Evaluation of bone mechanical strenght and fracture risk assessment (Frax) in patients with hip joint replacement surgery.

BACKGROUND Fracture risk assessment tools are useful to calculate the long term probability of osteoporotic fracture. However, how it reflects bone quality is unknown. The aim of this study was to correlate the WHO clinical fracture risk assessment tool, FRAX, with bone mechanical properties. METHODS Six patients submitted to hip replacement surgery, either due to osteoporotic fractures or to osteoarthritis, were evaluated. Bone samples were collected and the mechanical properties assessed by compression tests. Patients' data regarding the presence of clinical risk factors for fracture were registered. Laboratorial assessment of bone metabolic parameters and a dual X-ray absorptiometry(DXA) were done. RESULTS Analysis of the load-displacement curves showed that patients with fragility fractures (n=4) had low values of elastic modulus, yield load and energy absorbed until yield point. Osteoarthritis patients tend to have a better biomechanical performance.Femoral neck DXA scan was also performed in 3 patients. Fragility fracture patients had a lower bone mineral density than the patients with osteoarthritis. FRAX algorithm was applied and a positive relation was found between FRAX results and biomechanical parameters. Blood bone metabolic markers were within the normal range for all the subjects. CONCLUSIONS The worse mechanical properties observed in the fragility fracture patients were related to high probability of fracture given by FRAX. These observations, in a very small sample, need further confirmation. However, they suggest that the fracture risk assessment tool, FRAX, may reflect the current mechanical bone behavior of the patient.