Predicting Femoral Component Rotation in Mechanically Aligned Total Knee Arthroplasty: Can Preoperative Three-Joint Alignment Radiograph Help?

Articles in Press

Document Type : RESEARCH PAPER

Authors

a Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran, Iran. b Department of Orthopedic Surgery, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran.

10.22038/abjs.2025.83023.3781

Abstract

Objectives: Achieving precise femoral component external rotation (FCER) is crucial in Total Knee Arthroplasty (TKA) and prevents patellofemoral maltracking, implant loosening, pain, and wear. While CT scans and MRIs can help determine the rotational profile of the distal femur, their use is limited due to concerns about radiation and cost. This study explored the possible role of a preoperative three-joint alignment radiograph in predicting the necessary FCER in mechanically aligned TKA.

Methods: This retrospective cohort study was conducted on 922 patients (1208 knees) with varus knees who underwent primary TKA by a single knee surgeon from 2018 to 2020. The angular parameters of the three-joint alignment radiograph and FCER were extracted from the JRRC Knee Registry. These angular parameters included lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), joint line congruency angle (JLCA), and varus angle (VA). FCER had been determined intraoperatively based on standard anatomical criteria, including Whiteside’s line, trans-epicondylar line, posterior condylar axis, and anteroposterior axis and assessment of the proximal tibia cut. Data analysis was done using SPSS 26.

Results: We had 922 patients (57.9 % female, 42.1 % male) with a mean age of 65.39 ± 8.03 (43- 90) years. The FCER was 0° in 0.33%, 3° in 83.6%, 5° in 15.23%, and 7° in 0.82% of patients. FCER showed no correlation with MPTA, LDFA, and VA but significantly correlated with JLCA/LDFA, JLCA/MPTA, and JLCA/VA with cut-offs at 0.11, 0.12, and 0.62, respectively. JLCA/MPTA appeared to be the best predictor for FCER in TKA (sensitivity=48%, specificity=81%, and accuracy 0.67).

Conclusions: Preoperative three-joint alignment radiographs can guide the surgeon regarding the required FCER during TKA. If the ratios above exceed the established cut-offs, an FCER >3° will probably be necessary.

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The Archives of Bone and Joint Surgery

Articles in Press, Accepted Manuscript
Available Online from 05 October 2025

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History

  • Receive Date: 13 October 2024
  • Revise Date: 14 January 2025
  • Accept Date: 22 January 2025

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