Clinical Manifestations and Diagnosis

The cause of discoid meniscus is not defined, but it may be a failure of an embryologic sequence of degeneration of the center of the meniscus. The normal meniscus is attached around its periphery and glides anteriorly and posteriorly with knee motion, but a discoid meniscus is less mobile and may be torn. Occasionally, there is no peripheral attachment around the posterolateral aspect of the meniscus, which can allow it to become displaced anteriorly with knee flexion, producing a loud click or clunk.

The usual presenting complaint is that of a popping or snapping of the knee that is both heard and felt by the child or parent. This is often noted in children >6 yr of age. Most often the snapping is not painful and the child is active. A second type of presentation is of a child who has had no knee symptoms but presents spontaneously or after an injury with pain, snapping, popping, or locking located along the lateral joint line. Physical examination might show a mild effusion and tenderness with fullness over the lateral joint line and crepitation with motion. The typical findings include a palpable snapping as the knee flexes and extends. Along the lateral joint line, the examiner feels a bulge, as the meniscus seems to protrude beyond the margin of the tibia. As the knee moves, the meniscus snaps into the intercondylar notch and the bulge disappears.

Anteroposterior radiography of the knee can show widening of the lateral aspect of the knee joint. Other findings include flattening of the lateral femoral condyle (giving a squared off appearance) and cupping of the lateral aspect of the tibial plateau. MRI or arthroscopy is required for definitive diagnosis.

Treatment

Many children with discoid menisci require no treatment. These children should be followed and treated only if pain or loss of motion occurs. Surgery may be considered when DLM leads to locking, swelling, loss of motion, inability to run, or inability to participate in sports. The treatment is to excise tears and reshape the meniscus arthroscopically (Fig. 669-1). Meniscal instability can occasionally be repaired or reconstructed. Complete excision may be necessary if other procedures are unsuccessful.

Figure 669-1 Arthroscopic image of discoid meniscus and arthroscopic shaving with meniscectomy.

Clinical Manifestations and Diagnosis

The most common presenting complaint is vague knee pain. If the fragment becomes loose, there can be crepitation, popping, giving way, and occasionally locking of the knee with or without a mild effusion. Physical findings are minimal and can include parapatellar tenderness, quadriceps atrophy, and slight pain with range of motion. The Wilson test is noted to be a specific diagnostic sign. It is performed by flexing the knee to 90 degrees, fully rotating the tibia medially, and then gradually extending the knee. When the test is positive, there is pain at 30 degrees of flexion that is located over the medial femoral condyle anteriorly.

The lesion is usually noted on anteroposterior, lateral, and tunnel radiographs (notch view) of the knee. Early lesions manifest with a small radiolucency at the articular surface, and more advanced lesions have a well-demarcated segment of subchondral bone with a lucent line separating it from the condyle. In young children, small foci of ossification can appear beyond the margin of the main ossific nucleus. As revascularization occurs, the bone heals spontaneously. With increasing age, the risk increases for articular cartilage fracture and separation of the bony fragment, producing a loose body.

MRI is helpful in determining the integrity of the articular cartilage and stability of the lesion. Arthroscopy is the most reliable method of evaluating the status of the lesion (Fig. 669-2). Factors commonly associated with a good prognosis are younger age group, small lesion, non–weight-bearing location, and no displacement. Four stages are involved with the progression of osteochondritis dissecans. Stage I consists of a small area of subchondral compression; stage II consists of a partially detached fragment; in stage III, the fragment is completely detached but remains in the crater; and by stage IV, the fragment is loose in the joint.

Figure 669-2 Classic arthroscopic image of osteochondritis dissecans lesion.

Treatment

The initial management of osteochondritis dissecans in children with open growth plates includes observation with enough activity restrictions to allow the symptoms to resolve. Most stable lesions heal spontaneously over several months. Stage I and II lesions are managed with activity modification, isometric exercises, and a knee immobilizer. Healing can be confirmed by follow-up radiographs, at which point the patient can return to normal activity levels. Arthroscopy is indicated in patients in whom nonoperative treatment fails and in those with signs, symptoms, and other studies suggesting an unstable lesion. Stage III lesions are managed by drilling and stabilization with Kirschner wires or pins. Stage IV lesions, if small, are managed by excision, and large lesions or those involving the weight-bearing areas are either replaced or internally fixed. Bone and cartilage grafting may be necessary in very severe cases with loss of large fragments. After surgery, patients participate in a physical therapy program and may or may not be allowed to return to their preoperative activity levels. Treating osteochondritis dissecans early and effectively often prevents recurrent symptoms in adulthood, although some very severe lesions are symptomatic later in life.

Patellofemoral Disorders

Patellofemoral joint stability depends on balance among the restraining ligaments, muscle forces, and the articular anatomy of the patellofemoral groove. The multiple factors that contribute to patellofemoral instability include quadriceps insufficiency, internal femoral torsion, external tibial torsion, the shallow sulcus, lateral tether, medial capsular attenuation, condylar hypoplasia, and genu valgum.

The patella has a V-shaped bottom that guides it through the sulcus in the distal femur. The force of the muscles pulling through the quadriceps mechanism and the patellar tendon do not act in a straight line because the patellar tendon inclines in a slightly lateral direction with respect to the line of the quadriceps. This is normally called the Q angle. This lateral movement, coupled with the movement of the restraining ligaments, tends to move the patella in a lateral direction. The vastus medialis muscle is necessary to counteract the laterally acting forces. An abnormality of any one or a group of these factors can make the patellofemoral joint function abnormally. Excessive instability of the patellofemoral joint can manifest as acute patellar dislocation, recurrent patellar subluxation or dislocation, habitual dislocation, and chronic dislocation.

Clinical Manifestations and Diagnosis

Symptoms are usually produced by vigorous physical activities such as running. There is usually no history of antecedent trauma. There are no mechanical symptoms associated such as locking, giving way, or recurrent effusion.

Active and passive range of motion of the knee, alignment of the lower extremity, knee stability, patellar tracking, areas of focal tenderness, and gait should be evaluated to identify any obvious causes of knee pain or instability. Routine radiographs, including anteroposterior, lateral, and tunnel views, are not particularly helpful in evaluating the cause of adolescent anterior knee pain, except that they can eliminate other etiologies. In the adolescent group, radiographs of the hip should be considered in suspected cases to rule out a slipped capital femoral epiphysis that can manifest as ill-defined knee pain.

Treatment

The natural history of anterior knee pain is one of spontaneous resolution over a period of years. The treatment is predominantly nonoperative and may include flexibility exercises, strengthening exercises (isometric quadriceps), contrast therapies (ice and heat), orthoses, and medications (nonsteroidal anti-inflammatory drugs). A success rate of 70-90% can be anticipated. Arthroscopic evaluation of the knee and patellofemoral joint is rarely necessary.

Clinical Manifestations and Diagnosis

The physical examination findings usually suggest the diagnosis. After an acute dislocation, there may be a hemarthrosis from capsular tearing or an osteochondral fracture. If the child is seen after a recent dislocation, there may be parapatellar tenderness and a mild effusion.

Examination of a child with a maltracking patella that is predisposed to dislocation often shows terminal subluxation of the patella when the knee is brought into full extension. There may be tenderness to palpation over the inferior surface of the lateral facet of the patella. Observe the tracking of the patella as the patient is allowed to flex the knee from full extension. In the patient with instability, the patella shifts laterally just as the knee begins to flex and then shifts medially with further flexion. This lateral displacement of the patella followed by medial movement is termed J tracking. The other classic physical sign is the Fairbanks apprehension sign. With the knee in 30 degrees of flexion, the examiner manually displaces the patella laterally and yields a subjective feeling of subluxation, resulting in the patient grabbing the examiner’s hand to prevent manipulative dislocation.

It is important to assess the torsional profile of the patient to rule out possible rotational abnormalities of the femur or tibia or both.

Radiographic studies can help identify factors contributing to recurrent dislocation of the patella or after an acute dislocation. They should include anteroposterior, lateral, and skyline tangential views (obtained in full flexion) of the patella to assess for an osteochondral fracture from the lateral femoral condyle or the patella. Other views include the MacNab view (obtained with the knee in 40 degrees of flexion), which shows the relationship of the patella to the anterior part of the femoral intercondylar groove and might also demonstrate loose bodies and fractures of the patella or lateral condyle; the Merchant view obtained with the knee in 45 degrees of flexion; and the Laurin view with the knee in 20 degrees of flexion.

Treatment

An initial traumatic dislocation of the patella should be treated with a knee immobilizer for comfort. After a few days, the patient should begin isometric quadriceps-strengthening exercises, and more vigorous strengthening exercises can be done as the tenderness resolves. Once the immobilization is discontinued (∼6 wk), the isometric exercise program should be continued until the knee is fully rehabilitated. Using this method, approximately 75% of patients do not have recurrent dislocations.

Initial management of recurrent dislocation of the patella should be nonoperative. If patellar subluxation is due to dynamic muscle imbalance, a specific muscle rehabilitation program, such as strengthening the vastus medialis, may be successful. Patellar stabilizing orthosis may be useful, although the mechanism of action and efficacy is uncertain.

Operative stabilization may be necessary with continued episodes of dislocation or failure of conservative management for patellar subluxation. The surgical approaches to growing children focus on realigning the quadriceps mechanism usually in combination with a lateral release and the creation of a medial patellar restraint. Realignment of the extensor mechanism may be accomplished by altering the muscle itself, changing its insertion into the patella, or altering the attachment of the patella to the tibia. Depending on the extent of involvement, an arthroscopic lateral release with or without a soft-tissue reconstruction with a realignment procedure may be performed. Torsional abnormalities of the femur or tibia may be addressed with rotational osteotomy of the distal femur or proximal tibia, or rarely both as deemed necessary.