The knee is made of three bones: the femur (thighbone), the tibia (lower leg bone), and the patella (kneecap). Your patella sits in the middle of a large tendon that connects the front thigh muscles to the tibia bone. It acts to help your knee bend. It glides in a large groove on the front of the distal part of your thighbone. This groove is called the trochlea. The bottom of your patella and the top of the trochlea are covered with thick cartilage. The cartilage allows bones to move over each other easily. Damage to this cartilage from and injury and/or age can lead to arthritis.
Your patella is held in place by the strong muscles of the thigh, ligaments (which connect bone to bone), and tendons (which connect muscle to bone). The large tendon that connects your thigh muscles (quadriceps) to your patella is called the quadriceps (or “quad”) tendon. The strong tendon that attaches your patella to your tibia is called the patellar tendon.
The blood vessels to the patella come from behind the knee and wrap around the front to reach the patella.
Mechanism and Epidemiology
Patella fractures are relatively common. They can occur after a direct blow to your patella—often during a fall. They can also occur after a very strong contraction (tensing) of the muscles of the thigh. However, this is much less common.
If you break your patella, your knee will swell up and you may not be able to straighten your leg. You probably won’t be able to walk due to the pain and inability to use your leg. Generally, you will be seen in the emergency room (ER) or urgent care, where they will take x-rays of your knee. The x-rays will help the doctors determine if you have fractured your patella. If you tore tendons such as the patella tendon or quadriceps tendon it may not be clear on x-ray, so sometimes imaging such as an MRI is needed. MRIs show soft tissue injuries much better than x-rays, which show bony injuries. This may not be done in the ER and may need to be scheduled later. Generally, as long as the skin over the patella looks okay (no cuts and the bone is not pressing on your skin from the inside), you may be treated with a straight leg brace and able to go home. An appointment with your physician or an orthopaedic surgeon should be scheduled in the next few days to a week. If the bone cut through the skin (an open or compound fracture), you will likely be admitted to the hospital and undergo surgery more quickly.
Treatment is generally based on whether the bone pieces are touching or not, and if your leg can be straightened. If the pieces are pulled apart from each other, you likely will not be able to straighten your knee out because your thigh muscles are no longer connected to your lower leg. In that is the case, you will likely need an operation to put the bone pieces back together. This will restore your ability to extend your leg, which helps with walking.
Sometimes there is a crack in the patella but the bones are not pulled apart from one another. If that happens the strong soft tissues over/around your kneecap are still intact and your knee can still be straightened. You may not need surgery but will likely be treated with a brace and have restrictions on bending and weight bearing.
Surgery on a kneecap can be done many ways. The main goal is to reconnect the bones. This connects your thigh muscles back to your tibia so you can straighten your knee out again. Common ways to fix a patella are with wires, plates, sutures, or a combination of the three.
After surgery, you will likely be placed in a brace that limits the amount that you can bend your knee. You may be able to walk on your leg with your knee held straight by the brace. However, sometimes your surgeon may ask you not to put weight on your leg in order to protect your bone while it heals. You may be able to move your knee right away or you may be limited in how much your surgeon wants you to move. All patella fractures are different, so it’s important to follow the recommendations from your surgeon on how quickly you can progress to weight bearing and motion. Patellas break in a variety of ways, so sometimes activity can progress quickly and sometimes recovery is much slower. It all depends on the repair and what your surgeon thinks is best for you.
You will likely need some physical therapy after surgery. Depending on your injury, this may start right after surgery or after a few weeks of healing.
After healing, most people are able to get return to their previous level of activity. This can take several months. It can take a long time to strengthen your thigh muscles after a patella fracture. The patella has a thick layer of cartilage, which can be injured in the break. This may lead to arthritis of the knee joint. Arthritis can cause pain and stiffness. Your knee may also become stiff after healing has occurred. You may not be able to bend your knee or extend it as much as before. This may be from scar tissue that blocks motion or from weakness in your muscles. Sometimes a knee needs to be manipulated (moved) to regain motion. This is typically done while you are under anesthesia. It can be very uncomfortable, so it is important to follow the recommendations of your surgeon to try to prevent this.
If it bothers you, the hardware that was used to fix your patella may need to be removed after your bone heals. There is not much tissue between your skin and your patella, so your hardware may be uncomfortable when you touch your knee or when you kneel. Sometimes the wires or screw may become loose and need to removed. This requires another surgery. However, the recovery from this is generally easier than recovering from the original break.
On occasion, a patella fracture may not heal and the bone pieces will pull away from each other. If this happens, you will likely require another operation to reconnect the bones. Other issues that can occur are wound healing problems or blood clots. These are not common but do happen. It is important to follow the recommendations of your surgeon to try to prevent these complications.
Christopher Domes, MD
Edited by the OTA Patient Education Committee
All x-rays and pictures taken from the personal collection of Dr. Domes