Assessment of coronal plane subtalar joint alignment in peritalar subluxation via weight-bearing multiplanar imaging

Patients with adult-acquired flatfoot deformity (AAFD) develop peritalar subluxation, which may stem from valgus inclination of the inferior surface of the talus. We hypothesized that patients with AAFD would have an increased valgus tilt of the subtalar joint in the coronal plane compared to controls when assessed with a novel multiplanar weight-bearing imaging (MP-WB).

Eighteen normal and 36 stage II AAFD patients scheduled to undergo operative reconstruction were evaluated by MP-WB through measuring 3 novel angles of the subtalar joint in the coronal view: (1) angle between inferior facet of the talus and the horizontal/floor (inftal-hor), (2) angle between inferior and superior facets of the talus (inftal-suptal), and (3) angle between inferior facet of the talus and superior facet of the calcaneus (inftal-supcal). Intra- and interobserver reliability were evaluated via intraclass correlation coefficients (ICCs). Differences in angles between AAFD patients and controls were evaluated using Wilcoxon rank-sum test.

Intra- and interobserver reliability were excellent for inftal-hor (ICC .942 and .991, respectively) and inftal-suptal (ICC .948 and .989, respectively), and moderate-good for inftal-supcal (ICC .604 and .742, respectively). Inftal-hor and inftal-suptal angles were found to be significantly greater in AAFD patients (P < 0.001) at all 3 locations along the posterior subtalar joint, while inftal-supcal did not demonstrate a significant difference (P = .741). While controls exhibited varus orientation at the anterior aspect of the joint, AAFD patients maintained a valgus orientation throughout.

Inftal-hor and inftal-suptal angles provided a reliable means of evaluating the orientation of the subtalar joint axis in AAFD via MP-WB, and showed that the subtalar joint had increased valgus orientation in AAFD compared to controls. This may allow for identification of patients at risk for developing AAFD, and could potentially be used in guiding operative reconstruction.