The patellofemoral joint is where the back of the patella (kneecap) and the femur (thighbone) meet at the front of the knee. It involves climbing, walking on slopes, and several other knee exercises. It is also the joint affected by a common injury called “runner’s knee.”
The patellofemoral joint is a complex structure that involves not only bone but also a network of muscles and connective tissue. All bone surfaces within the patellofemoral joint are covered with articular cartilage, which is slippery and helps the bones slide smoothly over each other when the knee is bent or straightened.
The underside of the kneecap sits in a groove inside the thighbone called patellofemoral groove. Within this groove, the kneecap moves mostly longitudinally, but it has some side-to-side movement and can also tilt and rotate.
When you contract the quadriceps in your thigh, they pull on the quadriceps tendon that attaches to the kneecap. This will straighten your knee. During this movement, two other thigh muscles hold your kneecap in the groin — the vastus medialis oblique and the vastus lateralis, which are located on the inner and outer thighs.
Some daily exercises that work the patellofemoral joint include:
- walk uphill or downhill
- going up or down stairs
- Kneeling, squatting, or standing up from a sitting position
These are the types of everyday activities that the patellofemoral joint is designed and evolved to perform. It works great, but, like the rest of your body, it wears out with almost constant use over the years. Additionally, participating in sports can lead to overuse and damage to the patellofemoral joint.
Knee Pain: Causes and Treatment Options
Since the patellofemoral joint is involved in nearly all activities involving the leg, it is extremely vulnerable to injury and wear. The most common include:
- Patellofemoral arthritis
- Patellofemoral Pain Syndrome
- patellar dislocation
The joint becomes inflamed when the articular cartilage at the back of the groove and patella wears away. This is called patellofemoral arthritis. As the cartilage breaks down, it wears down and may expose the bone. The surfaces of the bones are rough and it hurts to rub against each other.
Your risk of developing patellofemoral arthritis may be increased if you’ve ever fractured the kneecap or have a condition called dysplasia, in which the patella doesn’t fit properly into the groove.
What to Know About Knee Arthritis
Patellofemoral Pain Syndrome
Misalignment or repeated contact of articular surfaces can lead to patellofemoral pain syndrome, which is characterized by joint irritation and inflammation, knee pain, and limited range of motion in the knee.
The main symptom of patellofemoral pain syndrome is pain under and around the kneecap. Irritation of this joint is usually caused by:
- Acute injury to the kneecap, such as if your knee is hit, you fall on it, or it gets sprained from a sudden twisting motion; playing football is a common cause
- Joint misalignment, such as when the kneecap no longer “tracks” properly within the patellofemoral groove
- Overrunning leads to overuse, especially 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 daily activities and sports
- poor foot mechanics
Patellofemoral joint irritation can also cause the cartilage (flexible connective tissue) under the kneecap to break down, which is called chondromalacia. In its most chronic form, this condition may require surgical repair. This is a common injury among runners, football players, skiers, and cyclists.
Symptoms of chondromalacia include dull pain under or around the kneecap. This may be felt when going up and down stairs or getting out of a chair. Chondromalacia can result from long-term wear and tear, muscle weakness, or problems with knee alignment, or it can develop after a fall.
Knee dislocation occurs when the kneecap slips out of the patellofemoral groove. This is very painful and can damage the joint cartilage. Causes of patellar luxation include:
- shallow patellofemoral groove
- Abnormal attachment between the patellar tendon and the tibia (shinbone)
- having a “high-riding” kneecap (more common in girls), a condition called upper patella
- Knee bumps (knees turn inward to each other when standing)
- High impact injuries, such as during sports
Once the patella is dislocated, it is more likely to happen again.
Treatment of patellofemoral joint injuries depends on the cause and severity. Possible treatments include:
- Nonsteroidal anti-inflammatory drugs (NSAIDs): Aspirin, naproxen, and ibuprofen reduce pain and swelling.
- Exercise: Regular exercise to reduce stiffness and strengthen the muscles that support the knee is a common treatment for patellofemoral pain syndrome.
- Physical therapy: Specific exercises can improve the knee’s range of motion. Exercises that strengthen the quadriceps will help reduce the pressure on the kneecap as you straighten your leg.
- Lose weight: If you’re overweight, losing just a few pounds can make a big difference in the amount of stress you put on your knees.
- Cortisone (steroid) injection: Cortisone is a powerful anti-inflammatory drug that can be injected directly into your knee.
- Viscous Supplement: Infused with a substance similar to natural joint fluid to reduce friction.
- Surgery: Surgery may be helpful when non-surgical treatments are ineffective; options range from minimally invasive surgery to partial or total knee replacement, which is most common in severe patellofemoral arthritis.
How your healthcare provider will test you for knee pain
Problems with the patellofemoral joint can cause severe pain and disability. However, you do have many treatment options available to get you back on your feet and walking on that leg. If your knee hurts or begins to experience pain that may indicate a patellofemoral joint problem, talk to your healthcare provider. The sooner you get diagnosed and treated, the sooner you’ll get back to normal.
Frequently Asked Questions
Where is the patellofemoral joint?
The patellofemoral joint is located in front of the knee joint and is a complex structure made up of muscle, connective tissue and bone. This is where your kneecap connects to your thigh and shinbone.
What Causes Patellofemoral Pain Syndrome?
Patellofemoral pain syndrome is usually caused by overuse during running or jumping sports, muscle imbalance or weakness, kneecap trauma, or ACL surgery. Commonly known as runner’s knee, its irritation and inflammation can cause pain in the front of the knee.
How is Patellofemoral Syndrome Treated?
Patellofemoral syndrome is treated with RICE (rest, ice, compression, and elevation), anti-inflammatory medications, and physical therapy exercises. In rare or more severe cases, surgery may be necessary.
Will Patellofemoral Syndrome Go Away?
Patellofemoral syndrome is usually treatable, but the time to find relief depends on the severity of the condition and whether there is any damage to surrounding tissue. If treatment is delayed, healing will take longer.
How is Patellofemoral Arthritis Treated?
Knee arthritis is usually caused by osteoarthritis, which is the gradual wear and tear of the protective cartilage in the patellofemoral joint. It is treated with physical therapy, exercise, heat or ice therapy, and pain relievers. In rare cases, it can be caused by rheumatoid arthritis, and disease-modifying antirheumatic drugs (DMARDs) can relieve and prevent further joint damage.
Other causes and treatment options for knee pain