Comparison of weight-bearing full-length radiography and three-dimensional computed tomography scan-based models for the assessment of knee joint coronal alignment following total knee arthroplasty

Abstract

Abstract Purpose: We evaluated measurement reliability and validity of long-leg radiography (LLR) after total knee arthroplasty (TKA) by comparing postoperative three-dimensional computed tomography (3DCT) scans of the lower extremities.Methods: We retrospectively collected data from 55 knees that underwent postoperative 3DCT, 5-day and 6-month LLR for coronal alignment after TKA. Coronal femoral component angle (CFA) and coronal tibial component angle (CTA) were measured with postoperative 3DCT, 5-day and 6-month LLR. The correlations between the hip–knee–ankle angle (HKAA), CFA, and CTA measured using 3DCT scans and radiographs (5-day and 6-month LLR) were analysed using Pearson’s correlation coefficient (PCC). Bland-Altman plots were constructed to assess agreement between 5-day and 6-month LLR and3DCT scan measurements.Results: The mean difference in the HKAA between 3DCT and 5-day and 6-month LLR was 1.3°±1° and 1.1°±0.7°, respectively. Differences of >1° in the HKAA between 3DCT and LLR were observed in 31 (56.4%) and 28 (50.9%) knees during 5-day and 6-month LLR, respectively. Differences of >2° in these parameters were observed in 15 (27.3%) and 9 (16.4%) knees during 5-day and 6-month LLR, respectively. However, 3DCT scan and LLR measurements showed a strong correlation (PCC, 0.81–0.92; P < 0.000) for all HKAA, CFA, and CTA, and the validity of the Bland-Altman plot was within acceptable limits.Conclusion: Coronal alignment measurement using LLR yielded good reliability and validity. However more than half of the HKA angle values measured by 3DCT scan and radiographs differed by more than 1°, and approximately 20% differed by more than 2°.Level of Evidence: Level IV