The patella tendon is a thick structure that extends from the bottom of the kneecap to the top of the shin bone. It can become torn and/or inflamed and degenerate with repeated use and particularly with poor biomechanics that put more strain through one area of it more than another.
The repeated rapid loading on the kneecap and thus the tendon attachment causes micro tears and damage to a structure which does not have great blood flow, much like the Achilles. It is the build-up of this trauma which does not necessarily heal well, especially if the trauma continues, that leads to degeneration and pain with or without associated inflammatory responses.
To help this it is essential to sort out your poor mechanics. The pattern is a common one and it is where the hip control by the glutes is poor allowing the leg to collapse inwards over the foot. Tightness in the ITB and hip flexor is part of this but the tightness in the ITB then pulls the kneecap towards the outside whilst the femur or thigh is turning inwards. This ‘perfect storm’ loads the inside of the kneecap and tendon attachment and problems arise.
It is compounded by tightness in the calf muscles, weakness in the foot stabilisers and calf and poor kneecap stability from the quads.