Can you break your knee cap and not know it?

Fractured left knee cap - looks like any knee injury.
Fractured left knee cap - looks like any knee injury.

Overview - Can you break your knee cap and not know it?

Your kneecap, the small bone that sits on your knee is very strong, but it still can break if it gets a large blow in a fall or accident. When your kneecap breaks it's called a patellar fracture.

The symptoms of a patellar fracture can be the same as any other knee injury: pain, swelling and stiffness. More severe fractures have more serious symptoms.

So you can break your knee cap and not know it!

Open patella braces are a great choice to speed up the regeneration.

Knee anatomy overview - what's the patella?

The patella (also known as the kneecap) is a small bone that sits at the front of your knee in the trochlear groove. It's function is to transmit the forces between your front thigh muscles and your shin bone, as it's connected to both of them with tendons.

The end of the thigh bone under the patella and the underside of the patella are covered with articular cartilage - this helps the patella glide in the groove. The cartilage on the underside of the patella is the strongest one in your body.

The ridges of the groove and the ligaments keep the patella in place so it hardly ever jumps out.

The patella is though, but it still can get damaged: the ligaments and tendons degrade with age, and it's the first body part you'll hit if you fall or you have an accident. Pain near the patella is more common as the tendons can get inflamed from overuse causing patellar tendonitis.

Knee cap fracture illustration.
Knee cap fracture illustration.

What happens when your patella breaks?

As your patella is at the front of your knee, this is the first thing you'll hit if you fall. The most common causes are falling from height, or a direct blow to your kneecap. In the end patella fractures make up 1% of all bone injuries.

Your patella could break into two or more pieces, your knee would swell, and if your skin is damaged in the accident this could become an open fracture. Your doctor will diagnose the extent of your injury, and will tell you how bad the fracture is.

If your fracture is simple and clean two piece break and the pieces did not move away it can be treated by wearing a splint or cast until the bone heals by itself.

Often the patella brakes into smaller pieces which move making your fracture more complicated. In this case surgery is necessary to put the kneecap together again and let it heal.

Depending on your injury you may not even realize that you fractured your patella - it's swollen and painful, even more so if you use your knee, so it looks just like any other knee injury.

X-ray of a patella fracture.
X-ray of a patella fracture.

How are patellar fractures categorized?

The seriousness of patellar fractures depend on their type, with the open fracture and the displaced fracture being the worst, while +3the stable fracture is the least problematic.

Types of patellar fractures - the stable fracture

If you have a stable fracture, it means that the bones either remained in contact or moved just a little bit, maybe a single millimeter. During healing the bones stay in place, and there's no need for a surgery.

Types of patellar fractures - the displaced fracture

If you have a displaced fracture, the bones have distanced and the smooth surface at the back of your patella is disrupted too. This kind of fracture usually requires a surgery, the fractured parts will be fixed together with wires, pins or screws.

Types of patellar fractures - the shattered fracture

If you have this type of fracture (also known as a comminuted fracture), your patella broke up and the got shattered into smaller pieces. This kind of fracture can be either stable or displaced.

Types of patellar fractures - open fracture

If you have an open fracture, your bone became visible from the outside - either your wound is deep and it goes down to the bone, or the bone shattered and a piece pierced through your skin from the inside.

An open fracture takes longer time to heal as more tissue is damaged, and bacteria, debris and viruses may have gotten into a wound and there is a risk of infection which needs time to heal too.

How is a patellar fracture diagnosed?

When your doctor examines your knee, he will ask you what kind of injury you had, and will try to feel the edges of the fracture through your skin.

He or she will also check if there is any blood inside the joint, as this could cause additional swelling. It there is, he or she may want to drain it with a needle to lessen your pain.

Your doctor will also have X-ray images made of your knee from different angles to get a clear picture of your fracture. With this it will be clear if you have a stable or a displaced fracture. If you have a stable fracture, without an X-ray you may never know you have on - you can break your knee cap and not even know it!

How to treat your patellar fracture?

If you have a stable, non-displaced fracture a surgery is usually not needed. Your doctor will either opt for a cast or a splint to stabilize your knee, and let the fracture heal by itself. If your leg is stretched and not moving, your patella will be in the ideal position for healing.

A lot depends on yout exact fracture, and your doctor may either allow you to use your leg to bear weight, or not. If not, it may take up to 8 weeks until you can use your knee again. If you only have a hairline crack you may start gentle exercises immediately and you'll only need to wear a brace.

A fracture this serious would need a surgery.
A fracture this serious would need a surgery.

When is a surgery required?

If you have a displaced fracture, you will probably need a surgery, as your patella may not heal by itself. As your thigh muscles are strong, they would pull the pieces apart and prevent healing.

Your doctor will probably suggest to wait a little bit until the swelling improves and your skin is healed before starting the surgery.

With an open fracture the surgery is more urgent, as your doctors will both clean your wound and your bone and fix the fractured parts during the surgery.

During the surgery, the broken pieces of your pattela will be put back together and fixed using wires, pins and screws. There are various wiring patterns which the surgeons can use to fix your patella.

If your kneecap is very badly damages the doctors may remove parts of it, or your whole kneecap.

Transverse fracture after surgery.
Transverse fracture after surgery.

How is a transverse fracture held together?

If you have a transverse (horizontal) fracture, your surgeons will most probably fix it using pins, wires and a tension band in a figure-of-eight configuration.

This works best if your fracture is near the center of the patella. A fracture at the side of your patella would be too small for these devices.

For smaller fractures using small screws works better.

How is a shattered fracture held together?

If you have a shattered or comminuted fracture, the bottom or the top of your patella is broken into multiple smaller pieces. This is usually a result of a double injury, a force pulls the patella into two pieces, and then it gets crushed into even more pieces, usually during a fall.

During the operation the doctors will remove the pieces which are too small to work with, and will fix the rest using screws or wires. This usually results in good healing.

Your doctors will rarely want to remove your whole kneecap.

How to recover from patellar fracture?

To recover from your patellar fracture, the most important is to have enough rest, elevate your injured leg, and use ice and over-the-counter medication for pain relief. Your knee will hurt for a few days to few weeks.

After surgery you will need to wear a brace to keep your knee extended. This will weaken your muscles and your knee joint will stiffen up a bit.

Once your bones start healing your doctor will ask you to start strengthening exercises to bring your knee joint and muscles back to their original strength. To get an idea of the kind of exercises you'll have to do, check out our article on knee dislocation and exercises.

You will still need to wear your brace for some time, and your doctor will likely ask you to stop wearing the brace for longer and longer times after about 3 months.

You should be able to start heavy exercises 4 to 6 months after the surgery if you are into that.

Depending on the type of the surgery you had, you may need another surgery to remove the wiring and the screws.

During rehabilitation your doctor or physical therapist will guide you through the exact steps and the exercises you should do.

Can I use my knee after patella fracture surgery?

Your doctor will tell you when you can start bearing weight on your leg. It's important to keep it gradual, and use a crutch to make sure you do not overload your knee accidentally.

What are the complications of a patellar fracture?

Patella fracture can have complication even if the surgery was successful:

Patella fracture complication - the posttraumatic arthritis

An injury can trigger arthritis, called posttraumatic arthritis. This happens because the cartilage on your bone gets damaged, and can lead to stiffness and pain. Mild to moderate arthritis is common, severe arthritis is rare fortunately.

Patella fracture complication - weak muscles

Rarely the front thigh muscle becomes weak from the weeks of inactivity, and has a hard time getting it's original strength back. Some patients experience a slight loss of range of motion too, fortunately this is rarely serious.

To improve your thigh muscle strength, check the exercises in our Knee dislocation article.

Chronic knee pain is a common long term side effect.
Chronic knee pain is a common long term side effect.

Patella fracture complication - chronic pain

For some patients the knee remains painful even long after the surgery. This is usually fixed by wearing a sleeve or a brace (such as the FitXpert sleeve), which gives additional support to the knee, and takes over some of the load.

Good to know

Depending on the your exact injury, the healing time could vary between a few weeks and a few months. A serious injury requiring surgery will take longer time to heal. Once you've finished the rehabilitation you can expect to have only almost no pain and almost no loss of range of motion.

Your doctor or physical therapist may help you by with suggestions which prevent further knee injuries, overuse or overloading. These can include avoiding squatting, avoiding stairs and losing weight if necessary.

Using a brace such as the FitXpert sleeve or the Mava sleeve could shorten your healing time.

To learn more about patellar fractures, check out Cedars-Sinai Hospital's article or head over to Wikipedia for a great overview.