What is the appropriate initial management for an adolescent experiencing knee pain and popping?

Initial Management of Adolescent Knee Pain with Popping

Begin with plain radiographs of the knee (anteroposterior and lateral views minimum) as the first-line imaging for all adolescents presenting with knee pain and popping. 1

Immediate Diagnostic Workup

Plain Radiography First

• Obtain two-view knee radiographs (AP and lateral) as the initial imaging study for all patients ≥5 years old with knee pain, regardless of whether symptoms are acute or chronic. 1
• Radiographs are essential to rule out fractures, osteochondritis dissecans (OCD), loose bodies, tumors, and other bony pathology even when clinical examination suggests soft tissue injury. 2, 1
• The popping sensation may indicate meniscal pathology, ligamentous injury, or intra-articular loose bodies—all of which require radiographic evaluation first. 2

Clinical Examination Priorities

• Perform the Lachman test at 20-30 degrees of knee flexion to assess for ACL injury, as a positive test has high probability for ACL rupture. 3
• Assess for joint effusion, focal tenderness, and ability to bear weight—these findings guide further imaging decisions. 4
• Evaluate for mechanical symptoms (locking, catching) that suggest meniscal tears or loose bodies requiring advanced imaging. 2

When Initial Radiographs Are Normal or Show Only Effusion

MRI Without Contrast

• If radiographs are normal or demonstrate only joint effusion, proceed with MRI without IV contrast as the next imaging step. 1
• MRI is the gold standard for evaluating soft tissue structures, menisci, ligaments, cartilage abnormalities, and bone marrow lesions with 97% diagnostic accuracy for ACL tears. 2, 3, 1
• MRI can identify causes of popping including meniscal tears, plica syndrome, discoid meniscus, ganglion cysts, and early OCD lesions. 2, 5, 6

Consider Arthrocentesis If Effusion Present

• Perform diagnostic arthrocentesis if significant effusion is present to rule out septic arthritis (orthopedic emergency), crystal disease, or lipohemarthrosis indicating occult fracture. 4
• Send synovial fluid for cell count with differential, Gram stain and culture, and crystal analysis. 4
• Lipohemarthrosis on gross examination indicates occult intra-articular fracture despite negative radiographs and may warrant CT imaging. 4

Common Pitfalls to Avoid

Don't Skip Radiographs

• Never proceed directly to MRI without obtaining plain films first—radiographs may reveal fractures, OCD, or loose bodies that fundamentally change management. 1
• Approximately 10% of fractures in young patients are only visible on follow-up radiographs if initial films are negative. 2

Don't Ignore Persistent Symptoms

• If initial radiographs are negative but symptoms persist or worsen, obtain follow-up clinical reassessment and consider MRI or repeat radiographs. 2
• Popping with persistent pain warrants MRI evaluation even with normal radiographs, as meniscal tears and early cartilage lesions are radiographically occult. 2, 1

Recognize Overuse Syndromes

• Chronic knee pain with popping in adolescents is frequently due to overuse syndromes, plica syndrome, or patellofemoral pain—these require detailed training history and biomechanical assessment. 6
• Conservative management with activity modification, physiotherapy, and pain control is first-line for overuse-related pathology. 6

Advanced Imaging Considerations

Ultrasound Has Limited Role

• Ultrasound is not appropriate as a comprehensive screening tool but may confirm effusions, guide aspiration, or detect Baker cysts. 1
• US has limited field of view and lower accuracy for fracture detection compared to radiographs. 2, 1

CT Reserved for Specific Indications

• CT without contrast is indicated when radiographically occult fractures are suspected or when MRI findings are not definitive for OCD or loose bodies. 2, 1
• CT arthrography may evaluate menisci and articular cartilage when MRI is contraindicated. 2

Age-Specific Considerations

Adolescent-Specific Pathology

• In adolescents, consider OCD (particularly of the medial femoral condyle), discoid meniscus, plica syndrome, and apophyseal injuries as causes of popping. 2, 6
• Hyperintense rim or cysts at osteochondral fragment periphery on MRI are less specific for OCD instability in children compared to adults, but MRI still guides treatment decisions. 2
• Symptomatic discoid meniscus may require operative intervention if conservative treatment fails. 6