Abstract
Osteoarthritis (OA) is a disease of the joints stemming from a variety of factors, including joint injuries and abnormally high mechanical loading. Although the traditional treatment alternatives for end-stage OA are arthroplasty in the case of the hip and knee, and arthroplasty or arthrodesis in the case of the ankle, these options are not ideal for younger, more active patients. For these patients, joint prostheses would be expected to fail relatively quickly, and ankle fusion is not amenable to maintaining their active lifestyles. In these cases, joint distraction has attracted investigative attention as a conservative OA treatment for younger patients9-14.
Based on the principle that decreasing the mechanical load on cartilage stimulates its regeneration15, distraction treatment calls for reduced loading of the joint during a period of typically 3 months, during which time the load customarily passing through the joint is taken up by an external fixator spanning the joint . By mounting the fixator components to the bone on each side of the joint, and then lengthening the rods connecting the proximal and distal portions of the fixator, the joint is distracted. Assuming the fixation is appropriately stiff, any load passes through the fixator instead of the joint, and the two articular surfaces will not be allowed to contact each other under physiologic loading. The exact mechanisms leading to cartilage regeneration during distraction are not yet understood.
A possible negative consequence of joint fixation is cartilage degeneration due to immobilization during the treatment. It has been shown by Haapala et al. and others that long-term immobilization can be detrimental to articular cartilage16-18.
Conversely, joint motion during fixation (even passive motion) is thought to stimulate or encourage cartilage regeneration19-22. Toward this end, considerable effort has been invested in the application of hinges to external fixation for joints Joint motion has also been suggested as a potentially beneficial factor in distraction treatment, as well10. This is borne out by data from an RCT comparing the use of a rigid vs motion external fixator. Change in joint biology due to resorption of cysts may be responsible for reversal of symptoms.
