Hoffa's Syndrome can also occur if the fat pad is pinched when the leg turns inward abnormally while running or playing soccer as two example.
The risk of this happening increases if you have instability in your knees or hips which can be a result of other conditions affecting the lower limbs. When favoring one side of the body, overcompensation issues will develop as more stress is placed on the opposite side. You begin to use improper mechanics to walk or run and this can lead to unbalanced loads and over straining one of your knees and/or hips. Over time, this extra load can lead to impingement in the joint and possible break down in tissues and cartilage as well.
Simply straightening the leg can cause the fat pad to become trapped, so this makes one susceptible to re-injury and can lead to a significant recovery time if not treated quickly and correctly.
Read more about the symptoms, tests, and other options for Hoffa's Syndrome symptoms (pain and stiffness) here: