Fifth metatarsal morphology does not predict presence or absence of fibularis tertius muscle in hominids

Quantifying the relationship between bone and soft tissue measures within the rhesus macaques of Cayo Santiago

OBJECTIVES

Interpretations of the primate and human fossil record often rely on the estimation of somatic dimensions from bony measures. Both somatic and skeletal variation have been used to assess how primates respond to environmental change. However, it is unclear how well skeletal variation matches and predicts soft tissue. Here, we empirically test the relationship between tissues by comparing somatic and skeletal measures using paired measures of pre- and post-mortem rhesus macaques from Cayo Santiago, Puerto Rico.

MATERIALS AND METHODS

Somatic measurements were matched with skeletal dimensions from 105 rhesus macaque individuals to investigate paired signals of variation (i.e., coefficients of variation, sexual dimorphism) and bivariate codependence (reduced major axis regression) in measures of: (1) limb length; (2) joint breadth; and (3) limb circumference. Predictive models for the estimation of soft tissue dimensions from skeletons were built from Ordinary Least Squares regressions.

RESULTS

Somatic and skeletal measurements showed statistically equivalent coefficients of variation and sexual dimorphism as well as high epiphyses-present ordinary least square (OLS) correlations in limb lengths (R2 >0.78, 0.82), joint breadths (R2 >0.74, 0.83) and, to a lesser extent, limb circumference (R2 >0.53, 0.68).

CONCLUSION

Skeletal measurements are good substitutions for somatic values based on population signals of variation. OLS regressions indicate that skeletal correlates are highly predictive of somatic dimensions. The protocols and regression equations established here provide a basis for reliable reconstruction of somatic dimension from catarrhine fossils and validate our ability to compare or combine results of studies based on population data of either hard or soft tissue proxies.

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.

Peroneus tertius revisited: The morphological variability of the bifurcated peroneus tertius insertion - An anatomical study

BACKGROUND

The peroneus tertius muscle (PT) is one of the extensor muscles of the lower leg, often described as a variable separation from the extensor digitorum longus muscle (EDL). According to literature it has six different types of insertion, one of them (Olewnik Type IV) having two tendons inserting to the fifth metatarsal bone (FMTB). Morphometric data about this type of insertion is sparse, especially the relation between the two tendons, albeit the PT is suspected to contribute to stress fractures of the FMTB. Therefore, we examined this type of insertion to give detailed information on the tendons, the insertion points and the respective relations.

METHODS

We examined 27 lower extremities of embalmed human bodies (12 paired, 15 single sided; 12 right and 15 left) with a distinguishable PT with two tendons inserting to the FMTB (Olewnik IV). The specimens were obtained of an undergrad dissection program, which in turn obtained them from a body donation program. After dissection of the PT and photo documentation in situ, resection and measurement of morphological properties of the tendons were performed with the PT attached to the fifth metatarsal bone.

RESULTS

Results of the respective measurements yielded a wide range of variation, especially in the insertion point of the anterior tendon on the fifth metatarsal and the relation between the two tendons, but with no significant difference between sides or sex, except for the length of the posterior tendon between sex. The distance between the base of the FMTB and posterior tendon varies from 0 to 9 mm, with one outlier at 24 mm (mean = 3.9 ± 4.8 mm), the distance between the insertions from 0 to 15 mm (mean = 4.7 ± 4.7 mm), resulting in how far of the FMTB the anterior tendon reaches varying from 17 to 60 mm (mean = 39.6 ± 11.5 mm) or 22-98% (mean = 64 ± 19%).

CONCLUSION

Our findings give a detailed overview of the morphological features the PTT can have, when attached with two tendons to the FMTB. Especially the varying relationship between those two insertions and varying point of the anterior insertion are of interest, as they might support its complex role in the occurrence of fractures of the fifth metatarsal by providing different amounts of torsional stress and its tendons can be used as tendon-grafts.

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.

Peroneus Tertius Syndrome: A Rare Cause of Anterolateral Ankle and Rearfoot Pain

There is limited literature describing anterolateral ankle or rearfoot pain associated with the peroneus tertius tendon. The purpose of this study is to define peroneus tertius syndrome, in which the peroneus tertius tendon causes catching or locking over the anterolateral ankle or rearfoot with accompanying pain. We present a retrospective case series involving 4 patients diagnosed with peroneus tertius syndrome, discuss symptoms for clinical diagnosis, review radiographic imaging, and outline a minimally invasive operative technique for resection of the symptomatic tendon. Furthermore, we sought to evaluate postoperative outcomes and satisfaction scores after surgical management. All patients experienced resolution of symptoms by the fourth postoperative week. There was a statistically significant improvement in visual analog scale scores (average ± SD, 7.75 ± 0.96 preoperative to 0.75 ± 1.19 postoperative) (p = .002). Overall patient satisfaction was 100%, with improved functional status and no evidence of recurrent symptoms at final follow-up (average 18.88 ± 8.68 months). Our results demonstrate that excision of a symptomatic peroneus tertius provides resolution of symptoms, facilitates a quick return to activity, and has excellent patient outcomes. We suggest that during the evaluation of anterolateral ankle or rearfoot pain, peroneus tertius syndrome be considered as part of the differential diagnosis.

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.

Fibularis tertius muscle in women & men: A surface anatomy cross-sectional study across countries

The fibularis tertius muscle (FTM) is a rare anatomic variation. The prevalence of this exclusively human structure, which is found in the anterior compartment of the leg, is often underestimated, and it is believed that foot and ankle conditions are more difficult to manage in patients with an FTM. The aim of this study was to assess the presence of the FTM palpation and determine whether its presence is associated with an individual’s sex, because the exact prevalence in males and females is unclear. An observational cross-sectional study was carried out. The study included 481 people (23.49% men and 76.51% women) with a mean age of 23.51±5.369 years, who were recruited from a Podiatric Medicine and Surgery Clinic (Spain). Data on routine demographic and clinical factors were recorded, and the presence or absence of the FTM was determined based on surface visual or palpated localization of the tendon (using a consistent protocol). The FTM was present in 38.25% (184/481) of the participants. Furthermore, FTM were present in 38.6% (142/481) of females and 37.2% (42/481) of males. The study revealed that the presence of the FTM varies between individuals and does not depend on an individual’s sex. Significant differences in the prevalence of the FTM between countries should be carefully evaluated rather than generalizing the results of this Spanish study to other non-Spanish populations. Larger numbers of participants should be enrolled in future studies in order to meet the statistical criteria.

Phylogenetic patterns and correlation of key structures for jumping: bone crests and cross-sectional areas of muscles in Leptodactylus (Anura, Leptodactylidae)

Anurans are characterized by their saltatory mode of locomotion, which is associated with a specific morphology. The coordinated action of the muscles and bones of the pelvic girdle is key to the transmission of the force of the hindlimbs to the axial skeleton during jumping. Two features are critical for optimal locomotory performance: the cross-sectional area of muscle and the bone crest attachment sites. The first character is a proxy of the force exerted by the muscle, whereas the crests are muscle attachments sites related to muscle force. The provisory relationship between these features has previously been identified and bone crest size can be used to infer the magnitude and, therefore, muscle force in fossils records. In this work, we explore the correlation between the cross-sectional area of essential muscles to the jumping mechanism (longissimus dorsi, extensor iliotibialis B, tenuissimus, puboischiofemoralis internus B, coccygeo-sacralis and coccygeo-iliacus) and the bone crests where these muscles are inserted (dorsal tubercle, dorsal crest and urostylar crest) in species of the genus Leptodactylus. This genus, along with other leptodactylids, exhibits a diversity of locomotor modes, including jumping, hopping, swimming and burrowing. We therefore analyzed the morphometric variation in the two features, cross-sectional area and bone crest area, expecting a correlation with different locomotor types. Our results showed: (i) a correlation between the urostylar crest and the cross-sectional area of the related muscles; (ii) that the bone crest surface area of urostyle and ilium and the cross-sectional area of the corresponding muscles can be utilized to infer locomotor faculties in leptodactylid frogs; and (iii) that the evolution of both characters demonstrates a general tendency from lower values in leptodactylid ancestors to higher values in the Leptodactylus genus. The results attest to the importance of the comparison of current ecological and phylogenetic analogues as they allow us to infer functionality and behavior in fossil and extant groups based on skeletal evidence. Phylogenetic patterns in character evolution and their correlation with locomotory types could imply that functional restrictions are also inherited in leptodactylid.

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.

A review of trabecular bone functional adaptation: what have we learned from trabecular analyses in extant hominoids and what can we apply to fossils?

Many of the unresolved debates in palaeoanthropology regarding evolution of particular locomotor or manipulative behaviours are founded in differing opinions about the functional significance of the preserved external fossil morphology. However, the plasticity of internal bone morphology, and particularly trabecular bone, allowing it to respond to mechanical loading during life means that it can reveal greater insight into how a bone or joint was used during an individual's lifetime. Analyses of trabecular bone have been commonplace for several decades in a human clinical context. In contrast, the study of trabecular bone as a method for reconstructing joint position, joint loading and ultimately behaviour in extant and fossil non-human primates is comparatively new. Since the initial 2D studies in the late 1970s and 3D analyses in the 1990 s, the utility of trabecular bone to reconstruct behaviour in primates has grown to incorporate experimental studies, expanded taxonomic samples and skeletal elements, and improved methodologies. However, this work, in conjunction with research on humans and non-primate mammals, has also revealed the substantial complexity inherent in making functional inferences from variation in trabecular architecture. This review addresses the current understanding of trabecular bone functional adaptation, how it has been applied to hominoids, as well as other primates and, ultimately, how this can be used to better interpret fossil hominoid and hominin morphology. Because the fossil record constrains us to interpreting function largely from bony morphology alone, and typically from isolated bones, analyses of trabecular structure, ideally in conjunction with that of cortical structure and external morphology, can offer the best resource for reconstructing behaviour in the past.

Insertional Characteristics of the Peroneus Tertius Tendon: Revisiting the Anatomy of an Underestimated Muscle

The present study was performed to describe the morphologic characteristics of the peroneus tertius (PT) tendon, evaluate the variations in its insertion point, investigate the interconnections with the tendons of the extensor digitorum longus, and discuss whether these insertion differences of the muscle tension might have an effect on fracture formation. The length and width of the PT tendon and the width at its midpoint were measured in 44 lower extremities. The data obtained were compared statistically. The PT was found to occur in 2 types according to the number of tendons: type 1, a single tendon without a slip; and type 2, 2 tendons with a slip. It has been suggested that the PT tendon could contribute to avulsion fractures of the tuberosity of the fifth metatarsal bone. Therefore, to understand the mechanism of Jones fracture, knowledge of the PT tendon would be beneficial to determine the insertion points.

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.

Differences in end-point force trajectories elicited by electrical stimulation of individual human calf muscles

The purpose of this study was to investigate the end-point force trajectories of the fibularis longus (FIB), lateral gastrocnemius (LG), and medial gastrocnemius (MG) muscles. Most information about individual muscle function has come from studies that use models based on electromyographic (EMG) recordings. In this study (N = 20 subjects) we used electrical stimulation (20 Hz) to elicit activity in individual muscles, recorded the end-point forces at the foot, and verified the selectivity of stimulation by using magnetic resonance imaging. Unexpectedly, no significant differences were found between LG and MG force directions. Stimulation of LG and MG resulted in downward and medial or lateral forces depending on the subject. We found FIB end-point forces to be significantly different from those of LG and MG. In all subjects, stimulation of FIB resulted in downward and lateral forces. Based on our results, we suggest that there are multiple factors determining when and whether LG or MG will produce a medial or lateral force and FIB consistently plays a significant role in eversion/abduction and plantar flexion. We suggest that the intersubject variability we found is not simply an artifact of experimental or technical error but is functionally relevant and should be addressed in future studies and models.

The significance of peroneus tertius muscle in ankle injuries: a prospective study

BACKGROUND

The peroneus tertius is absent in 5% to 17% of the human white population. The function of the peroneus tertius is eversion and dorsiflexion of the foot. These 2 strength parameters have been identified as important parameters in the development of ankle ligament injuries.

HYPOTHESIS

Subjects without the peroneus tertius are at higher risk for ankle ligament injuries.

STUDY DESIGN

Cohort study (Prevalence); Level of evidence, 1.

METHODS

One hundred physical education students were palpated for the presence of peroneus tertius before the start of their education; they were also isokinetically measured for eversion and dorsiflexion strength. All ankle injuries were registered during 2 years, and exposure to sport was recorded.

RESULTS

The peroneus tertius was absent in 37 of the 200 subjects (18.5%). In the group with peroneus tertius (n = 163), 21 ankle sprains (12.9%) were observed during the 2-year follow-up. In the group without peroneus tertius (n = 37), 7 ankle sprains (18.9%) were noted. Statistical analysis (Cox regression) showed no significant difference between both groups in the incidence of ankle sprains (P = .335). Comparisons between the group of subjects with peroneus tertius and the group without peroneus tertius concerning the concentric and eccentric isokinetic eversion and the concentric dorsiflexion strength did not attain significance at any tested velocity (P > .05).

CONCLUSION

This study shows that subjects without peroneus tertius are not at higher risk for an ankle ligament injury. In addition, subjects without peroneus tertius do not exhibit decreased eversion or dorsiflexion strength.

CLINICAL RELEVANCE

This study is the first to clarify the exact contribution of the peroneus tertius within the muscular system around the ankle. As a result, the clinical importance of the peroneus tertius concerning prevention and treatment of ankle ligament injuries is low.

Functional analysis of the foot and ankle myology of gibbons and bonobos

This study investigates the foot and ankle myology of gibbons and bonobos, and compares it with the human foot. Gibbons and bonobos are both highly arboreal species, yet they have a different locomotor behaviour. Gibbon locomotion is almost exclusively arboreal and is characterized by speed and mobility, whereas bonobo locomotion entails some terrestrial knuckle-walking and both mobility and stability are important. We examine if these differences in locomotion are reflected in their foot myology. Therefore, we have executed detailed dissections of the lower hind limb of two bonobo and three gibbon cadavers. We took several measurements on the isolated muscles (mass, length, physiological cross sectional area, etc.) and calculated the relative muscle masses and belly lengths of the major muscle groups to make interspecific comparisons. An extensive description of all foot and ankle muscles is given and differences between gibbons, bonobos and humans are discussed. No major differences were found between the foot and ankle musculature of both apes; however, marked differences were found between the ape and human foot. The human foot is specialized for solely one type of locomotion, whereas ape feet are extremely adaptable to a wide variety of locomotor modes. Apart from providing interesting anatomical data, this study can also be helpful for the interpretation of fossil (pre)hominids.