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No athlete I'm afraid. Overweight female, presently lost two stone and on the way down, so I know weight is probably a contributory factor.
Could it be related to another problem that I have? A couple years ago I was experiencing pain in my knees and found out that the muscle on the inside of my upper legs had never developed properly. So the outside muscles were pulling my knee caps outwards. The physio actually laughed at how weak my muscles were!