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A knee study provides encouraging evidence for knock-kneed runners.
Written by: Matt Fitzgerald
The knee is the most common sight of injury in runners. Almost half of all overuse injuries affecting runners occur at the knee. And the most common type of knee injury in runners is patellofemoral pain syndrome (PFPS). The weird thing about PFPS is that it is not associated with any specific area of structural damage in the joint. The injury is defined by its only symptom, pain, which usually manifests right below the kneecap.
Orthopedists used to believe that PFPS was associated with chondromalacia, or fissuring of the cartilage in the joint. But research has shown that people who have chondromalacia often don’t exhibit PFPS, and patients with PFPS often don’t have chondromalacia. I can tell you from personal experience that you can have both of these conditions without their being related. I suffered from PFPS for two years before having surgery on my knee. The surgeon found chondromalacia and filed down the chewed-up cartilage all nice and smooth. As soon as I started running again, the pain returned.
Experts also used to believe that the primary cause of PFPS was improper tracking of the patella during running. In other words, the problem originated right where it manifested: at the knee. But again, subsequent research proved otherwise. It now appears that the most common cause of PFPS is a genu valgum, or “knock knee” effect that is linked to weakness in the hip musculature. Here’s how it works: At the stance phase of running, when one foot is in contact with the ground, the muscles on the outside of the hip must become active to prevent the body from tipping toward the unsupported side. If those muscles are not able to do their job properly, the leg goes into genu valgum to compensate. This maladaptation to lack of hip stability causes the knee to be unnaturally pinched between the upper leg and lower leg, precipitating damage and pain.
Strengthening exercises for the hip abductors have become a standard treatment for PFPS. How well do they work? Researchers at the University of Calgary sought to find out in a new study. Twenty-five runners participated. Fifteen had ongoing cases of PFPS and the other 10 did not. Those with PFPS performed strengthening exercises for the hip abductors for three weeks. The uninjured runners sis not.
Both before and after this intervention, the researchers measured peak strength of the hip abductor muscles on both sides, the degree of genu valgum, stride-to-stride variability of knee kinematics during running, and pain ratings. Before the intervention, the injured runners exhibited less strength, greater differences in stride-to-stride knee joint variability, and no difference in genu valgum compared to the control group. After the intervention, strength was increased, stride-to-stride knee joint variability was reduced, pain was reduced, and no change in knee genu valgum was observed in the injured runners.
Diminishment of pain is the main thing, of course, but it’s impossible to say from this study that the hip strengthening exercises were responsible for the pain reduction. That would have required that injured runners who did not perform strengthening exercises be included in the study. Still, the study provides an encouraging sign that strengthening exercises for the hip abductors can alter knee joint kinematics in a way that reduces strain on the knee during running.
What’s a good hip abductor-strengthening exercise? My favorite is the resistance band lateral walk. Loop a resistance band around your lower legs and stand with your knees slightly bent and your feet far enough apart that there’s strong tension in the band. Now step to the right with your right foot. After planting your right foot, move your left foot an equal distance to the right. Take 20 total steps to the right and then reverse your direction, taking 20 steps to the left. To make the exercise more challenging, move the resistance band higher on your legs.
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