“There are only so many moguls in any given knee.” — Warren Miller, ski videographer.
I use Miller’s observation for many patients who love skiing but have arthritic knees. Skiing is actually pretty kind to the knee joints, as long as you don’t fall and if you don’t ski hard bumps all day long. Skiing powder uses all the muscles and improves balance and coordination without impact. I sometimes write prescriptions that say, “Must ski powder.”
Here’s why it’s helpful:
The bones of the knee joints are covered with a smooth layer called hyaline cartilage. This surface is made up of collagen, a protein fiber, and a matrix of charged sugar molecules that attract water. There are a few specialized cells within the matrix called chondrocytes. The surface has a boundary layer of lubricants called hyaluronate and lubricin. Together, these remarkable materials have a slickness five times smoother than ice on ice.
This beautiful construct can withstand skiing or running for a lifetime. It rarely wears out — unless there is a specific injury to it, to the meniscus fibrous shock absorber that protects it, or to the underlying bone.
In very general terms, there are four types of arthritis that can damage the joint surface. “Wear and tear” arthritis is really the name of a disease that occurs only after injury. Osteoarthritis, on the other hand, may be caused by an underlying genetic condition or possibly by an as yet unidentified infectious disease. Inflammatory arthritis commonly involves the reaction between the lining cells of the joint and circulating antibodies that damage the cartilage surface. Infectious arthritis is characterized by the damage done by enzymes released by bacteria during such infections.
Absent these diseases, what happens when the cartilage gets damaged is that the scarce cells within the cartilage matrix are not activated adequately to instigate a repair process. Just as a bulged-out area on a tire eventually leads to a failure of the surface and a flat, the damaged area of the joint surface fails to properly absorb the forces of walking or sports. The “flat tire” in arthritis produces bone spurs that form underneath the cartilage surface and at the edges of the bone, eventually deforming the knee joint. When worn severely enough, the knee misshapes into varus (or bowed leg) on the inside or valgus (knock-kneed) on the outside.
The solution is to repair these injuries as soon as they occur by stimulating a healing process in the damaged articular cartilage (articular cartilage paste grafting is our preferred method) and by repairing, regenerating, or replacing the damaged meniscus shock absorber as soon as it is injured.
Once arthritis is present, a range of effective treatments—including cartilage replacement—can be offered. All therapies, however, work better in people who remain active. Activity stimulates muscle development, improves blood flow to the joints, increases a sense of wellbeing, and increases free testosterone, pheromones and adrenaline.
So the message for my skiers with arthritis is, ski the powder. The smooth, non-impact runs will bring smiles to your faces and happiness to your knees.
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.