1. They Occur From Falls or Unexpected Bending of the Knee
A direct blow to the knee can cause the kneecap (patella) to break. The resulting muscle pull of the quadriceps (thigh) muscle can cause the pieces to pull apart. Another possibility is that these forces will act in concert. Falling causes you to instinctively try to regain your footing and fire your quadriceps muscle. This places the area under tension, then the knee strikes the ground and fractures.
2. They Result in Loss of Extension of the Knee
The extensor mechanism is the quadriceps muscle, which becomes the quadriceps tendon, which attaches to the patella, which is connected to the patellar tendon, which attaches to the tibia (shin bone). Together, these allow you to extend (straighten) your knee. A patella fracture with displacement can result in the loss of active knee extension. This is quite debilitating, making it impossible to walk or get up from a chair.
3. They Are Similar to Quadriceps-Tendon or Patellar-Tendon Ruptures
Essentially, the same mechanisms can result in quadriceps or patellar-tendon ruptures, instead of a patella fracture. Often, the tendon rips off the bone right at the attachment. These ruptures need to be repaired; otherwise, there will again be loss of extension. They are usually repaired via sutures that are pulled through the patellar bone to reconnect the two. Another alternative is to use suture anchors. These are placed in the bone and used to pull the tendon back to itself. The sutures are tied, again reattaching the tendon to the bone.
4. Some Fractures Can Be Treated With a Cast
Non-displaced patellar fractures can be treated with a cast or brace with the knee in full extension. Most often, you are able to walk with the knee straight, since this doesn't cause the quadriceps muscle to fire. Essentially, you're walking with a peg leg. With your knee straight, reach down and feel your kneecap and move it back and forth. There is actually not much tension of the patella with the knee extended.
5. Some Fractures Will Require Surgery
If the fractures are displaced or pulled apart, surgery is necessary. A combination of screws, pins and wires is used to pull the pieces together. Once the bone is healed in two to three months, you may want the metal to be taken out. That particular area is quite prominent and might cause discomfort, such as when you are kneeling.
