Knee orthoses 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.
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.