Orthopaedic Surgery - Knee Examination in the Child

Basics

Examination of the pediatric knee must take the child’s age, stage of skeletal development, normal alignment changes, and age-specific disorders into account.

The differential diagnosis differs considerably between infants, young children, and adolescents. Normal developmental variants must be distinguished from pathologic deformities, infection, trauma, inflammatory disease, and tumors.

Because pain from the hip frequently presents as knee pain, evaluation of the pediatric knee should routinely include assessment of the hip and entire lower extremity.

Congenital Hyperextension and Dislocation of the Knee

Congenital knee hyperextension represents a spectrum ranging from simple hyperextension to fixed anterior dislocation of the tibia relative to the femur.

The deformity is evident at birth.

A flexible hyperextended knee may resolve spontaneously or respond to gentle conservative treatment, whereas a fixed congenital knee dislocation often requires more intensive treatment and occasionally surgery.

Blount Disease

Blount disease, or tibia vara, results from abnormal development of the medial proximal tibial physis, producing progressive bowing of the lower extremity.

It occurs in infantile and adolescent forms.

Normal Varus-Valgus Development

Normal coronal alignment changes with growth.

At birth, children normally have approximately 10–15° of genu varum.

By approximately 12–18 months, the legs become nearly neutral.

Between approximately 3 and 5 years, physiologic valgus reaches its maximum, often around 10–15°.

During later childhood and early adolescence, valgus gradually decreases toward the adult range of approximately 5–10°.

Persistent or progressive deformity outside this expected pattern should be investigated.

Infantile Tibia Vara

Infantile Blount disease usually presents between approximately 2 and 4 years of age.

The child commonly has painless, progressive bowing of the legs.

Adolescent Tibia Vara

Adolescent Blount disease usually becomes apparent after approximately 9–10 years of age.

It is increasingly associated with obesity and mechanical overload of the proximal tibial growth plate.

Discoid Meniscus

A discoid meniscus is a congenital abnormality in which the meniscus, usually the lateral meniscus, remains abnormally broad and disc-shaped.

This morphology makes it more susceptible to:

Tearing, instability, snapping, pain, and mechanical symptoms.

Septic Arthritis of the Knee

Septic arthritis is a pyogenic infection of the knee joint.

Approximately two-thirds of pediatric cases historically occur before 3 years of age.

Affected children typically appear acutely ill and may present with:

Fever, joint swelling, severe pain, restricted motion, and refusal to bear weight.

Popliteal Cyst

A popliteal or Baker cyst arises from the posterior aspect of the knee.

In children, it commonly presents as:

An asymptomatic or minimally painful posteromedial mass at the popliteal crease.

Tibial Spine Fracture

A tibial spine fracture is an avulsion fracture involving the tibial insertion of the ACL.

It commonly occurs after:

Bicycle falls, sporting injuries, or other indirect twisting trauma.

In skeletally immature patients, the tibial spine may fail before the ACL itself ruptures.

Genu Valgum

Physiologic genu valgum normally decreases after early childhood.

Valgus deformity that becomes progressively greater after approximately 7 years of age should not be considered physiologic.

Significant deformity may be associated with knee pain and abnormal mechanical loading.

Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis may involve the knee and produce:

Persistent swelling, warmth, stiffness, synovitis, reduced motion, and sometimes pain.

Substantial effusion may be present despite relatively mild discomfort.

Osgood–Schlatter Disease

Osgood–Schlatter disease is a traction apophysitis of the tibial tubercle.

It occurs most commonly during rapid skeletal growth, usually between approximately 9 and 14 years of age.

Typical symptoms include:

Pain and tenderness over the tibial tubercle, aggravated by running, jumping, kneeling, and resisted knee extension.

Osteochondritis Dissecans

Osteochondritis dissecans is an osteochondral disorder in which a segment of subchondral bone and its overlying cartilage becomes abnormal.

The precise cause is uncertain.

The classic juvenile lesion occurs along the lateral aspect of the medial femoral condyle.

Iliotibial Band Syndrome

Iliotibial band syndrome is a common cause of lateral knee pain in athletes.

It is an overuse condition related to repetitive irritation of the iliotibial band near the lateral femoral epicondyle.

Pain is usually aggravated by running, cycling, or repetitive flexion and extension.

ACL Injury

ACL injuries occur through two broad mechanisms.

Younger children may sustain injury after direct trauma, whereas older children and adolescents more commonly experience:

Twisting, pivoting, or other indirect noncontact mechanisms.

Lyme Disease

Early Lyme disease may present with:

Fever and migratory arthralgia, often with little or no joint swelling.

Lyme Arthritis

Late Lyme arthritis may occur months or years after the initial infection.

The knee is commonly affected and may demonstrate:

A large but relatively painless effusion with low-grade inflammatory synovitis.

Slipped Capital Femoral Epiphysis

SCFE is an important cause of referred knee pain.

It typically affects an overweight child or adolescent, often between approximately 6 and 14 years of age.

Because knee pain may be the principal complaint, SCFE can be missed if the hip is not examined.

Unexplained knee pain associated with limp or limited hip rotation should therefore prompt hip examination and appropriate hip radiographs.

Diagnosis

History

The history should characterize:

Onset, duration, pain location, trauma, activity relationship, swelling, mechanical symptoms, instability, constitutional symptoms, and night pain.

Acute Pain

Acute pediatric knee pain may result from:

Ligament injury, meniscal tear, fracture, patellar instability, or septic arthritis.

Chronic Pain

Chronic or recurrent symptoms may occur with:

Genu valgum, juvenile idiopathic arthritis, Osgood–Schlatter disease, Sinding-Larsen–Johansson syndrome, osteochondritis dissecans, iliotibial band syndrome, Lyme disease, tendinopathy, or neoplasm.

Pain Location

The location of pain provides useful diagnostic information.

Anterior Knee Pain

Possible causes include:

Patellofemoral pain syndrome, patellar maltracking, symptomatic plica, and symptomatic bipartite patella.

Lateral Knee Pain

Pain over the lateral femoral epicondyle, particularly in an athlete, is suggestive of:

Iliotibial band syndrome.

Tibial Tubercle Pain

Pain localized to the tibial tubercle is typical of:

Osgood–Schlatter disease.

Inferior Patellar Pain

Pain at the inferior pole of the patella may represent:

Sinding-Larsen–Johansson syndrome.

Night Pain

Persistent or progressive night pain should raise concern for serious pathology, including:

Osteosarcoma, Ewing sarcoma, infection, or another neoplasm.

Swelling

Acute Swelling

Acute effusion may accompany:

Ligament tears, meniscal injuries, fractures, patellar dislocation, or septic arthritis.

Chronic Swelling

Persistent swelling may be associated with:

Juvenile idiopathic arthritis, Lyme arthritis, chronic synovitis, osteochondral disease, or neoplasm.

Mechanical Symptoms

Catching or Locking

These symptoms suggest:

Meniscal tearing, articular cartilage injury, or loose bodies, including fragments associated with osteochondritis dissecans.

Giving Way

A sensation that the knee is buckling or coming apart may indicate significant ligamentous instability.

Physical Examination

General Principles

The entire lower extremity should be exposed sufficiently to evaluate:

Alignment, swelling, muscle bulk, deformity, and gait.

When palpating, begin with the normal knee for comparison and to help relax the child.

Nonpainful examination maneuvers should be performed before potentially painful tests.

Inspection

Anterior View

Assess for:

Genu varum, genu valgum, effusion, patellar position, swelling, and muscular asymmetry.

In adolescence, normal standing alignment usually demonstrates mild valgus of approximately 5–10°.

Lateral View

Look for:

Flexion contracture, inability to reach full extension, or excessive hyperextension such as genu recurvatum.

Tibial Tuberosities

Compare the position and prominence of the tibial tubercles.

Asymmetry may suggest rotational deformity or developmental abnormality.

Palpation

Assess for warmth and tenderness along the:

Medial and lateral joint lines, MCL, LCL, patella, quadriceps tendon, patellar tendon, femoral condyles, tibial condyles, and tibial tubercle.

Localized tenderness should be correlated with the underlying anatomy.

Hip Examination

Because hip disorders may present entirely as knee pain, hip range of motion should be evaluated in every child with unexplained knee symptoms.

Assess:

Flexion, extension, abduction, internal rotation, and external rotation.

Restricted internal rotation or obligatory external rotation during flexion should raise concern for hip pathology such as SCFE.

Assessment for Knee Effusion

A large effusion obscures the normal contours of the knee and may make the patella ballotable.

Large effusions can occur with:

Hemarthrosis, septic arthritis, inflammatory arthritis, and synovitis.

A smaller effusion may cause only subtle loss of normal landmarks.

Blot and milking tests can help identify low-volume joint fluid.

Patellar Examination

Patellar Inhibition Test

This test assesses whether anterior knee pain is arising from the patellofemoral articulation.

With the patient supine and the knee extended, ask the child to perform a straight-leg raise while the examiner restricts superior movement of the patella.

Reproduction of anterior knee pain suggests patellofemoral pathology.

J Sign

The J sign evaluates patellar tracking.

Observe the patella while the patient actively extends the knee.

Normally, the patella tracks within the femoral trochlea.

A positive J sign occurs when the patella moves abruptly laterally near terminal extension, producing an upside-down J-shaped path.

This finding suggests:

Lateral patellar maltracking or instability.

Meniscal Examination

McMurray Test

The McMurray test is used to evaluate meniscal tears.

Medial Meniscus

Flex the hip and knee maximally.

Externally rotate the tibia and apply a valgus force while gradually extending the knee.

A painful palpable click or snap along the medial joint line suggests medial meniscal injury.

Lateral Meniscus

Flex the knee, internally rotate the tibia, and apply a varus force while extending the knee.

A painful click along the lateral joint line suggests lateral meniscal pathology.

Range of Motion

Flexion

Normal knee flexion is approximately 130–140°.

The patient can be examined sitting, supine, or prone.

Extension

Children commonly reach neutral extension and may demonstrate approximately 5° of physiologic hyperextension.

Comparison with the opposite knee is important.

Ober Test

The Ober test evaluates iliotibial band flexibility.

Technique

The patient lies on the unaffected side.

The pelvis is stabilized while the symptomatic hip is abducted and extended with the knee flexed.

The examiner then allows the thigh to fall into adduction.

Positive Test

If the thigh remains elevated and does not fall toward the examination table, the test suggests iliotibial band tightness.

This may support a diagnosis of iliotibial band syndrome.

Stability Testing

Anterior-posterior stability is provided predominantly by the:

ACL and PCL.

Mediolateral stability is provided primarily by the:

MCL and LCL.

ACL

The ACL is evaluated with:

Lachman and anterior drawer tests.

PCL

The PCL is evaluated with:

Posterior drawer and posterior sag tests.

Collateral Ligaments

Varus and valgus stress testing assesses the:

LCL and MCL, respectively.

Pediatric ligamentous laxity varies, so comparison with the opposite knee is especially useful.

Neurovascular Examination

A neurovascular examination is particularly important after acute injury.

Sensory Testing

Test sensation in the distributions of the:

Common peroneal, superficial peroneal, deep peroneal, and tibial nerves.

Motor Testing

Apply resistance while the patient:

Dorsiflexes and plantarflexes the ankle, inverts and everts the foot, and extends and flexes the great toe.

Pulses

Palpate the:

Popliteal, dorsalis pedis, and posterior tibial pulses.

Capillary refill and limb temperature should also be assessed if vascular injury is a concern.

Imaging

Standard Knee Radiographs

Common views include:

AP, lateral, tunnel, and patellofemoral axial views.

The specific views obtained should be tailored to the suspected diagnosis.

Skyline / Merchant View

The skyline or Merchant view is an axial image of the patellofemoral joint, usually obtained with approximately 35–45° of knee flexion.

It helps evaluate:

Patellar position, trochlear morphology, patellofemoral congruence, and osteochondral abnormalities.

Tunnel View

A flexed-knee AP or tunnel view is particularly helpful for identifying:

Osteochondritis dissecans lesions of the femoral condyles.

Standing Long-Leg Radiographs

A standing radiograph extending from the:

Hips through the knees to the ankles

is used to evaluate the mechanical axis and coronal alignment.

This is particularly useful for:

Blount disease and genu valgum.

MRI

MRI is the most useful advanced imaging modality for:

Meniscal tears, ligament injury, articular cartilage pathology, osteochondral lesions, and soft-tissue masses.

Congenital Knee Dislocation Imaging

Plain radiographs help distinguish:

Flexible hyperextension from fixed anterior tibial dislocation relative to the distal femur.

Blount Disease and Genu Valgum Imaging

The preferred study is an:

AP standing long-cassette radiograph of both lower extremities including the hips, knees, and ankles.

This demonstrates:

Mechanical-axis deviation, proximal tibial deformity, and abnormalities in joint orientation.

Discoid Meniscus Imaging

MRI is the most useful examination.

It can define:

Meniscal shape, thickness, tearing, and instability.

Plain radiographs may occasionally show:

Widening of the lateral joint space or squaring of the lateral femoral condyle.

Septic Arthritis Imaging

Early plain radiographs are often nonspecific and may show only:

Soft-tissue swelling or apparent joint-space widening caused by effusion.

Ultrasound may demonstrate an effusion and can guide aspiration.

MRI is useful when adjacent osteomyelitis or deeper infection is suspected.

Popliteal Cyst Imaging

Plain radiographs are generally normal and are usually needed only when pain or another diagnosis requires exclusion.

Ultrasound

Ultrasound can confirm the fluid-filled nature of the cyst and distinguish it from a solid soft-tissue mass.

MRI

MRI may be obtained when ultrasound findings are atypical or the lesion does not appear to be a simple homogeneous cyst.

Tibial Spine Fracture Imaging

AP and lateral radiographs are essential.

The lateral view is particularly useful for assessing the degree of displacement of the tibial spine fragment.

Juvenile Idiopathic Arthritis Imaging

Radiographs may remain normal early in the disease.

With progression, findings can include:

Periarticular osteopenia, soft-tissue swelling, synovial hypertrophy, effusion, and eventually joint-space loss or erosive changes.

Osgood–Schlatter Disease

Diagnosis is usually clinical.

Radiographs may demonstrate:

Irregularity, fragmentation, or prominence of the tibial tubercle apophysis.

Routine radiographs may be unnecessary in a typical bilateral presentation.

Unilateral, atypical, or severe symptoms should prompt imaging to exclude:

Neoplasm, infection, or fracture.

Sinding-Larsen–Johansson Syndrome

Radiographs may demonstrate irregularity or ossification at the inferior pole of the patella.

Diagnosis is primarily clinical.

Osteochondritis Dissecans Imaging

Plain radiographs may show:

A subchondral bone fragment separated from adjacent bone by a radiolucent line.

The classic lesion occurs along the lateral aspect of the medial femoral condyle, commonly involving its posterior portion.

Recommended views include:

AP, lateral, and tunnel radiographs.

MRI

MRI helps determine:

Lesion size, cartilage involvement, stability, and surrounding bone changes.

Iliotibial Band Syndrome Imaging

Routine radiographs are generally unnecessary because the diagnosis is usually based on history and examination.

Imaging is reserved for atypical cases or when another diagnosis is suspected.

ACL Injury Imaging

ACL injury is diagnosed primarily by physical examination.

Plain radiographs should nevertheless be obtained in children with significant suspected ligament trauma because they may reveal:

Tibial spine avulsion, fracture, osteochondral injury, or physeal injury.

MRI

MRI is useful when:

The examination is difficult to interpret, effusion persists, motion does not recover, or associated meniscal, ligamentous, or cartilage injuries require definition.

Patella Alta

Patellar position is best evaluated on a lateral radiograph with the knee flexed approximately 30°.

Insall–Salvati Ratio

The Insall–Salvati ratio compares:

Patellar tendon length with the greatest diagonal length of the patella.

A value near 1.0 is typical.

A deviation of more than approximately 20% may suggest:

Patella alta or patella baja.

Lyme Disease Imaging and Testing

Plain radiographs are generally nonspecific and mainly help exclude other causes of knee swelling.

Diagnosis of Lyme arthritis relies primarily on:

Clinical findings, appropriate exposure history, and positive serologic testing.

Important Clinical Principle

Pediatric knee symptoms should always be interpreted in relation to the child’s:

Age, skeletal maturity, alignment, activity level, gait, hip examination, pain location, swelling, and systemic symptoms.

Particularly important diagnoses not to miss include:

Septic arthritis, SCFE presenting as knee pain, malignancy, osteomyelitis, unstable osteochondral lesions, and major ligament or physeal injury.