Pain in most cases (but not all) is due to degenerative changes happening at the knee. There are many reasons for these changes but the 2 most common ones are:
Not all knees are the same, and in most of us our left knee is not the same as the right knee. The shape of the knee determines how loads are transferred through the joint. Common factors affecting the shape of our bones/joints are: genetic, working environment, fractures, age, nutrition and diseases like arthritis, gout, rheumatism etc.
Traumatic injuries usually occur suddenly and are often associated with injuries to other knee structures. Examples of traumatic injuries vary from a simple stumble on the pavement to skiing or road accidents.
How is an anterior knee pain diagnosed?
The most effective way of assessment is through a comprehensive history taking of the pain and any other symptoms. This is then followed by examining the affected joint and how it behaves under strain/load etc.
It is also very important to be aware that diagnostic imaging (X-ray, MRI, ultrasound) usually does not show structural changes that could cause the reported symptoms.