The Value of Axial Loading 3D CT as a Substitute for Full Weightbearing 3D CT: Comparison of Reproducibility According to Degree of Load

Category: Other Introduction/Purpose: Full weightbearing(WB) three dimensional computed tomography(3D CT) is an excellent imaging tool. However, due to its high cost, it is only used in a few hospitals. We evaluated the usefulness and cost-effectiveness of axial loading(AL) 3D CT by comparing bony alignments with standing radiographs, and assessed reproducibility according to the degree of AL. Methods: Eighty patients(156 feet), who underwent standing radiographs and 3D CT with an AL device from January 2016 to May 2017, were investigated. According to the degree of AL(AL force×100/body weight), the patients were randomly assigned to three groups: Group A(30-50%; n=21, 40 feet), Group B(50-70%; n=32, 63 feet), and Group C(70-100%; n=27, 53 feet). The following angles were measured three times by two orthopedists: hallux valgus(HVA), 1st-2nd intermetatarsal(IMA1-2), and talo-navicular coverage(TNCA), calcaneal pitch(CPA), talo-1st metatarsal(T1MA), and talo-calcaneal angle(TCA). Agreements between the two imaging methods were analyzed and compared according to the degree of axial loading in each group. Results: Intra- and interobserver reliability was excellent (>0.75). In Group A(30-50% AL), all of the angles except HVA and IMA1-2 differed (p<.05). In Group B(50-70%), TNCA (p= .023), T1MA (p= .017), and TCA (p=.035) differed. In Group C(70-100%), none of the angles differed between the two imaging methods (p> .05). Higher agreement between the two imaging methods was realized when 70% or more(>70%) AL was applied. Conclusion: AL 3D CT with >70% axial load has full WB effects and can be substituted for expensive full WB 3D CT.