2025 ISAKOS Biennial Congress ePoster
Differences In Coronal Plane Alignment Of The Knee (CPAK) Measured On Long-Leg Radiographs Compared To Computed Tomography For The Patients Undergoing Total Knee Arthroplasty
Kohei Kawaguchi, MD, PhD, Tokyo JAPAN
Mei Lin Tay, PhD, Auckland NEW ZEALAND
Bill Farrington, FRCS, Auckland NEW ZEALAND
Rupert S Van Rooyen, MBChB, FRACS, Auckland NEW ZEALAND
Matthew Walker, MBChB, FRACS, Auckland NEW ZEALAND
Ali Bayan, MBChB, FRACS, Auckland, New Zealand NEW ZEALAND
Simon W. Young, MD, FRACS, Auckland NEW ZEALAND
North shore hospital, Auckland, NEW ZEALAND
FDA Status Not Applicable
Summary
Differences in the CPAK parameters and the CPAK phenotype distributions were found when comparing measurements performed using LLR versus CT
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Abstract
Introduction
Assessment of coronal knee alignment for total knee arthroplasty (TKA) is usually performed with long-leg radiography (LLR) using Coronal Plane Alignment of the Knee (CPAK) classification. Considering the preoperative CPAK could be the key to improve postoperative clinical outcomes in TKA. The use of computed tomography (CT) is increasing for TKA with Robotics and CPAK algorithms have been applied to CT images. However, previous comparative studies regarding the difference between LLR and CT in coronal alignment parameters and phenotype distribution in CPAK have not been reached consensus. The purpose of this study was to compare CPAK parameters and the CPAK phenotype distribution measured with LLR and CT and, to investigate reasons for discrepancies.
Methods
This prospective-radiographic study was performed in 241 consecutive patients in robotic-assisted TKA. Medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), arithmetic hip-knee-ankle-angle (aHKA), joint line obliquity (JLO) in coronal alignment parameters in CPAK and CPAK phenotype distribution measured using preoperative LLR and CT were compared. Actual measurement values of MPTA and LDFA were classified into three groups based on differences between LLR and CT (LLR = CT (≤2°), LLR < CT (>2°) and LLR > CT (>2°)) and patient’s demographics and radiographic parameters among three groups were compared to identify the risk factors of discrepancies between LLR and CT.
Results
Differences in CPAK parameters measured LLR and CT were found, for MPTA (mean 87.1°vs 86.7° p<0.01), LDFA (87.8°vs 87.1° p<0.01) and JLO (174.9°vs 173.9° p<0.01). The distribution of CPAK phenotype was different(p=0.02). Apex distal JLO (CPAK Type I, II, III) was lower when measured using LLR (73.5 % vs CT 82.6%), and Neutral JLO (Type IV, V, VI) was higher when measured using LLR (25.4 % vs CT 17.0 %). The proportion of LLR = CT, LLR > CT, and LLR < CT group was respectively 66.0 %, 21.6 % and 12.4 % in MPTA and 84.6 %, 13.3 % and 12.1 % in LDFA. Patients with LLR < CT MPTA discrepancy demonstrated preoperative larger flexion knee contracture angle and larger preoperative varus knee deformity.
Conclusion
Differences in the CPAK parameters and the CPAK phenotype distributions were found when comparing measurements performed using LLR versus CT. Coronal knee alignment and knee flexion contracture were associated with differences in MPTA measurements.