Bipédie chez les primates

International audienc

Shortening effect influence of Distal Minimally Invasive Metatarsal Osteotomy in primary metatarsalgia

International audiencePurpose: In primary metatarsalgia, Distal Minimally invasive Metatarsal Osteotomy (DMMO) achieves a correct load distribution which is a factor in pain relief, but contrary to the elevation of the metatarsal head, shortening the metatarsal length has no influence on plantar-loading parameters, while the increased metatarsal length is a factor in the development of metatarsalgia. Thus, we hypothesized that metatarsalgia could be partly related to a functional imbalance between bone structure and soft tissues and pain relief after DMMO results from soft tissue relaxation. Methods: Many authors have highlighted the correlation between joint pressure and periarticular soft tissue tension. To test our hypothesis, we measured intra-operatively the MTPJ pressure of 19 patients suffering from primary metatarsalgia, before and after DMMO. This pressure is being analyzed as a reflection of joint decompression and forefoot soft tissue release. Many authors have highlighted the correlation between joint pressure and periarticular soft tissue tension. Results: Lower metatarsals presenting metatarsalgia show a significantly lower MTPJ pressure compared to asymptomatic rays, and DMMO induces a significant increase of MTPJ pressure. Conclusion: Those variations reflect the functional imbalance between bone structure and soft tissue in primary metatarsalgia. The biomechanical rationale of the shortening effect of DMMO could therefore be explained by the release of forefoot soft tissue, which could take part in the pain relief by restoring this balance

Correlation between first tarsometatarsal joint mobility and hallux valgus severity

International audiencePurpose: The mobility of the first tarsometatarsal (TMT1) is said to be correlated to the severity of hallux valgus determined using both clinical and radiographic criteria. The sagittal mobility of the TMT1 joint can be evaluated objectively using a new ultrasound test, which quantifies it in the form of a unitless value (ratio of two measurements). The objective of this study was to describe the relationship between TMT1 mobility on an ultrasound test and hallux valgus severity. Hypothesis TMT1 joint mobility increases with hallux valgus severity. Patients and methods: Forty-nine feet were included that were being treated for isolated hallux valgus and had no evidence of TMT1 hypermobility based on the dorsal drawer test. For each foot, the presence and intensity of load transfer (LT), the intermetatarsal angle (IMA), and the hallux valgus angle (HVA) were determined. Lastly, TMT1 mobility was evaluated with the ultrasound test. Results: Clinically, no LT was present in 20 feet; it was present only under M2 in 20 feet and reached at least M3 in the other nine feet. The mean IMA on radiographs was 14.6° and the mean HVA was 34.5°. The value of the ultrasound test was significantly different between the three groups of clinical hallux valgus severity: 1.17 with no LT, 1.31 with isolated M2 LT, and 1.72 when LT was at least at M3. Furthermore, this value was correlated with the IMA but not the HVA. Discussion: This study revealed a relationship between increased TMT1 mobility and hallux valgus severity based on clinical (LT) and radiographic (IMA) criteria. Thus, our working hypothesis is confirmed. However, there was no correlation between TMT1 mobility and HVA suggesting that this angle is less relevant for determining the severity of the condition. This is consistent with the classical pathophysiological concept of metatarsus primus varus where the hallux valgus originates in a metatarsus varus in the tarsometatarsal area. Conclusion: The severity of hallux valgus is correlated with increased mobility of the TMT1 joint, which appears to have a causal role in this condition

Impact des activités locomotrices sur la biomécanique du fémur : étude ontogénétique du babouin olive

International audienc

Increased performance in juvenile baboons is consistent with ontogenetic changes in morphology

International audienceObjectivesIn many primates, the greater proportion of climbing and suspensory behaviors in the juvenile repertoire likely necessitates good grasping capacities. Here, we tested whether very young individuals show near-maximal levels of grasping strength, and whether such an early onset of grasping performance could be explained by ontogenetic variability in the morphology of the limbs in baboons.Material and methodsWe quantified a performance trait, hand pull strength, at the juvenile and adult stages in a cross-sectional sample of 15 olive baboons (Papio anubis). We also quantified bone dimensions (i.e., lengths, widths, and heights) of the fore- (n = 25) and hind limb (n = 21) elements based on osteological collections covering the whole development of olive baboons.ResultsOne-year old individuals demonstrated very high pull strengths (i.e., 200% of the adult performance, relative to body mass), that are consistent with relatively wider phalanges and digit joints in juveniles. The mature proportions and shape of the forelimb elements appeared only at full adulthood (i.e., ≥4.5 years), whereas the mature hind limb proportions and shape were observed much earlier during development.DiscussionThese changes in limb performance and morphology across ontogeny may be explained with regard to behavioral transitions that olive baboons experience during their development. Our findings highlight the effect of infant clinging to mother, an often-neglected feature when discussing the origins of grasping in primates. The differences in growth patterns, we found between the forelimb and the hind limb further illustrate their different functional roles, having likely evolved under different ecological pressures (manipulation and locomotion, respectively)

Do femoral biomechanical properties follow locomotor changes in primates? An ontogenetic study of olive baboons ( Papio anubis )

International audienc

Increased performance in juvenile baboons is consistent with ontogenetic changes in morphology

International audienceObjectivesIn many primates, the greater proportion of climbing and suspensory behaviors in the juvenile repertoire likely necessitates good grasping capacities. Here, we tested whether very young individuals show near-maximal levels of grasping strength, and whether such an early onset of grasping performance could be explained by ontogenetic variability in the morphology of the limbs in baboons.Material and methodsWe quantified a performance trait, hand pull strength, at the juvenile and adult stages in a cross-sectional sample of 15 olive baboons (Papio anubis). We also quantified bone dimensions (i.e., lengths, widths, and heights) of the fore- (n = 25) and hind limb (n = 21) elements based on osteological collections covering the whole development of olive baboons.ResultsOne-year old individuals demonstrated very high pull strengths (i.e., 200% of the adult performance, relative to body mass), that are consistent with relatively wider phalanges and digit joints in juveniles. The mature proportions and shape of the forelimb elements appeared only at full adulthood (i.e., ≥4.5 years), whereas the mature hind limb proportions and shape were observed much earlier during development.DiscussionThese changes in limb performance and morphology across ontogeny may be explained with regard to behavioral transitions that olive baboons experience during their development. Our findings highlight the effect of infant clinging to mother, an often-neglected feature when discussing the origins of grasping in primates. The differences in growth patterns, we found between the forelimb and the hind limb further illustrate their different functional roles, having likely evolved under different ecological pressures (manipulation and locomotion, respectively)

: Do femoral biomechanics reflect locomotor behaviors? Study of the structural properties of the femoral diaphysis among catarrhines.

Durant la locomotion, la diaphyse fémorale subit des charges mécaniques impactant son organisation structurelle. L’étude de la structure corticale des vestiges fossiles représente donc un potentiel accès à la reconstruction de l’environnement mécanique des hominines fossiles, et donc à leur locomotion. Cependant, peu d’études ont abordé expérimentalement cette question et d’autres facteurs tels que l’âge, la masse et le niveau d’activité viennent complexifier cette relation entre structure fémoro-diaphysaire et locomotion. Une première étude menée sur un échantillon ontogénétique de babouins olive vivant à la Station de Primatologie du CNRS (UAR 846), a démontré une faible correspondance entre les variations de l’organisation du tissu cortical de la diaphyse fémorale et celles du répertoire posturo-locomoteur au cours de l’âge. Pour poursuivre l’étude de cette relation entre les propriétés biomécaniques de la diaphyse fémorale et la locomotion, nous avons analysé et comparé les cartographies d’épaisseur corticale et des paramètres de géométrie de section sur plus de 50 fémurs de primates catarhiniens adultes (genres Homo, Gorilla, Pan, Hylobates, Papio, Macaca), de morphologies et de répertoires posturo-locomoteurs différents.Nos résultats montrent l’existence de schémas biomécaniques variés, montrant une certaine proximité entre grands singes africains et hylobatidés, dont les babouins et surtout les humains se distinguent. Les propriétés biomécaniques de la diaphyse fémorale permettent de distinguer des grands groupes, mais pas de caractériser précisément les répertoires posturo-locomoteurs les plus diversifiés.Pour permettre une différenciation plus fine des répertoires posturo-locomoteurs complexes, exploitable dans une perspective paléoanthropologique, nous proposons l’intégration de l’approche biomécanique à de la morphométrie géométrique

Phylogenetic and biomechanical influences in the structural pattern of the femoral diaphysis among catarrhines

International audienceThe interpretation of hominin locomotor behaviors, which is largely based on actualism, implies a clear understanding of form-function relationship between the biomechanics of the skeleton and the locomotor behaviors of extant primates. In this study, we tested this relationship by measuring the structural properties of 127 femoral diaphyses from six genera and 10 species of catarrhine primates whose locomotor behaviors are well documented. The structural properties were assessed on the entire diaphysis via cross-sectional geometry properties including relative cortical area (%CA) and cross-sectional bending rigidity and shape (Ix/Iy and Imax/Imin), as well as the pattern of overall cortical bone distribution (cortical thickness maps). Concerning cross-sectional properties, our results highlight marked differences in CSG along the femoral diaphysis of locomotor-related groups such as knuckle-walker African apes and quadrupedal cercopithecoids. Humans seem to be distinctive in their anteroposterior bending rigidity, especially at midshaft, while brachiator hylobatids differ very little from all other groups. Concerning overall cortical bone distribution, humans differ from non-human primates. In the latter, a hominoid-cercopithecoid partition supports previously reported influence of phylogeny rather than locomotor behaviors in shaping the structural properties of the femoral diaphysis. Caution is therefore needed when inferring locomotor behavior in fossils solely based on femoral structural properties.L'interprétation des comportements locomoteurs des hominines, largement basée sur le principe d’actualisme, implique une compréhension claire de la relation forme-fonction existant entre la biomécanique du squelette et les comportements locomoteurs des primates actuels. Dans cette étude, nous avons testé cette relation en mesurant les propriétés endostructurales de 127 diaphyses fémorales provenant de six genres et de dix espèces de primates catarrhiniens, dont les comportements locomoteurs sont documentés. Les propriétés endostructurales ont été mesurées sur la totalité de la diaphyse par le biais des paramètres de géométrie de section, notamment l’aire corticale relative (%CA), la rigidité à la flexion et la forme des sections (Ix/Iy et Imax/Imin), ainsi que le modèle de distribution de l'os cortical (cartographies d'épaisseur corticale). Concernant les paramètres de géométrie de section de la diaphyse fémorale, nos résultats mettent en évidence des différences marquées entre des groupes dont la locomotion est proche, tels que les grands-singes africains knuckle-walkers et les cercopithécoïdes quadrupèdes. Les humains semblent se distinguer par une rigidité à la flexion orientée antéropostérieurement, en particulier à mi-diaphyse, tandis que les hylobatidés brachiateurs diffèrent très peu des autres groupes. Concernant le modèle de distribution de l'os cortical, les humains diffèrent des primates non-humains. Chez ces derniers, une distinction entre hominoïdes et cercopithécoïdes confirme une influence de la phylogénie plutôt que des comportements locomoteurs dans la modulation des propriétés endostructurales de la diaphyse fémorale, comme rapporté par de précédents travaux. Il convient donc d'être prudent lorsque des comportements locomoteurs de fossiles sont déduits uniquement sur la base des propriétés endostructurales du fémur