic vertebrae are necessary to investigate the effect of age on intravertebral fat.