Determination of Total Hip Arthroplasty Stem Stability by Intraoperative Measurement Using an Acoustic Testing Technique

Introduction: The lack of initial post-operative implant stability is recognized as an important determinant in the aseptic loosening process of cementless stem. However, there is no objective method to evaluate the mechanical stability at the time of implantation. In our previous study, it is confirmed that our system could successfully provide a criterion of the appropriate size of the rasp by measuring the acoustic energy(1). This study presents the intraoperative protocol derived from the previous in vitro study and the results of intraoperative measurements using an acoustic testing technique. Materials and Methods: The experimental apparatus consists of a custom microphone and a data acquisition system. The custom microphone is a bone contact microphone (Yamaha Corps, QQ1YSK001107). The data acquisition system consists of a portable microphone amplifier (Audio-Technica Inc., AT-MA2), a USB oscilloscope (Pico Technology, ADC-210/100) and a computer. A clinical evaluation was conducted during THA. A volunteer patient (a 73-year-old man with OA) was included in this study after informed consent and approval by the institutional review board. The femoral head of the femur was removed and the smallest rasp (#4) was inserted. Once the rasp seated at the neck level, the microphone was attached(Fig.1).