Plica Syndrome

Overview

A plica is a fold of the synovial membrane, the thin tissue that lines the knee joint. Plicae are normal remnants left over from how the knee forms before birth, and most people have them without any problem. Plica syndrome occurs when one of these folds, most often the one along the inner side of the kneecap, becomes inflamed, thickened, or irritated and rubs against nearby cartilage and bone.

The result is knee pain, sometimes with clicking or a sense of catching. The condition is usually related to overuse or minor injury and most often affects people who are physically active. It can closely resemble other knee problems, so it is often diagnosed after more common causes have been considered.

Symptoms

Symptoms typically affect the front and inner part of the knee. They may include:

• Dull, aching pain near the inner side of the kneecap, which can worsen with activity.
• Clicking, snapping, or popping as the knee bends and straightens.
• A feeling of catching or the knee giving way.
• Pain that increases with squatting, kneeling, climbing stairs, or sitting for long periods with the knee bent.
• Tenderness when pressing along the inner edge of the kneecap.
• Sometimes mild swelling.

Symptoms often build up gradually and may come and go depending on activity level.

Causes

Plica syndrome develops when a normally soft, pliable plica becomes irritated and loses its flexibility. Common contributors include:

• Overuse from repeated bending and straightening of the knee, such as in running, cycling, or stair climbing.
• Direct injury to the knee, such as a fall or blow.
• A sudden increase in training intensity or volume.
• Muscle imbalances or weakness around the hip and thigh that change how the kneecap moves.
• Prolonged periods with the knee bent.

Repeated irritation makes the plica thicker and less elastic, so it catches and rubs against the joint surfaces with movement, creating a cycle of inflammation and pain.

Risk Factors

Factors that may increase the likelihood of plica syndrome include:

• Participating in activities with repetitive knee bending, such as running, cycling, rowing, or swimming.
• A recent increase in exercise intensity or a return to activity after time off.
• Weak or tight muscles around the hip, thigh, and knee.
• A previous knee injury.
• Activities or jobs that involve a lot of kneeling or squatting.

Diagnosis

There is no single definitive test, so diagnosis relies on the history and physical examination, with imaging to rule out other problems. Evaluation may include:

• Physical examination, in which the doctor feels for a tender, cord-like band along the inner kneecap and checks for clicking or catching as the knee moves.
• Questions about activity, the pattern of pain, and any injury.
• Imaging such as MRI, which can sometimes show a thickened plica and helps rule out other conditions like a meniscus tear or cartilage damage.
• Arthroscopy in some cases, a procedure using a small camera inside the joint, which can both confirm the diagnosis and treat it.

Because the symptoms overlap with other knee conditions, doctors often diagnose plica syndrome after excluding more common causes.

Treatment

Most people improve with conservative, non-surgical care. Treatment usually starts with reducing the irritation and addressing its causes:

• Rest and activity changes to avoid movements that trigger pain.
• Ice to ease pain and swelling.
• Anti-inflammatory medicines such as ibuprofen, used as directed, to reduce inflammation and discomfort.
• Physical therapy to stretch tight muscles and strengthen the muscles around the hip and thigh so the kneecap tracks more smoothly.
• A corticosteroid injection in some cases to reduce inflammation.

If symptoms persist despite several months of conservative treatment, a minimally invasive arthroscopic procedure to remove the irritated plica may be considered, and it often relieves symptoms.

Prevention

Steps that may help prevent plica irritation or keep it from returning include:

• Increasing exercise intensity and duration gradually rather than suddenly.
• Keeping the muscles around the hips and thighs strong and flexible.
• Warming up before activity and using good technique.
• Avoiding long periods with the knee held in a bent position.
• Addressing knee pain early before it becomes chronic.

When to See a Doctor

See a doctor if knee pain lasts more than a couple of weeks, returns with activity, or comes with clicking, catching, or a sense of the knee giving way. Early evaluation can confirm the cause and prevent a long-lasting problem.

Seek prompt care if the knee becomes very swollen, red, and warm, if you cannot bear weight or straighten the knee, or if pain follows a significant injury, as these may point to a more serious problem that needs urgent attention.

Related Topics

Frequently Asked Questions

References

1. American Academy of Orthopaedic Surgeons (AAOS).
2. Mayo Clinic.
3. MedlinePlus, U.S. National Library of Medicine.