Knee Pain and Discomfort

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Construction Safety Association of Ontario

Summary Statement

Describes the way that the knee functions, injuries that can occur and potential treatments.
Autumn 2001

A look at common problems and treatment options

Years of research have revealed
the complexity of the knee joint.

After the back and spine, the knee is among the most commonly injured body parts in construction. It is also liable to injury, overuse, and wear and tear off the job.

The problem may be in the knee itself, and not necessarily the activities we do. The fact that the knee joint doesn't mature until we're in our mid to late 20s leaves it prone to damage for a number of years.

Years of research have revealed the complexity of the knee joint. The average knee matures in women at about 22-24 years and in men at about 25-27 years. Too often the knee is injured before it has had adequate time to mature. Common injuries result from stress on bone, muscle, ligaments, tendons, cartilage, and bursa (a small sac of fluid inside the joint that cushions impact).

Not a simple hinge

Injuries are often related to the fact that the knee doesn't move in a single plane. Some healthcare professionals try to treat the knee as they would a single planar joint that works like a door hinge. Such a joint is limited to simple flexion and extension. (Flexion means bending a joint; extension means straightening it.)

But the knee is much more complex. It moves not only in flexion and extension but also through abduction, adduction, internal rotation, and external rotation. These are technical terms describing a healthy knee's full range of motion.

In flexion and extension the massive muscles of the thigh provide much of the protection needed to prevent or reduce injury to the knee. But similar protective strength isn't available when the knee turns inward, outward, or rotates. These motions can exceed structural limits rather easily. The result is sprain or rupture to ligaments.


The long-term problem is that muscle strength weakens over time. Support tissues take on more of the protective role but aren't designed for that and subsequently fail.

The next stage of treatment is usually for bursitis (an inflammation of the bursa) or the osteoarthritic knee, which is commonly associated with knee swelling and pressure. These conditions can be managed best when symptoms are detected early and support is provided through a natural range of motion to enhance muscular strength and flexibility.


 Orthotics are devices such as braces designed to support or facilitate the functioning of muscles, bones, and joints. The correct orthotic can provide help for knees weakened or damaged by injury or overuse.

Piston hinge systems are available to protect and support the six degrees of freedom, that is, flexion, extension, abduction, adduction, internal rotation, and external rotation. These systems can enhance knee function and performance.

But unless the six motions are controlled, the device has a tendency to 'migrate,' that is, slip down the leg. When a brace migrates, it leaves the knee and leg unsupported and open to further injury. In an attempt to keep the brace in place many patients will strap it on too tight and thus create nerve and circulation problems. They may also experience irritation from friction between brace and skin.


Another common problem with braces controlling knee motion is the tendency for the thigh cuff to gap during flexion. As the cuff moves away from the thigh, it leaves the leg unsupported and vulnerable to strain and injury.

There are piston hinge systems that prevent migration and provide an envelope of safety. The most common system eliminates gapping at the thigh during flexion. The brace cuff is totally compliant with the leg and doesn't work counter to the knee's natural position, alignment, and movement.

Piston technologies also provide potential energy management through shock-absorbing aspects of the pistons and bearings.

For more information, contact
Professor Bill Morrison at 1-888-250-6698.