Coronal Plane Alignment of the Knee Classification Remains Best Determined on Long-Leg Radiographs Compared to...

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanical analysis

Background:

• Coronal plane alignment of the knee (CPAK) classification is crucial for constitutional limb alignment assessment.
• Traditionally, CPAK is determined using standing long-leg radiographs (LLRs).
• Alternative imaging like CT scanograms and short knee radiographs are used when LLRs are unavailable for total knee arthroplasty (TKA).

Purpose of the Study:

• To evaluate the correlation of lower limb alignment measurements between LLRs, CT scanograms, and short knee radiographs.
• To assess the agreement of CPAK classification derived from these three imaging modalities.

Main Methods:

• Retrospective review of 300 knees undergoing robotic-assisted TKA with preoperative LLRs, CT scanograms, and short knee radiographs.
• Independent measurement of mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle by two reviewers for each modality.
• Calculation of CPAK phenotypes and assessment of agreement between imaging techniques.

Main Results:

• Strong correlations (r > 0.8) were observed for mLDFA and mechanical medial proximal tibial angle measurements between LLRs and both CT scanograms and short knee radiographs.
• Moderate agreement was found for CPAK classification: 61.7% with CT scanograms and 68.7% with short knee radiographs compared to LLRs.
• Over 30% of knees showed a different CPAK classification when using CT scanograms or short knee radiographs compared to LLRs.

Conclusions:

• Despite strong measurement correlations, CT scanograms and short knee radiographs demonstrate only moderate agreement for CPAK classification.
• LLRs remain the gold standard for determining CPAK in TKA planning and outcome reporting.
• Surgeons should utilize LLRs when CPAK classification is critical for surgical strategy or reporting.