European Journal of Cardiovascular Medicine

The lower ends of the tibia and fibula together form an important anatomical and functional unit of the ankle region. The distal tibiofibular joint is created by the articulation between the medial convex surface of the distal fibula and the lateral concave surface of the fibular incisura of the tibia. This joint is classified as a syndesmosis type of fibrous joint, in which strong ligaments maintain close apposition between the two bones and provide stability to the ankle mortise [1-3]. Anatomically, the interosseous border of the tibia divides inferiorly into anterior and posterior ridges that extend as corresponding tubercles at the distal end. These structures collectively form and enclose the fibular incisura. The articulation between the fibular incisura and the distal fibula, along with the associated syndesmotic ligaments, constitutes the ankle mortise, which accommodates the talus at the talocrural joint. The stability of this anatomical unit largely depends on the shape and dimensions of the fibular incisura [4]. The lateral surface of the distal tibia presents a triangular fibular notch, also known as the fibular incisura, syndesmotic notch, peroneal groove, or incisural notch. Its anterior and posterior margins project as tubercles that converge proximally toward the interosseous border. While the proximal part of the notch is roughened by the attachment of the interosseous ligament, the distal portion is smooth to allow articulation with the fibula [2-5]. The anatomical relationship between the tibia and fibula at the ankle level is crucial for the normal function of the distal tibiofibular joint. In cases of ankle fractures, assessment of syndesmotic integrity is essential for proper treatment planning and prognosis. However, syndesmotic injuries may be difficult to detect radiographically due to rotational variations, differences in the depth of the fibular incisura, and variability in the morphology of the tibial tubercles. Morphometric analysis of the fibular incisura, therefore, has significant clinical relevance, particularly in imaging interpretation and surgical management of ankle fractures [5]. Despite its clinical importance, detailed morphometric data on this remain limited, especially from Eastern India. Bihar represents a densely populated region with considerable ethnic and genetic diversity, yet region-specific anatomical data are scarce. Population-based morphometric studies are important, as anatomical variations may influence surgical accuracy, implant positioning, and procedural safety. The present study was therefore undertaken to analyse the morphometric dimensions of the fibular incisura in adult human dry tibiae and to provide baseline anatomical data relevant to clinical and surgical practice.

This cross-sectional observational study was conducted on adult human dry tibias available in the Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Patna, Bihar (India). The genders of the skeletons in our collection were known from their records. All procedures were conducted in accordance with the ethical principles outlined in the Declaration of Helsinki.

Sample Size Calculation

The sample size for the present study was calculated using G*Power software (Version 3.1.9.7). Based on effect sizes reported in previously published morphometric studies of the distal tibia and fibular incisura, a medium effect size of 0.5 was assumed. A statistical power (1−β) of 0.80 and an α-error probability of 0.05 were considered for the calculation. The minimum required sample size was estimated to be 54 adult human tibiae.

To compensate for possible exclusion of damaged or incomplete specimens and to enable reliable subgroup analysis, the final sample size was increased to 60 adult dry tibiae. These included equal numbers of male and female specimens (30 each). Among the male tibiae, 16 were from the right side and 14 from the left side, while among the female tibiae, 17 were right-sided and 13 were left-sided. This distribution ensured adequate statistical power for both sex-wise and side-wise comparisons of the morphometric parameters of the fibular incisura.

Inclusion Criteria:

Adult human dry tibiae of known gender (male and female) with completely preserved distal ends were included in the study. Only well-preserved specimens without visible deformity were selected to ensure accurate morphometric evaluation of the fibular incisura. Both right- and left-sided tibiae were included to facilitate side-by-side comparison.

Exclusion Criteria:

Tibiae showing evidence of damage, erosion, fractures, or post-mortem breakage involving the distal end were excluded. Specimens exhibiting pathological alterations such as deformities, osteophyte formation, or signs of previous trauma affecting the fibular incisura were also excluded. Bones with indeterminate sex or unclear laterality were not included to minimise measurement bias.

Morphometric Measurements:

All measurements were taken directly from the dry tibial specimens using a digital vernier calliper with an accuracy of 0.01 mm. The tibia was positioned in an anatomical orientation before recording the measurements. The following morphometric parameters of the fibular incisura were assessed:

1. Width of the Fibular Incisura (from point P to Q): The width was measured as the distance between the tips of the anterior and posterior tubercles of the fibular incisura, taken at a point 1 cm proximal to the tibial plafond (Figure 1).
2. Depth of the Fibular Incisura (from point R to S): The depth was defined as the perpendicular distance from the deepest point of the fibular incisura to an imaginary line joining the tips of the anterior and posterior tubercles (Figure 1).
3. Height of the Fibular Incisura (from point T to U): The height was measured as the vertical distance from the tibial plafond to the point where the interosseous border of the tibia divides into the anterior and posterior ridges forming the fibular incisura (Figure 2).
4. Length of the Anterior (Chaput’s) Tubercle: This parameter was measured as the distance from the deepest point of the fibular incisura to the tip of the anterior tubercle.
5. Length of the Posterior (Volkmann’s) Tubercle: The length was recorded as the distance from the deepest point of the fibular incisura to the tip of the posterior tubercle.

All measurements were recorded in millimetres. Each parameter was measured carefully to ensure accuracy and reproducibility. To minimise observational error, all measurements were obtained twice by the same observer, and the mean of the two readings was used for analysis.

Figure 1: Schematic illustration of the distal end of the tibia showing the anatomical landmarks and reference points used for the morphometric assessment of the fibular incisura.

Figure 2: Diagrammatic representation of the distal tibia demonstrating the method used to measure the height of the fibular incisura.

Statistical Analysis:

All data were entered into Microsoft Excel and analysed using Statistical Package for the Social Sciences (SPSS) software (IBM SPSS Statistics, Version 25.0). Continuous variables were expressed as mean, standard deviation, and range. Normality of the data distribution was assessed before applying inferential statistics. Sex-wise (male vs female) and side-wise (right vs left) comparisons of the morphometric parameters of the fibular incisura were performed using the unpaired Student’s t-test. A p-value of less than 0.05 was considered statistically significant, with a confidence level of 95%.

A total of 60 adult human dry tibiae were examined in the present study, comprising 30 male and 30 female specimens. Of the male tibiae, 16 were right-sided, and 14 were left-sided, while among female tibiae, 17 were from the right side and 13 from the left side.

The gender-wise analysis of the fibular incisura parameters showed clear differences between male and female tibiae. The mean width of the fibular incisura was significantly greater in males compared to females, and this difference was statistically significant (p < 0.001). Similarly, the mean depth of the fibular incisura was higher in males than in females, with the difference reaching statistical significance (p = 0.004). The height of the fibular incisura also demonstrated a statistically significant gender difference, with male tibiae showing a greater mean height compared to female tibiae (p < 0.001). In addition, the mean length of the anterior (Chaput’s) tubercle was significantly longer in males than in females (p < 0.001). Although the mean length of the posterior (Volkmann’s) tubercle was higher in males compared to females, this difference did not reach statistical significance (p = 0.06). Overall, most morphometric parameters of the fibular incisura showed significant sexual dimorphism, except for the length of the posterior tubercle (Table 1).

The side-wise comparison between right and left tibiae revealed no statistically significant differences for any of the measured parameters. The mean width of the fibular incisura was slightly higher on the right side compared to the left, but this difference was not statistically significant (p = 0.18). Similarly, the mean depth of the fibular incisura showed minimal variation between the right and left sides, with no significant difference observed (p = 0.42). The height of the fibular incisura was marginally greater on the right side; however, this difference was also not statistically significant (p = 0.36). The lengths of both the anterior and posterior tubercles did not show any significant side-related differences, with p-values of 0.29 and 0.48, respectively. These findings suggest that the morphometric parameters of the fibular incisura are largely symmetrical between the right and left sides (Table 2).

Table 1: Gender-wise Comparison of Morphometric Parameters

Table 2: Side-wise Comparison of Morphometric Parameters

Normal ankle mechanics depend on the integrity of the distal tibiofibular syndesmosis (TS), which maintains the precise anatomical relationship between the distal tibia and fibula and ensures stability of the ankle mortise [6,7]. Disruption of this relationship, commonly seen in ankle sprains and fractures, may result in syndesmotic injury with or without fibular displacement, particularly in severe trauma where posterior displacement of the fibula can occur [8-11]. The fibular incisura (FI) of the tibia plays a central role in maintaining this stability, as it provides the bony contour within which the fibula is accommodated [10,11]. Despite its importance, morphometric data on the FI derived from dry bone studies remain limited, with most available information based on radiological investigations such as CT and MRI [8,10,11]. Mavi et al. [8], using MRI in patients with recurrent ankle sprains, reported increased depth of the FI, elongated anterior and posterior tubercles, and a more anteriorly positioned fibula in affected individuals. They also observed greater FI depth in males compared to females. Similarly, Yildirim et al. [11] suggested that anatomical differences in the FI may explain the higher susceptibility of women to syndesmotic injuries. These observations highlight the clinical relevance of FI morphology in ankle stability and injury patterns.

In the present study, the mean height of the FI was greater in males than in females, a finding consistent with reports by Misiani Musa et al., Mandela Pamela et al., and Kulkarni et al. However, higher values reported in the Turkish population by Taser et al. (2009) suggest the presence of population-specific anatomical variations. Such differences may be related to variations in the level of bifurcation of the interosseous tibial ridge, as a lower bifurcation produces a shorter FI, while a more proximal division results in a deeper incisura [12,13]. The significant sex difference observed in FI height in the present study may be attributed to generally smaller skeletal dimensions in females, a finding also supported by earlier studies by Ebraheim et al. and Taser et al.

The mean depth of the FI observed in this study was comparable with values reported by Kin et al., Taser et al., Misiani Musa et al., Mandela Pamela et al., and Yildirim et al., although lower than those reported by Sora et al. in a plastination-based study. This discrepancy may be explained by differences in study methodology and measurement techniques. The significantly greater FI depth in males observed in the present study contrasts with the findings of Taser et al., who reported no significant sex difference. Such variation may reflect differences in body habitus and osteometric characteristics across populations. Clinically, a shallow FI has been associated with increased risk of fibular displacement during fracture dislocations, contributing to instability of both the TS and ankle joints [12]. The width of the FI in the present study closely parallels values reported in earlier studies [10,11,15]. FI width is an important parameter as it reflects the size of the TS joint; increased width corresponds to greater separation between the anterior and posterior tubercles, resulting in a shallower incisura that may predispose individuals to syndesmotic instability [14].

Regarding the tibial tubercles, the anterior tubercle showed a significant sex difference, whereas the posterior tubercle did not. While earlier studies reported similar mean values for both tubercles, most did not find statistically significant gender differences. The significant variation in anterior tubercle length observed in the present study may be attributed to geographical and population-based anatomical diversity. The dimensions of these tubercles are clinically important, as they influence the position of the fibula within the FI [15]. A more posteriorly positioned fibula has been associated with reduced structural stability of the syndesmosis and an increased tendency for recurrent ankle sprains [16].

In the present study, no statistically significant differences were observed between the right and left sides for any of the morphometric parameters of the fibular incisura, including width, depth, height, and length of the anterior and posterior tubercles. This bilateral symmetry is in agreement with the findings of Kilic Safak et al. [17], who also reported no significant right–left differences for fibular notch width, depth, height, or facet lengths in dry tibial bones. Similar observations have been reported by Taser et al. [10], Gupta et al. [18], and Sreedevi et al. [19], all of whom found comparable measurements on both sides, suggesting that side dominance does not significantly influence fibular incisura morphology. Studies conducted using CT and MRI, including those by Park and Kim [20] and Rozis et al. [21], likewise demonstrated bilateral symmetry of the distal tibiofibular relationship. The consistency of these findings across different populations and methodologies supports the concept that the fibular incisura is largely symmetrical bilaterally. Clinically, this symmetry is important, as the contralateral ankle can be reliably used as a reference during radiological evaluation and surgical reconstruction of syndesmotic injuries, particularly in complex ankle fractures where anatomical landmarks may be distorted.

Overall, the findings of this study reinforce the importance of detailed morphometric knowledge of the fibular incisura. From a clinical perspective, awareness of sex-related and population-specific variations in FI morphology can aid radiologists in more accurate interpretation of ankle imaging and assist orthopaedic surgeons in optimising surgical reduction, fixation, and implant placement during the management of ankle fractures and syndesmotic injuries.

Limitations of the study: The present study has certain limitations that should be acknowledged. The morphometric analysis was conducted on a relatively limited number of adult dry tibiae, which may restrict the generalizability of the findings to the wider population. As the study was performed on dry bones, associated soft tissue structures such as cartilage and ligaments of the distal tibiofibular syndesmosis could not be evaluated. In addition, radiological correlation using imaging modalities such as computed tomography or magnetic resonance imaging was not undertaken. Furthermore, paired tibiae from the same individual were not available, which limited the assessment of true bilateral symmetry.

The present morphometric study highlights that the fibular incisura of the distal tibia shows significant sexual dimorphism, with most parameters being larger in males than in females, while no meaningful differences were observed between the right and left sides. These findings indicate that the morphology of the fibular incisura is largely bilaterally symmetrical but influenced by sex. The baseline data generated from this Eastern Indian population may be valuable for anatomists, radiologists, and orthopaedic surgeons in improving the assessment of syndesmotic integrity, enhancing surgical planning, and ensuring accurate implant placement in ankle fracture management.

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