Mechanical and morphological properties of trabecular bone samples obtained from third metacarpal bones of cadavers of horses with a bone fragility syndrome and horses unaffected by that syndrome.

OBJECTIVE: To determine morphological and mechanical properties of trabecular bone of horses with a bone fragility syndrome (BFS; including silicate-associated osteoporosis). SAMPLE: Cylindrical trabecular bone samples from the distal aspects of cadaveric third metacarpal bones of 39 horses (19 horses with a BFS [BFS bone samples] and 20 horses without a BFS [control bone samples]). PROCEDURES: Bone samples were imaged via micro-CT for determination of bone volume fraction; apparent and mean mineralized bone densities; and trabecular number, thickness, and separation. Bone samples were compressed to failure for determination of apparent elastic modulus and stresses, strains, and strain energy densities for yield, ultimate, and failure loads. Effects of BFS and age of horses on variables were determined. RESULTS: BFS bone samples had 25% lower bone volume fraction, 28% lower apparent density, 18% lower trabecular number and thickness, and 16% greater trabecular separation versus control bone samples. The BFS bone samples had 22% lower apparent modulus and 32% to 33% lower stresses, 10% to 18% lower strains, and 41 % to 52% lower strain energy densities at yield, ultimate, and failure loads, compared with control bone samples. Differences between groups of bone samples were not detected for mean mineral density and trabecular anisotropy. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that horses with a BFS had osteopenia and compromised trabecular bone function, consistent with bone deformation and pathological fractures that develop in affected horses. Effects of this BFS may be systemic, and bones other than those that are clinically affected had changes in morphological and mechanical properties.

Robust QCT/FEA models of proximal femur stiffness and fracture load during a sideways fall on the hip.

Clinical implementation of quantitative computed tomography-based finite element analysis (QCT/FEA) of proximal femur stiffness and strength to assess the likelihood of proximal femur (hip) fractures requires a unified modeling procedure, consistency in predicting bone mechanical properties, and validation with realistic test data that represent typical hip fractures, specifically, a sideways fall on the hip. We, therefore, used two sets (n = 9, each) of cadaveric femora with bone densities varying from normal to osteoporotic to build, refine, and validate a new class of QCT/FEA models for hip fracture under loading conditions that simulate a sideways fall on the hip. Convergence requirements of finite element models of the first set of femora led to the creation of a new meshing strategy and a robust process to model proximal femur geometry and material properties from QCT images. We used a second set of femora to cross-validate the model parameters derived from the first set. Refined models were validated experimentally by fracturing femora using specially designed fixtures, load cells, and high speed video capture. CT image reconstructions of fractured femora were created to classify the fractures. The predicted stiffness (cross-validation R (2) = 0.87), fracture load (cross-validation R (2) = 0.85), and fracture patterns (83% agreement) correlated well with experimental data.

Material properties are related to stress fracture callus and porosity of cortical bone tissue at affected and unaffected sites.

Stress fractures are overuse injuries of bone that affect elite athletes and military recruits. One response of cortical bone to stress fracture is to lay down periosteal callus. The objectives of this study were to determine if material properties are different among bones with different stages of stress fracture callus, at both a callus site and at a distal site. Cortical specimens were mechanically tested to determine their stress-strain response. Material property differences were examined using nonparametric and regression analyses. At the callus site, material properties were low during the earliest stages of callus, higher with increasing callus maturity, but dropped at the late stage of callus. At the distal site, the material properties were low during early stages of callus and approached, or returned to, those of bones without callus during the late stages of callus. The effects of stress fracture and bone callus are not limited to the focal site of stress fracture.