Risk factors and mechanisms of knee injury in runners

Approximately 36 million Americans participate in running each year, with 10.5 million running at least 100 d x yr(-1). Although running injuries are well understood medically, their potential risk factors are not. Thus, we presently have limited ability to identify individuals at high risk for overuse injuries.

This study aimed to identify behavioral and physiological risk factors that influenced potential knee injury mechanisms, including knee joint forces and knee moments.

Participants included 20 adults ranging in age from 20 to 55 yr (n = 7 males and n = 13 females). During the first screening visit, quadriceps and hamstring flexibility was assessed, and Q-angle, height, and weight were measured. During the second screening visit, participants completed a series of questionnaires and a gait analysis to calculate knee joint loads. An isokinetic dynamometer was used to measure eccentric and concentric knee extension strength.

Body weight (r = 0.48, P = 0.03), weekly mileage (r = 0.62, P = 0.005), and concentric knee extension strength (r=0.68, P = 0.0001) were significantly correlated with tibiofemoral compressive force. Knee extension moment displayed a negative correlation with hamstring flexibility (r = -0.47, P = 0.04). Both weekly mileage (r = 0.50, P = 0.03) and concentric knee extension strength (r = 0.60, P = 0.01) had significant positive correlations with patellofemoral force.

The results of this study relate larger knee joint loads to poor hamstring flexibility, greater body weight, greater weekly mileage, and greater muscular strength. Most of these risk factors could potentially be modified to reduce joint loads to lower the risk of injury.