While the careful methodical measurement of the amplitude or range of motion of joints offers an opportunity to obtain valuable clinical data, it is even more valuable to record the progress toward complete recovery of certain types of joint disability. Taken in connection with measurement of muscle power the usefulness of the proceedure is, in certain cases, increased.
A simple type of instrument should be used. It is not possible in the ordinary hospital to have a mensuration department and therefore the more cumbersome instruments are not recommended.
As all bones move from the joint on an arc of a circle we may accept measurements reading in degrees as recorded on the ordinary quadrant or protractor scale, but it would seem most desirable that all observers use the same method of taking and recording their measurements, and this necessitates the use of a constant base line for each joint, and that the angle be taken in relation to this base line. Doubtless no better base line can be found than the long axis of the proximal bone member of the joint under observation. For the shoulder and hip we use a line parallel to the long axis of the body and stopping at the anterior end of the axis of the motion. For rotation of the humerus and femur we use a vertical, in the first at the flexed (90 degrees) elbow and in the second at the sole of the foot. For supination and pronation the most convenient base line is a horizontal line across the closed fist with the hand in full supination.