This article stresses the importance of core strength in knee rehabilitation.
In any complex articulated structure it is important that each part of the structure is adequately strengthened or buttressed, or the whole edifice may become problematic.
Patellar problems, in particular, may not derive primarily from the patella, but from rotational problems of the other bones, and weakness of the hip and back. In any good knee rehabilitation programme, the physiotherapist will consider the knee as a part of a greater structure. He or she will take good note of issues relating to the feet, ankles, the knees (of course), the hips, and the lower trunk.
Landing badly because of poor core strength
This is an illustration of a girl landing badly from a jump. She has not landed straight, and the knee has gone into a knock-knee (or 'valgus') position.
If the trunk and hip muscles are weak, then the hip tilts and the femur (thighbone) rotates inwards. Because the foot is planted on the ground, the knee joint can do nothing but follow the rotation of the femur inwards. It is simply caught in the middle.
You can see the issues in the illustration of the the bony alignment....
Because the kneecap (patella) is a 'sesamoid bone', formed within the tendon of the quadriceps muscle, the forces of inward rotation on the femur and outward rotation on the tibia result in patellar forces that tend to force the patella towards the outer side of the knee. Here the increased pressure between its undersurface and the outer wall of the underlying femoral groove in which it rides, may result in pain felt in the kneecap region, although the underlying problem is in weak hip and lower back musculature!
Physiotherapy focused upon the trunk and hips would likely rectify the problem. Surgery on the kneecap to 'improve alignment' would be a disaster!