Reliability and correlation analysis of computed methods to convert conventional 2D radiological hindfoot measurements to a 3D setting using weightbearing CT

Purpose The exact radiographic assessment of the hindfoot alignment remains challenging. This is reflected in the different measurement methods available. Weightbearing CT (WBCT) has been demonstrated to be more accurate in hindfoot measurements. However, current measurements are still performed in 2D. This study wants to assess the use of computed methods to convert the former uniplanar hindfoot measurements obtained after WBCT towards a 3D setting. Methods Forty-eight patients, mean age of 39.6 ± 13.2 years, with absence of hindfoot pathology were included. A WBCT was obtained, and images were subsequently segmented and analyzed using computer-aided design operations. In addition to the hindfoot angle (HA), other ankle and hindfoot parameters such as the anatomical tibia axis, talocalcaneal axis (TCA), talocrural angle, tibial inclination (TI), talar tilt, and subtalar vertical angle were determined in 2D and 3D. Results The mean HA 2 D was 0 . 79 ∘ of valgus ± 3.2 and the HA 3 D was 8 . 08 ∘ of valgus ± 6.5. These angles differed significantly from each other with a P < 0.001 . The correlation between both showed to be good by a Pearson correlation coefficient ( r ) of 0.72 ( P < 0.001 ). The ICC 3 D showed to be excellent when compared to the ICC 2 D , which was good. Similar findings were obtained in other angles. The highest correlation was seen between the TI 2 D and TI 3 D ( r = 0.83, P < 0.001 ) and an almost perfect agreement in the TCA 3 D ( ICC 3 D = 0.99 ). Conclusion This study shows a good and reliable correlation between the HA 2 D and HA 3 D . However, the HA 3 D overcomes the shortcomings of inaccuracy and provides valuable spatial data that could be incorporated during computer-assisted surgery to assess the multiplanar correction of a hindfoot deformity.