A disposable medical device is especially an articulation for the relative positioning of fixation bars or of pins of an external fixator, having at least a clamping means (1, 10, 12) to be introduced into the medical device, Said clamping means (1, 10, 12) comprises an element (20, 30, 40) that alters when being heated over a threshold temperature, thus giving optical or mechanical information that the device should not be used a second time.