Patellofemoral Pain Syndrome

Overview

Patellofemoral pain syndrome (PFPS) is a common knee disorder, which often affects the senior athlete and those involved in running and jumping sports. Overuse, a change in activity, and an altered metabolic status are frequently responsible for the development of PFPS. Structural alignment and muscular weakness or imbalance may cause the patella (kneecap) to track improperly on the femur (thigh bone) during movement, leading to pain around the kneecap.

Other terms for patellofemoral pain are: retropatellar pain, peripatellar pain, anterior knee pain, and runner's knee.

Different disorders that cause pain around the kneecap include:

  • infrapatellar tendonitis (jumper's knee), which affects the tendon just below the kneecap
  • chondromalacia patella, which involves damage to the cartilage surface of the patella
  • quadriceps tendonitis, which affects the tendon attachment above the patella
  • plica syndrome, in which joint tissue becomes inflamed and/or stiff, causing pain and tightness in the joint

What is the patellofemoral joint?

As the knee bends and straightens, the patella slides within a slot on the femur called the trochlear groove. The patella moves in many directions within this groove to provide efficient, frictionless movement up and down, side-to-side, rotational, and tilting. The bone surfaces are covered with articular cartilage to make joint movement smooth.

What is patellofemoral pain syndrome and what can cause it?

Repeated abrasion on any of the surfaces of the patella and femur stresses the soft tissues of the patellofemoral joint and may even lead to a bone bruise. In some cases, the pain is caused by a weakening of the articular cartilage and/or swelling within the joint.

One or more of the following factors can lead to patellofemoral pain:

  • Overuse: the repetitive bending and straightening of the knee that occurs in running may lead to the disorder because of the increased pressure points between the patella and femur when the knee is bent. A constant bending motion, especially on the weighted leg, can irritate the patella and cause a bone bruise to form.
     
  • Alignment: The quadriceps alignment between the hip and the knee (the Q angle) is thought to affect patellar tracking. Patients with a larger than normal Q angle (greater than 20 degrees) may be more susceptible to patellofemoral pain because the patella has a tendency to track more laterally (to the outside). Pain may be felt more on the outside of the patella and femur because of increased pressure on these contact areas. The Q angle of growing female athletes enlarges as the pelvis widens during the maturing process, increasing the risk for patellofemoral pain.
     
  • Muscular weakness: A weakness or strength imbalance of the quadriceps muscles may alter the tracking of the patella.
     
  • Muscular tightness: Tight muscles and tendons may also affect patellar tracking. The muscular structures that cause movement in the knee and hip must be flexible. If any one muscle or muscle group is tighter than the rest, patellar instability can occur.
     
  • Flat feet (excessive foot pronation): Patients with little or no arch in the foot are also likely candidates for patellofemoral pain. As the foot rolls inward, the tibia compensates by rotating inward, disturbing the normal mechanics of the patellofemoral joint.
     
  • A decrease in patellar mobility: the kneecap tightens, losing its normal ability to move in many directions

What are the signs and symptoms of patellofemoral syndrome?

Generalized pain around the kneecap is the most common symptom of patellofemoral syndrome:
The patient may have a history of a dull, aching pain in the knee, not necessarily in one specific area.

If the pain is in front of the knee below the kneecap, it is probably caused by tendon inflammation called infrapatellar tendonitis or "jumper's knee".

Running, going down stairs, squatting, or sitting for a long time with knees bent usually increases pain.

Although full range of motion is usually possible, flexing the knee completely is painful.

Crepitus (a crackling noise under the patella) may occur during knee movement.

A slight swelling may exist

Symptoms may be present in one or both knees.

Decreased kneecap motion

How is patellofemoral pain syndrome diagnosed?

The doctor will first take a history from the patient to learn about the location of the pain, when it began, and whether it is injury-related. Knowing the patient's activity level, whether there is instability, and what motions increase pain help the doctor make the diagnosis.

In the physical examination the doctor will:

  • usually be able to reproduce the symptoms by pressing on the kneecap, particularly when the knee is bent and then straightened.
  • check for tenderness and patellar motion
  • assess alignment and flexibility
  • evaluate the muscular strength and coordination of the leg

X-rays show the bony structures of the knee, permitting the doctor to rule out:

  • arthritic conditions
  • loose bodies (bone fragments in the joint)
  • patellar mal-alignment
  • varus or valgus mal-alignment (bow-legs or knock-knees)
  • infection or a bone tumor

An MRI (Magnetic Resonance Imaging) or TEC (Technician 99 Radioisotope) Scan may be recommended if symptoms persist after conservative (non-operative) treatment. Both of these studies can show bone changes such as:

  • a bone bruise or stress fracture
  • cartilage loss or deterioration
  • infection or a tumor

An MRI can also reveal:

  • the condition of the ligaments, cartilage, and menisci
  • a swollen plica (a normal fold of tissue which can be painful when it becomes inflamed and enlarged).
  • Tendonitis or partial tearing with nodule formation in the patellar tendon

How is patellofemoral pain syndrome treated?

Non-Operative Treatment

Patellofemoral pain syndrome can usually be effectively treated with a non-operative treatment program. It can take the knee six weeks or more to show improvement once treatment begins; this is often the same length of time the pain has been present. The following options are typically used in a conservative treatment program:

  • Activity modification: physical activities should by decreased by 30% and should be limited to those with no impact, such as swimming or bicycling. Uphill walking or treadmill at a 7% grade is also a good choice. Exercises that cause pain should be avoided.
  • Anti-inflammatory medication such as ibuprofen is recommended
  • Icing
  • Specific exercises to strengthen and rebalance the muscles about the knee.
  • A knee sleeve, splint, or taping that will support the joint during healing. (Special sleeves can keep the patella tracking properly during motion.)
  • Special footwear or orthotics can support the arch and absorb impact.

Six weeks after treatment begins the patient will usually return for a follow-up appointment. At this time the doctor will evaluate the success of the program. If the symptoms have not improved, surgery may be recommended.

Operative Treatment

If surgery is recommended, a second opinion from another orthopaedic surgeon can help the patient make an informed decision. Surgery should only be considered as a last resort, when conservative treatment has failed to alleviate symptoms.

A diagnostic arthroscopy allows the doctor to examine and treat the inside of the joint. In this procedure, instruments are inserted through small incisions in the knee. Rough or frayed spots in the cartilage that covers the bone can be smoothed, plica can be trimmed, and the patella can be realigned if necessary.

What types of complications may occur?

The most common complications from surgery are persistent swelling, loss of muscle tone, and scar tissue formation.

Recovery from patellofemoral pain can be a long process. Non-operative recovery usually takes six weeks or more. Sport activities that heavily load the knee should only be resumed very gradually and cautiously. To reach pre-injury activity level, the patient must build greater strength and flexibility in the muscles around the knee than existed before the injury. By maintaining a high level of fitness, the patient will reduce the likelihood of re-injury.

Operative Recovery

Recovery after surgery for patellofemoral pain syndrome can take even longer than recovery from non-operative treatment. The patient should expect:

  • Crutch use, usually necessary for one to three weeks after surgery
  • Two to three months of healing and rehabilitation
  • A gradual return to desired activities that usually take between three and six months.

Q: Why does my knee hurt when I exercise?
A: A knee with patellofemoral pain syndrome hurts during exercise because of the increased fluid in the joint or swelling in the tissues. This interferes with the motion of the knee and can cause increased friction in the joint as the knee moves.

Q: How long will it take for my knee to heal?
A; A typical non-operative program can take six weeks or more. It is a good idea to give the knee at least as much time for the symptoms to begin to improve as it has experienced discomfort.

Q: What are my chances of avoiding surgery?
A: A very high percentage (about 95%) of patients with patellofemoral pain syndrome will respond successfully to a conservative, non-operative treatment program such as the one outlined here.

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