Abstract: Attempts have been made to facilitate orthopedic diagnostic procedures by microphonic detection of emissions from a moving joint, with analysis of such emissions to establish correlation with pathological conditions, but these attempts have failed. Success in such a procedure is now found to require detection of emissions extending into the subsonic frequency range. Preferably a piezoelectric accelerometer detector (10) is used in direct contact with the skin. A plurality of detectors can be used around a joint with comparative analysis to localize a condition. Analysis suitably involves a frequency analyzer (14) with the possible intermediary of a multi-track tape recorder (12), the analyzer output being displayed by a printer (15) preferably of ink-jet form. One useful correlating emission characteristic is peak frequency for early diagnosis for congenital dislocation of the hip in an infant.