Patellofemoral pain syndrome, also known as anterior knee pain syndrome, is a broad term used to describe pain in the front of the knee and around the patella (kneecap). It is sometimes called "runner's knee" or "jumper's knee" because it is common in people who participate in sports—particularly females and young adults—but patellofemoral pain syndrome can occur in nonathletes, as well. The pain and stiffness it causes can make it difficult to climb stairs, kneel down, and perform other everyday activities
Multiple factors may contribute to the development of patellofemoral pain syndrome, including problems with the alignment of the kneecap and overuse from vigorous athletics or training.
Symptoms are often relieved with conservative treatment, such as changes in activity levels or a therapeutic exercise program.
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(Left) The patella normally rests in a small groove at the end of the femur called the trochlear groove. (Right) As you bend and straighten your knee, the patella slides up and down within the groove.
Patellofemoral pain syndrome occurs when nerves sense pain in the soft tissues and bone around the kneecap. These soft tissues include the tendons, the fat pad beneath the patella, and the synovial tissue that lines the knee joint.
In some cases of patellofemoral pain, a condition called chondromalacia patella is present. Chondromalacia patella is the softening and breakdown of the articular (joint surface) cartilage on the underside of the kneecap. There are no nerves in articular cartilage—so damage to the cartilage itself cannot directly cause pain. It can, however, lead to inflammation of the synovium and pain in the underlying bone.
Cause
Overuse
In many cases, patellofemoral pain syndrome is caused by vigorous physical activities that put repeated stress on the knee —such as jogging, squatting, and climbing stairs. It can also be caused by a sudden change in physical activity. This change can be in the frequency of activity—such as increasing the number of days you exercise each week. It can also be in the duration or intensity of activity—such as running longer distances. Other factors that may contribute to patellofemoral pain include:
- Use of improper sports training techniques or equipment
- Changes in footwear or playing surface
Patellofemoral Malalignment
Patellofemoral pain syndrome can also be caused by abnormal tracking of the kneecap in the trochlear groove of the femur. In this condition, the patella moves out to one side of the groove when the knee is bent, most commonly to the lateral (outer) aspect of the knee. This abnormality may cause increased pressure between the back of the patella and the trochlea, irritating soft tissues and overloading the joint surface cartilage, which may lead to premature arthritis.
Factors that contribute to poor tracking of the kneecap include:
- Problems with the alignment of the legs between the hips and the ankles. Problems in alignment may result in a kneecap that shifts too far toward the outside (or more rarely inside) of the leg, or one that rides too high in the trochlear groove (a condition called patella alta).
- Muscular imbalances or weaknesses, especially in the quadriceps muscles at the front of the thigh. When the knee bends and straightens, the quadriceps muscles and quadriceps tendon help to keep the kneecap within the trochlear groove. Weak or imbalanced quadriceps can cause poor tracking of the kneecap within the groove, particularly with weakness of the inner quads muscle (vastus medialis).
- Patients with flexible joints or ligamentous laxity syndromes are more likely to develop patellofemoral maltracking.
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(Top) In these x-rays taken from above, both kneecaps are normally aligned within the trochlear groove. (Bottom) Both kneecaps have shifted laterally out of the trochlear groove and are pulled toward the outside of the knee.
Symptoms
The most common symptom of patellofemoral pain syndrome is a dull, aching pain in the front of the knee. This pain usually begins gradually and is frequently activity-related, and may be present in one or both knees. Other common symptoms include:
- Pain during exercise and activities that repeatedly bend the knee, such as climbing stairs, running, jumping, or squatting.
- Pain after sitting for a long period of time with your knees bent, such as one does in a movie theatre or when riding on an airplane.
- Pain related to a change in activity level or intensity, playing surface, or equipment.
- Popping or crackling sounds in your knee when climbing stairs or when standing up after prolonged sitting.
Diagnosis
A thorough history and physical examination will be performed. As well as looking for signs of ligamentous laxity, specific areas noted in the knee/leg examination will include:
- Alignment of the lower leg and the position of the patella
- Knee stability, hip rotation, and range of motion of knees, hips and ankles/feet
- The kneecap for signs of tenderness
- The attachment of thigh muscles to the kneecap
- Strength, flexibility, firmness, and tone of the hips, front thigh muscles (quadriceps), and back thigh muscles (hamstrings)
- Tightness of the heel cord and flexibility of the feet.
Imaging studies are often required, starting with plain X-Rays of the knee, including a skyline (patellar) view. CT scans may be needed to show dynamic maltracking/malalignment of the patella, as well as quantifying any rotational profile abnormality. MRI scans are needed if there is concern about joint surface damage or associated knee injury.
Treatment
Medical treatment for patellofemoral pain syndrome is designed to relieve pain and restore range of motion and strength. In most cases, patellofemoral pain can be treated nonsurgically.
Nonsurgical Treatment
In addition to activity modification, the RICE method (Rest, Ice, Compression, and Elevation), and anti-inflammatory medication, the following may be tried:
- Physical therapy exercises - Specific exercises will help you improve range of motion, strength, and endurance. It is especially important to focus on strengthening the inner quad muscle (vastus medialis) and stretching your quadriceps since these muscles are the main stabilizers of your kneecap. Core exercises may also be recommended to strengthen the muscles in your abdomen and lower back.
- Orthotics - Shoe inserts may help align and stabilize your foot and ankle, taking stress off of your lower leg. Orthotics can either be custom-made for your foot or purchased "off the shelf."
Surgical Treatment
Surgical treatment for patellofemoral pain is undertaken for cases that do not respond to nonsurgical treatment. Surgical treatments may include:
- Arthroscopy - During arthroscopy, a small camera, called an arthroscope, is inserted into your knee joint. The camera displays pictures on a television screen, and these images are used to guide miniature surgical instruments.
- Debridement - In some cases, removing damaged unstable articular cartilage from the surface of the patella, or the lateral trochlea or femoral condyle, can provide pain relief.
- Lateral release - If the lateral retinaculum ligament is tight or contracted enough to pull the patella out of the trochlear groove, a lateral release procedure can loosen the tissue and allow correction of the patellar malalignment.
- Medial Patellofemoral Ligament Repair – Often done in combination with a lateral release, the medial patellofemoral ligament is repaired usually by “double-breasting” to advance the line of pull of the medial quads, to maintain the patella in the trochlear groove.
- Tibial Tubercle Osteotomy/Transfer - In some cases, it may be necessary to realign the kneecap by moving the patellar ligament along with a portion of the tibial tubercle—the bony prominence on the tibia (shinbone). A traditional open surgical incision is required for this procedure. The tibial tubercle is partially detached and mobilised so that the bone and the tendon can be moved toward the inner side of the knee, often combined with some anterior displacement. The piece of bone is then reattached to the tibia using screws (or wires). In most cases, this transfer allows for better tracking of the kneecap in the trochlear groove.
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