Ontogeny of the distal femoral metaphyseal surface and its relationship to locomotor behavior in hominoids

Technical note: A freeware, equitable approach to dental topographic analysis

Dental topographic analysis has proved a valuable tool for quantifying dental morphology. Established workflows often use proprietary software for pre-processing dental surfaces, rendering the method expensive and inaccessible to many. This study explores the use of freeware pre-processing alternatives. We tested 4 decimation tools and 13 smoothing tools across 7 different freeware packages. Surfaces generated via proprietary software could not be replicated, but it was possible to obtain statistically similar measurements using freeware. Based on this investigation, we propose a freeware workflow for researchers to conduct dental topographic analysis, with the expectation that their results will be comparable to that obtained through proprietary methods.

Influence of tension-band plates on the mechanical loading of the femoral growth plate during guided growth due to coronal plane deformities

Introduction: Correction of knee malalignment by guided growth using a tension-band plate is a common therapy to prevent knee osteoarthritis among other things. This approach is based on the Hueter-Volkmann law stating that the length growth of bones is inhibited by compression and stimulated by tension. How the locally varying mechanical loading of the growth plate is influenced by the implant has not yet been investigated. This study combines load cases from the gait cycle with personalized geometry in order to investigate the mechanical influence of the tension-band plates. Methods: Personalized finite element models of four distal femoral epiphyses of three individuals, that had undergone guided growth, were generated. Load cases from the gait cycles and musculoskeletal modelling were simulated with and without implant. Morphological features of the growth plates were obtained from radiographs. 3D geometries were completed using non-individual Magnetic Resonance Images of age-matched individuals. Boundary conditions for the models were obtained from instrumented gait analyses. Results: The stress distribution in the growth plate was heterogenous and depended on the geometry. In the insertion region, the implants locally induced static stress and reduced the cyclic loading and unloading. Both factors that reduce the growth rate. On the contralateral side of the growth plate, increased tension stress was observed, which stimulates growth. Discussion: Personalized finite element models are able to estimate the changes of local static and cyclic loading of the growth plate induced by the implant. In future, this knowledge can help to better control growth modulation and avoid the return of the malalignment after the treatment. However, this requires models that are completely participant-specific in terms of load cases and 3D geometry.

Hominin locomotion and evolution in the Late Miocene to Late Pliocene

In this review, we present on the evolution of the locomotor adaptation of hominins in the Late Miocene to Late Pliocene, with emphasis on some of the prominent advances and debates that have occurred over the past fifty years. We start with the challenging issue of defining hominin locomotor grades that are currently used liberally and offer our own working definitions of facultative, habitual, and obligate bipedalism. We then discuss the nature of the Pan-Homo last common ancestor and characterize the locomotor adaptation of Sahelanthropus, Orrorin, and Ardipithecus-often referred to as facultative bipeds-and examine the debates on the extent of bipedality and arboreality in these taxa. Moreover, the question of Middle Pliocene hominin locomotor diversity is addressed based on information derived from the 'Little Foot' specimen from Sterkfontein, footprints from Laetoli, and the Burtele Foot in Ethiopia. Our review suggests that the most convincing evidence for locomotor diversity comes from Burtele, whereas the evidence from Sterkfontein and Laetoli is unconvincing and equivocal, respectively. Finally, we address the decades old issue of the significance of arboreality in the otherwise habitual biped, Australopithecus, with emphasis on Australopithecus afarensis and its implications for the paleobiology of these creatures. We conclude that many of the apelike features encountered, mostly in the upper part of the Australopithecus skeleton, were retained for their significance in climbing. Approaches that have investigated character plasticity and those exploring internal bone structure have shown that the shoulder and limbs in Au. afarensis and Australopithecus africanus were involved in arboreal activities that are thought to be key for feeding, nesting, and predator avoidance. We conclude that many of the so-called retained ape-like features persisted due to stabilizing selection, that early hominins engaged in a considerable amount of arboreality even after Australopithecus had become a habitual biped, and arboreality only ceased to be an important component of hominin locomotor behavior after the emergence of Homo erectus.

The effects of femoral metaphyseal morphology on growth plate biomechanics in juvenile chimpanzees and humans

The distal femoral metaphyseal surface presents dramatically different morphologies in juvenile extant hominoids-humans have relatively flat metaphyseal surfaces when compared with the more complex metaphyseal surfaces of apes. It has long been speculated that these different morphologies reflect different biomechanical demands placed on the growth plate during locomotor behaviour, with the more complex metaphyseal surfaces of apes acting to protect the growth plate during flexed-knee behaviours like squatting and climbing. To test this hypothesis, we built subject-specific parametric finite-element models from the surface scans of the femora of five Pan and six Homo juveniles. We then simulated the loading conditions of either a straight-leg or flexed-knee gait and measured the resulting stresses at the growth plate. When subjected to the simulated flexed-knee loading conditions, both the maximum and mean von Mises stresses were significantly lower in the Pan models than in the Homo models. Further, during these loading conditions, von Mises stresses were strongly negatively correlated with ariaDNE, a measure of complexity of the metaphyseal surface. These results indicate that metaphyseal surface morphology has a robust effect on growth plate mechanics.

The morphogenesis of porcine femoral head mammillary processes: A structural mechanism of biomechanical stability

The capital femoral physis is a growth plate located between the head of the femur and femoral neck, which forms a temporary joint where growth plate cartilage is converted to bone by endochondral ossification. The bone-cartilage-bone interface develops a unique radial pattern of interdigitating mammillary processes that interlock the femoral head with the metaphysis, increasing biomechanical stability. The arrangement of these mammillary processes may not be a random occurrence and likely serves to provide mechanical mechanisms to enhance biomechanical stability. In this study, we provide a qualitative and quantitative analysis of porcine femoral head mammillary processes and focus on the analysis of six key points of development: the epiphyseal tubercle, epiphyseal cupping, growth plate slope angles, expansion of the epiphyseal subchondral bone plate, epiphyseal elongation, and the emergence of smaller, radially arranged mammillary processes. We introduce a metric of surface roughness analysis to quantify mammillary processes and apply it to analyze the development of the observed radial pattern of peripheral mammillary processes from birth to adolescence. We hypothesized that these processes develop to form a radial pattern with some degree of periodicity beginning relatively early in development of the joint and increase in prominence with age and weight of the animal. These findings may have important implications in the early diagnosis and treatment of the hip disorder slipped capital femoral epiphysis (SCFE). Underdevelopment of femoral head mammillary processes may reduce joint stability and could be a risk factor in SCFE.