An equinus contracture is the inability to bring the foot up to a neutral position (a right angle to the lower leg) due to either tightness of the muscles and/or tendons in the calf, scarring of the ankle joint capsule and other restraining structures, or a bone spur at the front of the ankle that restricts normal ankle motion. It is named after horses (equine) who essentially walk “on their toes.”
A gastrocnemius equinus contracture (Figure 1) occurs when tightness in the outer calf muscle (gastrocnemius) leads to limited ankle dorsiflexion (motion through the ankle joint itself). To compensate for this tightness and allow the foot to settle on the ground compensatory motion will often occur in the joint in front of the ankle, the transverse tarsal joint, which is made up of the talonavicular joint and the calcaneal-cuboid joints (Figure 2). The hallmark of a gastrocnemius equinus contracture is that it will correct (i.e ankle motion will become full) when the knee is bent because the pressure is taken off the gastrocnemius muscle, since it attaches above the knee joint.
Figure 1: Limited motion through the ankle joint
Figure 2: Compensatory motion through the joints in front of the ankle joint
edited October 14th, 2012