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AJR 2004; 182:1279-1282
© American Roentgen Ray Society

Validity of the Anteroposterior Talocalcaneal Angle to Assess Congenital Clubfoot Correction

E. Ippolito1, L. Fraracci2, P. Farsetti1 and F. De Maio1

1 Department of Orthopaedic Surgery, University of Rome "Tor Vergata," Via Montpellier 1, Roma 00133, Italy.
2 Department of Radiology, IRCCS Santa Lucia Institute, Via Ardeatina 306, Roma 00179, Italy.

Received August 11, 2003; accepted after revision October 29, 2003.

 
Address correspondence to E. Ippolito.


Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The anteroposterior talocalcaneal angle (Kite's angle) is still considered a common parameter for assessing clubfoot correction, although some dissenting opinions about its accuracy have been expressed. The purpose of this study was to evaluate the validity of the anteroposterior talocalcaneal angle for assessing correction of congenital clubfoot in adults who received the treatment as children.

SUBJECTS AND METHODS. The anteroposterior talocalcaneal angle was measured in 48 treated idiopathic congenital clubfeet and 28 normal feet of 38 patients at the end of skeletal growth using both standing anteroposterior radiographs and 3D CT scan reconstructions. All the patients had been treated by manipulation, above-the-knee casting, and a complementary posteromedial release operation.

RESULTS. The radiographic measurement of the anteroposterior talocalcaneal angle corresponded to the measurement of the same angle on the 3D CT scan reconstructions in only the normal feet and 12 clubfeet. In the other 36 clubfeet, a statistically significant difference of a mean of 15° between the two measurements was noted, and the 3D CT scan reconstructions showed a superimposition of the talus and calcaneus, which had lost their normal anatomic divergence. In these cases, the marked medial angulation of the talar neck allowed a positive measurement of the anteroposterior talocalcaneal angle in the anteroposterior radiographic projection.

CONCLUSION. According to our findings, the measurement of the anteroposterior talocalcaneal angle on radiography was misleading for assessing the degree of hindfoot correction in 75% of the treated congenital clubfeet. We believe that other imaging parameters should be considered instead of this angle to evaluate clubfoot correction.


Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
The anteroposterior talocalcaneal angle, also known as Kite's angle, has been considered for many years to be a valid radiographic parameter for assessing congenital clubfoot correction in both children and adults [1–13]. The angle is formed by the intersection of two lines coincident with the longitudinal axes of both the talus and the calcaneus on the horizontal plane, and it indicates the normal divergence of the two bones in the standing position [1, 2, 5]. Howard and Benson [14] warned that measuring the anteroposterior talocalcaneal angle in the immature clubfoot on radiography is not valid because the ossific nucleus of the talus lies predominantly in the head and neck of the cartilaginous anlage of the talus. Therefore, the ossific nucleus forms an angle with the cartilage of the body that is wider in clubfeet than in normal feet, owing to the marked medial angulation of the neck of the talus in clubfeet [15, 16].

In our study, with the aid of 3D CT scan reconstructions, we investigated whether the radiographic measurement of the anteroposterior talocalcaneal angle corresponded to the real spatial relationship of the talus and calcaneus in adult-treated clubfeet and whether the angle is valid for assessing the correction of clubfoot deformity at maturity. In fact, 3D CT scan reconstructions eliminate the superimposition of the ankle on the hindfoot bones, which occurs in an anteroposterior radiographic view of the foot.


Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
For the radiographic and CT examinations, we obtained authorization from the ethics committee of our university hospital and informed consent from all the patients examined. Thirty-eight patients with congenital clubfoot were studied at the end of their skeletal growth using both conventional radiographs and 3D CT scan reconstructions. We selected these patients from a pool of 109 patients treated between 1973 and 1977. Fifty-six patients were excluded because they had been treated elsewhere initially, 12 had only mild or moderate deformity, and three were lost at follow-up. The remaining 38 patients were treated by manipulation begun soon after birth, application of a toe-to-groin plaster cast, and performance of a complementary posteromedial release operation at an average age of 10 months (range, 6–18 months). The operation was performed according to the technique described by Codivilla [17], which was later modified by Turco [18], but two incisions were made instead of the one originally described. An aluminum brace extending proximal to the knee was applied at night until the child was 3 years old. Before starting treatment, the clubfeet included in our study were graded as group III of the Manes et al. classification reported by Dimeglio et al. [19]. Group III includes feet with more than 20° equinovarus hindfoot deformity if the foot is short and fat and more than 45° if it is long and thin.

The average age of the patients was 25 years (range, 22–27 years). The study group comprised 28 men and 10 women. Twenty-eight patients presented with a unilateral deformity and 10 with bilateral for a total of 48 clubfeet and 28 normal feet. Each patient had both standing anteroposterior and lateral radiographs of the feet and a CT examination. The X-ray beam was angled cephalad 25° to allow the anteroposterior radiographic view to better dissociate the talus and the calcaneus from the superimposition of the ankle mortise. For the CT examination, the patient was placed supine on the machine platform with the knees bent at 60° and feet plantar-flexed at 10°. The longitudinal axis of the feet coincided with the longitudinal axis of the platform. A CT scanner (Somaton, Siemens) was used to obtain 2-mm-thick scans in both the coronal and the axial planes with a scan interval of 2 mm and a field of view of 38–42 cm.

Three-dimensional CT scan reconstructions were made of all 48 clubfeet and the 28 normal feet. Two lines coincident with the longitudinal axes of both the neck of the talus and the anterior tuberosity of the calcaneus were drawn on the anteroposterior views, and the anteroposterior talocalcaneal angle formed by the intersection of the two lines was measured. The same angle was formed on the 3D CT scan reconstructions by drawing a line coincident with the longitudinal axis of the calcaneus and a line coincident with the longitudinal axis of the talar neck, drawn from the posterior margin of the trochlea of the talus [20]. The declination angle of the neck of the talus (between the long axis of the body and the long axis of the neck of the talus) [21, 22] and the angle formed by the long axis of the posterior calcaneal facet of the subtalar joint with the longitudinal axis of the calcaneus [23] were also measured on the 3D CT scan reconstructions. The latter was defined as the angle of the posterior calcaneal facet of the subtalar joint. In some cases, we also evaluated the medial talar offset of the talus with respect to the calcaneus in the coronal plane on the scans taken at the level of the sustentaculum tali. The convergence or the divergence of the two longitudinal axes of the talus and the calcaneus has been evaluated in a diagram by drawing two lines dropped from the midpoint of the talus and the calcaneus perpendicular to the surface supporting the feet [24].

Results were expressed as means ± standard deviation (SD). For the statistical analysis, an unpaired Student's t test and Pearson's correlation coefficient were used. When the p value was less than 0.05, the difference or correlation was considered to be significant.


Results
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 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Measuring the anteroposterior talocalcaneal angle was always possible in the anteroposterior radiographic projection of both the normal feet and the treated congenital clubfeet because both the neck of the talus and the anterior tuberosity of the calcaneus were clearly visible on the radiographs. In the normal feet, the anteroposterior talocalcaneal angle measured 23° ± 4° (mean ± SD) on anteroposterior radiographs (Fig. 1A) and 21° ± 5° in the 3D CT scan reconstructions (Fig. 1B). The difference between the measurements was not statistically significant. The declination angle of the neck of the talus measured 18° ± 5° (Fig. 1B). On the frontal projection, the talus and calcaneus diverged at the level of the subtalar joint (Fig. 1C), whereas on the cephalad view, the angle of the posterior calcaneal facet of the subtalar joint measured 45° ± 2° (Fig. 1D).



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  		Fig. 1A. —25-year-old man with unilateral right clubfoot. Standing anteroposterior radiograph of both feet shows anteroposterior talocalcaneal angle measured 25° on left and 15° on right.

 


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  		Fig. 1B. —25-year-old man with unilateral right clubfoot. Three-dimensional CT scan reconstruction in cephalad view of feet at level of talar trochlea shows declination angle of neck of talus (dashed lines) measured 16° on left and 42° on right; increased medial angulation of neck of talus caused false radiographic projection instead of real anatomic relationship of talus and calcaneus. In fact, anteroposterior talocalcaneal angle (solid lines) measured 0° on right and 25° on left.

 


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  		Fig. 1C. —25-year-old man with unilateral right clubfoot. Three-dimensional CT scan reconstruction in coronal plane shows sustentaculum tali (arrows). Medial talar offset is absent in right clubfoot. Anatomic axes of talus and calcaneus () are coincident in right clubfoot and divergent in left normal foot.

 


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  		Fig. 1D. —25-year-old man with unilateral right clubfoot. Three-dimensional CT scan reconstruction in cephalad view obtained at level of sinus tarsi (ST) shows long axis of posterior facet of subtalar joint (PF) and longitudinal axis of calcaneus form angle of 42° on left normal foot and angle of 90° on right clubfoot.

 

We divided our patients into two groups on the basis of the values of the declination angle of the talar neck and the angle of the posterior calcaneal facet. In group 1 we included 36 clubfeet in which the declination angle of the talar neck and the angle of the posterior calcaneal facet were abnormal [21, 23], and in group 2 we included the remaining clubfeet in which the declination angle of the talar neck and the angle of the posterior calcaneal facet were normal.

In group 1, which included 36 of the 48 clubfeet, the anteroposterior talocalcaneal angle measured 15° ± 6° on anteroposterior radiographs (Fig. 1A). In the 3D CT scan reconstructions, the calcaneus lay beneath the talus and their two longitudinal axes were more or less coincident, so the anteroposterior talocalcaneal angle measured 0° (Fig. 1B); the talus and the calcaneus converged on the frontal projection (Fig. 1C). The difference between the radiographic and the 3D CT scan measurements of the anteroposterior talocalcaneal angle was statistically significant (p < 0.0001). The declination angle of the talar neck was wider than normal, measuring 40° ± 7° (Fig. 1B), whereas the angle of the posterior calcaneal facet of the subtalar joint measured 84° ± 5° (Fig. 1D). The difference of the declination angle of the neck of the talus and the angle of the posterior calcaneal facet between clubfeet and normal feet was statistically significant (p < 0.0001).

In group 2, which included the remaining 12 clubfeet, the anteroposterior talocalcaneal angle measured 20° ± 6° on anteroposterior radiographs. In the 3D CT scan reconstructions, the talus and calcaneus diverged, just as in normal feet, and formed an anteroposterior talocalcaneal angle of 18° ± 4°. The declination angle of the neck of the talus measured 21° ± 4°, whereas the angle of the posterior calcaneal facet of the subtalar joint measured 50° ± 3°. The difference between the radiographic and the 3D CT scan measurements of the anteroposterior talocalcaneal angle was not statistically significant. In addition, the difference in the declination angle of the neck of the talus and the angle of the posterior calcaneal facet between clubfeet and normal feet was not statistically significant.


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Kite [25–28] stated that to radiographically assess whether correction of the clubfoot has been achieved, the talus should be aligned with the first metatarsal and the calcaneus with the fifth metatarsal, but he never mentioned the anteroposterior talocalcaneal angle as a radiographic index of clubfoot correction. Nevertheless, in several books and articles [6, 9, 11, 13], that angle, first described by Wisbrun [1] in 1932, has been attributed to Kite.

With the patient in the standing position, the normal anteroposterior talocalcaneal angle varies on anteroposterior radiography according to the position of the calcaneus underneath the talus and to the stiffness of the foot ligaments [4, 5]. Our study shows that the declination angle of the neck of the talus and the angle of the posterior calcaneal facet of the subtalar joint are two additional factors influencing the anteroposterior talocalcaneal angle on anteroposterior radiography.

In normal feet, the mean value of the anteroposterior talocalcaneal angle on standing radiographs was approximately 2° greater than that same angle on the 3D CT scan reconstructions. This difference was not statistically significant and might result from the different weight-bearing conditions of the foot when the radiographs and CT scans were obtained.

In 75% of treated congenital clubfeet, we observed a statistically significant difference of 15° between the radiographic and the 3D CT scan reconstruction measurements of the anteroposterior talocalcaneal angle. In these cases, the 3D CT scan reconstruction showed that the calcaneus lay beneath the talus, which had a declination angle that was markedly increased; the two anatomic axes of both talus and calcaneus were coincident; and the anteroposterior talocalcaneal angle was close to zero, although it was still measurable on the radiographs. We believe that in these cases the radiographic projection of the neck of the talus, which was markedly angulated medially, gave the false image of a divergence between the talus and the calcaneus on the anteroposterior radiographs.

In 25% of treated congenital clubfeet, we did not observe a statistically significant difference between the radiographic and the 3D CT scan reconstruction measurements of the anteroposterior talocalcaneal angle. In these cases, the talus and calcaneus diverged, as in normal feet, and both the angle of the posterior calcaneal facet of the subtalar joint and the declination angle of the neck of the talus were greater, but not statistically different from normal.

Waisbrod [15] measured the declination angle of the talus in eight fetuses with congenital clubfoot and in fetuses with normal feet. He found that the angle was abnormally high in five clubfeet, measuring an average of 46°, and close to normal, measuring an average of 27°, in three clubfeet, whereas it measured an average of 26° in the normal feet. In three stillborns with congenital clubfoot, Howard and Benson [23] first described an abnormal orientation of the posterior calcaneal facet of the subtalar joint. This abnormality has been insufficiently emphasized [29], but, together with the abnormal shape of the subtalar joint [16], they might represent the inborn pathologic clubfoot abnormalities that could make reestablishing the normal anatomic relationships between the calcaneus and talus difficult with any treatment.

In this study, we identified two clubfoot groups. The larger group was composed of clubfeet in which both the declination angle of the neck of the talus and the angle of the posterior calcaneal facet of the subtalar joint were wide and the difference from normal was statistically significant. In this group, the anteroposterior talocalcaneal angle on anteroposterior radiography did not correspond to the real anatomic relationships between calcaneus and talus, as shown by the 3D CT scan reconstructions. As for the smaller group, both the declination angle of the neck of the talus and the angle of the posterior calcaneal facet of the subtalar joint were not statistically different from normal. In this smaller group, the anteroposterior talocalcaneal angle on anteroposterior radiography corresponded to the real anatomic relationships between the calcaneus and talus. However, both the treatment protocol and the degree of clinical severity at the onset of treatment were the same for both groups. It remains speculative whether the difference between the two groups is due to a technical difference in applying the same treatment protocol to the single clubfoot cases; to a different response of the clubfoot series to the same treatment protocol, because of a different range of severity of the original intrinsic pathology [15, 23]; or to both.

In stillborns with congenital clubfoot, Howard and Benson [14] showed that the anteroposterior talocalcaneal angle does not correspond to the real anatomic relationships of the talus and calcaneus, owing to the position of the ossific nucleus of the talus into the cartilage of its neck, which is markedly angulated medially in comparison to normal. Some authors have questioned the objective value of Kite's angle in both children and adults, and no statistical correlation has been found between the anteroposterior talocalcaneal angle and the functional results in several clinical reports on congenital clubfoot [30–34]. Therefore, on the basis of our results, we believe that the measurement of the anteroposterior talocalcaneal angle on anteroposterior radiography is not a valid parameter for evaluating congenital clubfoot correction at any age and that other imaging parameters should be considered instead of this angle. However, the assessment of an abnormal angle of the talar neck and an abnormal orientation of the posterior calcaneal facet during treatment might be useful to identify a treatment that more accurately corrects the deformity. On the basis of the results of our study, we believe that the adequacy of the correction of severe congenital clubfoot could be assessed by 3D CT scan, although the functional status of the treated clubfoot seems to be the most important factor to address a correct treatment.


Acknowledgments
 
We thank Riccardo Geiger and Albano Savino for their technical assistance in performing the 3D CT scan reconstructions.


References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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