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I am going to take a leap of faith and follow my surgeon's suggestion to have an operation on my knee called a high-tibial osteotomy (or something like that). Can you tell me in a little more about how my knee joint knows to start making its own cartilage cells after this kind of procedure?

The knee joint has several different layers of cartilage and bone. You are probably familiar with the meniscus. That's a C- or horse-shoe shaped piece of thick cartilage between the femur (upper leg bone) and tibia (lower leg bone). Then there's the articular cartilage. Articular cartilage lines the joint and is located between the meniscus and the first layer of bone (called the subcondral bone). Damage to the articular cartilage (before it reaches all the way down into the subcondral bone) can potentially regenerate itself. One way to encourage restoration of damaged articular cartilage is to remove load and pressure on the joint where the damage is located. An osteotomy accomplishes this by shifting the load from one side of the joint more toward the other side (or at least a more even distribution). Collagen tissue that makes up articular cartilage has a special type of cell woven into and through it. This extracellular matrix includes molecules called glycosaminoglycans (GAGs) provide compressive strength to the cartilage. In theory, taking load off the joint surface allows the joint to make more GAG. A higher concentration of GAG creates a more normal articular cartilage (not just a dense fibrous cartilage). Researchers are studying the effects of osteotomy and load on GAG concentration. They are able to use special MRIs with dye that seeps into the cartilage and subchondral bone to show the effects of this procedure. In one small study recently published, results showed that patients were able to generate some articular cartilage but not back to a normal amount. Changes were visible at the six month check-up. Improvements continued to be seen at the 12 month and 24 month follow-up appointments. Knee function was also significantly improved. It's possible that continued changes occurred after the 24 month mark. Further study will be done to see if the joint cartilage reaches a level close to normal.

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