Commonly Prescribed Orthoses for the Lower Limb

The word "orthosis" is derived from the Greek word "ortho," which means "to make straight." Orthoses (plural for orthosis) do "straighten" bones, but they also prevent deformities, enhance walking, assist with daily activities, alleviate pain, protect limbs, promote osteogenesis (bone growth), and strengthen the limbs and spine. An orthosis is an externally applied mechanical appliance or an apparatus that provides control, correction, and support of a limb. A brace (one type of orthotic) can either resist or assist motion to control a deformity, and often weight can be added or shifted to provide corrective measures. Orthoses are used to correct malalignments and deformities of the lower limbs, upper limbs, and spine. Perhaps the most widely recognized orthoses are those for the lower limbs, especially those pertaining to the foot, such as shoe inserts.

The most commonly prescribed orthoses for the lower extremity are the various types of ankle-foot orthoses, foot orthoses, and knee orthoses. These devices control, assist, or resist motion and are categorized by the joints and regions they control. They are often custom fabricated or custom fitted by making a cast of the patient's lower extremity or by taking measurements of the area.

The ankle-foot orthosis is widely used for various neuromuscular (nerve and muscle) disorders and to achieve a functional outcome after injury or surgery (Fig. 1). Ankle-foot orthoses eliminate foot-to-ground placement problems that affect heel contact and foot clearance. Ankle-foot orthoses also restore foot stability during the stance and the swing phases of walking and compensate for quadriceps (thigh muscle) weakness to prevent knee buckling. Ankle-foot orthoses are usually fabricated out of thermoplastic or metal. The design and material of an ankle-foot orthosis depend on the type of disorder and the desired functional outcome.

A foot orthosis (Fig. 2) is used to align and support the foot; to prevent, correct, or accommodate foot deformities; and to improve overall function of the foot. During walking, the normal foot changes from a supple, shock-absorbing structure to a rigid lever for push off. A flat foot that is supple and does not invert and become rigid does not effectively form a rigid lever for push off. Just the opposite occurs with a cavus, or high-arched, foot. A cavus foot is rigid and lacks shock absorption. During walking, the high-arched foot remains locked and fails to become supple for a comfortable stance. Flexible and rigid (unbending) shoe inserts can be purchased over the counter. Many people who suffer with foot problems try a store-bought insert first; then if the problem is not resolved, they seek the advice of their health care professional for a custom-made insert.

Knee orthoses are designed to control ligament deficiencies around the knee and are often custom made. For example, a knee orthosis for a patient with an injured anterior cruciate ligament resists abnormal forward translation of the tibia (large lower leg bone) on the femur (thigh bone). This is most often achieved through a control system that prevents hyperextension (extreme/excessive extension) of the knee (Fig. 3).

For osteoarthritis of the knee, similar orthoses are used, but they work on a different biomechanical principle. In osteoarthritis, the joint space between the femur and tibia is reduced due to degeneration and inflammation, resulting in chronic pain in the knee. Osteoarthritis of the knee occurs more often in the medial (inner aspect) compartment than in the lateral (outer aspect) compartment. During normal walking, the knee joint is subjected to a varus (inward bending) force, which shifts the joint load to the medial compartment. To reduce this load in the patient with osteoarthritis, the orthosis applies a valgus (outward bending) correction using three-point pressure, which ultimately shifts the load to the lateral compartment of the knee.

An orthosis should be prescribed by a health care professional who understands the patient's current physical condition and recognizes how an orthotic device can help to improve the condition. The health care provider will consider the condition of the affected area, the patient's overall health, the cost of the orthosis versus surgical intervention, and the patient's willingness to be compliant with the orthosis. Working with an orthotist (a professional who has been trained in the fabrication, fitting, and use of orthotics), the physician can prescribe the best possible device to meet both the needs and lifestyle of the patient.

Ashish Doshi, C.P.O.
Columbus, Georgia

Reference:
Goldberg B, Hsu JD. Atlas of Orthoses and Assistive Devices. 3rd ed. St Louis, MO: Mosby-Year Book; 1997: 416, 427, 463.

Further reading:
Cailliet R. Foot and Ankle Pain. 3rd ed. Philadelphia, PA: FA Davis; 1997.