Scientists Discover How to Regenerate Knee Cartilage—Without Surgery

Stanford Medicine researchers have discovered a way to regenerate knee cartilage by blocking a single aging protein, potentially eliminating the need for knee replacement surgery. The breakthrough treatment reversed cartilage loss in old mice and prevented arthritis development after injuries similar to ACL (anterior cruciate ligament) tears that plague athletes.

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 researchers targeted a protein called 15-PGDH—dubbed a "gerozyme" because it increases as we age—that acts as a master regulator of aging throughout the body.

When scientists injected old mice with a drug that blocks 15-PGDH activity, something remarkable happened: their thin, worn knee cartilage thickened across the entire joint surface. "Cartilage regeneration to such an extent in aged mice took us by surprise," said Nidhi Bhutani, associate professor of orthopedic surgery at Stanford. "The effect was remarkable."

How Does the Treatment Work?

The treatment addresses osteoarthritis at its root cause. Osteoarthritis affects 20% of Americans—roughly one in five adults—and costs about $65 billion in direct healthcare expenses annually. Currently, no drug can slow or reverse the disease; doctors can only manage pain and eventually replace damaged joints.

The 15-PGDH protein normally breaks down prostaglandin E2, a molecule essential for tissue regeneration. By blocking this protein, the treatment allows prostaglandin E2 levels to rise, triggering cartilage cells to regenerate functional tissue. The approach worked on human tissue samples from knee replacement surgeries, suggesting it could translate to human patients.

What About ACL Injuries and Sports Medicine?

The treatment showed particular promise for preventing arthritis after ACL tears—injuries common in sports requiring sudden pivoting like soccer, basketball, and skiing. About 50% of people develop osteoarthritis within 15 years of an ACL injury, even after surgical repair.

Mice that received the gerozyme inhibitor twice weekly for four weeks after injury dramatically reduced their chances of developing osteoarthritis. Untreated animals developed arthritis within four weeks, while treated animals moved more normally and put more weight on their affected leg.

Meanwhile, other researchers are exploring non-surgical approaches to knee pain management. Recent studies have identified three promising strategies for existing arthritis sufferers:

• Weight Loss Medications: Tirzepatide (Mounjaro, Zepbound) showed superior cost-effectiveness compared to diet and exercise alone for people with both obesity and knee arthritis
• Gait Modification: Learning to walk with toes turned slightly inward reduced walking-related pain by shifting pressure away from the most commonly affected part of the knee
• Online Tai Chi Programs: Free 12-week programs resulted in clinically meaningful pain reduction for 73% of participants with knee arthritis

"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 and senior author of the cartilage study.

An oral version of the 15-PGDH inhibitor is already in clinical trials for age-related muscle weakness, suggesting human applications may not be far behind. For the millions of Americans facing knee pain—50% of adults will develop knee osteoarthritis during their lifetime—this research offers hope for regenerating damaged cartilage rather than simply managing symptoms until joint replacement becomes necessary.