Acoustic transmission in normal human hips

A non-invasive acoustical system has been developed for the measurement of transmission properties of acoustic waves in the hip joints. The instrumentation consists of three sub-systems. An excitation system applies a vibratory force at the sacrum of the test subjects. A transduction system includes a pair of identical microphones installed in the tubes of two stethoscopes, which were placed at the greater trochanters on both sides for picking up the acoustic signals transmitted across the hip joints. The data acquisition and analysis system is a portable frequency analyser with a dual channel digital filter program for measuring the power of acoustic signal in 1/3-octave frequency bands. Twenty-seven healthy adults, 20 healthy pre-school children and 19 normal neonates were randomly selected for testing. Coherence function and transfer function were measured during the testing. Results from the three groups showed that there was a high coherence of the signals (>0.9) and a small discrepancy (<3 dB) between bilateral hips in the frequency range 200-315 II. For normal neonates, there was a wider frequency range (160-315 Hz) in which the acoustic signals maintained a high coherence (>0.94) and a smaller discrepancy (<2 dB) was observed between bilateral hips. This study has shown that the development of the acoustical technique provided a practical method with objective parameters. The results obtained in this study can offer a baseline for further investigation of hip disorders particularly those related to structural abnormalities of the hip.