Skeletal Bone Structure and Repair in Small Mammals, Birds, and Reptiles

Osteohistological analysis of metatarsals reveals new information on pathology and life history of troodontids from the Campanian Dinosaur Park Formation, Alberta, Canada

Troodontidae is a family of small-bodied theropods known predominantly from Asia but are comparatively scarce in North America. In the Dinosaur Park Formation (DPF) of Alberta, Canada, they are known predominantly from isolated material, precluding taxonomic and ontogenetic precision for this clade. Previously never sampled histologically within the DPF, here we attempt to fill in gaps in our knowledge about the life histories of the clade in this formation by histologically surveying metatarsals, which are among the most abundant and identifiable troodontid elements in the DPF. We sampled 11 metatarsals (three metatarsal IIs, three metatarsal IIIs and five metatarsal IVs) of varying sizes and included three pathological individuals to describe the microanatomy of both healthy and pathological metatarsals, determine the ontogenetic status of each element and graph their pattern of growth. Osteohistology reveals that troodontid metatarsals grew and remodelled asymmetrically within the cortex, ceasing growth and remodelling primarily along articular surfaces and entheses. Pathological individuals ranged from displaying features of response to localised stress (chronic callus formation and avulsion/chip fracture) to extreme modification in response to trauma and inflammation at the distal joint. Only the latter appeared to be related to overall growth, suggesting the condition either developed early and stunted growth or another underlying cause was responsible for both the stunted growth and the resulting pathological features observed. Overall, tracking the growth of the specimens reveals that there are at least two growth trajectories within the DPF differentiated by the timing of major growth spurts and growth plateaus. Whether this represents sexual dimorphism, taxonomic diversity, or another form of variation warrants further investigation.

Histologic characterization of fracture repair process in wild birds in association with gross appearance of the bone lesion

This study aims to provide an in-depth examination of the histological changes that occur during the repair of untreated bone fractures in avian species, correlating these microscopic alterations with gross anatomical characteristics observed during different tissue repair phases. A total of 93 bone fractures from different wild birds were analyzed and classified based on temporality (acute, subacute, and chronic) according to the color changes of the hematoma and morphology (open or closed; simple, comminuted, or greenstick fractures). From a microscopic standpoint, a strong correlation was observed between the temporal progression observed macroscopically and the histological changes evident in each temporal category. Microscopic variations were found to depend on the nature of the fracture. Lesional patterns directly related to the macroscopic appearance of the fracture were established. Acute fractures exhibited extensive hematomas and an intense inflammatory response; subacute fractures showed immature granulation tissue and early signs of soft callus formation; and finally, chronic fractures were characterized by prominent soft calluses and hard calluses in different stages of development. The possible factors influencing each phase of the healing process, such as the characteristics of the type of fracture, the stability of the fracture site, bacterial contamination, the chronicity of the fracture, and the potential differences in the progression of histological changes between different animal species, are discussed. This association may be of clinical utility in decision-making for the treatment and prognosis of bone fractures in birds.

Anaerostipes caccae CML199 enhances bone development and counteracts aging-induced bone loss through the butyrate-driven gut-bone axis: the chicken model

BACKGROUND

The gut microbiota is a key regulator of bone metabolism. Investigating the relationship between the gut microbiota and bone remodeling has revealed new avenues for the treatment of bone-related disorders. Despite significant progress in understanding gut microbiota-bone interactions in mammals, research on avian species remains limited. Birds have unique bone anatomy and physiology to support egg-laying. However, whether and how the gut microbiota affects bone physiology in birds is still unknown. In this study, we utilized laying hens as a research model to analyze bone development patterns, elucidate the relationships between bone and the gut microbiota, and mine probiotics with osteomodulatory effects.

RESULTS

Aging led to a continuous increase in bone mineral density in the femur of laying hens. The continuous deposition of medullary bone in the bone marrow cavity of aged laying hens led to significant trabecular bone loss and weakened bone metabolism. The cecal microbial composition significantly shifted before and after sexual maturity, with some genera within the class Clostridia potentially linked to postnatal bone development in laying hens. Four bacterial strains associated with bone development, namely Blautia coccoides CML164, Fournierella sp002159185 CML151, Anaerostipes caccae CML199 (ANA), and Romboutsia lituseburensis CML137, were identified and assessed in chicks with low bacterial loads and chicken primary osteoblasts. Among these, ANA demonstrated the most significant promotion of bone formation both in vivo and in vitro, primarily attributed to butyrate in its fermentation products. A long-term feeding experiment of up to 72 weeks confirmed that ANA enhanced bone development during sexual maturity by improving the immune microenvironment of the bone marrow in laying hens. Dietary supplementation of ANA for 50 weeks prevented excessive medullary bone deposition and mitigated aging-induced trabecular bone loss.

CONCLUSIONS

These findings highlight the beneficial effects of ANA on bone physiology, offering new perspectives for microbial-based interventions for bone-related disorders in both poultry and possibly extending to human health. Video Abstract.

Retrospective Analysis of Pelvic Limb Fracture Management in Companion Psittacine Birds (60 Cases)

Pelvic limb fractures carry significant morbidity in avian patients, and although management options are well researched, published data on long-term complication rates and mortality outcomes are limited. Here, we present a cross-sectional study evaluating pelvic limb long bone fractures in companion psittacine birds presenting to an exotic-only veterinary hospital in the United Kingdom between 2005 and 2020, focusing on fixation techniques and long-term outcomes. Of the 60 cases that met the inclusion criteria, 22 separate species were represented, with an age range of 8 weeks to 25 years and an even distribution of sexes, among those that had been sexed. The majority of fractures (71.7%) were tibiotarsal; femoral (15%) and tarsometatarsal (13.3%) bones represented the other fracture sites. Several different fracture management methods were used, including external coaptation, surgery, or cage rest. Average time from fracture identification to healing was 33 days, with a median of 31 days and a range of 11-121 days. Satisfactory resolution of fracture repair was achieved in 85.5% (47/55) of cases that were able to be followed to conclusion. Complications were identified in 41.7% (25/60) of fractures of all pelvic long bones. Complications during fracture management were more common in cases treated with external coaptation. The most common complication reported was patient interference with bandages, splints, or both. This study provides an overview of pelvic limb long bone fracture management outcomes, which should prove useful for avian practitioners in clinical practice.

Chronic fracture and osteomyelitis in a large-bodied ornithomimosaur with implications for the identification of unusual endosteal bone in the fossil record

Paleopathological diagnoses provide key information on the macroevolutionary origin of disease as well as behavioral and physiological inferences that are inaccessible via direct observation of extinct organisms. Here we describe the external gross morphology and internal architecture of a pathologic right second metatarsal (MMNS VP-6332) of a large-bodied ornithomimid (~432 kg) from the Santonian (Upper Cretaceous) Eutaw Formation in Mississippi, using a combination of X-ray computed microtomography (microCT) and petrographic histological analyses. X-ray microCT imaging and histopathologic features are consistent with multiple complete, oblique to comminuted, minimally displaced mid-diaphyseal cortical fractures that produce a "butterfly" fragment fracture pattern, and secondary osteomyelitis with a bone fistula formation. We interpret this as evidence of blunt force trauma to the foot that could have resulted from intra- or interspecific competition or predator-prey interaction, and probably impaired the function of the metatarsal as a weight-bearing element until the animal's death. Of particular interest is the apparent decoupling of endosteal and periosteal pathological bone deposition in MMNS VP-6332, which produces transverse sections exhibiting homogenously thick endosteal pathological bone in the absence of localized periosteal reactive bone. These distribution and depositional patterns are used as criteria for ruling out a pathological origin in favor of a reproductive one for unusual endosteal bone in fossil specimens. On the basis of MMNS VP-6332, we suggest caution in their use to substantiate a medullary bone identification in extinct archosaurians.

Untargeted metabolomics study on the effects of rearing ducks in cages on bone quality

The cage rearing model of the modern poultry industry makes the bones of birds more vulnerable to deterioration. In this study, at 8 wk of age, a total of 60 birds were randomly allocated to 2 groups, including the floor rearing group (FRD) and cage rearing group (CRD), and their body weight was measured every 2 wk. At the age of 20 wk, the tibia, femur, and humerus were collected from each group (n = 12) to determine the bone quality parameters such as weight, size, bone mineral density (BMD), breaking strength, cortical thickness, and area, ash content, calcium (Ca) content, and phosphorus (P) content. Meanwhile, the serum metabolome composition of both groups was detected by untargeted metabolome technology. The results showed that there were no significant differences in body weight, bone weight, and size between the 2 groups (P > 0.05), but the humerus mineral density and the breaking strength, cortical bone thickness, cortical bone area percentage of tibia, femur, and humerus of CRD was significantly lower than those of FRD (P < 0.05), indicating that the cage rearing system caused the deterioration of bone quality. Based on nontarget metabolomics, 49 metabolites were correlated with bone quality parameters, and 10 key metabolites were strongly correlated, including erucic acid, citric acid, and ketoleucine. In addition, the KEGG analysis showed that the caged system mainly perturbed amino acid metabolism, lipid metabolism, and energy metabolism, which led to changes in related metabolite levels, produced ROS, and altering energy supply, thus leading to a deterioration of bone quality of cage rearing ducks. Therefore, our findings were helpful to further understand the potential mechanism of the deterioration of duck bone quality in cage rearing system, provided a theoretical basis for reducing the occurrence of poultry osteoporosis, and ensuring the healthy development of poultry breeding.