How many radiographic views are recommended for the initial evaluation of a knee complaint?

Initial Knee Radiographic Evaluation: Two Views Required

For the initial evaluation of acute knee trauma, a minimum of two radiographic views—anteroposterior (AP) and lateral—should be obtained. 1

Standard Two-View Protocol

The American College of Radiology definitively establishes that two views constitute the minimum standard for initial knee trauma imaging:

• Anteroposterior view: Weight-bearing when possible, to assess overall alignment and joint space 1
• Lateral view: Obtained with the knee at 25-30 degrees of flexion in the lateral decubitus position, with the patella in profile 1

The lateral view is particularly critical because it allows evaluation for joint effusion and, when obtained as a cross-table lateral with horizontal beam, enables visualization of lipohemarthrosis—a key finding in intra-articular fractures. 1

When to Add a Third View

Additional views beyond the standard two are supplemental, not routine, and should be obtained based on specific clinical suspicion:

• Patellofemoral (skyline) view: Add when patellar fracture, subluxation, or dislocation is suspected 1
• Internal/external oblique views: Consider for better characterization of specific fracture patterns 1

The ACR guidelines explicitly state these are "additional commonly performed supplemental imaging projections" rather than routine requirements. 1

Clinical Decision Framework

Apply this algorithm:

1. First, determine if imaging is needed using Ottawa Knee Rules (age >55, isolated patellar tenderness, isolated fibular head tenderness, inability to flex to 90°, inability to bear weight for 4 steps) 1, 2, 3

2. If imaging indicated, order two views minimum (AP + lateral) 1

3. Add patellofemoral view only if focal patellar tenderness or clinical suspicion for patellar pathology exists 1, 3

Common Pitfalls to Avoid

• Don't routinely order three views for all knee complaints—this increases cost and radiation exposure without improving diagnostic yield in most cases 1
• Don't skip the lateral view—some pathologies (posterior structures, quadriceps/patellar tendon injuries, certain avulsion fractures) are only visible on lateral projection 4
• Don't obtain patellofemoral views reflexively—reserve them for specific patellar concerns, as they have higher technical failure rates and may not be interpretable 5, 6

The evidence consistently supports two views as the standard, with selective addition of a third view based on clinical findings rather than routine three-view protocols. 1, 3