Sideways Fall Research Articles

Effects of body configuration on pelvic injury in backward fall simulation using 3D finite element models of pelvis–femur–soft tissue complex

Injuries due to backward fall apart from sideways fall are a major health problem, particularly among the aged populations. The objectives of this study was to evaluate the responses to changing body configurations (angle between the trunk and impacting floor as 0°, 15°, 45° and 80°) during backward fall, based on a previously developed CT-scan-derived 3D non-linear and non-homogeneous finite element (FE) model of pelvis–femur–soft tissue complex with simplified biomechanical representation of the whole body. Under constant impact energy, these FE models evaluated the pelvic injury situations on the basis of peak impact force (7.64–16.74kN) and peak principal compressive strain (more than 1.5%), consistent with the clinically observed injuries (sacral insufficiency, coccydynia). Also the change in location of peak strain and increase in peak impact force for changing configurations from 0° to 80° indicated the effect of whole body inertia during backward fall. It was also concluded that the inclusion of sacro-iliac and acetabular cartilages in the above FE models will further reduce above findings marginally (9.2% for 15° fall). These quantifications would also be helpful for a better design and development of safety structures such as safety floor for the nursing home or home for the aged persons.

During sideways falls proximal femur fractures initiate in the superolateral cortex: Evidence from high-speed video of simulated fractures

Results of recent imaging studies and theoretical models suggest that the superior femoral neck is a location of local weakness due to an age-related thinning of the cortex, and thus the site of hip fracture initiation. The purpose of this study was to experimentally determine the spatial and temporal characteristics of the macroscopic failure process during a simulated hip fracture that would occur as a result of a sideways fall. Twelve fresh frozen human cadaveric femora were used in this study. The femora were fractured in an apparatus designed to simulate a fall on the greater trochanter. Image sequences of the surface events related to the fractures were captured using two high-speed video cameras at 9111 Hz. The videos were analyzed with respect to time and load to determine the location and sequence of these events occurring in the proximal femur. The mean failure load was 4032 N (SD 370 N). The first surface events were identified in the superior femoral neck in eleven of the twelve specimens. Nine of these specimens fractured in a clear two-step process that initiated with a failure in the superior femoral neck, followed by a failure in the inferior femoral neck. This cadaveric model of hip fracture empirically confirms hypotheses that suggested that hip fractures initiate with a failure in the superior femoral neck where stresses are primarily compressive during a sideways fall impact, followed by a failure in the inferior neck where stresses are primarily tensile. Our results confirm the superolateral neck of the femur as an important region of interest for future hip fracture screening, prevention and treatment research.

Martial arts fall training to prevent hip fractures in the elderly

Hip fractures are a common and serious consequence of falls. Training of proper fall techniques may be useful to prevent hip fractures in the elderly. The results suggested that martial arts fall techniques may be trainable in older individuals. Better performance resulted in a reduced impact force. Hip fractures are a common and serious consequence of falls. Fall training may be useful to prevent hip fractures in the elderly. This pilot study determined whether older individuals could learn martial arts (MA) fall techniques and whether this resulted in a reduced hip impact force during a sideways fall. Six male and nineteen female healthy older individuals completed a five-session MA fall training. Before and after training, force and kinematic data were collected during volitional sideways falls from kneeling position. Two MA experts evaluated the fall performance. Fear of falling was measured with a visual analog scale (VAS). After fall training, fall performance from a kneeling position was improved by a mean increase of 1.6 on a ten-point scale (P < 0.001). Hip impact force was reduced by a mean of 8% (0.20 N/N, P = 0.016). Fear of falling was reduced by 0.88 on a VAS scale (P = 0.005). MA techniques may be trainable in older individuals, and a better performance may reduce the hip impact force in a volitional sideways fall from a kneeling position. The additional reduction of fear of falling might result in the prevention of falls and related injuries.

Prediction of femoral strength in a sideways fall configuration using QCT-based finite element analysis

Prediction of femoral strength in a sideways fall configuration using QCT-based finite element analysis

Femoral bone strength and its relation to cortical and trabecular changes after treatment with PTH, alendronate, and their combination as assessed by finite element analysis of quantitative CT scans.

The "PTH and Alendronate" or "PaTH" study compared the effects of PTH(1-84) and/or alendronate (ALN) in 238 postmenopausal, osteoporotic women. We performed finite element analysis on the QCT scans of 162 of these subjects to provide insight into femoral strength changes associated with these treatments and the relative roles of changes in the cortical and trabecular compartments on such strength changes. Patients were assigned to either PTH, ALN, or their combination (CMB) in year 1 and were switched to either ALN or placebo (PLB) treatment in year 2: PTH-PLB, PTH-ALN, CMB-ALN, and ALN-ALN (year 1-year 2) treatments. Femoral strength was simulated for a sideways fall using nonlinear finite element analysis of the quantitative CT exams. At year 1, the strength change from baseline was statistically significant for PTH (mean, 2.08%) and ALN (3.60%), and at year 2, significant changes were seen for the PTH-ALN (7.74%), CMB-ALN (4.18%), and ALN-ALN (4.83%) treatment groups but not for PTH-PLB (1.17%). Strength increases were primarily caused by changes in the trabecular density regardless of treatment group, but changes in cortical density and mass also played a significant role, the degree of which depended on treatment. For PTH treatment at year 1 and for ALN-ALN treatment at year 2, there were significant negative and positive strength effects, respectively, associated with a change in external bone geometry. Average changes in strength per treatment group were somewhat consistent with average changes in total hip areal BMD as measured by DXA, except for the PTH group at year 1. The relation between change in femoral strength and change in areal BMD was weak (r(2) = 0.14, pooled, year 2). We conclude that femoral strength changes with these various treatments were dominated by trabecular changes, and although changes in the cortical bone and overall bone geometry did contribute to femoral strength changes, the extent of these latter effects depended on the type of treatment.

Women and men with hip fractures have a longer femoral neck moment arm and greater impact load in a sideways fall

In a case control study, we report that women and men with hip fractures have a longer moment arm of the force applied on the proximal femur during a sideways fall, a structural feature that may contribute to fracture risk. The impact load and its direction during a sideways fall onto the greater trochanter are partly determined by the geometry of the proximal femur. We hypothesized that the hip geometry in elderly with hip fractures produces a greater impact on the hip during a sideways fall. We studied 41 female (77.2 +/- 9.9 years) and 22 male (76.2 +/- 12.1 years) patients with hip fractures and 40 female (85.7 +/- 6.0 years) and 17 male (84.3 +/- 10.1 years) controls. Hip geometry was analyzed on the nonfracture hip in patients and left hip in controls using dual-energy X-ray absorptiometry. There was no difference in areal bone mineral density (aBMD), hip axis length, femoral neck axis length, or neck-shaft angle between cases and controls. However, the moment arm of the force on the hip during a sideways fall was 7.3% and 9.5% longer resulting in 5.6% and 9.1% greater moment in such a fall in female and male cases relative to their respective controls independent of height and weight (all p < 0.056). In multivariate logistic regression analysis, only the moment arm length in a sideways fall was associated with increased risk of hip fracture in females (odds ratio = 1.91, 95%CI: 1.14-3.20 for each SD increase in moment arm length of sideways fall, p = 0.02) and males (odds ratio = 2.69, 95% CI, 1.19-6.09, p = 0.01). A longer moment arm in the sideways fall increases the resultant force applied to the hip predisposing to hip fracture.

Theoretical Implications of the Biomechanical Fracture Threshold

Because of the dichotomous nature of a bone fracture, when Phi, the ratio of the applied impact force to the bone strength, is greater than a critical value--the biomechanical fracture threshold--fracture should occur. We sought to elucidate the conceptual implications of this biomechanical fracture threshold with application to hip fracture. We used data from the PaTH study, a 2-yr clinical trial in postmenopausal women treated with alendronate, PTH, or their combination. Outcomes included the force applied to the hip in a sideways fall as estimated from subject height and weight; femoral strength as determined by QCT-based finite element analysis; the load-to-strength ratio Phi; and total hip areal BMD from DXA. Results indicated that those with "very low" femoral strength (<2000 N) invariably had load-to-strength ratio Phi values well above the theoretical biomechanical fracture threshold (Phi = 1), but those with "moderately low" femoral strength (2000-4000 N) displayed Phi values both above and below the theoretical biomechanical fracture threshold. This finding implies that the risk of a hip fracture can be high in those with only moderately low BMD because femoral strength can be low relative to fall impact forces. The observed weak correlation between areal BMD and the load-to-strength ratio Phi (r2 = 0.14) suggests that consideration of the biomechanical fracture threshold may improve fracture risk assessment, particularly for those in the osteopenic range. Regarding treatment effects, only those subjects having load-to-strength ratio Phi values within a relatively narrow "transition zone" of +/- 20% of the assumed biomechanical fracture threshold at baseline were predicted to change fracture status during the trial. In theory, outcomes of fracture trials may be dominated by the responses of those within the "transition zone" at baseline, and treatment benefits in terms of fracture efficacy may depend the patient's baseline status with respect to the biomechanical fracture threshold. We conclude that consideration of the theoretical implications of the biomechanical fracture threshold may lead to new insights and advances in the assessment and treatment of osteoporosis.

Effect of soft shell hip protectors on pressure distribution to the hip during sideways falls

While hip protectors represent a promising strategy for preventing hip fractures, clinical efficacy has been limited by poor user compliance. Soft shell protectors may be more acceptable to users than traditional hard shell designs. However, before embarking on clinical trials to assess efficacy, laboratory experiments are required to determine how soft shell protectors affect the force applied during impact to the hip. This was the goal of the current study. Fifteen women participated in "pelvis release experiments," which safely simulate the impact stage of a sideways fall. During the trials, we measured total impact force and mean pressure over the greater trochanter with the participant unpadded, and while wearing two commercially available soft shell protectors. Mean pressure over the greater trochanter was reduced by 76% by a 14-mm thick horseshoe-shaped protector and by 73% by a 16-mm thick continuous protector. Total force was reduced by 9% by the horseshoe and by 19% by the continuous protector. Soft shell hip protectors substantially reduce the pressure over the greater trochanter, while only modestly reducing total impact force during simulated sideways falls. These data support the need for clinical trials to determine whether soft shell protectors reduce hip fracture risk in vulnerable populations.

Contribution of Trochanteric Soft Tissues to Fall Force Estimates, the Factor of Risk, and Prediction of Hip Fracture Risk*

We compared trochanteric soft tissue thickness, femoral aBMD, and the ratio of fall force to femoral strength (i.e., factor of risk) in 21 postmenopausal women with incident hip fracture and 42 age-matched controls. Reduced trochanteric soft tissue thickness, low femoral aBMD, and increased ratio of fall force to femoral strength (i.e., factor of risk) were associated with increased risk of hip fracture. The contribution of trochanteric soft tissue thickness to hip fracture risk is incompletely understood. A biomechanical approach to assessing hip fracture risk that compares forces applied to the hip during a sideways fall to femoral strength may by improved by incorporating the force-attenuating effects of trochanteric soft tissues. We determined the relationship between femoral areal BMD (aBMD) and femoral failure load in 49 human cadaveric specimens, 53-99 yr of age. We compared femoral aBMD, trochanteric soft tissue thickness, and the ratio of fall forces to bone strength (i.e., the factor of risk for hip fracture, phi), before and after accounting for the force-attenuating properties of trochanteric soft tissue in 21 postmenopausal women with incident hip fracture and 42 age-matched controls. Femoral aBMD correlated strongly with femoral failure load (r2 = 0.73-0.83). Age, height, and weight did not differ; however, women with hip fracture had lower total femur aBMD (OR = 2.06; 95% CI, 1.19-3.56) and trochanteric soft tissue thickness (OR = 1.82; 95% CI, 1.01, 3.31). Incorporation of trochanteric soft tissue thickness measurements reduced the estimates of fall forces by approximately 50%. After accounting for force-attenuating properties of trochanteric soft tissue, the ratio of fall forces to femoral strength was 50% higher in cases than controls (0.92 +/- 0.44 versus 0.65 +/- 0.50, respectively; p = 0.04). It is possible to compute a biomechanically based estimate of hip fracture risk by combining estimates of femoral strength based on an empirical relationship between femoral aBMD and bone strength in cadaveric femora, along with estimates of loads applied to the hip during a sideways fall that account for thickness of trochanteric soft tissues. Our findings suggest that trochanteric soft tissue thickness may influence hip fracture risk by attenuating forces applied to the femur during a sideways fall and provide rationale for developing improved measurements of trochanteric soft tissue and for studying a larger cohort to determine whether trochanteric soft tissue thickness contributes to hip fracture risk independently of aBMD.

Simulation of hip fracture in sideways fall using a 3D finite element model of pelvis–femur–soft tissue complex with simplified representation of whole body

Hip fractures due to sideways falls are a worldwide health problem, especially among the elderly population. The objective of this study was to simulate a real life sideways fall leading to hip fracture. To achieve this a computed tomography (CT) scan based three-dimensional (3D) finite element (FE) model of the pelvis–femur complex was developed using a wide range of mechanical properties in the bone of the complex. For impact absorption through large deformation, surrounding soft tissue was also included in the FE model from CT scan data. To incorporate the inertia effect, the whole body was represented by a spring-mass-dashpot system. For trochanteric soft tissue thickness of 14 mm, body weight of 77.47 kg and average hip impact velocity of 3.17 m/s, this detailed FE model could approximately simulate a sideways fall configuration and examine femoral fracture situation. At the contact surface, the peak impact load was 8331 N. In spite of the presence of 14 mm thick trochanteric soft tissue, within the trochanteric zone the most compressive peak principal strain was 3.5% which exceeds ultimate compressive strain. The modeled trochanteric fracture was consistent with clinical findings and with the findings of previous studies. Further, this detailed FE model may be used to find the effect of trochanteric soft tissue thickness variations on peak impact force, peak strain in sideways fall, and to simulate automobile side impact and backward fall situations.

Prevention of hip fracture with hip protectors

The prevention of fractures amongst older people consists of (i) prevention and treatment of osteoporosis, (ii) prevention of falling and (iii) prevention of fractures using injury-site protection. As the great majority of hip fractures are caused by a sideways fall with direct impact on the greater trochanter of the proximal femur, one approach to prevention is the use of an adequately configured padded, firm-shield external hip protector. With this type of two-part design, the impacting force and energy are, at the time of the fall-impact, first weakened by the padding part of the protector and then diverted away from the greater trochanter by the shield part of the same. Following this line, a series of consecutive studies by the Accident & Trauma Research Center at the UKK Institute, Tampere, Finland, found that a padded, strong-shield hip protector was effective in preventing hip fractures. In the context of the wider literature on hip protectors, these more encouraging results suggest the need for a more rigorous regulation of protector design and characteristics. Alongside inadequacies of design, the other most frequent general problem with hip protectors is compliance. Not all elderly people with a high risk of hip fracture will agree to use hip protectors and in those who do, long-term adherence may decrease. Caregiver motivation and involvement appear therefore to be crucial.

Femoral neck cortical geometry measured with magnetic resonance imaging is associated with proximal femur strength

Magnetic resonance imaging (MRI) is a promising medical imaging technique that we used to assess femoral neck cortical geometry. Our primary objective was to assess whether cortical bone in the femoral neck assessed by MRI was associated with failure load in a simulated sideways fall, with and without adjustment for total bone size. Our secondary objective was to assess the reliability of the MRI measurements. We imaged 34 human cadaveric proximal femora using MRI and dual-energy X-ray absorptiometry (DXA). MRI measurements of cross-sectional geometry at the femoral neck were the cortical cross-sectional area (CoCSA(MRI)), second area moment of inertia (x axis; Ix(MRI)), and section modulus (x axis; Zx(MRI)). DXA images were analyzed with the standard Hologic protocol. From DXA, we report the areal bone mineral density (aBMD(DXA)) in the femoral neck and trochanteric subregions of interest. The femora were loaded to failure at 100 mm/s in a sideways fall configuration (15 degrees internal rotation, 10 degrees adduction). Failure load (N) was the primary outcome. We observed that the femoral neck CoCSA(MRI) and Ix(MRI) were strongly associated with failure load (r (2)=0.46 and 0.48, respectively). These associations were similar to those between femoral neck aBMD and failure load (r (2)=0.40), but lower than the associations between trochanteric aBMD and failure load (r (2)=0.70). We report that MRI holds considerable promise for measuring cortical bone geometry in the femoral neck and for predicting strength at the proximal femur.

Association of Geometric Factors and Failure Load Level With the Distribution of Cervical vs. Trochanteric Hip Fractures

We experimentally studied the distribution of hip fracture types at different structural mechanical strength. Femoral neck fractures were dominant at the lowest structural strength levels, whereas trochanteric fractures were more common at high failure loads. The best predictor of fracture type across all failure loads and in both sexes was the neck-shaft angle. Bone geometry has been shown to be a potential risk factor for osteoporotic fractures. Risk factors have been shown to differ between cervical and trochanteric hip fractures. However, the determinants of cervical and trochanteric fractures at different levels of structural mechanical strength are currently unknown. In addition, it is not known if the distribution of fracture types differs between sexes. The aim of this experimental study on excised femora was to investigate whether there exist differences in the distribution of cervical and trochanteric fractures between different structural mechanical strength levels and different sexes and to identify the geometric determinants that predict a fracture type. The sample was comprised of 140 cadavers (77 females: mean age, 81.7 years; 63 males: mean age, 79.1 years) from whom the left femora were excised for analysis. The bones were radiographed, and geometrical parameters were determined from the digitized X-rays. The femora were mechanically tested in a side impact configuration, simulating a sideways fall. After the mechanical test, the fracture patterns were classified into cervical and trochanteric. The overall proportion of cervical fractures was higher in females (74%) than in males (49%) (p = 0.002). The fracture type distribution differed significantly across load quartiles in females (p = 0.025), but not in males (p = 0.205). At the lowest load quartiles, 94.7% of fractures in female and 62.5% in males were femoral neck fractures. At the highest quartiles, in contrast, only 52.6% of fractures in females and 33.3% in males were cervical fractures. Among geometric variables, the neck-shaft angle was the best predictor of fracture type, with higher values in subjects with cervical fractures. This finding was made in females (p < 0.001) and males (p = 0.02) and was consistent across all failure load quartiles. Femoral neck fractures predominate at the lowest structural mechanical strength levels, whereas trochanteric fractures are more common at high failure loads. Females are more susceptible to femoral neck fractures than males. The best predictor of fracture type across all structural strength levels and both sexes was the neck-shaft angle.

Time Requirement for Young and Elderly Women to Move Into a Position for Breaking a Fall With Outstretched Hands

Risk for hip fracture during a fall is reduced by contacting the ground first with the outstretched hands. However, it is unclear whether the time required for young and elderly individuals to move the hands into a protective position exceeds that available during a typical fall. We tested whether young (n = 30; aged 18-35 years) and elderly women (n = 30; aged 70-88 years) differed in the time required to move their hands into a protective position for breaking a fall. Participants stood either facing or sideways to shoulder-height targets (simulating forward and sideways falls, respectively), which they were instructed to contact as quickly as possible after hearing an aural go cue. Total contact time was partitioned into reaction time and movement time. Young women contacted the targets faster than elderly women in both forward (530 +/- 60 vs 615 +/- 88 ms; p <.001) and sideways trials (658 +/- 80 vs 799 +/- 145 ms; p <.001). This difference was due to faster movement times for young participants. There was no difference between groups in reaction time. Previous studies have shown that during actual falls from standing, wrist and pelvis contact occur at 680 +/- 116 and 715 +/- 160 ms, respectively. Comparing these values to our results suggests that the typical elderly woman should be able to move her hands quickly enough to break a forward fall, but not a sideways fall.

Relation between age, femoral neck cortical stability, and hip fracture risk

Hip fracture risk rises 100 to 1000-fold over 60 years of ageing. Loss of resistance to bending is not a major feature of normal ageing of the femoral neck. Another cause of fragility is local buckling or elastic instability. Bones adapt to their local experience of mechanical loading. The suggestion that bipedalism allows thinning of the underloaded superolateral femoral neck cortex arises from the failure of walking to transmit much mechanical load to this region. We aimed to measure whether elastic instability increases greatly with age since it might trigger hip fracture in a sideways fall. We measured with computed tomography the distribution of bone in the mid-femoral neck of 77 proximal femurs from people who died suddenly aged 20-95 years. We then calculated the critical stress, from the geometric properties and density of the cortical zone most highly loaded in a sideways fall, as a threshold for elastic instability. With normal ageing, this thin cortical zone in the upper femoral neck became substantially thinner. Relative to mean values at age 60 years, female cortical thickness declined by 6.4% (SD 1.1) per decade (p<0.0001), and critical stress by 13.2% (4.3) per decade (p=0.004) in the superoposterior octant compressed most in a sideways fall. Similar, but significantly smaller, effects were evident in men (p=0.004). This thinning compromised the capacity of the femur to absorb energy independently of osteoporosis. Patients with hip fracture had further reduced stability. As women age, hip fragility increases because underloading of the superolateral cortex leads to atrophic thinning. Because walking does not sufficiently load the upper femoral neck, the fragile zones in healthy bones may need strengthening, for example with more well targeted exercise.

Protective Movements during Sideways Falls from Standing Height

To examine the effect of protective movements during sideways falls from standing height (i.e., from the standing position), a two-step study was performed. In the first step, 80 young male and female volunteers freely fell onto a sport-mat. All falls were recorded on videotape, and replayed to analyze movements in response to the falls. Several protective movements were observed; forward flexion and lateral flexion were observed with a particularly high frequency. In the second step, impact velocities of the head and hip were measured by a three-dimensional motion analyzer regarding three types of falls: stiff falls, forward flexion falls and lateral flexion falls. Both types of flexion reduced impact velocities of the head, but not those of the hip. The reduction of the impact velocity on the head correlated with the lowering of the height of the head from the floor.

Falls, fractures, and hip pads

Improvement of balance along with bone-enhancing pharmacotherapy can improve the level of an individual's physical activity and mobility. Balance can be improved with enhancement of postural proprioception and muscular strength. Postural deformities have been shown to impair quality of life of osteoporotic individuals. Kyphotic posture has been demonstrated to contribute to propensity to fall in osteoporotic individuals. Kyphotic posturing and gait disorders can be managed through proprioceptive training, use of a weighted kypho-orthosis, muscle re-education, and safe resistance exercises. Proprioceptive balance training can reduce falls and fracture. Sarcopenia and osteoporotic fractures create musculoskeletal challenges that cannot be met with pharmacotherapy alone. Bone loss, imbalance, and gait disorder along with cognitive concerns can increase with aging. Even in healthy persons, predisposition to falls increases with age-related neuromuscular changes. Muscle strength decreases approximately 50% from age 30 to 80. Furthermore, the amount of body sway increases with reduction of proprioception. Therefore, measures that can decrease imbalance can reduce the risk for falls and fracture. In normal balance, ankle strategies are recruited rather than hip strategies. Strengthening of the lower extremity muscles reduces the risk for falls. Gait aids can also decrease the risk for falls. During a fall, the risk for hip fracture increases 30-fold if there is direct impact to the hip. The use of hip protectors can decrease the risk for hip fracture during a sideways fall. Training in effective safe-landing strategies should be included in fall prevention programs.

THE FORCE ATTENUATION EFFECT OF FOAM MATTRESS IN SIMULATED SIDEWAYS FALL OF HIP ON LEVEL SURFACE

While there have been studies on the impact attenuation of different floor coverings, the effectiveness of using foam mattress as protective floor covering against geriatric hip fracture is still unknown. The objective of current study is to compare the force attenuation of foam mattress with that of teak wooden block when subjected to an impact force that the human hipbone would experience in accidental fall. A porcine hip fall simulator which consisted of a 12-kg impactor and a surrogate pelvis made by 8 month old porcine hipbone and with effective stiffness of 75 kN/m was set up to simulate sideways fall of human hip. The porcine hip fall simulator was allowed to drop freely on the surrogate pelvis from a height starting from 10 cm to a final height of 50 cm. The results showed the use of one piece and two pieces of foam mattress provided significant force reduction ranging from 21% to 37% and from 38% to 61% respectively when compared to wooden impact, and the optimal force reduction occurred when impact energy approached 18 to 24 joules. We found the foam mattress worked best only in those falls where the impact load was of relatively low energy. Relevance: Prevention of geriatric hip fracture is one of the major health issues in the foreseeable future. This study highlight the fact that the use of a protective floor covering may reduce the impact force on the hip in accidental fall and could be a relatively economical and practical way to reduce the risk of geriatric hip fracture.

Discrimination between cases of hip fracture and controls is improved by hip structural analysis compared to areal bone mineral density. An ex vivo study of the femoral neck

In vivo bone densitometry is affected by measurement inaccuracies arising from the assumptions made about soft tissue and marrow composition. This study tested the hypothesis that section modulus (SM, a measure of bending resistance) when measured ex vivo, would discriminate cases of hip fracture from controls better than areal bone mineral density (aBMD). The biopsies were from ( n = 22, female) subjects that had suffered an intracapsular hip fracture. The control material ( n = 24, female) was from post-mortem subjects. Serial peripheral quantitative computed tomography (pQCT) 1-mm thick cross-sectional images of femoral neck previously embedded in methacrylate were obtained with the Densiscan 1000 pQCT densitometer and matched for lateral location. The image voxels were converted to units of bone mass, which were then used to derive the section modulus. The data were used to derive means from which receiver operating characteristic (ROC) curves could be generated. The area under the curves (AUC) showed that discrimination between the fracture cases and controls was better for SM than aBMD [SM: AUC = 0.83 (95% confidence interval: 0.71, 0.96), aBMD: AUC = 0.70 (0.54, 0.85); P = 0.034]. To simulate the forces experienced during a sideways fall, the model's neutral axis was rotated by 210°. The results for section modulus were predictable from those at 0° ( r 2 = 0.97). We conclude that biomechanical analysis of the distribution of bone within the femoral neck may offer a marked improvement in the ability to discriminate patients with an increased risk of intracapsular fracture. Progress towards implementing this form of analysis in clinical densitometry should improve its diagnostic value, but may depend in part on better image resolution and more accurate corrections for the variability between subjects in regional soft tissue composition.

Strategies for avoiding hip impact during sideways falls.

During a fall, hip fracture risk increases 30-fold if there is direct impact to the hip. We conducted sideways falling experiments and found that subjects were able to avoid hip impact by rotating forward or by rotating backward during descent. These simple safe-landing strategies should be considered in designing hip fracture prevention programs. Ninety percent of hip fractures in the elderly are caused by falls. During a fall, hip fracture risk is increased 6-fold by falling sideways (instead of backward or forward) and 30-fold if direct impact occurs to the hip. Previous studies suggest that impact to the hip during a sideways fall can be avoided by rotating forward during descent to land on the outstretched hands. Presumably, an alternative strategy for avoiding hip impact is to rotate backward to land on the buttocks. We conducted sideways falling experiments to test the hypothesis that each of these falling strategies is equally effective in allowing one to avoid hip impact. Twenty-two young adult women participated in trials where they were released from an inclined standing position into a sideways fall onto a foam mattress. Subjects were instructed to "land as softly as possible" and to "avoid impacting the hip" by either rotating forward or rotating backward during descent. We found that absolute values of the hip proximity angle, which described how close the impact site was to the lateral aspect of the pelvis, were not different in forward rotation and backward rotation trials (mean = 55.9 +/- 22.4 degrees versus 61.5 +/- 15.8 degrees, respectively). However, compared with forward rotation trials, backward rotation trials involved greater pelvis impact velocity (2.95 +/- 0.25 versus 2.45 +/- 0.77 m/s; p = 0.001) and greater whole-body kinetic energy at impact (238 +/- 70 versus 156 +/- 90 J; p = 0.001). These results suggest that, during a sideways fall, individuals can avoid impact to the hip and thereby lower the risk for hip fracture by rotating forward or by rotating backward during descent. These simple yet effective safe-landing strategies should be considered in designing exercise-based hip fracture prevention programs.