Knee Examination in the Child

Table of Contents



  • It is important, during a knee examination, to keep in mind the child’s age and to understand the age-specific pediatric knee disorders.
  • Congenital hyperextension or dislocation of the knee:
    • Varies from simple hyperextension to anterior dislocation of the tibia on the femur
    • Hyperextended knee presents at birth.
    • A hyperextensible knee resolves spontaneously, whereas a dislocated knee requires surgery.
  • Blount disease (infantile tibia vara and adolescent tibial vara):
    • Abnormality of the proximal tibial growth plate causes excessive varus alignment of the knees (bowed legs) in children.
    • Varus/valgus natural history:
      • Birth: Normal bowing of 10-15°
      • 12-18 months: Varus decreases to 0°.
      • 3-5 years: Maximum valgus reached (10-15°).
      • Early adolescence: Valgus decreases to normal adult values (5-10°).
    • Infantile tibia vara, a common cause of pathologic bowed legs in children, usually presents at age 2-4 years and is painless.
    • Adolescent tibial vara, which is becoming more common, usually presents after age 9-10 years.
  • Discoid meniscus:
    • Congenital abnormality in which the lateral meniscus does not acquire a discoid shape during embryologic development, which makes it more susceptible to tearing.
  • Septic arthritis of the knee:
    • Pyogenic infection of the knee
    • 2/3 of all cases occur before 3 years of age.
    • Patient is acutely ill and nonweightbearing.
  • Popliteal cyst:
    • Cyst arising from the posterior knee joint
    • Typically presents as an asymptomatic mass on the posteromedial aspect of the knee at the popliteal crease
  • 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
  • Genu valgum:
    • Valgus of the knee that increases after age 7 years is not physiologic.
    • Knee pain is a common feature.
  • JIA
  • OSD:
    • Traction apophysitis of the tibial tubercle
    • Occurs during time of rapid growth (ages 9-14 years)
    • Typical presentation is pain over the tibial tubercle exacerbated by running, jumping, and kneeling
  • Osteochondritis dissecans: Condition of unknown cause in which a segment of subchondral bone undergoes AVN
  • ITBS:
    • Most common cause of lateral knee pain in athletes
    • An overuse condition secondary to friction of the iliotibial band over the lateral femoral condyle
    • Presents as pain over the lateral femoral condyle that is worsened by activity
  • ACL injury:
    • 2 general mechanisms:
      • Direct trauma to the anterior aspect of the knee (more in young children)
      • Indirect injury by twisting motion
  • Lyme disease: Early in the disease, presents as fever and migratory arthralgia, with little or no joint swelling
  • Lyme arthritis:
    • Occurs months to years after the initial infection
    • Typically a low-grade inflammatory synovitis with a large and relatively painless joint effusion
  • SCFE:
    • Overweight child, aged 6-14 years
    • Pain referred to the knee (often missed)
    • Obtain hip radiographs in such children.


Signs and Symptoms

  • Pain:
    • Acute: Ligament and meniscal tears, fractures, septic arthritis
    • Chronic: Genu valgum, JIA, OSD, Sinding-Larsen-Johansson syndrome, osteochondritis dissecans, ITBS, Lyme disease, tendinitis, neoplasm
    • Specific location:
      • Anterior (patellofemoral pain syndrome): Patellar maltracking, pathologic plica, symptomatic bipartite patella.
      • Lateral: ITBS
      • Tibial tubercle: OSD
      • Inferior pole of the patella: Sinding-Larsen-Johansson syndrome
    • At night: Neoplasm (osteosarcoma, Ewing sarcoma)
  • Swelling:
    • Acute: Ligament and meniscal tears, fractures, septic arthritis
    • Chronic: JIA, Lyme disease, synovitis, neoplasm
  • Mechanical factors:
    • Catching or locking: Meniscal tears, articular cartilage damage, loose bodies (e.g., as in osteochondritis dissecans)
    • Giving way or coming apart:
      • Complete ligamentous injuries

Physical Exam

  • General considerations:
    • The entire lower extremity should be exposed.
    • When palpating, start with the normal knee to facilitate comparison and patient relaxation.
    • Start with examination steps not likely to hurt.
  • Inspection:
    • Anterior:
      • Inspect for valgus or varus deformity.
      • In adolescence, normal standing alignment is slight valgus (5-10°)
      • Look for evidence of effusion.
    • Lateral:
      • Look for incomplete extension resulting from flexion contracture or excessive hyperextension (recurvatum deformity).
      • Look for symmetry of the tibial tuberosities.
    • 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.
  • 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).
  • Testing for effusion:
    • In marked effusions, the landmarks are obscured and the patella is ballotable, as seen with hemarthrosis, arthritis, and synovitis.
    • 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).
  • Patellar assessment:
    • Inhibition test:
      • To determine if anterior knee pain is secondary to pressure in the patellofemoral joint
      • With the patient supine and knee extended, have the patient do a straight-leg raise.
      • Hold the patella to prevent it from ascending along the femoral sulcus.
      • Any pain is a positive test, which may indicate a patellofemoral disorder.
    • J sign:
      • Observe the patella as the patient actively extends the knee.
      • As the knee extends, the patella remains in the femoral sulcus as it ascends along the axis of the femur.
      • As the knee reaches full extension, the patella deviates laterally like an upside-down J, a positive J sign.
  • Menisci assessment:
    • McMurray test:
      • Flex the knee and hip maximally, and apply a valgus (varus) force to the knee.
      • Externally (internally) rotate the foot and passively extend the knee.
      • A palpable, painful snap or pop during extension suggests a tear of the medial (lateral) meniscus.
  • ROM:
    • Flexion (normal, 130-140°):
      • Have the patient sit or lie prone and fully flex each knee.
      • The angle between the leg and the thigh is the degrees of flexion.
    • Extension (normal, 5°):
      • With the patient lying supine with extended knees, stabilize the thigh and lift the foot.
      • The angle between leg and table is degrees of extension.
  • Ober test:
    • Assesses the flexibility of the iliotibial band.
    • With the patient lying on the unaffected side, stabilize the pelvis with 1 hand and abduct and extend the hip with the knee flexed.
    • Support the patient’s ankle and allow the thigh to drop.
      • If the thigh does not become parallel to the table, the test is positive.
    • A positive test is associated with ITBS.
  • Stability tests:
    • AP stability is provided by the ACL and OSD.
    • Mediolateral stability is provided by the MCL and LCL.
    • See the Knee Anatomy and Examination chapter for details of the Lachman test, anterior and posterior drawer tests, and varus and valgus stress tests.
  • Neurovascular examination: Especially important for acute injuries
    • Sensation: Test sensation to light touch and pinprick in the peroneal, superficial peroneal, and tibial nerve distributions.
    • Motor: Apply resistance while the patient:
      • Dorsiflexes and plantarflexes the foot
      • Inverts and everts the foot
      • Dorsiflexes and plantarflexes the great toe
    • Pulses: Check popliteal, dorsalis pedis, and posterior tibial pulses.



  • General considerations:
    • Standard radiographs of the knee joint: AP, lateral, tunnel, and patellar views
    • Skyline (Merchant, patellar) view:
      • 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
      • Is an axial view of the patellofemoral joint with the knee flexed to 35-45°.
    • 25°AP (tunnel) view aids in the detection of osteochondritis dissecans.
    • A standing view of entire femur and tibia is needed to assess ligament alignment accurately.
    • MRI is best for evaluating soft-tissue masses and injury to menisci or ligaments.
  • 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.
  • 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.
  • Discoid meniscus:
    • MRI is the most useful imaging modality.
    • Plain radiographs may reveal a widened lateral joint space with squaring of the lateral femoral condyle.
  • Septic arthritis of the knee:
    • Plain films usually are not useful because they may show only widening of joint space secondary to swelling.
  • Popliteal cyst:
    • Plain films show no bony abnormality and are needed only in the presence of pain.
    • Transillumination with a penlight confirms benign cystic nature.
    • Ultrasound is another option for documenting the cystic nature of the lesion and ruling out solid soft-tissue lesions.
    • MRI is indicated if ultrasound or transillumination does not show a typical homogenous fluid-filled cyst.
  • Tibial spine fracture:
    • AP and lateral radiographs are essential for evaluating the degrees of displacement of the anterior tibial spine.
    • Fracture is best seen on a lateral radiograph.
  • JIA:
    • Often no specific radiologic findings early in the course of JIA
    • As it progresses, periarticular osteopenia, localized soft-tissue swelling and, occasionally, joint space widening from effusion or synovial hypertrophy often are present.
  • OSD/Sinding-Larsen-Johansson syndrome:
    • Radiographs confirm the clinical diagnosis.
    • If bilateral involvement, radiographs usually are not needed.
    • If unilateral involvement, obtain radiographs to rule out neoplasms.
  • Osteochondritis dissecans:
    • Radiography:
      • Diagnostic
      • Reveals a fragment of avascular bone demarcated from the adjacent femur by a radiolucent line
      • 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
    • MRI is a useful adjunct for determining the extent of articular cartilage involvement and the stability of the lesion.
  • ITBS: Radiographs are unnecessary because diagnosis is based on the patient’s symptoms.
  • ACL injury:
    • Diagnosis is based primarily on the physical examination.
    • Plain radiographs should be obtained for all patients suspected of knee ligament injury.
    • 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.
  • Patella alta:
    • Position of the patella is best seen on a lateral radiograph with the knee flexed to 30°.
    • Patellar height:
      • Can be assessed via the Insall ratio (length of patella ligament = diagonal length of patella).
      • Variations of >20% are deemed abnormal.
  • Lyme disease:
    • Plain films rule out other causes.
    • Diagnosis usually is based on clinical findings and positive blood serology.


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.


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