Enthesopathy formation in the humerus: Data from known age-at-death and known occupation skeletal collections

Entheseal variation and locomotor behavior during growth

Entheses are acknowledged as skeletal markers capable of revealing several biological and behavioral aspects of past individuals and populations. However, entheseal changes (ECs) of juvenile individuals have not yet been studied with a systematic approach. This contribution aims at investigating the morphological changes occurring at the femoral insertion of the gluteus maximus and tibial origin of the soleus muscles to highlight a potential link between the morphological features of those entheses and skeletal maturity in relation to sex, age, and locomotor developmental patterns. The sample consisted of 119 skeletons (age-at-death: 0-30 years) belonging to the Documented Human Skeletal Collection of the Certosa Cemetery (Bologna, Italy). The entheseal variation during the last stages of skeletal maturation in young adults was assessed using existing recording standards. A recording protocol for each enthesis was developed for immature individuals to subdivide the morphological variability into discrete categories. Univariate, bivariate, and multivariate statistical analyses were performed to investigate the variation of entheseal morphologies and measurements in relation to bone metrics, degree of epiphyseal closure, sex, age, and locomotor developmental patterns. A statistically significant relationship was observed between ECs morphological patterns and age for both entheses, while sexual differences were negligible. A relationship between ECs morphological pattern and locomotor milestones emerged only for the gluteus maximus. Even though further testing is needed on other documented skeletal collections, our protocol could be usefully applied in forensic and archaeological fields and serving as important reference for evolutionary investigations.

Entheseal surface (Sharpey's fiber insertion) alterations identify past trauma; bone base robusticity, level of routine activity

Sharpey's fiber alterations, referred to as entheseal reaction or enthesopathy, have long been considered an indicator of daily activities. Such semantic transformation seems to conflate processes which alter the characteristics of tendonous and ligamentous attachments to bone with the rugosity and extent of their base/footprint. Rather than reflecting normal activities, it is suggested that surface reactions are actually the response to the application of sudden or unconditioned repetitive stresses-analogous to stress fractures. Thus, they are distinct from enlargement of the base/footprint, the bone remodeling process responsible for the robusticity of the area to which the enthesis attaches, which is actually a measure of actual muscle activity. Surface reactions in attachment areas represent injury, be it mechanical stress fracture-equivalents or inflammation-derived. Bone base/footprint is the reaction of the enthesis to stresses of routine physical activities. The character of underlying bone supporting Sharpey's fibers may be augmented by applied stress, but there is neither a physiologic mechanism nor is there evidence for significant addition of Sharpey's fibers beyond ontogeny. Behavior is responsible for the physiologic response of robusticity; spiculation, pathology.

Muscle attachment sites and behavioral reconstruction: An experimental test of muscle-bone structural response to habitual activity

OBJECTIVE

Behavioral reconstruction from muscle attachment sites (entheses) is a common practice in anthropology. However, experimental evidence provides mixed support for the assumed association between enthesis size and shape with changes in habitual activity. In this study, a laboratory mouse model was used to experimentally test whether activity level and type alters muscle architecture and the underlying bone cross-sectional geometry of entheses in order to assess the underlying assumption that behavioral changes lead to quantifiable differences in both muscle and enthesis morphology.

MATERIALS AND METHODS

Female wild-type mice were separated into one control group and two experimentally increased activity groups (running, climbing) over an 11-week study period. At the start of the experiment, half of the mice were 4 weeks and half were 7 weeks of age. The postmortem deltoideus and biceps brachii muscles were measured for potential force production (physiological cross-sectional area) and potential muscle excursion (fiber length). Bone cross-sectional geometry variables were measured from microCT scans of the humerus and radius at the enthesis and non-enthesis regions of interest across activity groups.

RESULTS

Activity level and type altered potential force production and potential muscle excursion of both muscles in the younger cohort. We observed differences in cortical bone geometry in both the humerus enthesis and radius non-enthesis region driven exclusively among the younger wheel-running mice.

DISCUSSION

These results indicate that in addition to muscle architectural changes, bone structural properties at the enthesis do show an adaptive response to increased activity, such as running but only during earlier development. However, further research is required in order to apply these findings to the reconstruction of living behavior from anthropological specimens.

Morphometric Maps of Bilateral Asymmetry in the Human Humerus: An Implementation in the R Package Morphomap

In biological anthropology, parameters relating to cross-sectional geometry are calculated in paired long bones to evaluate the degree of lateralization of anatomy and, by inference, function. Here, we describe a novel approach, newly added to the morphomap R package, to assess the lateralization of the distribution of cortical bone along the entire diaphysis. The sample comprises paired long bones belonging to 51 individuals (10 females and 41 males) from The New Mexico Decedent Image Database with known biological profile, occupational and loading histories. Both males and females show a pattern of right lateralization. In addition, males are more lateralized than females, whereas there is not a significant association between lateralization with occupation and loading history. Body weight, height and long-bone length are the major factors driving the emergence of asymmetry in the humerus, while interestingly, the degree of lateralization decreases in the oldest individuals.

Estimation of adult age-at-death from entheseal robusticity: A test using an identified Italian skeletal collection

OBJECTIVES

The present study tests the effectiveness of entheseal robusticity (ER) as a potential predictor of adult age-at-death by applying multiple regression models to a large contemporary identified skeletal sample.

MATERIALS AND METHODS

ER was recorded for 23 bilateral postcranial entheses on 481 adult individuals (271 females and 210 males) from the Frassetto identified skeletal collection of Sassari (Italy), following the method of Mariotti et al. 2007. ER scores were used as predictors in multiple regression analyses with age as the dependent variable; the performance of the resulting models was tested through standard error of estimate, the correlation coefficient between predicted and documented age, and the percentage of correctly classified individuals.

RESULTS

ER show a higher correlation with age in females, resulting in more accurate estimates when compared with those obtained for males. Age-at-death is overestimated for male individuals under 45 years old and underestimated for older individuals. Regression models including a reduced set of ER sites result in better estimates compared with those using the complete set of variables.

DISCUSSION

Results suggest the potential usefulness of ER for the estimation of age, especially for female skeletal remains. If used with caution, ER may be a valid complement to existing methods for the reconstruction of the biological profile of skeletal remains of archaeological and forensic interest.

Osteoarthritis – a problematic skeletal trait in past human populations. Osteoarthritic changes vs. entheseal changes in the late medieval and early modern population form Łekno

According to medical knowledge, physical activity plays a role in osteoarthritic changes formation. The impact of occupation on osteoarthritic changes development in past human populations is not clear enough, causing problems with interpretation. The aim of the current study is to examine the relationship between osteoarthritis and entheseal changes. Skeletal material comes from the late medieval, early modern population from Łekno (Poland). The sample consists of 110 males and 56 females (adults only). Osteophytes, porosity and eburnation were analyzed in the shoulder, elbow, wrist, hip, knee, and ankle. Entheses on the humerus, radius, femur, and tibia were examined. Standard ranked categorical scoring systems were used for the osteoarthritic and entheseal changes examination.

Males with more developed osteophytes in the shoulder have more “muscular” upper limbs (higher values of muscle markers). Males with more developed osteophytes in the hip and knee are predicted to have more “muscular” lower limbs. Males with more developed osteoarthritis in the shoulder, wrist, hip, and knee exhibit more developed entheseal changes. Males with more developed entheses tend to yield more developed osteophytes (all joints taken together) and general osteoarthritis (all changes and all joints taken together). Females with more developed entheses have more developed osteoarthritis in the elbow, wrist, and hip. Individuals with more developed entheses have much more developed osteophytes. When all the three types of changes are taken together, more “muscular” females exhibit more developed osteoarthritis. The lack of uniformity of the results, wild discussions on the usage of entheses in activity patterns reconstruction and other limitations do not allow to draw unambiguous conclusions about the impact of physical activity on the osteoarthritis in past populations and further studies are needed.

Elevated activity levels do not influence extrinsic fiber attachment morphology on the surface of muscle-attachment sites

Extrinsic fibers (EFs) are a type of penetrating collagenous fiber, closely related to the periodontal ligament, which help anchor soft tissue into bone. These fibers are associated with muscle attachment sites (entheses). Their size and grouping patterns are thought to be indicative of the loading history of the muscle. EFs are of particular significance in anthropology as potential tools for the reconstruction of behavior from skeletal remains and, specifically, entheses. In this study, we used a mouse model to experimentally test how activity level alters the morphology of EF insertion sites on the bone surface of a fibrocartilaginous enthesis, the biceps brachii insertion. Further, we adapted surface metrological techniques from studies of dental wear to perform automated, quantitative and non-destructive analysis of bone surface histology. Our results show that experimentally increased activity had no significant effect on the quantity or density of EF insertions at the enthesis, nor on the size of those insertions. Although EF presence does indicate muscle attachment, activity did not have an observable effect on EF morphology.

Osteoarthritis: A problematic disease in past human populations. A dependence between entheseal changes, body size, age, sex, and osteoarthritic changes development

Osteoarthritis is a problematic trait in terms of etiology and interpretation in past human populations. The relationships between osteoarthritic changes (osteophytes, porosity, and eburnation) and entheseal changes, body mass, stature, bone massiveness, sex, and age on the basis of skeletal material from Łekno (Poland) are analyzed here. Entheses were the strongest contributor to the prediction of osteophyte expression and when all types of changes and all joints were taken together. Stature demonstrates a negative dependence on porosity. When each joint was analyzed separately, entheses were the strongest contributor to the prediction of arthritis expression in the wrist and hip. Age was the strongest contributor to the prediction of arthritis expression in the elbow. Body mass, stature, bone massiveness, and sex had no effect on osteoarthritic changes in any of the examined joints. The results of the present study suggest an important dependence between entheses and osteoarthritic changes. Other factors had little to no effect on differences in OA severity. These results do not dispel all doubts but enrich knowledge about the effect of etiological factors on osteoarthritic change formation. This knowledge is essential for proper, reliable interpretation of osteoarthritic changes in the context of past human biology, ecology, and behavior.

"The dead shall be raised": Multidisciplinary analysis of human skeletons reveals complexity in 19th century immigrant socioeconomic history and identity in New Haven, Connecticut

In July 2011, renovations to Yale-New Haven Hospital inadvertently exposed the cemetery of Christ Church, New Haven, Connecticut's first Catholic cemetery. While this cemetery was active between 1833 and 1851, both the church and its cemetery disappeared from public records, making the discovery serendipitous. Four relatively well-preserved adult skeletons were recovered with few artifacts. All four individuals show indicators of manual labor, health and disease stressors, and dental health issues. Two show indicators of trauma, with the possibility of judicial hanging in one individual. Musculoskeletal markings are consistent with physical stress, and two individuals have arthritic indicators of repetitive movement/specialized activities. Radiographic analyses show osteopenia, healed trauma, and other pathologies in several individuals. Dental calculus analysis did not identify any tuberculosis indicators, despite osteological markers. Isotopic analyses of teeth indicate that all four were likely recent immigrants to the Northeastern United States. Nuclear and mitochondrial DNA were recovered from three individuals, and these analyses identified ancestry, hair/eye color, and relatedness. Genetic and isotopic results upended our initial ancestry assessment based on burial context alone. These individuals provide biocultural evidence of New Haven's Industrial Revolution and the plasticity of ethnic and religious identity in the immigrant experience. Their recovery and the multifaceted analyses described here illuminate a previously undescribed part of the city's rich history. The collective expertise of biological, geochemical, archaeological, and historical researchers interprets socioeconomic and cultural identity better than any one could alone. Our combined efforts changed our initial assumptions of a poor urban Catholic cemetery's membership, and provide a template for future discoveries and analyses.

The mechanical hypothesis of septal aperture formation tested in an early medieval population from Ostrów Lednicki (Poland)

The aetiology of septal aperture formation is still an open question. The influence of bone robusticity, osteoarthritis, osteoporosis, and the size and shape of ulnar processes has been discussed. Some researchers have shown that weaker muscles lead to greater joint hypermobility, the impingement of ulnar processes on the humeral lamina, and, consequently, septal aperture formation. Assuming this theory is correct, the question is whether flexion or extension or both play a role in septal lamina perforation. The aim of the study was to examine the mechanical hypothesis of septal aperture formation in samples of skeletal material derived from an early medieval cemetery in Ostrów Lednicki (Poland). A total of 136 pairs of bones (humeri and ulnae) were examined. Septal aperture was scored as present or absent. Entheseal changes in ulna were used as markers of activity patterns, especially involving elbow extension and flexion. Entheseal changes were assessed based on a three-point rating scale. A significant negative correlation between septal aperture and triceps muscles was noted in right bones in females (τ = -0.331) and in both sexes combined (τ = -0.322). The relationship between septal aperture and the brachialis muscle was positive but non-significant. This means that looser triceps lead to greater looseness of the elbow, greater protrusion of the olecranon process, and consequent septal aperture formation. Different results were obtained for the brachialis, which may suggest that forearm flexion does not significantly affect septal lamina perforation.

Investigation of a Medieval Pilgrim Burial Excavated from the Leprosarium of St Mary Magdalen Winchester, UK

We have examined the remains of a Pilgrim burial from St Mary Magdalen, Winchester. The individual was a young adult male, aged around 18–25 years at the time of death. Radiocarbon dating showed the remains dated to the late 11^th–early 12^th centuries, a time when pilgrimages were at their height in Europe. Several lines of evidence in connection with the burial suggested this was an individual of some means and prestige. Although buried within the leprosarium cemetery, the skeleton showed only minimal skeletal evidence for leprosy, which was confined to the bones of the feet and legs. Nonetheless, molecular testing of several skeletal elements, including uninvolved bones all showed robust evidence of DNA from Mycobacterium leprae, consistent with the lepromatous or multibacillary form of the disease. We infer that in life, this individual almost certainly suffered with multiple soft tissue lesions. Genotyping of the M.leprae strain showed this belonged to the 2F lineage, today associated with cases from South-Central and Western Asia. During osteological examination it was noted that the cranium and facial features displayed atypical morphology for northern European populations. Subsequently, geochemical isotopic analyses carried out on tooth enamel indicated that this individual was indeed not local to the Winchester region, although it was not possible to be more specific about their geographic origin.

This multidisciplinary research article, involving biomolecular analysis, osteology, strontium and oxygen isotopic analyses and archaeology, examines the remains of a Pilgrim burial excavated from the medieval leprosy hospital of St Mary Magdalen, Winchester, UK. Radiocarbon dating showed the remains dated to the late 11^th–early 12^th centuries, a time when pilgrimages were at their height in Europe. The leprosarium at Winchester is one of the earliest excavated examples from Western Europe and has been the subject of a series of recent academic papers. The site is remarkable for the high number of burials displaying skeletal lesions characteristic of leprosy (86%) and the state of preservation of biomolecular markers of the disease, including mycolipids and DNA. Genotyping of the M.leprae strain showed this belonged to the 2F lineage, today associated with cases from South-Central and Western Asia. Several aspects of the burial and dietary isotope analysis indicated this was an individual of some prestige and means; an unusual cranial morphology pointed to possible origin outside of the British Isles. Strontium and oxygen isotopic analyses confirmed he was not local to the Winchester area but were not able to pinpoint his precise origins. Overall these findings confirm the benefits of a multidisciplinary approach which allows investigation of the wider relationship between leprosy, medieval pilgrimage and M.leprae transmission.

Morphology of muscle attachment sites in the modern human hand does not reflect muscle architecture

Muscle attachment sites (entheses) on dry bones are regularly used by paleontologists to infer soft tissue anatomy and to reconstruct behaviors of extinct organisms. This method is commonly applied to fossil hominin hand bones to assess their abilities to participate in Paleolithic stone tool behaviors. Little is known, however, about how or even whether muscle anatomy and activity regimes influence the morphologies of their entheses, especially in the hand. Using the opponens muscles from a sample of modern humans, we tested the hypothesis that aspects of hand muscle architecture that are known to be influenced by behavior correlate with the size and shape of their associated entheses. Results show no consistent relationships between these behaviorally-influenced aspects of muscle architecture and entheseal morphology. Consequently, it is likely premature to infer patterns of behavior, such as stone tool making in fossil hominins, from these same entheses.

Locomotor activity influences muscle architecture and bone growth but not muscle attachment site morphology

The ability to make behavioural inferences from skeletal remains is critical to understanding the lifestyles and activities of past human populations and extinct animals. Muscle attachment site (enthesis) morphology has long been assumed to reflect muscle strength and activity during life, but little experimental evidence exists to directly link activity patterns with muscle development and the morphology of their attachments to the skeleton. We used a mouse model to experimentally test how the level and type of activity influences forelimb muscle architecture of spinodeltoideus, acromiodeltoideus, and superficial pectoralis, bone growth rate and gross morphology of their insertion sites. Over an 11-week period, we collected data on activity levels in one control group and two experimental activity groups (running, climbing) of female wild-type mice. Our results show that both activity type and level increased bone growth rates influenced muscle architecture, including differences in potential muscular excursion (fibre length) and potential force production (physiological cross-sectional area). However, despite significant influences on muscle architecture and bone development, activity had no observable effect on enthesis morphology. These results suggest that the gross morphology of entheses is less reliable than internal bone structure for making inferences about an individual's past behaviour.

The influence of life history and sexual dimorphism on entheseal changes in modern humans and African great apes

Entheseal changes have been widely studied with regard to their correlation to biomechanical stress and their usefulness for biocultural reconstructions. However, anthropological and medical studies have demonstrated the marked influence of both age and sex on the development of these features. Studies of entheseal changes are mostly aimed in testing functional hypotheses and are mostly focused on modern humans, with few data available for non-human primates. The lack of comparative studies on the effect of age and sex on entheseal changes represent a gap in our understanding of the evolutionary basis of both development and degeneration of the human musculoskeletal system. The aim of the present work is to compare age trajectories and patterns of sexual dimorphism in entheseal changes between modern humans and African great apes. To this end we analyzed 23 postcranial entheses in a human contemporary identified skeletal collection (N = 484) and compared the results with those obtained from the analysis of Pan (N = 50) and Gorilla (N = 47) skeletal specimens. Results highlight taxon-specific age trajectories possibly linked to differences in life history schedules and phyletic relationships. Robusticity trajectories separate Pan and modern humans from Gorilla, whereas enthesopathic patterns are unique in modern humans and possibly linked to their extended potential lifespan. Comparisons between sexes evidence a decreasing dimorphism in robusticity from Gorilla, to modern humans to Pan, which is likely linked to the role played by size, lifespan and physical activity on robusticity development. The present study confirms previous hypotheses on the possible relevance of EC in the study of life history, pointing moreover to their usefulness in evolutionary studies.