Runner's knee is pain often experienced in runners where they are bothered by pain at the front or on the outer side of the knee.
Differential diagnosis of runner's knee
There are a number of conditions that may contribute to such pain, and attention needs to be paid to those factors that affect patellar alignment and tracking.
[Diseases and overuse injuries of the lower extremities in long distance runners]. Tschopp M and Brunner F. Z Rheumatol. 2017 Jun;76(5):443-450. doi: 10.1007/s00393-017-0276-6.
Changes in Knee Biomechanics After a Hip-Abductor Strengthening Protocol for Runners With Patellofemoral Pain Syndrome. Ferber R, Kendall KD and Farr L. J Athl Train. 2011 Mar-Apr; 46(2): 142–149.