Recreating the knee in a lab

At the AO Research Institute Davos, scientists are recreating knee movement in the laboratory to better understand how joints respond to motion—and why the right kind of movement can help protect cartilage and support healing. 

Every step we take depends on our knees. Walking, climbing stairs, and standing up from a chair all rely on a joint that must be strong, flexible, and precisely balanced. When something goes wrong in the knee, the effects are felt immediately: pain, stiffness, and loss of mobility. 

At the AO Research Institute Davos (ARI), scientists are studying the knee in an unusual way—by recreating key aspects of its movement in the laboratory. Martin Stoddart, the ARI’s Vice Director, likes to call this approach “knee in a lab.”  

The aim is simple but powerful: to better understand how movement affects joint tissue, and how this knowledge can support better treatment and recovery for patients. 

Why the knee is hard to heal

Unlike skin or bone, cartilage has no blood vessels. This means damaged cartilage—common after injury or in early osteoarthritis—has very limited ability to repair itself. Over time, small problems can grow into long‑term joint damage. 

Movement matters in both injury and recovery. Too much load can harm tissue, but too little movement can also be damaging. However, understanding which types of movement help, and why, is difficult to study directly in patients. 

Bringing movement into the lab 

That is where the laboratory comes in. In the ARI’s labs, researchers work with small tissue models that represent key parts of the knee joint. These models are placed into bioreactors—designed and built by the ARI—that can gently move and load the tissue in controlled ways. A bioreactor is a laboratory device that keeps living cells or tissue alive outside the body. It creates a controlled environment—with the right temperature, nutrients, oxygen, and movement—so cells can behave as they would in the human body. 

Instead of testing just “pressure,” the researchers focus on realistic joint motion. The knee does not only carry weight; its surfaces also slide against each other when we walk or bend the leg. In the lab, this sliding motion is recreated using smooth components that move back and forth while applying gentle pressure—much like what happens inside a healthy knee.

The tissue inside the bioreactor is surrounded by a nourishing fluid, similar to what cells experience in the body. Each day, the system applies movement for a limited time, followed by rest—reflecting how joints are used in everyday life. 

Studying this carefully in the lab helps researchers understand which movement patterns are helpful and which may be harmful. Research at the ARI and elsewhere has shown that when joint cells experience the right kind of movement, they can switch on signals that support cartilage health. Some of these signals encourage cells to behave more like healthy cartilage cells, producing substances that give cartilage its cushioning and shock‑absorbing properties. 

Supporting safer, smarter research 

The ARI’s “knee in a lab” does not replace clinical studies or patient care. However, it can help answer key questions before new treatments are tested in people. By learning more in the laboratory, researchers can better design rehabilitation strategies and future studies. 

There is another benefit as well. Improving laboratory models helps reduce reliance on animal experiments, supporting more ethical and efficient research practices. 

For clinicians, this work offers deeper insight into why movement and rehabilitation matter after knee injury or surgery. For patients, it reinforces an important message: The right kind of movement is not just safe—it can be part of healing.