Apparatus for testing an implant (3) attached to a bone (4) of a human or animal subject comprises a cantilever beam (1) releasably attached to the implant. The beam carries a transducer (5) for exciting the beam (1) with a variable frequency AC signal, and a transducer (6) for detecting a resonance frequency of the beam. The detected resonance frequency is used to assess the degree of attachment of the implant (3) to the bone (1).