After surgery to repair or reconstruct a torn or ruptured anterior cruciate ligament (ACL), patient and physical therapist diligently work to restore normal knee range-of-motion. Why is this so important?
Because studies show that loss of knee motion can lead to osteoarthritis in later years. And restoring and maintaining knee motion is one thing patients can do to possibly prevent (or at least delay) osteoarthritis from developing.
In this article, an orthopedic surgeon and a physical therapist team up to discuss the problem of osteoarthritis after ACL surgery. The surgeon focuses on surgical techniques that can prevent impingement while the therapist provides details on how to accurately measure and restore knee motion. Together, they review and present the results of six studies on this topic. They also discuss what is “normal” knee motion.
Most studies examining joint motion after ACL surgery are not long-term. Funding, maintaining contact with patients, and other factors make it more difficult to continue following patients for 10, 20, or more years in order to look for trends in osteoarthritis.
Only six studies were available with X-rays to confirm osteoarthritic changes in the joint after ACL surgery. And the results reported were mixed: some studies reported a link between ACL, loss of knee motion, and osteoarthritis. Others showed a trend but not a clear association. In all of the studies there was a decline in patients’ subjective sense of how the knee was functioning.
Besides loss of motion, there was one other important factor in the development of osteoarthritis after ACL surgery: damage to the knee cartilage. This included both the C-shaped meniscus and the articular (joint surface) cartilage. There is nothing the patient or therapist can do to regenerate knee cartilage. But together they can continue to work on restoring normal, full motion.
That brings us to the second topic of the article: what is normal knee motion? The authors suggest using the standard range from zero (full knee extension) to 135 (full knee flexion) won’t work for everyone. Some people naturally have knee extension beyond zero. That condition is called hyperextension.
Restoring knee extension to zero after ACL surgery in someone who has five or 10 degrees of extra extension (or flexion) in the other knee isn’t going to feel “normal.” Rehab must continue until both knees have equal amounts of motion. This of course assumes the other knee has not been injured or altered from normal.
Using a series of photos with a patient who has uneven knee extension, the therapist shows how to properly assess and measure knee joint motion. Another series of photos demonstrate ways to treat the knee to gain additional flexion and extension. A detailed description is provided of the techniques for both measuring and restoring knee motion.
With proper measuring, the therapist can identify even small (three to five degree) losses of motion early on. This is important while the graft tissue is still remodeling in order to regain full motion. Waiting too long can result in a stiff, painful, and weak knee. Studies show that small losses of either knee flexion or extension can lead to knee osteoarthritis. This is especially true when there is any damage to the cartilage.
Early postoperative rehab focuses on reducing swelling and preventing bleeding into the joint. This can be done with special leg stockings, cold therapy, and emphasizing knee motion. Knee extension is restored first, and then knee flexion. When knee motion on the operative side equals motion on the uninvolved side, then the patient progresses to the next stage of strengthening and motor control.
The long-term studies that are available showed a significant increase in the number of patients with loss of knee motion who developed abnormal joint findings as seen on X-rays. Such changes were observed as early as five years after ACL surgery in patients who had loss of knee motion. On the flip side, patients with known cartilage damage but who maintained normal knee motion were much less likely to develop knee osteoarthritis.
And there is one more factor to consider. Studies show that patients who go into knee surgery with no swelling and full motion are more likely to regain their normal motion early on after surgery. So this finding points to the need for a delay in surgery in order to give the patient time to complete a preoperative therapy program. When there is no measurable swelling and joint motion is “normal” for that patient, then surgery can be scheduled.
In summary, the authors of this article point out that a loss of knee motion may be a significant contributor to knee osteoarthritis after ACL surgery. In the past, our thinking was that the loss of motion developed as a result of the osteoarthritis, not as a primary factor in causing the arthritis. This is a shift in thinking that will require a change in when and how knee joint motion is measured. There also needs to be a shift in the way ACL rehab is carried out (both pre- and post-operatively).