- Discussion:
- slightly concave, is situated on the sustenaculum tali;
- sustenaculum forms the floor of middle facet;
- between middle & posterior articular facets lies interosseous sulcus (calcaneal groove),
which opens broadly laterally & forms, w/ talar sulcus, sinus tarsi;
- Radiology:
-
medial oblique axial view:
- demonstrates middle & post facets of
sub-talar joint;
- since nl posterior & middle facets are in parallel planes at approx 45 deg to sole of foot, these two
areas can be identified on axial (
Harris, or ski jump) view (described by Korvin in 1933);
- effectiveness of
harris view for visualizing
subtalar joint is enhanced by measuring angle of
posterior facet on lateral view & then adjusting the Harris View to this inclination;
- radiographic appearance of two facets either in same plane or at angle > 20 deg to each
other suggests coalition;
- angulation of the middle facet by more than 20 deg off horizontal is consistent w/
coalition, even if joint space is open;
- posterior & middle facet of calcaneus, which articulate w/ talus, are normally in parallel planes
and are usually best visualized on axial radiographs at 45 deg;
- in
talocalcaneal coalition, angle of the middle facet may vary;
-
anterior facet is in a different plane and cannot be seen on axial views because it is obsurred
by the head of the talus;
