European Journal of Radiology. 15 (1992) 22-25 0



1992 Elsevier Science Publishers

B.V. All rights reserved. 0720-048X/92/$05.00


Talocalcaneal coalition: computed tomography and magnetic resonance imaging diagnosis Carlo Masciocchi,

Claudio D’Archivio, Antonio Barile, Eva Fascetti, Bruno Beomonte Massimo Gallucci and Roberto Passariello


Department of Radiology, University of L ;4quila, Italy

(Received 28 June 1991; accepted after revision 2 December

Key words: Foot, abnormality;





coalition; Magnetic resonance

imaging, talocalcaneal



A correct evaluation of site and extension of the talocalcaneal coalition inducing biomechanical ankle alterations is very important for planning therapy. Four male patients were submitted to computed tomography (CT) and three of them were also examined by means of magnetic resonance imaging (MRI). In one patient, studied by CT only, a bilateral talocalcaneal coalition was present, while the other three patients, controlled with CT and MRI, were affected by monolateral talocalcaneal coalition which was of osseous type in one case and fibrocartilaginous in two cases. CT and MRI provided detailed information on type and extension of the coalition and both helped in distinguishing between osseous and fibrocartilaginous forms. Only MRI showed an area of subchondral ischemic disease of the posterior subtalar joint in one patient with monolateral tibrocartilaginous talocalcaneal coalition. Compared with CT, MRI proved to be more accurate in evaluation of the talocalcaneal coalition, due to its wider display capability.


Material and methods

Tarsal coalition is an uncommon disorder caused by fibrocartilaginous or bony union of the tarsal bones [l-5]. The most frequently observed form is the calcaneonavicular coalition, but biomechanically the most relevant is the talocalcaneal. The symptomatology is often represented by pain and functional disability of the subtalar joint. A flat foot in the valgus position and painful spasms are sometimes associated with coalition [6-81. Conventional radiography performed with standard views is mostly unreliable [ 91; scintigraphy, though positive in some cases, is not considered the examination of choice [ 10). This report compares the diagnostic roles of magnetic resonance imaging (MRI) and computed tomography (CT) in patients with talocalcaneal coalition [ 10-151.

Between December 1989 and January 1991, we examined four male patients with talocalcaneal coalition; their ages ranged between 17 and 25 years (mean: 20 years). All patients presented functional disability of the hind foot; two patients, in particular, had limits in pronation and supination of the foot. The other two cases showed flat foot in the valgus position with painful spasms persisting after months of care with orthopedic shoes. On plain film talocalcaneal coalition was diagnosed in only one patient, was doubtful in another case and negative in the remaining two patients. The doubtful case was also submitted to scintigraphy, which showed a tracer accumulation at the level of the talocalcaneal space, thus confirming the clinically suspected tarsal coalition. CT examination was performed in all four cases and MRI in three of these patients; only one was submitted to CT after surgery, although all of them had been surgically treated.

Correspondence to: Carlo Masciocchi,

M.D., Department of Radiology, University of L’Aquila, S. Maria di Collemaggio Haspital, 67100 I’Aquila, Italy.


CT examinations were performed on an Ansaldo Atom X 1200 S unit, with high definition technique. Thin slice thickness (2 mm) and coronal scans, associated with axial ones, were employed for contemporary evaluation and comparison of both feet. MRI was performed using a permanent system (Esatom PM 4000), operating at 0.2 T. Dedicated coil, spin-echo Tl and T2 sequences, axial, sag&al, and coronal planes were employed. Slice thickness was 3 mm, intersection gap 1 mm. Results One patient, submitted to CT only, showed a bilateral talocalcaneal coalition of fibrocartilaginous type (Fig. 1). Comparative study of both feet accurately defined the exact extension and site of the coalition by means of axial and coronal scans. The other three patients were studied by CT and MRI. In one case (Fig. 2), MRI was superior to CT in revealing an incomplete osseous talocalcaneal coalition; CT cannot define the partial union with the same level of accuracy. In this case, by coronal scan, both CT and MRI evidenced an in valgus angle of the heel. In the other two patients, there was presence of unilateral fibrocartilaginous talocalcaneal coalitions of the medial side (Fig. 2). MRI was more accurate than CT in defining the presence and extension of an area of subchondral ischemic disease with fibrotic changes of the posterior subtalar joint due to non-physiological biomechanical load, associated with coalition (Fig. 3). All patients underwent surgery which confirmed the presence of talocalcaneal coalition and, in those cases evidenced with MRI, the chondral and subchondral ischemic alteration of the posterior subtalar joint. All cases were controlled by clinical follow-up at 6 months and in one case also by CT study. Discussion The talocalcaneal coalition was first described by Zuckerkandl in 1877 [ 51, but the anatomo-pathological and radiographic findings were correlated to clinical data only in 1948 by Harris and Beath [ 81. Other authors tried to explain the pathogenesis of this disease ascribing its origin to a failure in segmentation and differentiation of the primitive parenchyma, or to the interposition of an accessory bone, or sustentaculi, between talus and heel [ l-41. Other more infrequently acquired forms are observed due to trauma, surgical treatment, infections and rheumatoid arthritis.

Fig. 1. (A) CT coronal scan and (B) oblique transaxial scan: bilateral talocalcaneal coalition (white arrows) with evidence of fibrocartilaginous type on right side and partial ossification on the left side (black arrows).

A correct diagnosis of talocalcaneal coalition is very important, because the synostosis can lead to severe biomechanical disorders and foot disability, particularly when ankle-stressing activities are performed. The talocalcaneal coalition is mainly observed in male patients and symptoms generally occur during the second decade with continuous, dull pain. The type and location of the coalition cannot always be diagnosed with standard views on plain radiographs. Axial oblique planes at 45” can evidence the talocalcaneal coalition [ 91, but not the fibrous and cartilaginous forms. Even though without high accuracy, with plain radiography it is possible to evaluate the secondary signs of the coalition (i.e., alterations of joint edges, presence of talar beaking and flat foot secondary to peroneal spasms). The site and extension of the coalition have been


Fig. 2. Talocalcaneal coalitions. (A and B) Fibrocartilaginous type well depicted on both coronal CT (A) and MR (B) scans (black arrows); (C-D) Ossified talocalcaneal coalition with the same accuracy on coronal CT (C) and MR (D) scans (white arrows).

better evaluated since the introduction of CT [ 10-151. The use of coronal planes in this technique provides scans parallel to the coalition axis, contemporary evaluation and comparison of both feet, which is very useful to avoid overlooking a possible bilateral coalition. CT enables good depiction of the sustentaculo-talar region and allows to distinguish between bone coalition and fibrous and cartilaginous forms. At MRI, images obtained with coronal oblique planes, slice thickness of 3 mm and Tl weighted sequences allow a correct differentiation of the bone structures from muscles and fat tissue. In fact, the bone structures are documented by high signal intensity on Tl weighted sequences, while the surrounding structures appear as hypointense areas, which well delineate the bone morphology. It is therefore possible to distinguish bone from librocartilaginous coalition and, if the coalition is of a bony nature, the complete form from the uncomplete forms. Compared with CT, MRI provides more information about the subtalar joint region; moreover, it allows identification of the possible tibio-tarsal involvement

Fig. 3. Fibrocartilaginous talocalcaneal coalition shown on parasagittal (A) and sagittal (B) MR scans (solid white arrows) with evidence of an area of subchondral ischemic disease on posterior subtalar joint (open white arrows). CT (C) confirms MR diagnosis of coalition (white arrow), but does not define the fibrotic changes secondary to ischemic disease. Post-surgical CT control (D) (white arrow).

and/or other disorders secondary to or associated with the coalition itself. The possibility of obtaining this information by simply changing the scan plane without repositioning the foot, as is required with CT, means that the time required for MRI is about equal to that of CT. In our experience, T2-weighted sequences employed on both the transverse and longitudinal scan planes, did not provide helpful information for assessment of the talocalcaneal coalitions. In conclusion, we believe that neither conventional radiography, even when employing oblique planes, nor scintigraphy provide good depiction of the talocalcaneal coalition. CT is a diagnostically valuable technique, its limitations being mainly due to a narrower display capability compared with MRI. MRI is therefore expected to become the method of choice for study of the talocalcaneal coalition; this due to the ability of MRI to accurately display the detailed morphology of this portion of the joint.


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Talocalcaneal coalition: computed tomography and magnetic resonance imaging diagnosis.

A correct evaluation of site and extension of the talocalcaneal coalition inducing biomechanical ankle alterations is very important for planning ther...
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