Damaged knee cartilage has long been considered irreparable. Knee distraction may be changing that. The procedure is intended to stimulate tissue regeneration and help patients with severe osteoarthritis delay knee replacement for many years. Early studies have shown encouraging results, though experts caution that expectations should remain realistic.

Osteoarthritis and Joint Replacement

Overall, 1 in 2 women and 1 in 3 men older than 65 years have osteoarthritis. Many of those affected will eventually require a knee replacement. When the cartilage between the bones wears away and the joint surfaces rub directly against each other, it causes pain. Damaged knee cartilage has very limited ability to regenerate on its own. According to data from the German Endoprosthesis Registry, approximately 199,000 people received a hip replacement and more than 173,000 received a knee replacement in 2024.

However, even an artificial knee does not last indefinitely. It often needs to be replaced after 15-20 years. This particularly affects younger patients with osteoarthritis. Due to the increased risk of revision surgery in this patient group, it is important to avoid knee replacement surgery in patients younger than 65 years whenever possible.

Could Knee Distraction Lead to Better Outcomes?

A new surgical method could help these patients. Knee distraction is intended to stimulate cartilage repair in osteoarthritis and thereby delay the need for an artificial joint. This is precisely the goal of the procedure, explained Mylene Paulien Jansen, PhD, assistant professor in the Department of Rheumatology and Clinical Immunology at University Medical Center Utrecht in Utrecht, Netherlands, in a Zweites Deutsches Fernsehen (ZDF) documentary, Germany’s national public service broadcaster. Together with her team, Jansen developed a device designed to support cartilage regeneration and give patients with osteoarthritis several years of symptom relief.

In knee distraction, an external distraction system is attached to the leg for 6 weeks. Surgeons insert special screws into the bone above and below the knee. The joint surfaces are then separated by 5 mm, creating a gap that may encourage cartilage repair. The joint is fixed in this position. The procedure itself takes only 30-45 minutes. Springs built into the system generate intermittent pressure changes during weight-bearing to promote tissue repair.

Strong Scientific Foundations

“Knee distraction is an exciting procedure. The scientific basis and the available studies are very sound and truly well conducted,” said Philipp Niemeyer, MD, PhD, senior physician in orthopedic surgery in Munich, Germany, and chairman of the Tissue Regeneration Working Group of the German Society for Orthopedics and Trauma Surgery, in an interview with Medscape.

The procedure itself is relatively straightforward, according to Niemeyer. “The 5-year data show a significant reduction in pain among patients with severe osteoarthritis. The study design is well-conceived and truly sound.”

After 6 weeks, the external fixator is removed, and patients can begin bearing weight on the previously immobilized leg again. Niemeyer said he was initially surprised that 6 weeks of weight-bearing restriction had such a long-term effect, but the studies clearly demonstrated the benefit. He also noted that new tissue formation can be detected during the recovery period.

He takes a critical view of how the procedure is portrayed in the media. “It’s often claimed that the cartilage can regrow and regenerate completely. In my opinion, that gives patients false hope,” he said.

Replacement Tissue, Not Normal Cartilage

Other procedures have also shown that replacement tissue can form. “However, this replacement tissue does not match high-quality articular cartilage and is therefore not comparable to it. Although some molecular markers associated with cartilage tissue do increase to a degree, that does not mean it is truly the cartilage found in a healthy joint,” Niemeyer explained.

The frequently heard statement that “the cartilage grows back” should therefore be interpreted cautiously. It must also be clearly communicated that the procedure does not cure osteoarthritis.

Niemeyer also recommends providing patients with comprehensive information in advance. Many are unaware that the fixator remains on the knee for 6 weeks and that the leg must be completely immobilized during this time. “Some patients are quite hesitant when they learn this,” the expert noted.

The goal of the treatment is to delay the implantation of a knee replacement for as long as possible. The procedure is now offered at about 10-15 clinics in Germany. It is primarily an option for patients with advanced or severe osteoarthritis who no longer respond adequately to conservative measures such as pain management and physical therapy.

How Durable Are the Results?

Kaywan Izadpanah, Section Head for Knee and Cartilage Surgery at the Department of Orthopedics and Trauma Surgery at Medical Center – University of Freiburg in Freiburg, Germany, has been performing knee distraction procedures. “For a long time, we thought cartilage regeneration was no longer possible once osteoarthritis had set in. This procedure has proven us wrong,” Izadpanah said in the ZDF documentary. He said he was skeptical at first. However, the study results from Jansen and her team changed his assessment.

In their 10-year follow-up publication, Jansen and colleagues reported that cartilage in the weight-bearing area of the joint was significantly thicker 2 years after treatment than before the procedure. Although thickness gradually declined after 5 years, cartilage remained thicker even 10 years after treatment. Niemeyer said the procedure may last long enough in some patients to avoid knee replacement altogether, although he stressed that there is no reliable evidence for that yet. At the same time, however, he emphasized, “We don’t know that yet. There is no reliable evidence for that so far.”

Statutory health insurers do not yet cover the cost of knee distraction. In an interview with ZDF, Izadpanah explained that patient registries are being established and that data are being collected in Freiburg and at other clinics offering the procedure. If results are sufficiently positive, the data may help persuade insurers to cover the procedure. The goal is to make the procedure routinely available in Germany.

This story was translated from Medscape’s German edition.