A goniometer (also sometimes referred to as an arthrometer, fleximeter, or pronometer) for measuring the range of motion of an animal knee includes an anchor platform to which an animal's upper leg (femur) may be affixed, and a mobile platform to which the animal's lower leg (shin and tibia) may be affixed so that the upper and lower leg are situated along a common axis. The mobile platform is preferably movable in two degrees of freedom (translational and rotational) about the anchor platform so that the relative motion of the platforms causes the upper and lower leg to move about the intermediate knee joint. A force transducer (such as a spring scale) and/or a torque transducer (such as a common torque wrench) may be used to obtain measurements of the laxity of the knee joint.