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A three-dimensional (3D) understanding of muscle attachment footprints became increasingly relevant for musculoskeletal modeling. The established method to project attachments as points ignores patient-specific individuality. Research focuses on investigating certain muscle groups rather than comprehensively studying all muscles spanning a joint. Therefore, we present a reliable method to study several muscle attachments in order to reconstruct the attachment sites in 3D based on CT imaging for future applications in musculoskeletal modeling. For the present feasibility study, 23 knee-related muscle attachments were CT-scanned postmortem from four nonadipose male specimens. For this, the specific muscle attachments were dissected and marked with a barium sulfate containing paint (60 g BaSO4 in 30 mL water and 10 mL acrylic paint). Subsequently, bone geometries and muscle attachments were reconstructed and evaluated from CT datasets. Bone morphology and footprint variations were studied. Exemplarily, variations were high for pes anserinus insertions (mean 56%) and the origins of M. biceps femoris (mean 54%). In contrast, the origins of the vastus muscles as well as the insertion of the Achilles tendon showed low variation (mean 9% and 13%, respectively). Most attachment sites showed variation exceeding the individuality of bone morphology. In summary, the present data were consistent with the few published studies of specific muscle footprints. Our data shed light on the high variability of muscle attachments, which need to be addressed when studying muscle forces and movements through musculoskeletal modeling. This is the first step to achieving a more profound understanding of muscle morphology to be utilized in numerical simulations. [ABSTRACT FROM AUTHOR]

Objectives: Sex‐based occupational variability constitutes a fundamental component of human behavior and a major focus of research focusing on biocultural evolution. However, the reliability of reconstructing physical activity in past women is often compromised by the lack of female skeletal collections with adequately documented lifetime occupations, domestic living conditions, medical records, and socioeconomic status. Here, we attempt to reconstruct habitual manual activity in a skeletal sample of early industrial women with uniquely archived life histories. Materials and Methods: We rely on the application of our "Validated Entheses‐based Reconstruction of Activity" method on the hand skeletons of 38 extensively documented individuals from the Basel‐Spitalfriedhof collection. Our comparisons also include 40 documented males from the same collection. Results: As expected, we found evidence of increased entheseal variability among women sharing the same unspecialized occupation (maids and factory workers). Moreover, certain entheseal patterns were almost exclusive to the men involved in occupations not associated with the female sex (mainly construction workers). Importantly, all six women known to have practiced more specific occupational activities (e.g., seamstresses) showed distinctive entheseal patterns, seemingly associated with more demanding physical practices. This within‐sex variation was not correlated with differences in biological age, estimated body size, socioeconomic status, relatedness, or the presence of reported children. Discussion: Our findings directly reflect the rich historical sources on the working lives of low‐status women in early industrial Basel. These results highlight the high potential value of our documented sample as a reference basis for reconstructing the division of labor in bioarchaeological contexts. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) understanding of muscle attachment footprints became increasingly relevant for musculoskeletal modeling. The established method to project attachments as points ignores patient-specific individuality. Research focuses on investigating certain muscle groups rather than comprehensively studying all muscles spanning a joint. Therefore, we present a reliable method to study several muscle attachments in order to reconstruct the attachment sites in 3D based on CT imaging for future applications in musculoskeletal modeling. For the present feasibility study, 23 knee-related muscle attachments were CT-scanned postmortem from four nonadipose male specimens. For this, the specific muscle attachments were dissected and marked with a barium sulfate containing paint (60 g BaSO4 in 30 mL water and 10 mL acrylic paint). Subsequently, bone geometries and muscle attachments were reconstructed and evaluated from CT datasets. Bone morphology and footprint variations were studied. Exemplarily, variations were high for pes anserinus insertions (mean 56%) and the origins of M. biceps femoris (mean 54%). In contrast, the origins of the vastus muscles as well as the insertion of the Achilles tendon showed low variation (mean 9% and 13%, respectively). Most attachment sites showed variation exceeding the individuality of bone morphology. In summary, the present data were consistent with the few published studies of specific muscle footprints. Our data shed light on the high variability of muscle attachments, which need to be addressed when studying muscle forces and movements through musculoskeletal modeling. This is the first step to achieving a more profound understanding of muscle morphology to be utilized in numerical simulations.

Computational musculoskeletal modeling represents a valuable approach to examining biological systems in physical anthropology. Probabilistic modeling builds on computational musculoskeletal models by associating mathematical distributions of specific musculoskeletal features within known ranges of biological variability with functional outcomes. The purpose of this study was to determine if overlap in rotator cuff muscle force predictions would occur between species during the performance of an evolutionarily relevant horizontal bimanual arm suspension task. This necessitated creating novel probabilistic models of the human and chimpanzee glenohumeral joint through augmentation of previously published deterministic models. Glenohumeral musculoskeletal features of anthropological interest were probabilistically modeled to produce distributions of predicted human and chimpanzee rotator cuff muscle force that were representative of the specific anatomical manipulations. Musculoskeletal features modeled probabilistically included rotator cuff origins and deltoid insertion, glenoid inclination, and joint stability. Predicted human rotator cuff muscle force distributions were mostly limited to alternating between infraspinatus and teres minor, with both 100% and 0% muscle force predicted for both muscles. The chimpanzee model predicted low‐to‐moderate muscle force across all rotator cuff muscles. Rotator cuff muscle force predictions were most sensitive to changes of muscle origins and insertions. Results indicate that functional rotator cuff overlap is unlikely between chimpanzees and humans without greater modifications of the glenohumeral musculoskeletal phenotypes. The results also highlight the low efficacy of the human upper extremity in overhead, weight‐bearing tasks, and propensity for rotator cuff injury. [ABSTRACT FROM AUTHOR]

Abstract Background Clavicle fractures are common injuries, especially in young, active individuals. Operative treatment is recommended for completely displaced clavicle shaft fractures, and plate fixation is stronger than the use of intramedullary nails. Few studies have reported on iatrogenic injuries to the muscle attached to the clavicle during fracture surgery. The aim of this study was to clarify the area of the insertion sites of muscles attached to the clavicle in Japanese cadavers using gross anatomy and three-dimensional (3D) analysis. We also aimed to compare the effects of anterior plate templating and superior plate templating on clavicle shaft fractures using 3D images. Methods Thirty-eight clavicles from Japanese cadavers were analyzed. We removed all clavicles to identify the insertion sites and measured the size of the insertion area of each muscle. Three-dimensional templating was performed on both the superior and anterior plates of the clavicle using data obtained from computed tomography. The areas covered by these plates on the muscles attached to the clavicle were compared. Histological examination was performed on four randomly selected specimens. Results The sternocleidomastoid muscle was attached proximally and superiorly; the trapezius muscle was attached posteriorly and partly superiorly; and the pectoralis major muscle and deltoid muscles were attached anteriorly and partially superiorly. The non-attachment area was located mainly in the posterosuperior part of the clavicle. It was difficult to distinguish the borders of the periosteum and pectoralis major muscles. The anterior plate covered a significantly broader area (mean 6.94 ± 1.36 cm2) of the muscles attached to the clavicle than did the superior plate (mean 4.11 ± 1.52 cm2) (p

Background: Clavicle fractures are common injuries, especially in young, active individuals. Operative treatment is recommended for completely displaced clavicle shaft fractures, and plate fixation is stronger than the use of intramedullary nails. Few studies have reported on iatrogenic injuries to the muscle attached to the clavicle during fracture surgery. The aim of this study was to clarify the area of the insertion sites of muscles attached to the clavicle in Japanese cadavers using gross anatomy and three-dimensional (3D) analysis. We also aimed to compare the effects of anterior plate templating and superior plate templating on clavicle shaft fractures using 3D images. Methods: Thirty-eight clavicles from Japanese cadavers were analyzed. We removed all clavicles to identify the insertion sites and measured the size of the insertion area of each muscle. Three-dimensional templating was performed on both the superior and anterior plates of the clavicle using data obtained from computed tomography. The areas covered by these plates on the muscles attached to the clavicle were compared. Histological examination was performed on four randomly selected specimens. Results: The sternocleidomastoid muscle was attached proximally and superiorly; the trapezius muscle was attached posteriorly and partly superiorly; and the pectoralis major muscle and deltoid muscles were attached anteriorly and partially superiorly. The non-attachment area was located mainly in the posterosuperior part of the clavicle. It was difficult to distinguish the borders of the periosteum and pectoralis major muscles. The anterior plate covered a significantly broader area (mean 6.94 ± 1.36 cm2) of the muscles attached to the clavicle than did the superior plate (mean 4.11 ± 1.52 cm2) (p < 0.0001). On microscopy, these muscles were inserted directly into the periosteum. Conclusion: Most of the pectoralis major and deltoid muscles were attached anteriorly. The non-attachment area was located mainly from the superior to posterior part of the clavicle midshaft. Both macroscopically and microscopically, the boundaries between the periosteum and these muscles were difficult to demarcate. The anterior plate covered a significantly broader area of the muscles attached to the clavicle than that by the superior plate. [ABSTRACT FROM AUTHOR]

For reconstructing physical activity in the past, the surfaces of bones where muscles and ligaments attach, “entheses,” are routinely studied. Previous research has introduced an experimentally validated virtual approach for reconstructing habitual activity based on entheses. The present study relies on this virtual method to further investigate the effects of various biological factors on entheses, including variation by ancestry. Our skeletal sample includes 39 individuals from the well-preserved Pretoria Bone Collection in South Africa. Although the size of the sample is limited, all selected individuals present excellently preserved left- and right-hand bones. Moreover, all individuals are reliably documented for sex, biological age, and ancestry (i.e., African or European origin). Multivariate analyses were run on both raw and size-adjusted hand entheseal three-dimensional measurements. Our findings showed that, after size adjustment, entheseal multivariate patterns did not significantly vary by sex, biological age, or estimated body mass. However, a significant (p-value = 0.01) variation was found between individuals of different ancestries in only the right-hand side of our South African skeletal sample. The observed entheseal patterns were consistent with the habitual performance of power grasping in individuals of African origin, while our small sample’s European individuals showed distinctive indications of precision grasping behaviors. This pilot research provided important new insights into potentially activity-induced differences between population samples from South Africa, supporting the value of the applied protocol in reconstructing aspects of past human lifestyles. In the future, the functional interpretations of this study on interpopulation variation may be validated using increased sample sizes and individuals with long-term occupational documentation. [ABSTRACT FROM AUTHOR]

Objectives: Cuncaicha, a rockshelter site in the southern Peruvian Andes, has yielded archaeological evidence for human occupation at high elevation (4,480 masl) during the Terminal Pleistocene (12,500–11,200 cal BP), Early Holocene (9,500–9,000 cal BP), and later periods. One of the excavated human burials (Feature 15‐06), corresponding to a middle‐aged female dated to ~8,500 cal BP, exhibits skeletal osteoarthritic lesions previously proposed to reflect habitual loading and specialized crafting labor. Three small tools found in association with this burial are hypothesized to be associated with precise manual dexterity. Materials and methods: Here, we tested this functional hypothesis through the application of a novel multivariate methodology for the three‐dimensional analysis of muscle attachment surfaces (entheses). This original approach has been recently validated on both lifelong‐documented anthropological samples as well as experimental studies in nonhuman laboratory samples. Additionally, we analyzed the three‐dimensional entheseal shape and resulting moment arms for muscle opponens pollicis. Results: Results show that Cuncaicha individual 15‐06 shows a distinctive entheseal pattern associated with habitual precision grasping via thumb‐index finger coordination, which is shared exclusively with documented long‐term precision workers from recent historical collections. The separate geometric morphometric analysis revealed that the individual's opponens pollicis enthesis presents a highly projecting morphology, which was found to strongly correlate with long joint moment arms (a fundamental component of force‐producing capacity), closely resembling the form of Paleolithic hunter‐gatherers from diverse geo‐chronological contexts of Eurasia and North Africa. Discussion Overall, our findings provide the first biocultural evidence to confirm that the lifestyle of some of the earliest Andean inhabitants relied on habitual and forceful precision grasping tasks. [ABSTRACT FROM AUTHOR]

Seismic signalling in the form of hind foot drumming plays an integral role in the communication of several species of African mole‐rats (Bathyergidae). To produce these vibrational signals, alternating hind limbs strike the ground repetitively at high speeds by flexion and extension of the hip and knee. This descriptive study aimed to determine whether anatomical differences in hind limb osteology and/or musculature between drumming and non‐drumming species of three Bathyergidae species could be detected. Formalin‐fixed left and right hind limbs of 24 animals (N = 48) consisting of three species (n = 16 each) of two drumming species, Georychus capensis and Bathyergus suillus, and one non‐drumming species, Cryptomys hottentotus natalensis, were dissected to determine the origins and insertions of individual muscles. After dissection, all soft tissue was removed by maceration. Hind limb bones, including the pelvis, were photographed, and the exact muscle origin and insertion points were electronically mapped onto the images using imaging software. On lateral view, the acetabular position was parallel to the sacrum in G. capensis, while being more ventral in position in the other two species. The shape of the femur head was spherical and the neck defined in all species. The distal shaft of the femur was gracile and the epicondyles were robust and prominent in the non‐drumming C. h. natalensis compared with the drumming species. Shallow and relatively wide patellar grooves were observed in all three species. In the two drumming species, m. gracilis was single, whereas it was double in C. h. natalensis. In all three species, m. tensor fasciae latae was absent. The more dorsal positioning of the acetabulum in G. capensis may be needed to increase the stability of the spine and allow for more force to be exerted on the pelvis during drumming. It is unlikely that m. gracilis plays a role in drumming, as the singularity or doubling thereof is variable among rodents. It is additionally postulated that m. gluteus superficialis has taken the hip rotator role of m. tensor fasciae latae as it partially inserted onto the lateral fascia of the thigh. The more robust ilia, femoral shafts and tibiae observed in the two drumming species studied here are possible adaptations for hind foot drumming, as robust bones are able to withstand the additional biomechanical loading during drumming. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The purpose of this study was to put forth a precise landmark‐based technique for reconstructing the three‐dimensional shape of human entheseal surfaces, to investigate whether the shape of human entheses is related to their size. The effects of age‐at‐death and bone length on entheseal shapes were also assessed. Materials and methods: The sample comprised high‐definition three‐dimensional models of three right hand entheseal surfaces, which correspond to 45 male adult individuals of known age. For each enthesis, a particular landmark configuration was introduced, whose precision was tested both within and between observers. The effect of three‐dimensional size, age‐at‐death, and bone length on shape was investigated through shape regression. Results: The method presented high intra‐observer and inter‐observer repeatability. All entheses showed significant allometry, with the area of opponens pollicis demonstrating the most substantial relationship. This was particularly due to variation related to its proximal elongated ridge. The effect of age‐at‐death and bone length on entheses was limited. Discussion: The introduced methodology can set a reliable basis for further research on the factors affecting entheseal shape. Using both size and shape, variables can provide further information on entheseal variation and its biomechanical implications. The low entheseal variation by age verifies that specimens under 50 years of age are not substantially affected by age‐related changes. The lack of correlation between entheseal shape and bone length or age implies that other factors may regulate entheseal surfaces. Future research should focus on multivariate shape patterns among entheses and their association with occupation. [ABSTRACT FROM AUTHOR]

To generate subject-specific musculoskeletal models for clinical use, the location of muscle attachment sites needs to be estimated with accurate, fast and preferably automated tools. For this purpose, an automatic method was used to estimate the muscle attachment sites of the lower extremity, based on the assumption of a relation between the bone geometry and the location of muscle attachment sites. The aim of this study was to evaluate the accuracy of this morphing based method. Two cadaver dissections were performed to measure the contours of 72 muscle attachment sites on the pelvis, femur, tibia and calcaneus. The geometry of the bones including the muscle attachment sites was morphed from one cadaver to the other and vice versa. For 69% of the muscle attachment sites, the mean distance between the measured and morphed muscle attachment sites was smaller than 15 mm. Furthermore, the muscle attachment sites that had relatively large distances had shown low sensitivity to these deviations. Therefore, this morphing based method is a promising tool for estimating subject-specific muscle attachment sites in the lower extremity in a fast and automated manner. [ABSTRACT FROM AUTHOR]

For individualization of a biomechanical model, it is necessary to estimate the muscle attachments of the person to whom it is to be adapted. One of the methods to estimate muscle attachments is to use model transformations to transform a model with known muscle attachments to the bones of a person. We hypothesize that the location and shape of muscle attachment sites correlate with the shape of the bones they are attached to. If this hypothesis holds, it is possible to predict the location of muscle attachments when the shape of the bones is known. To validate this hypothesis, geometric models of three sets of shoulder bones were built. These models consist of 3-D surface models of the scapula, clavicle, and humerus, with the muscle attachment contours connected to them. By means of geometric transformations, the models were transformed, so the muscle attachments of the different data sets could be compared. Using these techniques, 50 per cent of the muscle attachment contours could be predicted with high accuracy. The muscle attachment contours that could not be predicted were all influenced by measurement errors. For 30 per cent of the muscle attachment contours, it was not possible to distinguish the interindividual differences from the inaccuracies of the method used. From this study, we concluded that most muscle attachment contours can be predicted by means of geometric models of the bones. [Copyright &y& Elsevier]

A class of recessive lethal zebrafish mutations has been identified in which normal skeletal muscle differentiation is followed by a tissue-specific degeneration that is reminiscent of the human muscular dystrophies. Here, we show that one of these mutations, sapje, disrupts the zebrafish orthologue of the X-linked human Duchenne muscular dystrophy (DMD) gene. Mutations in this locus cause Duchenne or Becker muscular dystrophies in human patients and are thought to result in a dystrophic pathology through disconnecting the cytoskeleton from the extracellular matrix in skeletal muscle by reducing the level of dystrophin protein at the sarcolemma. This is thought to allow tearing of this membrane, which in turn leads to cell death. Surprisingly, we have found that the progressive muscle degeneration phenotype of sapje mutant zebrafish embryos is caused by the failure of embryonic muscle end attachments. Although a role for dystrophin in maintaining vertebrate myotendinous junctions (MTJs) has been postulated previously and MTJ structural abnormalities have been identified in the Dystrophin-deficient mdx mouse model, in vivo evidence of pathology based on muscle attachment failure has thus far been lacking. This zebrafish mutation may therefore provide a model for a novel pathological mechanism of Duchenne muscular dystrophy and other muscle diseases. [ABSTRACT FROM AUTHOR]

The extent to which neighboring muscles and the fascia contribute to the formation of the supraspinous and interspinous ligaments is not clear from the literature. The purpose of this investigation is to examine the midline attachments of tendons and the posterior layer of thoracolumbar fascia in order to determine their respective contributions to the formation of these ligaments throughout the thoracolumbar spine. Study of the dense connective tissue organization in the posterior ligamentous system was carried out on two cadavers serially sectioned into thin (2.5-mm) epoxy resin plastinated slices. Additional observations were taken from a gross anatomical study of the midline anatomy in two adult cadavers. The results show that the spinal attachments of trapezius, rhomboideus major and splenius cervicis combine with the deep fascia to form the supraspinous ligament in the upper thoracic spine. The posterior layer of the thoracolumbar fascia makes a major contribution to the supraspinous and interspinous ligaments in the lower thoracic spine. In addition to the posterior layer of thoracolumbar fascia, longissimus thoracis and multifidus combine to form the lumbar supraspinous and interspinous ligaments. Their spinal attachments produce a system of dense connective tissue with marked regional variation in fiber orientation and arrangement. The findings support the description of the supraspinous and interspinous ligaments as structures formed by both muscle tendons and aponeuroses along the length of the thoracic and lumbar spine, with regional differences in their connective tissue architecture. [ABSTRACT FROM AUTHOR]

Systematic tool production and use is one of humanity's defining characteristics, possibly originating as early as >3 million years ago. 1–3 Although heightened manual dexterity is considered to be intrinsically intertwined with tool use and manufacture, and critical for human evolution, its role in the emergence of early culture remains unclear. Most previous research on this question exclusively relied on direct morphological comparisons between early hominin and modern human skeletal elements, assuming that the degree of a species' dexterity depends on its similarity with the modern human form. Here, we develop a new approach to investigate the efficiency of thumb opposition, a fundamental component of manual dexterity, in several species of fossil hominins. Our work for the first time takes into account soft tissue as well as bone anatomy, integrating virtual modeling of musculus opponens pollicis and its interaction with three-dimensional bone shape form. Results indicate that a fundamental aspect of efficient thumb opposition appeared approximately 2 million years ago, possibly associated with our own genus Homo , and did not characterize Australopithecus , the earliest proposed stone tool maker. This was true also of the late Australopithecus species, Australopithecus sediba , previously found to exhibit human-like thumb proportions. In contrast, later Homo species, including the small-brained H omo naledi , show high levels of thumb opposition dexterity, highlighting the increasing importance of cultural processes and manual dexterity in later human evolution. • Increased thumb opposition efficiency was present about 2 million years ago • This evolutionary advantage was less pronounced in Australopithecus • This dexterity is shared with all recent hominins, including Homo naledi Karakostis et al. integrate virtual muscle modeling with three-dimensional bone shape analysis to investigate biomechanical efficiency for thumb opposition in the fossil human record. They report the earliest evidence of increased manual dexterity, a vital component of human-like tool use, in thumb bones dated to about 2 million years ago. [ABSTRACT FROM AUTHOR]