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Orthopedic and Rehabilitation Engineering

Orthopedic and Rehabilitation Engineering - Poster Session D

Poster K9 - Postnatal Development of the Goat Phalanges and Metacarpal Trabecular Architecture

Friday, October 25, 2024
3:30 PM – 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Trabecular bone only makes up 20% of the human skeleton, yet it is the main load-bearing compartment of bone. While bone mineral density (BMD) is commonly used to measure bone strength, it has been identified that combining it with 3D trabecular microstructural indices improves the accuracy of assessing mechanical properties (Ulrich et al. Bone 1999). Investigating trabecular osteogenesis, specifically trabecular microarchitecture, is therefore crucial for understanding bone development and improving diagnosis of bone-related diseases. In this study, goats were used as an animal model to study long bone development because they experience similar levels of loading to humans. Unlike humans, goats only have 2 phalanges, and their metacarpus is fused for both phalanges, thus one phalanx can be purposefully overloaded and the other under-loaded. Ruminants have previously been used as large animal models in bone development research, including studies on osteoporosis (Dias et al., Curr Osteoporos Rep, 2018). In this experiment, high-resolution micro-computed tomography (µCT) was used to quantify trabecular bone microarchitecture by calculating morphometric indices and bone volume in goat proximal phalanges 1 (P1) and metacarpus from birth to adulthood. The fusion of the epiphyseal metacarpus in goats occurs during postnatal development and was quantified by measuring the fusion length at the different maturation stages. The aim of this study is to establish a baseline of trabecular bone growth to encourage future research on the underlying mechanobiology and effects of mechanical cues on bone development.

Materials and

Methods:  The analysis was performed on 44 goats at different postnatal stages: 3 days (neonate, n=9), 1.5 months (1.5M, n=6), 3 months (3M, n=5), 6 months (6M, n=6), 9 months (9M, n=6), 12 months (12M, n=6), and 3.5 years (adult, n=6).
To prepare for imaging, the bone samples were wrapped in gauze and submerged in PBS (scanning medium). The image acquisition was performed in a Scanco µCT45 system with an X-ray intensity of 145 µA, an energy of 55 kVP, an integration time of 400 ms and a resolution of 10.4 µm (isotropic voxel size). In the reconstructed scans, the trabecular region in each sample was segmented semi-automatically through a combination of manual contouring and range extrapolation across ~2,000 slices. The bone volume fraction (BV/TV) was measured from the 2D sections while trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp) were calculated using a sphere-fitting method. To measure the epiphyseal fusion length (FL) in the metacarpi, the voxel size was multiplied by the total number of slices from the first fusion point below the growth plate to the last point of fusion.
For each sample, the data from lateral and medial metacarpal bones were averaged, as were the data from the right and left phalanges. A one-way analysis of variance (ANOVA) with a Tukey’s post-hoc test (ɑ = 0.05) was conducted to identify significant differences between groups.

Results, Conclusions, and Discussions: An increase in P1 BV/TV was observed (Fig.1B), reflecting rapid bone growth relative to total tissue as it matures. The increase in Tb.N and Tb.Th indicates formation of new trabeculae and their increased thickness (Fig.1C-D). The decline in Tb.Sp (Fig.1E) highlights reduced spacing between trabeculae, forming a denser network. This implies that the bone is becoming stronger and better able to sustain mechanical loading.

Metacarpi BV/TV and Tb.Th consistently increased (Fig.2B-D). However, Tb.N didn't change significantly until 12M, suggesting that postnatal development of the metacarpi is characterized by strengthening existing trabeculae rather than forming new ones (Fig.2C), as opposed to P1. No significant changes in Tb.Sp were observed (Fig.2E), meaning alteration to trabecular spacing isn’t a factor in bone maturation. Between 3M-6M, a decrease in BV/TV, Tb.Th and Tb.N, coupled with an increase in Tb.Sp may represent a period of bone remodeling (Fig.1-2).

The metacarpus fused at 3M and FL rose through 12M, before experiencing a significant drop (Fig.2F). This decline may result from the complete bone fusion at all points, unlike in younger samples.

This study outlines trabecular development in goat phalanges and metacarpi, revealing dynamic growth in P1 and stable growth in metacarpi. Future studies will employ histology to explore changes in cellular architecture during postnatal development. Furthermore, we plan to use goats as a model system to alter the mechanical environment to examine how mechanical loading affects trabecular osteogenesis and metacarpal fusion.

Acknowledgements (Optional):