Alterations in Bone Development Resulting from Growth-Period Lower Limb Loading in Guinea Fowl

open_access
Open Access
Author:
Ortiz, Valeria
Millennium Scholars Program:
Biomedical Engineering (BME)
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisor:
Jonas Rubenson, Thesis Supervisor
Justin Lee Brown, Honors Advisor
Keywords:
bone growth
guineafowl
cross-sectional geometry
exercise
differential limb-loading
growth-period development
biomechanics
Abstract:
Humans have become increasingly sedentary in recent generations, leading to a variety of health complications. Meanwhile, bone development and remodeling are complex, difficult to predict, and poorly understood, especially during the growth stage. In this study, we aimed to observe the effects of differential loading on the lower limbs of guinea fowl. We hypothesize the loaded limb will develop shorter bone lengths and an increase in cortical bone strength as a result of loading during the growth period. We used 20 two-day old guinea fowl to test our hypothesis, with 10 control (CON) and 10 limb-loaded (EXP) birds, where the EXP birds had a mass of ~4% body weight attached to their right tarsometatarsus (EXP R-LL) starting at 2 weeks. All birds were exercised 3 times per week for 30 minutes over 14 weeks. The left (unloaded) and right (limb-loaded) tibiotarsus and tarsometatarsus bones were imaged using micro-CT, processed via FIJI, and segmented using a Regularized Deep Network approach. Monte-Carlo randomization tests were performed to evaluate the right-left differences and compare the experimental and control groups using cross-sectional geometric (CSG) properties and bone lengths. Contrary to our hypothesis, we did not see functionally significant differences in bone length. The statistical analyses found that between the left and right EXP group tarsometatarsi, the right was significantly (p < 0.05) thicker (a greater cortical area) than the left in the 30-60% of bone length regions, supporting the hypothesis. For the EXP group tibiotarsi, the left was significantly thicker than the right in the 30-80% of bone length regions. A significant difference in maximum second moment of area was found from the 40-60% of tarsometatarsus bone length with the right limb moments greater than the left, while the tibiotarsus left limb moments were significantly greater than the right through the entire 20-80% of bone length region studied. For the polar section modulus, significant differences were found in the tarsometatarsus in the 40-60% bone length region, and in the tibiotarsus across the entire 20-80% bone length region observed. Our study shows that different levels of activity can trigger a plastic response in the bone development of animals, even bilaterally within the same individual. This further reveals the importance of the type of activity done in the growth period and emphasizes that differential loading throughout childhood significantly alters the size and shape of our bones.