The knee is the largest joint in the body and one of the most complex. A fractured knee can cause pain, swelling, and reduced range of motion. Treatment for this fracture may involve surgery or casting.

A knee fracture is an injury that causes damage to the patella bone in the knee joint. About 1% of all fractures in humans are patellar fractures. “Fracture” is the medical term for a broken bone.

Knee fractures may result from a direct blow to the knee or from the leg twisting while it is bearing weight. A person with a fractured patella may have pain in their kneecap and difficulty moving their leg.

This article explains the symptoms of a knee fracture. It also discusses types of fractures, treatment, complications, and more.

A person wearing a leg brace for a knee fracture.Share on Pinterest
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The knee is a hinge joint consisting of three bones: the femur, or thighbone; tibia, or shinbone; and patella, or kneecap. The knee allows the leg to bend and straighten.

Doctors may also call a knee fracture a patellar fracture. A patellar fracture is a break in the round patella bone. Ligaments attach the patella to the quadriceps muscles in the thighs and to the shinbone.

Doctors classify knee fractures into types depending on their severity and the displacement of bone.

The symptoms of a patellar fracture include:

  • pain
  • swelling
  • bruising
  • an inability to straighten or bend the knee
  • the ability to feel the break through the skin

Doctors categorize fractures into different types depending on the exact displacement of the bones.

Stable or nondisplaced fracture

In this type of fracture, the pieces of bone remain either in contact with each other or just a millimeter or two away. Stable fractures usually heal easily. They occur when there is no break in any of the bones, but there is a crack or chip in one or more of them.

Displaced fracture

A displaced fracture occurs when a break in one or more of the bones causes the bones to shift out of place. They do not align properly, and this type of fracture often requires surgery to realign and stabilize the broken bone.

Comminuted fracture

The bone shatters into three or more pieces in this type of fracture. To diagnose a comminuted fracture, a doctor will examine the bone. If the pattern of the fracture is stable, it is best to treat the injury with immobilization. If the fracture pattern is unstable, surgery may be necessary to repair or remove one or more pieces of bone.

Open fracture

In an open fracture, the bone breaks so that bone fragments stick out through the skin or a wound penetrates down to the bone. This often damages surrounding soft tissues, which can take time to heal.

A break in the skin causes an open fracture. This type of fracture is particularly serious because it carries a higher risk of infection. The bone breaks the skin, and bacteria that usually live on the body can enter the wound and cause an infection.

A knee fracture may happen after a person falls directly onto their knee. It may also happen when the knee receives a direct blow, which may occur while playing sports or during a vehicle collision.

People with health conditions that cause weak bones, such as osteoporosis, may be more likely to fracture their knee.

Learn more about bone diseases here.

To diagnose a knee injury, a doctor will first ask about a person’s symptoms. The doctor will examine the knee to check for tenderness, stiffness, and swelling and check the person’s range of movement.

If a person has a displaced fracture, the doctor may be able to feel the fractured bone through the skin. They may arrange for an X-ray to confirm the diagnosis. They may also order an ultrasound or radiograph.

Learn about X-rays here.

Doctors will recommend surgical or nonsurgical treatments depending on the severity and location of the fracture.

Nonsurgical treatment

The treatment for hairline breaks is immobilization for a number of weeks. Doctors may apply a cast or splint to the knee to prevent movement and keep the bones in place while they heal.

Some people may be able to bear weight on the leg while wearing a cast, but this is not advisable for other fractures. A doctor will give guidance based on a person’s injury.


If a fracture involves any displacement or other complications, such as dislocations or open wounds, then surgery may be necessary to repair the damage. Surgeons can realign the knee and remove any unnecessary bone fragments. They may use screws, pins, and wires to hold the pieces of knee bone together.

In comminuted fractures, some pieces of bone may be too small to reattach. The surgeon will remove them and reattach the patellar tendon to the remaining patella bone.

Learn about bone fracture repair here.

Many complications can arise from a knee fracture, including:

Post-traumatic arthritis (PTA)

The most common complication from a knee fracture is PTA, a type of arthritis that develops after an injury.

PTA occurs when there is damage to the cartilage covering the ends of bones. Over time, cartilage loss means that bones rub against each other, causing inflammation and pain.

Learn more about PTA here.

Chronic pain

Many people experience long-term pain after a knee fracture. According to the American Academy of Orthopaedic Surgeons, it is not clear why some people experience this, but it may be related to PTA, stiffness, and muscle weakness. Wearing a knee brace or other support may bring relief.

Learn more about chronic knee pain here.

Muscle weakness

A knee fracture can injure muscles and other soft tissues around the knee. A person may have permanent quadriceps muscle weakness in the front of the thigh after a fracture. They may also have a reduced ability to bend and straighten the leg.

Recovery usually takes 3–6 months but may take longer. It depends on:

  • the severity of the fracture
  • whether a person has surgery
  • how a person conducts their rehabilitation period

Knee fractures often cause pain for a few days or weeks. To help manage pain and allow the knee to heal, a person can:

If a person’s pain is severe, a doctor may prescribe a stronger pain relief medication, such as an opioid. However, opioids can cause dependency, so doctors prescribe them for only a short time.

A doctor or physical therapist may suggest specific exercises a person can do during their recovery to:

  • improve range of motion in the knee
  • decrease stiffness
  • strengthen the leg muscles

Learn about knee surgery rehabilitation here.

If someone injures their knee, they should try applying ice to it and using pain medication. If the pain does not subside or worsens, people should contact a doctor.

People should also seek medical advice if they:

  • cannot put weight on the knee
  • notice swelling
  • have a high temperature, feel hot and cold at the same time, and have redness or heat around the knee

Most people with a knee fracture recover function in the knee, but symptoms can take up to 6 months to subside and allow a person to return to their usual activities.

The outlook for a knee fracture depends on the severity of the fracture and damage to surrounding tissues. If the fracture is mild, it can heal with rest and limited activity. People with severe fractures may have a longer recovery period.

A knee fracture involves damage to the patella bone at the front of the knee. It can range in severity from a mild hairline fracture to a completely shattered bone that damages surrounding tissues.

Closed fractures do not break through the skin. Open fractures break through the skin, exposing the bone beneath, and may lead to infection if a person does not receive prompt treatment.

Symptoms of a knee fracture include pain, swelling, and bruising at the site of injury; joint instability; limited range of motion; and difficulty bearing weight to walk or stand.

Treatment for knee fractures may involve wearing a cast to immobilize the leg, elevating it when sitting, and using pain relief medications. Some fractures require surgery to realign the knee.

Recovery from a knee fracture may take 3–6 months or longer.