Standardization of the Foot Sagittal Axis for Measurement of Hindfoot Alignment Using Weight- Bearing Computed Tomography (WBCT)

Abstract

Category: Hindfoot; Other Introduction/Purpose: The radiographic measurement of hindfoot alignment (HA) suggested by Saltzman, worldwide accepted, uses the medial aspect of the foot as the sagittal axis. When defining the medial face of the foot as its axis, the adduction and abduction deformities of the forefoot are disregarded, making it necessary to rotate the ankle internally or externally to acquire the radiographic image according to Saltzman protocol. The emergence of weight-bearing computed tomography (WBCT) allowed immeasurable advancements for a better understanding of the joints relations of the foot and ankle under stress. Previous studies using this technology adopted several sagittal axes to measure HA. Our hypothesis is that the adduction observed in the forefoot of the cavovarus feet illusively accentuates the real deformity of the hindfoot. Methods: Two evaluators calculated the HA of twenty-eight feet - 14 cavovarus and 14 neutral or slightly valgus (control group) - in three different sagittal axes (second metatarsal axis, calcaneus - second metatarsal axis and talar dome axis). Measurements were compared by Student's t-test after normality test by Shapiro-Wilk method. Observers' agreement was evaluated by intraclass correlation coefficient (ICC). P-values <.05 were considered significant. Results: We found excellent intra-observer (0.93) and inter-observer (0.9) agreements following the measuring assessment. The average Foot and Ankle Offset (FAO) of the cavovarus feet group was -3.35 (-0.64 - -7.01), while the control group was 2.01 (-1.3 - 6.4). The mean difference in HA when comparing the axis of the talar dome with the axis of the second metatarsal was 9.88 ° (3.1 ° - 17 °), while in the control group the mean difference was 3.16 (0.2 ° - 7.5 °). All of these data showed statistical significance. Conclusion: As a great variability was observed in the measurements of hindfoot alignment in the cavovarus foot group in the sagittal axes analyzed, this article suggests standardizing the measurement of hindfoot alignment using the talar dome axis. In addition, it becomes possible to quantify adaptations of the hindfoot secondary to modifications of the forefoot in an isolated manner.