Reliability of the talocalcaneal angle for the evaluation of hindfoot alignment

Recent studies suggest that hindfoot deformity should be considered in the surgical treatment of tarsal coalitions. Many authors have used the angle between the talus and the calcaneus (TCA) for decision-making. However, its reliability has not been demonstrated and the measurement technique has not been standardized. The objective of this study was to standardize the TCA measurement technique, and to evaluate the inter and intra-observer reproducibility of the proposed technique.

The foot CT scans of a group of 30 patients between 10 and 17 years of age were analysed. Ten patients had talocalcaneal coalitions, ten calcaneonavicular coalitions and ten had no coalitions. The inter and intra-observer reproducibility of the TCA was evaluated by the intraclass correlation coefficient (ICCs). A mixed-effects ANOVA model was used to calculate the ICCs for ICC2 agreement (A, 1). This procedure was applied to the three observers (inter-observer variability), and to the test-retest of observer 1 (intra-observer variability). A two-tailed p value of ≤.05 was considered significant.

The inter-observer and intra-observer agreements were excellent for the TCA. Inter-observer agreement: ICC2 (A, 1)=.95 (p<.001, CI 95%: .77-.93). Intra-observer agreement: ICC2 (A, 1)=.99 (p<.001, CI 95%: .97-.99).

The TCA is a reliable way to evaluate hindfoot alignment. This method of measurement, as described in this study, can be safely used for surgical planning in patients with tarsal coalitions.