Patellofemoral syndrome: How to perform a basic knee evaluation

Little attention was paid to the patellofemoral joint until the mid 1950s.9 Today, anterior knee pain is one of the most common reasons for seeking medical attention, especially among athletes.1,3,9 Patellofemoral pain was overlooked during the embryonic stage of orthopedic surgery because of the prevalence of more life- and limb-threatening conditions such as open fractures, osteomyelitis, pyogenic arthritis, tuberculosis, polio, and birth defects.9 Little emphasis was placed on playing sports during World Wars I and II and the Great Depression. During the World Wars, the focus was kept on trauma care and infection prevention.9 The advent of antibiotics in the 1940s and the introduction of the polio vaccine in the 1950s changed the scope of orthopedic surgery. Bone infections and the need for corrective surgery in patients with polio were greatly reduced. The prosperity of the 1950s and 1960s led to increased participation in recreational, scholastic, and professional sports.9

The biomechanics of the patellofemoral joint was not wellunderstood, and clinicians were ill prepared to manage PFS complaints. Many normal menisci were removed because of “giving way” or because of internal derangement symptoms that are now known to be caused by patellofemoral dysfunction. Frequently, patellectomy was the answer to perplexing and unsolved clinical problems. The subspecialty of sports medicine emerged in the mid 1970s, along with the development of accurate radiographic techniques and arthroscopy.9

ANATOMY AND BIOMECHANICS OF THE KNEE JOINT

An understanding of the anatomy and biomechanics of the knee is fundamental to understanding PFS (see Figure 1). The extensor mechanism of the knee includes the quadriceps femoris, quadriceps tendon, patella, and patella tendon.3-10,12-14 The hamstring muscles serve as antagonistic muscles to the quadriceps and provide dynamic control for flexion and extension of the knee.3 The medial quadricep, or vastus medialis obliquus (VMO), is the only medial stabilizer for extension and patellar alignment.3,12,13 The medial quadricep is assisted by the medial retinaculum.3 Lateral forces on the patella include the ITB, the lateral retinaculum, and the lateral quadricep.3,12,13 The patella increases the effective extension force by as much as 50%. Medial and lateral stabilizing forces compress the patella against the femur. The greater the tension generated by the quadriceps, the greater the patellofemoral joint reactive force (PFJRF).3 The patella transmits force to the subchondral bone.3 The force at 15° flexion is equal to a person's body weight; at 30°, double the body weight; at 45°, triple the body weight; and at 75°, 6 times the body weight.3 In a typical 200-lb man, the forces on the articular surface of the patella can vary from 600 lb to 3,000 lb per square inch during activities ranging from walking to running.4

The surfaces of the knee contribute to the rotational pattern of the knee throughout flexion and extension.15 The medial femoral condyle is larger than the lateral femoral condyle and projects further posteriorly and distally7,15 (see Figure 1 inset). The medial condyle diverges from the sagittal midline from anterior to posterior.15 The proximal tibia consists of a tibial tubercle and two condylar surfaces. The medial condyle is more concave and longer in the sagittal anteroposterior (AP) plane, while the lateral is flatter.15 The size difference between the medial and lateral tibial condylar surfaces matches the femoral condyles.15 The tibial tubercle is the point of insertion of the patella ligament.15 External rotation of the tubercle leads to an increase in the quadriceps angle and contributes to lateral patellar tracking.15 The femoral sulcus articulates with the patellar facets throughout the range of motion (ROM).15

The degree of flexion determines the contact area, defined as the percentage of the undersurface of the patella that articulates with the trochlear groove. The contact area is designed to respond to increases in PFJRF induced by flexion.12,13 The patella does not remain in contact with the same surface area throughout the ROM, nor does it track in a straight line.16 At 30° flexion, normal tibial internal rotation pulls the patella centralized within the trochlea;15,16 at 60°, the mid patella and mid trochlea are in contact; and at 90°, the proximal portion of the patella and distal portion of the trochlea are in contact.16 The bony architecture and contact areas help define the three-dimensional rotation of the knee.15 The patella begins in full extension on the lateral side of the femoral sulcus, then centralizes on the anterior surface of the femur. If the sulcus angle of the femur is flattened, the patella tracking becomes less controlled and lateral subluxation can occur.15 The position of the hips necessitates a valgus position at the knee.16 The valgus angle created by pull of the quadriceps and the patella tendon is called the Q angle.12,13,16

SIGNS AND SYMPTOMS OF PFS

The typical complaints and symptoms of PFS are anterior knee pain, catching or giving way, or a slipping sensation. Patellofemoral pain is usually a consequence of chronic, repetitive overload to the musculoskeletal structures.3,9 Pain can be located at either the bone or soft tissue.3 The onset of pain is usually insidious except when a direct precipitating trauma has occurred.3,4,8,9 Patients with PFS have pain when the patellofemoral load is increased via knee flexion.3,8,9,13 The patient experiences difficulty arising from a squatting position, after sitting for a prolonged period with the knee flexed at 90° (known as a positive theatre sign), going up and down stairs or hills, and jumping.3-5,7-9,13 Often, patients first complain of pain when descending rather than ascending stairs.3 The knee is flexed approximately 118° when descending, but only 87° when ascending stairs.3 Catching or giving way are common complaints of patients with PFS.4,8,9,12,13 Catching occurs when inflamed tissue is caught on the bony prominences, the patellar surface is rough, or the plica is inflamed.8 Giving way is the sudden reflex relaxation of the quadriceps rather than knee instability, 6,12,13 and occurs most frequently when the patient climbs stairs or walks down an incline.12,13 PFS symptoms can range from mild catching sensations caused by the patella slipping laterally to a feeling that the patella has completely left the trochlear groove.8

PHYSICAL EXAMINATION OF THE KNEE

No single test is diagnostic for PFS. A variety of physical examination techniques are used to assess the patient with suspected PFS.1 Examinations should include standing limb alignment and seated and supine ROM evaluations.4,9 Evaluation of the knee joint includes assessment of ROM,

muscle strength, neurovascular status, ligament stability, and soft tissue with the patient in various positions.

Standing examinations Foot pronation, femoral anteversion (internal rotation of the hip), and patella alignment can be assessed by having the patient stand and by observing the patient's gait.4,6,9,12 The patella facing toward the opposite knee when walking is an indication of hip anteversion. The presence of genu valgum can also be seen during a standing and walking examination.

The Q angle can be seen as a line down the femur to the center of the patella and down through the tibial tubercle.16 The term is derived from the shape of the letter Q, where the patella is the circle and the patella tendon is the extension off the circle. The Q angle is measured with the knee in extension—the patient can be supine or standing. An angle more than 15% to 20% is considered abnormal.2,6,9,16-18 Larger Q angles reflect lateral movement of the quadricep contraction and are often found in patients with PFS.19

Seated examinations Dynamic evaluation during active flexion and extension of the knee is performed with the patient seated. The J sign is observed when there is a persistent lateral movement of the patella with flexion of the knee.6 At the end of extension, the patella may sublux laterally out of the femoral sulcus; as the knee resumes flexion, the patella jumps back into place.15 The patella tracking follows the pattern of an inverted J.9

The lateral pull sign demonstrates VMO insufficiency.6 With the knee extended and the quadriceps contracted, the patella should be pulled superiorly in a straight line. An abnormal result is when the patella is pulled excessively in a lateral direction.6,15

The presence of crepitus can aid in localizing segmental chondral lesions. The knee is flexed and extended while under a load by palpation with manual resistance applied at the ankle. The presence of pain at certain degrees of flexion indicates where the lesion has occurred.3,6,9,15

The patellar glide test is performed with the patient in a seated position and the knee relaxed and flexed at 30°.6,9 Moving the patella laterally and medially demonstrates the retinacular contracture or laxity. Excessive lateral movement indicates medial laxity and possible rupture of the medial patellofemoral ligament. Restricted medial movement indicates a tight lateral retinaculum. Increased medial glide is a normal finding in hyperlax persons and after a lateral surgical release.9

Supine examinations The patellofemoral grind test, also referred to as the patellar inhibition test, is performed with the patient in the supine position. The patient contracts the quadriceps while the examiner gently compresses the patella into the femoral sulcus.12,13,15 Pain indicates a positive result.15 Pain with crepitus and recurrent effusion suggest degenerative changes; pain alone suggests articular injury.15

Tightness of the lateral retinaculum may be assessed with the patellar tilt test.15,16 With the patient in the supine position, knee extended and quadriceps relaxed, the examiner attempts to elevate the lateral edge of the patella.6,15 A negative tilt is present when the patella is below the horizontal line made by the anterior femur and tibia and indicates a tight lateral retinaculum.6,15

RADIOGRAPHIC EVALUATION

Imaging studies can be helpful in diagnosing PFS and ruling out other disorders.8 The standard AP view with the patient in extension and weight-bearing positions is used to evaluate soft tissue abnormalities, fractures, joint space narrowing, osteochondritis dissecans (OCD), loose bodies, and overall alignment. Posteroanterior view at 45° is used to evaluate early joint space narrowing and OCD.6 This view is more specific for assessing articular cartilage loss in the posterior compartment of the knee.9

The lateral view with the knee flexed at 30º and the patella fully engaged in the trochlea is the best view for assessing patella height relative to the joint line.2,6-9,16,18 In Blumensaat's line, the lower border of the patella should lie on a line extended through the roof of the intercondylar notch with the knee flexed at 30°.6,7,18 If the patella is located above the line, the diagnosis is patella alta; if the patella is below the line, the diagnosis is patella baja.1

The infrapatellar or axial view discloses lateral tilting and subluxation of the patella.8 Projections used for this evaluation include Settegast's, Jaroschy (also known as Hughston's), Laurin's, Ficat, and Merchant's.6,9,12,13 In the clinical evaluation of the patient, Merchant's view is the most helpful.8,12,13 This projection is taken with the knee flexed at 45° and the beam projected caudal at an angle of 30°.6 One line is drawn connecting the most anterior portions of the femoral condyles, and another line is drawn along the slope of the lateral patellar facet.18 A neutral angle or medial opening is considered abnormal.18 However, static radiographs of a patient with severe patellofemoral disability may appear normal because of the dynamic nature of the disease.8

CT offers sequential images at different degrees of knee flexion, using the midtransverse patella as a stable plane of reference.13 CT accurately defines the relationship between the patella and its contact area on the femur.12,13 CT of both knees, bilaterally and at 10° flexion, is useful in comparing lateral patella tilt.1 Serial CT scans at 0º, 15°, 30°, and 45° flexion are used to detect patella subluxation6,12,13 (see Figure 2). MRI is not that helpful in assessing patellar alignment;12 however, MRI is able to show intra-articular pathways for specific lesions6,7,18 and has been used for preoperative location of cartilage damage, meniscus or ligament tears, or suspected tumors.6,7,9,12,18

DIFFERENTIAL DIAGNOSIS

In patients with PFS, pain may be associated with referred pain from the ankle, the hips, and the lower part of the back; OCD of the femur or patella; Osgood-Schlatter disease; bone tumors, especially with unilateral symptoms; osteoarthritis; meniscus disorders; synovial plica; patellar malalignment; patellar tendinitis; quadriceps tendinitis; prepatellar bursitis; fat pad syndrome; chronic effusion; ITB friction syndrome; saphenous neuralgia and varices; cruciate ligament insufficiency; and reflex sympathetic dystrophy.3,4,6,8,12,13 Bony tumors, including quadriceps hemangiomas, synovial chondromatosis, osteoid osteomas, and osteochondromas, can manifest as anterior knee pain. An accurate diagnosis will help in determining which treatment should be prescribed. Patients with patellofemoral pain should respond to adequately prescribed treatment measures.3 If the patient does not improve, the diagnosis of PFS should be reconsidered and other potential problems be addressed.

INITIAL TREATMENT OF PFS

Most patellofemoral symptoms are due to chronic repetitive overload that causes damage to the patella tendon and lateral retinaculum with degeneration and scar formation.3 However, the condition usually has an acute, painful presentation.3 Symptomatic treatment begins with the judicious use of NSAIDs and pain medication.3,4,6-8,13,16-18,20 Initial treatment is physical therapy.8 Intra-articular corticosteroid injection, administered under local anesthetic, may be necessary.9,13 Physical therapy includes relative rest and conditioning of the kinetic chain.3,18 Relative rest is used to avoid abusive or stressful activities to the knee such as deep knee bends, squatting, and stair climbing.3,16,17 Conditioning of the kinetic chain includes exercises using the uninvolved leg and arms such as stationary bicycle, arm ergometers, swimming, and hip strengthening.3-5,13,20 Home exercises consist of straight leg raises.12

Patella taping can be used to correct patellar glide, tilt, and rotation.3 Taping concepts introduced by Jennie McConnell revolutionized rehabilitation.3,9,13 The McConnell protocol is designed to reduce the abnormal forces on the extensor mechanism.9 Proper taping allows the patient to exercise and strengthen the muscles without pain, which is helpful during the rehabilitation process.13,21,22

INTRA-ARTICULAR JOINT FLUID REPLACEMENT THERAPY

Patients who cannot obtain adequate relief from NSAIDs and physical therapy may be candidates for intra-articular hyaluronic acid (HA) injections. HA is a glucosaminoglycan extracted from chicken combs and found in connective tissue such as synovial fluid, cartilage, skin, vessel walls, the umbilical cord, and the vitreous body of the eye. HA forms a viscous synovial fluid that lubricates joints, absorbs mechanical shock, and protects the surface of the articular cartilage. In 1942, Balazs observed the physiochemical characteristics and suggested the use of HA as a therapeutic tool.23,24 In 1970, he obtained excellent results in treating traumatic arthritis and osteoarthritis in race horses. Use of hyaluronan in humans was investigated by researchers from several countries from the late 1960s to early 1970s.23,24 Currently HA is used in the United States, Japan, Korea, Sweden, Finland, Iceland, Austria, Italy, China, Portugal, Denmark, and Spain.

HA is administered as a series of 3 to 5 intra-articular injections given one week apart. Because HA is a major component of synovial fluid, it is considered a safe and useful therapeutic agent. The series of injections can be repeated annually. HA is classified as a medical device by the FDA. Currently, HA is used primarily to treat osteoarthritis; however, HA can be used to treat PFS if there is evidence of osteoarthritis.

SUMMARY

PFS is one of the most common orthopedic problems. As long as overloading and malalignment of the knee is occurring, the patient will continue to experience pain. A proper understanding of anatomy and biomechanics of the knee is critical for an accurate diagnosis and treatment plan. As with most medical problems, a detailed history and physical examination help determine the proper treatment. Radiographs and CT can aid in diagnosis and treatment. NSAIDs, physical therapy, and HA therapy can prevent the need for surgical intervention in 80% to 90% of patients. JAAPA

Judi Price works in the Department of Orthopaedics, Kaiser Permanente, Sacramento, California. She has indicated no relationships to disclose relating to the content of this article.

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