Sex-specific developmental changes in muscle size and bone geometry at the femoral shaft

INTRODUCTION

When expressed as a percentage of the average result in young adults, bone mineral content lags behind bone length before puberty. Even though this observation has led to speculation about bone fragility in children, such relationships could simply be due to scaling effects when measures with different geometrical dimensions are compared.

METHODS

The study population comprised 145 healthy subjects (6-25 years, 94 females). Magnetic resonance imaging and dual-energy X-ray absorptiometry were used to determine femur length, bone mineral content, cortical bone mineral density, cross-sectional bone geometry (bone diameter; cortical thickness; total, cortical and medullary areas; cross-sectional and polar moments of area; bone strength index) and muscle area at the proximal one-third site of the femur. Results were dimensionally scaled by raising two-, three- and four-dimensional variables to the power of 1/2, 1/3 and 1/4, respectively. Sex-differences were also assessed before and after functionally adjusting variables for femur length and weight or muscle size.

RESULTS

In prepubertal children, unscaled results expressed as percentages of adult values were lowest for variables with the highest dimensions (e.g., moments of area<bone mineral content<cross-sectional areas<femur length). However, when dimensionally scaled, results in children represented similar percentages of the respective average adult values, even after functional adjustments. Before puberty, there was no sex-difference in adjusted bone or muscle variables. After puberty, males had greater total and cortical bone area, bone diameter, moments of area, bone strength index and muscle area than women, both in absolute terms as well as adjusted for femur length and weight. The largest sex-difference was found for muscle area. When compared relative to muscle size, young adult women attained greater total and cortical bone area than men.

CONCLUSIONS

Growth in femoral length, diameter, mass and strength appears well coordinated before puberty. Postpubertal females have narrower femora, less bone strength and muscle size than males. However, when muscle size is taken into account, females have a larger femoral bone cross-section and more cortical bone. These sex-differences likely result from a combination of mechanical and hormonal effects occurring during puberty.

A comparison of bone geometry and cortical density at the mid-femur between prepuberty and young adulthood using magnetic resonance imaging

In upper extremity bones, a sexual dimorphism exists in the development of periosteal and endocortical bone surfaces during growth. Little is known about developmental patterns of bone geometry at weight-bearing bones like the femur. Using MRI and dual energy X-ray absorptiometry (DXA), this study assessed the differences in mid-femoral total (TA), cortical (CA) and medullary areas (MA), cortical thickness, and cortical density (BMD(compartment)) between prepuberty and young adulthood in 145 healthy subjects (94 females) 6 to 25 years old. Additionally, agreement between mid-femoral total bone volume (TV) measurements by DXA and MRI were investigated. In both sexes, TA, CA, MA, and cortical thickness were significantly larger in adults compared to prepubertal subjects (P < 0.001), and males had greater values than females. This sex difference persisted for TA, CA, and cortical thickness (P < 0.05), but not MA, after adjusting for femur length and weight. Mean (SD) cortical BMD increased from 1.05 (0.07) and 1.09 (0.10) g/cm(3) in prepubertal children to 1.46 (0.14) and 1.42 (0.1) g/cm(3) in young adults, females and males, respectively (P < 0.001). TV measurements by DXA were significantly greater than by MRI (P < 0.001) in young adults. In conclusion, periosteal and endocortical expansion and increasing cortical BMD are the growth processes found at the mid-femur in both sexes. Our findings contrast to that in upper extremity bones, where MA is constant in females during growth. The difference in femoral bone development may be due to higher strains caused by weight bearing and genetic factors. DXA, in contrast to MRI, is inaccurate in the determination of mid-femoral TV measures.

Measurement of midfemoral shaft geometry: repeatability and accuracy using magnetic resonance imaging and dual-energy X-ray absorptiometry

Although macroscopic geometric architecture is an important determinant of bone strength, there is limited published information relating to the validation of the techniques used in its measurement. This study describes new techniques for assessing geometry at the midfemur using magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA) and examines both the repeatability and the accuracy of these and previously described DXA methods. Contiguous transverse MRI (Philips 1.5T) scans of the middle one-third femur were made in 13 subjects, 3 subjects with osteoporosis. Midpoint values for total width (TW), cortical width (CW), total cross-sectional area (TCSA), cortical cross-sectional area (CCSA), and volumes from reconstructed three-dimensional (3D) images (total volume [TV] and cortical volume [CVol]) were derived. Midpoint TW and CW also were determined using DXA (Lunar V3.6, lumbar software) by visual and automated edge detection analysis. Repeatability was assessed on scans made on two occasions and then analyzed twice by two independent observers (blinded), with intra- and interobserver repeatability expressed as the CV (CV +/- SD). Accuracy was examined by comparing MRI and DXA measurements of venison bone (and Perspex phantom for MRI), against "gold standard" measures made by vernier caliper (width), photographic image digitization (area) and water displacement (volume). Agreement between methods was analyzed using mean differences (MD +/- SD%). MRI CVs ranged from 0.5 +/- 0.5% (TV) to 3.1 +/- 3.1% (CW) for intraobserver and 0.55 +/- 0.5% (TV) to 3.6 +/- 3.6% (CW) for interobserver repeatability. DXA results ranged from 1.6 +/- 1.5% (TW) to 4.4 +/- 4.5% (CW) for intraobserver and 3.8 +/- 3.8% (TW) to 8.3 +/- 8.1% (CW) for interobserver variation. MRI accuracy was excellent for TV (3.3 +/- 6.4%), CVol (3.5 +/- 4.0%), TCSA (1.8 +/- 2.6%), and CCSA (1.6 +/- 4.2%) but not TW (4.1 +/- 1.4%) or CW (16.4 +/14.9%). DXA results were TW (6.8 +/- 2.7%) and CW (16.4 +/- 17.0%). MRI measures of geometric parameters of the midfemur are highly accurate and repeatable, even in osteoporosis. Both MRI and DXA techniques have limited value in determining cortical width. MRI may prove valuable in the assessment of surface-specific bone accrual and resorption responses to disease, therapy, and variations in mechanical loading.

Simultaneous financial evaluation of a complex set of capital budgeting alternatives: a mathematical model

Capital budgeting technics provide for financial evaluation of planned purchases of equipment or other major investments. In capital budgeting, the laboratorian often is faced with a complex set of alternatives, including leasing, installment purchasing, contracting work to another laboratory, and outright purchasing. This paper presents a mathematical model useful for simultaneously evaluating the financial worth of all such alternatives under the same set of assumptions. Armed with the results of financial evaluation and evaluations of quality, turnaround time, and other patient-care factors, the laboratorian can make better decisions regarding the choice of method which, in turn, will affect the productivity of the laboratory. The model is tended for application to mutually exclusive alternatives and includes three useful capital budgeting technics: (1) payback period, (2) net present value, and (3) profitability index. The technics are demonstrated as well as a method of programming the model in financial planning software for solution by microcomputer.

What is productivity?

Effective laboratory management and planning requires an evaluation of current levels of activity, review of past experience, and projection of future trends. This need can be met in large part by measuring workload, and if the method of measurement is codified into a system, comparative studies among cooperating laboratories can be made. In this article, the authors describe and compare three such systems for measuring workload, and review standards for productivity which various authors have provided in the past.

Eastern equine encephalomyelitis in upstate New York: studies of a 1976 epizootic by a modified serologic technique, hemagglutination reduction, for rapid detection of virus infections

An extensive outbreak of eastern equine encephalomyelitis (EEE) occurred in upstate New York during the summer of 1976, with 37 cases confirmed in horses by isolation of virus and/or by serologic examination. Other specimens collected in the affected area yielded 16 further isolates: 9 from 818 pools of 33,365 mosquitoes, 5 from tissues of 64 birds and 2 from 4 sentinel pheasants with serologic conversions. EEE antibodies were also detected in 81 of 499 wild birds tested. Our data implicate sparrows, cowbirds, and catbirds in the amplification of EEE virus and Culiseta melanura mosquitoes as vectors among avians. During the course of this epizootic a modified serologic technique involving hemagglutination reduction gave reliable diagnoses of EEE as early as 24 hours after receipt of field specimens.