What imaging is required for a patient scheduled for right total knee arthroplasty who experienced a knee buckling episode yesterday and nearly fell?

Imaging for Pre-TKA Patient with Knee Buckling Episode

Start with plain radiographs (anteroposterior and lateral views) of the right knee immediately 1.

Initial Imaging Approach

A knee buckling episode with near-fall constitutes acute knee trauma and warrants radiographic evaluation. The ACR Appropriateness Criteria (2020) explicitly state that radiographs should be obtained in patients with prosthetic hardware regardless of clinical decision rules 1. While this patient doesn't yet have prosthetic hardware, they are scheduled for TKA, making baseline imaging essential.

Specific Radiographic Views Required

Obtain at minimum:

• Anteroposterior (AP) view of the affected knee
• Lateral view with knee at 25-30 degrees flexion in lateral decubitus position, demonstrating patella in profile 1
• Consider cross-table lateral with horizontal beam to visualize lipohemarthrosis if intra-articular fracture suspected 1
• Patellofemoral view if patellar instability or fracture suspected given the buckling mechanism 1

Clinical Decision Framework

The knee buckling episode likely meets Ottawa Rule criteria (inability to bear weight or near-inability), which mandates radiographic evaluation 1. The guidelines emphasize that physician judgment should supersede clinical decision rules 1, and in a pre-surgical patient, any acute traumatic event requires imaging to:

• Rule out acute fracture (particularly periprosthetic or stress fractures in osteoarthritic bone)
• Assess for joint effusion suggesting acute injury
• Document baseline status before proceeding with planned surgery
• Identify any contraindications to proceeding with scheduled TKA

Advanced Imaging Considerations

If Radiographs Are Negative But Clinical Concern Persists:

MRI is NOT routinely indicated for pre-TKA evaluation 2. A 2023 study found that 7.68% of TKA patients received MRI within one year prior to surgery, representing potential overutilization costing $45 million, as TKA is performed for advanced degenerative changes already evident on plain films 2.

However, MRI may be justified in this specific scenario if:

• Radiographs are negative AND
• There is concern for acute ligamentous injury (ACL/PCL tear) that could affect surgical planning
• Suspicion of occult fracture that would delay surgery
• Need to evaluate soft tissue injury that might contraindicate immediate surgery 1

CT is an alternative if radiographs are negative and occult fracture is the primary concern, with 100% sensitivity for tibial plateau fractures versus 83% for radiographs 1. CT also has high specificity (98%) for bony avulsion fractures 1.

Critical Pitfalls to Avoid

1. Do not skip imaging assuming the knee is "already bad" since TKA is planned - acute fractures or ligamentous injuries change surgical timing and approach
2. Do not order MRI reflexively - it's overutilized in pre-TKA patients and rarely changes management 2
3. Do not ignore the buckling mechanism - this suggests either extensor mechanism failure, ligamentous instability, or acute structural damage requiring evaluation
4. Document any acute findings that might necessitate delaying TKA or modifying the surgical approach

Practical Algorithm

1. Immediate plain radiographs (AP, lateral, consider patellofemoral views)
2. If fracture identified: Delay TKA, treat fracture appropriately
3. If radiographs negative but high clinical suspicion for structural injury affecting surgical candidacy: Consider CT for occult fracture or MRI for ligamentous/meniscal injury
4. If imaging reassuring: Proceed with physical therapy/strengthening to address buckling before scheduled TKA

The buckling episode in a pre-TKA patient represents a red flag that cannot be dismissed without imaging evaluation, as it may indicate acute pathology requiring intervention before proceeding with elective arthroplasty.