Scientists Discover How to Regenerate Damaged Hip and Knee Cartilage—Without Surgery

Stanford Medicine researchers have discovered a breakthrough treatment that can regenerate damaged cartilage in hip and knee joints without surgery. By blocking a single protein called 15-PGDH—dubbed a "gerozyme" because it increases with age—scientists successfully restored cartilage in old mice and prevented arthritis development after injuries similar to ACL tears.

What Makes This Cartilage Treatment Different?

Unlike previous approaches that rely on stem cells, this treatment works by making existing cartilage cells act younger. The protein 15-PGDH normally breaks down prostaglandin E2, a molecule essential for tissue repair. When researchers blocked 15-PGDH activity with injections, cartilage-producing cells called chondrocytes began generating new, functional cartilage without needing stem cell involvement.

"This is a new way of regenerating adult tissue, and it has significant clinical promise for treating arthritis due to aging or injury," said Helen Blau, professor of microbiology and immunology at Stanford Medicine.

How Effective Is the Cartilage Regeneration Treatment?

The results were dramatic across multiple scenarios. In aged mice, knee cartilage that had become markedly thinner and less functional actually thickened across the joint surface after treatment. The researchers tested both systemic injections into the abdomen and direct joint injections, with both approaches successfully regenerating hyaline cartilage—the smooth, glossy type that provides low-friction movement in hips, knees, and other joints.

For injury prevention, mice receiving twice-weekly injections for four weeks after ACL-like injuries showed remarkable protection against arthritis development. Untreated animals developed osteoarthritis within four weeks, while treated mice moved more normally and put more weight on their affected legs.

• Aging Impact: Levels of 15-PGDH increased about two-fold in old mice compared to young mice, directly correlating with cartilage loss
• Treatment Response: Human tissue samples from knee replacement surgeries responded to the treatment by making new, functional cartilage
• Clinical Pipeline: An oral version of this gerozyme inhibitor is already in clinical trials for treating age-related muscle weakness

What Does This Mean for Hip and Knee Replacement Surgery?

This discovery could transform treatment for the 20% of Americans affected by osteoarthritis, a condition that costs approximately $65 billion in direct healthcare costs annually. Currently, no drug can slow or reverse osteoarthritis—the primary treatments are pain management and joint replacement surgery. About 790,000 total knee replacements and 450,000 hip replacements are performed yearly in the United States.

"Millions of people suffer from joint pain and swelling as they age," said Nidhi Bhutani, associate professor of orthopedic surgery at Stanford. "Until now, there has been no drug that directly treats the cause of cartilage loss. But this gerozyme inhibitor causes a dramatic regeneration of cartilage beyond that reported in response to any other drug or intervention."

The treatment addresses osteoarthritis at its root cause. When joints are stressed by aging, injury, or obesity, cartilage-producing cells begin releasing inflammatory molecules and breaking down collagen, the primary structural protein of cartilage. As collagen is lost, cartilage thins and softens, causing the joint swelling and pain characteristic of arthritis.

While experts acknowledge we're still years away from eliminating joint replacements entirely, this research represents a significant step forward. The ability to regenerate cartilage rather than simply managing symptoms could fundamentally change how we approach hip pain, knee injuries, and age-related joint deterioration.