Overview of ACL Surgery and Osteoarthritis in the Knee
ACL reconstructions are among the most common orthopaedic procedures performed in the United States. However, despite surgery intended to stabilize the joint, individuals who undergo an ACL reconstruction have a 3 to 5 times greater risk of developing posttraumatic arthritis of the knee. Thus, it is important to develop early and effective interventions to prevent posttraumatic arthritis after ACL surgery for this population. In our hands, we try to address this by having patients initiate physical therapy immediately after surgery in an effort to restore their quadriceps function. It has been documented that a restoration of quadriceps function improves overall joint absorption and may lead to a slowdown of progression of arthritis after injury.
One of the important things to recognize about posttraumatic arthritis, compared to age-related degenerative arthritis is that there is a discrete episode known at the time of the injury. Since the starting point of this injury is known, early therapeutic intervention may be possible in the future to slow down the biologic responses that lead to the progression of posttraumatic arthritis.
Articular cartilage injury after an impaction force, which is most commonly seen with an ACL tear, has been widely documented. The presence of blood in the joint and the resultant inflammatory process that occur after a traumatic joint injury is well known. There are numerous inflammatory degenerative cytokines, activated macrophages, and other degenerative products which can lead to early chondrocyte death, chondrocyte loss over time, and ultimately osteoarthritis progression these patients.
Osteoarthritis in the Knee
Osteoarthritis has been ranked number 5 in the top 10 most costly medical conditions after heart disease, cancer, mental and trauma related disorders with an estimated cost burden of $185.5 billion in the USA. According to the American Academy of Orthopaedic Surgeons, every year 9 million adults in the United States are diagnosed with arthritis and 600,000 total joint replacements are performed. It is recognized that over time, osteoarthritis of the knee occurs in 50% to 60% of patients following a joint injury. This is because cartilage cells have a very low capacity to regenerate damaged cartilage tissue after injury. Today, all of our cartilage restoration procedures do not restore the cartilage back to normal unless there is a fresh osteoarticular allograft procedure performed.
Treatment of Osteoarthritis in the Knee
Research in the biologic repair of articular cartilage defects is still in its infancy. It is definitely felt that the healing process can be improved and that trying to get stem cells to migrate to the area, investigating which cytokines would stimulate migration of peripheral stem cells, and other treatment methods may allow us to better resurface articular cartilage defects in the future. One of the most important forms of osteoarthritis is posttraumatic osteoarthritis. This is responsible for approximately 12% of patients with symptomatic osteoarthritis in the US and corresponds to about 6 million people. The important thing about posttraumatic arthritis is that it has been reported to occur earlier than other forms of arthritis because the injuries are often sustained by younger patients. Therefore, there is a much longer duration of their overall symptoms. This younger population affected with posttraumatic arthritis is associated with significant health care costs, lost work time, and more disability affected life years.
From the molecular level, biologic and cell therapies are being investigated in the context of chondral protection and tissue regeneration in some instances of arthritis. It is well recognized that interleukin-1 (IL-1) is one of the most potent catabolizers which leads to cartilage breakdown in the joint. Thus, prevention of activation of the inflammatory IL-1 signal cascade is one of the most important means that scientists are currently investigating to try to slow down the progression of arthritis. One of the most important disease modifying drugs would be one that would inhibit IL-1 activity to decrease the incidence of arthritis. There is a drug, anakinra, which is an interleukin-1 receptor antagonist. However, it has a short life of less than 4 hours so its long-term ability to stop the progression of arthritis is unknown. In addition, the metalloproteinases have been reported to be important cytokines that lead to arthritis. MMP-13 has been found to be one of the most important cytokines to try to target to deactivate to prevent cartilage wear over time. Further research in this area is ongoing.
Patients who sustain an ACL tear are at a higher risk for the development of osteoarthritis. While there are no current disease modifying drugs, an early postoperative rehabilitation program and restoration of knee motion are believed to be essential to slow down the risk of developing arthritis after an ACL tear.