Pediatric Annals

Chronic Anterior Knee Pain in the Adolescent

Barry Goldberg, MD

Abstract

Pain in the anterior region of the knee is one of the most common complaints that brings young athletes to the attention of a pediatrician. Variously called chondromalacia patella, anterior knee pain, patellofemoral dysfunction, patellalgia, and patellar compression syndrome, this overuse syndrome is common to all sporting activities. Garrick found that of 16 748 patients presenting with problems from a variety of sports, 11.3% were diagnosed with anterior knee pain.1 Thus, 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.

PATHOPHYSIOLOGY

Abnormal patellar tracking appears to he the underlying cause of anterior knee pain. The patella enhances the quadriceps mechanism, stabilizes and protects the patellar tendon, and minimizes the direct forces placed on the femoral condyles. The articular cartilage of the patella is designed for its load-bearing function with horizontal fibrils on the surface, interwoven fibrils in the center, and vertical fibrils in the deep layer at the interface with bone. Nutritional support is derived from the articular fluid, which is driven to the chondroblasts by alternating pressures that occur with patella movement.2 Destruction of the articular cartilage can arise from a lack of alternating pressures3 or possibly from the opposite effect, excessive pressure.4

The contact of the patella with the trochlear facets varies with the degree of knee flexion. At full extension, the patella sits above the trochlea. The patella begins to move downward in an S shaded direction making first contact with the trochlea at 20° of flexion, and after 90° it contacts the condylar facets. The movement of the patella is controlled by the quadriceps muscle in the superior- inferior plane, the vastus medialis oblique muscle medially, and the vastus lateralis muscle and a section of the iliotibial band laterally.2 The patella is also restrained in its movement by the patellofemoral ligament, the patellotibial ligament, and the retinaculum. The mode of tracking is additionally affected by the shape of the femoral condyles, the configuration of the patella facets, a highly positioned patella, extreme valgus, and an increased 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°. 5 Optimal patellofemoral contact allows for an even distribution of stress forces and for patellar stability. Abnormalities of the muscle units, the ligamentous stabilizers, or the osseous structures may shift the delicate balance of patellofemoral movement and result in the distribution of abnormal uneven and excessive forces. Excessive forces also may result from knee instability, congenital synovia! plica, hamstring tightness, and structural abnormalities of the foot.

The end result of excessive patellofemoral forces is inflammation and potentially actual destruction (chondromalacia) of the articular cartilage of the patella. As the articular cartilage does not have nerve endings, the source of pain remains unclear. Suggestions for the source of pain include the subchondral bone of the patella, the synovium, the capsule, and venous engorgement.2'4'6'7

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.8'10 In two thirds of the cases, the pain will be bilateral, and a family history of similar symptoms may be reported (Table 1 ). Occasionally, the onset of symptoms may have been abrupt, following direct trauma to the patella…

Pain in the anterior region of the knee is one of the most common complaints that brings young athletes to the attention of a pediatrician. Variously called chondromalacia patella, anterior knee pain, patellofemoral dysfunction, patellalgia, and patellar compression syndrome, this overuse syndrome is common to all sporting activities. Garrick found that of 16 748 patients presenting with problems from a variety of sports, 11.3% were diagnosed with anterior knee pain.1 Thus, 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.

PATHOPHYSIOLOGY

Abnormal patellar tracking appears to he the underlying cause of anterior knee pain. The patella enhances the quadriceps mechanism, stabilizes and protects the patellar tendon, and minimizes the direct forces placed on the femoral condyles. The articular cartilage of the patella is designed for its load-bearing function with horizontal fibrils on the surface, interwoven fibrils in the center, and vertical fibrils in the deep layer at the interface with bone. Nutritional support is derived from the articular fluid, which is driven to the chondroblasts by alternating pressures that occur with patella movement.2 Destruction of the articular cartilage can arise from a lack of alternating pressures3 or possibly from the opposite effect, excessive pressure.4

The contact of the patella with the trochlear facets varies with the degree of knee flexion. At full extension, the patella sits above the trochlea. The patella begins to move downward in an S shaded direction making first contact with the trochlea at 20° of flexion, and after 90° it contacts the condylar facets. The movement of the patella is controlled by the quadriceps muscle in the superior- inferior plane, the vastus medialis oblique muscle medially, and the vastus lateralis muscle and a section of the iliotibial band laterally.2 The patella is also restrained in its movement by the patellofemoral ligament, the patellotibial ligament, and the retinaculum. The mode of tracking is additionally affected by the shape of the femoral condyles, the configuration of the patella facets, a highly positioned patella, extreme valgus, and an increased 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°. 5 Optimal patellofemoral contact allows for an even distribution of stress forces and for patellar stability. Abnormalities of the muscle units, the ligamentous stabilizers, or the osseous structures may shift the delicate balance of patellofemoral movement and result in the distribution of abnormal uneven and excessive forces. Excessive forces also may result from knee instability, congenital synovia! plica, hamstring tightness, and structural abnormalities of the foot.

The end result of excessive patellofemoral forces is inflammation and potentially actual destruction (chondromalacia) of the articular cartilage of the patella. As the articular cartilage does not have nerve endings, the source of pain remains unclear. Suggestions for the source of pain include the subchondral bone of the patella, the synovium, the capsule, and venous engorgement.2'4'6'7

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.8'10 In two thirds of the cases, the pain will be bilateral, and a family history of similar symptoms may be reported (Table 1 ). Occasionally, the onset of symptoms may have been abrupt, following direct trauma to the patella or an episode of subluxation or dislocation. The site of the pain is usually nonspecific, although the area medial to the patella is often specified as most uncomfortable. Symptoms are usually worse after activity, particularly if the activity is descending or ascending stairs, running hills, or doing deep knee bends or squats. Discomfort often will be felt while engaging in these activities as well.

The patient may describe aching and stiffness after sitting with the knees flexed for an extended period of time, and the stiffness may sometimes seem to be locking because of a delay in initiating motion. Significant swelling and true locking rarely occur, but a complaint of mild swelling and a feeling of grating, clicking, or catching is not uncommon. A sense of the knee "giving way" is common, but true dropping usually implies that the patella is subluxing or dislocating. Popliteal discomfort is occasionally reported after symptoms have been present for some time. The patient also may describe a recent unrelated injury to the involved leg.

Table

TABLElHistory Usually Obtained From Patients With Anterior Knee Pain

TABLEl

History Usually Obtained From Patients With Anterior Knee Pain

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. The peripatellar tissues, including the patellar facets, should be palpated to determine if there is local tenderness. A careful examination of the medial peripatellar areas also may permit the detection of a congenital synovial plica, which is best felt as a tender band medially. Compression of the patella with the quadriceps contracted and the knee flexed between 30°, 60°, and 90° may elicit pain. Patellofemoral stability should be evaluated by sliding the patella in an inferior, medial and lateral direction. Draping the patient's leg over the examiner's leg (while both are sitting at a 90° angle to each other) and maintaining the patient's knee at 45° of flexion facilitates the performance of this assessment. This "glide" test has not been standardized, but excessive laxity as compared to the other patella or greater than 50% displacement of the patella past the midline can be considered abnormal. Lateral displacement of the patella may elicit quadriceps contraction and apprehension, indicative of patella subluxation. Patella tracking can be observed by having the patient extend and flex the knee while sitting on the examining table.11

Factors that may predispose to abnormal patellar tracking should also be carefully appraised. Causes of malalignment include femoral anteversion, tibial torsion, and pronation of the foot. The Q angle should be measured and considered abnormal if greater than 20°, and the position of the patella in relation to the long axis of the leg should be evaluated for internal (squinting) or external (frog's eyes) placement. With the patient sitting with the knees flexed at 90°, patella alta positioning can be diagnosed by noting the patella pointing toward the ceiling and patella baja positioning by noting the narrow space between the patella and the tibial plateau. Care also should be taken in evaluating the insertion of the vastus medialis obliquus muscle. A weak vastus medialis obliquus muscle or its high insertion to the patella may predispose to anterior knee pain. Weak hip flexors and tight hamstrings also are associated with patella pathology.

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, isotope scanning, double contrast arthrography, and arthroscopy can be performed.12'15 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 x-ray performed at 30° of knee flexion permits appraisal of patella height by either relating the association of the intercondylar notch with the inferior pole of the patella or relating the length of the patella to the patella ligament. The intrapatella views provide the most valuable information concerning the patellofemoral joint. The 30° flexion view permits the appraisal of the patella facets and demonstrates evidence of subluxation. Contact abnormalities can be identified with a 90° flexion view.

The presence of patella tilt, patella displacement, and condylar height, as well as measurement of the sulcus angle of the patella with its surrounding structures and more complicated angular relationships of the patella with its surrounding structures can be ascertained using other radiographie studies. Newer diagnostic methods to determine patellofemoraÍ relationships are currently being developed and should provide useful diagnostic and therapeutic information in the future.

Minkoff and Fein1 5 point out that diagnostic studies may assist in the distinction between patella subluxation as it is related to sulcus instability and patella malalignment in which patella tracking is improper through all or part of the knee's full range of motion. They state that current radiographie appraisals are effective in documenting a patellofemoral abnormality, but are much less effective in assisting in the choice of, or potential success of, various therapeutic interventions.

DIFFERENTIAL DIAGNOSIS

The child with anterior knee pain will most likely have a patellofemoral problem, it is essential that other diagnostic entities be considered when the problem is first presented to the physician.8·16'17 These potential diagnoses are presented below.

Tumors

Bone tumors can be found in and around the knee and may present with nonspecific findings that can include pain and swelling. The most common benign tumors include osteochondroma and nonossifying fibroma; of the malignant tumors, osteosarcoma occurs most commonly. Routine radiographs usually will detect the presence of the lesion with greater definition provided by more elaborate modalities, such as magnetic resonance imaging.

Meniscal Lesions

A torn meniscus may present with the symptoms of anterior knee pain, locking, clicking, and "giving way." Restrictions in the range of motion, joint line tenderness, a history of injury, and a positive McMurray's test help to distinguish this entity. With this test, the knee should be flexed maximally in both internal rotation ( lateral meniscus ) and external rotation (medial meniscus). Bringing the knee to full extension while maintaining rotation will cause a painful "pop" to occur when a meniscus tear is present. Occasionally, magnetic resonance imaging is required to establish the diagnosis.

Tendinitis

Tendinitis of either the quadriceps tendon or the patella tendon creates anterior knee pain. The distinction of tendinitis from patellofemoral problems can usually be made by palpating local tenderness and swelling over the involved tendon, by a history of participation in jumping sports, and, if chronic, by the occasional appearance of calcification on the radiographs.

Slipped Capital Femoral Epiphysis

Dull vague anterior knee pain with or without a limp can occur with a slipped capital femoral epiphysis. Usually, the involved leg will be held in external rotation, and internal rotation at the hip will be significantly diminished. The involved leg may be slightly shorter than the other and have weak abductors. Radiographie studies of the hip will usually establish the diagnosis.

Legg-Calvé-Perthes Disease

Idiopathic necrosis of the capital femoral epiphysis can present with anterior knee pain and a limp. This entity occurs most commonly in prepubertal boys who are usually short and have delayed skeletal maturation. Examination of the hip may reveal limitations of extension, abduction, and internal rotation. A definitive diagnosis is established radiographically.

InfrapateHar Tendon Bursitís

In the space between the proximal tibia and the patella tendon sits the intrapatellar bursa, which can become inflamed from overuse. Active extension and passive flexion of the knee usually will produce pain as will palpation around the patella tendon. Frequently, the swollen bursa is visible and can be aspirated if essential to establish a diagnosis.

Recurrent Subluxation or Dislocation of the Patella

True recurrent subluxation or dislocation of the patella is found more commonly in the 20- to 30-year-old age group and is associated with more specific symptoms of giving way, slippage, and swelling. Displacement is almost always lateral with a tearing of the medial retinaculum on the initial episode. Patellar tilt or actual subluxation may be seen on radiographs and small bony fragments also may be present. True chondromalacia may be associated with recurrent subluxation or dislocation.

Osteochondritis Dissecane

Osteochondritis dissecane is demonstrated by an area of radiolucent subchondral bone usually adjacent to overlying articular cartilage; the femoral condyles are a common location. Pain is usually nonspecific, of gradual onset, and worsened by activity, although acute symptoms may result if a loose body breaks off Radiographie studies will usually establish the diagnosis of the lesion, which is most commonly found on the lateral aspect of the medial femoral condyle.

Other pathological entities that may be confused with anterior knee pain syndrome include intrapatellar fat pad lesions, rheumatoid arthritis, subacute osteomyelitis, Osgood-Schlatter's disease, bursitis of the pes anserine bursa, pigmented villonodular synovitis, quadriceps contracture, peripatellar soft tissue stress syndrome, bipartite patella, acute fracture of the patella, stress fracture of the proximal tibia or patella, osteochondral and chondral fractures, and suprapatellar plica.

TREATMENT

The treatment of patellofemoral dysfunction requires patience, an attention to detail, and the capacity to motivate the young athlete to faithfully adhere to the prescribed directions (Table 2). The slow progress of improvement is often frustrating, but more than 90% of patients can be spared a surgical procedure by using conservative therapy.18 The improvement may result from the prescribed therapy or a "remodeling" of patella dynamics with growth, but within 6 months to 2 years, 67% of patients will have returned to full activity and another 25% will be able to participate at some restricted level.19

Table

TABLE 2Treatment of Patellofemoral Dysfunction

TABLE 2

Treatment of Patellofemoral Dysfunction

The goal of conservative therapy is to control symptoms and improve patellofemoral tracking. Upon first presentation, the adolescent usually is quite uncomfortable, as this is often the reason for initiating the visit. Nonsteroidal anti-inflammatory drugs and ice therapy will, in most instances, control the pain. Occasionally, stronger analgesics and a knee immobilizer may be needed for a brief period. A careful history of activity should be obtained, and the athlete must be instructed to diminish the overall intensity of activity and to avoid aggravating movements such as running on hills or performing deep knee bends. The degree of "rest" will depend on the intensity of symptoms, but it is always best to allow some activities to continue. Complete rest is poorly tolerated by most athletes.

As symptoms subside, therapeutic exercise can be initiated. The purpose of these exercises is to increase muscular strength, particularly that of the vastus medialis, and to increase flexibility without increasing patella pain. The latter is accomplished by avoiding exercises whose arc extends beyond the last 15° to 30° of knee extension. Exercise can begin with isometric quadriceps exercise sets, holding the extended leg for 8 to 10 seconds with 10 repetitions to be performed five times per hour. Frequently, the patient will need to be instructed to observe the patella pulled backward while palpating the muscle to ensure that an adequate contraction has occurred. The isometric exercises can increase strength and allow the involvement of a greater number of motor units through neuromuscular training. The exercises should be done several times a day.

After the isometric quadriceps exercises can be performed easily, the patient can begin straight leg raising in four quadrants. The first exercise is performed in tbe supine position with the contralateral hip and knee flexed to provide back support. The quadriceps muscle is contracted, the leg is raised slowly 12 inches and then slowly lowered. A weight, usually beginning with 1 to 2 pounds, is placed on the foot to provide a resistance. Three sets of 12 repetítions are performed once or twice each day. Hip abduction and adduction is performed similarly, with the patient on his or her side and the leg lifted 8 to 12 inches. Again, the contralateral knee is flexed for support, and the ipsilateral knee should be maintained in full extension. Hip flexion is performed with the patient sitting on a table. The weight remains on the foot, and the knee is lifted 8 inches off the table. When each of the exercises can be performed easily at a given weight, the weight should be 2 to 5 pounds. Velcro ankle weights are the easiest to use but a belt placed through a disc weight is an alternative. Generally, improvement in knee discomfort will be experienced when weights of 10 pounds and above are lifted. When patients reach weights of 15 to 20 pounds, they can proceed to the next exercise pro20

Further strength training involves more aggressive therapy. The patient should start with short arc exercises, which allows knee extension and flexion but only to a maximum of the last 150° of extension. Pillows or another support should be placed under the knee to allow it to be raised approximately 12 inches off the floor. Weights are again placed on the foot, and the resistance is increased by 2 to 5 pounds based on tolerance. When more than 10 pounds has been achieved and symptoms have not improved, then referral to an orthopedic surgeon or physical therapist is advised. The physical therapist may institute eccentric and isokinetic exercises.21

There are several adjuncts to the treatment of patients with patellofemoral dysfunction. For the patient with structural misalignment due to excessive pronation, an orthotic device can be used to alter tibial rotation. Patients who demonstrate patellar instability or subluxation can use a patella restraining brace to improve tracking and stabilize the patella.22 A stretching program for the quadriceps, hamstrings, calf, and iliotibial tract muscles should always be prescribed as almost all patients will exhibit some degree of tightness in these muscles. These should be sustained, 20 to 30 second stretches performed twice a day. The stretching of the lateral retinaculum combined with forced patella compression to augment cartilage metabolism has been used to reduce excessive lateral pressure.25 Recently, the use of specialized tape to improve tracking and patellar tilt has been used with promising results.24 This technique is particularly useful for the patient who has a level of discomfort that makes strength training difficult to accomplish.

Once the athlete demonstrates improvement, a gradual return to full activity can be permitted. This must be carefully emphasized as a sudden return to full activity can cause an immediate return of symptoms. It is also important to motivate the athlete to remain on a maintenance strength program, at least on alternate days. All too often, when patients have been relieved of symptoms, they will cease therapeutic exercises only to have the symptoms recur.

The natural course of anterior knee pain is that of gradual improvement and quite often complete and permanent recovery. Patience is essential, and at least 6 months should be provided before surgical intervention is considered. Surgical procedures include lateral retinaculum release, chondrectomy, excision of an osteochondral ridge, facetectomy, extensor mechanism realignment patelloplasty, tibial tubercle plasty, and patellectomy.8 Fortunately, only about 10% of patients will require surgical intervention.

REFERENCES

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11. ReiderB, Marshall JL, Ring B. Patellar tracking. CIm On/iop. 1981;157:143-!48.

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14- Merchant AC, Mercer RL, Jacobsen RH, et al. Roentgenographic analysis of patellofemoral congruence. Ì Bone Joint Surg. ?974?56?:1391-139?.

15. Minkoff J, Fein L. The role uf radiography in the evaluation and treatment of common anarthrotic disorders of the patellofemorat joint. Clin Spora MoL 1989;8:203260.

16. Jacobson KE, Flandry FC. Diagnosis of anterior knee pain. CIm Sports Med. 1989;8:179-195.

17. Main WK, Hetshman EB. Chronic knee pain in the adolescent athlete. The Physician and Sportsmedicine. In press.

18 Sandow MJ, Goodfellow JW. The natural history of anterior knee pain in adolescents. J Bane iaim Surg. 1985;67B:36-38.

19. Dehaven KE, Man WA, Mayer PJ. Chondromalacia patellae in athletes. Clinical presentation and conservative managemen t . AmJ Sports Med. ?979;7?5-11.

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21. Bennett JG, Stauber WT. Evaluation and treatment of anterior knee pain using eccentric exercise. Med Sei Sports E)KTC. 1986: 18:5?6-530.

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23. Kramer PG. rotella malalignment syndrome: rationale to reduce excessive lateral ptessuie. Orthopedic Sports and Physical Therapy. 1986;8: 30 1-309.

24. McConnell J. The management of Chondromalacia patellae: a long term solution. Aust J Physiotherapy 1986;32:215-222.

TABLEl

History Usually Obtained From Patients With Anterior Knee Pain

TABLE 2

Treatment of Patellofemoral Dysfunction

10.3928/0090-4481-19910401-07

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