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Strong Correlation Between Standing Long-Leg Radiographs and CT Scans in Measuring Coronal Knee Alignment
Andreas Fontalis1,2, Thomas Luyckx3, Thomas Vanspauwen4
1Department of Trauma and Orthopaedic Surgery, University College Hospital, London, United Kingdom.
Summary
Computed tomography (CT) scanograms show strong correlation with long-leg radiographs (LLRs) for measuring lower-limb coronal alignment in knee arthroplasty planning. CT scanograms may replace LLRs, but proper patient positioning is crucial for accuracy.
Area of Science:
- Orthopedic surgery
- Medical imaging
- Biomechanical analysis
Background:
- Preoperative planning for robotic-arm-assisted knee arthroplasty relies on accurate lower-limb coronal alignment measurements.
- Long-leg radiographs (LLRs) and computed tomography (CT) scanograms are used, but their comparative accuracy needs evaluation.
Purpose of the Study:
- To assess the correlation between LLRs and CT scanograms for measuring lower-limb coronal alignment.
- To determine if CT scanograms can reliably substitute LLRs in preoperative planning for knee arthroplasty.
Main Methods:
- A multicenter cohort study of 300 patients undergoing robotic-arm-assisted total or unicompartmental knee arthroplasty.
- Measurement of key coronal alignment parameters including hip-knee-ankle angle (HKA), arithmetic HKA (aHKA), medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), joint line obliquity (JLO), and joint-line convergence angle (JLCA).
Main Results:
- Strong correlations (p < 0.001) were found between LLRs and CT scanograms for HKA (0.912), aHKA (0.883), MPTA (0.820), LDFA (0.871), and JLO (0.778).
- Weaker correlation for JLCA in valgus versus varus knees (0.412 vs. 0.518).
- Agreement was influenced by preoperative deformity and CT scan limb positioning; initial JLCA within ±5° showed higher agreement.
Conclusions:
- CT scanograms demonstrate strong correlation with LLRs for estimating knee coronal alignment.
- CT scanograms can potentially replace LLRs in preoperative planning for robotic-arm-assisted knee arthroplasty.
- Appropriate radiographic positioning and vigilance for substantial deformities are essential for optimal agreement.
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