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Patella - intro

Submitted by admin on March 14, 2008 - 11:17am.

 

Although it is a bone, the patella is actually contained right within the tendon of the quads just above the joint line.

Image showing the position of the patella within the tedon of the quads muscle

This is very unusual in the body - to find a bone inside a tendon - a so-called sesamoid bone - and what it means in reality is that any alteration of the direction of forces in the whole quads muscle/tendon/bone complex has to affect the patella.

Now, the undersurface of the patella is v-shaped and sits within a groove in the underlying femur and, although it is free to slide up and down the groove, it is not free to move from side to side.

If there is any alteration in the extensor mechanism tending to pull the patella over to the side, it is normally contained by the walls of this groove (the trochlea). There are also fibrous restraints (see below) on both sides of the patella to keep its alignment central.
Image showing position of the patella in the trochlear groove

Take a look at this video, which has been taken during arthroscopic surgery, and which shows the patella from above as in the sketch we have just seen.

 

 

As the knee is bent by the surgeon, the patella engages in the groove of the femur and slips out of view. A curtain-like suprapatellar plica stretches horizontally across the field of view on the left. The shadowy stuff on the right is just some unimportant loose tissue floating into view. (Courtesy of The Knee Foundation)

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