Characterizing Three-Dimensional Alignment of the Hip, Knee, Ankle and Foot under Physiological Upright Load. A Weight-Bearing Computed Tomography Study in Arthritic Joints and Healthy Controls

Abstract

Category: Ankle Arthritis; Other Introduction/ Purpose: Lower limb alignment assessment is commonly performed using two-dimensional (2D) conventional- radiographs. Weight-Bearing Computed-Tomography (WBCT) imaging that allows concomitant 3D imaging of the hip, knee, ankle, and foot, a more complete and multidimensional assessment of the entire overall lower limb alignment is now possible. The aims of this study were: (1) to characterize the normal relative 3D alignment of the center of the Hip, Knee, and Ankle joints in relation to the weight bearing Foot Tripod in a cohort of healthy control volunteers with no lower extremity pathologies, using WBCT imaging. (2) to perform the same 3D WBCT assessment in a cohort of patients with either hip osteoarthritis (HOA), knee osteoarthritis (KOA) or ankle osteoarthritis (AOA), and to compare the results between arthritic cases and controls. Methods: Prospective comparative and controlled cohort-study contained 7 HOA limbs (4 patients), 17 KOA limbs (10 patients), 7 AOA limbs (4 patients) and 10 control limbs (5 patients) that received WBCT imaging of the full lower extremity. Using multiplanar reconstruction WBCT images, 3D landmark coordinates (on X, Y, and Z planes) were manually measured by two observers. The utilized software (CubeVue®) generated an automatic calculation of the Foot-Hip Offset (FHO), Foot-Knee Offset (FKO) and Foot and Ankle Offset (FAO). The relationship between the center of the hip, knee and ankle joints and the bisecting line of the foot tripod was assessed and compared between HOA, KOA, AOA patients and controls. Examples of measurements for arthritic patients and controls is presented in Figure 1. Continuous data was assessed for normality with the Shapiro-Wilk test, and variables were compared using ANOVA or Kruskal- Wallis Rank Sum. P-Values of less than 0.05 were considered significant. Results: The average FAO and 95%-Confidence-intervals-(CI) for respectively HOA, KOA, AOA and controls were respectively: 3.62% (0.4 to 6.8) (neutral), 2.8% (0.78 to 4.9) (neutral), -4.68% (-7.8 to -1.4) (varus), and 2.12% (-0.5 to 4.8) (neutral). The FAO- differences were found to be significant between the groups (p=0.0077), with AOA patients being significantly different than all the other groups (Figure 2). Similarly, the HFO was found to be significantly different-between the groups (p=0.002), with the following average values and 95%CI for respectively HOA, KOA, AOA and controls: 0.7% (-6.4 to 7.8), 2.3% (-2.3 to 6.8), -10.1% (-17.2 to -3.0), and 5.3% (-0.6 to 11.3). Again, the AOA patients were found to be significantly different than the other groups. No significant differences were found between the groups when assessing the KFO (p=0.37). Conclusion: The baseline 3D lower limb alignment and relative position of the hip, knee, ankle and foot was assessed and established for the first time in the literature. When comparing 3D alignment in arthritic patients with hip, knee or ankle OA and controls, we observed that AOA was found to be the one affecting more the overall 3D alignment of the lower extremity, with no complete compensation of the deformity through the other joints, resulting in significantly different values of HFO, KFO and FAO in patients with ankle OA. Additional prospective studies with longer cohorts of patients are needed.