Synovial fluid depletion: successful arthrodesis without operative cartilage removal

Operative arthrodesis has been thought to require surgical removal of remaining joint cartilage, but we have found in rabbits that even a joint with intact cartilage can fuse if rigidly fixed. This may enable new percutaneous techniques for arthrodesis. Rigid adaptation of the joint surfaces deprives the cartilage of mechanical stimulation and depletes the cells of synovial fluid transport of oxygen and nutrition. To better understand the requirements for successful arthrodesis, we studied the histological consequences of the complete absence of mechanical stimulation alone or in combination with synovial depletion by placing a metal cap over part of the joint cartilage in rabbits. The cap was either closed or had an opening to permit synovial fluid to reach the cartilage. We also studied if penetration of the bone-cartilage junction by a drill hole would facilitate cartilage resorption. Synovial fluid depletion in combination with a drill hole through the bone-cartilage junction led to disappearance of all cartilage matrix after 7 weeks. Synovial fluid depletion with an intact bone-cartilage junction led to complete disappearance of the cartilage matrix in four of seven rabbits after 7 weeks. With a hole in the cap for synovial fluid, the cartilage matrix was still present to varying degrees after 7 weeks in all the rabbits. In conclusion, percutaneous arthrodesis by rigid adaptation may lead to cartilage disappearance due to synovial depletion rather than due to the absence of mechanical stimulation. A combination with perforation of the bone-cartilage junction appears to lead to reasonably quick removal of the cartilage matrix.