Basics
Description
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It is important, during a knee examination, to keep in mind the child’s age and to understand the age-specific pediatric knee disorders.
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Congenital hyperextension or dislocation of the knee:
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Varies from simple hyperextension to anterior dislocation of the tibia on the femur
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Hyperextended knee presents at birth.
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A hyperextensible knee resolves spontaneously, whereas a dislocated knee requires surgery.
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Blount disease (infantile tibia vara and adolescent tibial vara):
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Abnormality of the proximal tibial growth plate causes excessive varus alignment of the knees (bowed legs) in children.
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Varus/valgus natural history:
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Birth: Normal bowing of 10-15°
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12-18 months: Varus decreases to 0°.
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3-5 years: Maximum valgus reached (10-15°).
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Early adolescence: Valgus decreases to normal adult values (5-10°).
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Infantile tibia vara, a common cause of pathologic bowed legs in children, usually presents at age 2-4 years and is painless.
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Adolescent tibial vara, which is becoming more common, usually presents after age 9-10 years.
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Discoid meniscus:
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Congenital abnormality in which the lateral meniscus does not acquire a discoid shape during embryologic development, which makes it more susceptible to tearing.
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Septic arthritis of the knee:
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Pyogenic infection of the knee
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2/3 of all cases occur before 3 years of age.
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Patient is acutely ill and nonweightbearing.
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Popliteal cyst:
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Cyst arising from the posterior knee joint
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Typically presents as an asymptomatic mass on the posteromedial aspect of the knee at the popliteal crease
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Tibial spine fracture: Avulsion of the tibial attachment of the ACL, usually from a bicycle fall, sporting injuries, or other indirect trauma to the knee
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Genu valgum:
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Valgus of the knee that increases after age 7 years is not physiologic.
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Knee pain is a common feature.
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JIA
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OSD:
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Traction apophysitis of the tibial tubercle
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Occurs during time of rapid growth (ages 9-14 years)
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Typical presentation is pain over the tibial tubercle exacerbated by running, jumping, and kneeling
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Osteochondritis dissecans: Condition of unknown cause in which a segment of subchondral bone undergoes AVN
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ITBS:
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Most common cause of lateral knee pain in athletes
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An overuse condition secondary to friction of the iliotibial band over the lateral femoral condyle
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Presents as pain over the lateral femoral condyle that is worsened by activity
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ACL injury:
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2 general mechanisms:
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Direct trauma to the anterior aspect of the knee (more in young children)
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Indirect injury by twisting motion
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Lyme disease: Early in the disease, presents as fever and migratory arthralgia, with little or no joint swelling
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Lyme arthritis:
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Occurs months to years after the initial infection
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Typically a low-grade inflammatory synovitis with a large and relatively painless joint effusion
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SCFE:
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Overweight child, aged 6-14 years
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Pain referred to the knee (often missed)
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Obtain hip radiographs in such children.
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Diagnosis
Signs and Symptoms
History
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Pain:
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Acute: Ligament and meniscal tears, fractures, septic arthritis
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Chronic: Genu valgum, JIA, OSD, Sinding-Larsen-Johansson syndrome, osteochondritis dissecans, ITBS, Lyme disease, tendinitis, neoplasm
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Specific location:
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Anterior (patellofemoral pain syndrome): Patellar maltracking, pathologic plica, symptomatic bipartite patella.
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Lateral: ITBS
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Tibial tubercle: OSD
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Inferior pole of the patella: Sinding-Larsen-Johansson syndrome
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At night: Neoplasm (osteosarcoma, Ewing sarcoma)
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Swelling:
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Acute: Ligament and meniscal tears, fractures, septic arthritis
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Chronic: JIA, Lyme disease, synovitis, neoplasm
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Mechanical factors:
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Catching or locking: Meniscal tears, articular cartilage damage, loose bodies (e.g., as in osteochondritis dissecans)
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Giving way or coming apart:
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Complete ligamentous injuries
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Physical Exam
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General considerations:
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The entire lower extremity should be exposed.
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When palpating, start with the normal knee to facilitate comparison and patient relaxation.
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Start with examination steps not likely to hurt.
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Inspection:
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Anterior:
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Inspect for valgus or varus deformity.
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In adolescence, normal standing alignment is slight valgus (5-10°)
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Look for evidence of effusion.
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Lateral:
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Look for incomplete extension resulting from flexion contracture or excessive hyperextension (recurvatum deformity).
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Look for symmetry of the tibial tuberosities.
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Palpation: Assess for warmth and check for tenderness along the medial and lateral joint lines, medial and collateral ligaments, patella and its supporting ligaments, femoral and tibial condyles, and tibial tubercles.
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Hip examination: Because knee pain often is referred from the hip, any child presenting with knee pain should have an evaluation of hip ROM (see Hip Examination of the Child chapter).
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Testing for effusion:
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In marked effusions, the landmarks are obscured and the patella is ballotable, as seen with hemarthrosis, arthritis, and synovitis.
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Mildly obscured landmarks suggest a mild joint effusion or fluid collection in the bursae (see Knee Anatomy and Examination chapter for details of the Blot and Milk tests for knee effusions).
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Patellar assessment:
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Inhibition test:
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To determine if anterior knee pain is secondary to pressure in the patellofemoral joint
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With the patient supine and knee extended, have the patient do a straight-leg raise.
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Hold the patella to prevent it from ascending along the femoral sulcus.
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Any pain is a positive test, which may indicate a patellofemoral disorder.
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J sign:
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Observe the patella as the patient actively extends the knee.
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As the knee extends, the patella remains in the femoral sulcus as it ascends along the axis of the femur.
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As the knee reaches full extension, the patella deviates laterally like an upside-down J, a positive J sign.
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Menisci assessment:
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McMurray test:
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Flex the knee and hip maximally, and apply a valgus (varus) force to the knee.
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Externally (internally) rotate the foot and passively extend the knee.
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A palpable, painful snap or pop during extension suggests a tear of the medial (lateral) meniscus.
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ROM:
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Flexion (normal, 130-140°):
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Have the patient sit or lie prone and fully flex each knee.
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The angle between the leg and the thigh is the degrees of flexion.
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Extension (normal, 5°):
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With the patient lying supine with extended knees, stabilize the thigh and lift the foot.
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The angle between leg and table is degrees of extension.
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Ober test:
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Assesses the flexibility of the iliotibial band.
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With the patient lying on the unaffected side, stabilize the pelvis with 1 hand and abduct and extend the hip with the knee flexed.
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Support the patient’s ankle and allow the thigh to drop.
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If the thigh does not become parallel to the table, the test is positive.
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A positive test is associated with ITBS.
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Stability tests:
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AP stability is provided by the ACL and OSD.
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Mediolateral stability is provided by the MCL and LCL.
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See the Knee Anatomy and Examination chapter for details of the Lachman test, anterior and posterior drawer tests, and varus and valgus stress tests.
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Neurovascular examination: Especially important for acute injuries
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Sensation: Test sensation to light touch and pinprick in the peroneal, superficial peroneal, and tibial nerve distributions.
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Motor: Apply resistance while the patient:
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Dorsiflexes and plantarflexes the foot
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Inverts and everts the foot
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Dorsiflexes and plantarflexes the great toe
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Pulses: Check popliteal, dorsalis pedis, and posterior tibial pulses.
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Tests
Imaging
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General considerations:
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Standard radiographs of the knee joint: AP, lateral, tunnel, and patellar views
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Skyline (Merchant, patellar) view:
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Shows the location of the patella in the femoral groove and the thickness of the cartilage, which may be beneficial in identifying causes of anterior knee pain
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Is an axial view of the patellofemoral joint with the knee flexed to 35-45°.
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25°AP (tunnel) view aids in the detection of osteochondritis dissecans.
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A standing view of entire femur and tibia is needed to assess ligament alignment accurately.
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MRI is best for evaluating soft-tissue masses and injury to menisci or ligaments.
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Congenital knee dislocation: Radiographs help differentiate mild from the more severe hyperextension deformity characterized by a fixed anterior dislocation of the tibia on the distal femur.
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Blount disease and genu valgum: AP, standing, long cassette radiograph of both lower extremities, which includes the hips, knees, and ankles, is best for assessing the mechanical axis and any deviation in joint alignment.
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Discoid meniscus:
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MRI is the most useful imaging modality.
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Plain radiographs may reveal a widened lateral joint space with squaring of the lateral femoral condyle.
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Septic arthritis of the knee:
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Plain films usually are not useful because they may show only widening of joint space secondary to swelling.
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Popliteal cyst:
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Plain films show no bony abnormality and are needed only in the presence of pain.
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Transillumination with a penlight confirms benign cystic nature.
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Ultrasound is another option for documenting the cystic nature of the lesion and ruling out solid soft-tissue lesions.
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MRI is indicated if ultrasound or transillumination does not show a typical homogenous fluid-filled cyst.
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Tibial spine fracture:
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AP and lateral radiographs are essential for evaluating the degrees of displacement of the anterior tibial spine.
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Fracture is best seen on a lateral radiograph.
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JIA:
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Often no specific radiologic findings early in the course of JIA
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As it progresses, periarticular osteopenia, localized soft-tissue swelling and, occasionally, joint space widening from effusion or synovial hypertrophy often are present.
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OSD/Sinding-Larsen-Johansson syndrome:
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Radiographs confirm the clinical diagnosis.
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If bilateral involvement, radiographs usually are not needed.
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If unilateral involvement, obtain radiographs to rule out neoplasms.
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Osteochondritis dissecans:
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Radiography:
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Diagnostic
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Reveals a fragment of avascular bone demarcated from the adjacent femur by a radiolucent line
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AP, lateral, and a tunnel view, which is best for seeing the lesion in the classic location on the lateral aspect and posterior 2/3 of the medial femoral condyle
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MRI is a useful adjunct for determining the extent of articular cartilage involvement and the stability of the lesion.
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ITBS: Radiographs are unnecessary because diagnosis is based on the patient’s symptoms.
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ACL injury:
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Diagnosis is based primarily on the physical examination.
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Plain radiographs should be obtained for all patients suspected of knee ligament injury.
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MRI is indicated only for the patient in whom ROM does not improve and who has a persistent effusion after conventional therapy, or in whom the physical examination is difficult to interpret.
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Patella alta:
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Position of the patella is best seen on a lateral radiograph with the knee flexed to 30°.
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Patellar height:
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Can be assessed via the Insall ratio (length of patella ligament = diagonal length of patella).
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Variations of >20% are deemed abnormal.
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Lyme disease:
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Plain films rule out other causes.
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Diagnosis usually is based on clinical findings and positive blood serology.
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Miscellaneous
FAQ
Q: Is an MRI needed if I suspect a popliteal cyst?
A: Not if the history is typical, and the swelling transilluminates.
Q: Where is the tenderness located in OSD?
A: Over the tibial tubercle only.