Christopher B. Ruff

Predicting femoral neck strength from bone mineral data. A structural approach.

An interactive computer program was developed to derive femoral neck geometry from raw bone mineral image data for an estimate of hip strength using single plane engineering stress analysis. The program, which we call Hip Strength Analysis (HSA), was developed as an attempt to improve the predictive value of hip bone mineral data for osteoporosis fracture risk assessment. We report a series of experiments with an aluminum phantom and with cadaver femora, designed to test the accuracy of derived geometric measurements and strength estimates. Using data acquired with both Lunar DP3 (DPA) and Hologic QDR-1000 (x-ray) scanners, HSA computed femoral neck cross-sectional areas (CSA) and cross-sectional moments of inertia (CSMI) on an aluminum phantom were in excellent agreement with actual values (r greater than .99). Using Lunar DP3 data, CSA and CSMI measurements at mid-femoral necks of 22 cadaver specimens were in good general agreement with literature values. HSA computed cross-sectional properties of three of these specimens were compared with measurements derived from sequential CT cross-sectional images. Discrepancy between the two methods averaged less than 10% along the length of the femoral neck. Finally, breaking strengths of 20 of the femora were measured with a materials testing system, showing better agreement with HSA predicted strength (r = .89, percent standard of the estimate (%SEE) = 21%) than femoral neck bone mineral density (r = .79, %SEE = 28%).

Structural Trends in the Aging Femoral Neck and Proximal Shaft: Analysis of the Third National Health and Nutrition Examination Survey Dual‐Energy X‐Ray Absorptiometry Data

Hip scans of U.S. adults aged 20–99 years acquired in the Third National Health and Nutrition Examination Survey (NHANES III) using dual‐energy X‐ray absorptiometry (DXA) were analyzed with a structural analysis program. The program analyzes narrow (3 mm wide) regions at specific locations across the proximal femur to measure bone mineral density (BMD) as well as cross‐sectional areas (CSAs), cross‐sectional moments of inertia (CSMI), section moduli, subperiosteal widths, and estimated mean cortical thickness. Measurements are reported here on a non‐Hispanic white subgroup of 2719 men and 2904 women for a cortical region across the proximal shaft 2 cm distal to the lesser trochanter and a mixed cortical/trabecular region across the narrowest point of the femoral neck. Apparent age trends in BMD and section modulus were studied for both regions by sex after correction for body weight. The BMD decline with age in the narrow neck was similar to that seen in the Hologic neck region; BMD in the shaft also declined, although at a slower rate. A different pattern was seen for section modulus; furthermore, this pattern depended on sex. Specifically, the section modulus at both the narrow neck and the shaft regions remains nearly constant until the fifth decade in females and then declined at a slower rate than BMD. In males, the narrow neck section modulus declined modestly until the fifth decade and then remained nearly constant whereas the shaft section modulus was static until the fifth decade and then increased steadily. The apparent mechanism for the discord between BMD and section modulus is a linear expansion in subperiosteal diameter in both sexes and in both regions, which tends to mechanically offset net loss of medullary bone mass. These results suggest that aging loss of bone mass in the hip does not necessarily mean reduced mechanical strength. Femoral neck section moduli in the elderly are on the average within 14% of young values in females and within 6% in males.

Sexual dimorphism in human lower limb bone structure: relationship to subsistence strategy and sexual division of labor

Abstract Cross-sectional geometric properties of the human femur and tibia are compared in males and females in a number of recent and archaeological population samples extending back to the Middle Paleolithic. There is a consistent decline in sexual dimorphism from hunting-gathering to agricultural to industrial subsistence strategy levels in properties which measure relative anteroposterior bending strength of the femur and tibia in the region about the knee. This trend parallels and is indicative of reductions in the sexual division of labor, in particular differences in the relative mobility of males and females. Sexual dimorphism in mediolateral bending strength near the hip shows no consistent temporal trend, probably reflecting relatively constant sex differences in pelvic structure related to the requirements of childbirth. Upper and Middle Paleolithic samples are indistinguishable in terms of sexual dimorphism from modern huntergatherers, suggesting a similar sexual division of labor. The results illustrate the utility of cross-sectional geometric parameters of long bone diaphyses in reconstructing behavioral differences within and between past populations. Some variations in the accuracy of sexing techniques based on diaphyseal measurements of the lower limb long bones may also be explained by these behavioral and structural factors.

Climate and body shape in hominid evolution

The very broad pelvis of small early hominids (AL 288-1, STS 14, etc.) has previously been interpreted in obstetrical and biomechanical terms. However, neither of these considerations can explain the subsequent decrease in maximum pelvic breadth relative to stature in larger more recent hominids. It is shown here that this increase in relative linearity of the body with an increase in body size is consistent with basic thermoregulatory principles. Specifically, to maintain a constant surface area/body mass ratio, absolute body breadth should remain constant despite differences in body height. Variation among modern humans supports the prediction: populations living in the tropics vary greatly in stature, but show little variation in body breadth. In contrast, populations living in colder climates have absolutely wider bodies, and thus lower surface area/body mass, regardless of stature. All African early hominids—small australopithecines as well as the very tallHomo erectus KNM-WT 15000—have absolute body breadths within the modern human tropical-subtropical range; variations in relative body linearity are due almost entirely to variations in stature. A later hominid from a cold temperate climate (the Kebara 2 Neandertal) has an absolutely wide body, similar to living higher latitude populations. Thermoregulatory constraints on absolute body breadth, together with obstetric and biomechanical factors, may have contributed to the evolution of the rotational birth process and secondary altriciality with increased body and brain size inHomo erectus. Thermoregulatory considerations also suggest that AfricanH. erectus would most likely have been limited to relatively open/dry environments, while australopithecines could have inhabited either open/dry or closed/wet environments.

Stress fracture in military recruits : Gender differences in muscle and bone susceptibility factors

A total of 693 female U.S. Marine Corps recruits were studied with anthropometry and dual-energy X-ray absorptiometry (DXA) scans of the midthigh and distal third of the lower leg prior to a 12 week physical training program. In this group, 37 incident stress fracture cases were radiologically confirmed. Female data were compared with male data from an earlier study of 626 Marine recruits extended with additional cases for a total of 38 stress fracture cases. Using DXA data, bone structural geometry and cortical dimensions were derived at scan locations and muscle cross-sectional area was computed at the midthigh. Measurements were compared within gender between pooled fracture cases and controls after excluding subjects diagnosed with shin splints. In both genders, fracture cases were less physically fit, and had smaller thigh muscles compared with controls. After correction for height and weight, section moduli (Z) and bone strength indices (Z/bone length) of the femur and tibia were significantly smaller in fracture cases of both genders, but patterns differed. Female cases had thinner cortices and lower areal bone mineral density (BMD), whereas male cases had externally narrower bones but similar cortical thicknesses and areal BMDs compared with controls. In both genders, differences in fitness, muscle, and bone parameters suggest poor skeletal adaptation in fracture cases due to inadequate physical conditioning prior to training. To determine whether bone and muscle strength parameters differed between genders, all data were pooled and adjusted for height and weight. In both the tibia and femur, men had significantly larger section moduli and bone strength indices than women, although women had higher tibia but lower femur areal BMDs. Female bones, on average, were narrower and had thinner cortices (not significant in the femur, p = 0.07). Unlike the bone geometry differences, thigh muscle cross-sectional areas were virtually identical to those of the men, suggesting that the muscles of the women were not relatively weaker.

Differential Susceptibility to Hypertension Is Due to Selection during the Out-of-Africa Expansion

Hypertension is a leading cause of stroke, heart disease, and kidney failure. The genetic basis of blood pressure variation is largely unknown but is likely to involve genes that influence renal salt handling and arterial vessel tone. Here we argue that susceptibility to hypertension is ancestral and that differential susceptibility to hypertension is due to differential exposure to selection pressures during the out-of-Africa expansion. The most important selection pressure was climate, which produced a latitudinal cline in heat adaptation and, therefore, hypertension susceptibility. Consistent with this hypothesis, we show that ecological variables, such as latitude, temperature, and rainfall, explain worldwide variation in heat adaptation as defined by seven functional alleles in five genes involved in blood pressure regulation. The latitudinal cline in heat adaptation is consistent worldwide and is largely unmatched by latitudinal clines in short tandem repeat markers, control single nucleotide polymorphisms, or non-functional single nucleotide polymorphisms within the five genes. In addition, we show that latitude and one of these alleles, GNB3 (G protein β3 subunit) 825T, account for a major portion of worldwide variation in blood pressure. These results suggest that the current epidemic of hypertension is due to exposures of the modern period interacting with ancestral susceptibility. Modern populations differ in susceptibility to these new exposures, however, such that those from hot environments are more susceptible to hypertension than populations from cold environments. This differential susceptibility is likely due to our history of adaptation to climate.

Hindlimb articular surface allometry in hominoidea and Macaca, with comparisons to diaphyseal scaling

The scaling of hindlimb articular surface dimensions with body mass is investigated in Pan, Gorilla, Pongo, Macaca fascicularis, and, for the femoral head, two population samples of recent Homo sapiens sapiens. Articular dimensions scale very strongly with body mass within pongids at close to isometry. Body mass can be estimated relatively precisely given the appropriate reference group, with femoral head dimensions giving the best estimates. Several deviations from general scaling trends are also present and have functional implications. Positive allometry of the medial femoral condyle, and thus condyle asymmetry, is shown to be related to degree of varus (bowleggedness) of the knee, most marked in gorillas and declining in the smaller pongids and macaques. Macaques show somewhat smaller hindlimb articulations for their body mass, while modern humans have large femoral heads relative to body mass. Relative to diaphyseal cross-sectional dimensions (Ruff, 1987), orangutans and modern humans have large articulations and macaques small articulations. These proportional differences are explained in terms of differences between species in joint excursion, mode of locomotion, and activity level. Orangutans load their hind limbs less than other pongids due to more pronounced forelimb suspensory behavior and thus have less robust diaphyses, but maintain relatively large articulations to allow greater joint excursion, particularly hip abduction. Relatively smaller hindlimb articulations in macaques may be linked to reduced joint mobility relative to pongids. Modern humans, due to their bipedality, load the lower limb more than quadrupedal primates and thus have relatively large joints, but shaft dimensions remain smaller than expected, possibly at least partly because of lower activity levels. Within recent humans, femoral head dimensions are highly positively allometric. Because of this, femoral head size in two relatively complete early hominids (AL 288-1 and KNM-WT 15000) is approximately at or above what would be predicted for hominids of their respective body masses.

Body size and body shape in early hominins – implications of the Gona Pelvis

Discovery of the first complete Early Pleistocene hominin pelvis, Gona BSN49/P27, attributed to Homo erectus, raises a number of issues regarding early hominin body size and shape variation. Here, acetabular breadth, femoral head breadth, and body mass calculated from femoral head breadth are compared in 37 early hominin (6.0-0.26 Ma) specimens, including BSN49/P27. Acetabular and estimated femoral head sizes in the Gona specimen fall close to the means for non-Homo specimens (Orrorin tugenesis, Australopithecus africanus, Paranthropus robustus), and well below the ranges of all previously described Early and Middle Pleistocene Homo specimens. The Gona specimen has an estimated body mass of 33.2kg, close to the mean for the non-Homo sample (34.1kg, range 24-51.5kg, n=19) and far outside the range for any previously known Homo specimen (mean=70.5kg; range 52-82kg, n=17). Inclusion of the Gona specimen within H. erectus increases inferred sexual dimorphism in body mass in this taxon to a level greater than that observed here for any other hominin taxon, and increases variation in body mass within H. erectus females to a level much greater than that observed for any living primate species. This raises questions regarding the taxonomic attribution of the Gona specimen. When considered within the context of overall variation in body breadth among early hominins, the mediolaterally very wide Gona pelvis fits within the distribution of other lower latitude Early and Middle Pleistocene specimens, and below that of higher latitude specimens. Thus, ecogeographic variation in body breadth was present among earlier hominins as it is in living humans. The increased M-L pelvic breadth in all earlier hominins relative to modern humans is related to an increase in ellipticity of the birth canal, possibly as a result of a non-rotational birth mechanism that was common to both australopithecines and archaic Homo.

Age-related changes in female femoral neck geometry: Implications for bone strength

SummaryBone strength is a function of both bone mass and its geometric distribution, a factor that is obscured in the conventional bone mineral analysis. Structural geometry is particularly important in areas such as the femoral neck that are exposed to bending loadsin vivo. Here we present results of a study examining age changes in the structural geometry of the female femoral neck derived from dual photon absorptiometry (DPA) data. In a previous study, differences in the aging patterns of males and females over the entire adult age range were demonstrated. In that study, only males showed “compensatory” geometric restructuring of the femoral neck which tended to offset loss of bone mineral with age. In the present study, femoral neck structural properties from 1044 women were examined for aging trends before and after the approximate age of menopause (50 years). Women in the premenopausal age range showed a 4% decline per decade in femoral neck BMD, but no change in the femoral neck cross-sectional moment of inertia (CSMI). This aging pattern is similar to that of males in our earlier study, and in both cases resulted in little or no increase in femoral neck bending stresses. After age 50, however, women show a more rapid decline in femoral neck BMD (7% per decade) accompanied by a decline in CSMI of 5% per decade. These changes result in increases in femoral neck stresses of 4–12% per decade due to the apparent lack of compensatory restructuring to offset the loss of bone mineral. These results shed further light on the age-related mechanisms underlying sex differences in fracture incidence among the elderly. They also argue for the routine use of such structural analyses in any study of age-related osteopenia or the effects of therapeutic intervention on this condition.

Stature and body mass estimation from skeletal remains in the European Holocene

Techniques that are currently available for estimating stature and body mass from European skeletal remains are all subject to various limitations. Here, we develop new prediction equations based on large skeletal samples representing much of the continent and temporal periods ranging from the Mesolithic to the 20th century. Anatomical reconstruction of stature is carried out for 501 individuals, and body mass is calculated from estimated stature and biiliac breadth in 1,145 individuals. These data are used to derive stature estimation formulae based on long bone lengths and body mass estimation formulae based on femoral head breadth. Prediction accuracy is superior to that of previously available methods. No systematic geographic or temporal variation in prediction errors is apparent, except in tibial estimation of stature, where northern and southern European formulae are necessary because of the presence of relatively longer tibiae in southern samples. Thus, these equations should bebroadly applicable to European Holocene skeletal samples.