An apparatus for detecting loosening of an implant imbedded in a bone of a limb of a patient, includes a vibrator is pressed into engagement with the limb to impart vibratory motion to the bone. The vibrator is controlled to cause the vibratory motion to have a predetermined recurring pattern. A pickup device is pressed into engagement with the limb spaced from the vibrator over the same bone near the implant, for detecting the vibratory motion transmitted through the bone implant composite to generate an output signal. Implant loosening is determined when the recurring pattern of the output signal transmitted through the bone implant composite demonstrates sustained superimposition on the oscilloscope and/or significant secondary harmonics on the spectrum analyzer.