PATTERNS OF SUPERIOR ARTICULAR FACET AND MORPHOMETRIC STUDY OF NEPALESE DRY CALCANEI

Introduction: The three important articulating facets in the superior aspect of the calcaneum are the anterior, middle and posterior articulating facet. Descriptions of the posterior talar facet on the dorsum of the calcaneus are similar. However, there are differences when facet for the head of the talus on the calcaneus is considered. Four types (pattern I, II, III, IV) of calcaneus having different talar facets are reported in the literature. Objective: This study aims to describe the calcaneal bone by measuring its dimensions and determining the variations of talar articulating facet. Materials and methods: Overall 142 calcanei (68 right, 74 left) with unidentified gender, were assessed. Vernier calipers and Goniometry were used. Results: In this study Type I calcaneus (56.34 %) was the most prevalent type with Type II calcaneus (42.25 %) as the second most common type followed by Type IV (1.41 %) as the third frequently found pattern of calcaneus. Conclusion: Type I calcaneus was the most frequent type in the Nepalese showing similarity to the results of the studies performed in Spanish, American, African and various Indian population. Bohler’s angle of the right and left calcanei was 34.92° ± 8.09° and 35.4° ± 7.30° respectively. Development of database of calcaneal measurements in various populations is recommended.


INTRODUCTION
Calcaneus is the longest, largest and one of the major weight bearing tarsal bones forming the talocalcaneal joint with the talus. This joint is also termed as subtalar joint where eversion and inversion of the foot takes place (1). There are three facets for synovial joints between the talus and calcaneus, anterior, middle and posterior talar facet with variations seen in the arrangement of these facets as described in this study. Calcaneal fractures are the most commonly encountered tarsal fractures mostly involving the intra-articular subtalar joint (2). The majority of bony coalition commonly involves the middle talar facet of the talocalcaneal joint, also a common cause of painful flatfoot (3). Morphometric values of calcanei are essential for the science of anatomy, treatment and diagnosis procedures on orthopedic surgery, kinesiology, physical treatment and rehabilitation sessions (4). Structural dissimilarity of the calcanei has an impact on the fixed and kinetic dynamics of the foot. The relationship of talus and the calcaneus should be thoroughly considered during the treatment of talocalcaneal coalition, congenital club foot, subtalar instability, cases of severe pronation, valgus deformities, designing subtalar implants and others (5, 6, 7). Bohler's angle is commonly evaluated via radiography during calcaneal fractures for proper diagnosis and treatment. There is a significant loss or decrease of this angle in a severe case of heel fracture (8,9,10).
With the means of facet variation and bone dimension, this study attempts to describe the calcaneus bone of Nepalese race.

MATERIALS AND METHODS
A total of 142 dried calcanei (68 right, 74 left) without major defects and unidentified gender were assessed. All the bones were classified with Type I, II and IV identified as the predominant finding of our study. Pattern of articular facet on the superior aspect of the calcaneus was classified as follows:

RESULTS
The talar articular facets in 142 dry calcanei were classified into four different types with three types being identified in this study (Table 1) and the same com-pared to that of other studies ( Table 2). Type I (56.34%) was recognized as the most prevalent type (Figure 1   Morphometric measurements and their findings are shown in Table 3. Boehler's angle in the right and left calcanei are shown in Table 4.

DISCUSSION
The common pattern of the articular facets on the superior surface of the calcaneus for the head of the talus in our study is Type I (56.34%) and II (42.25%) as shown in Table 1. From Table 2 it is clear that the outcome of our study is consistent with the studies done by different authors previously. The prevalence of Type III pattern of calcanei was observed to a greater degree in Egyptians in an article by EI-Eishi (11) and Americans in a study by Verhagen FD (12) implying that the facets could be genetically determined as stated by Bunning and Barnett (13). A relatively small sample of Type IV patterned facet was common to the Africans (5), Indians (14) and our study. This finding may possibly be used as a racial characteristic. Additionally, Table 2 reveals, that in the Americans (12), Africans (5, 13) and Indians (14) the percentage of Type II is almost about half of Type I, whereas Spanish (15) and Egyptian (11) population has equal preponderance of Type I and Type II facet. Interestingly in the British (5, 13), Type II facets are almost twice as frequent as Type I, explaining another probable racial attribute. Geographical region, human habits like squatting, use of shoes and genetic factors may be the predisposing cause to the variations observed in the facets, with Type I more common in females (13).
The configuration of talar articulating facet also plays a key role in the stability of the subtalar joint is consistent with Bruckner's hypothesis that the joints with two facet configuration are comparatively more stable (16). This stability also depends on the height of the longitudinal arch, which is usually referred to as a cavus foot (16,17). Computerized tomography scans show that the flat foot (planus foot) has no anterior sustentaculum tali facet (18). These findings suggests that the population with continuous facet and medial only facet pattern of the sustentaculum tali may be at a greater risk for subtalar joint instability than those with two facet type pattern (12). Furthermore, study by Chavan et al. suggests that leggedness, right or left could also be the contributing factor to the development of talar articulating patterns seen in human calcanei (19).
Calcaneal fracture accounts for 33% of foot fractures with 100% association to the posterior talocalcaneal facet in intra-articular fractures (20). The evaluation of vertical length of calcaneus may be a supportive criterion of calcaneus fractures (21). In our study the height, transverse and anterior-posterior length of right and left calcaneus was insignificant when compared to each other ( Table 3). The given dimensions may provide a landmark for postoperative assessment of status of fractured calcanei.
Decompression fractures particularly alters Boehler's angle. Preserving normal Boehler's angle postoperatively demonstrates surgical success. Study by Khoshhal et al. in the Saudi population found the mean Boehler's angle to be 31.21°not related to age, gender, or side of body (9). Similarly in the study by Uygur et al. the Boehler's angles of right and left calcanei were found as mean 30.8°± 4.9°and 30.09°± 5°, respectively with left Boehler's angle correlating with the left vertical length of the calcaneus (4). The mean Bohler's angle of the right and left calcanei estimated in our study was somewhat greater than these studies with the similarity that Boehler's angle did not relate to the sides of calcanei (Table 4). When Boehler's angles of congenital clubfoot were compared to the normal side by Kalenderer et al. no differences were noted between them (22). The mean Boehler's angle in their study measured 35.2°which was close to that of our study.
Bohler's angle has a significant prognostic value in terms of predicting morbidity of calcaneal fractures. There was much poorer two year outcome regardless of treatment of fractures with a markedly diminished Bohler's angle (8). Also, significant correlation between preoperative Böhler's angle and the injury severity of displaced intra-articular calcaneal fractures was observed with only the postoperative Böhler's angle parameters found to have a significant correlation with functional recovery (23). Due to the lack of studies in Boehler's angle involving different population group, development of database for reference purpose, prognosis and treatment especially during postoperative angle measurements could be recommended.

Aknowledgement
We would like to thank the Department of Anatomy of Birat Medical College, Tribuvan University Teaching Hospital (Kathmandu, Maharajgunj) and Chitwan Medical College for providing bones to conduct this study. Also our sincere thanks go to the faculties of anatomy department of the mentioned institutes for their support and cooperation.

DECLARATION OF INTEREST
The autors declare that there are no conflicts of interests.