These articles have quotations from film adaptations of J.R.R. Tolkien's novel The Lord of the Rings and related works: 1  The Lord of the Rings.  J.R.R. Tolkien's The Lord of the Rings (1978)
This causes a twisting on the tibia and changes its relationship to your kneecap. This can cause tracking problems as well. If your quadriceps or hamstring muscles are too tight, they also will affect the mechanics of the knee and lead to compensation patterns that cause pain.
Muscle weaknesses/imbalances can cause the kneecap to pull to the left or right of the groove, resulting in the underside of the kneecap rubbing against the thighbone and becoming irritated (see runners knee page for more info on pain caused by poor knee tracking).