Joint Load and Knee OsteoarthritisLet's look at knee osteoarthritis, since the knee is the joint most commonly affected by the disease; it's also a weight-bearing joint. Your knee, if aligned perfectly, has its load-bearing axis in a straight line that runs through the hip, knee and ankle joints. If your knee is malaligned because of deformity associated with cartilage damage, abnormal force is applied to specific areas of the knee.
The abnormal force applied to the knee can cause increased pain and other symptoms. Researchers also have linked increased joint loading of the knee to progression of osteoarthritis. Something called the knee adduction moment (torque) is a factor related to the distribution of load between the medial (inner) and lateral (outer) plateaus of the knee joint. The peak knee adduction moment, which is the maximum medial joint load incurred during walking (through gait analysis), is greater in people with knee osteoarthritis than in those without the disease.
Mechanical measures determined by gait analysis, such as moments and forces, vary depending on the activity performed. Studies have consistently estimated maximum compressive forces of the knee joint to be four to 4.5 times body weight during daily activities. During level walking, some studies have even estimated a higher number. Descending stairs hikes the force to six times body weight; downhill walking hikes the force to eight times body weight; and jumping adds joint load at 20 times body weight. Suffice to say, the knee takes a beating over time. These estimates not only point out the need for reducing joint load, but they also are factored into designing long-lasting knee prostheses.
Decreasing Joint LoadResearchers have evaluated the effect of footwear, cane use and weight loss on joint load in knee osteoarthritis. Each factor made a difference. The shoes you choose can impact the joint load on your knee. Read what researchers concluded after comparing high-heel shoes, moderate-heel shoes, arch supports and walking barefoot.
In a study that analyzed the effect of cane use on knee-joint loading, researchers concluded that with a cane, there was an average of 10% decrease in knee adduction moment. Read more about why using a cane made a significant difference.
The problem with carrying excess weight is obvious. Being overweight or obese adds stress to weight-bearing joints. Did you know that people who are overweight have about four times the risk of developing knee osteoarthritis compared to people who maintain their ideal body weight? Imagine what being overweight does to joints already damaged by osteoarthritis.
Lateral-wedge insoles and knee braces are additional options for reducing joint load of the knee. Lateral-wedge insoles change the mechanics of the knee by reducing the varus torque (twisting the knee inward when walking). Regarding knee braces, an "unloader" knee brace is specifically designed to unload stress from the knee.
The Bottom LineIt makes common sense that decreasing joint load is beneficial for osteoarthritis patients. Depending on the joints affected in your individual case, discuss your options with your doctor.
Reducing joint loading in medial knee osteoarthritis. Kemp G. et al. Arthritis & Rheumatism. May 2008.
Knee pain and joint loading in subjects with osteoarthritis of the knee. Journal of Orthopaedic Research. Hurwitz DE et al. July 2000.
Joint Load Considerations in Total Knee Replacement. Kuster MS et al. Journal of Bone and Joint Surgery January 1997.
Abnormal and Cumulative Loading in Knee Osteoarthritis. Medscape. Maly MR. October 1, 2008.