“Runner’s knee” is a term that describes a painful and sometimes debilitating ailment of the knee present in a quarter of active people. The condition is often associated with runners, but anyone who participates in activities requiring knee bending can become affected. The exact cause of runner’s knee—otherwise known as patellofemoral pain syndrome (PFPS)—has remained a mystery. According to research from the University of North Carolina at Chapel Hill, that mystery may now be solved.

Published in the November 2009 issue of the American Journal of Sports Medicine (2009; 37 [11], 2108–16), the study followed nearly 1,600 midshipmen from the U.S. Naval Academy for 2.5 years. Each participant underwent three-dimensional motion analysis during a jump landing task; six lower-extremity isometric strength tests; and postural alignment measurements that included Q angle and navicular drop (arch flattening during weight bearing). By the end of the study, 24 women and 16 men had developed runner’s knee.

The researchers identified several circumstances associated with the condition: weak hamstrings and quadriceps increased the probability of developing runner’s knee by 2.9 and 5.5 times, respectively; excessive navicular drop and smaller knee flexion angle during jumping were also contributing factors.

“Overall, these people generally have weaker quads and hamstrings,” stated study co-author Darin Padua, PhD. “As a result, they don’t bend their knees as much when doing tasks such as running or jumping. This means the contact area between the kneecap and the femur is smaller, so pressure is focused and pinpointed on a smaller area.” To assess a client’s potential for developing PFPS, the researchers
suggested looking for the following:

  • knees moving forward of the big toe during a squat
  • collapsed arches while landing from a jump
  • minimal knee bend during jump landing

“Prevention programs should focus on increasing strength of the lower-extremity musculature along with instructing proper mechanics during dynamic movements to decrease the incidence of PFPS,” added the authors.