European Journal of Cardiovascular Medicine

The supratrochlear foramen (STF) is an important and relatively common anatomical variation observed at the lower end of the humerus in humans. It is formed due to the perforation of a thin, transparent bony septum, known as the supratrochlear septum, that separates the olecranon and coronoid fossae. This septum, which varies in thickness from 0.5 mm to 1 cm, is lined by the synovial membrane of the elbow joint in its fresh state. In some cases, this septum may develop perforations, leading to the formation of a distinct aperture referred to as the supratrochlear aperture or supratrochlear foramen. First described by Mekel in 1825 [1], the STF has been designated by various names, including intercondylar foramen, olecranon foramen, and epitrochlear foramen [2, 3]. The development of the STF is age-dependent. The bony septum between the olecranon and coronoid fossae is consistently present until the age of seven years, after which it may undergo absorption, resulting in the formation of the STF [4]. Individuals possessing this anatomical variation may exhibit hyperextension at the elbow joint [5]. Interestingly, the STF is not exclusive to humans; it has also been documented in other species, including hyenas, dogs, and non-human primates [6]. Septal apertures are observed across most mammalian species, with a slightly higher prevalence among Old and New World apes [7]. Charles Darwin even considered the presence of this foramen in humans as evidence of evolutionary linkage to primates [8]. The genetic basis of STF formation has been explored in recent studies, with the T-Box (TBX) gene family playing a potential role. These genes regulate the synthesis of TBX proteins, which are crucial for limb and cardiac development during embryogenesis [9]. Govoni further postulated that TBX genes may influence postnatal limb development, providing a possible explanation for the persistence or formation of the STF [10].

From a clinical standpoint, the STF was once considered a mere anatomical curiosity, but recent orthopaedic surgical experience has highlighted its significant implications. The presence of an STF has been associated with a narrow intramedullary cavity, which can complicate fracture management [11]. Supracondylar fractures, common in the paediatric population, are often treated with intramedullary nailing [12]. However, the presence of an STF may interfere with retrograde nailing techniques, which are typically performed through the medial and lateral epicondyles or solely through the lateral epicondyle [13]. Additionally, the proximity of neurovascular structures raises concerns about potential nerve injuries during surgical interventions. Thus, the identification of an STF is crucial in preoperative planning for fractures involving the distal humerus [11, 12]. Moreover, the STF can pose diagnostic challenges during radiological assessments, where it may be misinterpreted as a pathological lesion or cystic formation [13]. Given these clinical and diagnostic implications, a thorough understanding of the STF’s incidence and morphology is essential for orthopaedic surgeons and radiologists.

Aim and Objectives: This study aimed to conduct a morphometric analysis of the supratrochlear foramen of the humerus that belonged to the Indian population and investigate its clinical significance. The findings may contribute to improved surgical techniques, fracture management, and accurate radiological interpretations, ultimately enhancing patient care.

In this cross-sectional study, adult dry humerus bones of unknown gender and age were studied in the Department of Anatomy, National Institute of Medical Science and Research, Jaipur, Rajasthan (India), and Indira Gandhi Institute of Medical Sciences, Patna, Bihar (India).  

Sample Size Calculation:

The sample size for the present study was estimated using a power analysis conducted with G*Power, version 3.0.1 (Franz Faul, Universität Kiel, Germany). The sample size estimation was performed at a 5% alpha error (α = 0.05), with an effect size of 60%, based on findings from previous literature [14] and a study power of 80%. This calculation ensured adequate statistical power to detect significant differences in the morphometric parameters of the supratrochlear foramen (STF) between the right and left humeri, while accounting for variability in anatomical prevalence and dimensions reported in prior research. The resulting sample size of 100 dry humeri (50 right and 50 left) was deemed sufficient to achieve reliable and generalizable results for the Indian population under investigation.

Inclusion Criteria:

• Sample Type:
  • Dry, macerated adult human humeri (both sexes) with intact distal ends.
• Population:
  • Skeletons or radiological data obtained from Indian populations to maintain regional specificity.
• Age and Gender:
• Bones from adult individuals (aged 18 years and above) were taken to exclude developmental variations seen in paediatric bones.
• Both male and female bones were considered.
• Morphological Features:
  • Humeri with a clearly identifiable supratrochlear septum, perforations, or a fully formed supratrochlear foramen (STF).

Proper handling and care were exercised to maintain the integrity of the specimens throughout the study.

Exclusion Criteria:

• Damaged or Pathological Specimens:
  • Humeri with fractures, erosions, or pathological lesions (e.g., tumors, osteomyelitis) that obscure the supratrochlear region.
• Incomplete or Immature Bones:
  • Paediatric or adolescent bones (below 18 years) due to ongoing ossification and developmental changes.
  • Fragmented humeri where the distal end is missing or severely damaged.
• Non-Human or Non-Relevant Specimens:
  • Animal bones or non-human primate specimens (unless used for comparative analysis in discussion).
  • Humeri from populations outside the study’s geographical focus (unless used for comparative studies).
• Surgically Altered Bones:
  • Humeri with prior surgical modifications (e.g., prosthetic implants, drilled holes) that may mimic or obscure the STF.

The presence of the supratrochlear foramen (STF) was carefully examined, and its shape was categorized into three types: oval, round, and irregular. The transverse and vertical diameters of the foramen were measured using a digital vernier caliper (Figure 1). All findings were systematically recorded in tabular format.

Figure 1: Showing the different points used for the measurements of the supratrochlear foramen: AB. Transverse diameter and CD. Vertical diameter.

Linear measurements were taken with the help of a digital vernier caliper, which had a sensitivity of 0.01 mm, and the least count observed was 0.01 mm. Measurements were taken twice, and the average was included in the analysis. The obtained data is expressed in terms of Mean and standard deviation. A p-value less than 0.05 was considered significant in this study for the analysis. The findings were tabulated and analyzed statistically by using the GraphPad Prism version 9 software.

We examined 100 humeri, among which the supratrochlear foramen (STF) was present in 29 bones, accounting for an overall prevalence of 29%. When evaluated side-wise, both the right and left humeri were equally represented, with 50 bones (50%) each. The STF demonstrated a distinct laterality pattern, being more prevalent in left-sided humeri (34%, n=17) compared to right-sided specimens (24%, n=12) (Table 1).

Three distinct shapes of the supratrochlear foramen (STF) were observed in this study: round, oval, and irregular (Figure 2). Among the 29 humeri with a supratrochlear foramen, the most common shape observed was round, present in 14 specimens (48.27%), with 5 occurring on the right side (17.24%) and 9 on the left side (31.03%). The oval shape was found in 12 specimens (41.38%), distributed as 5 on the right (17.24%) and 7 on the left (24.14%). The irregular shape was the least common, noted in only 3 specimens (10.35%), with 2 on the right side (6.90%) and 1 on the left side (3.45%). The comparison between the right and left sides showed no statistically significant difference in the distribution of foramen shapes, as indicated by a p-value of 0.864 (Table 2).

The mean transverse diameter of the supratrochlear foramen was significantly greater on the right side (4.64 ± 1.02 mm) compared to the left side (3.23 ± 0.89 mm), with a p-value of less than 0.0001, suggesting a statistically significant difference. In contrast, the mean vertical diameter was slightly higher on the left side (3.89 ± 1.04 mm) than on the right side (3.65 ± 1.04 mm), but this difference was not statistically significant, as indicated by a p-value of 0.248 (Table 3 and Figure 3).

Table 1: Showing the side allocation of the supratrochlear foramen

Table 2: Showing the different shapes of the supratrochlear foramen

Figure 2: Showing the various shapes of the supratrochlear foramen (STF): (A) Round STF. (B) Oval STF. (C) Irregular STF.

Table 3: Showing the diameters of the supratrochlear foramen

Figure 3: Showing the comparison of the diameters of the supratrochlear foramen

Foramina are typically defined as openings through which nerves and blood vessels pass, while apertures are simple openings in bone without any known conduit function [15]. The supratrochlear foramen (STF) does not transmit any anatomical structures, making the term "foramen" technically inaccurate by definition. Its precise origin and function remain unclear. Two primary theories have been proposed regarding its formation. One widely accepted view suggests that the STF develops due to mechanical stress, such as from prominent olecranon or coronoid processes, or due to greater flexion-extension movements at the elbow joint [15]. This mechanical theory is further supported by evidence from prehistoric and Neolithic human populations, in whom STF was more commonly observed. Hirsch hypothesized that if a correlation between STF and increased elbow joint mobility could be proven, its significance as a functional adaptation would be better understood. Such an adaptation may have diminished over time, as modern humans generally exhibit a reduced range of motion compared to their prehistoric ancestors, in whom this feature was more consistently present.

Embryologically, the humerus does not show STF during early development. It typically forms later, during adolescence or adulthood, due to incomplete ossification or gradual resorption of the thin bony septum. The septal aperture is considered to be more prevalent in ancient populations, particularly among late Europeans. Its decreasing frequency since the Paleolithic and Neolithic eras suggests a possible evolutionary regression. Some researchers have also suggested that inadequate blood supply to the region may contribute to septal resorption and subsequent formation of STF [16]. The variability in its shape and frequency may thus reflect both mechanical and developmental influences. The observed higher prevalence on the left side in many studies may be attributed to handedness, with the non-dominant limb often being less robust, making it more susceptible to forming the STF [15,17].

In the present study, the STF was observed in 29% of specimens. Globally, its prevalence ranges widely from 0.3% to nearly 60% (Table 4). Macalister, in a study on Libyan skeletons, reported a prevalence of 57% [18]. The communication between the olecranon and coronoid fossae, in absence of trauma or pathology, likely represents a rare congenital anomaly. Although a search of the OMIM database yielded no known genetic disorders linked to distal humeral perforations, it is speculated that certain genetic or biomechanical factors, such as overly prominent processes or increased joint laxity, could predispose individuals to develop the foramen. This laxity, more frequently seen in females, might explain both the occasional bilateral occurrence of STF and its higher prevalence among women. Conversely, Papaloucas et al. found the prevalence to be just 0.3% in Greeks [19]. Consistent with earlier reports from studies on Korean, Egyptian, and Eastern Indian populations, our study also showed a higher incidence of STF on the left side [2, 20, 21]. Prevalence data from various populations, as reported by different authors, are summarized in Table 4 [22-25]. Hrdlicka noted that STF appeared more frequently in Australians, various non-European populations (excluding the Lapps), and people of African descent compared to European whites [26]. Benfer and McKern found a 6.9% prevalence in American samples [27].

In our study, the most commonly observed STF shape was round (48.27%), followed by oval (41.38%) and irregular (10.35%). These findings align closely with those of Veerappan et al. [28], who reported oval shapes in 42.85%, round in 37.71%, triangular in 14.28%, and sieve-like in 7.14% of their specimens. Nayak et al. observed septal translucency in 56.7% of humeri, while Veerappan et al. reported it in 50% [12, 28].

Regarding morphometric analysis, our study found that the mean transverse diameter of the STF was 3.23 mm on the left and 4.64 mm on the right, while the vertical diameter measured 3.89 mm and 3.65 mm, respectively. These findings are comparable to those reported by Mathew et al. [29]. Notably, the transverse diameter showed a statistically significant difference between sides (p < 0.0001), whereas the vertical diameter did not. Our results were compared with those from Nayak et al. [12], Krishnamurthy et al. [25], and Veerappan et al. [28] (Table 5).

Clinically, STF has relevance in pediatric orthopedics, where supracondylar fractures constitute around 17% of trauma cases. Retrograde intramedullary nailing is a common intervention [30]. Since the presence of STF may indicate a narrower medullary canal, an antegrade approach might be preferred in such cases. Furthermore, STF may appear radiolucent on imaging and can be mistaken for osteolytic or cystic lesions. The structure also shows marked racial variation, making it a useful anthropological marker. Its evolutionary implications allow anthropologists to use it for dating and identifying ancient skeletal remains [31].

Table 4: Showing the prevalence of the supratrochlear foramen in different populations

Table 5: Showing the comparison of the diameters of the supratrochlear foramen in different studies

[TD: Transverse diameter; VD; Vertical diameter]

Limitations: The limitation of the present study was the unavailability of age and sex data for the humerus bones, which prevented further analysis based on these factors.

The supratrochlear foramen (STF) is well-known among anatomists and anthropologists but remains largely overlooked by clinicians, as reflected by its minimal or absent coverage in most clinical textbooks. Since it does not transmit any neurovascular structures, we suggest the term “supracondylar aperture” to better describe this anatomical feature. Its recognition is crucial for orthopaedic surgeons during preoperative planning of distal humerus fracture fixation and for radiologists to distinguish it from pathological osteolytic or cystic lesions. Overall, a thorough understanding of the STF is valuable for anthropologists, orthopaedic surgeons, and radiologists in both clinical and academic contexts

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