TWO-DIMENSIONAL FINITE ELEMENT ANALYSIS OF THE FORELIMB DISTAL SESAMOID BONE IN THE RACING THOROUGHBRED.
Heidi A. Wolgamuth, MS, Ph.D., Clifford R. Berry, DVM, Simon C. Roe BVSc, Ph.D., C. Frank Abrams, Ph.D., Jeff W. Eischen, Ph. D. College of Veterinary Medicine and College of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC 27606.
INTRODUCTION/PURPOSE: Remodeling of the distal sesamoid bone (DSB) has been shown to occur along the flexor cortex and in areas of ligamentous attachment sites. These remodeling changes can be seen in clinically normal and abnormal horses. Bands of high stress and areas of high strain within the DSB have been suggested to indicate locations of bone remodeling. A two-dimensional finite element model (2D-FEM) of the DSB can simulate the principal stresses and strains within the DSB. The purpose of this study was to develop 2D-FEMs of the midsagittal section of forelimb DSBs and analyze the principal stress and strain distributions within each model.
METHODS: Using quantitative computed tomography, the material properties and geometry of 15 DSBs from racing Thoroughbreds were incorporated into a 2D-FEM of each bone. Boundary conditions and forces were estimated based on previous data1 and cadaver measurements. Loading conditions that simulated a gallop were applied to the 2D-FEMs and the principal stresses and strains were analyzed. Areas of maximal stress and strain were compared with the flexor central eminence (FCE) and the intramedullary cavity on the microradiographs (100 mm thick) taken of the midsagittal section of the DSB using chi-square analysis.
RESULTS: Based on the principal stress and strain analysis of the 2D-FEMs, the areas of maximal stress occurred between the ligamentous attachment sites in all of the 2D-FEMs. Region 2 (area deep to the mid FCE) contained an area of maximal stress in 12/15 FEMs. The areas of maximal strain occurred in both the intramedullary cavity and the synovial invagination in 7/15 of the 2D-FEMs, and in just the intramedullary cavity in 8/15 of the 2D-FEMs. The correlation between the band of principal stress found in each 2D-FEM analysis, to the compaction of the reinforcement line in the respective microradiographs, was statistically significant, (p < 0.05). A trend was evident between the areas of maximal strain and sites on the microradiographs having an increased porosity.
DISCUSSION/CONCLUSIONS: Results from the 2D-FEM analysis support that active bone remodeling coincides with the principal stresses. The highest areas of stress correlated morphologically with areas of increased remodeling such as the compaction process and reinforcement line. The highest areas of strain appeared to correlate with areas of minimal remodeling and increased porosity (e.g.: synovial invaginations and the intramedullary cavity). The reinforcement line and compaction remodeling process along the inner surface of the flexor cortex follows along the direction of biomechanical loading between the suspensory ligament of the DSB and the distal (impar) ligament of the DSB.
1Bartel, D. L., H. F. Schryver, J. E. Lowe, and R. A. Parker. 1978. Locomotion in the Horse: A Procedure for Computing the Internal Forces in the Digit. Am. J. Vet. Res., 39, no. 11: 1721-1227.