Abstract
Background:
Foot and ankle offset (FAO) is a semiautomatic weightbearing computed tomography (WBCT) measurement that assesses the 3-dimensional (3D) relationship between the ankle joint center and the foot tripod, offering a global view of hindfoot alignment (HA). Because FAO does not isolate subtalar alignment, we introduce and assess the reliability of subtalar joint offset (SJO), a 3D WBCT measure of SJ alignment relative to the foot tripod.
Methods:
We conducted a retrospective study on 204 feet categorized as neutral (n = 30), valgus (n = 107), or varus (n = 67) based on FAO values (−0.6% < neutral < 5.2%). SJO was calculated by identifying the position of the SJ calcaneal middle facet in relation to the foot tripod using WBCT software (Talas, Cubevue; CurvebeamAI). Intra- and interobserver intraclass correlation coefficients (ICCs) were calculated. We calculated the SJO-FAO difference in millimeters on the same reference plane and analyzed correlations by group (Bonferroni-adjusted α = 0.006).
Results:
ICC values were excellent (intraobserver: 0.98; interobserver: 0.92). FAO significantly differed across groups: neutral (2.52 ± 2.38), valgus (10.68 ± 4.03), and varus (−8.9 ± 6.92) (P < .001). SJO also varied significantly: neutral (15.3 ± 2.07), valgus (20.85 ± 2.78), and varus (10.32 ± 3.08) (P < .001). The SJO-FAO difference was smallest in valgus (10.16 ± 2.01), intermediate in neutral (12.88 ± 2.67), and largest in varus (19.08 ± 5.12) (P < .001). A moderate correlation was found between FAO and SJO in the varus and valgus groups (ρ = 0.68, r² = 0.51; and ρ = 0.68, r² = 0.57), and low in the neutral group (ρ = 0.47, r² = 0.36) (all P < .001).
Conclusion:
SJO is a reliable WBCT metric for distinguishing subtalar alignment across valgus, neutral, and varus HA. Prospective, multicenter studies should test whether the SJO-FAO difference quantifies subtalar contribution and informs realignment surgery.
Get full access to this article
View all access options for this article.
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
