Patellofemoral Pain Syndrome (PFPS), more commonly known as "Runner's Knee" in the running community, is one of the most common conditions to afflict avid runners. Many runners and doctors often confuse this condition with pain associated with knee joint arthritis, meniscus injuries, or even stress fractures around the knee. So what actually is it and where does it come from? Seems simple right? Of course, pounding the pavement is going to cause TONS of pressure to go into the knee and cause pain in the knee cap... but does it have to?
What is Runner's Knee?
Patellofemoral Pain Syndrome is defined by pain in the front of the knee with exercise or activities that repetitively bend the knee like running, climbing stairs, jumping, etc., or sitting with the knees bent for a long time. It is commonly seen in runners and jumping athletes like basketball and volleyball players, so the names "Runner's Knee" and "Jumper's Knee" became popular. It was thought that swelling and irritation of the patella (or knee cap) rubbing repetitively on the femur underneath of it was the cause of the pain and that anti-inflammatory medication and rest would correct the problem. The pain kept returning!
Now, the belief is that Patellar Maltracking Syndrome is the cause. It is thought that muscle imbalance in the thigh and around the knee causes the patella to "track" towards the outside of the leg rather than fit in the groove designed for it, causing painful rubbing and inflammation. A better theory and patients were sent to physical therapy to "strengthen" the inside leg muscles to counteract the outside muscle pull. But still, these patients have the pain! So what ACTUALLY is causing the pain?
Dynamic MRI of the knee joint showed during knee bending, the “lateral patellar displacement” was actually movement of the femur into the patella, not the other way around! So the theory of the two bones rubbing together excessively was correct, but for the wrong reasons, so the rehab exercises did not work. Instead of focusing on strengthening the quadriceps muscles to control patella movement, rehab should be focused on controlling femur movement at the hip, as well as improving ankle mobility and foot arch endurance to act as a "shock" to reduce the amount of force going into the knee joint.
How Do We Fix It and Prevent It?
In a study done in the Journal of Orthopaedic & Sports Physical Therapy, it was shown that "PFPS patients compared to asymptomatic controls had 26% less hip abductor strength compared to controls and 36% less hip external rotator strength compared to controls." These patients had less strength in their gluteal muscle that control femur rotation which was allowing the femur to shift into the patella during exercise.
We also know that when ankle dorsiflexion (or foot toward your face movement) is limited, compensation occurs to accomplish the movement still. That compensation is internal rotation of the tibia (shin bone) and femur to allow the foot to dorsiflex outwards rather than straight forward. That also drives the femur into the patella causing runner's knee symptoms.
Reiterating our main point, rehab should be focused on controlling femur movement at the hip, as well as improving ankle mobility and foot arch endurance to act as a "shock" to reduce the amount of force going into the knee joint. If can strengthen the hip stability muscles, the femur will not rotation inward and bump into the patella as much, reducing some inflammation and stress there. If ankle dorsiflexion is improved through joint manipulation and soft tissue mobilization, less compensation occurs and less internal rotation of the leg occurs as well! Lastly, improving arch function in the foot or supporting the arch with flexible yet rigid orthotics acts like the shocks on your car, absorbing a lot of force from the ground so less force hits the knee.