Surg Radiol Anat DOI 10.1007/s00276-015-1472-1
ORIGINAL ARTICLE
Types of subtalar joint facets Min-Ho Jung1 • Byoung Young Choi1 • Ji Yong Lee3 • Chang Sung Han4 Jin Suk Lee1 • Young Chul Yang1 • Byung Pil Cho1,2
•
Received: 10 February 2015 / Accepted: 23 March 2015 Ó Springer-Verlag France 2015
Abstract Articular facets of the clinical subtalar joint (CSTJ) were analyzed using a total of 118 (right 57, left 61) dry, paired calcanei and tali from 68 Korean adult cadavers. The CSTJ facets were classified into the following three types depending on their continuity: type A, all three facets are separated; type B, the anterior and middle facets are partially connected; and type C, the anterior and middle facets are fused to form a single facet. The continuity between the anterior and middle facets was represented by the degree of separation (DS), which ranged between 2.00 (type A) and 1.00 (type C). Type A was most common (39.0 %) in calcanei and rarest (11.0 %) in tali. Matching of calcaneus-talus pairs yielded five combined types: A–A (11.0 %), A–B (28.0 %), B–B (18.6 %), B–C (13.6 %), and C–C (28.8 %). The mean DS was slightly greater in calcanei (1.53) than in tali (1.32), and decreased in the order of types A–A, A–B, B–B, B–C, and C–C. The intersecting angles between the anterior and middle facets, which are related to the mobility of the CSTJ, were inversely related to the DS. These findings indicate that the anterior and middle facets are fused more frequently in tali M. H. Jung and B. Y. Choi contributed equally as first authors. & Byung Pil Cho [email protected] 1
Department of Anatomy, Yonsei University Wonju College of Medicine, 20 Ilsan-ro, Wonju, Kangwon-Do, Republic of Korea
2
Institute of Lifestyle Medicine, Yonsei University Wonju College of Medicine, Wonju, Republic of Korea
3
Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea
4
Pocheon Public Health Center, Pocheon, Republic of Korea
than in calcanei, and combinations of different CSTJ facet types (A–B, B–C) exist over 40 % of feet. Our results indicate that types with a smaller DS (such as B–C and C– C) are relatively mobile but less stable compared to those with a greater DS (such as A–A and A–B). Keywords Subtalar joint Articular facet Calcaneus Talus Degree of separation
Introduction The subtalar complex, the most extensive and important joint of the foot, permits inversion and eversion, and each joint involved in the complex influences the others. It consists of two components, the talocalcaneal or clinical subtalar joint (CSTJ) and the transverse tarsal joint formed by talonavicular and calcaneocuboid joints [18]. The CSTJ is composed of three sets of articular facets forming two different joints between the talus and calcaneus. The anterior and middle articular facets represent the talocalcaneal part of the talocalcaneonavicular joint, while the posterior facets comprise the subtalar joint or anatomical subtalar joint [28]. Among the three pairs of CSTJ facets, the posterior facets are, except for a few rare cases, well separated from the middle facets by the sulcus tali in the talus and by the calcaneal sulcus in the calcaneus. However, the anterior and middle facets, which are part of the talocalcaneonavicular joint, are frequently connected to each other and thus show diverse morphological variations. Knowledge about anatomical variations in the articular surfaces of a joint may be important for analysis of motor mechanics and joint images, post-operative fixation, and artificial joint production. To develop more effective treatments for disabilities of the subtalar complex,
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anatomic features should be precisely evaluated and correlated with biomechanical and physiologic data [18]. Thus, analysis of the articular surfaces of the CSTJ may provide important information for understanding motor dynamics of the foot. In general, the shape of the articular facet of a bone is expected to be identical or very similar to that of another bone participating in the same synovial joint. In reality, Bruckner [4] suggested that the subtalar facets of the talus show the same variations as those of the calcaneus. Nevertheless, the comparison of data from numerous previous studies indicates that CSTJ facet types of tali [1, 3, 12, 20, 22] are considerably different from those of calcanei [2, 6, 10, 11, 13, 19, 30, 34–36, 38]. This discrepancy implies the presence of heterotypic combinations of talar and calcaneal facets forming the same CSTJ, and actually a few cases in which different types of CSTJ facets coexist in calcaneus-talus pairs have been identified [2]. However, systemic investigations as well as detailed analysis of this phenomenon have never been performed. To determine the reason for this discrepancy, we classified the types of articular facets forming CSTJs using paired calcanei and tali and analyzed their interrelationship in this study. In addition, to evaluate the functional significance of different types of CSTJs, we measured several structures that may be involved in their mobility and/or stability, such as intersecting angles between the anterior and middle facets.
classified the CSTJ facets in somewhat different ways from those of Bunning and Barnett [5, 6] because of the lack of occurrence of the single facet configuration (type C of Bunning and Barnett). The articular facets of the CSTJ were classified into three types (Fig. 1) based on previous studies on the calcaneal [4, 9] and talar CSTJ facets [4, 22]. The facets were largely divided into a separate type (type A) and a continuous type, and the latter was further divided into two (types B and C) according to continuity of the anterior and middle facets. Criteria for CSTJ facet types were as follows: (1) Type A: All three articular facets are separated from each other. (2) Type B: The posterior facet is separated but the anterior and middle facets are partially connected. The connection between the two facets forms an angle by which they are identifiable. Outlines of the two connected facets are usually constricted at the connected site. (3) Type C: The posterior facet is separated but the anterior and middle facets are fused to form a single facet. The large, elongated fused facet has a smooth, rounded surface with slight convexity in the talus or with slight concavity in the calcaneus. The incidence of each type was calculated for individual bones. Then, combinations of CSTJ facet types were identified using paired calcanei and tali. Incidences of the combined types were also calculated for paired bones.
Materials and methods
The DS was designed to quantify how much the middle facet is separated from the anterior facet in type B. The DS
Measurement of the degree of separation (DS) between anterior and middle facets
Materials A total of 118 (right 57, left 61) dry, paired calcanei and tali were used. These bones were obtained from 68 Korean adult cadavers (42 males, 26 females) donated to the Yonsei University Wonju College of Medicine for education. The cadavers were 21–101 years old, and the average age was 67.8 ± 18.8 years (male, 63.1 ± 19.7 years; female, 75.3 ± 14.8 years). All samples used in this study were limited to paired calcanei and tali with intact CSTJ facets. Methods Classification of CSTJ facets During the 1960s, Bunning and Barnett [5, 6] classified the calcaneal CSTJ facets into three types: type A, in which the calcanei bear three facets; type B, in which they bear two; and type C, which bears a single facet only. Thereafter, the CSTJ facets of calcanei and tali were classified in various ways by different authors. In the present study, we
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Fig. 1 Types of clinical subtalar joint (CSTJ) facets of the calcaneus and talus
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of type A was determined to be 2.00, which means that the anterior and middle facets exist as two separate entities. The DS of type C was determined to be 1.00, indicating that the anterior and middle facets are fused to form a single facet. The DS of type B was defined as follows: 1.00? the ratio of disconnected parts at the constriction to the total width of the anterior and middle facets (Fig. 2). Thus, the DS of type B was between 1.00 and 2.00 because the anterior and middle facets are partially connected in this type. Measurement of the intersecting angle between anterior and middle facets In the talus, the anterior facet usually makes a convex angle with the middle facet to form a ridge between the two facets (Fig. 3a). When the two bones are in the articulated position, this ridge is accommodated by an angular groove between the anterior and middle facets of the calcaneus (Fig. 3b). All tali and calcanei were photographed in a position that disclosed the intersecting angle between the anterior and middle facets and the images were transferred to a computer. Then, the intersecting angles were measured
Fig. 3 Measurement of the intersecting angle (h) between the anterior and middle facets in the talus (a) and calcaneus (b)
with CorelDRAW X4 (Corel Corporation, Ottawa, Ontario, Canada). In type C, angles formed by round convexities (tali) or concavities (calcanei) were measured. Measurement of the tarsal canal width The tarsal canal and sinus are an interconnected funnelshaped space accommodating several ligamentous structures between the talocalcaneonavicular joint and the (anatomical) subtalar joint below the neck of the talus. The canal and sinus are formed by coupling the sulcus tali superiorly and the calcaneal sulcus inferiorly. The tarsal sinus is the larger, cone-shaped anterolateral space with its base facing laterally, and the tarsal canal refers to the narrow, tunnel-shaped posteromedial space. To assess the dimensions of the tarsal canal, the shortest width of the sulcus tali (Fig. 4a) and that of the calcaneal sulcus (Fig. 4b) was measured separately. Measurements were performed using a Vernier caliper (Mitutoyo, Tokyo, Japan) and repeated three times to minimize measurement errors. Finally, their mean values were used as raw data. Statistics Fig. 2 Measurement of the degree of separation (SD) in the talus of type B (a, b) and calcaneus of type B (c, d). The DS of type B was calculated as follows: 1.00? width of disconnected parts at the constriction (arrows in b, d)/total width of anterior and middle facets (arrows in a, c)
Data were evaluated with SAS (ver. 8.2, SAS Institute Inc., Cary, NC, USA), a statistical software package for personal computers. Descriptive statistics were generated for all metric variables (means, standard deviations, ranges, etc.).
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Surg Radiol Anat Table 1 Incidence of clinical subtalar joint (CSTJ) facet types Bone
Calcaneus
Talus
Paired calcaneustalus
Fig. 4 Measurement of tarsal canal width. The narrowest dimensions of the sulcus tali (arrow in a) and calcaneal sulcus (arrow in b) were measured
Sex differences in incidences of CSTJ facet types were identified by Student’s t tests. Differences in intersecting angles and tarsal canal widths according to CSTJ facet types were verified by Chi square tests and ANOVA. P values indicating statistical significance were set at 0.05 and 0.01.
Results Types of CSTJ facets In type B, the two connected facets were identified by an angular ridge between them in the talus and by an angular groove in the calcaneus. Constrictions on their outline at the connected site served as a good guide for distinguishing the two facets (Figs. 1, 2). However, sometimes it was quite difficult to distinguish type B from the type C due to almost complete fusion of the two facets without distinct indentations on their outlines. In these cases, if the two facets were divided by a faint angular ridge or groove it was classified as type B. In type C, the anterior and middle facets were fused to form a large, elongated single facet with no angular ridges or grooves. The articular surface was characterized by a smooth, rounded convexity in the talus of type C, and by a smooth, rounded concavity in the calcaneus of type C. In calcanei, type A, in which all three facets are separated from each other, appeared most frequently (39.0 %), and types B (32.2 %) and C (28.8 %) followed (Table 1). On the other hand, in tali, type B was most common (46.6 %) and was followed by type C (42.4 %).
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Type
Female
Total
n
n
n
%
%
%
A
25
35.7
21
43.8
46
39.0
B
23
32.9
15
31.3
38
32.2
C
22
31.4
12
25.0
34
28.8
A
9
12.9
4
8.3
13
11.0
B
30
42.9
25
52.1
55
46.6
C
31
44.3
19
39.6
50
42.4
A–A A–B
9 16
12.9 22.9
4 17
8.3 35.4
13 33
11.0 28.0
B–B
14
20.0
8
16.7
22
18.6
B–C
9
12.9
7
14.6
16
13.6
C–C Total
Male
22
31.4
12
25.0
34
28.8
70
100.0
48
100.0
118
100.0
Interestingly, type A, which was identified as the most common type in the calcaneus, was quite rare and showed the lowest frequency (11.0 %) in the talus. There were no significant differences between males and females in the incidence of CSTJ facet types for both calcanei and tali. Five combined types were identified by matching CSTJ facet types of calcaneus-talus pairs (Fig. 5; Table 1). The calcaneus of type A matched with the talus of type A (A– A) or type B (A–B). The calcaneus of type B was paired with the talus of type B (B–B) or type C (B–C). The calcaneus of type C was paired with the talus of type C (C–C) only. Other combinations were not found. Among the five combined types, types C–C (28.8 %) and A–B (28.0 %) were the most common, followed by types B–B (18.6 %), B–C (13.6 %), and A–A (11.0 %). The incidence of combined types did not differ significantly between sexes. Degree of separation (DS) between anterior and middle facets As described previously, the DS of type A was arbitrarily set at 2.00 and that of type C at 1.00. The DS of type B was between 1.00 and 2.00, depending on the ratio of the disconnected part between the anterior and middle facets. The DS of type B was 1.43 in the calcaneus and 1.45 in the talus (Table 2). Overall, the mean DS of the calcaneus was 1.53, and that of the talus was 1.32. In the combined type of articular facets, the mean DS declined in the order of types A–A (2.00), A–B (1.74), B–B (1.45), B–C (1.18), and C–C (1.00). As the combined type became more similar to type C–C, the DS of type B decreased both in calcanei and tali.
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Fig. 5 Five combined types of CSTJ facets identified by matching of calcaneus-talus pairs
Table 2 Degree of separation (DS) between anterior and middle facets Type
Calcaneus
Talus
A
2.00 ± 0.00
2.00 ± 0.00
B
1.43 ± 0.15
1.45 ± 0.12
C
1.00 ± 0.00
1.00 ± 0.00
1.53 ± 0.42
1.32 ± 0.34
2.00 ± 0.00
2.00 ± 0.00
Intersecting angle (°) Calcaneus
Talus
Average
Individual type A
137.9 ± 7.3**
136.8 ± 9.2**
137.70 ± 7.68
B
145.0 ± 7.1**
138.7 ± 9.6**
141.28 ± 9.17
C
151.8 ± 7.1**
150.4 ± 8.8**
151.00 ± 8.10
Combined type
Combined type A–A
Type
Average
Individual type
Average
Table 3 Intersecting angle between anterior and middle facets
2.00 ± 0.00
A–B
2.00 ± 0.00
1.48 ± 0.17
1.74 ± 0.09
B–B
1.49 ± 0.12
1.40 ± 0.13
1.45 ± 0.09
B–C
1.36 ± 0.15
1.00 ± 0.00
1.18 ± 0.07
C–C
1.00 ± 0.00
1.00 ± 0.00
1.00 ± 0.00
Data are expressed as means ± standard deviations
A–A
136.3 ± 5.2**
136.8 ± 9.2**
136.6 ± 7.3**
A–B
138.6 ± 8.0**
138.4 ± 9.4**
138.5 ± 8.6**
B–B
144.0 ± 6.6**
139.2 ± 10.0**
141.6 ± 8.7**
B–C
146.4 ± 7.8**
149.8 ± 10.1**
148.1 ± 9.0**
C–C
151.8 ± 7.1**
150.8 ± 8.2**
151.3 ± 7.6**
Data are expressed as means ± standard deviations **p \ 0.01 between each type
Intersecting angle between anterior and middle facets The intersecting angle between the anterior and middle facets was inversely related to the DS both in individual and combined types (Table 3). In individual types, the angle of the calcaneus was 137.9° in type A, and this was the smallest measurement. The greatest angle was noted in the calcaneus of type C as 151.8°. The angle of the calcaneus in type B showed an intermediate value (145.0°) between that of types A and C. The angle of the talus showed the same tendency in terms of a gradual increase
from type A to type C. All measurements differed significantly (p \ 0.01) between each type for both calcanei and tali. In combined types, the average angle ranged from 136.6° (A–A) to 151.3° (C–C), and increased in the order of types A–A, A-B, B–B, B–C, and C–C. Likewise, the intersecting angle of both calcanei and tali forming combined types also increased in the same pattern. All measurements were significantly different (p \ 0.01) between each combined type.
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Tarsal canal width Very similar to the intersecting angle, the widths of the calcaneal sulcus and sulcus tali were inversely related to the DS except for a few minor variations (Table 4). In individual types, the width of the sulcus tali was smallest (4.2 mm) in type A, and greatest (5.4 mm) in type C with that of type B (4.7 mm) between them. The width of the calcaneal sulcus was greater in the continuous type (types B and C) than in the separate type (type A), and increased from type A to type C. All measurements were significantly different between types in both calcanei and tali. In combined types, the mean width of the sulcus tali was narrowest (4.2 mm) in type A–A, widest (5.5 mm) in the type C–C, and increased in the order of types A–A, A–B, B–B, B–C, and C–C. The mean width of the calcaneal sulcus showed the same tendency except that the width of type B–C was slightly greater than that of type C–C. As a result, the average width of the tarsal canal showed the same pattern with the calcaneal sulcus in that the greatest width was noted in type B–C (5.5 mm) instead of type C–C (5.4 mm). Despite this, the average width of the tarsal canal tended to be inversely related to the DS. There were statistically significant differences between each combined type for all measurements.
Discussion We classified the CSTJ facets into three types based on continuity of the facets, as proposed by some authors [4, 22]. Previous studies on the calcaneus or talus reported rare cases in which the three articular facets are fused to form a single facet [5, 6, 15, 21] or the anterior facet is absent [4, Table 4 Width of tarsal canal Type
Width (mm) of tarsal sinus Calcaneal sulcus
Sulcus tali
Average
Individual type A
4.8 ± 1.0*
4.2 ± 1.1**
B
5.3 ± 1.1*
4.7 ± 1.0**
C
5.4 ± 1.4*
5.4 ± 0.9**
Combined type A–A
4.6 ± 1.0*
4.2 ± 1.1**
4.4 ± 1.0**
A–B
4.9 ± 1.1*
4.5 ± 1.1**
4.7 ± 1.1**
B–B
5.0 ± 1.2*
5.1 ± 0.9**
5.0 ± 1.0**
B–C
5.7 ± 0.9*
5.2 ± 0.9**
5.5 ± 1.1**
C–C
5.4 ± 1.4*
5.5 ± 1.0**
5.4 ± 1.1**
Data are expressed as means ± standard deviations *p \ 0.05 between each type **p \ 0.01 between each type
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10, 11, 15, 19]. These types were excluded from the classification system in this study because such variations were not found. With regard to the calcaneus in the present study, type A, in which all three articular facets are separated from each other, was most common, followed by types B and C. These results were similar to or coincided with those of numerous previous studies (Table 5). Type A was reported to be most common among the three types in calcanei of various nationalities including Spanish [11], Koreans [19], Turks [38], Belgians [2, 35], and Indians [34]. In addition, several authors, who did not divide the continuous type (types B and C) into subtypes, reported that the frequency of type A exceeded 30 % in calcanei of British [6], Nigerians [6], Egyptians [10], Americans [21], and Indians [29]. A relatively low occurrence of type A was also noted by some authors, but its incidence exceeded 20 % in almost all studies reported. This was in stark contrast to the very low occurrence of this type, less than 10 %, in tali (Table 5). Examination of CSTJ facets using paired calcanei-tali revealed that patterns of talar facets are remarkably different from those of calcaneal facets (Table 5). In contrast to calcanei, type A was the rarest (11.0 %) type in tali, while the ratio of the continuous type was much greater in tali (89.0 %) than in calcanei (61.0 %). This finding was also similar to those of many previous studies. The separate type (type A) in tali was rarely (3.2–9.3 %) found in Indians [1, 3, 12, 20] and Koreans [22]. These findings suggest that the anterior and middle facets of the tali tend to be fused more frequently than those of the calcanei. Among the continuous type of tali in this study, the frequency of type B was slightly greater than that of type C. Similarly, several previous studies reported the same results [1, 3, 12, 22], but the frequency of type B (60.5–79.0 %) was much greater than that of type C (10.0–39.0 %) compared to our results. These differences might be due to differences in interpretation of the transitional shape of some facets between the two types by different authors. Interestingly, Barbaix et al. [2] reported an exceptionally high incidence (39.0 %) of the separate type (type A) in tali, and an even greater occurrence (61.0 %) of this type in the calcanei of Belgians (Table 5). Even though tali in their study had the highest incidence of the separate type ever reported, their results suggest the same conclusion as ours in that the anterior and middle facets of tali are fused more frequently than those of calcanei. It can also be deduced from their study that the marked predominance of type A both in calcanei and tali might be characteristic of some European populations. The high frequency of the separate type (type A) in European calcanei was first recognized by Bunning and
Surg Radiol Anat Table 5 Incidence of CSTJ facet types in different nationalities Bone
Calcaneus
Nationalities
American
References
Drayer-Verhagen [9] Kelikian and Sarrafian [21]
Type (%) Separate
Continuous
A
B
C
Others B?C
191
26.7
54.5
18.9
50
34.0
64.0
2.0
134 49
61.0 36.7
28.0 53.1
11.0 10.2
Belgian
Barbaix et al. [2] Shahabpour et al. [35]
British
Bunning and Barnett [6]
194
67.0
33.0
0.0
Egyptian
El-Eishi [10]
200
40.0
49.0
11.0
Indian
Bunning and Barnett [6]
78
21.8
78.2
0.0
Korean
14.0 24.5
28.0
14.0 28.6
Gupta et al. [15]
401
25.9
66.8
7.2
Padmanabhan [30]
272
34.9
65.1
0.0
39.0
8.5
Madhavi et al. [20]
222
19.4
72.1
Muthukumaravel et al. [25]
237
33.3
65.8
0.8
Sharada et al. [36]
300
28.6
50.3
16.6
66.9
4.3
50
26.0
40.0
34.0
74.0
0.0
24.0
32.0
Mini et al. [27]
Talus
Number of cases
Seema et al. [34]
300
35.0
Garg et al. [13]
310
24.5
56.0
9.0
72.3
3.2 2.2
Kang et al. [19]
226
39.4
37.6
20.8
58.4
Present study (2015)
118
39.0
32.2
28.8
61.0
0.0
Nigerian Spanish
Bunning and Barnett [6] Forriol Campos and Gomez Pellico [11]
492 176
35.8 39.8
29.0
24.4
63.4 53.4
0.8 6.8
Turk
Uygur et al. [38]
221
34.4
25.3
33.0
58.4
7.2
Belgian
Barbaix et al. [2]
122
39.0
28.0
21.0
49.0
11.0
Indian
Korean
Arora et al. [1]
500
3.2
79.0
15.8
94.8
2.0
Bilodi [3]
240
5.0
66.7
10.0
76.7
18.4
Garg et al. [12]
300
5.3
49.7
39.0
88.7
6.0
Kaur et al. [20]
100
5.0
33.0
45.0
78.0
17.0
76
9.3
60.5
30.3
90.8
0.0
118
11.0
46.6
42.4
89.0
0.0
Lee et al. [22] Present study (2015)
Barnett [6]. They found a significantly higher incidence of type A in a British study population compared with Africans and Indians, in whom the continuous type predominates (Table 5). They noted that racial differences are also present in fetuses. Based on these observations, Bunning and Barnett [6] suggested that these features are probably genetically determined rather than resulting from differences in gait or other post-natal factors. However, it seems improbable that the high occurrence of the separate type is common among all European populations because other studies of Belgian [35] and Spanish [11] populations showed a relatively low occurrence of type A, similar to studies of other races (Table 5). Additional studies on CSTJ facets of other European populations will be helpful in determining whether these features are unique to certain European populations. Bruckner [4] noted that CSTJ facets on the talus exhibited the same variation as the calcaneus in a study using
32 cases. On the other hand, Barbaix et al. [2] found 7 cases, among 30 pairs of calcanei and tali, in which type A1 calcanei (=type A of our study) were paired with type A2 tali (=type B of our study), and suggested that talar CSTJ facets are more frequently fused because they are located on the convex talar head situated within the concavity of the corresponding facets on the calcaneus. However, there has never been a systemic analysis of CSTJ facet types using paired calcanei and tali. In the present study, we found five combinations of CSTJ facet types, including heterotypic combinations, by examining 118 paired calcanei and tali (Table 1). The calcaneus of type A was paired with the talus of type A (A–A) or more frequently with the talus of type B (A–B). The calcaneus of type B was paired with the talus of type B (B–B) or with the talus of type C (B–C). The calcaneus of type C was paired with the talus of type C only, and type C–C was most frequently observed among the five combined types.
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Thus, it is obvious that combinations of different types (A– B, B–C) exist in greater than 40 % of feet, and this answers the question why patterns of calcaneal CSTJ facets are so different from those of talar CSTJ facets. The findings discussed above indicate that the anterior and middle facets are fused more frequently in tali than in calcanei as proposed by Barbaix et al. [2], and that those of calcanei are separated from each other more frequently than those of tali. To quantify and compare how much the anterior and middle facets are separated, we measured the DS between the two facets (Table 2). The DS of type A was arbitrarily set at 2.00 and that of type C at 1.00. The DS of type B was ranged between 1.00 and 2.00 based on the actual measurement. Thus, the closer the DS is to 2.00, the more separated the two facets are, and the closer the DS is to 1.00, the more fused the two facets are. There were no significant differences between the DS of the calcaneus of type B (1.44) and that of the talus of type B (1.45). However, the mean DS of the calcanei overall (1.53) was greater than that of the tali overall (1.32), indicating that the anterior and middle facets are more separated in calcanei than in tali. This finding was due to the fact that the separate type (type A) is more common while the continuous type (type B, type C) is rarer in the calcaneus compared to the talus (Table 1). The DS of the combined types decreased gradually in the order of types A–A, A–B, B–B, B–C, and C–C. According to the transition of types from A–A to C–C, the DS of type B decreased both in calcanei and tali; the mean calcaneal DS of type B–C (1.36) was smaller than that of type B–B (1.49), and the mean talar DS of type B–B (1.40) was smaller than that of type A–B (1.48) (Table 2). This result clearly demonstrates that partially connected anterior and middle facets of type B show a higher tendency toward coalescence both in calcanei and tali as the combined type approaches type C–C. A convex-downward angle is formed between the anterior and middle facets of the talus, which fits into a concave, V-shaped groove with a similar intersecting angle on the calcaneus. In the calcaneus, the intersecting angle of the separate type (type A) was previously reported as 121.5°[27]–127.8°[9] and that of the continuous type (types B and C) as 137.1°[24]–151.6°[27]. We achieved similar, but more detailed measurements (Table 3). The calcaneal intersecting angle of type A was 137.8°, type B was 144.4°, and type C was 151.2°. Likewise, talar angles increased from type A to type C, and were similar but slightly smaller than those of calcanei. Intersecting angles of both calcanei and tali were inversely related to the DS. These results indicate that the more the facets are connected, the greater the intersecting angles are. These features are thought to be related to the mobility and stability of the CSTJ. The relatively acute intersecting
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angle of the separate type allows the talar head to be placed tightly within the V-shaped groove on the calcaneus, restraining movement of the talar head. In the foot with a type A–A CSTJ, this spatial relationship constrains the talar head and limits medial rotation of the talus during the heel strike [9]. Additionally, CSTJs with three articular facets (type A) have smaller articular surface areas and higher subtalar axis angles [4]. A higher subtalar axis angle is responsible for a higher longitudinal arch [25, 31], and high-arched feet are described clinically as rigid [14]. In pes cavus, a foot with a high arch, the subtalar joint axis is more vertical and a more rigid CSTJ permits less subtalar motion during walking [16]. The generalized rigidity of the foot and the limited motion in the subtalar joint often are surprising in this condition [26]. Moreover, in the separate type, the talus perches on the calcaneus through an articular tripod formed by three well-separated facets [4]. Thus, CSTJs of type A with smaller intersecting angles were determined to be relatively stable structures with decreased mobility [4, 9]. On the other hand, smooth, larger and relatively flat articular facets with greater intersecting angles of the continuous type (types B and C) may permit relatively free movement of the talar head. The larger intersecting angle of the continuous type presents less of an impediment to medial rotation of the talar head than the relatively acute angle of type A [9]. It was found that continuous type CSTJs have lower subtalar axis angles and greater joint mobility [4], consistent with clinical observations indicating that low-arched feet are hypermobile [32] and people with asymptomatic flat feet usually show a greater range of subtalar motion than do persons with normal feet [26]. Excessive motility of the talar head of the continuous type may cause lasting excessive pressure on the plantar calcaneonavicular (or spring) ligament, which supports the talar head and plays an important role in maintaining the longitudinal arch of the foot, resulting in the laxity of this ligament [9] that is responsible for mobile or unstable feet [17, 18, 32]. A higher incidence of arthritic lipping or other stress-related arthritic changes of CSTJ facets in the continuous type compared to the separate type has been suggested as reliable evidence of the hypermobility and instability of this type of CSTJs [9, 24]. Since the intersecting angle was greatest in type C, it was considered to be the most probable structural predisposition in the setting of ligamentous laxity leading to foot instability. In the combined type, the intersecting angle was inversely related to DS, and increased in the order of types A–A, A–B, B–B, B–C, and C–C. As a result, type C–C was thought to not only be the most mobile, but also the most unstable. We also found that the width of the tarsal canal is related to CSTJ facet type (Table 4). The widths of both the calcaneal sulcus and sulcus tali were greater in the continuous
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type than in the separate type. In terms of the combined types, the tarsal canal widths increased from A–A to B–C/ C–C, with an inverse relationship to the DS. These results indicate that a wider tarsal canal is characteristic of the continuous type, and that the more the facets are fused, the greater the widths are. The tarsal canal and sinus accommodate parts of the CSTJ joint capsules and several intrinsic and extrinsic ligaments related to the stability and mobility of the CSTJ. The most anterior and posterior borders of the tarsal canal and sinus are attached by the posterior part of the talocalcaneonavicular joint capsule and the anterior part of the (anatomical) subtalar joint capsule. Between them, three major ligamentous structures are found: the ligament of the tarsal canal, the cervical ligament, and the deep extensions of the inferior extensor retinaculum [7, 8, 37, 39]. The deep extensions of the inferior extensor retinaculum and the cervical ligament are located in the tarsal sinus, and they limit inversion [7, 23, 37]. The former is composed of three (medial, intermediate, and lateral) roots that extend from the stem of the Y-shaped inferior extensor retinaculum [7, 8, 23, 37]. The tarsal canal holds the ligament of the tarsal canal and the medial root of the inferior extensor retinaculum [7, 37]. The latter plays a role in limiting inversion together with other parts of the inferior extensor retinaculum. The ligament of the tarsal canal was named by Smith [37] and is sometimes called the interosseous talocalcaneal ligament [23] or the talocalcaneal interosseous ligament of the canalis tarsi [33]. It arises from the floor near the center of the tarsal canal and runs superomedially into the medial end of the roof of the tarsal canal [7]. Smith [37] suggested that this ligament plays a role in limiting eversion; however, Cahill [7] suggested that the ligament of the tarsal canal serves as a tether to maintain the apposition of the two bones with little or no function in limiting either inversion or eversion. In addition, several other functions have been proposed for this ligament, such as a proprioceptive function [8], or as the central pivot of the CSTJ controlling all movement [23]. The functional significance of our findings that a wider tarsal canal is characteristic of the continuous type is unclear. It might be helpful for understanding the interrelationship between the dimensions of the tarsal canal and those of the ligamentous structures within it, but currently the functional role of the ligament of the tarsal canal remains controversial. In the present study, the incidences of talar CSTJ facet types were reconfirmed to be different from those of calcaneal facet types. By matching of paired calcaneal and talar facets, we identified five combined types (A–A, A–B, B–B, B–C, and C–C) of CSTJ facets. Among them, types C–C and A–B were the most common. Combinations of different types (A–B and B–C) of CSTJ facets existed over 40 % of
feet examined. These findings indicate that the anterior and middle facets of CSTJs are more often fused in tali, and more often separated in calcanei. This tendency was confirmed also by the smaller DS of tali and the greater DS of calcanei. Measurements of intersecting angles between anterior and middle facets, which influence the stability and/or biomechanics of the CSTJ, revealed that this tendency is related to facilitation of talar movement on the calcaneus. Taken together, our results indicate that types with a smaller DS (i.e., combination of continuous types such as B–C and C–C) are relatively mobile but less stable compared to those with a greater DS (i.e., combination of separate types or combination of separate-continuous types such as A–A or A–B). The former can predispose people to foot pain or CSTJ instability, especially later in life. These results provide valuable information in the understanding of motor mechanics of the feet and will contribute to the diagnosis and identification of risk factors for foot instability. Acknowledgments The authors are deeply grateful to the donors of the cadavers used in this study. We would also like to thank Mr. Young Chul Kim and Mr. Dae Seong Park for their expert technical support. Conflict of interest
None.
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ORIGINAL ARTICLE
Types of subtalar joint facets Min-Ho Jung1 • Byoung Young Choi1 • Ji Yong Lee3 • Chang Sung Han4 Jin Suk Lee1 • Young Chul Yang1 • Byung Pil Cho1,2
•
Received: 10 February 2015 / Accepted: 23 March 2015 Ó Springer-Verlag France 2015
Abstract Articular facets of the clinical subtalar joint (CSTJ) were analyzed using a total of 118 (right 57, left 61) dry, paired calcanei and tali from 68 Korean adult cadavers. The CSTJ facets were classified into the following three types depending on their continuity: type A, all three facets are separated; type B, the anterior and middle facets are partially connected; and type C, the anterior and middle facets are fused to form a single facet. The continuity between the anterior and middle facets was represented by the degree of separation (DS), which ranged between 2.00 (type A) and 1.00 (type C). Type A was most common (39.0 %) in calcanei and rarest (11.0 %) in tali. Matching of calcaneus-talus pairs yielded five combined types: A–A (11.0 %), A–B (28.0 %), B–B (18.6 %), B–C (13.6 %), and C–C (28.8 %). The mean DS was slightly greater in calcanei (1.53) than in tali (1.32), and decreased in the order of types A–A, A–B, B–B, B–C, and C–C. The intersecting angles between the anterior and middle facets, which are related to the mobility of the CSTJ, were inversely related to the DS. These findings indicate that the anterior and middle facets are fused more frequently in tali M. H. Jung and B. Y. Choi contributed equally as first authors. & Byung Pil Cho [email protected] 1
Department of Anatomy, Yonsei University Wonju College of Medicine, 20 Ilsan-ro, Wonju, Kangwon-Do, Republic of Korea
2
Institute of Lifestyle Medicine, Yonsei University Wonju College of Medicine, Wonju, Republic of Korea
3
Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea
4
Pocheon Public Health Center, Pocheon, Republic of Korea
than in calcanei, and combinations of different CSTJ facet types (A–B, B–C) exist over 40 % of feet. Our results indicate that types with a smaller DS (such as B–C and C– C) are relatively mobile but less stable compared to those with a greater DS (such as A–A and A–B). Keywords Subtalar joint Articular facet Calcaneus Talus Degree of separation
Introduction The subtalar complex, the most extensive and important joint of the foot, permits inversion and eversion, and each joint involved in the complex influences the others. It consists of two components, the talocalcaneal or clinical subtalar joint (CSTJ) and the transverse tarsal joint formed by talonavicular and calcaneocuboid joints [18]. The CSTJ is composed of three sets of articular facets forming two different joints between the talus and calcaneus. The anterior and middle articular facets represent the talocalcaneal part of the talocalcaneonavicular joint, while the posterior facets comprise the subtalar joint or anatomical subtalar joint [28]. Among the three pairs of CSTJ facets, the posterior facets are, except for a few rare cases, well separated from the middle facets by the sulcus tali in the talus and by the calcaneal sulcus in the calcaneus. However, the anterior and middle facets, which are part of the talocalcaneonavicular joint, are frequently connected to each other and thus show diverse morphological variations. Knowledge about anatomical variations in the articular surfaces of a joint may be important for analysis of motor mechanics and joint images, post-operative fixation, and artificial joint production. To develop more effective treatments for disabilities of the subtalar complex,
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anatomic features should be precisely evaluated and correlated with biomechanical and physiologic data [18]. Thus, analysis of the articular surfaces of the CSTJ may provide important information for understanding motor dynamics of the foot. In general, the shape of the articular facet of a bone is expected to be identical or very similar to that of another bone participating in the same synovial joint. In reality, Bruckner [4] suggested that the subtalar facets of the talus show the same variations as those of the calcaneus. Nevertheless, the comparison of data from numerous previous studies indicates that CSTJ facet types of tali [1, 3, 12, 20, 22] are considerably different from those of calcanei [2, 6, 10, 11, 13, 19, 30, 34–36, 38]. This discrepancy implies the presence of heterotypic combinations of talar and calcaneal facets forming the same CSTJ, and actually a few cases in which different types of CSTJ facets coexist in calcaneus-talus pairs have been identified [2]. However, systemic investigations as well as detailed analysis of this phenomenon have never been performed. To determine the reason for this discrepancy, we classified the types of articular facets forming CSTJs using paired calcanei and tali and analyzed their interrelationship in this study. In addition, to evaluate the functional significance of different types of CSTJs, we measured several structures that may be involved in their mobility and/or stability, such as intersecting angles between the anterior and middle facets.
classified the CSTJ facets in somewhat different ways from those of Bunning and Barnett [5, 6] because of the lack of occurrence of the single facet configuration (type C of Bunning and Barnett). The articular facets of the CSTJ were classified into three types (Fig. 1) based on previous studies on the calcaneal [4, 9] and talar CSTJ facets [4, 22]. The facets were largely divided into a separate type (type A) and a continuous type, and the latter was further divided into two (types B and C) according to continuity of the anterior and middle facets. Criteria for CSTJ facet types were as follows: (1) Type A: All three articular facets are separated from each other. (2) Type B: The posterior facet is separated but the anterior and middle facets are partially connected. The connection between the two facets forms an angle by which they are identifiable. Outlines of the two connected facets are usually constricted at the connected site. (3) Type C: The posterior facet is separated but the anterior and middle facets are fused to form a single facet. The large, elongated fused facet has a smooth, rounded surface with slight convexity in the talus or with slight concavity in the calcaneus. The incidence of each type was calculated for individual bones. Then, combinations of CSTJ facet types were identified using paired calcanei and tali. Incidences of the combined types were also calculated for paired bones.
Materials and methods
The DS was designed to quantify how much the middle facet is separated from the anterior facet in type B. The DS
Measurement of the degree of separation (DS) between anterior and middle facets
Materials A total of 118 (right 57, left 61) dry, paired calcanei and tali were used. These bones were obtained from 68 Korean adult cadavers (42 males, 26 females) donated to the Yonsei University Wonju College of Medicine for education. The cadavers were 21–101 years old, and the average age was 67.8 ± 18.8 years (male, 63.1 ± 19.7 years; female, 75.3 ± 14.8 years). All samples used in this study were limited to paired calcanei and tali with intact CSTJ facets. Methods Classification of CSTJ facets During the 1960s, Bunning and Barnett [5, 6] classified the calcaneal CSTJ facets into three types: type A, in which the calcanei bear three facets; type B, in which they bear two; and type C, which bears a single facet only. Thereafter, the CSTJ facets of calcanei and tali were classified in various ways by different authors. In the present study, we
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Fig. 1 Types of clinical subtalar joint (CSTJ) facets of the calcaneus and talus
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of type A was determined to be 2.00, which means that the anterior and middle facets exist as two separate entities. The DS of type C was determined to be 1.00, indicating that the anterior and middle facets are fused to form a single facet. The DS of type B was defined as follows: 1.00? the ratio of disconnected parts at the constriction to the total width of the anterior and middle facets (Fig. 2). Thus, the DS of type B was between 1.00 and 2.00 because the anterior and middle facets are partially connected in this type. Measurement of the intersecting angle between anterior and middle facets In the talus, the anterior facet usually makes a convex angle with the middle facet to form a ridge between the two facets (Fig. 3a). When the two bones are in the articulated position, this ridge is accommodated by an angular groove between the anterior and middle facets of the calcaneus (Fig. 3b). All tali and calcanei were photographed in a position that disclosed the intersecting angle between the anterior and middle facets and the images were transferred to a computer. Then, the intersecting angles were measured
Fig. 3 Measurement of the intersecting angle (h) between the anterior and middle facets in the talus (a) and calcaneus (b)
with CorelDRAW X4 (Corel Corporation, Ottawa, Ontario, Canada). In type C, angles formed by round convexities (tali) or concavities (calcanei) were measured. Measurement of the tarsal canal width The tarsal canal and sinus are an interconnected funnelshaped space accommodating several ligamentous structures between the talocalcaneonavicular joint and the (anatomical) subtalar joint below the neck of the talus. The canal and sinus are formed by coupling the sulcus tali superiorly and the calcaneal sulcus inferiorly. The tarsal sinus is the larger, cone-shaped anterolateral space with its base facing laterally, and the tarsal canal refers to the narrow, tunnel-shaped posteromedial space. To assess the dimensions of the tarsal canal, the shortest width of the sulcus tali (Fig. 4a) and that of the calcaneal sulcus (Fig. 4b) was measured separately. Measurements were performed using a Vernier caliper (Mitutoyo, Tokyo, Japan) and repeated three times to minimize measurement errors. Finally, their mean values were used as raw data. Statistics Fig. 2 Measurement of the degree of separation (SD) in the talus of type B (a, b) and calcaneus of type B (c, d). The DS of type B was calculated as follows: 1.00? width of disconnected parts at the constriction (arrows in b, d)/total width of anterior and middle facets (arrows in a, c)
Data were evaluated with SAS (ver. 8.2, SAS Institute Inc., Cary, NC, USA), a statistical software package for personal computers. Descriptive statistics were generated for all metric variables (means, standard deviations, ranges, etc.).
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Surg Radiol Anat Table 1 Incidence of clinical subtalar joint (CSTJ) facet types Bone
Calcaneus
Talus
Paired calcaneustalus
Fig. 4 Measurement of tarsal canal width. The narrowest dimensions of the sulcus tali (arrow in a) and calcaneal sulcus (arrow in b) were measured
Sex differences in incidences of CSTJ facet types were identified by Student’s t tests. Differences in intersecting angles and tarsal canal widths according to CSTJ facet types were verified by Chi square tests and ANOVA. P values indicating statistical significance were set at 0.05 and 0.01.
Results Types of CSTJ facets In type B, the two connected facets were identified by an angular ridge between them in the talus and by an angular groove in the calcaneus. Constrictions on their outline at the connected site served as a good guide for distinguishing the two facets (Figs. 1, 2). However, sometimes it was quite difficult to distinguish type B from the type C due to almost complete fusion of the two facets without distinct indentations on their outlines. In these cases, if the two facets were divided by a faint angular ridge or groove it was classified as type B. In type C, the anterior and middle facets were fused to form a large, elongated single facet with no angular ridges or grooves. The articular surface was characterized by a smooth, rounded convexity in the talus of type C, and by a smooth, rounded concavity in the calcaneus of type C. In calcanei, type A, in which all three facets are separated from each other, appeared most frequently (39.0 %), and types B (32.2 %) and C (28.8 %) followed (Table 1). On the other hand, in tali, type B was most common (46.6 %) and was followed by type C (42.4 %).
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Type
Female
Total
n
n
n
%
%
%
A
25
35.7
21
43.8
46
39.0
B
23
32.9
15
31.3
38
32.2
C
22
31.4
12
25.0
34
28.8
A
9
12.9
4
8.3
13
11.0
B
30
42.9
25
52.1
55
46.6
C
31
44.3
19
39.6
50
42.4
A–A A–B
9 16
12.9 22.9
4 17
8.3 35.4
13 33
11.0 28.0
B–B
14
20.0
8
16.7
22
18.6
B–C
9
12.9
7
14.6
16
13.6
C–C Total
Male
22
31.4
12
25.0
34
28.8
70
100.0
48
100.0
118
100.0
Interestingly, type A, which was identified as the most common type in the calcaneus, was quite rare and showed the lowest frequency (11.0 %) in the talus. There were no significant differences between males and females in the incidence of CSTJ facet types for both calcanei and tali. Five combined types were identified by matching CSTJ facet types of calcaneus-talus pairs (Fig. 5; Table 1). The calcaneus of type A matched with the talus of type A (A– A) or type B (A–B). The calcaneus of type B was paired with the talus of type B (B–B) or type C (B–C). The calcaneus of type C was paired with the talus of type C (C–C) only. Other combinations were not found. Among the five combined types, types C–C (28.8 %) and A–B (28.0 %) were the most common, followed by types B–B (18.6 %), B–C (13.6 %), and A–A (11.0 %). The incidence of combined types did not differ significantly between sexes. Degree of separation (DS) between anterior and middle facets As described previously, the DS of type A was arbitrarily set at 2.00 and that of type C at 1.00. The DS of type B was between 1.00 and 2.00, depending on the ratio of the disconnected part between the anterior and middle facets. The DS of type B was 1.43 in the calcaneus and 1.45 in the talus (Table 2). Overall, the mean DS of the calcaneus was 1.53, and that of the talus was 1.32. In the combined type of articular facets, the mean DS declined in the order of types A–A (2.00), A–B (1.74), B–B (1.45), B–C (1.18), and C–C (1.00). As the combined type became more similar to type C–C, the DS of type B decreased both in calcanei and tali.
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Fig. 5 Five combined types of CSTJ facets identified by matching of calcaneus-talus pairs
Table 2 Degree of separation (DS) between anterior and middle facets Type
Calcaneus
Talus
A
2.00 ± 0.00
2.00 ± 0.00
B
1.43 ± 0.15
1.45 ± 0.12
C
1.00 ± 0.00
1.00 ± 0.00
1.53 ± 0.42
1.32 ± 0.34
2.00 ± 0.00
2.00 ± 0.00
Intersecting angle (°) Calcaneus
Talus
Average
Individual type A
137.9 ± 7.3**
136.8 ± 9.2**
137.70 ± 7.68
B
145.0 ± 7.1**
138.7 ± 9.6**
141.28 ± 9.17
C
151.8 ± 7.1**
150.4 ± 8.8**
151.00 ± 8.10
Combined type
Combined type A–A
Type
Average
Individual type
Average
Table 3 Intersecting angle between anterior and middle facets
2.00 ± 0.00
A–B
2.00 ± 0.00
1.48 ± 0.17
1.74 ± 0.09
B–B
1.49 ± 0.12
1.40 ± 0.13
1.45 ± 0.09
B–C
1.36 ± 0.15
1.00 ± 0.00
1.18 ± 0.07
C–C
1.00 ± 0.00
1.00 ± 0.00
1.00 ± 0.00
Data are expressed as means ± standard deviations
A–A
136.3 ± 5.2**
136.8 ± 9.2**
136.6 ± 7.3**
A–B
138.6 ± 8.0**
138.4 ± 9.4**
138.5 ± 8.6**
B–B
144.0 ± 6.6**
139.2 ± 10.0**
141.6 ± 8.7**
B–C
146.4 ± 7.8**
149.8 ± 10.1**
148.1 ± 9.0**
C–C
151.8 ± 7.1**
150.8 ± 8.2**
151.3 ± 7.6**
Data are expressed as means ± standard deviations **p \ 0.01 between each type
Intersecting angle between anterior and middle facets The intersecting angle between the anterior and middle facets was inversely related to the DS both in individual and combined types (Table 3). In individual types, the angle of the calcaneus was 137.9° in type A, and this was the smallest measurement. The greatest angle was noted in the calcaneus of type C as 151.8°. The angle of the calcaneus in type B showed an intermediate value (145.0°) between that of types A and C. The angle of the talus showed the same tendency in terms of a gradual increase
from type A to type C. All measurements differed significantly (p \ 0.01) between each type for both calcanei and tali. In combined types, the average angle ranged from 136.6° (A–A) to 151.3° (C–C), and increased in the order of types A–A, A-B, B–B, B–C, and C–C. Likewise, the intersecting angle of both calcanei and tali forming combined types also increased in the same pattern. All measurements were significantly different (p \ 0.01) between each combined type.
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Surg Radiol Anat
Tarsal canal width Very similar to the intersecting angle, the widths of the calcaneal sulcus and sulcus tali were inversely related to the DS except for a few minor variations (Table 4). In individual types, the width of the sulcus tali was smallest (4.2 mm) in type A, and greatest (5.4 mm) in type C with that of type B (4.7 mm) between them. The width of the calcaneal sulcus was greater in the continuous type (types B and C) than in the separate type (type A), and increased from type A to type C. All measurements were significantly different between types in both calcanei and tali. In combined types, the mean width of the sulcus tali was narrowest (4.2 mm) in type A–A, widest (5.5 mm) in the type C–C, and increased in the order of types A–A, A–B, B–B, B–C, and C–C. The mean width of the calcaneal sulcus showed the same tendency except that the width of type B–C was slightly greater than that of type C–C. As a result, the average width of the tarsal canal showed the same pattern with the calcaneal sulcus in that the greatest width was noted in type B–C (5.5 mm) instead of type C–C (5.4 mm). Despite this, the average width of the tarsal canal tended to be inversely related to the DS. There were statistically significant differences between each combined type for all measurements.
Discussion We classified the CSTJ facets into three types based on continuity of the facets, as proposed by some authors [4, 22]. Previous studies on the calcaneus or talus reported rare cases in which the three articular facets are fused to form a single facet [5, 6, 15, 21] or the anterior facet is absent [4, Table 4 Width of tarsal canal Type
Width (mm) of tarsal sinus Calcaneal sulcus
Sulcus tali
Average
Individual type A
4.8 ± 1.0*
4.2 ± 1.1**
B
5.3 ± 1.1*
4.7 ± 1.0**
C
5.4 ± 1.4*
5.4 ± 0.9**
Combined type A–A
4.6 ± 1.0*
4.2 ± 1.1**
4.4 ± 1.0**
A–B
4.9 ± 1.1*
4.5 ± 1.1**
4.7 ± 1.1**
B–B
5.0 ± 1.2*
5.1 ± 0.9**
5.0 ± 1.0**
B–C
5.7 ± 0.9*
5.2 ± 0.9**
5.5 ± 1.1**
C–C
5.4 ± 1.4*
5.5 ± 1.0**
5.4 ± 1.1**
Data are expressed as means ± standard deviations *p \ 0.05 between each type **p \ 0.01 between each type
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10, 11, 15, 19]. These types were excluded from the classification system in this study because such variations were not found. With regard to the calcaneus in the present study, type A, in which all three articular facets are separated from each other, was most common, followed by types B and C. These results were similar to or coincided with those of numerous previous studies (Table 5). Type A was reported to be most common among the three types in calcanei of various nationalities including Spanish [11], Koreans [19], Turks [38], Belgians [2, 35], and Indians [34]. In addition, several authors, who did not divide the continuous type (types B and C) into subtypes, reported that the frequency of type A exceeded 30 % in calcanei of British [6], Nigerians [6], Egyptians [10], Americans [21], and Indians [29]. A relatively low occurrence of type A was also noted by some authors, but its incidence exceeded 20 % in almost all studies reported. This was in stark contrast to the very low occurrence of this type, less than 10 %, in tali (Table 5). Examination of CSTJ facets using paired calcanei-tali revealed that patterns of talar facets are remarkably different from those of calcaneal facets (Table 5). In contrast to calcanei, type A was the rarest (11.0 %) type in tali, while the ratio of the continuous type was much greater in tali (89.0 %) than in calcanei (61.0 %). This finding was also similar to those of many previous studies. The separate type (type A) in tali was rarely (3.2–9.3 %) found in Indians [1, 3, 12, 20] and Koreans [22]. These findings suggest that the anterior and middle facets of the tali tend to be fused more frequently than those of the calcanei. Among the continuous type of tali in this study, the frequency of type B was slightly greater than that of type C. Similarly, several previous studies reported the same results [1, 3, 12, 22], but the frequency of type B (60.5–79.0 %) was much greater than that of type C (10.0–39.0 %) compared to our results. These differences might be due to differences in interpretation of the transitional shape of some facets between the two types by different authors. Interestingly, Barbaix et al. [2] reported an exceptionally high incidence (39.0 %) of the separate type (type A) in tali, and an even greater occurrence (61.0 %) of this type in the calcanei of Belgians (Table 5). Even though tali in their study had the highest incidence of the separate type ever reported, their results suggest the same conclusion as ours in that the anterior and middle facets of tali are fused more frequently than those of calcanei. It can also be deduced from their study that the marked predominance of type A both in calcanei and tali might be characteristic of some European populations. The high frequency of the separate type (type A) in European calcanei was first recognized by Bunning and
Surg Radiol Anat Table 5 Incidence of CSTJ facet types in different nationalities Bone
Calcaneus
Nationalities
American
References
Drayer-Verhagen [9] Kelikian and Sarrafian [21]
Type (%) Separate
Continuous
A
B
C
Others B?C
191
26.7
54.5
18.9
50
34.0
64.0
2.0
134 49
61.0 36.7
28.0 53.1
11.0 10.2
Belgian
Barbaix et al. [2] Shahabpour et al. [35]
British
Bunning and Barnett [6]
194
67.0
33.0
0.0
Egyptian
El-Eishi [10]
200
40.0
49.0
11.0
Indian
Bunning and Barnett [6]
78
21.8
78.2
0.0
Korean
14.0 24.5
28.0
14.0 28.6
Gupta et al. [15]
401
25.9
66.8
7.2
Padmanabhan [30]
272
34.9
65.1
0.0
39.0
8.5
Madhavi et al. [20]
222
19.4
72.1
Muthukumaravel et al. [25]
237
33.3
65.8
0.8
Sharada et al. [36]
300
28.6
50.3
16.6
66.9
4.3
50
26.0
40.0
34.0
74.0
0.0
24.0
32.0
Mini et al. [27]
Talus
Number of cases
Seema et al. [34]
300
35.0
Garg et al. [13]
310
24.5
56.0
9.0
72.3
3.2 2.2
Kang et al. [19]
226
39.4
37.6
20.8
58.4
Present study (2015)
118
39.0
32.2
28.8
61.0
0.0
Nigerian Spanish
Bunning and Barnett [6] Forriol Campos and Gomez Pellico [11]
492 176
35.8 39.8
29.0
24.4
63.4 53.4
0.8 6.8
Turk
Uygur et al. [38]
221
34.4
25.3
33.0
58.4
7.2
Belgian
Barbaix et al. [2]
122
39.0
28.0
21.0
49.0
11.0
Indian
Korean
Arora et al. [1]
500
3.2
79.0
15.8
94.8
2.0
Bilodi [3]
240
5.0
66.7
10.0
76.7
18.4
Garg et al. [12]
300
5.3
49.7
39.0
88.7
6.0
Kaur et al. [20]
100
5.0
33.0
45.0
78.0
17.0
76
9.3
60.5
30.3
90.8
0.0
118
11.0
46.6
42.4
89.0
0.0
Lee et al. [22] Present study (2015)
Barnett [6]. They found a significantly higher incidence of type A in a British study population compared with Africans and Indians, in whom the continuous type predominates (Table 5). They noted that racial differences are also present in fetuses. Based on these observations, Bunning and Barnett [6] suggested that these features are probably genetically determined rather than resulting from differences in gait or other post-natal factors. However, it seems improbable that the high occurrence of the separate type is common among all European populations because other studies of Belgian [35] and Spanish [11] populations showed a relatively low occurrence of type A, similar to studies of other races (Table 5). Additional studies on CSTJ facets of other European populations will be helpful in determining whether these features are unique to certain European populations. Bruckner [4] noted that CSTJ facets on the talus exhibited the same variation as the calcaneus in a study using
32 cases. On the other hand, Barbaix et al. [2] found 7 cases, among 30 pairs of calcanei and tali, in which type A1 calcanei (=type A of our study) were paired with type A2 tali (=type B of our study), and suggested that talar CSTJ facets are more frequently fused because they are located on the convex talar head situated within the concavity of the corresponding facets on the calcaneus. However, there has never been a systemic analysis of CSTJ facet types using paired calcanei and tali. In the present study, we found five combinations of CSTJ facet types, including heterotypic combinations, by examining 118 paired calcanei and tali (Table 1). The calcaneus of type A was paired with the talus of type A (A–A) or more frequently with the talus of type B (A–B). The calcaneus of type B was paired with the talus of type B (B–B) or with the talus of type C (B–C). The calcaneus of type C was paired with the talus of type C only, and type C–C was most frequently observed among the five combined types.
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Surg Radiol Anat
Thus, it is obvious that combinations of different types (A– B, B–C) exist in greater than 40 % of feet, and this answers the question why patterns of calcaneal CSTJ facets are so different from those of talar CSTJ facets. The findings discussed above indicate that the anterior and middle facets are fused more frequently in tali than in calcanei as proposed by Barbaix et al. [2], and that those of calcanei are separated from each other more frequently than those of tali. To quantify and compare how much the anterior and middle facets are separated, we measured the DS between the two facets (Table 2). The DS of type A was arbitrarily set at 2.00 and that of type C at 1.00. The DS of type B was ranged between 1.00 and 2.00 based on the actual measurement. Thus, the closer the DS is to 2.00, the more separated the two facets are, and the closer the DS is to 1.00, the more fused the two facets are. There were no significant differences between the DS of the calcaneus of type B (1.44) and that of the talus of type B (1.45). However, the mean DS of the calcanei overall (1.53) was greater than that of the tali overall (1.32), indicating that the anterior and middle facets are more separated in calcanei than in tali. This finding was due to the fact that the separate type (type A) is more common while the continuous type (type B, type C) is rarer in the calcaneus compared to the talus (Table 1). The DS of the combined types decreased gradually in the order of types A–A, A–B, B–B, B–C, and C–C. According to the transition of types from A–A to C–C, the DS of type B decreased both in calcanei and tali; the mean calcaneal DS of type B–C (1.36) was smaller than that of type B–B (1.49), and the mean talar DS of type B–B (1.40) was smaller than that of type A–B (1.48) (Table 2). This result clearly demonstrates that partially connected anterior and middle facets of type B show a higher tendency toward coalescence both in calcanei and tali as the combined type approaches type C–C. A convex-downward angle is formed between the anterior and middle facets of the talus, which fits into a concave, V-shaped groove with a similar intersecting angle on the calcaneus. In the calcaneus, the intersecting angle of the separate type (type A) was previously reported as 121.5°[27]–127.8°[9] and that of the continuous type (types B and C) as 137.1°[24]–151.6°[27]. We achieved similar, but more detailed measurements (Table 3). The calcaneal intersecting angle of type A was 137.8°, type B was 144.4°, and type C was 151.2°. Likewise, talar angles increased from type A to type C, and were similar but slightly smaller than those of calcanei. Intersecting angles of both calcanei and tali were inversely related to the DS. These results indicate that the more the facets are connected, the greater the intersecting angles are. These features are thought to be related to the mobility and stability of the CSTJ. The relatively acute intersecting
123
angle of the separate type allows the talar head to be placed tightly within the V-shaped groove on the calcaneus, restraining movement of the talar head. In the foot with a type A–A CSTJ, this spatial relationship constrains the talar head and limits medial rotation of the talus during the heel strike [9]. Additionally, CSTJs with three articular facets (type A) have smaller articular surface areas and higher subtalar axis angles [4]. A higher subtalar axis angle is responsible for a higher longitudinal arch [25, 31], and high-arched feet are described clinically as rigid [14]. In pes cavus, a foot with a high arch, the subtalar joint axis is more vertical and a more rigid CSTJ permits less subtalar motion during walking [16]. The generalized rigidity of the foot and the limited motion in the subtalar joint often are surprising in this condition [26]. Moreover, in the separate type, the talus perches on the calcaneus through an articular tripod formed by three well-separated facets [4]. Thus, CSTJs of type A with smaller intersecting angles were determined to be relatively stable structures with decreased mobility [4, 9]. On the other hand, smooth, larger and relatively flat articular facets with greater intersecting angles of the continuous type (types B and C) may permit relatively free movement of the talar head. The larger intersecting angle of the continuous type presents less of an impediment to medial rotation of the talar head than the relatively acute angle of type A [9]. It was found that continuous type CSTJs have lower subtalar axis angles and greater joint mobility [4], consistent with clinical observations indicating that low-arched feet are hypermobile [32] and people with asymptomatic flat feet usually show a greater range of subtalar motion than do persons with normal feet [26]. Excessive motility of the talar head of the continuous type may cause lasting excessive pressure on the plantar calcaneonavicular (or spring) ligament, which supports the talar head and plays an important role in maintaining the longitudinal arch of the foot, resulting in the laxity of this ligament [9] that is responsible for mobile or unstable feet [17, 18, 32]. A higher incidence of arthritic lipping or other stress-related arthritic changes of CSTJ facets in the continuous type compared to the separate type has been suggested as reliable evidence of the hypermobility and instability of this type of CSTJs [9, 24]. Since the intersecting angle was greatest in type C, it was considered to be the most probable structural predisposition in the setting of ligamentous laxity leading to foot instability. In the combined type, the intersecting angle was inversely related to DS, and increased in the order of types A–A, A–B, B–B, B–C, and C–C. As a result, type C–C was thought to not only be the most mobile, but also the most unstable. We also found that the width of the tarsal canal is related to CSTJ facet type (Table 4). The widths of both the calcaneal sulcus and sulcus tali were greater in the continuous
Surg Radiol Anat
type than in the separate type. In terms of the combined types, the tarsal canal widths increased from A–A to B–C/ C–C, with an inverse relationship to the DS. These results indicate that a wider tarsal canal is characteristic of the continuous type, and that the more the facets are fused, the greater the widths are. The tarsal canal and sinus accommodate parts of the CSTJ joint capsules and several intrinsic and extrinsic ligaments related to the stability and mobility of the CSTJ. The most anterior and posterior borders of the tarsal canal and sinus are attached by the posterior part of the talocalcaneonavicular joint capsule and the anterior part of the (anatomical) subtalar joint capsule. Between them, three major ligamentous structures are found: the ligament of the tarsal canal, the cervical ligament, and the deep extensions of the inferior extensor retinaculum [7, 8, 37, 39]. The deep extensions of the inferior extensor retinaculum and the cervical ligament are located in the tarsal sinus, and they limit inversion [7, 23, 37]. The former is composed of three (medial, intermediate, and lateral) roots that extend from the stem of the Y-shaped inferior extensor retinaculum [7, 8, 23, 37]. The tarsal canal holds the ligament of the tarsal canal and the medial root of the inferior extensor retinaculum [7, 37]. The latter plays a role in limiting inversion together with other parts of the inferior extensor retinaculum. The ligament of the tarsal canal was named by Smith [37] and is sometimes called the interosseous talocalcaneal ligament [23] or the talocalcaneal interosseous ligament of the canalis tarsi [33]. It arises from the floor near the center of the tarsal canal and runs superomedially into the medial end of the roof of the tarsal canal [7]. Smith [37] suggested that this ligament plays a role in limiting eversion; however, Cahill [7] suggested that the ligament of the tarsal canal serves as a tether to maintain the apposition of the two bones with little or no function in limiting either inversion or eversion. In addition, several other functions have been proposed for this ligament, such as a proprioceptive function [8], or as the central pivot of the CSTJ controlling all movement [23]. The functional significance of our findings that a wider tarsal canal is characteristic of the continuous type is unclear. It might be helpful for understanding the interrelationship between the dimensions of the tarsal canal and those of the ligamentous structures within it, but currently the functional role of the ligament of the tarsal canal remains controversial. In the present study, the incidences of talar CSTJ facet types were reconfirmed to be different from those of calcaneal facet types. By matching of paired calcaneal and talar facets, we identified five combined types (A–A, A–B, B–B, B–C, and C–C) of CSTJ facets. Among them, types C–C and A–B were the most common. Combinations of different types (A–B and B–C) of CSTJ facets existed over 40 % of
feet examined. These findings indicate that the anterior and middle facets of CSTJs are more often fused in tali, and more often separated in calcanei. This tendency was confirmed also by the smaller DS of tali and the greater DS of calcanei. Measurements of intersecting angles between anterior and middle facets, which influence the stability and/or biomechanics of the CSTJ, revealed that this tendency is related to facilitation of talar movement on the calcaneus. Taken together, our results indicate that types with a smaller DS (i.e., combination of continuous types such as B–C and C–C) are relatively mobile but less stable compared to those with a greater DS (i.e., combination of separate types or combination of separate-continuous types such as A–A or A–B). The former can predispose people to foot pain or CSTJ instability, especially later in life. These results provide valuable information in the understanding of motor mechanics of the feet and will contribute to the diagnosis and identification of risk factors for foot instability. Acknowledgments The authors are deeply grateful to the donors of the cadavers used in this study. We would also like to thank Mr. Young Chul Kim and Mr. Dae Seong Park for their expert technical support. Conflict of interest
None.
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