The evaluation of bone remodeling about orthopaedic implants with ultrasound

Total hip arthroplasty causes biomechanical changes in the normal femur, including a redistribution and concentration of stress. These mechanical alterations in the femur cause local remodeling and resorption that affect the geometry and mechanical properties of the bone. Two complementary ultrasonic techniques were used to study the local adaptive remodeling of bone due to prosthesis implantation. An ultrasonic wave propagation technique was used to determine elastic properties and a new scanning acoustic microscope (SAM) mapped the acoustic impedance profile of each section. The effects of the implantation of two types of hip prostheses, an uncemented bipolar prosthesis with an Austin-Moore type stem and a cemented Charnley prosthesis, were investigated. Both prostheses had a detrimental effect on local elastic properties as determined by acoustic velocity measurements. The SAM system provided information about local inhomogeneities in bone properties not obtainable by any other means. The acoustic impedance maps highlighted bone resorption and bone remodeling on a microstructural level.