Why Do We Have Knee Caps Anyway?

Ever stop to wonder what your knee cap (patella) is there for? It’s somewhat of strange thing to think about–and there’s generally not much reason to until something goes wrong with it, like dislocation or fracture. But despite being a bit of an oddity, its presence is certainly not incidental. Given the remarkable design of the body, you can rest assured the patella’s there for a good reason.

In fact, it actually serves a very important function–it makes your quadriceps muscles (on the front of the thigh) more effective.  The tendon of the quadriceps muscle crosses over the knee joint, attaching on the leg just under the front of the knee. When the muscle contracts, it rotates the knee into extension by pulling up on the lower leg. Because the patella lies right between the tendon and the knee, it positions the tendon farther away from the point of rotation than it would otherwise be.  Just that little bit of increased distance imparts a major mechanical advantage.  It’s simple physics–the farther away from the center of rotation, the less force needed to rotate the object. (It’s the same reason you’d prefer to use a long lever to jack up a piece of heavy furniture rather than a short lever….being farther away means you can lift the same weight with less effort). In reality, the knee cap makes the quadriceps muscle approximately 30% more powerful than without it!