What is the recommended imaging protocol for a patient presenting with knee pain and suspected Lateral Collateral Ligament (LCL) tear?

Imaging Protocol for Suspected LCL Tear with Knee Pain

Start with standard knee radiographs (AP and lateral views at 25-30° flexion), then proceed directly to MRI if radiographs are negative or non-diagnostic, as MRI is the gold standard for detecting ligamentous injuries including LCL tears and associated soft-tissue damage. 1

Initial Imaging: Plain Radiographs

Obtain radiographs first to exclude fractures and bony avulsions, which commonly accompany LCL injuries and would alter surgical planning. 1

• The minimum two-view series includes anteroposterior (AP) and lateral views, with the lateral taken at 25-30 degrees of knee flexion. 2
• Add a tangential patellar view to complete the standard three-view series for comprehensive initial evaluation. 2
• Radiographs are mandatory even when soft-tissue injury seems obvious clinically, as approximately 20% of patients inappropriately receive MRI without recent radiographs. 2
• Look specifically for Segond fractures (lateral capsular avulsion), which indicate anterolateral ligament injury and frequently accompany cruciate ligament tears. 1
• The lateral view can identify lipohemarthrosis (fat-fluid level) when obtained as a cross-table lateral with horizontal beam, indicating intra-articular fracture. 2

Advanced Imaging: MRI as Next Step

If radiographs show no fracture but LCL tear is suspected, MRI is the definitive next study to evaluate the ligament itself and identify concomitant injuries. 1

Why MRI is Essential for LCL Evaluation:

• MRI detects 93.5% of acute knee injuries which are soft-tissue rather than osseous. 1
• MRI provides accurate diagnosis that facilitates earlier surgical intervention and improves treatment decision-making. 1
• LCL tears rarely occur in isolation—MRI identifies associated injuries to the ACL, PCL, posterolateral corner structures (popliteus tendon, popliteofibular ligament), and menisci that would require combined reconstruction. 3, 4
• MRI detects bone marrow contusions that predict specific injury patterns and associated soft-tissue damage. 1
• Posterolateral corner injuries occur in 19.7% of ACL ruptures and, if missed, lead to considerable morbidity and reconstruction failure. 1

MRI Technical Considerations:

• Standard MRI protocols are sufficient; MR arthrography is not routinely indicated for acute trauma evaluation. 1
• MRI performed within 6 weeks of acute trauma detects more anterolateral ligament injuries than delayed imaging, as some injuries become less visible with chronicity. 1

What NOT to Do

Avoid these common pitfalls:

• Do not skip radiographs and go directly to MRI, even when effusion or instability strongly suggests ligamentous injury—you must exclude fractures first. 2
• Do not order CT as the next study for suspected LCL tear—while CT has 87.5-100% sensitivity for ACL tears, it shows low sensitivity for collateral ligament injuries and is inferior to MRI for soft-tissue evaluation. 1
• Do not rely on ultrasound, which has limited utility in acute knee trauma and cannot adequately assess deep ligamentous structures. 1
• Do not use bone scan with SPECT/CT—this modality is not routinely indicated and has lower sensitivity than MRI for meniscal and ligamentous injuries. 1

Clinical Examination Pearls

Before imaging, document these findings that influence management:

• Perform varus stress testing—isolated LCL tears increase varus opening by 1-4°, while combined LCL-popliteus injuries show 5-9° increased opening. 4
• Check the heel height test (modified external rotation recurvatum test), which facilitates detection of LCL tears combined with ACL injury. 4
• Document ability to bear weight and flex to 90°, as these findings guide whether imaging is needed per Ottawa Knee Rules. 2, 5
• Consider arthrocentesis if significant effusion is present to rule out lipohemarthrosis (indicating occult fracture) or septic arthritis. 6

Algorithmic Summary

1. Patient presents with knee pain and suspected LCL tear → Obtain standard radiographs (AP + lateral at 25-30° flexion + patellar view). 2
2. If radiographs show avulsion fracture → Surgical consultation for repair consideration. 1
3. If radiographs negative but clinical suspicion remains → Proceed to MRI for definitive ligamentous evaluation. 1
4. MRI reveals isolated grade I-II LCL tear → Conservative management typically appropriate. 3
5. MRI shows complete LCL tear or combined posterolateral corner injury → Surgical reconstruction indicated, especially with >9-10 mm arthroscopic opening. 3, 4