A biomechanical analysis of finger joint forces and stresses developed during common daily activities

The problem of modelling stresses incurred at the finger joints is critical to the design of durable joint replacements in the hand. The goal of this study was to characterise the forces and stresses at the finger and thumb joints occurring during activities such as typing at a keyboard, playing piano, gripping a pen, carrying a weight and opening a jar. The metacarpal and proximal phalanx were modelled using a COMSOL-based finite element analysis. Analysis of these activities indicates that joint forces in excess of 100 N may be common at the metacarpophalangeal joint (MCP) due to carrying objects such as groceries or while opening jars. The model predicted that stresses in excess of 2 MPa, similar to stresses at the hip, occur at the MCP with the properties of cancellous bone playing a significant role in the magnitude and distribution of stress.     

A biomechanical analysis of finger joint forces and stresses developed during common daily activities

The problem of modelling stresses incurred at the finger joints is critical to the design of durable joint replacements in the hand. The goal of this study was to characterise the forces and stresses at the finger and thumb joints occurring during activities such as typing at a keyboard, playing piano, gripping a pen, carrying a weight and opening a jar. The metacarpal and proximal phalanx were modelled using a COMSOL-based finite element analysis. Analysis of these activities indicates that joint forces in excess of 100 N may be common at the metacarpophalangeal joint (MCP) due to carrying objects such as groceries or while opening jars. The model predicted that stresses in excess of 2 MPa, similar to stresses at the hip, occur at the MCP with the properties of cancellous bone playing a significant role in the magnitude and distribution of stress.     

The interplay between speed,kinetics, and hand postures during primate terrestrial locomotion

Nonprimate terrestrial mammals may use digitigrade postures to help moderate distal limb joint moments and metapodial stresses that may arise during high‐speed locomotion with high‐ground reaction forces (GRF). This study evaluates the relationships between speed, GRFs, and distal forelimb kinematics in order to evaluate if primates also adopt digitigrade hand postures during terrestrial locomotion for these same reasons. Three cercopithecine monkey species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway instrumented with a force platform. Three‐dimensional forelimb kinematics and GRFs were measured when the vertical force component reached its peak. Hand posture was measured as the angle between the metacarpal segment and the ground (MGA). As predicted, digitigrade hand postures (larger MGA) are associated with shorter GRF moment arms and lower wrist joint moments. Contrary to expectations, individuals used more palmigrade‐like (i.e. less digitigrade) hand postures (smaller MGA) when the forelimb was subjected to higher forces (at faster speeds) resulting in potentially larger wrist joint moments. Accordingly, these primates may not use their ability to alter their hand postures to reduce rising joint moments at faster speeds. Digitigrady at slow speeds may improve the mechanical advantage of antigravity muscles crossing the wrist joint. At faster speeds, greater palmigrady is likely caused by joint collapse, but this posture may be suited to distribute higher GRFs over a larger surface area to lower stresses throughout the hand. Thus, a digitigrade hand posture is not a cursorial (i.e. high speed) adaptation in primates and differs from that of other mammals. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

The effect of the sagittal ridge angle on cartilage stress in the equine metacarpo-phalangeal (fetlock) joint

Fatigue failure of bones of the metacarpo-phalangeal (fetlock, MCP) joint is common in thoroughbred racehorses. Stresses within the fetlock joint cartilages are affected by the morphology of the third metacarpal bone (MC3) and proximal phalangeal bone, and the steepness of the median sagittal ridge of MC3 is believed to be associated with fracture. This study investigated the influence of the steepness of the sagittal ridge on cartilage stress distribution using a finite element model of the joint. Changes to the steepness of the sagittal ridge were made by applying a parabolic function to the mesh, creating four different models with sagittal ridge angles ranging from 95° to 105°. In the fetlock joint of Thoroughbred racehorses, sagittal ridge angles of >100° were associated with higher Von Mises stresses in cartilage at the palmar aspect of the condylar groove than such stresses in joints with sagittal ridge angles of <100°. Stresses were high in the specific region where fractures are known to originate in MC3. This aspect of morphology of the fetlock joint thus appears to play an important role in the magnitude and distribution of cartilage stresses, which, when acting on the underlying hard tissues of the articular calcified cartilage and subchondral bone may play a role in the initiation of fatigue fracture in the third metacarpal bone.     

The functional morphology of the cercopithecoid wrist and inferior radioulnar joints, and their bearing on some problems in the evolution of the Hominoidea.

The cercopithecoid wrist joint differs from the wrist joints of hominoids in several ways. The distal ulna, the distal radius, the pisiform, the triquetrum, the hamate, and the base of the fifth metacarpal are on the one hand remarkably alike among cercopithecoid genera, and on the other remarkably distinct from homologous bones in the Hominoidea. Functionally, the triquetrum and the pisiform, in conjuction with the ulnar styloid process, check the proximal carpal row during ulnar deviation, and are possibly important in stabilizing the wrist during dorsiflexion as well. The head of the ulna almost certainly betokens a range of radioulnar supination in cercopithecoids that is substantially less than is to be found in any of the hominoid genera. The articulation between the hamate bone and the base of the fifth metacarpal allows for considerable dorsiflexion in the Cercopithecoidea; this potential was not evidenct in any of the hominoids examined. Behaviorally, the cercopithecoid wrist can most profitably be viewed as an adaptation for a quadrupedal life style involving dorsiflexion of the wrist and palmigrade/digitigrade substrate contact. The hominoid wrist joint is not adapted for such a behavioral potential.     

Functional anatomy of the hand of Australopithecus africanus

The Sterkfontein hand bones, attributed to Australopithecus africanus, were analysed to determine potential hand function of the power grip type of this species. The metacarpus is as stable as that of modern humans, as indicated by the depth of the groove on the base of metacarpal 2, the styloid process of metacarpal 3, the base articular surface areas, and the ligament markings on the bases of the metacarpals. The flexion and rotation of metacarpal 5 might have been less than that of modern humans, due to a more marked ventral articular lip on the base. The metacarpus acts as a lever, acting in various planes. The extensor carpi ulnaris and extensor carpi radialis longus muscles were probably better developed than in modern humans. The extensor carpi radialis brevis and flexor carpi radialis muscles would probably have been as well developed as in modern humans. None of the long tendons have a mechanical disadvantage as compared to modern humans. The metacarpals have a high robusticity index. The proximal phalanges show some midshaft swelling, slightly greater curvature than in modern humans, and some side to side bowing: pongid features. The fibrous flexor sheath markings are well developed, but resemble those of modern humans rather than those of the pongids. A single middle phalanx resembles that of modern humans, and has well developed ridges for insertion of the flexor digitorum superficialis muscle. The distal phalanx of the thumb has a well developed region for insertion of the flexor pollicis longus muscle, and has a mechanical advantage over modern humans for action of this muscle at the interphalangeal joint. The features indicate that the hand of A. africanus was well adapted to powerful hand use, as in hammering, striking, chopping, scraping, and gouging actions, as well as for throwing and climbing activities.     

Does trabecular bone structure within the metacarpal heads of primates vary with hand posture?

Reconstructing function from hominin fossils is complicated by disagreements over how to interpret primitively inherited, ape-like morphology. This has led to considerable research on aspects of skeletal morphology that may be sensitive to activity levels during life. We quantify trabecular bone morphology in three volumes of interest (dorsal, central, and palmar) in the third metacarpal heads of extant primates that differ in hand function: Pan troglodytes, Pongo pygmaeus, Papio anubis, and Homo sapiens. Results show that bone volume within third metacarpal heads generally matches expectations based on differences in function, providing quantitative support to previous studies. Pongo shows significantly low bone volume in the dorsal region of the metacarpal head. Humans show a similar pattern, as manipulative tasks mostly involve flexed and neutral metacarpo-phalangeal joint postures. In contrast, Pan and Papio have relatively high bone volume in dorsal and palmar regions, which are loaded during knuckle-walking/digitigrady and climbing, respectively. Regional variation in degree of anisotropy did not match predictions. Although trabecular morphology may improve behavioral inferences from fossils, more sophisticated quantitative strategies are needed to explore trabecular spatial distributions and their relationships to hand function.     

Clinical anatomy of the m. flexor carpi radialis tendon sheath

At the transitional zone from the forearm to the hand the insertion tendon of the m.flexor carpi radialis (FCR) glides on a fibrous and fatty cushion, which is connected dorsally with the joint capsule of the radiocarpal articulation. The tendon distally crosses the palmar side of the scaphoid tubercle and enters the dorsally curved rim of the trapezoid tubercle. At the level of the wrist joint the narrow tendon sheath begins, which extends to the insertion at the metacarpus. Immediately after entering the gliding tunnel the tendon branches off radially as a rule with an accessory fibre strand 8 mm in width to the scaphoid, trapezium and the joint capsule between these two bones. The insertion tendon regularly is attached to the palmar and radial surfaces of the second and third metacarpal bones. The wall of the osteofibrous gliding tunnel can be prominent following trauma, inflammation or arthrosis deformans in the trapezio-scaphoideal joint and may irritate the tendon (tendovaginosis stenosans). Against resistance forces pain will occur in the wrist joint during palmar flexion. The typical point of tenderness is situated at the entering of the tendon in the thenar region. Operative decompression will be effective by opening the radial wall of the tendon sheath from the carpal tunnel.     

Hand biomechanics during simulated stone tool use

Human radial digits have derived features compared with apes, with long robust thumbs, relatively larger joint surfaces, and hypertrophic thenar muscles. Here we test the hypothesis that these features evolved in the context of making and using stone tools, specifically for producing large gripping forces and for countering large joint contact stresses. We used portable force plates simulating early stone tools to: 1) document and compare the magnitude of external/internal forces and joint stresses in the radial digits during hardhammer percussion and flake use, and 2) examine how variation in digit morphology affects muscle and joint mechanics during stone tool use. Force and kinematic data were collected from a sample representing normal variation in digit morphology (n = 25). The effects of digit size/shape on digit biomechanics were evaluated using partial correlations, controlling for tool reaction forces and impact velocities. Results show that individuals with longer digits require relatively less muscle force to stabilize digital joints, and are exposed to relatively lower joint contact stresses during stone tool use, due in part to an increase in the robusticity of metacarpals and phalanges in humans relative to chimpanzees. These analyses further suggest that Pan- or australopith-like pollical anatomy presents serious performance challenges to habitual tool use. Our data support the hypothesis that evolutionary increases in thumb length, robusticity, and thenar muscle mass enabled Homo to produce more force and to tolerate higher joint stresses during tool use.     

Hand and foot remains from the Gran Dolina Early Pleistocene site (Sierra de Atapuerca, Spain).

We report here the study of the 22 hand and foot remains from the Early Pleistocene level TD6 of the Gran Dolina site at Sierra de Atapuerca (Burgos, Spain) recovered from 1994 to 1996. These remains are paratypes of Homo antecessor. All of the elements are briefly described and compared with other fossil hominids. The capitate has a constricted neck, well developed head, strong attachment for the ligamentum interosseum trapezoid-capitate, a palmarly placed trapezoid facet with a distinctive small dorsal trapezoid facet, a highly curved and oblique orientation of the second metacarpal facet, and a transversally oriented dorsodistal border. A hamate with a moderately projecting and lightly built hamulus; an inferred reduced styloid process on the third metacarpal base; a wide second metacarpal head; and middle phalanges with well marked insertions for the flexor digitorum superficialis muscle and wide heads. The morphology and dimensions of the pedal remains from TD6 are very similar to modern humans; but the base, proximal articular surface and shafts of the proximal hallucal phalanges are more rounded and the midshaft of the proximal toe phalanx is wider.     

Neanderthal hand and foot remains from Moula‐Guercy,Ardèche,France

The hand and foot remains from Moula‐Guercy cave (Ardèche, France) comprise 24 specimens of Eemian age (ca. 120 ka). The specimens include primarily complete elements, which are rare among the Moula‐Guercy postcrania. The hand remains have several characteristic Neanderthal traits including a laterally facing (parasagittally oriented) second metacarpal‐capitate articulation, a short styloid process, a wide proximal articular surface on the third metacarpal, and absolutely expanded apical tuberosities on the distal hand phalanges relative to modern humans. The foot remains include several incomplete elements along with an antimeric pair of naviculars, a medial cuneiform and cuboid, and a single complete element from each of the distal segments (one each: metatarsal, proximal foot phalanx, intermediate foot phalanx, distal foot phalanx). Consistent among the specimens are relatively wide diaphyses for length in the metatarsals and phalanges and large and prominent muscle attachments, both consistent with previously published Neanderthal morphology. The hand and foot collection from Moula‐Guercy is an important dataset for future studies of Neanderthal functional morphology, dexterity, and behavior as it represents a previously undersampled time period for European Neanderthals. Am J Phys Anthropol 152:516–529, 2013. © 2013 Wiley Periodicals, Inc.     

Relaxed Evolution in the Tyrosine Aminotransferase Gene Tat in Old World Fruit Bats (Chiroptera: Pteropodidae)

Frugivorous and nectarivorous bats fuel their metabolism mostly by using carbohydrates and allocate the restricted amounts of ingested proteins mainly for anabolic protein syntheses rather than for catabolic energy production. Thus, it is possible that genes involved in protein (amino acid) catabolism may have undergone relaxed evolution in these fruit- and nectar-eating bats. The tyrosine aminotransferase (TAT, encoded by the Tat gene) is the rate-limiting enzyme in the tyrosine catabolic pathway. To test whether the Tat gene has undergone relaxed evolution in the fruit- and nectar-eating bats, we obtained the Tat coding region from 20 bat species including four Old World fruit bats (Pteropodidae) and two New World fruit bats (Phyllostomidae). Phylogenetic reconstructions revealed a gene tree in which all echolocating bats (including the New World fruit bats) formed a monophyletic group. The phylogenetic conflict appears to stem from accelerated TAT protein sequence evolution in the Old World fruit bats. Our molecular evolutionary analyses confirmed a change in the selection pressure acting on Tat, which was likely caused by a relaxation of the evolutionary constraints on the Tat gene in the Old World fruit bats. Hepatic TAT activity assays showed that TAT activities in species of the Old World fruit bats are significantly lower than those of insectivorous bats and omnivorous mice, which was not caused by a change in TAT protein levels in the liver. Our study provides unambiguous evidence that the Tat gene has undergone relaxed evolution in the Old World fruit bats in response to changes in their metabolism due to the evolution of their special diet.     

Trabecular Bone Structure Correlates with Hand Posture and Use in Hominoids

Bone is capable of adapting during life in response to stress. Therefore, variation in locomotor and manipulative behaviours across extant hominoids may be reflected in differences in trabecular bone structure. The hand is a promising region for trabecular analysis, as it is the direct contact between the individual and the environment and joint positions at peak loading vary amongst extant hominoids. Building upon traditional volume of interest-based analyses, we apply a whole-epiphysis analytical approach using high-resolution microtomographic scans of the hominoid third metacarpal to investigate whether trabecular structure reflects differences in hand posture and loading in knuckle-walking (Gorilla, Pan), suspensory (Pongo, Hylobates and Symphalangus) and manipulative (Homo) taxa. Additionally, a comparative phylogenetic method was used to analyse rates of evolutionary changes in trabecular parameters. Results demonstrate that trabecular bone volume distribution and regions of greatest stiffness (i.e., Young''s modulus) correspond with predicted loading of the hand in each behavioural category. In suspensory and manipulative taxa, regions of high bone volume and greatest stiffness are concentrated on the palmar or distopalmar regions of the metacarpal head, whereas knuckle-walking taxa show greater bone volume and stiffness throughout the head, and particularly in the dorsal region; patterns that correspond with the highest predicted joint reaction forces. Trabecular structure in knuckle-walking taxa is characterised by high bone volume fraction and a high degree of anisotropy in contrast to the suspensory brachiators. Humans, in which the hand is used primarily for manipulation, have a low bone volume fraction and a variable degree of anisotropy. Finally, when trabecular parameters are mapped onto a molecular-based phylogeny, we show that the rates of change in trabecular structure vary across the hominoid clade. Our results support a link between inferred behaviour and trabecular structure in extant hominoids that can be informative for reconstructing behaviour in fossil primates.     

Evolution of a repeat sequence in the parathyroid hormone-related peptide gene in primates

A polymorphism of the variable number of tandem repeat (VNTR) type is located 97 bp downstream of exon VI of the parathyroid hormone-related peptide (PTHrP) gene in humans. The repeat unit has the general sequence G(TA)_nC, where n equals 4–11. In order to characterize the evolutionary history of this VNTR, we initially tested for its presence in 13 different species representing four main groups of living primates. The sequence is present in the human, great apes, and Old World monkeys, but not in New World monkeys; and this region failed to PCR amplify in the Loris group. Thus, the evolution of the sequence as part of the PTHrP gene started at least 25–35 millions years ago, after divergence of the Old World and New World monkeys, but before divergence of Old World monkeys and great apes and humans. The structural changes occurring during evolution are characterized by a relatively high degree of sequence divergence. In general, the tandem repeat region tends to be longer and more complex in higher primates with the repeat unit motifs all being based on a TA-dinucleotide repeat sequence. Intra-species variability of the locus was demonstrated only in humans and gorilla. The divergence of the TA-dinucleotide repeat sequence and the variable mutation rates observed in different primate species are in contrast to the relative conservation of the flanking sequences during primate evolution. This suggests that the nature of the TA-dinucleotide repeat sequence, rather than its flanking sequences, is responsible for generating variability. Particular features of the sequence may allow it to form stable secondary structures during DNA replication, and this, in turn, could promote slipped-strand mispairing to occur.     

HERV-K(OLD): ancestor sequences of the human endogenous retrovirus family HERV-K(HML-2)

Sequences homologous to the human endogenous retrovirus (HERV) family HERV-K(HML-2) are present in all Old World primate species. A previous study showed that a central region of the HERV-K(HML-2) gag genes in Hominoidea species displays a 96-bp deletion compared to the gag genes in lower Old World primates. The more ancient HERV-K(HML-2) sequences present in lower Old World primates were apparently not conserved during hominoid evolution, as opposed to the deletion variants. To further clarify the evolutionary origin of the HERV-K(HML-2) family, we screened GenBank with the 96-bp gag-sequence characteristic of lower Old World primates and identified, to date, 10 human sequence entries harboring either full-length or partially deleted proviral structures, probably representing remnants of a more ancient HERV-K(HML-2) variant. The high degree of mutations demonstrates the long-time presence of these HERV-K(OLD) proviruses in the genome. Nevertheless, they still belong to the HML-2 family as deduced from dot matrix and phylogenetic analyses. We estimate, based on the family ages of integrated Alu elements and on long terminal repeat (LTR) divergence data, that the average age of HERV-K(OLD) proviruses is ca. 28 million years, supporting an integration time before the evolutionary split of Hominoidea from lower Old World primates. Analysis of HERV-K(OLD) LTR sequences led to the distinction of two subgroups, both of which cluster with LTRs belonging to an evolutionarily older cluster. Taken together, our data give further insight into the evolutionary history of the HERV-K(HML-2) family during primate evolution.     

Metacarpal head biomechanics: a comparative backscattered electron image analysis of trabecular bone mineral density in Pan troglodytes, Pongo pygmaeus, and Homo sapiens

Great apes and humans use their hands in fundamentally different ways, but little is known about joint biomechanics and internal bone variation. This study examines the distribution of mineral density in the third metacarpal heads in three hominoid species that differ in their habitual joint postures and loading histories. We test the hypothesis that micro-architectural properties relating to bone mineral density reflect habitual joint use. The third metacarpal heads of Pan troglodytes, Pongo pygmaeus, and Homo sapiens were sectioned in a sagittal plane and imaged using backscattered electron microscopy (BSE-SEM). For each individual, 72 areas of subarticular cortical (subchondral) and trabecular bone were sampled from within 12 consecutive regions of the BSE-SEM images. In each area, gray levels (representing relative mineralization density) were quantified.Results show that chimpanzee, orangutan, and human metacarpal III heads have different gray level distributions. Weighted mean gray levels (WMGLs) in the chimpanzee showed a distinct pattern in which the ‘knuckle-walking’ regions (dorsal) and ‘climbing’ regions (palmar) are less mineralized, interpreted to reflect elevated remodeling rates, than the distal regions. Pongo pygmaeus exhibited the lowest WMGLs in the distal region, suggesting elevated remodeling rates in this region, which is loaded during hook grip hand postures associated with suspension and climbing. Differences among regions within metacarpal heads of the chimpanzee and orangutan specimens are significant (Kruskal–Wallis, p < 0.001). In humans, whose hands are used for manipulation as opposed to locomotion, mineralization density is much more uniform throughout the metacarpal head. WMGLs were significantly (p < 0.05) lower in subchondral compared to trabecular regions in all samples except humans. This micro-architectural approach offers a means of investigating joint loading patterns in primates and shows significant differences in metacarpal joint biomechanics among great apes and humans.     

The articular disc of the hand.

The carpal articular disc have been studied in serial sectioned embryonal and fetal hands. It can be concluded that the articular disc is an extensive fibrous system that comes from the ulnar edge of the distal end of the radius and reaches, bordered by the deep layer of the antebrachial fascia, the base of metacarpal V. In this course, insertions take place into the ulnar aspect of the head of the ulna, into the ulnar styloid process and into the ulnar carpals. Emphasis has been laid upon the fact that the sheath of the m. extensor carpi ulnaris tendon is part of the fibrous system of the disc. The positions of the dorsal tendons seen with respect to the fascial implicate a mutual shift during pronation and supination of the hand. The relations between the so-called ligamentum subcruentum and prestyloid recess have been established, the presence of cartilaginous primordia in the developing dis has been discussed. We come to the conclusion that the evidence for drawing a parallel between phylogenetic and human embryological phenomena is still insufficient. In this connection we have stressed the modus of development of the pisotriquetral joint space.     

The capitate of Australopithecus afarensis and A. africanus

The capitates of Australopithecus afarensis (AL 288-lw and AL 333–40) and A. africanus (TM 1526) have the identical combination of modern pongid, modern hominid, and unique characteristics. These traits include the combination of a length that is proximodistally shortened (Homo sapiens-like), a facet for the second metacarpal that is distolaterally facing (unique), the reduced styloid process on the third metacarpal (pongidlike), a dorsally placed trapezoid facet (pongidlike), mediolaterally constricted metacarpal III facet (pongidlike), a prominent palmar beak (pongidlike), a single elongated facet for the second metacarpal (H. sapiens-like), a waisted neck (pongidlike), and a reduced amount of “cupping” in the third metacarpal facet (H. sapiens-like). In overall shape the bones are more like H. sapiens than other extant hominids, although they are uniquely different. The two A. afarensis capitates provide no evidence that there are two postcranial morphotypes at Hadar. Available evidence shows that A. afarensis and A. africanus are strikingly similar postcranially. The morphological differences between the capitate of Australopithecus and H. sapiens may relate to the retention of climbing ability and an absence of certain grip capabilities in these early hominids.