Knee Examination in the Child

• 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.

Imaging

• 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.