ORIGINAL ARTICLE
C sign: Talocalcaneal Coalition or Flatfoot Deformity? Luis Moraleda, MD, PhD,* George D. Gantsoudes, MD,w and Scott J. Mubarak, MDz
Background: C sign is used to alert the physician of the possible presence of talocalcaneal coalition (TCC), so that advanced imaging can be ordered. The purpose of this study was to know the prevalence of the C sign among patients with TCC and its relationship to the presence of a TCC or to hindfoot alignment. Methods: Retrospective reviews of the presence of C sign in radiographs of 88 feet with TCC (proved by computed tomography scan or surgical findings) and 260 flexible flatfeet were conducted. C sign was classified as complete and interrupted (types A, B, and C). The interobserver variability of the C sign was studied. Seven radiographic parameters were measured to analyze the relationship of these measurements with the presence or absence of the C sign. Results: C sign was present in 68 feet (77%) with TCC: 14.5% complete and 62.5% interrupted (26% type A, 19.5% type B, and 17% type C). C sign was present in 116 flatfeet (45%), all of them interrupted (0.4% type A, 5.5% type B, and 39% type C). The talo-first metatarsal angle, the talohorizontal angle, the calcaneal pitch, the calcaneo-fifth metatarsal angle, and the naviculocuboid overlap presented a more pathologic value when a C sign was present. The k-value for the presence of a C sign was 0.663. Conclusions: The so-called true C sign (complete or interrupted type A) indicates the presence of a TCC and it is not related to flatfoot deformity. However, it is only present in 41% of the cases. The interrupted C sign is much more likely to be related to flatfoot deformity than to the presence of a TCC, specifically when a type C is found. Level of Evidence: Diagnostic Study level I. Key Words: coalition, radiograph, diagnosis, talocalcaneal, flatfoot, C sign (J Pediatr Orthop 2014;34:814–819)
T
arsal coalition is an uncommon condition with an incidence rate of 30 degrees. The radiographs were weight-bearing in all patients of the flatfoot group and 80% of the talocalcaneal group. Two pediatric orthopaedic fellows instructed in recognizing the C sign and blinded to the diagnosis of coalition or idiophatic flatfoot reviewed the radiographs. To ensure unbiased results, the radiographs were shown to the investigators with code numbers. The fellows were asked to indicate the presence or absence of a C sign and, in case of positive finding, to indicate if it was continuous or interrupted. Looking at the example Lateur et al published in their paper,4 we observed 2 different types of interrupted C sign based on the characteristics of the borders of the posteromedial part of the talar dome and the posterior part of the sustentaculum tali. Interrupted C sign could correspond to types 1 and 3 TCC according to Rozansky et al5 classification. According to this, we defined 3 types of interrupted C sign (Fig. 2): type A, where
there is a linear interruption with rarefaction of the edges; type B, where there is a narrow interruption with round borders well defined; and type C, where there is a wide interruption with round borders well defined. Fellows were asked to indicate the type of interrupted C sign (A, B, or C) if present. The prevalence of C sign among the talocalcaneal group and the flatfoot group is described. The interobserver variability of the C sign is presented. C sign is used to alert the physician of the possible presence of TCC, so that advanced imaging can be ordered. Because of that, we did not investigate the intraobserver variability. Furthermore, we measured, in the lateral radiograph of 135 flatfeet, 7 parameters used to describe the alignment of the foot.12 We analyzed the relationship of these measurements with the presence or absence of the C sign.
RESULTS The presence of C sign and the type of sign in the TC coalition and the flatfoot group are described in Table 2. Among patients with TCC, the C sign was present in 68 feet (77%): complete in 13 feet (14.5%), interrupted type A in 23 feet (26%), interrupted type B in 17 feet (19.5%), and interrupted type C in 15 feet (17%). Among patients with flexible flatfoot, the C sign was present in 116 feet (45%): complete in no case, interrupted type A in 1 foot (0.4%), interrupted type B in 14 feet (5.5%), and interrupted type C in 101 feet (39%). Looking at these results, we considered a true C sign the complete sign and the interrupted type A sign. The
TABLE 1. Review of the Literature C Sign (%) Lateur et al4 Sakellariou et al6 Taniguchi et al7 Brown et al8 Liu et al9
Age (y)
Standing X-ray
TCC
Control
Assess Flatfoot
Sensitivity
Specificity
NA 21-36 20 < 35 26
No Yes Yes No Yes
15 20 55 10 32
458 22 55 32 62
No No No Yes No
87 98 49 40 84
93 98 91 50 94
TCC indicates talocalcaneal coalition.
r
2014 Lippincott Williams & Wilkins
www.pedorthopaedics.com |
815
J Pediatr Orthop
Moraleda et al
Volume 34, Number 8, December 2014
FIGURE 2. Lateral radiographs of the foot of patients with TCC showing no C sign (absent), a complete C sign (complete), and the 3 different types of interrupted C sign: type A (A), wherein there is a linear interruption (arrow) with rarefaction of the edges; type B (B), wherein there is a narrow interruption (arrow) with round borders well defined; and type C (C), wherein there is a wide interruption (arrow) with round borders well defined.
true C sign was present in 36 (41%) and 1 (0.8%) feet of the TCC and flatfoot group, respectively. In contrast, the false C sign (an interrupted C sign type B or C) was present in 32 (36%) and 115 (44%) feet of the TCC and flatfoot group, respectively. k is one measure of interobserver agreement.13 The k-value for the presence of a C sign was 0.663, which is considered a substantial agreement. The k-value for the determination of incomplete versus complete C sign was 0.477, which is considered a moderate agreement. The k-value for the determination of type A, B, or C among interrupted sings was 0.313, which is considered a fair agreement. The k-value for the differentiation of true (complete/type A) from false (type B/type C) sign was 0.20, which is considered a slight agreement.
The mean values of the 7 parameters measured in the lateral radiograph of 135 flexible flatfeet with and without a C sign are listed in Table 3. There were significant differences between flatfeet with C sign compared with flatfeet without C sign in the mean value of the talo-first metatarsal angle, the talohorizontal angle, the calcaneal pitch, the calcaneo-fifth metatarsal angle, and naviculocuboid overlap. These measurements presented a more pathologic value when a C sign was present.
DISCUSSION TCC is a congenital connection between the talus and the calcaneus that prevents normal motion of the subtalar joint. It is an uncommon condition with an
TABLE 2. Prevalence of the C Sign and its Different Types in the Talocalcaneal Coalition Group and the Flatfoot Group n (%) TC coalition Flatfoot Total
C Sign
Complete
Type A
Type B
Type C
No C Sign
Total
68 (77) 116 (45) 184 (53)
13 (14.5) 0 13 (4)
23 (26) 1 (0.5) 24 (7)
17 (19.5) 14 (5.5) 31 (9)
15 (17) 101 (39) 116 (33)
20 (23) 144 (55) 164 (47)
88 260 348
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2014 Lippincott Williams & Wilkins
J Pediatr Orthop
Volume 34, Number 8, December 2014
TABLE 3. Seven Parameters Were Measured in the Weightbearing Lateral Radiograph of Foot Talo-first MTT angle Talocalcaneal angle Talohorizontal angle Calcaneal pitch Calcaneal—fifth MTT angle Lateral first to fifth MTT angle NC overlap
C Sign
Mean
SD
P
No Yes No Yes No Yes No Yes No Yes No Yes No Yes
16.22 22.20 46.52 47.44 31.36 35.83 15.33 12.28 22.59 19.43 7.68 6.27 60.94 82.09
10.67 10.30 8.80 7.78 8.73 8.57 6.67 6.52 7.51 6.99 4.93 4.83 19.59 16.44
0.000* 0.462 0.001* 0.003* 0.004* 0.056 0.000*
*Indicates statistically significant P value. MTT indicates metatarsal; NC, naviculocuboid. Their values describe the alignment of the foot. Mean values in 135 flatfeet with and without C sign are presented in this table.
incidence reported of
C sign: Talocalcaneal Coalition or Flatfoot Deformity? Luis Moraleda, MD, PhD,* George D. Gantsoudes, MD,w and Scott J. Mubarak, MDz
Background: C sign is used to alert the physician of the possible presence of talocalcaneal coalition (TCC), so that advanced imaging can be ordered. The purpose of this study was to know the prevalence of the C sign among patients with TCC and its relationship to the presence of a TCC or to hindfoot alignment. Methods: Retrospective reviews of the presence of C sign in radiographs of 88 feet with TCC (proved by computed tomography scan or surgical findings) and 260 flexible flatfeet were conducted. C sign was classified as complete and interrupted (types A, B, and C). The interobserver variability of the C sign was studied. Seven radiographic parameters were measured to analyze the relationship of these measurements with the presence or absence of the C sign. Results: C sign was present in 68 feet (77%) with TCC: 14.5% complete and 62.5% interrupted (26% type A, 19.5% type B, and 17% type C). C sign was present in 116 flatfeet (45%), all of them interrupted (0.4% type A, 5.5% type B, and 39% type C). The talo-first metatarsal angle, the talohorizontal angle, the calcaneal pitch, the calcaneo-fifth metatarsal angle, and the naviculocuboid overlap presented a more pathologic value when a C sign was present. The k-value for the presence of a C sign was 0.663. Conclusions: The so-called true C sign (complete or interrupted type A) indicates the presence of a TCC and it is not related to flatfoot deformity. However, it is only present in 41% of the cases. The interrupted C sign is much more likely to be related to flatfoot deformity than to the presence of a TCC, specifically when a type C is found. Level of Evidence: Diagnostic Study level I. Key Words: coalition, radiograph, diagnosis, talocalcaneal, flatfoot, C sign (J Pediatr Orthop 2014;34:814–819)
T
arsal coalition is an uncommon condition with an incidence rate of 30 degrees. The radiographs were weight-bearing in all patients of the flatfoot group and 80% of the talocalcaneal group. Two pediatric orthopaedic fellows instructed in recognizing the C sign and blinded to the diagnosis of coalition or idiophatic flatfoot reviewed the radiographs. To ensure unbiased results, the radiographs were shown to the investigators with code numbers. The fellows were asked to indicate the presence or absence of a C sign and, in case of positive finding, to indicate if it was continuous or interrupted. Looking at the example Lateur et al published in their paper,4 we observed 2 different types of interrupted C sign based on the characteristics of the borders of the posteromedial part of the talar dome and the posterior part of the sustentaculum tali. Interrupted C sign could correspond to types 1 and 3 TCC according to Rozansky et al5 classification. According to this, we defined 3 types of interrupted C sign (Fig. 2): type A, where
there is a linear interruption with rarefaction of the edges; type B, where there is a narrow interruption with round borders well defined; and type C, where there is a wide interruption with round borders well defined. Fellows were asked to indicate the type of interrupted C sign (A, B, or C) if present. The prevalence of C sign among the talocalcaneal group and the flatfoot group is described. The interobserver variability of the C sign is presented. C sign is used to alert the physician of the possible presence of TCC, so that advanced imaging can be ordered. Because of that, we did not investigate the intraobserver variability. Furthermore, we measured, in the lateral radiograph of 135 flatfeet, 7 parameters used to describe the alignment of the foot.12 We analyzed the relationship of these measurements with the presence or absence of the C sign.
RESULTS The presence of C sign and the type of sign in the TC coalition and the flatfoot group are described in Table 2. Among patients with TCC, the C sign was present in 68 feet (77%): complete in 13 feet (14.5%), interrupted type A in 23 feet (26%), interrupted type B in 17 feet (19.5%), and interrupted type C in 15 feet (17%). Among patients with flexible flatfoot, the C sign was present in 116 feet (45%): complete in no case, interrupted type A in 1 foot (0.4%), interrupted type B in 14 feet (5.5%), and interrupted type C in 101 feet (39%). Looking at these results, we considered a true C sign the complete sign and the interrupted type A sign. The
TABLE 1. Review of the Literature C Sign (%) Lateur et al4 Sakellariou et al6 Taniguchi et al7 Brown et al8 Liu et al9
Age (y)
Standing X-ray
TCC
Control
Assess Flatfoot
Sensitivity
Specificity
NA 21-36 20 < 35 26
No Yes Yes No Yes
15 20 55 10 32
458 22 55 32 62
No No No Yes No
87 98 49 40 84
93 98 91 50 94
TCC indicates talocalcaneal coalition.
r
2014 Lippincott Williams & Wilkins
www.pedorthopaedics.com |
815
J Pediatr Orthop
Moraleda et al
Volume 34, Number 8, December 2014
FIGURE 2. Lateral radiographs of the foot of patients with TCC showing no C sign (absent), a complete C sign (complete), and the 3 different types of interrupted C sign: type A (A), wherein there is a linear interruption (arrow) with rarefaction of the edges; type B (B), wherein there is a narrow interruption (arrow) with round borders well defined; and type C (C), wherein there is a wide interruption (arrow) with round borders well defined.
true C sign was present in 36 (41%) and 1 (0.8%) feet of the TCC and flatfoot group, respectively. In contrast, the false C sign (an interrupted C sign type B or C) was present in 32 (36%) and 115 (44%) feet of the TCC and flatfoot group, respectively. k is one measure of interobserver agreement.13 The k-value for the presence of a C sign was 0.663, which is considered a substantial agreement. The k-value for the determination of incomplete versus complete C sign was 0.477, which is considered a moderate agreement. The k-value for the determination of type A, B, or C among interrupted sings was 0.313, which is considered a fair agreement. The k-value for the differentiation of true (complete/type A) from false (type B/type C) sign was 0.20, which is considered a slight agreement.
The mean values of the 7 parameters measured in the lateral radiograph of 135 flexible flatfeet with and without a C sign are listed in Table 3. There were significant differences between flatfeet with C sign compared with flatfeet without C sign in the mean value of the talo-first metatarsal angle, the talohorizontal angle, the calcaneal pitch, the calcaneo-fifth metatarsal angle, and naviculocuboid overlap. These measurements presented a more pathologic value when a C sign was present.
DISCUSSION TCC is a congenital connection between the talus and the calcaneus that prevents normal motion of the subtalar joint. It is an uncommon condition with an
TABLE 2. Prevalence of the C Sign and its Different Types in the Talocalcaneal Coalition Group and the Flatfoot Group n (%) TC coalition Flatfoot Total
C Sign
Complete
Type A
Type B
Type C
No C Sign
Total
68 (77) 116 (45) 184 (53)
13 (14.5) 0 13 (4)
23 (26) 1 (0.5) 24 (7)
17 (19.5) 14 (5.5) 31 (9)
15 (17) 101 (39) 116 (33)
20 (23) 144 (55) 164 (47)
88 260 348
816 | www.pedorthopaedics.com
r
2014 Lippincott Williams & Wilkins
J Pediatr Orthop
Volume 34, Number 8, December 2014
TABLE 3. Seven Parameters Were Measured in the Weightbearing Lateral Radiograph of Foot Talo-first MTT angle Talocalcaneal angle Talohorizontal angle Calcaneal pitch Calcaneal—fifth MTT angle Lateral first to fifth MTT angle NC overlap
C Sign
Mean
SD
P
No Yes No Yes No Yes No Yes No Yes No Yes No Yes
16.22 22.20 46.52 47.44 31.36 35.83 15.33 12.28 22.59 19.43 7.68 6.27 60.94 82.09
10.67 10.30 8.80 7.78 8.73 8.57 6.67 6.52 7.51 6.99 4.93 4.83 19.59 16.44
0.000* 0.462 0.001* 0.003* 0.004* 0.056 0.000*
*Indicates statistically significant P value. MTT indicates metatarsal; NC, naviculocuboid. Their values describe the alignment of the foot. Mean values in 135 flatfeet with and without C sign are presented in this table.
incidence reported of
