Monitoring time interval for pQCT-derived bone outcomes in postmenopausal women

Evidence of measurement precision, annual changes and monitoring time interval is essential when designing and interpreting longitudinal studies. Despite the precise measures, small annual changes in bone properties led to monitoring time intervals (MTIs) of 2-6 years in peripheral quantitative computed tomography (pQCT)-derived radial and tibial bone area, density, and estimated strength in postmenopausal women.

INTRODUCTION

The purpose of the study was to determine the precision error, annual change, and MTI in bone density, area, and strength parameters in postmenopausal women.

METHODS

Postmenopausal women (n = 114) from the Saskatoon cohort of the Canadian Multicentre Osteoporosis Study had annual pQCT scans of the distal and shaft sites of the radius and tibia for 2 years. Median annualized rates of percent change and the MTI were calculated for bone density, area, and strength parameters. Root mean squared coefficients of variation (CV%) were calculated from duplicate scans in a random subgroup of 35 postmenopausal women.

RESULTS

CV% ranged from 1.4 to 6.1 % at the radius and 0.7 to 2.1 % at the tibia. MTIs for the distal radius were 3 years for total bone density (ToD) and 4 years for total bone cross sectional area (ToA), trabecular area, and bone strength index. At the diaphyseal radius, MTI was 3 years for ToA, 5 years for cortical density, and 6 years for polar stress strain index (SSIp). Similarly, MTI for total and trabecular density was 3 years at the distal tibia. At the diaphyseal tibia, MTI for ToA was 3 years and SSIp 4 years.

CONCLUSION

MTI for longitudinal studies in older postmenopausal women should be at least 2-6 years at the radius and tibia, with specific monitoring of the total and trabecular area, total density, and bone strength at the radius and total and trabecular density, total area, and bone strength at the tibia.

Bone geometry according to menstrual function in female endurance athletes

Athletes have higher bone mineral density (BMD) relative to nonathletes. In amenorrheic athletes BMD may be compromised by estrogen deficiency, but it is unknown whether this is accompanied by structural differences. We compared femoral neck bone geometry and density of a-/oligomenorrheic athletes (AAs), eumenorrheic athletes (EAs), and eumenorrheic controls (ECs). We recruited 156 women: (68 endurance athletes and 88 controls). Femoral neck BMD, section modulus (Z), and width were measured using dual-energy X-ray absorptiometry. Menstrual function was assessed by questionnaire and classified as EA (≥10 periods/year) or AA (≤9 periods/year): 24 athletes were AA and 44 EA. Femoral neck BMD was significantly higher in EA than AA (8 %, difference) and EC (11 % difference): mean [SE] 1.118 [0.015], 1.023 [0.020] and 0.999 [0.014] g cm(-2), respectively; p < 0.001. Z was significantly higher in EA than EC (11 % difference): EA 667 [19], AA 625 [21], and EC 592 [10] cm(3); p < 0.001. Femoral neck width did not differ between groups. All differences persisted after adjustment for height, age, and body mass. The higher femoral neck Z and BMD in athletes, despite similar width, may indicate that exercise-related bone gains are endosteal rather than periosteal. Athletes with amenorrhea had smaller increments in bone mass rather than structural adaptation. The maintained femoral neck width in controls may be an adaptive mechanism to conserve bone strength in bending despite inactivity-related bone decrement.

Risk factors for stress fracture in female endurance athletes: a cross-sectional study

OBJECTIVE

To identify psychological and physiological correlates of stress fracture in female endurance athletes.

DESIGN

A cross-sectional design was used with a history of stress fractures and potential risk factors assessed at one visit.

METHODS

Female-endurance athletes (58 runners and 12 triathletes) aged 26.0±7.4 years completed questionnaires on stress fracture history, menstrual history, athletic training, eating psychopathology and exercise cognitions. Bone mineral density, body fat content and lower leg lean tissue mass (LLLTM) were assessed using dual-x-ray absorptiometry. Variables were compared between athletes with a history of stress fracture (SF) and those without (controls; C) using χ&sup2;, analysis of variance and Mann-Whitney U tests.

RESULTS

Nineteen (27%) athletes had previously been clinically diagnosed with SFs. The prevalence of current a/oligomenorrhoea and past amenorrhoea was higher in SF than C (p=0.008 and p=0.035, respectively). SF recorded higher global scores on the eating disorder examination questionnaire (p=0.049) and compulsive exercise test (p=0.006) and had higher LLLTM (p=0.029) compared to C. These findings persisted with weight and height as covariates. In multivariate logistic regression, compulsive exercise, amenorrhoea and LLLTM were significant independent predictors of SF history (p=0.006, 0.009 and 0.035, respectively).

CONCLUSIONS

Eating psychopathology was associated with increased risk of SF in endurance athletes, but this may be mediated by menstrual dysfunction and compulsive exercise. Compulsive exercise, as well as amenorrhoea, is independently related to SF risk.