John A. Herring
Knee injuries present frequently in virtually all age groups within a pediatric practice. The age and mechanism of injury are guidelines to a correct diagnosis. A swollen, painful knee in an infant should raise the suspicion of child abuse or infection. In the young child, significant ligament or meniscal injuries are rare, but epiphyseal separations and fractures are more frequent. In the adolescent, internal injuries to menisci and ligaments are common and most often result from sports activities, with or without contact. Patellar dislocations are also more common in adolescents.
The examiner should note bruising, swelling about the knee, the presence or absence of an effusion, and the ability to walk or bear weight. Most significant injuries are accompanied by an effusion or hemarthrosis, and the swollen knee is difficult to examine due to pain and limited motion. After the initial swelling has resolved, specific findings of an internal derangement can be elicited. The torn anterior cruciate is indicated by a positive anterior drawer sign in which the tibia can be anteriorly subluxated with the knee flexed.1 Meniscal tears often produce a clicking or grinding when the knee is fully flexed and extended with medial or lateral stress. Medial collateral and lateral collateral ligament injuries allow the joint to open either medially or laterally with stress in a 20° flexed position.
Radiographs should be evaluated and will show swelling only in the case of meniscal or ligamentous injury. Widening of the distal femoral growth plate suggests a separation injury of the growth plate (Salter 1). Elevation of the tibial spine indicates an injury in which the anterior cruciate pulls a fragment of bone up from the tibial articular surface.
Initial treatment usually consists of splinting with compression using a prefabricated knee immobilizer and ACE bandage.2 Aspiration of the knee is not necessary. Reevaluation at 2 weeks allows for a better physical exam for significant injury. Minor injuries will usually be recovering by then, and significant injuries will show persistent physical findings. A magnetic resonance imaging (MRI) examination will help to define internal injuries that will require orthopedic consultation.
A discoid meniscus is an abnormally shaped lateral meniscus found in children of all ages (Fig. 214-1).3,4 It may slip in and out of the joint causing the patient to feel something pop over the lateral aspect of the knee joint. This may be somewhat painful. The examiner can feel something pop along the lateral joint line as the knee is flexed and extended. Over time, this may become more painful and the “popping” may begin to limit function.
An anteroposterior radiograph of the knee may show widening of the lateral joint space, and an MRI provides a definitive diagnosis. Arthroscopic reconstruction or removal of the meniscus is the treatment of choice for those with significant symptoms.5
PATELLO-FEMORAL PAIN SYNDROME
Adolescents with vague knee pain are commonly seen in a primary care office.6,7 The complaint is pain around the patella, aggravated by activities, especially physical education. The knee is often painful when the person sits in a car or theater where it is difficult to extend the knee. Straightening the knee gives immediate relief. This has been called chondromalacia patella, yet there is little evidence of damage to the cartilage of the patella. It has also been called the malalignment syndrome, and many patients have excessive femoral anteversion with patellae that face toward one another as the patient walks.
Radiographs will show no abnormalities, and the treatment is aimed at symptom relief. Nonsteroidal anti-inflammatory drugs (NSAIDs) are helpful. A well-planned physiotherapy program that emphasizes strengthening of the quadriceps and hamstrings as well as the hip abductors and external rotators will help most patients recover.
FIGURE 214-1. Diagram of partial resection of a discoid meniscus highlighting the line of incision. Note that the posterior and anterior attachments of the meniscus are left intact. (Herring JA, editor. Tachjian’s Pediatric Orthopaedics. Philadelphia: Saunders; 2008, p. 932.)
PATELLAR INSTABILITY AND DISLOCATION
In this condition, there is an anatomic mal-alignment of the patella and quadriceps complex which results in recurrent lateral subluxation or dislocation of the patella.8 The dislocations may reduce spontaneously or may require sedation and closed reduction. The subluxations are annoying and painful to the patient but do not require reduction.
The examination will show that the patella tends to move laterally as the knee approaches full, active extension. As the knee begins to flex, the patella moves medially into its normal position in the femoral notch, a physical finding called the “J” sign. With the patient relaxed and the knee in full extension, the examiner can push the patella laterally and begin to flex the knee. The patient with this condition will quickly react to prevent this, and this is termed “the apprehension sign.”9
Treatment begins with quadriceps strengthening and rehabilitation as described for patello-femoral pain syndrome.10 The patient with recurrent dislocation often requires surgical correction in which the medial restraints to patellar motion are reconstructed.
An osteochondritis dissecans lesion is an area of articular cartilage and underlying bone in the knee which becomes loose or separated from the adjacent articular surface of the knee. These vary in size from a few millimeters to several centimeters in diameter. They also may be slightly mobile, but others may become completely detached and free in the joint. The etiology is probably traumatic.
The patient complains of soreness in the anterior knee with activity and occasionally swelling, popping, or crepitance. The physical findings are nonspecific unless there is tenderness next to the patella, or palpable crepitance.11Radiographs show a lucent area on the femoral condyle, especially seen on a tunnel view with the knee partially flexed. Treatment is initially conservative, followed by arthroscopic evaluation and treatment when the condition persists.12
In this condition, there is tenderness and enlargement of the tibial tubercle in a growing child, usually in early adolescence.13 It is aggravated by activity, especially stair climbing and running. It represents a stress reaction of the growth cartilage into which the patellar tendon inserts. The enlargement often creates concern for a possible tumor. Radiographs will show variable lucency and density of the tibial tubercle, which are normal findings in the involved age group.14 Treatment is symptomatic, with reduction of activities to tolerance. If the child can continue sports without limping during the activity, he or she should be allowed to continue. The symptoms usually resolve with skeletal maturity, with only an occasional person having a symptomatic nodule at the tubercle as an adult.
This is a condition similar to Osgood-Schlatter disease in which there is a stress reaction at the distal pole of the patella. The patient complains of pain and tenderness at the lower pole of the patella, and the symptoms are aggravated by activities that load the knee. The patient may complain of generalized knee pain, but the exam should reveal exquisite tenderness at the inferior patellar pole. Radiographs will show fragmentation of the bone at the distal pole of the patella. Treatment is symptomatic, directed toward reducing loading activities such as jumping, running the stairs, and deep knee bends. Children will outgrow this condition without any residual problems.
FIGURE 214-2. Infant with Larsen syndrome and bilateral dislocated knee as well as hips and severe clubfeet. (Reprinted with permission from Herring, JA, Tachdjan’s Pediatric Orthopaedics, Vol 2. Amsterdam: Elsevier; 2008:921.)
CONGENITAL DISLOCATION OF THE KNEE
When a baby is born with the knees markedly hyperextended, with the feet under the chin, parents and medical personnel alike are usually very distressed (Fig. 214-2). Fortunately, this is a condition that usually responds very well to treatment and generally has a good outcome. This condition, frequently associated with breech position, is divided into three categories.15 Hyperextension of the knee implies that the tibia and femur are in alignment, subluxation indicates that the tibia is in contact with the femur but is anterior to it, and dislocation means that the tibia is all the way anteriorly displaced relative to the femur.16
The first 2 degrees of deformity usually respond to serial cast manipulation and have a benign prognosis with fully normal function. True dislocation of the knee, often associated with other syndromes, such as Larsen syndrome, may require surgical correction and may have some lasting disability.
POPLITEAL (BAKER) CYST
Children with this condition present with a mass in the popliteal fossa which may or may not be painful.17 It arises spontaneously and is not usually related to trauma or activity. The cyst, which is filled with a congealed, jelly-like condensation of joint fluid, arises as an extension of the synovium of the joint. In adults, these are usually associated with an internal derangement of the knee, but in children the knee is usually normal.
The examiner finds a firm mass in the popliteal fossa, best appreciated with the patient prone and the knee fully extended. With the knee flexed, there is some mobility to the mass, but it remains firm. In a dark room the mass will transilluminate. Radiographs show no abnormalities. If there is suspicion of a tumor, an MRI will resolve the issue but is usually unnecessary.
Treatment is observation and reassurance. The mass will usually resolve gradually, but may occasionally enlarge for a time. Excision is often complicated with recurrence and is rarely necessary.