- Discussion:
- coalition bewteen talus & calcaneus may be difficult to detect on xray
- cartilaginous coalition between the talus and calcaneus in the area of the
middle facet may also be detected by
an irregularity of the joint surfaces of the talus and calcaneus;
-
anterior facet is not seen on the axial x-ray, and tomography is required to visualized it properly;
- Lateral View:
- CT Scan:
- 5 mm cuts are acceptable but 3 mm cuts are more optimal;
- Harris View:
- since normal posterior &
middle facet are in parallel planes at approx 45 deg to sole of foot,
these two areas can be identified on an Axial 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 Harris view to this inclination;
- normally the middle facet is perpendicular to the axis of the tibia;
- angulation of
middle facet by > 20 deg off horizontal is consistent w/ coalition, even if the joint space is open;
- posterior & middle facet of calcaneus, which articulate w/ talus, are nl in parallel planes & are usually best visualized on axial radiographs at 45 deg;
- in
talocalcaneal coalition, angle of
middle facet may vary;
-
anterior facet is in a different plane and is not seen axial views because it is obsurred by head of the talus;
Evaluation of tarsal coalition by computed tomography.
CA Stoskopf. J. Pediatric Orthopedics. Vol 4. 1984. p 365-369.
Computerized tomography scanning technique for the hindfoot.
RW Smith and TW Staple.
CORR. Vol 177. 1983. p. 34-38.
