Connecting the Hip to the Knee

Article

by Coach Janet Hamilton, MA, RCEP, CSCS

Have a knee injury? It's probably not the knee's fault. For years researchers have evaluated injured runners and the evidence has been piling up that runners with knee injuries tend to have weaker hips than their uninjured compatriots. This is what's known in research jargon as "association" and the studies that found that association were retrospective studies, meaning that the athlete is already injured when the researcher is evaluating them. There's a little whisper of doubt that comes into this... "what if their hips are weak because they have a knee injury?" In other words, you have a chicken and an egg - but you don't know which came first. You just know that you find weak hips in runners with knee injuries. A study published in the June 2013 issue of Medicine & Science in Sports and Exercise adds another piece of evidence to the argument that hip weakness contributes to knee injury among runners. Brian Norehren and his colleagues studied 400 healthy female runners in an attempt to find out what sort of characteristics might be in place prior to the athletes becoming injured. This is what's known as a prospective study. You measure things and then wait for the injury to occur and see if there are any correlations between your measurements and the resulting injury. The study subjects were all uninjured female runners between the ages of 18 and 45, who were currently running a minimum of 20 miles per week. Detailed gait analysis was performed using high tech motion analysis equipment and then the athletes were followed for a period of two years to identify any running related injuries. Runners who subsequently developed patellofemoral pain (PFP) were then identified and matched with a control group of the subjects who were similar in age and mileage, but didn't develop PFP. Of the initial 400 runners followed, 38 reported knee pain and 15 of these were medically diagnosed as PFP and included in the data analysis. In previous retrospective studies, researchers have identified a greater amount of hip adduction (see photo above) in runners with PFP.  This motion is often referred to by coaches as "hip drop" and is considered to be indicative of weakness in the muscles that help stabilize the hips - specifically the abductors (gluteus medius, gluteus maximus, and core muscles like the quadratus lumborum are prime suspects here). The question became - was there a greater amount of hip adduction in those runners before they got injured or did it occur as a consequence of their injury?  This prospective study concluded that runners who go on to develop patellofemoral pain have a statistically significant increase in hip adduction compared to runners who do not develop patellofemoral pain. This significant finding lends even more weight to the guidance that runners should work to develop good core and hip strength in order to reduce their risk of knee injury. Your knee's best friend is a strong set of hips and a strong core! (Med. Sci. Sports Exerc., Vol. 45, No. 6, pp. 1120-1124, 2013)