Patellofemoral pain syndrome—otherwise known as anterior knee pain and runner’s knee—is the most common running injury, accounting for roughly 20 percent of all running injuries. The main symptom is pain below the kneecap that is generally mild at first and experienced only during running but becomes progressively more intense during running and also increasingly felt at rest if training continues.
Many theories about the nature of the damage underlying the pain have come and gone. The reason behind this revolving door of proposed etiologies is that, unlike other injuries such as knee meniscus damage, there is no obvious structural abnormality associated with PFPS, whether the joined is examined by x-ray, MRI or surgical arthroscope. Recently this reality has lead orthopedists to a new view of PFPS in which pain itself—or, more specifically, chronic stimulation of pain nerves in the knee—is understood as the essence of the injury.
Any of a number of varieties of relatively minor tissue degradation, such as inflammation of the synovium, a pouch that contains the knee’s lubricating fluid, may underlie this pain nerve stimulation. But because these breakdowns are relatively minor and hard to identify, they need not be targeted. It’s the pain itself that must be targeted.
Treatment and Prevention
How do you target the pain? First, you avoid doing anything, including running, that causes the knee to hurt, but you also do as much running as you can do pain-free. This approach will enable the damaged tissues to restore homeostasis (or their natural equilibrium state of breakdown and regeneration) yet will also keep the knee well-adapted to the stress of running. Many runners with PFPS can do some pain-free running. You might find that you can run for a certain duration (say, 20 minutes) and no longer without pain. In this case, run only that far until your limit increases. Or you might find that you can run every other day, but not every day, without pain. Then run every other day for a while. After a few weeks, try a test run 24 hours after a previous run to see whether the limit remains. Continue to increase your running gradually back toward pre-injury levels as comfort allows, reversing this process briefly whenever soreness emerges anew.
Where there is pain there is almost always inflammation. Taking a non-steroidal anti-inflammatory medication such as ibuprofen according to label directions and placing an ice pack on your knee for 10 minutes at a time, three times a day, may accelerate the resolution of this inflammation.
Consider whether poor shoe selection, biomechanical factors, and/or muscle weakness might have contributed to your injury. Weakness in the hip abductors and hip external rotators is often seen in PFPS sufferers. In runners whose hip stabilizers are weak, the thigh tends to rotate internally as the foot comes in contact with the ground. This is a compensatory movement that is performed unconsciously to enable other muscles to take up the slack of stabilizing the pelvis. But the slack is not entirely picked up by these other muscles, and consequently the pelvis tilts laterally toward the ground on the side of the unsupported leg. The thigh tilts with it, like a falling tower, while the lower leg remains upright, pinching the knee between them. It is likely that this pinching effect, as well as the twisted (or “knock-kneed”) position of the thigh relative to the knee when it absorbs impact forces, causes damage to occur within the joint. If you are a knock-kneed runner, train yourself to actively contract the muscles on the outside of your hips when you run to keep your pelvis level and keep those thighs in their natural, neutral alignment.In addition, begin doing exercises to strengthen these muscles.
It is possible that pronounced heel striking, or overstriding, also increases the risk for PFPS. While this link has not been shown directly, studies have demonstrated that runners who experience excessive impact shock are more likely to develop PFPS, and that heel strikers experience greater impact shock than midfoot strikers. So if you are a pronounced heel striker and you have PFPS, train yourself to short our stride and land your foot flat underneath your hips instead of heel-first out in front of your body.
If reducing impact shock is an effective means of reducing the risk for PFPS, then switching to running shoes that reduce impact shock may also protect the knees. The problem is that research on the relationship between shoe cushioning and impact shock has produced muddled results. Some studies have found that impact forces are actually greater in running shoes with softer cushioning due to unconscious stride changes that are made in different shoes. However, it has been suggested that such counterintuitive results may have been caused by inadequate measurement techniques. At least one recent study provides evidence that added shoe cushioning reduces specific impact variables that are now seen as the best indicators of injury risk—namely, peaking loading rate (the abruptness of impact) and tibial acceleration rate (or the rate at which the lower leg approaches the ground). However, it still seems to be the case that interaction between the specific shoe and the individual runner has a major effect on impact characteristics, such that the right level of cushioning is different for each runner and it’s impossible to predict the level that is right for any single runner.
Since you can’t undergo comprehensive impact testing when shopping for running shoes, how do you select the shoe with the right amount of cushioning to minimize your risk of developing PFPS and other injuries? Some research indicates that comfort is a fairly reliable guide. Subjective assessments of comfort coupled with on-the-road experience are even better. To begin, buy and wear the most comfortable shoe you can find. If it keeps you injury-free, buy another pair (or buy the most similar pair you can find when that particular model is inevitably phased out or replaced with a newer version). If you do get injured in that shoe, try a different shoe with a little more or less cushioning that is also very comfortable. Keep experimenting with different shoes until you find your optimal shoe type (but keep in mind that even the optimal shoe will not prevent all injuries).
The good news about patellofemoral pain syndrome is that it’s a relatively minor condition. Indeed, it’s really just a chronic failure of tissues within the knee to fully recovery from running-induced damage between runs. The bad news is that it can be just as debilitating and last just as long as more serious breakdowns. Use the tips I’ve just given you to minimize the impact (so to speak) of knee pain on your running, if and when it strikes.