2D size of trabecular bone structure units (BSU) correlate more strongly with 3D architectural parameters than age in human vertebrae.

Bone tissue is continuously remodeled. In trabecular bone, each remodeling transaction forms a microscopic bone structural unit (BSU), also known as a hemiosteon or a trabecular packet, which is bonded to existing tissue by osteopontin-rich cement lines. The size and shape of the BSUs are determined by the size and shape of the resorption cavity, and whether the cavity is potentially over- or under-filled by the subsequent bone formation. The present study focuses on the recently formed trabecular BSUs, and how their 2D size and shape changes with age and trabecular microstructure. The study was performed using osteopontin-immunostained frontal sections of L2 vertebrae from 8 young (aged 18.5-37.6 years) and 8 old (aged 69.1-96.4 years) control females, which underwent microcomputed tomography (µCT) imaging prior to sectioning. The contour of 4230 BSU profiles (181-385 per vertebra) within 1024 trabecular profiles were outlined, and their 2D width, length, area, and shape were assessed. Of these BSUs, 22 (0.5%) were generated by modeling-based bone formation (i.e. without prior resorption), while 99.5% were generated by remodeling-based bone formation (i.e. with prior resorption). The distributions of BSU profile width, length, and area were significantly smaller in the old versus young females (p < 0.005), and the median profile width, length, and area were negative correlated with age (p < 0.018). Importantly, these BSU profile size parameters were more strongly correlated with trabecular bone volume (BV/TV, p < 0.002) and structure model index (SMI, p < 0.008) assessed by µCT, than age. Moreover, the 2D BSU size parameters were positively correlated to the area of the individual trabecular profiles (p < 0.0001), which were significantly smaller in the old versus young females (p < 0.024). The BSU shape parameters (aspect ratio, circularity, and solidity) were not correlated with age, BV/TV, or SMI. Collectively, the study supports the notion that not only the BSU profile width, but also its length and area, are more influenced by the age-related bone loss and shift from plates to rods (SMI), than age itself. This implies that BSU profile size is mainly driven by changes in the trabecular microstructure, which affect the size of the resorption cavity that the BSU refills.

Evaluating a theoretical and an empirical model of "side effects" in cancellous bone.

Accurate measurement of cancellous bone's apparent elastic modulus, E, is confounded by the experimental artefacts created when trabeculae are severed during specimen preparation. Although standardized axial testing protocols have been developed to deal with the so-called "end effects" caused by severed trabeculae at the loading surfaces, much less attention has been given to the "side effects" around the periphery and the specimen size dependence they create. Two models (one theoretical, one empirical) have been proposed in the literature to predict the reduction in E with decreasing specimen diameter. The current study used finite element method (FEM) modelling to analyze bovine cancellous bone from five different anatomic sites and quantify the changes in E that occurred with specimen diameter. The two models were adapted so that they could predict E based on diameter and architectural parameters (BV/TV, DA, Tb.Sp) alone, without requiring that a "true" modulus be known a priori. Both models fit the data equally well; however, the empirical model gives simpler estimations as a function of trabecular separation (Tb.Sp). A minimum diameter of 5-8 Tb.Sp is recommended.

Four degree-of-freedom lumped parameter model of the foot-ankle system exposed to vertical vibration from 10 to 60 Hz with varying centre of pressure conditions.

Modelling the foot-ankle system (FAS) while exposed to foot-transmitted vibration (FTV) is essential for designing inhibition methods to prevent the effects of vibration-induced white-foot. K-means analysis was conducted on a data set containing vibration transmissibility from the floor to 24 anatomical locations on the right foot of 21 participants. The K-means analysis found three locations to be sufficient for summarising the FTV response. A three segment, four degrees-of-freedom lumped parameter model of the FAS was designed to model the transmissibility response at three locations when exposed to vertical vibration from 10 to 60 Hz. Reasonable results were found at the ankle, midfoot, and toes in the natural standing position (mean-squared error (ε) = 0.471, 0.089, 0.047) and forward centre of pressure (COP) (ε = 0.539, 0.058, 0.057). However, when the COP is backward, the model does not sufficiently capture the transmissibility response at the ankle (ε = 1.09, 0.219, 0.039). Practitioner summary The vibration transmissibility response of the foot-ankle system (FAS) was modelled with varying centre of pressure (COP) locations. Modelling the FAS using three transmissibility locations and two foot segments (rearfoot and forefoot) demonstrated reasonable results in a natural standing and forward COP position to test future intervention strategies. Abbreviations: COP: centre of pressure; DOF: degrees-of-freedom; FAS: foot-ankle system; FTV: foot-transmitted vibration; HAVS: hand-arm vibration syndrome; LDV: laser Doppler vibrometer; LP: lumped-parameter; VWT: vibration-induced white-toes; WBV: whole-body vibration.

Misalignment Error in Cancellous Bone Apparent Elastic Modulus Depends on Bone Volume Fraction and Degree of Anisotropy.

Cancellous bone is an anisotropic structure with architectural and mechanical properties that vary due to both skeletal site and disease state. This anisotropy means that, in order to accurately and consistently measure the mechanical properties of cancellous bone, experiments should be performed along the primary mechanical axis (PMA), that is, the orientation in which the mechanical properties are at their maximum value. Unfortunately, some degree of misalignment will always be present, and the magnitude of the resulting error is expected to be architecture dependent. The goal of this work is to quantify the dependence of the misalignment error, expressed in terms of change in apparent elastic modulus (ΔE), on both the bone volume fraction (BV/TV) and the degree of anisotropy (DA). Finite element method (FEM) models of bovine cancellous bone from five different skeletal sites were created at 5 deg and 20 deg from the PMA determined for each region. An additional set of models was created using image dilation/erosion steps in order to control for BV/TV and better isolate the effect of DA. Misalignment error was found to increase with increasing DA and decreasing BV/TV. At 5 deg misaligned from the PMA, error is relatively low (<5%) in all cases but increases to 8-24% error at 20 deg. These results suggest that great care is needed to avoid introducing misalignment error into experimental studies, particularly when studying regions with high anisotropy and/or low bone volume fraction, such as vertebral or osteoporotic bone.

Stabbing angle alters peak force and work during sharp force trauma of porcine ribs.

Forensic anthropologists have traditionally relied on a qualitative scale (mild, moderate, severe) for describing the forces required to generate a bony injury; however, recently efforts have focused on providing more quantitative data. The current study considers the effects of blade angle on the peak force, average force, and work measured during an instrumented sharp force impact. Sixty-two porcine side ribs were stabbed with the long axis of the blade perpendicular to the convex surface and the blade edge in one of three orientations (0°, 45°, 90°). Peak force was highest when the cutting edge was perpendicular to the long axis of the rib (90°) and lowest when it was aligned (0°). Conversely, work was highest when the blade was at an oblique angle (45°) to the rib. These results confirm that the orientation of a sharp force event must be considered when estimating the mechanical loading required to generate an injury.

Development and commissioning of an instrumented pneumatic device to simulate blunt- and sharp-force trauma.

Forensic investigators commonly interpret bone fracture patterns to estimate the force required to generate that trauma. Unfortunately, these estimates are limited to qualitative values such as "mild", "moderate" or "extreme" force. This work presents a new experimental forensic device developed to simulate blunt- and sharp-force trauma injuries, while recording the forces and velocities involved, so that a more quantitative relationship between force and trauma can be established. The machine design is described in some detail, its capabilities are outlined, and the results of the commissioning and validation tests are presented. Preliminary results for both blunt- and sharp-force testing of porcine ribs, conducted at 3.8m/s, indicate the average peak force (733±95N versus 392±73N), average force (334±49N versus 101±24N), and work (2.34±0.26J versus 0.68±0.09J) are significantly higher in the blunt case. The experimental data generated by this instrumented device will allow forensic investigators to create a better quantitative link between incident conditions (velocity, force, work) and the resulting fracture patterns.

Epidemiology of Foot Injuries Using National Collegiate Athletic Association Data From the 2009-2010 Through 2014-2015 Seasons.

CONTEXT: Researchers analyzing data from the National Collegiate Athletic Association Injury Surveillance Program have not considered the differences in foot injuries across specific sports and between males and females. OBJECTIVE: To describe the epidemiologic differences in rates of overall foot injuries and common injuries among sports and between sexes. DESIGN: Descriptive epidemiology study. SETTING: Online injury-surveillance data from 15 unique sports involving males and females that demonstrated 1967 injuries over 4 821 985 athlete-exposures. PATIENTS OR OTHER PARTICIPANTS: Male and female athletes competing in National Collegiate Athletic Association sports from the 2009-2010 through 2014-2015 seasons. MAIN OUTCOME MEASURE(S): Foot injury rates (per 10 000 athlete-exposures) and the proportion of foot injuries were calculated for each sport. The effect of sex was calculated using Poisson-derived confidence intervals for 8 paired sports. A risk analysis was performed using a 3 × 3 quantitative injury risk-assessment matrix based on both injury rate and mean days of time loss. RESULTS: Foot injury rates differed between sports, with the highest rates in female gymnastics, male and female cross-country, and male and female soccer athletes. Cross-country and track and field had the highest proportions of foot injuries for both female and male sports. The 5 most common injuries were foot/toe contusions, midfoot injuries, plantar fascia injuries, turf toe, and metatarsal fractures. Only track and field athletes demonstrated a significant sex difference in injury rates, with female athletes having the higher rate. The quantitative injury risk-assessment matrix identified the 4 highest-risk injuries, considering both rate and severity, as metatarsal fractures, plantar fascia and midfoot injuries, and foot/toe contusions. CONCLUSIONS: Important differences were present among sports in terms of injury rates, the most common foot injuries, and the risk (combination of frequency and severity) of injury. These differences warrant further study to determine the mechanisms of injury and target intervention efforts.

Standing centre of pressure alters the vibration transmissibility response of the foot.

Vibration-white foot as an occupational disease has underscored the need to better understand the vibration response of the foot. While vibration transmissibility data exist for a natural standing position, it is anticipated that weight distribution will affect the response. The purpose of this study was to determine the effects of changes in centre of pressure (COP) on the foot's biomechanical response. Twenty-one participants were exposed to vertical vibration of 30 mm/s, with a sine sweep from 10-200 Hz. Z-axis (vertical) vibration was measured at 24 locations on the right foot, with the COP shifted forward or toward the heel. A mixed model analysis at each location revealed significant differences (p < .001) in the transmissibility response when the COP was altered to the forefoot and rearfoot. In general, the peak frequency of the average vibration response increased for a region of the foot when the COP was shifted toward that region. Practitioner Summary: Altering the centre of pressure location resulted in changes in the transmission of vibration through the foot. The forward lean position was associated with the greatest amplitude of vibration transmissibility at the toes. This information is relevant for clinicians studying vibration-induced white-foot and engineers designing protective equipment.

Biomechanical response of the human foot when standing in a natural position while exposed to vertical vibration from 10-200 Hz.

Exposure to foot-transmitted vibration (FTV) can lead to pain and numbness in the toes and feet, increased cold sensitivity, blanching in the toes, and joint pain. Prolonged exposure can result in a clinical diagnosis of vibration-induced white foot (VIWFt). Data on the biomechanical response of the feet to FTV is limited; therefore, this study seeks to identify resonant frequencies for different anatomical locations on the human foot, while standing in a natural position. A laser Doppler vibrometer was used to measure vertical (z-axis) vibration on 21 participants at 24 anatomical locations on the right foot during exposure to a sine sweep from 10-200 Hz with a peak vertical velocity of 30 mm/s. The most notable differences in the average peak frequency occur between the toes (range: 99-147 Hz), midfoot (range: 51-84 Hz) and ankle (range: 16-39 Hz). Practitioner Summary: The biomechanical response of the human foot exposed to foot-transmitted vibration, when standing in a natural position, was measured for 21 participants. The foot does not respond uniformly; the toes, midfoot, and ankle regions need to be considered independently in future development of isolation strategies and protective measures.

Failure behaviour of rat vertebrae determined through simultaneous compression testing and micro-CT imaging.

Skeletal fractures, including those resulting from osteoporosis, result in significant healthcare and societal costs on an annual basis. Therefore, it is important to understand the mechanisms by which these fractures occur. Incremental compression testing combined with micro-CT imaging has been used to visualize the progression of failure in trabecular bone samples; however, these studies have ignored the potential contributions of the cortical shell. In the current study, incremental compression testing with simultaneous micro-CT imaging was performed on rat vertebrae from multiple disease states (healthy control, osteoporotic, osteoporotic + treatment). These tests allowed the progression of failure through an entire vertebral body to be visualized for the first time. Three distinct failure modes were observed throughout all specimens, independent of disease state. Two of these failure modes (types I and II), which were observed in 93% of all specimens, were associated with the vascular apertures in the vertebrae's dorsal and ventral surfaces. This behaviour is likely caused by the stress concentrations in the cortical shell resulting from the apertures themselves, coupled with the reduced trabecular bone volume adjacent to them. These results suggest that the combined contributions of both the cortical shell and trabecular bone must be considered when studying the compressive failure behaviour of rat vertebrae.

Incidence and Severity of Foot and Ankle Injuries in Men's Collegiate American Football.

BACKGROUND: American football is an extremely physical game with a much higher risk of injury than other sports. While many studies have reported the rate of injury for particular body regions or for individual injuries, very little information exists that compares the incidence or severity of particular injuries within a body region. Such information is critical for prioritizing preventative interventions. PURPOSE: To retrospectively analyze epidemiological data to identify the most common and most severe foot and ankle injuries in collegiate men's football. STUDY DESIGN: Descriptive epidemiology study. METHODS: Injury data were obtained from the National Collegiate Athletic Association (NCAA) Injury Surveillance System (ISS) for all foot and ankle injuries during the 2004-2005 to 2008-2009 seasons. Injuries were analyzed in terms of incidence and using multiple measures of severity (time loss, surgeries, medical disqualifications). This frequency and severity information is summarized in tabular form as well as in a 4 × 4 quantitative injury risk assessment matrix (QIRAM). RESULTS: The rate of foot and ankle injuries was 15 per 10,000 athletic exposures (AEs). Five injuries were found to be responsible for more than 80% of all foot and ankle injuries: lateral ankle ligament sprains, syndesmotic (high ankle) sprains, medial ankle ligament sprains, midfoot injuries, and first metatarsophalangeal joint injuries. Ankle dislocations were found to be the most severe in terms of median time loss (100 days), percentage of surgeries (83%), and percentage of medical disqualifications (94%), followed by metatarsal fractures (38 days, 36%, and 49%, respectively) and malleolus fractures (33 days, 41%, and 59%, respectively). Statistical analysis suggests that the 3 measures of severity are highly correlated (r > 0.94), thereby justifying the use of time loss as a suitable proxy for injury severity in the construction of the QIRAM. CONCLUSION: Based on the QIRAM analysis, the 5 highest risk injuries were identified based on both incidence and severity (ankle dislocations, syndesmotic sprains, lateral ankle ligament sprains, metatarsal fractures, and malleolus fractures). A better understanding of the relative incidence and severity of these injuries will allow coaches, trainers, and researchers to more effectively focus their preventative interventions.

Etiology and Biomechanics of Midfoot (Lisfranc) Injuries in Athletes.

Tarsometatarsal (TMT) dislocations are an uncommon but debilitating athletic injury. When symptomatic midfoot instability persists, an injured athlete frequently requires surgical stabilization and rehabilitation for up to 9 months before returning to full athletic participation. Unfortunately, the limited biomechanical knowledge of this injury prevents prophylactic measures from being developed that could reduce an athlete's risk of injury. The goal of this article is to summarize the literature on TMT dislocations, with a particular emphasis on the relevant biomechanics, in an attempt to clarify the circumstances and mechanisms under which these injuries occur. Since athletic injuries represent only a small portion of all TMT dislocations, other categories of injuries are also considered for the insight they provide. This review first summarizes the anatomy of the TMT joint as well as the clinical details surrounding TMT dislocations. The various hypothesized injury mechanisms are then reviewed with particular attention given to cadaveric studies that investigate these mechanisms. Based on this critical review, gaps in the research related to epidemiologic data, full-scale and component testing, numerical modeling, and countermeasure development, are identified. Only by improving our understanding of the causes and biomechanics can steps be taken to protect athletes from these injuries.

Etiology and Biomechanics of Tarsometatarsal Injuries in Professional Football Players: A Video Analysis.

BACKGROUND: Tarsometatarsal (TMT) dislocations are uncommon yet debilitating athletic injuries, particularly in American football. To date, the mechanisms of athletic TMT dislocation have been described only anecdotally. This lack of information confounds the development of preventative countermeasures. PURPOSE: To use video analysis to provide direct, independent identification of the etiologic and mechanistic variables responsible for TMT dislocations in professional football players. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Sixteen professional National Football League players who sustained publicly reported TMT dislocations were identified. Publicly broadcast game footage of the plays in which injury occurred was reviewed by a panel of 5 biomechanists. Consensus was reached regarding the details surrounding injury, and a weighting was assigned to each detail based on the panel's confidence. RESULTS: Roughly 90% of injuries occurred while the injured player was engaged with or by another player, a detail that has heretofore been undocumented. Few injuries resulted from direct loading of either the foot or the ipsilateral limb; however, the injured foot was frequently subjected to axial loading from ground engagement with the foot in plantar flexion and the toes dorsiflexed. Injurious loading was often due to external rotation of the midfoot (86%). Fifteen of 16 injuries were season ending. CONCLUSION: TMT dislocations are frequently associated with engagement by or with a second player but infrequently caused by a direct blow to the foot. Axial loading of the foot, external rotation, and pronation/supination are the most common conditions during injurious loading.

Development of an injury risk function for first metatarsophalangeal joint sprains.

INTRODUCTION: Sprains of the first metatarsophalangeal (1MTP) joint, also known as turf toe, are debilitating athletic injuries. Because 85% of 1MTP sprains result from excessive hallux dorsiflexion, interventions that limit motion to subinjurious levels would greatly benefit athletes. Hallux dorsiflexion range of motion (hdROM) cannot be overly constrained, however, lest athletic performance be compromised. Therefore, the tolerance of the 1MTP joint to excessive dorsiflexion injury must be quantified before appropriate hdROM limitations may be developed. The purpose of this study was to develop a quantitative injury risk function for 1MTP sprains on the basis of hallux dorsiflexion angle. METHODS: Twenty cadaveric limbs were tested to both subinjurious and injurious levels of hallux dorsiflexion. Motion capture techniques were used to track six-degree-of-freedom motion of the first proximal phalanx, first metatarsal, and calcaneus. Specimens were examined by physicians posttest to diagnose injury occurrence and ensure clinical relevance of the injuries. RESULTS: A two-parameter Weibull hazard function analysis reveals that a 50% risk of injury occurs at 78° of dorsiflexion from anatomical zero. CONCLUSION: Methods presented here drove cadaveric 1MTP joints to various degrees of dorsiflexion, resulting in both noninjurious and injurious trials, which were formed into an injury risk function.

Foot kinematics and loading of professional athletes in American football-specific tasks.

The purpose of this study was to describe stance foot and ankle kinematics and the associated ground reaction forces at the upper end of human performance in professional football players during commonly performed football-specific tasks. Nine participants were recruited from the spring training squad of a professional football team. In a motion analysis laboratory setting, participants performed three activities used at the NFL Scouting Combine to assess player speed and agility: the 3-cone drill, the shuttle run, and the standing high jump. The talocrural and first metatarsophalangial joint dorsiflexion, subtalar joint inversion, and the ground reaction forces were determined for the load bearing portions of each activity. We documented load-bearing foot and ankle kinematics of elite football players performing competition-simulating activities, and confirmed our hypothesis that the talocrural, subtalar, and metatarsophalangeal joint ranges of motion for the activities studied approached or exceeded reported physiological limits.

Age, sex, causal and injury patterns in tarsometatarsal dislocations: a literature review of over 2000 cases.

BACKGROUND: The causes and mechanisms of tarsometatarsal (TMT) dislocations are poorly characterized. Unfortunately, the rarity of these injuries makes it difficult and costly to gather the epidemiological data needed to better understand the populations at risk and the circumstances under which injury is most likely to occur. METHODOLOGY: To address this issue, literature reports of TMT dislocations were identified and analyzed to generate statistical descriptions of the common causes of injury, the age and sex of those injured, and the pattern of injury. Over 2000 injuries were identified from 187 articles. RESULTS: The analysis reveals that over 40% of injuries were related to traffic accidents. Based on the Hardcastle classification system, more than 60% of TMT dislocation were partial (type B) injuries. Over 55% of the injured were between 15 and 35 years of age, and males were injured more than twice as frequently. Conversely, the victims of falls tended to be older and represented a larger proportion of females. The age and sex of those injured by TMT dislocations vary by cause. CONCLUSION: An improved understanding of the epidemiologic patterns will benefit research into the mitigation and prevention of these injuries.

Specimen size effect in the volumetric shrinkage of cancellous bone measured at two levels of dehydration.

Water is commonly removed from bone to study its effect on mechanical behaviour; however, dehydration also alters the bone structure. To make matters worse, measuring structural changes in cancellous bone is complicated by a number of factors. Therefore, the goals of this study were to address these issues by (1) comparing Archimedes' method and a helium pycnometer as methods for measuring cancellous bone volume; (2) measuring the apparent dimensional and volumetric tissue shrinkage of cancellous bone at two levels of dehydration; and, (3) identifying whether a size effect exists in cancellous bone shrinkage. Cylindrical specimens (3, 5 and 8.3 mm diameters) of cancellous bone were taken from the distal bovine femur. The apparent dimensions of each cylindrical specimen were measured in a fully hydrated state (HYD), after drying at room temperature (AIR), and after oven drying at 105 degrees C (OVEN). Tissue volume measurements for those three hydration states were obtained using both a helium pycnometer and Archimedes' method. Aluminium foams, which mimic the cancellous structure, were used as controls. The results suggest that the helium pycnometer and Archimedes' method yield identical results in the HYD and AIR states, but that Archimedes' method under-predicts the nominal OVEN volume by incorporating the collagen-apatite porosity. A distinct size effect on volumetric shrinkage is observed (p<0.025) using the pycnometer in both AIR and OVEN states. Apparent dimensional shrinkage (2% and 7%) at the two dehydration levels is much smaller than the measured volumetric tissue shrinkage (16% and 29%), which results in a reduced dehydrated bone volume fraction.