[3-dimensional imaging of thalamic fractures of the calcaneum. Validation of classifying fractures into 3 forms].
Three dimensional CT scans enables to visualize the calcaneum and to follow the fracture pattern without any risk of errors.


OBJECTIVE
This technique has been used to validate our previous classification (using three forms: vertical, horizontal, and mixed) which resulted from a two dimensional tomodensitometric study.


METHODS
The study was based on a series of 74 fractures, all of them studied with 3D CT and 71 of which were operated.


METHODS
The previous classification relied on correlation between lateral radiographs and position on coronal CT plane of the Palmer's fracture line. This we called the Fundamental Line (FL); so the vertical form had medial fundamental line, with thalamic verticalization; and so that the horizontal form with thalamic horizontalization had a lateral FL; the mixed form had a medio thalamic FL with double contoured image.


RESULTS
In vertical fractures (16 cases, i.e. 20 per cent), the FL was seen denting the thalamus inwards, continuing forward and damaging the forward facet in about two thirds of cases. The thalamic fragment tilted on its axes frequently, with a great rotation movement; in about half cases, it extended backwards (propagated variation). This lateral fragment, called "cortico thalamic" (CT) explained the vertical thalamic x-ray image. In the horizontal fractures (15 cases, i.e. 20 per cent), the FL dents the thalamus outwards, the medial fragment, pushed downwards, explaining the horizontal image. In the mixed cases (40 cases i.e. 55 per cent) the FL was medio thalamic; the two fragments, downed medially and tilted laterally, are of equivalent importance, hence the double contoured image. In half cases, an accessory line separates the sustentaculum tali, creating the two lined mixed form (14 cases i.e. 35 per cent of the mixed). In those cases, the medial thalamic fragment is unsoldered, when in 50 per cent of cases (i.e. 7 out of 14), the pre-thalamic line, following the sinus tarsi, separates it from the forward part and completely isolates it. Therefore, the initial classification in three forms was in fact confirmed. Moreover, the fundamental line appears in all three forms, being the boundary between the lateral thalamic fragment (always tilted) and the medial fragment (always pushed downside). The anterior of cuboidian joint facets are frequently damaged by the forward prolongation of the Fundamental Line according to studied cases.


CONCLUSIONS
This three form classification emphasizes the role of the Fundamental Line, which in effect acts as a boundary between the two typical displacements of this fracture: downward or rotation movement of the thalamic fragments (since it is there that the main displacements occur). A comparison with the Eastwood and Sanders classifications has been carried out.


CONCLUSIONS
This three dimensional CT approach validates, visualizes and completes the three form classification. This will help us to understand fracture displacements in different forms, and therefore, the particular fracture reduction and osteosynthesis best suited for each case.
Utheza
G
G
Service de Chirurgie Orthopédique et Traumatologique, C.H.U. Rangueil, Toulouse.
Goldzak
M
M
Chaminade
B
B
Zographos
S
S
Chiron
P
P
D002111:Calcaneus / Q000000981:diagnostic imaging / Q000293:injuries* / Q000601:surgery; D050723:Fractures, Bone / Q000145:classification / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D007091:Image Processing, Computer-Assisted; D014057:Tomography, X-Ray Computed