Can the contralateral limb be used as a control during the growing period in a rodent model?
Introduction
Bilateral symmetry of long bones is used by the researchers in musculoskeletal research and clinical practice. It is a commonly hypothesized concept used in geometric, biological and clinical studies. It is deemed as a reflection symmetry in which similar anatomical parts are arranged on opposite sides of a median axis so that only one plane of symmetry can divide the individual into substantially identical halves [1]. Usually, symmetries are perceived as extrinsic geometric and volumetric properties of shapes [2], implying that with a different orientation, the geometric shape of a structure is similar to another structure. The use of a contralateral limb as a reference is not new in animal studies. It has been used in various clinical, forensic and anthropological studies [3], [4], with the implicit presumption of minimal or no significant differences between bilateral limb. Many rat bone modeling and remodeling studies have been conducted employing bilateral limbs with one of the limbs as control from experimental animals [5], [6]. Rat tibial models have been used to investigate the effects of aging, mechanical loadings, surgical treatments, and genetic mutations on the changes in the microarchitecture and morphological parameters of the bones [7], [8]. Also, they have been used for assessing the bone response under mechanical loading conditions [7]. Comparisons of the anatomical, morphological, and mechanical properties in one tibia are contrived respective to the bilateral limb based on the hypothesis that the observed changes under experimental conditions would be identical in both control and experimental tibiae [9]. Studies have been performed to establish physical and geometric similarities in animal models with paired bones [10]. However, there are no reports comparing three-dimensional (3D) symmetry for rat tibiae.
A comprehensive study of tibial morphology and anatomical features would be useful in understanding its adaptation to loading, medical treatment, and surgical intervention. Previous studies have assessed the asymmetry of long bones by evaluating cross-sectional, limited volumetric and mechanical properties [11], [12], and implemented partial aspects to quantify left-right symmetry rather than using a full 3D geometric comparison. The most common methods implemented include measuring distances between anatomical landmarks [13], comparing mechanical strength and stiffness [14], as well as morphometric data [15], and geometric parameters [12]. These analyses do not fully assess the degree of deviation between bilateral limbs in 3D geometric form. To our knowledge, there are no studies quantifying the symmetrical/asymmetrical nature of the rat tibial bones, a bone model commonly used by the scientific community. In some studies [16], [17], bones were investigated during the rat growing period, where bones experienced developmental changes along with the effects of the experimental conditions. Comparisons were made either between experimented tibia with the contralateral controls or between run-trained, and jump-trained groups with paired experimented limbs comparing each other, assuming that there are no significant differences between the bilateral limbs. However, there is still a paucity of data on the investigation of mechanical, geometrical and morphological symmetry between bilateral tibiae to determine whether the contralateral tibia can be used as an equivalent control in experimental studies.
The goal of this study was two-fold. First, to determine the extent of overall 3D similarity between left and right growing rat tibiae. Secondly, the bone morphology, including cortical and trabecular bony segments, the whole bone geometry as well as the bone mechanical properties, were assessed and the degree of bilateral variability among the tibial pairs with developmental stages was investigated.
Section snippets
Animals
Eighteen (n = 18) male Sprague–Dawley rats (Charles River Laboratories, Montreal) were divided into three groups (n = 6 per group): 4, 8 and 12-week old. Rats were housed at 25°C with a 12-h light/dark cycle and provided with a standard laboratory diet and water ad libitum. On the experiment day, body weights were measured, rats were euthanized with carbon dioxide inhalation, and both tibiae were carefully dissected. The tibiae were imaged with micro-CT, and three-point bending tests were then
Overall 3D bone geometry
Results showed non-uniform deviation contours along the tibiae for the three age groups (Figs. 2 and 3). The maximum, mean positive and negative deviations, as well as RMS, are given in Table 1. The maximum and mean surface deviations, inward and outward, increased from 4 to 8 and 12-week old groups (Table 1), except for average positive deviation of the 12-week old group. A comprehensive distribution of the extent of deviation between left and right tibial geometry is presented in Table 2. The
Discussion
The purpose of this study was to investigate the symmetry of bone biomechanical strength and morphology in the rat tibiae during the adolescent period to assess the efficacy of using contralateral leg in various bone investigation studies involving immature rats. To do so, we first determined the degree of symmetry in the 3D whole geometry of bilateral rat tibiae during the growing period. Secondly, we evaluated the symmetry of morphological and biomechanical properties of rat tibiae in the
Conclusions
In summary, left and right rat tibiae exhibited a high degree of symmetry during the adolescent period, with no significant differences among all evaluated mechanical, geometrical and morphological parameters between the bilateral tibiae. This suggests that right and left tibiae can be considered symmetrical in nature. Left-right bilateral symmetry analysis for long bones (i.e., tibia) has great importance for biomechanical testing, design of implants, and for the use of the contralateral bone
Acknowledgments
The authors acknowledge helpful contributions and technical skills of laboratory team members as well as Sainte-Justine University Hospital's animal care technicians. Funding for this study was provided by NSERC (IV), the CRC Program (IV) and the NSERC/CREATE program (TM).
Competing interests
None declared.
Ethical approval
Not required.
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