A rheumatism scanner has a hand rest arranged between a radiation source and a detector unit and a holder for immobilizing the examined finger joint on the hand rest. The holder is a finger sled which can be fastened to the finger joint at a location remote from the hand rest, and thus remote from the rest of the scanner, and which is provided with a continuous joint recess. After a finger is fixed in the finger sled the finger sled can be brought into engagement with, and positioned exactly at, the hand rest by adjusting and/or fixing elements.