During Early Stages Of Arthritis, High-Impact Exercise Can Damage Cartilage
Jason Pierce, MSN, MBA, RN for redOrbit.com — Your Universe Online
A new paper published in the Biophysical Journal explains why cartilage may be more susceptible to damage from high impact physical activities such as jumping or running during the early stages of osteoarthritis. The results could lead to early diagnostic tests or new designs for replacement cartilage.
Cartilage can be found in the joints between bones. It is a flexible tissue protecting the bones from rubbing together, and allows the bones to slide within the joint space. It is a collection of about 100 highly charged molecules called glycosaminoglycans (GAGs) that gives cartilage the ability to firm up when under pressure and protect the bones.
“The cartilage is a stiff sponge, filled with fluid, and as we compress it, fluid has to percolate through these closely spaced GAG chains,” says senior author Alan Grodzinsky, an MIT professor of biological, electrical and mechanical engineering. “The GAG chains provide resistance to flow, so the water can´t get out of our cartilage instantly when we compress it. That pressurization at the nanoscale increases the stiffness of our cartilage to high-loading-rate activities.”
In osteoarthritis, the cartilage has begun to break down. This allows bones to rub together and causes pain and stiffness in the joint. Osteoarthritis is a progressive disorder and the cartilage will continue to break down as more pressure is applied to the tissue. The onset of the condition may be gradual, and the early stages may not produce pain.
Engineers at MIT published the study comparing the properties of healthy cartilage exposed to high impact loads to damaged or deteriorating cartilage under the same loads. The deteriorating cartilage simulated the changes found in early osteoporosis. The researchers found that when exposed to very high loading rates normal cartilage was able to absorb fluid and stiffen normally. However, in the deteriorating tissue, fluid leaked out rapidly.
“That´s what puts the collagen in trouble, because now this becomes a very floppy sponge, and if you load it at higher rates the collagen network can be damaged,” Grodzinsky says. “At that point you begin an irreversible series of activities that can result in damage to the collagen and eventually osteoarthritis.”
These findings should be of particular interest to physicians caring for patients who have had knee injuries. Cartilage tissue that has not had enough time to heal after a joint injury experiences continued damage during high impact activities. This continued damage can lead to the functional changes seen in osteoarthritis. In fact, according to Grodzinsky, at least 12 percent of all osteoarthritis cases stem from a traumatic joint injury.
“It´s a clear signal to be careful of going right back out,” says Grodzinsky. “Even though your knee may be stabilized, there´s the possibility that deformation of cartilage at a high loading rate is still going to put it at risk.”
Grodzinsky´s team is working on possible drugs to slow the progression of osteoarthritis, and trying to develop cartilage tissue for patients who need replacement surgery. “These two aspects are really important: preventing cartilage degradation after injury and, if the cartilage is already damaged beyond its ability to be repaired, replacing it,” Grodzinsky says.