What Is the Patellofemoral Joint?

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The patellofemoral joint is where the back of your patella (kneecap) and femur (thigh bone) meet at the front of your knee. It's involved in climbing, walking on an incline, and several other knee movements. It's also the joint affected by a common injury called "runner's knee."

Illustration of knee anatomy
BruceBlaus / Wikimedia Commons / CC BY 3.0

Structure

The patellofemoral joint is a complex structure involving not only bones, but a network of muscles and connective tissues. All of the bony surfaces inside the patellofemoral joint are covered with articular cartilage, which is slippery and helps the bones glide smoothly against each other when the knee bends or straightens.

The underside of your kneecap sits in a groove within your thigh bone called the patellofemoral groove. Within this groove, the kneecap mostly moves lengthwise, but it has some side-to-side movement and can tilt and rotate as well.

When you contract the quadriceps muscles of your thigh, they pull on the quadriceps tendon that attaches to your kneecap. This makes your knee straighten. Two other thigh muscles keep your kneecap in the femoral groove during this motion—the vastus medialis obliquus and the vastus lateralis, which are located on the inside and the outside of your thigh.

Function

Some daily motions that work your patellofemoral joints include:

  • Walking uphill or downhill
  • Going up or down stairs
  • Kneeling, squatting, or getting up from a seated position

These are the types of everyday activities the patellofemoral joint was designed and evolved to perform. It works well, but, like the rest of your body, it undergoes wear and tear from almost constant use over the years. In addition, taking part in sports can lead to overuse and damage to the patellofemoral joint.

Associated Conditions

Since the patellofemoral joint is involved in almost everything that involves your legs, it's highly susceptible to injuries and wear-and-tear. The most common ones include:

  • Patellofemoral arthritis
  • Patellofemoral pain syndrome
  • Chondromalacia
  • Patellar dislocation

Patellofemoral Arthritis

When the articular cartilage in the groove and on the back of the patella wears away, the joint becomes inflamed. This is called patellofemoral arthritis. As the cartilage breaks down, it becomes frayed and can leave the bone exposed. The surface of bones is rough, and it's painful when they grind against each other.

Your risk of patellofemoral arthritis may increase if you've ever fractured your kneecap or have a condition called dysplasia, in which the patella doesn't fit properly inside the groove.

Patellofemoral Pain Syndrome

Misalignment or repeated contact of the joint surfaces may lead to patellofemoral pain syndrome, which is characterized by joint irritation and inflammation, knee pain, and limited range of motion in the knee.

The key symptom of patellofemoral pain syndrome is pain under and around your kneecap. Irritation of this joint is generally caused by:

  • Acute injury to the kneecap, such as if your knee is hit, you fall on it, or it's wrenched with a sudden twisting motion; getting tackled in football is a common cause
  • Misalignment of the joint, such as when the kneecap no longer "tracks" properly within the patellofemoral groove
  • Overuse from excessive running, particularly if the knee muscles are weak, which is why "runner's knee" is another name for this syndrome
  • Chronic wear and tear of the knee joint from everyday activity and sports
  • Poor foot mechanics

Chondromalacia

Patellofemoral irritation may also lead to the breakdown of cartilage (flexible connective tissue) on the underside of the kneecap, which is called chondromalacia. In its most chronic form, this condition may require surgical repair. This is a common injury in runners, soccer players, skiers, and cyclists.

Symptoms of chondromalacia include a dull pain under or around the kneecap. This may be felt when going up or down stairs or getting out of a chair. Chondromalacia can be due to long-term wear and tear, muscle weakness, or knee-alignment problems, or it can develop after a fall.

Patellar Dislocation

Knee dislocations happen when the kneecap slips out of the patellofemoral groove. This is very painful and can damage the joint cartilage. Causes of patellar dislocation include:

  • Having a shallow patellofemoral groove
  • Abnormal attachment between the patellar tendon and the shin bone (tibia)
  • Having a "high-riding" kneecap (more common in girls), a condition called patella alta
  • Having knock knees (knees that turn in toward each other when you stand)
  • High-impact injury, such as during sports

Repeated Injury

Once a patella has been dislocated, it's easier for it to happen again.

Treatment Options

Treatment for an injury to the patellofemoral joint depends on the cause and severity. Possible treatments include:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs): Aspirin, naproxen, and ibuprofen reduce both pain and swelling.
  • Exercise: Regular exercise to decrease stiffness and strengthen the muscles supporting your knee is a common treatment for patellofemoral pain syndrome.
  • Physical therapy: Specific exercises can improve range of motion in your knee. Exercises to strengthen the quadriceps muscles will help relieve pressure on the kneecap when you straighten your leg.
  • Weight loss: If you are overweight, losing just a few pounds can make a big difference in the amount of stress you place on your knee.
  • Cortisone (steroid) injections: Cortisone is a powerful anti-inflammatory medicine that can be injected directly into your knee.
  • Viscosupplementation: A substance similar to natural joint fluid is injected to reduce friction.
  • Surgery: When nonsurgical treatments aren't effective, a surgical procedure may help; options range from minimally-invasive procedures to partial or total knee replacement, which is most common with severe patellofemoral arthritis.

Frequently Asked Questions

What kind of joint is the patellofemoral joint?

The patellofemoral joint is where your kneecap connects to the thigh and shin. The joint sits in front of the knee and is a complex structure of muscles, connective tissue, and bones.

What causes patellofemoral pain syndrome?

Commonly known as runner’s knee, patellofemoral pain syndrome is irritation and inflammation that causes pain at the front of the knee. It’s often caused by overuse during running or jumping sports, muscle imbalances or weaknesses, trauma to the kneecap, or ACL surgery. 

How do you treat patellofemoral syndrome? 

Runner’s knee is treated with RICE (rest, ice, compression, and elevation), anti-inflammatory medication, and physical therapy exercises. In rare cases, surgery may be required.

Does patellofemoral syndrome ever go away? 

Runner’s knee is usually treatable, but how long it takes to find relief depends on the severity of the condition and if there is any damage to surrounding tissues. If treatment is delayed, it will take longer to heal. 

How is arthritis of the patellofemoral joint treated? 

Knee arthritis is typically due to osteoarthritis, a progressive wearing away of the protective cartilage in the patellofemoral joint. It is treated with physical therapy, exercise, heat or ice therapy, and pain medication. In rare cases, it can be caused by rheumatoid arthritis, and disease-modifying anti-rheumatology drugs (DMARDs) can bring relief and prevent further joint damage. 

A Word From Verywell

Problems with the patellofemoral joint can cause significant pain and disability. However, you do have a lot of treatment options available that can get you up and walking on that leg again. If you injure your knee or begin having pains that could signal a patellofemoral joint problem, see your doctor about it. The sooner you get a diagnosis and treatment, the sooner you'll be functional again.

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