What is the appropriate initial evaluation and management for a patient with knee compartment narrowing after a fall presenting with pain and mild functional limitation?

Initial Evaluation and Management of Knee Compartment Narrowing After Fall

Obtain anteroposterior and lateral knee radiographs immediately as the first-line imaging study, then manage based on clinical findings and radiographic results rather than pursuing advanced imaging for compartment narrowing alone. 1, 2

Initial Imaging Protocol

Plain radiographs are the mandatory first step for any patient meeting Ottawa Knee Rule criteria, which include focal tenderness, joint effusion, or inability to bear weight. 1, 3

• Obtain a minimum of two views: anteroposterior and lateral (with knee flexed 25-30 degrees). 1, 2
• The lateral view allows evaluation for joint effusion and, when obtained as a cross-table horizontal beam projection, can demonstrate lipohemarthrosis indicating intra-articular fracture. 1
• Additional views (patellofemoral, internal/external oblique) may be added based on specific clinical findings such as patellar tenderness. 1

Interpretation of Compartment Narrowing on Radiographs

Compartment narrowing visible on plain films typically represents pre-existing osteoarthritis rather than acute traumatic pathology. 2

• In patients with known osteoarthritis who fall, negative radiographs (no fracture) require no further imaging as standard of care. 2
• The presence of compartment narrowing does not automatically necessitate MRI; such findings are often chronic and unrelated to the acute trauma event. 2
• Approximately 20% of patients inappropriately receive MRI without recent radiographs or clear clinical indication. 2

Clinical Assessment to Guide Further Management

Reassess the patient 2 days after injury to evaluate specific clinical parameters that determine whether advanced imaging is needed. 2

Key clinical findings to document:

• Weight-bearing ability: Inability to bear weight after 5-7 days warrants consideration of MRI. 2
• Joint effusion: Large effusion with inability to bear weight should prompt joint aspiration to exclude septic arthritis. 2
• Mechanical symptoms: Locking or catching suggests meniscal injury requiring MRI evaluation. 2
• Joint instability: Instability on examination indicates ligamentous injury and warrants MRI or orthopedic referral. 2
• Range of motion: Inability to flex to 90 degrees is an Ottawa criterion requiring initial radiographs. 1, 3

When to Order MRI After Negative Radiographs

MRI without contrast is appropriate only when persistent clinical findings suggest internal derangement, not based on radiographic compartment narrowing alone. 2, 3

Specific indications for MRI include:

• Persistent inability to bear weight after 5-7 days of conservative management. 2
• Significant joint effusion with mechanical symptoms (locking, catching). 2
• Clinical instability suggesting cruciate or collateral ligament injury. 2
• Audible "pop" at injury with persistent pain and limited mobility despite normal radiographs. 3

Do not order MRI solely because the patient requests it or "to be thorough"—this does not align with evidence-based guidelines. 2

When to Order CT Instead of MRI

CT is indicated when occult fracture is specifically suspected, not for soft tissue evaluation. 1, 2

• CT achieves 100% sensitivity for tibial plateau fractures versus 83% for plain radiographs. 1, 2
• CT has low sensitivity for meniscal and ligamentous injuries, limiting its usefulness for internal derangement. 2
• Consider CT when there is focal bony tenderness with negative radiographs and high clinical suspicion for fracture. 1

Critical Red Flags Requiring Immediate Action

Certain findings mandate urgent orthopedic referral regardless of radiographic compartment narrowing. 2

• Gross deformity or palpable mass. 1, 2
• Vascular compromise (absent pulses, pallor)—knee dislocations carry ~30% risk of vascular injury requiring urgent CTA. 2, 4
• Inability to bear weight with large effusion (aspirate to exclude septic arthritis). 2

Conservative Management Algorithm

For patients with compartment narrowing on radiographs, negative for fracture, and mild functional limitation:

1. Initial management: Rest, ice, compression, elevation, and NSAIDs for pain control. 5
2. Reassessment at 2 days: Evaluate weight-bearing, effusion, stability, and range of motion. 2
3. Reassessment at 5-7 days: If unable to bear weight or mechanical symptoms persist, order MRI without contrast. 2
4. Orthopedic referral: Arrange expedited follow-up if instability, persistent effusion, or mechanical symptoms are present. 5

Common Pitfalls to Avoid

• Do not skip plain radiographs and proceed directly to MRI—radiographs must precede advanced imaging to exclude fracture. 1, 2
• Do not assume compartment narrowing from chronic osteoarthritis requires MRI after trauma—meniscal tears are frequently incidental in older adults, and prevalence of asymptomatic tears is high in patients >70 years. 2
• Do not order MR arthrography for acute trauma—it is reserved for chronic conditions and adds unnecessary cost without improving diagnostic yield. 2
• Do not forget to image the hip if knee radiographs are unremarkable—hip pathology commonly refers pain to the knee, especially in elderly patients. 2, 4