Subtalar joint configuration on weightbearing CT scan

Standard values that describe the morphology of the subtalar (ST) joint have previously been obtained from cadaveric studies or by using conventional unloaded radiographs. It is known that these parameters differ significantly from those measured in vivo and in loaded images, limiting the diagnostic value of the previously published morphological parameters in the literature. However, the morphology of the ST joint clearly affects its function. The objective of this study was to determine the morphology of the posterior facet of the ST joint using loaded computed tomography (CT) images and to describe the different configurations found in asymptomatic patients.

A weightbearing CT scan was performed on 59 patients without any history of hindfoot and ankle pathology. The shape of the posterior facet and the subtalar vertical angle (SVA) were measured in 3 different coronal planes of the ST joint.

The posterior facet was concave in 88% and flat in 12%. The posterior facet was oriented in valgus in 90% and varus in 10% when measured in the middle coronal plane. However, the SVA changed depending on which coronal plane it was measured in.

We believe it is important to get a better insight into the morphological parameters of the ST joint.

Knowledge of subtalar joint morphology could help clarify why certain failures have occurred in reconstructive hindfoot surgery and thus might help plan the surgical procedure to reduce these failures in the future.