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Evaluating the reliability of 2D techniques for tibial anatomical axis definition and posterior tibial slope
1Department of Orthopedic Surgery, Zhongshan Hospital, Fudan University, 180 Fenglin Rd, Shanghai, 200032, China.
Introduction:
Various 2D imaging techniques have been introduced to define the tibial anatomical axis and measure the posterior tibial slope (PTS), but their reliability remains uncertain.
Methods:
This study included 104 patients who underwent full-length tibial computed tomography (CT) scans. The anatomical axis was defined at two levels in tomographic imaging: at the tibial head and below the tibial tubercle. For the lateral projection technique, the axis was manually drawn. A 3D tibial coordinate system was established to define the standard anatomical axis and measure the medial and lateral PTS (MPTS and LPTS). The anatomical axes defined by the 2D techniques were imported into the 3D coordinate system to evaluate their deviation angles. The agreements of MPTS and LPTS measurements across the three techniques were evaluated.
Results:
Defining the anatomical axis at the tibial head using tomographic imaging introduced instability, leading to only moderate agreement with the 3D reference values for MPTS (intraclass correlation coefficient (ICC) = 0.659, 95 % CI: 0.535-0.756) and LPTS (ICC = 0.622, 95 % confidence interval [CI]: 0.489-0.727). In contrast, establishing the axis below the tibial tubercle improved stability and produced strong agreement with the 3D reference for MPTS (ICC = 0.788, 95 % CI: 0.702-0.851) and LPTS (ICC = 0.78, 95 % CI: 0.692-0.846). The lateral projection technique yielded a minimal anatomical axis deviation angle and strong MPTS agreement with the 3D reference (ICC = 0.774, 95 % CI: 0.684-0.841), but LPTS agreement was poor (ICC = 0.4, 95 % CI: 0.259-0.574).
Conclusion:
In tomographic imaging, the anatomical axis definition below the tibial tubercle yields greater stability and more reliable PTS measurements. Although the lateral projection technique accurately defines the axis, it is only applicable to MPTS assessment.
Implications For Practice:
The tibial anatomical axis should be defined below the tibial tuberosity when measuring PTS using tomographic imaging.
