Living With Polio

Joint Deformities

Modern biomechanical and gait analyses identify excessive demands being placed on the joints and muscles. Overly strained muscles, tendons, and ligaments wear out. The proper therapeutic approach is to correct any deformities and to reduce excessive strain with appropriate orthoses (bracing), assistive devices (canes, crutches, etc.), changes in lifestyle, or selective reconstructive surgery.

Joint deformities are most common in the lower extremities. An individual’s function may be limited due to the abnormal postures required for standing and walking. Deformities, also a source of pain, can be grouped based on their cause: soft tissue contractures, excessive ligamentous laxity, and abnormal bony angulation.

Contractures (restrictive soft tissue tightness) develop from muscle imbalances around a joint. If opposing muscle lacks the strength to move a joint through its normal range of motion, the stronger muscle may become short and the opposing weaker muscle may become stretched. Additionally, the joint and ligaments may become stiff and limited in the direction of the weaker muscle. For example, a fixed drop foot (ankle equinus) is caused by a tight heelcord which develops when the muscles on the front of the leg no longer can lift the foot. Walking with such a deformity creates additional strains on the knee and twisting of the foot. Ankle equinus can be accommodated with an orthosis if the ankle is stabilized in the equinus position and a compensatory heel lift is added. Applying heat and stretching can be tried, but often the only satisfactory answer is surgery to lengthen (release) the tendon. The foot corrected by surgery may require an orthotic support.

Ligamentous laxity allows excessive joint motion. Because ligaments, the tissue which connects bones to bones, may be the weight-bearing substitute for paralyzed muscles, they can become stretched by long-term use. For example, when the quadriceps is paralyzed, the individual may lock the knee in an excessive hyperextensive position (back knee). If the back knee deformity is only 10%, the stress on the ligaments behind the knee is minimal and can be tolerated for years. A 20% deformity doubles the force and threatens the stability of the ligaments. With constant abuse, the individual muscle fibers yield to the strain, the deformity progresses, and pain follows. These symptoms can be relieved with a knee-ankle-foot orthosis (KAFO) designed to limit the back knee angle while allowing enough hyperextension to substitute for the absent quadriceps. There is no effective surgical answer.

Bony deformities most often develop in childhood when postural substitutions due to weak and/or paralyzed muscles create uneven loading of the bone’s growth plates. For example, if the abductor muscles are paralyzed, the polio survivor may use a lateral trunk sway to stabilize the hip, resulting in a stretching strain to the inside knee joints, producing “knock knee.” Later, the bony deformity may increase as the joint surfaces erode with constant uneven weight-bearing. Knee bracing or KAFO can often relieve the pain. Corrective surgery may be necessary if secondary pressure areas develop or if orthotics break repeatedly.

Excerpt from PHI’s “Handbook on the Late Effects of Poliomyelitis for Physicians and Survivors.” © 1999

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