“Cartilage doesn’t heal.” Doctors often say this when our joints hurt and move when osteoarthritis wears down and damages the flexible tissue in our hips, knees, and shoulders. I’ve certainly heard this myself from orthopedic surgeons who explain that the cartilage doesn’t have the blood supply to repair cells and nutrients to the site of injury. However, it always amazes me that living tissue cannot replace damaged cells. Recent studies have shown that our ability to repair articular cartilage, a type of joint, is limited. New insights into this ability raise hopes for treatments that can improve healing and protect damaged cartilage from further deterioration.

To visualize articular cartilage, imagine a hard, white coating on the end of a chicken bone. Most of it is a spongy material called the extracellular matrix, a mixture of water and fibrous proteins secreted by cells called chondrocytes. “As with all tissues except tooth enamel, there is internal regeneration where new tissue is formed and old tissue is chewed away and washed away,” explains Virginia Kraus, a rheumatologist at Duke University School of Medicine. However, he pointed out that the cartilage regeneration process is slow. It is true that adult cells do not have a blood supply. Instead, the cartilage gets help from what experts call dynamic loading—the stress or weight on the joint that causes synovial fluid, which contains nutrients, to leak out. “That’s why exercise is so important for joint health,” notes Kraus. “Nutrition reaches cartilage through movement.”

Kraus is one of the few scientists studying the slow turnover of this tissue. In a surprising discovery, he and his team reported in 2019 that the production of a protein associated with recovery and repair varies by joint: It’s higher in the ankle than in the knee, and higher in the knee than in the hip. Kraus calls this gradient “our inner salamander,” explaining that this ability in salamanders and other animals capable of regenerating lost limbs is stronger in the lower leg than the upper leg.

His research showed that there is more genetic material associated with joint damage in joints than in healthy joints. Just as a limb injury starts a salamander’s rehabilitation program, Kraus suspects that osteoarthritis is driving the disease in humans, but “the program we have is definitely not enough.” However, the recovery process may be at work in the ankle, which is much less common than in knee and hip arthritis, he notes.

There is other evidence that human cartilage can regenerate. Arthritis distraction is being tested as a way to promote healing in patients with osteoarthritis of the knee who are too young to undergo total knee replacement. (Artificial knees last 15 to 20 years and then require complex surgical replacement.) The procedure involves placing needles above and below the knee and using an external device over six weeks to separate the upper and lower leg bones by five millimeters. . It opens the joint space. Patients are encouraged to walk, but the device reduces stress by bathing the knee in nutrient-rich fluid without overstressing it.

Dutch researchers have shown that the procedure leads to a slight increase in joint cartilage and pain relief, which lasts for at least two years, and in some patients as long as 10 years. Philip Conaghan, a rheumatologist at the University of Leeds in England, says the technique needs larger clinical trials, but it’s an impressive model.

Conaghan is researching new anti-arthritis drugs, including a growth factor called sprifermin, which slows cartilage loss in some patients. He is also studying the anti-inflammatory canakinumab, which has been tested as a cardiovascular drug and has shown surprising side effects: recipients had significantly fewer joint replacements than the placebo group. But Conaghan cautions that the search for a drug that thickens cartilage is difficult because of the slow and uncertain nature of repair: “The change is so small that even with the best imaging, it’s hard to pick up.”

For now, strength training remains the best strategy for people with joint damage. A walk to Conaghan Reservoir is recommended. “Strong quads can greatly reduce knee pain no matter what you’re dealing with,” he says. “All life consists of strong muscles.”

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