What is the appropriate evaluation and treatment plan for a patient with abnormal knee findings, considering their age, medical history, and current symptoms?

Evaluation of Knee Findings

Start with plain radiographs as the initial imaging study for any patient presenting with knee findings, including at minimum anteroposterior and lateral views, plus a tangential patellar view. 1

Initial Imaging Approach

• Radiographs are the mandatory first-line study before any advanced imaging, regardless of whether the presentation is acute trauma or chronic pain 1, 2
• Required views include: anteroposterior projection, lateral view (knee at 25-30 degrees flexion), and tangential patellar view 1, 2
• Approximately 20% of patients inappropriately receive MRI without recent radiographs (within the prior year), which represents a critical practice gap to avoid 1

Clinical Assessment Framework

For Acute Trauma Presentations

Apply Ottawa Knee Rules to determine imaging urgency 1, 2:

• Age ≥55 years
• Focal tenderness at patella or fibular head
• Inability to bear weight for 4 steps immediately after injury
• Inability to flex knee to 90 degrees

If any Ottawa criteria are positive, obtain radiographs immediately 1, 2, 3

For Chronic Pain Presentations

Key history elements to elicit 4, 5:

• Timing and onset (acute vs. insidious)
• Ability to bear weight
• Mechanical symptoms (locking, popping, giving way)
• Constitutional symptoms (fever, weight loss)
• Location specificity (anterior, medial, lateral, posterior)

Critical physical examination components 4, 5, 6:

• Focal tenderness over specific structures (joint line, patella, tibial tubercle, fibular head)
• Joint effusion assessment
• Range of motion testing
• Ligamentous stability testing (Lachman, drawer signs)
• Meniscal testing (McMurray test, joint line tenderness)
• Always examine the hip with range of motion and impingement testing to rule out referred pain 1, 4, 7

When to Proceed to MRI

MRI without contrast is indicated when 1, 2:

• Initial radiographs are normal or show only effusion, but pain persists after 4-6 weeks of conservative treatment
• Radiographs show specific findings requiring surgical planning (osteochondritis dissecans, loose bodies)
• Suspected occult fracture not visible on radiographs
• Significant joint effusion with inability to fully bear weight after 5-7 days
• Mechanical symptoms suggesting meniscal injury (locking, catching)
• Joint instability suggesting ligamentous injury

MRI evaluates for 7:

• Meniscal tears (though these occur with similar frequency in painful and asymptomatic knees in ages 45-55)
• Bone marrow lesions (strongly associated with knee pain intensity)
• Articular cartilage damage
• Subchondral insufficiency fractures
• Synovitis

Critical Pitfalls to Avoid

• Never order MRI without recent radiographs (within the prior year) 1, 4
• Always examine the hip when knee radiographs are unremarkable, as hip pathology commonly refers pain to the knee 1, 4, 7
• Consider lumbar spine evaluation if knee radiographs are unremarkable and clinical evidence suggests radiculopathy or neurogenic claudication 1, 7
• Recognize that asymptomatic meniscal tears are common, especially in older adolescents and middle-aged adults, so MRI findings must correlate with clinical presentation 4, 7

Special Imaging Considerations

CT without IV contrast may be indicated for 1:

• Patellofemoral anatomy evaluation in chronic subluxation or maltracking
• Better characterization of complex fractures (especially tibial plateau)
• Trochlear morphology and tibial tubercle-trochlear groove distance assessment

CTA of lower extremity is indicated for 1, 2:

• Knee dislocation with suspected vascular injury (occurs in ~30% of posterior dislocations)
• Significant trauma with concern for popliteal artery injury

Conservative Management Before Advanced Imaging

For chronic knee pain without red flags, initiate 4-6 weeks of conservative treatment before MRI 4:

• Activity modification
• Physical therapy
• NSAIDs (oral or topical)
• Ice application

Red flags requiring immediate imaging or specialist referral 4:

• Acute trauma with focal tenderness or effusion
• Inability to bear weight
• Constitutional symptoms
• Neurologic deficits
• Palpable mass
• Gross deformity