I. CT anatomy of the calcaneus
- Multidetector CT with multiplanar reformation (MPR) is commonly used for the assessment of calcaneal fractures.
- The CT scan is obtained with the patient lying supine on the scanner with the knee flexed and the foot as plantigrade as the patient would allow.
Reconstruction CT planes are obtained in 3mm slice thickness.
The ankle joint is used on the axial images as a reference to obtain true sagittal and coronal planes of the hindfoot.
For Sanders classification,
the axial and coronal images are reformatted parallel and perpendicular to the anatomic posterior facet of the sagittally reconstructed images.
- Axial CT images ( Fig. 4 ) show the posterior facet,
heel varus,
calcaneal widening,
calcaneocuboid joint and lateral wall.
The coronal CT images ( Fig. 5 ) evaluate posterior facet involvement,
height and width of the calcaneus,
subtalar congruency and lateral malleolus.
Sagittal reconstruction images ( Fig. 6 ) can help assess the rotational abnormality of the posterior facet fragment,
loss of height,
degree of impaction and the calcaneocuboid joint.
II. CT features of calcaneal fractures
- CT has changed the evaluation of calcaneal fractures because it allows better visualization of subtalar joint than conventional radiography.
Through MPR and VR reconstruction,
CT permits to assess accurately the fracture lines,
dislocation,
crushing,
the morphology and the involvement of articular surfaces,
allowing to choose the appropriate treatment and have a better prognosis evaluation.
- Fractures of the calcaneum have been divided into intra-articular and extra-articular fractures based on the involvement of the posterior facet of the subtalar joint as seen on multidetector CT scans and MPR images.
A. Intra-articular fractures
- Intra-articular fractures account for about 75% of all calcaneal fractures in adults.
Several classification systems have been developed,
of which the Sanders system is the most commonly used,
with several studies having showthis system to correlate with management and prognosis.
*The Sanders classification system ( Fig. 7 )
- It relies on axial and coronal images oriented parallel and perpendicular,
respectively,
to the posterior facet of the subtalar joint as shown on a sagittal MPR image.
This evaluation allows the classification of fractures into four types on the basis of fracture line location at the posterior facet :
- Type I: nondisplaced fractures (displacement < 2mm) regardless of fracture lines.
- Type II ( Fig. 8 ): fractures with two articular pieces from a single intraarticular fracture line,
subdivided into three subtypes on the basis of whether the fracture line location is lateral (IIA),
central (IIB),
or medial (IIC).Medial fractures are harder to evaluate and manage surgically.
- Type III ( Fig. 9 ): fractures with three articular pieces from two fracture lines,
subdivided into types IIIAB (lateral and central primary lines relative to the posterior facet and subtalar joint),
IIIAC (lateral and medial primary lines),
and IIIBC (central and medial primary lines).
- Type IV ( Fig. 10 ): comminuted fractures with more than three intraarticular fracture lines and more than four articular fragments.
- The Sanders classification system is useful not only in treatment planning but in helping to determine prognosis.
Type I fractures are treated without surgery with excellent results.
Patients with type II and type III fractures,
who underwear surgery,
have excellent or good clinical results in 73% and 70% of cases,
respectively.
Only 9% of patients with type IV fractures have excellent or good clinical results after surgical treatment; success is not guaranteed,
possibly related to cartilage necrosis at the time of injury.
*Other items to detail
- CT represents a spectacular tool for surgical decision making.
When a lateral surgical approach (the most common strategy) is used,
the entire calcaneus is rebuilt in reference to the sustentacular fragment.
Only CT can give a clear understanding of the size of this fragment and the number of fracture lines that must be identified and surgically reduced.
In addition,
CT shows the location and plane of variable fracture lines that separate the anterolateral fragment.
The precise location of the lateral wall,
particularly in relation to the lateral malleolus and peroneal tendons,
is easily appreciated with CT.
Besides,
CT can clearly demonstrate the number of different fractures and their location along the posterior facet.
This depiction allows the surgeon to estimate the feasibility of achieving an anatomic reduction that is secure enough to begin early motion.
- In summary,
other than the involvement of posterior subtalar joint,
CT evaluation must detail other elements:
- The degree of comminution and the number of fragments
- Presence of intra-articular bone fragment ( Fig. 11 )
- The congruency of the posterior talocalcaneal joint and the degree of impaction ( Fig. 12 )
- The congruency of the calcaneocuboid joint ( Fig. 13 )
- State of the anterior process ( Fig. 14 )
- Swelling and infiltration of soft tissue ()
B. Extra-articular fractures
- Extra-articular fractures account for about 25% to 30% of all calcaneal fractures and include all fractures that do not involve the posterior facet of the subtalar joint.
- Generally,
extra-articular calcaneal fractures fall into one of three categories depending on whether the involvement of the calcaneus is anterior,
middle or posterior ( Fig. 16 ):
-Type A: fractures involve the anterior process of the calcaneus
-Type B ( Fig. 17 ): fractures involve the midcalcaneus or body including the trochlear process,
sustentaculum tali and lateral process
-Type C ( Fig. 18 ): fractures involve the posterior calcaneus including the posterior tuberosity and the medial tubercle.
- Avulsion fractures of the calcaneal tuberosity tend to occur in elderly osteoporotic patients from avulsion of the Achilles tendon with its bony insertion.
The fracture is subcutaneous and fragment displacement may result in skin compromise.
- It’s important to differentiate complex fractures that separate articular facets and distort the three-dimensional anatomy of the subtalar joint from the more simple extra-articular fractures.
C. Treatment implications
*Medical or conservative treatment is indicated in:
-Closed non-displaced or minimally displaced fractures (Sanders type I).
-Extra-articular fractures
*Surgical treatment:
-Open reduction and external fixation are indicated in displaced and open intra-articular fractures.
-Arthrodesis is reserved for comminuted fractures.
III. Standardized CT report
- Other than the CT report,
four films are delivered to the surgeon including axial,
sagittal,
coronal 2D bone reconstruction and 3D reconstruction illustrating the calcaneal fracture.
Soft tissue reconstruction can be added.
1.Involvement of the posterior talocalcaneal joint :
No: extra-articular fracture ο
yes: intra-articular fracture ο
A.
Intra-articular fracture:
-The degree of comminution: number of bone fragments ………
-Location of fracture lines………
-Sanders classification………
-Congruency of the talocalcaneal joint: preserved ο
not preserved ο
If not preserved: degree of impaction……
-Presence of intra-articular bone fragment: no ο
yes ο (number…...
size…..)
-Congruency of the calcaneocuboid joint: preserved ο
not preserved ο
-Involvement of the anterior process: no ο yes ο
*size of the anterior process…
-Varus or valgus deformation of the calcaneus….
B.
Extra-articular fracture:
-Type A: Anterior process of the calcaneus
-Type B:
Body ο; Sustentaculum tali ο; Trochlear process ο; Lateral process ο
-Type C: Posterior calcaneus
-Displacement…
-Calcaneocuboid articular surface involvement…
2.
Associated findings:
-Soft tissue swelling and infiltration….
-Peroneal tendon injury……
-Achilles tendon rupture …