When are four views of the knee, including anteroposterior (AP), lateral, sunrise, and tunnel views, necessary for a patient with a suspected complex knee injury or condition, such as a fracture, dislocation, or osteochondral defect, particularly in those with a history of trauma, osteoarthritis, or underlying conditions like osteoporosis?

When Four Views of the Knee Are Needed

For acute knee trauma, a minimum of two views (AP and lateral) is standard, but four views should be obtained when there is suspected patellar fracture, subluxation/dislocation, or when initial two-view radiographs are negative despite high clinical suspicion for fracture. 1, 2

Standard Initial Imaging Protocol

Two views (AP and lateral) are sufficient for most acute knee trauma evaluations when patients meet Ottawa Knee Rule criteria (age >55, focal tenderness at patella or fibular head, inability to bear weight for 4 steps, or inability to flex knee to 90 degrees). 1, 2

• The lateral view should be obtained with the knee at 25-30 degrees of flexion in the lateral decubitus position, demonstrating the patella in profile. 1
• A cross-table lateral view with horizontal beam enables visualization of lipohemarthrosis, which indicates intra-articular fracture. 1, 2, 3

When to Add Supplemental Views (Making It Four Views)

Suspected Patellar Pathology

Add a patellofemoral view (sunrise/Merchant view) when patellar fracture, subluxation, or dislocation is suspected. 1, 2

• Vertical patellar fractures are often nondisplaced and best evaluated with sunrise views. 4
• Osteochondral fractures of the patella are optimally visualized on sunrise or internal oblique views. 4
• Clinical indicators warranting this additional view include inability to perform straight leg raise, palpable patellar defect, severe focal patellar tenderness, or large knee effusion. 2

Suspected Tibial Plateau or Posterior Compartment Injuries

Add internal and external oblique views when standard two views are negative but clinical suspicion remains high for fracture. 1, 5

• Four-view examinations demonstrate significantly higher sensitivity (85%) compared to two views (79%) for acute fracture detection. 5
• Tibial plateau fractures clinically suspected but unseen on standard views may be visualized on tangential or tunnel projections. 4
• Segond fractures (lateral capsular avulsion indicating ACL injury) occasionally are seen only on tunnel views when not visible on standard AP radiographs. 4

Specific Fracture Patterns That May Require Additional Views

Oblique views are particularly valuable for detecting subtle avulsion fractures and assessing joint congruity. 1, 4

• Fibular head fractures and dislocations require careful evaluation of tibiofibular joint congruity on lateral projection, sometimes necessitating oblique views for confirmation. 4
• Avulsion fractures from proximal or distal patellar poles are best evaluated with lateral views. 4

Common Pitfalls to Avoid

• Do not skip imaging in patients with gross deformity, palpable mass, penetrating injury, prosthetic hardware, altered mental status, neuropathy, or history suggesting increased fracture risk—these patients require radiographs regardless of Ottawa Rule criteria. 1
• Do not order MRI as the initial study; radiographs must come first unless specific contraindications exist. 2
• Do not assume two views are adequate when lipohemarthrosis is present on lateral view—this indicates intra-articular fracture and warrants additional views or advanced imaging. 1, 3
• Do not miss occult fractures by failing to obtain appropriate supplemental views when clinical suspicion is high despite negative initial radiographs. 4, 5

Algorithm for View Selection

1. Start with AP and lateral views for all patients meeting Ottawa Knee Rule criteria. 1, 2
2. Add patellofemoral view if any patellar-specific clinical findings are present (inability to straight leg raise, palpable defect, focal tenderness). 1, 2, 4
3. Add oblique views if initial two views are negative but clinical suspicion for fracture remains high, particularly for tibial plateau or subtle avulsion injuries. 4, 5
4. Consider cross-table lateral specifically to assess for lipohemarthrosis when intra-articular fracture is suspected. 1, 2

Next Steps When Radiographs Are Negative

MRI without contrast is the appropriate next study for suspected occult fractures or internal derangement when radiographs are negative but clinical suspicion remains high. 2

• CT may be considered for better characterization of suspected occult bony injuries, but MRI remains superior for soft tissue evaluation. 1, 2
• Do not routinely use bone scan, ultrasound, MR arthrography, or MRA as initial or follow-up studies for acute knee trauma. 1, 2