An optical detection method is provided, wherein a body part (5) comprising at least one joint is irradiated with light. Local attenuation of the light by the body part (5) is detected as attenuation measurements (2) at the position of the at least one joint and at the position of at least one other portion of the body part (5); and wherein blood flow to and/or from the body part (5) is temporarily at least partially blocked and thereafter enabled again (3). Distinct local attenuation measurements for the at least one joint and for at least one other portion of the body part (5) are performed for at least two of the times before (I), during (II), and after (III) the blocking of blood flow.