European Journal of Cardiovascular Medicine

The calcaneum, the largest and strongest bone among the tarsals, is a key component of the hindfoot and plays a critical role in supporting and transmitting body weight from the tibia to the ground during standing, walking, and other locomotor activities¹. Superiorly, it articulates with the talus through three articular facets—anterior, middle, and posterior—that collectively form the subtalar joint. This joint is vital for both stability and controlled mobility of the foot, enabling essential movements such as inversion and eversion, which allow adaptation to uneven terrain and maintenance of balance². The posterior facet is typically the largest and is responsible for bearing the majority of the load transmitted through the talus, while the anterior and middle facets provide supplementary stability and facilitate smooth motion. Together, these facets ensure an optimal distribution of forces across the joint surfaces, minimizing localized stress and protecting against degenerative changes³.

However, considerable anatomical variation exists in the morphology of these calcaneal facets, with differences in shape, size, and arrangement observed both within and between populations. The most common variations involve either the fusion of the anterior and middle facets or their complete separation into three distinct surfaces. These structural differences can significantly influence the biomechanics of the subtalar joint⁴. For instance, configurations that allow for a larger articular contact area can enhance joint stability and resistance to excessive inversion or eversion, thereby reducing the risk of ligament injuries. Conversely, patterns that result in reduced contact or altered load distribution can increase localized stress, predisposing the cartilage to wear and tear and accelerating the onset of subtalar arthritis⁵.

From a clinical perspective, understanding calcaneal facet morphology is particularly important in the context of injury management and surgical intervention. In cases of calcaneal fractures, subtalar dislocations, or degenerative joint disease, accurate knowledge of the patient’s specific facet configuration can guide the surgeon in selecting the most appropriate approach for fixation, arthrodesis, or reconstructive procedures⁶. Precise awareness of facet relationships is essential for correct screw placement and alignment preservation, both of which are critical to restoring normal biomechanics and preventing long-term disability. Furthermore, variations in facet arrangement may influence post-operative outcomes, rehabilitation protocols, and the likelihood of future degenerative changes⁷.

Aims & Objectives

To study the incidence of pattern of variation in the talar facets on calcanei & its clinical importance in Haryanvi population.

The present study was undertaken with the objective of examining and classifying the morphological variations in calcaneal facets among a representative sample of the North Indian population. The study was carried out in the Department of Anatomy, Pt. B.D. Sharma Post Graduate Institute of Medical Sciences (PGIMS), Rohtak, Haryana, India. A total of 104 dry human calcanei of unknown sex were included in the analysis. All bones used in the study were obtained from the departmental bone collection and represented adult specimens, as evidenced by the fact that each bone was fully ossified, with no signs of incomplete epiphyseal fusion. To maintain the accuracy and reliability of the observations, only calcanei that were free from visible pathological changes, post-mortem distortion, fractures, or gross deformities were selected.

Each calcaneum was subjected to meticulous examination to assess the morphology of its superior articular surface, particularly focusing on the talar facets. The anterior, middle, and posterior facets were identified, and their size, shape, orientation, and degree of separation or fusion were carefully observed. The classification of these facets was based on well-established anthropometric and osteological criteria used in previous anatomical and orthopedic studies. Using these criteria, the calcanei were grouped into five distinct morphological patterns. These patterns were defined by the arrangement and continuity (or lack thereof) between the anterior, middle, and posterior articular facets. For example, in some cases, the anterior and middle facets were found to be fused into a single continuous surface, while in others they were distinctly separated. In certain patterns, all three facets were completely separate, whereas in others, a combination of fusion and separation was observed.

The process of classification was carried out systematically to ensure reproducibility of findings. Each bone was examined in adequate lighting conditions, and measurements, where necessary, were taken with precision instruments such as a digital vernier caliper to confirm facet dimensions and distances between them. Visual inspection was supplemented with palpation to confirm the borders of each facet. Observations for each calcaneum were recorded in a structured data sheet, noting the specific pattern type assigned to that bone. The total number of calcanei falling into each morphological category was then counted to determine the incidence of each pattern within the study sample.

By carefully controlling selection criteria, employing a standardized classification system, and recording observations with precision, the present study aimed to generate accurate and reproducible data on calcaneal facet morphology. These findings can serve as a reference for orthopedic surgeons, anthropologists, and anatomists in understanding subtalar joint biomechanics and planning surgical interventions in the North Indian demographic.

Figure 1: Human left calcaneus bone (medial view) showing a single continuous articular facet on the sustentaculum tali (highlighted in yellow)- consistent with Pattern 1 configuration.

Figure 2: Human calcaneus bone (medial view) showing two distinct articular facets—one on the sustentaculum tali and a second on its distal part (highlighted in yellow) - consistent with Pattern 2 configuration.

Figure 3: Human calcaneus bone (medial view) showing a single well-marked articular facet located on the sustentaculum tali (highlighted in yellow), with absence of any anterior facet—characteristic of Pattern 3 configuration.

Table 1: Patterns of the facet of sustantaculum tali

In present study done in Haryanvi population, out of five only three patterns for talar facets were observed in calcaneum. In this study pattern I (67%) was seen to be  more than pattern II(27%) & very less people with pattern III (4%) were observed and 0% of pattern IV & V was seen, which was in accordance with study done in Egyptian population.

Talocalcaneal facets morphology plays an important factor in subtalar joint stability. In present study done in north Indian population only three pattern for talar facets were observed in calcaneum bone. The same pattern was reported in Egyptian population. Gupte reported that arthritic lipping was less common in pattern III than in comparison to other configurations. This suggest that talocalcaneal facets morphology plays an important factor in subtalar joint stability⁶.

 Bruckner also said that joint with pattern III facets are more stable than other configuration. Talus and calcaneum articulate at two discrete location. This articular surface are divided by a groove and form a V shaped articular surface with an average angle of 127.5 degree, constraining the talar head and limiting medial mrotation of talus. In flat and smooth articular surface of calcaneiwith continous facet an average angle is 148 degree. This large angle causes less impediment to medial rotation of talar head than relatively acute angle of calceni with pattern III¹.

This lack of talar head constraint in individuals with continous faceta leads to shipped bolt. Eventually causing ligamentous laxity because talar head continuously is putting pressure on spring ligament which connects the suatentacular tali to the navicular. Laxity of ligaments and mscles is thoughtto be responsible for mobileor unstable feet⁷.

Stability of the subtalar joint also depends on the height of longitudinal arch, which are determined by the inclination of the subtalar joint axis⁸. 

A high arch are more stable structure and are referred to as rigid or cavas foot⁹.Bruckner reported that joint with 2 facet configuration have higher subtalar joint axis then other configuration¹. Relative to rounded, continous facet, the two facet configuration has an anterior facet that is slanted upwards and raises the total subtalar joint axis⁹.

On the other hand the continous facet is horizontally inclined, which results in lower arch and less stable foot¹⁰.

Sustantaculum tali with only medial facet have inadequate talar head support which allowsexcessive anterior and inferior rotation of the talus during weight bearing. This results in valgus position of the calcaneum and a downward tilt of talar head. The vastly increased pressure on the anterior subtalar joint capsule causes ligamentous laxity⁸.

CT scans show that the planus foot (hypermobile or flat foot) has no anterior sustentaculum tali facet¹¹. Present study show that certain morphological variations of talar facet of calcaneum may predispose people to joint instability, ligament laxity and the development of arthritic changes. In this study pattern I  was seen to be more than pattern II and very less people with pattern III were reported. This study shows that north Indian population have subtalar joint instability. In different literature it was seen  that arthritic lipping was less common in pattern III & this pattern is more stable than other configurations, but in our study very less % of pattern III were seen, hence Haryanvi population is more liable to have arthritic changes as compared to those who have this pattern.

The calcaneal facets are not merely anatomical structures for articulation but are functionally dynamic components that determine the stability, flexibility, and overall health of the subtalar joint. Their morphology has direct implications for biomechanics, injury risk, surgical planning, and population-based orthopedic care, making their study essential for both clinical and research purposes.

The present study highlights significant morphological variations in the talar facets of the calcaneum among the North Indian (Haryanvi) population and their clinical implications. Among the five described patterns, only three (I, II, and III) were observed, with Pattern I (a continuous facet on the sustentaculum tali) being the most prevalent (67%), followed by Pattern II (27%) and Pattern III (4%). The absence of Pattern IV and V was consistent with observations from Egyptian populations.

Thus, knowledge of the morphological patterns of calcaneal facets can provide valuable insights in clinical orthopedics, rehabilitation, and surgical planning, especially in patients presenting with foot instability or subtalar joint pathologies.

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