Muscle Lever Arms Research Articles

Contribution to the study of stresses in the thumb column during key pinch grip

ObjectivesThe aim of this study was to calculate the stress acting on the trapeziometacarpal joint during an key pinch grip. MethodWe used profile X-rays of the thumb to measure the various bony and muscle lever arms. We assessed the angles of action of the muscular elements involved in the thumb column. Based on this data, we established a two-dimensional geometric model that enabled us to determine the forces at each joint level, as a function of stresses and muscular contributions. We were also able to calculate the participation of the different muscle groups in obtaining a balanced situation. ResultsOur results, as a function of the degree of flexion of the interphalangeal and metacarpophalangeal joints, show a multiplying factor of 2.9–3.19 in relation to the key pinch grip force. DiscussionPrevious studies modelling a key pinch grip are showed multiplying factors from 6 to 13 in relation to the key pinch grip force. They are not compatible with the characteristics of the polyethylene used for trapeziometacarpal prostheses, whereas numerous articles in the literature show survival rates that are more or less comparable to those of total hip prostheses. These studies required an excessive number of assumptions, which could lead to error. Our results are compatible with the results of trapeziometacarpal prosthesis and with those of a recent study measuring intra-articular trapeziometacarpal pressure in a cadaveric model. Our model allows us to test different configurations of the thumb spine depending on the degree of flexion of the interphalangeal and metacarpophalangeal joints.

Latarjet’s muscular alterations increase glenohumeral joint stability: A theoretical study

The surgical Latarjet procedure aims to stabilise the glenohumeral joint following anterior dislocations. Despite restoring joint stability, the procedure introduces alterations of muscle paths which likely modify the shoulder dynamics. Currently, these altered muscular functions and their implications are unclear. Hence, this work aims to predict changes in muscle lever arms, muscle and joint forces following a Latarjet procedure by using a computational approach.Planar shoulder movements of ten participants were experimentally assessed. A validated upper-limb musculoskeletal model was utilised in two configurations, i.e., a baseline model, simulating normal joint, and a Latarjet model simulating its related muscular alterations. Muscle lever arms and differences in muscle and joint forces between models were derived from the experimental marker data and static optimisation technique.Lever arms of most altered muscles, hence their role, were substantially changed after Latarjet. Altered muscle forces varied by up to 15% of the body weight. Total glenohumeral joint force increased by up to 14% of the body weight after Latarjet, mostly due to increase in compression force.Our simulation indicated that the Latarjet muscular alterations lead to changes in the muscular recruitment and contribute to the stability of the glenohumeral joint by increasing compression force during planar motions.

Trunk muscle forces and spinal loads during heavy deadlift: Effects of personalization, muscle wrapping, muscle lever arm, and lumbopelvic rhythm.

Heavy deadlift is used as a physical fitness screening tool in the U.S. Army. Despite the relevance of such a screening tool to military tasks performed by Service Members, the biomechanical impact of heavy deadlift and its risk of low-back injury remain unknown. A kinematics-driven musculoskeletal model of spine was implemented to investigate biomechanics of the lower back in a volunteer (23 years old, height of 1.82 m, and body mass of 98.8kg) during a 68 kg deadlift. In search of protective mechanisms, effects of model personalization and variations in trunk musculature and lumbopelvic rhythm were also investigated. The net moment, compression and shear forces at the L5-S1 reached peaks of 684 Nm, 17.2 and 4.2kN, respectively. Geometrical personalization and changes in lumbopelvic rhythm had the least effects on predictions while increases in muscle moment arms (40%) had the largest effects that caused, respectively, 32% and 36% decrease in the maximum compressive and shearing forces. Initiating wrapping of back muscles at farther distances from the spine had opposing effects on spinal loads; peak compression at the L5-S1 decreased by 12% whereas shear increased by 19%. Despite mechanisms considered, spinal loads during heavy deadlift exceed the existing evidence concerning the threshold of injury for spinal segments, suggesting the vulnerability to injury. Chronic exposure to such high-spinal loads may lead to (micro) fractures, degeneration, pathoanatomical changes and finally low-back pain.

Low effective mechanical advantage of giraffes’ limbs during walking reveals trade-off between limb length and locomotor performance

Giraffes (Giraffa camelopardalis) possess specialized locomotor morphology, namely elongate and gracile distal limbs. While this contributes to their overall height and enhances feeding behavior, we propose that the combination of long limb segments and modest muscle lever arms results in low effective mechanical advantage (EMA, the ratio of in-lever to out-lever moment arms), when compared with other cursorial mammals. To test this, we used a combination of experimentally measured kinematics and ground reaction forces (GRFs), musculoskeletal modeling, and inverse dynamics to calculate giraffe forelimb EMA during walking. Giraffes walk with an EMA of 0.34 (±0.05 SD), with no evident association with speed within their walking gait. Giraffe EMA was about four times lower than expectations extrapolated from other mammals, ranging from 0.03 to 297 kg, and this provides further evidence that EMA plateaus or even diminishes in mammals exceeding horse size. We further tested the idea that limb segment length is a factor which determines EMA, by modeling the GRF and muscle moment arms in the extinct giraffid Sivatherium giganteum and the other extant giraffid, Okapia johnstoni. Giraffa and Okapia shared similar EMA, despite a four to sixfold difference in body mass (Okapia EMA = 0.38). In contrast, Sivatherium, sharing a similar body mass with Giraffa, had greater EMA (0.59), which we propose reflects behavioral differences, such as a somewhat increased capability for athletic performance. Our modeling approach suggests that limb length is a determinant of GRF moment arm magnitude and that unless muscle moment arms scale isometrically with limb length, tall mammals are prone to low EMA.

Morphological differences in the calcaneus among extant great apes investigated by three-dimensional geometric morphometrics

Investigating the morphological differences of the calcaneus in humans and great apes is crucial for reconstructing locomotor repertories of fossil hominins. However, morphological variations in the calcaneus of the great apes (chimpanzees, gorillas, and orangutans) have not been sufficiently studied. This study aims to clarify variations in calcaneal morphology among great apes based on three-dimensional geometric morphometrics. A total of 556 landmarks and semilandmarks were placed on the calcaneal surface to calculate the principal components of shape variations among specimens. Clear interspecific differences in calcaneal morphology were extracted, corresponding to the degree of arboreality of the three species. The most arboreal orangutans possessed comparatively more slender calcaneal tuberosity and deeper pivot region of the cuboid articular surface than chimpanzees and gorillas. However, the most terrestrial gorillas exhibited longer lever arm of the triceps surae muscle, larger peroneal trochlea, more concave plantar surface, more inverted calcaneal tuberosity, more everted cuboid articular surface, and more prominent plantar process than the orangutans and chimpanzees. These interspecific differences possibly reflect the functional adaptation of the calcaneus to locomotor behavior in great apes. Such information might be useful for inferring foot functions and reconstructing the locomotion of fossil hominoids and hominids.

Variation in Articular Cartilage Thickness Among Extant Salamanders and Implications for Limb Function in Stem Tetrapods

The size and shape of articular cartilage in the limbs of extant vertebrates are highly variable, yet they are critical for understanding joint and limb function in an evolutionary context. For example, inferences about unpreserved articular cartilage in early tetrapods have implications for how limb length, joint range of motion, and muscle leverage changed over the tetrapod water-land transition. Extant salamanders, which are often used as functional models for early limbed vertebrates, have much thicker articular cartilage than most vertebrate groups, but the exact proportion of cartilage and how it varies across salamander species is unknown. I aimed to quantify this variation in a sample of 13 salamanders representing a broad range of sizes, modes of life, and genera. Using contrast-enhanced micro-CT, cartilage dimensions and bone length were measured non-destructively in the humerus, radius, ulna, femur, tibia, and fibula of each specimen. Cartilage correction factors were calculated as the combined thickness of the proximal and distal cartilages divided by the length of the bony shaft. Articular cartilage added about 30% to the length of the long bones on average. Cartilage was significantly thicker in aquatic salamanders (42 ± 14% in the humerus and 35 ± 8 in the femur) than in terrestrial salamanders (21 ± 7% in both humerus and femur). There was no consistent relationship between relative cartilage thickness and body size or phylogenetic relatedness. In addition to contributing to limb length, cartilage caps increased the width and breadth of the epiphyses by amounts that varied widely across taxa. To predict the effect of salamander-like cartilage correction factors on muscle leverage, a simplified model of the hindlimb of the Devonian stem tetrapodAcanthostegawas built. In this model, the lever arms of muscles that cross the hip at an oblique angle to the femur was increased by up to six centimeters. Future reconstructions of osteological range of motion and muscle leverage in stem tetrapods and stem amphibians can be made more rigorous by explicitly considering the possible effects of unpreserved cartilage and justifying assumptions based on available data from extant taxa, including aquatic and terrestrial salamanders.

Calcaneal allometry in humans and nonhuman primates

Body mass critically impacts locomotion because it largely determines the mechanical requirements for supporting and propelling the body against gravity. Primate long bone proportions relative to body mass and locomotion have been extensively studied; however, these relationships are less well understood in the foot. The scaling of the calcaneus is particularly important because of its weight-bearing role during locomotion. Here, we analyze calcaneal allometry in humans (n=120) and nonhuman primates (n=278) to investigate scaling relationships relative to known locomotor differences. Twelve linear measures, as well as articular facet surface areas, were collected on calcaneus surface models in Avizo Lite 9.0.1. Femoral head superoinferior breadth and established regression equations were used to estimate body mass (EBM). Calcaneal measures were regressed against EBM using phylogenetic least squares regression analyses conducted at different taxonomic levels to determine how the inclusion of multiple (sub)species within a genus impacted the presence of phylogenetic signal in our dataset. Reduced major axis ANCOVAs were used to test for significant differences between humans and (pooled) nonhuman primates. Residuals from isometry both among and within genera were evaluated with ANOVAs and post hoc multiple comparison tests. When analyzed at the (sub)species level, all but two dimensions relative to EBM exhibit phylogenetic signals. These signals are no longer apparent at the genus level, suggesting variation among the genera is driven by some factor other than phylogeny, such as body size or locomotion. Bipedally adapted humans display relatively larger calcaneal dimensions than nonhuman primates. Among nonhuman great apes, more arboreal taxa exhibit relatively larger cuboid facet surface areas, increasing midfoot mobility for movement over unpredictable substrates. More terrestrial taxa exhibit relatively longer calcaneal tubers for EBM, which serves to increase the muscle lever arm, and thus mechanical advantage, of the triceps surae muscle.

The biomechanical role of the lacertus fibrosus of the biceps brachii Muscle

The lacertus fibrosus (LF) is involved in various surgeries. However, the biomechanical contribution of the LF remains unclear. The aim of this study was to determine the role of the lacertus fibrosus on the elbow and forearm kinematics and on the biceps brachii muscle lever arms. This biomechanical study was performed on seven fresh-frozen upper limbs of cadavers. Elbow flexion, forearm supination, and biceps brachii muscle lever arms were analyzed in the intact conditions (I) and after superficial (R) and deep part (R2) of the lacertus fibrosus release, respectively. Elbow flexion shows a significant difference (p < 0.0001) between I, R, R2. Abduction/adduction shows a significant difference between I-R (p < 0.0001) and I-R2 (p < 0.0001). Supination does not show a significant difference in mean maximum amplitude, but between 40 and 70%, there are significant differences. There is a significant mean decrease of lever arm in flexion (28%) and supination (50%) after superficial and deep part of the lacertus fibrosus release. The results of this study show that the lacertus fibrosus increases the lever arm during flexion and supination. It limits the flexion and abduction of the elbow and supination of the forearm. Lacertus fibrosus maintains the rhythmicity between the elbow flexion and supination of the forearm. Basic science study, biomechanics.

Ontogeny of effective mechanical advantage in eastern cottontail rabbits (Sylvilagus floridanus).

Juvenile animals must survive in the same environment as adults despite smaller sizes, immature musculoskeletal tissues, general ecological naïveté and other limits of performance. Developmental changes in muscle leverage could constitute one mechanism to promote increased performance in juveniles despite ontogenetic limitations. We tested this hypothesis using a holistic dataset on growth and locomotor development in wild eastern cottontail rabbits (Sylvilagus floridanus) to examine ontogenetic changes in hindlimb muscle effective mechanical advantage (EMA). EMA is a dimensionless index of muscle leverage, equal to the quotient of average muscle lever length and the load arm length of the ground reaction force (GRF), effectively representing the magnitude of output force arising from a given muscle force. We found that EMA at the hip and ankle joints, as well as overall hindlimb EMA, significantly declined across ontogeny in S. floridanus, whereas EMA at the knee joint remained unchanged. Ontogenetic decreases in EMA were due to isometric scaling of muscle lever arm lengths alongside positive ontogenetic allometry of GRF load arm lengths - which in turn was primarily related to positive allometry of hindlimb segment lengths. Greater EMA limits the estimated volume of hindlimb extensor muscle that has to be activated in young rabbits, likely mitigating the energetic cost of locomotion and saving metabolic resources for other physiological functions, such as growth and tissue differentiation. An additional examination of limb growth allometry across a diverse sample of mammalian taxa suggests that ontogenetic decreases in limb joint EMA may be a common mammalian trend.

Effective Mechanical Advantage Allometry of Felid Elbow and Knee Extensors

Larger terrestrial mammals have generally been found to use more extended limb postures, a mechanism which maintains muscular requirements at larger sizes by improving the effective mechanical advantage (EMA) of limb musculature. Felids, however, have been documented to maintain joint angles across body sizes. If felid morphology scales isometrically, it would mean larger felids have relatively weaker muscles, compromising locomotor activities. Here, we examine the allometric relationships between the EMA of the elbow and knee extensors and body mass, finding that the EMA of the triceps brachii and quadriceps muscles scale with positive allometry. When species-specific joint angles were used rather than felid-average joint angles, EMA scales to body mass with more positive allometry. When the scaling of the muscle and ground reaction force (GRF) lever arms were investigated individually the allometric signal was lost; however, the muscle lever arms generally have allometric slope coefficients that are consistent with positive allometry, while the GRF lever arms demonstrate negative allometric slope coefficients. This suggests there are subtle alterations to limb morphology allowing different felid species to achieve an increased EMA via distinctive mechanisms. The quadriceps EMA was found to scale with sufficient positive allometry to compensate for increases in size without alteration in muscular anatomy; however, this is not the case for the triceps brachii EMA. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:775-784, 2019. © 2018 Wiley Periodicals, Inc.

Evaluating the primary stability of standard vs lateralised cementless femoral stems – A finite element study using a diverse patient cohort

BackgroundRestoring the original femoral offset is desirable for total hip replacements as it preserves the original muscle lever arm and soft tissue tensions. This can be achieved through lateralised stems, however, the effect of variation in the hip centre offset on the primary stability remains unclear. MethodsFinite element analysis was used to compare the primary stability of lateralised and standard designs for a cementless femoral stem (Corail®) across a representative cohort of male and female femora (N = 31 femora; age from 50 to 80 years old). Each femur model was implanted with three designs of the Corail® stem, each designed to achieve a different degree of lateralisation. An automated algorithm was used to select the size and position that achieve maximum metaphyseal fit for each of the designs. Joint contact and muscle forces simulating the peak forces during level gait and stair climbing were scaled to the body mass of each subject. FindingsThe study found that differences in restoring the native femoral offset introduce marginal differences in micromotion (differences in peak micromotion <21 μm), for most cases. Nonetheless, significant reduction in the interfacial strains (>3000 με) was achieved for some subjects when lateralized stems were used. InterpretationFindings of this study suggest that, with the appropriate size and alignment, the standard offset design is likely to be sufficient for primary stability, in most cases. Nonetheless, appropriate use of lateralised stems has the potential reduce the risk of peri-prosthetic bone damage. This highlights the importance of appropriate implant selection during the surgical planning stage.

Ontogenetic changes to muscle architectural properties within the jaw-adductor musculature of Macaca fascicularis.

Changes to soft- and hard-tissue components of the masticatory complex during development can impact functional performance by altering muscle excursion potential, maximum muscle forces, and the efficiency of force transfer to specific bitepoints. Within Macaca fascicularis, older individuals exploit larger, more mechanically resistant food items and more frequently utilize wide-gape jaw postures. We therefore predict that key architectural and biomechanical variables will scale during ontogeny to maximize bite force and gape potential within older, larger-bodied individuals. We analyzed 26 specimens of M. fascicularis, representing a full developmental spectrum. The temporalis, superficial masseter, and deep masseter were dissected to determine muscle mass, fiber length, and physiologic cross-sectional area (PCSA). Lever-arm lengths were also measured for each muscle, alongside the height of the temporomandibular joint (TMJ) and basicranial length. These variables were scaled against two biomechanical variables (jaw length and condyle-molar length) to determine relative developmental changes within these parameters. During ontogeny, muscle mass, fiber length, and PCSA scaled with positive allometry relative to jaw length and condyle-molar length within all muscles. TMJ height also scaled with positive allometry, while muscle lever arms scaled with isometry relative to jaw length and with positive allometry (temporalis) or isometry (superficial and deep masseter) relative to condyle-molar length. Larger individuals demonstrate adaptations during development towards maximizing gape potential and bite force potential at both an anterior and posterior bitepoint. These data provide anatomical evidence to support field observations of dietary and behavioral differences between juvenile and adult M. fascicularis.

Allometry of Felid Knee and Elbow Effective Mechanical Advantage

Body size has a profound impact on animal locomotion because all terrestrial animals must support and move their mass against gravity. If large animals were isometrically scaled versions of smaller animals, then larger animals would have relatively weaker muscles and bones, as both are a function of area. The loads associated with locomotion however, are largely equivalent to body mass, a function of volume. To contend with this problem, larger animals have been observed to use more extended limb postures; increasing the effective mechanical advantage (EMA) of their muscles. Felids however, maintain the same limb posture across body sizes, suggesting they are not increasing EMA through limb extension. To investigate how felids maintain the same posture across body sizes we analyzed the relationship between the EMA of the triceps brachii and quadriceps and body mass in nine species of felids with kinematic data from the literature.Ulnae (n=37) and femora (n=30) of nine species of felids were surface scanned using a 3D NextEngine laser scanner. Linear measurements were taken on the tibia, patella, talus, calcaneus, navicular, third cuneiform and third metatarsal. Ulna and femur surface models were aligned in virtual space using anatomical and biomechanical axes. Triceps brachii EMA was calculated as the ratio of the muscle lever arm to the GRF lever arm, which were both collected on the ulna surface model. The quadriceps muscle and GRF lever arms were calculated using the femur surface models, linear measurements of limb and foot bones and kinematic data. Joint EMAs, muscle lever arms and GRF lever arms were regressed against body mass using PGLS regressions incorporating a phylogeny from 10kTrees. Pagel's λ was zero for all analyses, so data were reanalyzed using reduced major axis (RMA) regressions without phylogenetic information.The triceps brachii and quadriceps EMA scale to body mass with slopes of 0.15 and 0.13, respectively, indicating positive allometry, meaning that larger felids have a relatively greater EMA and suggesting that some aspect of felid joint morphology is altered. For both joints neither the muscle lever arms nor the GRF lever arms are statistically different from isometry, however the muscle lever arms generally trend toward positive allometry, while the GRF lever arms lean toward negative allometry. This indicates that either there are subtle changes to both lever arms or that different felid species accomplish an increased EMA in distinct ways.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inferring the Diets of Extinct Giant Lemurs from Osteological Correlates of Muscle Dimensions.

The jaw adductor muscles of extinct mammals are often reconstructed to elucidate paleoecological relationships and to make broad comparisons among taxa. Muscle lever arms, bite load arms, muscle dimensions, and gape are often also reconstructed to better understand feeding. Several different approaches to these and related goals are discussed here. A protocol for reconstructing muscle dimensions and bite force using biomechanically informative skull measurements and osteological proxies of muscle dimensions is described and applied to a case study of subfossil Malagasy lemurs. The results of this case study show that most subfossil lemurs emphasized the masseter and medial pterygoid muscles over the temporalis. This supports the inference that these extinct lemurs depended heavily on tough food like leaves. Exceptions include signals of hard-object feeding in Archaeolemur that vary between A. majori and A. edwardsi. Reconstructions of soft-tissue and function are important for understanding past ecological relationships. Even those based on well-supported osteological proxies from extant analogues have limitations for making precise inferences. Anat Rec, 301:343-362, 2018. © 2018 Wiley Periodicals, Inc.

Could Wading in Shallow Water Account for the Unique Shape of the &amp;lt;i&amp;gt;Australopithecus afarensis&amp;lt;/i&amp;gt; Pelvis?

A 3D Geometric Morphometric (GM) analysis of the shape of the pelvis and femur of various extinct hominids and extant humans and apes is described. Observed differences in shape are then discussed in the context of the wading hypothesis, a model of the evolution of hominin bipedalism that has rarely been seriously considered despite some compelling arguments in its favour. The general shape of the pelvis of Australopithecus afarensis is confirmed to be fundamentally different from both Homo and extant great apes, and not intermediate between them. Although it includes some human-like traits indicating a strong propensity to bipedalism, there are also sufficient differences to indicate that australopithecines probably exhibited a different type of bipedality to the relatively efficient striding gait associated with modern humans. An analysis of putative muscle lever arm ratios is described, which generated over 135,000 ratios in all. This data was then explored using the Pivot Table feature of Microsoft Excel. Succinct species summaries of broad lever arm groups, such as those pertaining to abduction compared to those pertaining to extension were generated. The results indicate that the australopithecine hip was more adapted, than modern humans or extant great apes, to adduction, abduction and rotation of the thigh during locomotion. It is argued that this apparent lateral biomechanical advantage complements the broad platypelloid shape as a putative adaptation to side-to-side wading. This adds further evidential weight to the wading hypothesis of bipedal origins in addition to the already compelling arguments from extant ape behaviour in shallow water and the favourable evidence of the paleohabitats of the earliest bipeds.

A key to high‐amplitude movement synthesis: the muscle lever arm

AbstractPulling actuators play an important role in biomechanical simulations. In most animals, muscles are the actuators exerting torques onto the joints. These torques highly depend on the muscle line of action or, in other words, muscle lever arms. Common methods focus either on single‐joint movements, on two‐dimensional problems, or on imitating physiological lever arms only in a small working range. However, especially in complex multibody simulations, where reduced descriptions of muscles as massless, visco‐elastic, active bands are used, a correct representation of lever arms is mandatory for a large range of joint angles for all degrees of freedom. To address these issues, we developed a new design and computational algorithm for modeling the path of linear pulling actuators. The method is based on finding the shortest muscle path while the actuator is lead through a small number of two‐dimensional shapes. It allows for multiple degree of freedom and high‐amplitude movements as well as combinations of both, ensuring reasonable lever arms at all possible joint configurations even for muscles spanning more than one joint. We applied this method to a multibody model of the human musculoskeletal system. (© 2017 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Myology of the forelimb of Majungasaurus crenatissimus (Theropoda, Abelisauridae) and the morphological consequences of extreme limb reduction.

Forelimb reduction occurred independently in multiple lineages of theropod dinosaurs. Although tyrannosaurs are renowned for their tiny, two-fingered forelimbs, the degree of their reduction in length is surpassed by abelisaurids, which possess an unusual morphology distinct from that of other theropods. The forelimbs of abelisaurids are short but robust and exhibit numerous crests, tubercles, and scars that allow for inferences of muscle attachment sites. Phylogenetically based reconstructions of the musculature were used in combination with close examination of the osteology in the Malagasy abelisaurid Majungasaurus to create detailed muscle maps of the forelimbs, and patterns of the muscular and bony morphology were compared with those of extant tetrapods with reduced or vestigial limbs. The lever arms of muscles crossing the glenohumeral joint are shortened relative to the basal condition, reducing the torque of these muscles but increasing the excursion of the humerus. Fusion of the antebrachial muscles into a set of flexors and extensors is common in other tetrapods and occurred to some extent in Majungasaurus. However, the presence of tubercles on the antebrachial and manual elements of abelisaurids indicates that many of the individual distal muscles acting on the wrist and digits were retained. Majungasaurus shows some signs of the advanced stages of forelimb reduction preceding limb loss, while also exhibiting features suggesting that the forelimb was not completely functionless. The conformation of abelisaurid forelimb musculature was unique among theropods and further emphasizes the unusual morphology of the forelimbs in this clade.

Model-Based Estimation of Ankle Joint Stiffness.

We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model’s inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements.

Adding Stiffness to the Foot Modulates Soleus Force-Velocity Behaviour during Human Walking.

Previous studies of human locomotion indicate that foot and ankle structures can interact in complex ways. The structure of the foot defines the input and output lever arms that influences the force-generating capacity of the ankle plantar flexors during push-off. At the same time, deformation of the foot may dissipate some of the mechanical energy generated by the plantar flexors during push-off. We investigated this foot-ankle interplay during walking by adding stiffness to the foot through shoes and insoles, and characterized the resulting changes in in vivo soleus muscle-tendon mechanics using ultrasonography. Added stiffness decreased energy dissipation at the foot (p < 0.001) and increased the gear ratio (i.e., ratio of ground reaction force and plantar flexor muscle lever arms) (p < 0.001). Added foot stiffness also altered soleus muscle behaviour, leading to greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001). Despite this shift in force-velocity behaviour, the whole-body metabolic cost during walking increased with added foot stiffness (p < 0.001). This increased metabolic cost is likely due to the added force demand on the plantar flexors, as walking on a more rigid foot/shoe surface compromises the plantar flexors’ mechanical advantage.

Increased Fracture Collapse after Intertrochanteric Fractures Treated by the Dynamic Hip Screw Adversely Affects Walking Ability but Not Survival.

In osteoporotic hip fractures, fracture collapse is deliberately allowed by commonly used implants to improve dynamic contact and healing. The muscle lever arm is, however, compromised by shortening. We evaluated a cohort of 361 patients with AO/OTA 31.A1 or 31.A2 intertrochanteric fracture treated by the dynamic hip screw (DHS) who had a minimal follow-up of 3 months and an average follow-up of 14.6 months and long term survival data. The amount of fracture collapse and shortening due to sliding of the DHS was determined at the latest follow-up and graded as minimal (<1 cm), moderate (1-2 cm), or severe (>2 cm). With increased severity of collapse, more patients were unable to maintain their premorbid walking function (minimal collapse = 34.2%, moderate = 33.3%, severe = 62.8%, and p = 0.028). Based on ordinal regression of risk factors, increased fracture collapse was significantly and independently related to increasing age (p = 0.037), female sex (p = 0.024), A2 fracture class (p = 0.010), increased operative duration (p = 0.011), poor reduction quality (p = 0.000), and suboptimal tip-apex distance of >25 mm (p = 0.050). Patients who had better outcome in terms of walking function were independently predicted by younger age (p = 0.036), higher MMSE marks (p = 0.000), higher MBI marks (p = 0.010), better premorbid walking status (p = 0.000), less fracture collapse (p = 0.011), and optimal lag screw position in centre-centre or centre-inferior position (p = 0.020). According to Kaplan-Meier analysis, fracture collapse had no association with mortality from 2.4 to 7.6 years after surgery. In conclusion, increased fracture collapse after fixation of geriatric intertrochanteric fractures adversely affected walking but not survival.