Pediatric Annals

Patellofemoral Malalignment

Barry Goldberg, MD

Abstract

Anterior knee pain represents one of the most common musculoskeletal complaints of adolescents. Although other disorders such as tumors, meniscal lesions, tendinitis, hip disorders, infrapatellar tendonitis, and osteochondritis dissecans enter the differential diagnosis and are discussed in another article, patellofemoral maialignment overwhelmingly remains the most common disorder. After reviewing my comments from an article written 5 years ago for Pediatrie Annals,1 it appears that we may have a better understanding of pathophysiology and diagnosis, but we are still battling with therapeutic intervention. Patellofemoral maialignment can amount to 10% of patient visits to a sports medicine facility.2 As such, anterior knee pain represents a disorder in which there has been a broad clinical experience and yet it represents a most difficult and frustrating entity for the athlete to endure and for the physician to treat. This same sentence was included in the article written 5 years ago.

PATHOPHYSIOLOGY

The patella has a significant role by enhancing the quadriceps mechanism, reducing the direct forces placed on the femoral condyles, and protecting the knee joint and the patella tendon. Forces across the patellofemoral joint may represent the highest forces per unit area in the body, with reaction forces reaching 3.3 times body weight on ascending or descending stairs.3 The articular cartilage of the patella is thick and adapted to such forces, but it can be appreciated that if compressive or sheer forces increase as a result of abnormal tracking, pathology of the patella and the surrounding tissues will occur. Additionally, nutritional support for the cartilage is derived from the articular fluid, which is driven to the chondroblasts from the altering pressures of patella movement. Abnormalities of movement can affect this nutrient function.

The patella sits above the trochlea at full extension but comes in contact when the knee is flexed to 20°, and in the progression to 90°, it comes in contact with the condyle facets. Many structures dictate the motion of the patella; these include the quadriceps muscle, the vastus medialis oblique muscle, the vastus lateralis, the iliotibial band, the patellofemoral ligament, the patellotibial ligament, and the medial and lateral retinaculum. The shape of the femoral condyles, the structure of the patella facets, the vertical position of the patella, a valgus or varus position of the leg, congenital synovial plica, hamstring tightness, and structural abnormalities of the foot also are involved in patella movement. Optimal patella tracking places an even distribution of contact forces on the patella, and on the surrounding tissues. A deficiency in the above musculotendinous structures can cause abnormal fitting and tracking of the patella resulting in inflammation of the peripatellar structures and eventually changes in the articular cartilage. It is therefore important to recognize that all patellofemoral pain does not arise from articular cartilage changes (chondromalacia), but rather, for example, from patella subchondral bone, the retinaculum, the synovium, or the capsule.4'6 Malalignment and abnormal patella tracking can be marginal or result in varying degrees of subluxation or complete dislocation. Significant subluxation and dislocation can lead to significant pathology and the eventual development of osteoarthritis, although the actual incidence of arthritis resulting from patella subluxation and tilt remains to be determined.

HISTORY OF COMPLAINTS

The patient with anterior knee pain is typically a young male or female with the insidious development of vague aching over the peripatellar region or even posteriorly over the popliteal fossa.7'10 Occasionally, a history of an acute fall on the patella may be given or the patient may relate that the pain began after his or her foot planted with the femur in internal rotation and the tibia fixed in external rotation. Symptoms are often…

Anterior knee pain represents one of the most common musculoskeletal complaints of adolescents. Although other disorders such as tumors, meniscal lesions, tendinitis, hip disorders, infrapatellar tendonitis, and osteochondritis dissecans enter the differential diagnosis and are discussed in another article, patellofemoral maialignment overwhelmingly remains the most common disorder. After reviewing my comments from an article written 5 years ago for Pediatrie Annals,1 it appears that we may have a better understanding of pathophysiology and diagnosis, but we are still battling with therapeutic intervention. Patellofemoral maialignment can amount to 10% of patient visits to a sports medicine facility.2 As such, anterior knee pain represents a disorder in which there has been a broad clinical experience and yet it represents a most difficult and frustrating entity for the athlete to endure and for the physician to treat. This same sentence was included in the article written 5 years ago.

PATHOPHYSIOLOGY

The patella has a significant role by enhancing the quadriceps mechanism, reducing the direct forces placed on the femoral condyles, and protecting the knee joint and the patella tendon. Forces across the patellofemoral joint may represent the highest forces per unit area in the body, with reaction forces reaching 3.3 times body weight on ascending or descending stairs.3 The articular cartilage of the patella is thick and adapted to such forces, but it can be appreciated that if compressive or sheer forces increase as a result of abnormal tracking, pathology of the patella and the surrounding tissues will occur. Additionally, nutritional support for the cartilage is derived from the articular fluid, which is driven to the chondroblasts from the altering pressures of patella movement. Abnormalities of movement can affect this nutrient function.

The patella sits above the trochlea at full extension but comes in contact when the knee is flexed to 20°, and in the progression to 90°, it comes in contact with the condyle facets. Many structures dictate the motion of the patella; these include the quadriceps muscle, the vastus medialis oblique muscle, the vastus lateralis, the iliotibial band, the patellofemoral ligament, the patellotibial ligament, and the medial and lateral retinaculum. The shape of the femoral condyles, the structure of the patella facets, the vertical position of the patella, a valgus or varus position of the leg, congenital synovial plica, hamstring tightness, and structural abnormalities of the foot also are involved in patella movement. Optimal patella tracking places an even distribution of contact forces on the patella, and on the surrounding tissues. A deficiency in the above musculotendinous structures can cause abnormal fitting and tracking of the patella resulting in inflammation of the peripatellar structures and eventually changes in the articular cartilage. It is therefore important to recognize that all patellofemoral pain does not arise from articular cartilage changes (chondromalacia), but rather, for example, from patella subchondral bone, the retinaculum, the synovium, or the capsule.4'6 Malalignment and abnormal patella tracking can be marginal or result in varying degrees of subluxation or complete dislocation. Significant subluxation and dislocation can lead to significant pathology and the eventual development of osteoarthritis, although the actual incidence of arthritis resulting from patella subluxation and tilt remains to be determined.

HISTORY OF COMPLAINTS

The patient with anterior knee pain is typically a young male or female with the insidious development of vague aching over the peripatellar region or even posteriorly over the popliteal fossa.7'10 Occasionally, a history of an acute fall on the patella may be given or the patient may relate that the pain began after his or her foot planted with the femur in internal rotation and the tibia fixed in external rotation. Symptoms are often bilateral, and a family history of similar problems may be given. A recent growth spurt may have occurred, or a new demanding sport may have been started. When the aching pain occurs during activity, a tracking abnormality or significant subluxation may be occurring, whereas pain after activity usually represents inflammation of the peripatellar structures. The patient may complain of a popping or snapping sensation, a slipping out of the patella, or a catching of the patella. This may reflect abnormal tracking or a synovial plica band. Effusions may intermittently occur but they are generally small and resolve rapidly.

Specific activities also will elicit symptoms. Pain on going down and up stairs often occurs as does pain after prolonged sitting in one position, such as at a movie or after a long drive in a car. Sports that place the knee chronically between 30° and 90°, such as a catcher in baseball or a runner training in a hilly area also exacerbates pain.

When the patella tracking exhibits significant subluxation or even dislocation, complaints of "giving away" or actually falling frequently are given. A sense of locking of the knee also may occur although this usually represents subluxation and can be overcome. True locking is rare except when a true disio' cation occurs.

PHYSICAL EXAMINATION

The examination of the patient with anterior knee pain requires both a careful assessment of the patella and a complete examination of the extremity to assess characteristics that may predispose to abnormal patella tracking.3,011

The initial component of the examination involves observation of the patella. The entire extremity leg alignment should be assessed in multiple positions to look for tibial torsion, femoral anteversion, varus or valgus of the leg, pronation, the position of the patella (internal rotation, squinting or external rotation, or "frogs eyes placement") and the Q angle. The Q angle is created by a line drawn from the anterosuperior iliac spine to the middle of the patella and a line from the middle of the patella to the tibial tubercle with the knee in full extension. For men, the average Q angle is 14° and for women, it is 17°. Q angles >20° often reflect underlying maltracking.12 The A angle, or the relationship between the patella to the tibial tubercle, also increases the suspicion of patellofemoral maltracking. Symptomatic patients have A angles at a mean of 23.2° while controls are at 12.2°. l3

Palpation of the knee initially permits the determination of sources of tenderness. The peripatellar tissues and the patellar facets should be palpated. A synovial plica, particularly on the medial side, may be present and felt as a tender band. The quadriceps muscle must be evaluated carefully with a manual muscle test, looking for hypertrophy of the vastus lateralis and weakness or atrophy of the vastus medialis obliquus. A high insertion of the vastus medialis obliquas implies less stabilization than a lower insertion. Retinacular laxity is also important to evaluate. A tight lateral retinaculum with a loose medial retinaculum is a common sign indicating the direction of the movement of the patella.

Various maneuvers can help ascertain the diagnosis. If the patient kneels and the back moves posteriorly to the heels, this implies quadriceps atrophy and patellar discomfort. When sitting with the knees and hips forward at 90°, a superior and lateral position of the patella can be detected with the patella pointing upward; this is associated with patella malalignment. High-riding patellas14 and lateral patella tilt frequently are found in symptomatic patients.15 With the patient supine and the knee extended, ballottment may reveal effusion and synovial thickening.16 Compression of the patella to assess for pain and crepitus may be a sign of advanced cartilage degeneration. Finally, patella subluxation can be evaluated by placing the patient in 30° of knee flexion. A medial directed force to sublux the patella can create an apprehension sign. The laxity of the patella in the medial and lateral direction also should be determined in extension.17 A high-riding patella in conjunction with a palpable enlarged fat pad is another finding in patellofemoral malalignment.

Patella motion can be affected by muscle tightness, particularly the hamstrings and the iliotibial band. Therefore groin, quadriceps, hamstring, and iliotibial band flexibility should be assessed. Strength loss also can be found proximal to the knee and a manual muscle test should be performed on the knee, and hip musculature.

DIAGNOSTIC TESTS

Tests to assist in the diagnosis of anterior knee pain include standard anteroposterior, lateral, and intrapatella roentgenographs at 30° and 90° flexion. When indicated in more complicated situations, stress films, magnetic resonance imaging, computerized tomography (CT), isotope scanning, double contract arthrography, and arthroscopy may need to be performed.18'20

The anteroposterior projection permits the appraisal of the patella's positioning over the femoral sulcus and allows for the assessment of other diagnostic entities such as bipartite patella, tumor, and stress fracture. The lateral radiograph performed at 30° of knee flexion permits the comparison of the position of the two patellas. Contact abnormalities can be identified with a 90° flexion view.

The relationship of the patella with its surrounding structures can be evaluated by other radiographie studies. Minkoff and Fein20 point out that diagnostic studies may assist in the evaluation of patella subluxation and structural abnormalities, but are much less effective in assisting in the choice of potential success of various therapeutic interventions. Recently, Inoue et al21 demonstrated that an increase of lateral tilt on CT scan when the knee is moved from 30° to full extension is more accurate of subluxation than plain radiographs. Electron microscopic studies of the patella cartilage have revealed a stage 1 lesion that reflects an intact surface cartilage that is swollen and dull and a stage 2 lesion that reveals surface fissures. As stage 2 lesions seem to have a limited repair response, they reinforce the need for aggressive intervention.22 Magnetic resonance imaging of patellar cartilage was able to define six stages with only the last three stages detectable by conventional radiograph.23

TREATMENT

The treatment of patellofemoral dysfunction requires patience, an attention to detail, and the capacity to motivate the athlete to faithfully adhere to the prescribed program. The slow progress of improvement is often frustrating, but more than 90% of patients can be spared a surgical procedure by using conservative therapy,24 at least for 6 to 8 months, unless extremes of diagnostic or symptomatic findings exist. Whether as the result of prescribed therapy, remolding of the patella dynamics with growth, or a change in activity, 67% of patients will have no limitations, and 25% will have minimal limitations by 6 months to 2 years.25

The goal of conservative therapy is to control symptoms and improve patellofemoral tracking. Cryotherapy, nonsteriodal anti-inflammatory drugs, and modified activity most often will control pain, although rarely stronger analgesics and a brief period of time in a knee immobilizer may be required. Activity that does not provoke pain can be continued in a modified fashion to maintain aerobic capacity and the psychological state of an athlete.

Therapeutic exercises should be initiated as symptoms are resolving. Quadriceps isometric contractions should be started and may represent the most effective means for strengthening.26 Ten repetitions of a 4second contraction performed over 1 minute and done 3 to 5 times a day to reach a goal total of 50 represents an effective beginning to exercise. If this cannot be tolerated, electrical stimulation to create a quadriceps contraction can be tried prior to the institution of isometric sets. The next set of exercises to be introduced should be straight leg raising in hip extension, abduction, adduction, and flexion with a weight raised 1 2 inches and held in the raised position for 3 seconds. The contralateral knee should be flexed for support.27,28 The quadriceps should be contracted isometrically before the leg is raised. These exercises can be done up to 3 times per day but a daily or alternateday program may receive better compliance. Three sets of 10 exercises are done with weight progressed by 2.5 to 5 Ib until a maximum of approximately 30 Ib or one-third body weight is reached. When weights 5*10 pounds are reached, further exercises can be introduced, and one should expect a measure of symptomatic improvement.

More aggressive exercises begin with short arc, which allows knee extension and flexion only to a maximum of 150° of extension. Support should be placed under the knee to allow it to be raised approximately 12 inches off the table. Continued exercise is designed to enhance neurological motor unit recruitment and activation, and cellular hypertrophy.29 Specificity is added to attain static and dynamic stability, strength, and speed of movement. Apparatus such as the Multi-Hip (Cybex, Ronkonkoma, New York) and the leg press30·31 can be used to further enhance strength and isolate muscle groups.

Isokinetics is another mechanism for strengthening both concentric and eccentric contraction. Bishop et al32 demonstrated that eccentric training at 60%econd and 120°/second developed concentric hamstring strength but not quadriceps strength, and general improvement from isokinetic eccentric training was shown by Bennett and Stauber.33 Closed chain rehabilitative techniques that can be used include hiking with the seat in a high position, hopping, skipping rope, jumping on a mini-trampoline, carioca, performing mini-squats and bent leg walking. When these tasks are completed, a return to jogging and running can be started with an eventual return to the sport.

Strength training is an important part of rehabilitation, but stretching, particularly of the quadriceps, iliotibial band, patellar retinaculum, and hamstring, are also important.34,35 It is essential to motivate the patient to continue to perform strength and flexibility training when asymptomatic as a preventive measure. Other adjuncts to therapy include patellar restraining sleeves, orthotic devices for patients with excessive pronation, and bracing and taping to control tracking at the patellofemoral joint.36,37 Patella taping also has been used with effective results both for sports participation and the reduction of discomfort during rehabilitation.38

For the majority of patients with anterior knee pain that results from patellofemoral dysfunction, the conservative management of improved strength and flexibility with adjunctive support from orthotics, braces, and taping can relieve symptoms.39 For the few with an unsuccessful result, surgical intervention is required. These procedures include lateral retinaculum release, proximal and distal realignment, chondrectomy, excision of an osteochondral ridge, patelloplasty, tibial tubercle plasty, and patellectomy. The limits of this article preclude a discussion of these procedures but much is yet to be done to improve results and the selection of the appropriate surgical approach for a given problem. With ongoing research, the patient with patellofemoral disease should be afforded a surgical intervention with a high degree of long-term success.

SUMMARY

Anterior knee pain represents one of the most common musculoskeletal complaints of adolescents. It is a disorder in which there is broad clinical experience and yet it represents a difficult and frustrating entity for the athlete to endure and for the physician to treat. An appropriate clinical examination and selected diagnostic studies can define the diagnosis and the introduction of conservative therapy usually will correct the problem. Occasionally, surgical intervention is required, and debate remains as to the optimal techniques that should be used.

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10.3928/0090-4481-19970101-07

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