Knee pain

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Diagnostic approach

• Targeted clinical evaluation
• X-ray: initial imaging for most patients (See also “Ottawa knee rules.”)
• CT: to evaluate complex fracture or dislocation
• MRI: suspected ligamentous or meniscal injury
• Ultrasound: effusion or bursitis
• Cultures and PCR testing: of synovial, blood, and exposed mucosa for suspected gonococcal arthritis
• Arthrocentesis with synovial fluid analysis: to help differentiate between subtypes of arthritis
• See “Diagnosis of septic arthritis” for labs for infection and inflammation.

Management checklist

• Uncomplicated musculoskeletal pain: POLICE principle, pain management, WBAT
• Acute soft tissue injuries: Stabilize with a functional brace.
• Consult orthopedic surgery for patients with acute traumatic injuries, severe mechanical issues, or end-stage osteoarthritis.
• See also “Acute internal knee derangement,” “Acute gout management,” and “Treatment of septic arthritis.”

Red flag features

• Inability to bear weight
• Reduced range of motion
• Severe pain or swelling
• Fever or signs of infection
• Deformity or instability
• Decreased or absent pulses
• Signs of peroneal or tibial nerve injury (sensory loss, weakness)
• Knee dislocation or fracture
• Extensor mechanism disruption (patellar or quadriceps tendon rupture)

Life-threatening causes

• Septic arthritis
• Tibiofemoral dislocation with neurovascular injury (e.g., popliteal artery injury)
• Acute compartment syndrome

Knee pain can arise from acute traumatic causes (e.g., knee ligament injuries, meniscus tears, or fractures) and nontraumatic conditions (e.g., knee osteoarthritis). Clinical assessment includes pain characteristics (e.g., onset, duration, and exacerbating symptoms) and a focused examination of the knee. Imaging and/or laboratory studies (e.g., synovial fluid analysis) are based on the suspected underlying cause. Knee radiographs are typically the first-line imaging modality. Management is determined by the underlying cause.

Lower extremity osteopathy is discussed separately.

Traumatic ^[2]

See ”Acute internal knee derangement” for details.

• Knee ligament injuries
• Traumatic meniscus tears
• Fractures (e.g., tibial plateau fractures, proximal fibular fractures, patellar fracture)
• Dislocations (e.g., tibiofemoral joint dislocation, patellar dislocation)

Nontraumatic ^[2][3][4]

• Degenerative or overuse
  • Knee osteoarthritis
  • Degenerative meniscus tears
  • Chondromalacia patellae
  • Patellofemoral pain syndrome
  • Tendinopathies (e.g., patellar tendinopathy, iliotibial band syndrome)
  • Bursitis (e.g., prepatellar bursitis)
  • Pes anserinus pain syndrome
  • Osgood-Schlatter disease
• Infectious: septic arthritis
• Inflammatory
  • Crystalline arthropathies (e.g., CPPD, gout)
  • Rheumatoid arthritis
  • Popliteal cyst
• Referred pain (e.g., from hip or spine pathology)

Focused history ^[2]

• Inciting factor or injury
• Onset, location, alleviating or aggravating factors
• Other localizing pain (e.g., hip, spine)
• Constitutional symptoms
• Past medical history
  • Systemic illnesses (e.g., gout, autoimmune conditions)
  • Prior knee injury or surgery

Focused examination ^[2]

• Examination of the knee (e.g., joint effusion, Lachman test, McMurray test)
• Skin and neurovascular examination
• Examination of the spine
• Examination of gait

In an undifferentiated acute traumatic knee injury, acute pain management and initial investigations (e.g., imaging) are advised before clinical evaluation, which may be limited due to pain and swelling. ^[5]

Choice of diagnostic study is guided by the suspected diagnosis and whether the presentation is acute or chronic.

Imaging ^[6][7]

• Knee x-rays
  • For acute traumatic knee pain according to Ottawa knee rules: full knee x-ray series
  • For chronic knee pain ≥ 6 weeks: frontal (e.g., anteroposterior), lateral, and tangential patella views ^[2]
• Knee ultrasound: for effusions and/or evaluation of superficial structures (e.g., prepatellar bursa)
• CT knee without contrast: for acute knee pain in patients with complex fractures (e.g., tibial plateau fractures) or suspected occult fractures
• CT angiogram lower extremity with IV contrast: for significant trauma (e.g., suspected tibiofemoral dislocation)
• MRI knee without contrast
  • For acute knee pain with any of the following:
    • Occult fracture suspected
    • Acute internal knee derangement
    • Complex fractures
    • Meniscus tears or knee ligament injuries ^[3]
  • For chronic knee pain with negative initial knee x-rays and/or any of the following:
    • Suspected osteomyelitis
    • Joint effusion
    • Osteochondritis dissecans
    • Loose bodies
    • History of cartilage or meniscal repair
    • Prior osseous injury

Laboratory studies ^[2]

• CBC and ESR: assessment for infection or inflammation
• Rheumatoid factor, anti-CCP: evaluation for rheumatoid arthritis
• Serum uric acid: for suspected gout
• Synovial fluid analysis: for suspected septic arthritis or crystalline arthropathy
• Cultures and PCR testing: for suspected disseminated gonococcal arthritis