Search PubMed⌕ Search

Biomedical subjects

J D Wark

Publications and source records attributed to J D Wark.

At least 73 records · Page 4Linked to original sources
PubMed1997

Prospective ten-month exercise intervention in premenarcheal girls: positive effects on bone and lean mass.

Enhancement of bone mineral acquisition during growth may be a useful preventive strategy against osteoporosis. The aim of this study was to explore the lean mass, strength, and bone mineral response to a 10-month, high-impact, strength-building exercise program in 71 premenarcheal girls, aged 9-10 years. Lean body mass, total body (TB), lumbar spine (LS), proximal femur (PF), and femoral neck (FN) bone mineral were measured using the Hologic QDR 2000+ bone densitometer. Strength was assessed using a grip dynamometer and the Cybex isokinetic dynamometer (Cybex II). At baseline, no significant difference in body composition, pubertal development, calcium intake, physical activity, strength, or bone mineral existed between groups. At completion, there were again no difference in height, total body mass, pubertal development, calcium intake, or external physical activity. In contrast, the exercise group gained significantly more lean mass, less body fat content, greater shoulder, knee and grip strength, and greater TB, LS, PF, and FN BMD (exercise: TB 3.5%, LS 4.8%, PF 4.5%, and FN 12.0%) compared with the controls (controls: TB 1.2%, LS 1.2%, PF 1.3%, and FN 1.7%). TB bone mineral content (BMC), LS BMC, PF BMC, FN BMC, LS bone mineral apparent density (BMAD), and FN bone area also increased at a significantly greater rate in the exercise group compared with the controls. In multiple regression analysis, change in lean mass was the primary determinant of TB, FN, PF, and LS BMD accrual. Although a large proportion of bone mineral accrual in the premenarcheal skeleton was related to growth, an osteogenic effect was associated with exercise. These results suggest that high-impact, strength building exercise is beneficial for premenarcheal strength, lean mass gains, and bone mineral acquisition.

Body Height↗
PubMed1997

Large, rapid skeletal changes after parathyroidectomy.

We report dramatic increases in spine and hip bone mineral density six weeks following parathyroidectomy in renal patients. We have previously reported a cross-sectional association between parathyroidectomy and higher axial bone mineral density in dialysis patients. Large axial increases in bone mineral density after surgery for primary hyperparathyroidism have been recorded by others at one year postoperatively. Bone mineral density was recorded before and six weeks after parathyroidectomy. Scans were performed at the lumbar spine, hip and non-dominant radius. Values were expressed as Z-scores (standard deviations from the mean of an age- and gender-matched reference population). Large increases in lumbar were spine and femoral neck bone mineral density seen at six weeks post parathyroidectomy. Median increases were 0.57 (p = 0.006) and 0.26 (p = 0.039) Z-score units for these sites, respectively. Individual six-week increases were as large as 1.3 Z-score units at the spine and 1.0 Z-score units at the femoral neck. No significant cohort change was detected at the forearm but individual forearm changes were highly variable. Several mechanisms to explain these large rapid increases can be postulated. These include: mineralization of osteoid and/or contraction of the remodeling space. The changes illustrate the extent to which the skeleton is capable of rapid and profound change in mineral content. Our findings emphasize that the skeleton is a heterogeneous organ and that bone density should be measured at multiple skeletal sites.

Absorptiometry, Photon↗
PubMed1996

Retired elite female ballet dancers and nonathletic controls have similar bone mineral density at weightbearing sites.

Elite female ballet dancers exhibit several risk factors for osteoporosis during their performing years. To study the long-term effect of this lifestyle, we compared the bone mineral density (BMD) of 101 retired elite female ballet dancers (mean age 51 years, SD = 14 years) and 101 normal controls, derived from a twin study, matched hierarchically for age, height, weight, and menopausal status. The dancers, who had been retired for a mean of 25.6 years (range 1-53 years) reported a greater prevalence of previous menstrual disturbance, greater lifetime alcohol intake and smoking, and a lower dietary milk intake in adolescence than controls (all p < 0.05). However, current exercise in the dancers was twice that of the controls (p < 0.01). The BMD of retired dancers did not differ from that of the controls at weightbearing sites. The mean +/- SE difference in BMD (dancers minus controls) was 0.009 +/- 0.013 at the total body, -0.009 +/- 0.018 at the total hip, 0.005 +/- 0.017 at the femoral neck, 0.014 +/- 0.018 at the femoral trochanter, 0.036 +/- 0.022 at the femoral intertrochanter and -0.017 +/- 0.021 at the lumbar spine. Retired dancers had lower mean (+/- SE) BMD at the nonweightbearing sites: ultradistal radius (-0.029 +/- 0.008) (p < 0.01) and at the midthird radius (-0.019 +/- 0.011) (p < 0.05). There was no difference in the proportion in each of the World Health Organization (WHO) categories of osteopenia (t score -1.0 to -2.5) and osteoporosis (t score < -2.5) at any of the measured sites. Regression analysis revealed that menstrual disturbance was negatively associated with BMD at the lumbar spine and the ultradistal radial sites, but not at the weightbearing femoral sites. This sample of retired elite ballet dancers who had multiple historical risk factors does not appear to have an increased risk for future hip or vertebral fracture based on WHO standards.

Absorptiometry, Photon↗
PubMed1996

Osteoporotic fractures: background and prevention strategies.

OBJECTIVES: To review current knowledge of the epidemiology, pathogenesis, prevention and treatment of osteoporosis, with particular reference to issues related to the menopause. METHODS: Peer-reviewed publications were assessed. RESULTS: Much international variation exists in the prevalence of osteoporosis and the incidence of fracture. Risk fractures for osteoporosis are numerous. The menopause and other causes of hypogonadism in both women and men strongly predispose to osteoporosis. Various endocrinopathies, especially glucocorticoid excess, also are important. The contribution of family history may be explained by one or more genetic markers. Poor vitamin D and calcium nutrition, smoking, high alcohol consumption and inactivity increase risk. Reduced bone mass is a major risk factor for fracture, although the magnitude of that risk may vary between populations. In addition, bone fragility, length of the femoral neck (for hip fracture), history of prior fracture (for vertebral fracture) and falls affect fracture risk. Useful methods for measuring bone density are available for both epidemiologic surveillance and for clinical practice. Dual energy x-ray absorptiometry is the most desirable method in clinical care settings. Some risk factors can be modified for prevention of osteoporosis. Postmenopausal bone loss can be inhibited with estrogen or estrogen plus progestin therapy. Bone loss in the elderly may be moderated with calcium and vitamin D supplementation. Maintenance of muscle tone and strength through exercise may reduce falls. CONCLUSIONS. Osteoporosis is a large and growing health problem in many countries. Prevention of osteoporosis is a high priority, especially because treatment of the established disease remains sub-optimal. Prevention requires immediate, intermediate-term and long-term strategies. First line therapy for established osteoporosis in women in many countries is estrogen or estrogen plus progestin, calcium and vitamin D. Prospects for improved prevention of osteoporotic fractures are encouraging.

Absorptiometry, Photon↗
PubMed1996

Determinants of hip axis length in women aged 10-89 years: a twin study.

Hip axis length (HAL), a measure of femoral geometry, has been shown to predict hip fracture in white women over the age of 67 years, independently of bone mineral density at the femoral neck. A cross-sectional study of 304 pairs of female twins [176 monozygous (MZ) and 128 dizygous (DZ)], aged between 10 and 89 years, was performed to examine the influence of age, constitutional, lifestyle, and genetic factors on HAL. HAL was calculated from dual energy X-ray absorptiometry scans of the proximal femur using an automated technique with an Hologic QDR-1000W. Lean mass, fat mass, height, and weight were also measured. Maximum mean HAL was achieved by the age of 15 years. After this age there was no discernible dependency of mean HAL on age. Using within-pair differences, after adjusting for height there were no other independent constitutional or lifestyle predictors. Cross-sectionally, after adjustment for height, MZ and DZ correlations were 0.79 (95% CI: 0.73-0.84) and 0.54 (95% CI: 0.39-0.68), respectively, and independent of age. The MZ correlation exceeded the DZ correlation (p < 0.001). The best-fitting model apportioned 79% (SE 7%) of variation in height-adjusted HAL to additive genetic factors. There was marginal evidence that an environmental influence shared by twins explained 31% (SE 16%) of height-adjusted variance (p = 0.07), in which case the genetic variance was reduced to 51% (SE 15%). Adjustment for height had reduced the magnitude of total variance by 26%, and 95% of this reduction was in the additive genetic component. Applying a previously described theoretical model, approximately 10% of the increased risk of hip fracture associated with a maternal history of hip fracture could be attributed to the genetic factors determining HAL. We conclude that, in women, adult HAL is achieved by midadolescence. After adjustment for height, which is itself largely under genetic influence, other genetic factors appear to play the predominant role in explaining variation in HAL.

Adolescent↗
PubMed1996

Prevalence and risk factors for osteopenia in dialysis patients.

Dialysis patients are at risk for low bone mineral density (BMD) consequent of hyperparathyroidism, 1,25-dihydroxyvitamin D deficiency, previous immunosuppression, chronic acidosis, secondary amenorrhea, and chronic heparin and aluminum exposure. We wanted to determine the prevalence and distribution of osteopenia and the influence of risk factors for osteopenia in dialysis patients. Dual energy x-ray absorptiometry was used to record BMD at the lumbar spine (LS), hip, and nondominant forearm. Results were expressed as Z-scores (standard deviations from the mean of a healthy age- and gender-matched reference population). Osteopenia was defined as a Z-score worse than -2. In the 250 dialysis patients studied, the prevalence of osteopenia at the LS, femoral neck (FN) and ultradistal radius (UD) was 8%, 13% and 20%, respectively. The median Z-scores at these sites were all significantly different from the healthy reference population median of 0 and were 0.29 (P = 0.008), -0.67 (P < 0.001), and -1.01 (P < 0.001), respectively. Previous transplantation was associated with as much as a one Z-score lower BMD at the FN (P = 0.0069) and UD (P = 0.0011) and a marginally significant reduction at the LS (P = 0.0777). Previous parathyroidectomy was associated with a markedly higher LS BMD (P = 0.0001) and a higher BMD at the FN (P = 0.0017) but not the UD (P = 0.3691). A history of secondary amenorrhea was associated with a lower FN BMD (P = 0.0047) but not a significantly lower BMD at the LS (P = 0.0978) or UD (P = 0.2327). In hemodialysis patients without a history of transplantation, parathyroidectomy, or secondary amenorrhea, there was no correlation between Z-score at any site and duration of dialysis. Thus, osteopenia in dialysis patients occurs in both axial and appendicular sites and sites of compact and cancellous bone. It is more common with previous transplantation and secondary amenorrhea, whereas a history of parathyroidectomy is associated with increased BMD. No relationship was found between BMD and duration of hemodialysis, which suggests that important changes in BMD occur during the predialysis stage of chronic renal failure.

Absorptiometry, Photon↗
PubMed1996

Risk factors for secondary hyperparathyroidism in a nursing home population.

OBJECTIVE: Secondary hyperparathyroidism may cause bone loss and structural deterioration of bone and may thus be a cause of fracture in the elderly. Vitamin D deficiency, renal impairment and medications are potential causes of hyperparathyroidism and may also directly predispose to fracture. We present the first findings of an ongoing study of hip fracture, vitamin D deficiency and hyperparathyroidism in a large Australian nursing home. DESIGN: Descriptive prevalence study. PATIENTS: Two hundred and fifty-one nursing home residents were eligible for inclusion. Informed consent and successful venepuncture were obtained for 99. Residents were of median age 83 years with interquartile range (IR) 77-89 years. MEASUREMENTS: 25-Hydroxyvitamin D (25OHD), intact parathyroid hormone (PTH), creatinine and biochemistry, demographic data and current medications. RESULTS: Fifty-two per cent of 99 subjects had 25OHD below the reference range of 28-165 nmol/l and 96.5% were below the reference range mean. Those with low 25OHD had lower plasma calcium corrected for albumin than those with normal 25OHD (medians 2.34 vs 2.41 mmol/l, 95% confidence interval for the difference between medians (CI) -0.10 to -0.04 mmol/l, P = 0.0001) and higher PTH (medians 5.8 vs 3.9 pmol/l, CI 0.10-2.6 pmol/l, P = 0.0360). Twenty-eight per cent of 97 residents had PTH above the upper reference range limit of 6.5 pmol/l. Residents receiving frusemide had higher PTH than other residents (medians 6.95 vs 3.45 pmol/l, CI 1.9-4.2 pmol/l, P < 0.0001). In linear modelling, the most important predictor of the natural logarithm of PTH was daily frusemide dose, adjusted R2 (Ra2) = 31.8%, F = 39.3, P < 0.001. Creatinine and the reciprocal of 25OHD were other significant predictors with the final Ra2 = 39.4%, F = 17.7, P < 0.001. CONCLUSIONS: Vitamin D deficiency is a common risk factor for secondary hyperparathyroidism in nursing home residents despite a climate in which vitamin D nutrition is thought to be ample. However, the daily frusemide dose is a more important predictor of PTH in this population.

25-Hydroxyvitamin D 2↗
PubMed1996

Models for the pathogenesis of stress fractures in athletes.

It would seem that the development of a stress fracture results from unsuccessful adaptation of bone to a change in its mechanical environment caused by repetitive loading. It involves the physiological processes of microdamage production and remodelling. Whether the initiating factor is microdamage production or activation of remodelling through direct effects of strain is unclear. The remodelling process involves both the removal of bone which has become fatigue damaged or is extraneous to the requirements of the new loading environment, and the addition of new bone in an manner that is best suited to withstand the new mechanical strain. Normally this process is well modulated and does not cause symptoms. If the amount of bone removed is not sufficient to unduly weaken bone structure and the addition of new bone occurs sufficiently rapidly to correct any weakness before failure occurs or to repair microdamage, the process will successfully lead to a bone with appropriate material strength and geometry to withstand the new strain environment. However, if there is imbalance between bone removal and replacement, together with accumulation of microdamage, signs and symptoms of a stress fracture may result. Any factors which influence bone load, bone strength, or remodelling have the potential to result in a stress fracture. Attention should be paid to the identification of these factors in an attempt to prevent this overuse injury in athletes.

Adaptation, Physiological↗
PubMed1996

Patellar tendinosis (jumper's knee): findings at histopathologic examination, US, and MR imaging. Victorian Institute of Sport Tendon Study Group.

PURPOSE: To determine the histopathologic findings of patellar tendinosis ("jumper's knee") demonstrated with ultrasonography (US) and magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twenty-four athletes (28 knees) with jumper's knee (23 men, one women; mean age, 30.9 years) scheduled to undergo open tenotomy underwent US patellar tendon examination. Seventeen patients (19 knees) also underwent MR imaging. Tissue was obtained for histopathologic examination in all 28 cases. Eleven age-, height-, and weight-matched athletes (22 knees) without previous knee symptoms served as control subjects for the US examination. Control material for histopathologic examination was obtained in 20 cadavers (39 knees). Data were analyzed with standard statistical methods. RESULTS: MR imaging and US both revealed an abnormal zone at the proximal patellar tendon attachment. Histopathologic examination revealed mucoid degeneration in all tendons in patients and in 8% (three of 39) of tendons in cadavers (P < .01). CONCLUSION: Jumper's knee is characterized by consistent changes at MR imaging, US, and histopathologic examination and is appropriately described as patellar tendinosis.

Adult↗
PubMed1996

Bone turnover markers and bone density across the menopausal transition.

We measured lunbar spine and femoral neck bone mineral density (BMD); urine markers of bone resorption; serum markers of bone formation; and serum gonadotrophin, estradiol and inhibin concentrations in a population-based cohort of 281 women aged 45-57 yr. Women were classified into pre-, peri-, and postmenopausal groups, depending on menstrual bleeding patterns. Compared with premenopausal women, BMD was lower only in postmenopausal women but not in women currently using hormone replacement therapy (HRT). BMD decreased with age in the perimenopausal group. Compared with premenopausal women, perimenopausal women had 20% greater urine N-telopeptide excretion (P < 0.05) and a doubling of gonadotrophin levels (P < 0.01), whereas serum estradiol and bone formation marker concentrations were no different. Postmenopausal Women had greater levels of bone turnover markers (P < 0.0001), except free deoxypyridinoline and type I procollagen propeptide. Among postmenopausal women, bone resorption markers were lower in those using HRT. Levels of nearly all bone turnover markers were positively related to serum FSH concentrations (P < 0.0001). Overall, the major independent predictors of BMD were age, urine N-telopeptide, serum bone alkaline phosphatase, and serum, FSH, whereas urine free deoxypyridinoline was positively related to BMD in pre- and perimenopausal women. In conclusion, the perimenopause is associated with elevated bone resorption rates and declining BMD, and factors in addition to estrogen deficiency may also contribute to the pathogenesis of postmenopausal osteoporosis.

Aging↗
PubMed1996

Bone mineral density and hormone levels in menopausal Australian women.

To assess the relationships between bone mineral density (BMD) at the lumbar spine and femoral neck and menopausal status, age, physical variables, and lifestyle and gynecological factors. BMD and follicle-stimulating hormone (FSH), estradiol and inhibin levels were measured in 167 women born in Australia, aged 46-57 years, who had no record of receiving hormone replacement therapy. Using the premenopausal group as a baseline, the FSH level was higher in peri- and postmenopausal subjects (p < 0.0005), and estradiol and inhibin levels in the postmenopausal women were lower (p < 0.0005). Mean (+/- SE) lumbar spine and femoral neck BMD were 15 +/- 3% and 10 +/- 3% lower, respectively, in postmenopausal than in premenopausal women. Lumbar spine BMD decreased with increasing age in perimenopausal women only (p < 0.005), and femoral neck BMD decreased with increasing age in the pre-, peri-(p < 0.05) and postmenopausal women. The difference between femoral neck BMD in the pre- and postmenopausal women was explained by the difference in age between these groups, whereas for lumbar spine BMD the menopausal status was an additional determining factor. There was a negative effect of smoking on femoral neck BMD (p < 0.05) in postmenopausal women. In the perimenopausal decade the femoral neck BMD is primarily dependent on age, whereas lumbar spine BMD is dependent on both age and menopausal status.

Aging↗
PubMed1996

Bone loss accompanying diet-induced or exercise-induced weight loss: a randomised controlled study.

OBJECTIVE: To compare the effects of two weight loss interventions, diet or exercise, on changes in bone, fat and lean tissue. DESIGN: Prospective, long term, worksite, randomised and controlled weight-loss study using a low fat diet ad libitum or moderate aerobic exercise. SUBJECTS: 66 overweight men (mean age 43.4 +/- 5.7 y, BMI 29.0 +/- 2.6 kg/m2). MEASUREMENTS: Body weight, lean mass, fat mass, bone mass (BMC), bone mineral density (BMD) by dual-energy X-ray absorptiometry. RESULTS: Dieters lost 1.4% BMC (1.5% BMD) with 6.4 kg weight loss; there was no significant change in BMC (or in BMD) in exercisers (2.6 kg weight loss) or in control subjects (no weight change). Changes in BMC were correlated with fat loss with both interventions: 11.7 g BMC/kg fat loss in dieters, 11.4 g BMC change/kg fat loss in exercisers. CONCLUSION: BMC loss with diet-induced weight loss reflects loss of weight and especially loss of body fat. Further study to determine whether similar BMC loss will accompany equivalent weight loss induced by exercise is needed.

Absorptiometry, Photon↗
PubMed1995

Determinants of bone mass in 10- to 26-year-old females: a twin study.

This cross-sectional twin study aimed to quantify the roles of constitutional and lifestyle factors on bone mass in adolescent and young adult women. Areal bone density (BMD) at the lumbar spine, femoral neck, Ward's triangle, and total hip, total body bone mineral content (BMC), and lean mass and fat mass were measured using dual energy X-ray absorptiometry (DXA) in 215 female volunteer twin pairs (122 monozygotic [MZ], 93 dizygotic [DZ]) aged 10 to 26 years. Height, weight, menarchial history, dietary calcium intake, physical activity, current tobacco use, and alcohol consumption were determined by questionnaire. Mean BMD increased with age to around 16 years, when it reached a plateau. Within-pair differences in BMD at the lumbar spine (expressed as a percentage of the pair mean BMD) were univariately associated with pair differences in menarchial status (14 +/- 3%), height (0.7 +/- 0.1% per cm), weight (0.4 +/- 0.1% per kg), lean mass (1.0 +/- 0.1% per kg), and fat mass (0.5 +/- 0.1% per kg). Only menarchial status, height, and lean mass, however, were independent predictors. At the proximal femoral sites, within-pair BMD differences were associated with within-pair lean mass differences (1.0 to 1.1 +/- 0.2%/kg), and no other factor was significant. The same conclusions applied to within-pair differences in BMD/height. Total body BMC was independently associated with menarchial status, height, lean mass, and fat mass; the effects of the latter two variables were stronger in pairs both premenarchial. After adjusting for constitutional factors, no lifestyle factor was independently predictive. By reducing collinearity, the cotwin method clearly identified that lean mass, not fat mass, was the major independent determinant of bone mass at the hip, both pre- and postmenarche.

Absorptiometry, Photon↗
PubMed1995

Bone density determinants in elderly women: a twin study.

This cross-sectional twin study examined the influence of constitutional, lifestyle, and genetic factors on bone mineral density (BMD) in elderly women. BMD, at the lumbar spine, femoral neck, Ward's triangle, total hip, and total forearm, total body bone mineral content (BMC), and lean mass and fat mass were measured using dual energy X-ray absorptiometry in 69 volunteer female twin pairs (37 monozygotic [MZ], 32 dizygotic [DZ]) aged 60-89 years. Height and weight were measured. Medical history and lifetime tobacco and alcohol use were determined by questionnaire. In terms of within-pair differences, lean mass was independently associated with BMD at all sites. In contrast, fat mass was not associated with BMD at any site once allowance had been made for lean mass. Lifetime tobacco use was independently associated with BMD at the lumbar spine, total hip, and forearm. Total body BMC was independently predicted by lean mass, fat mass, tobacco use, and alcohol consumption. Age and the above independently predictive body composition and lifestyle factors accounted for 20-33% of variation in BMD. After allowing for these covariates, MZ and DZ correlations were consistent with about 75% of residual variation in BMD at the nonforearm sites being determined by genetic factors. For total body BMC, the covariates explained 75% of total variation, and genetic factors 76% of the residual variation. Therefore, at the proximal femur and lumbar spine, after taking into account the relation of BMD with lean mass and smoking, genetic factors appear to play a substantial role in explaining variation in BMD in elderly women.

Absorptiometry, Photon↗
PubMed1995

Do Australian women have greater spinal bone density than North American women?

The interpretation of bone mineral densitometry results for a particular individual relies on valid reference data from a representative population sample. To establish local reference data, 411 Australian female volunteers had bone mineral densitometry performed at a single medical centre at the proximal femur and lumbar spine using a Hologic QDR 1000-W dual-energy X-ray absorptiometer. These data were compared with reference material from North American women compiled by Hologic. The Australian volunteers had, on average, 7% greater bone mineral density at the lumbar spine for the age range 25-55 years. Possible explanations for this include an actual population difference or the presence of a differential selection bias between the two samples.

Adolescent↗
PubMed1995

The potential of sheep for the study of osteopenia: current status and comparison with other animal models.

There is a great need to develop an animal model for postmenopausal osteoporosis; a model that will be useful for the understanding of the pathogenesis of the disease as well as the investigation of new therapies. The requirements for such an animal model are discussed and ones that have been used in the past include nonhuman primates, dogs, cats, rodents, rabbits, guinea pigs, and minipigs. Advantages and disadvantages of these models are briefly reviewed. Sheep are a promising model for various reasons; they are docile, easy to handle and house, relatively inexpensive, available in large numbers, spontaneously ovulate, and have hormone profiles similar to women. Ovariectomy results in a slight loss of bone from the ovine iliac crest, and biochemical markers such as osteocalcin are well characterized. Physiological disadvantages are lack of natural menopause, that normal estrus cycles are restricted to fall and winter and that they have a different gastrointestinal system. Sheep have cortical bone that is plexiform in structure although haversian remodeling is seen in older animals. When and if biomechanical incompetence of bone follows ovariectomy is presently unknown. There is no ideal model for the study of postmenopausal osteoporosis; all have advantages and disadvantages. Researchers in this field must recognize the limitations of the model they choose, and select one that will fulfill their needs.

Absorptiometry, Photon↗