What is the initial workup for a patient presenting with knee pain?

Initial Workup for Knee Pain

The initial workup for knee pain should begin with radiographs, which should include at least anteroposterior and lateral views of the affected knee, especially in patients meeting Ottawa rule criteria with focal tenderness, effusion, or inability to bear weight. 1

History and Physical Examination Components

• Assess for acute trauma versus chronic pain (pain persisting >3 months) to guide appropriate workup pathway 2, 3
• Evaluate for focal tenderness, effusion, and weight-bearing ability, which are key criteria in the Ottawa rules for determining need for imaging 1
• Document presence of gross deformity, palpable mass, penetrating injury, prosthetic hardware, or altered mental status, which warrant immediate radiographic evaluation regardless of other findings 1
• Assess for mechanical symptoms such as locking, catching, or giving way which may indicate meniscal or ligamentous pathology 2
• Consider age-related patterns: osteoarthritis is most common in patients >45 years, while patellofemoral pain typically affects those <40 years 2

Initial Imaging Recommendations

For Acute Knee Trauma:

• Radiographs should be the initial imaging modality when one or more Ottawa rule criteria are present 1
• Minimum of two radiographic views (anteroposterior and lateral) should be obtained 1
• Additional views may include:
  • Cross-table lateral view to visualize lipohemarthrosis in intra-articular fractures 1
  • Patellofemoral view for suspected patellar fractures or subluxation/dislocation 1
  • Internal and external oblique views for comprehensive evaluation 1

For Chronic Knee Pain:

• Radiographs should include at least one frontal projection (anteroposterior, Rosenberg, or tunnel), a tangential patellar view, and a lateral view 1
• Consider radiographs of the hip if knee radiographs are unremarkable and referred pain from the hip is suspected 1
• Consider radiographs of the lumbar spine if knee radiographs are unremarkable and referred pain from the lower back is suspected 1

Advanced Imaging Considerations

• MRI is not routinely used as the initial imaging study for acute knee trauma but should be considered when:

  • Initial radiographs are normal but pain persists 1
  • Surgery is being contemplated 4, 5
  • Evaluation of soft tissue structures (menisci, ligaments, cartilage) is needed 1, 5

• CT may be appropriate as the next imaging study when:

  • Radiographically occult fractures are suspected 1
  • Detailed evaluation of patellofemoral anatomy is needed for chronic pain related to subluxation or maltracking 1

Common Pitfalls and Caveats

• Avoid ordering MRI without recent (within the prior year) radiographs, which occurs in approximately 20% of patients with chronic knee pain 1
• Be aware that meniscal tears are often incidental findings in older patients, with the majority of people over 70 years having asymptomatic tears 1
• Remember that clinical judgment should supersede clinical guidelines in specific cases 1
• Ultrasound is not routinely used as the initial imaging study for knee pain but can be useful for detecting synovial pathology 1, 4

Special Considerations

• For patients with suspected fracture but normal radiographs, CT has shown 100% sensitivity in detecting tibial plateau fractures compared to 83% with radiographs 1
• In chronic knee pain with normal radiographs, MRI can detect bone marrow lesions, which are associated with increased pain, especially in males or patients with family history of osteoarthritis 1
• For patients with suspected internal derangement after trauma with normal radiographs, MRI is the preferred next study rather than proceeding directly to arthroscopy 5