By Cary Groner
People who participate in running and jumping sports are particularly prone to a type of knee pain known as patellofemoral pain, or PFP, typically felt at the front of the knee, under the kneecap. Researchers and clinicians have only recently begun to agree on the causes of this debilitating condition. That's good news to the athletes who have it, because once you understand the causes, you're on the way to finding cures.
PFP accounts for about a fifth of all running injuries, and women get it up to 10 times as often as men. As if that's not bad enough, the condition can become chronic; research shows that 94 percent of patients still report pain four years after being diagnosed with PFP, and even after 20 years, a quarter of patients still have pain.
PFP's greater prevalence in women is a clue to what causes it. Because of how their bodies are structured, and how their muscles and ligaments work, women tend to land in more knock-kneed positions than men when running and jumping. This angle — known to clinicians as the Q-angle, or valgus knee — stresses the knee joint and can place athletes at risk for problems like PFP. Related issues include internal rotation of the femur, decreased flexibility of the calf and quadriceps muscles and muscle weaknesses or imbalances, including the ratio of quadriceps-to-hamstring strength (H/Q ratio).
When female athletes don't optimally recruit the muscles they need to control knee motion, the body naturally tries to compensate by transferring stress to the ligaments. This may just worsen the problem, though, because women typically have looser ligaments than men.
Just because you're born female doesn't mean anatomy is destiny, however. Recently, clinicians have developed a variety of exercises to address problems that may predispose athletes to PFP, including ways to decrease Q-angle and improve knee alignment. Evidence suggests that these interventions decrease the incidence of PFP and help cure it when it occurs.
What primarily drives the position of the knee is not the knee itself but the muscles of the trunk and hips. It's not so much a matter of strength as of neuromuscular control — how those muscles are recruited during exercise. Muscle imbalances are different in everybody, so your physician, physical therapist, or fitness trainer will need to accurately evaluate your individual biomechanics to determine the best exercises for you.
In general, however, interventions will focus on muscles that affect the angle and rotation of the femur. These include the gluteal muscles as well as those that control the hip and femur, known as extensors, abductors and external rotators. As noted above, the H/Q ratio is also critical to controlling the knee's motion.
Warm-up exercises and exercises focused on neuromuscular training — which may include balance training, gait training, core strengthening, speed training and jumping and hopping exercises — increase control and decrease landing forces. Coaches and clinicians who have tested these routines in female adolescent athletes, including soccer players, report a dramatic drop — by a third to a half — in PFP and other lower extremity injuries in those who participated.
Some clinicians believe that although muscle control at the trunk and hip is paramount, issues related to the feet should be addressed as well. Severe pronation (turning or rotating your foot inward when weight is applied) can lead to valgus knees, so athletes who pronate may be advised to wear shoe inserts or custom orthoses to support the arch. Research also suggests that landing with more of a forefoot strike when running, rather than a heel strike, naturally shortens the stride and decreases the high impact loading associated with heel striking, potentially decreasing PFP risk. (Changing your footstrike pattern may lead to other problems, though, so don't set out to do this without professional guidance.)
Researchers have also discovered that women often experience more knee pain during menstruation. This may be because they're more sensitive to pain generally during their periods; it may also be related to natural declines in tissue laxity and neuromuscular control. The take-home message may be to back off on the exercise until your period is over and these factors reverse themselves.
Of course, men get PFP too, just a lot less frequently. Researchers are finding that although the pain is similar, the risk factors are different. Men don't typically have the same frequency of knock knees that occurs in women; in fact, when they develop PFP, it's often because they tend to be more bowlegged — to have varus knees, in the clinical terminology. Extremes of either position (valgus knees in women, varus knees in men) seem to be related to the risk of developing PFP. If you're a guy, you may need a whole different set of exercises to address the biomechanical imbalances that cause the problem. This is relatively new research, though, so if your doctor doesn't know about it, don't be surprised.
It's important to remember that just because you have patellofemoral pain, it doesn't necessarily mean that the knee is the root of the problem. It could be related to your feet, but it will almost certainly have something to do with how you recruit the big muscles of the hip and trunk when you run, and how these affect the alignment and rotation of the femur. A sports medicine specialist should be able to assess your individual biomechanical and neuromuscular issues, and prescribe an approach to help you heal.
Published March 6, 2012.
Cary Groner is a writer based in the San Francisco Bay Area. His recent novel, "Exiles," placed fourth on the Chicago Tribune's list of the best books of 2011.