European Journal of Cardiovascular Medicine

The supratrochlear foramen (STF) is a relatively common anatomical variation found at the distal end of the humerus in humans. It develops when the thin, translucent bony partition known as the supratrochlear septum, which separates the olecranon and coronoid fossae, becomes perforated. This septum varies in thickness from about 0.5 mm to 1 cm and, in its fresh state, is lined by the synovial membrane of the elbow joint. In some individuals, the septum undergoes perforation, resulting in an opening called the supratrochlear aperture or supratrochlear foramen. The STF was first reported by Mekel in 1825 [1] and has since been described by various names, such as the intercondylar foramen, olecranon foramen, and epitrochlear foramen [2, 3]. The formation of STF is influenced by age. The septum between the olecranon and coronoid fossae is consistently present until around seven years of age, after which it may undergo resorption, leading to the appearance of the foramen [4]. Individuals with STF may also demonstrate an increased degree of elbow hyperextension [5]. The occurrence of STF is not limited to humans; it has been documented in hyenas, dogs, and several non-human primates [6]. In fact, septal apertures are common across mammalian species and are somewhat more frequent in both Old and New World apes [7]. Darwin even regarded the presence of STF in humans as evidence of evolutionary continuity with primates [8].

Recent studies suggest that STF formation may have a genetic basis, particularly involving the T-Box (TBX) gene family. These genes regulate TBX proteins, which play a critical role in limb and cardiac development during embryogenesis [9]. Govoni further proposed that TBX genes may also influence postnatal limb development, which could explain the persistence or appearance of STF in certain individuals [10]. Clinically, STF was once thought to be of little consequence, but its importance is now well recognized. The presence of STF is often associated with a narrower intramedullary canal, which can complicate fracture management [11]. Supracondylar fractures, particularly in children, are commonly treated with intramedullary nailing [12]; however, STF can interfere with retrograde nailing techniques performed through the medial and lateral epicondyles, or via the lateral epicondyle alone [13]. The close relationship of neurovascular structures in this region further raises the risk of nerve injury during surgical procedures. Consequently, identifying STF becomes an essential step in preoperative planning for distal humeral fractures [11, 12]. In radiology, STF may also mimic pathological entities such as cysts or lytic lesions, potentially leading to misdiagnosis [13]. Thus, a clear understanding of the incidence, morphology, and clinical implications of STF is vital for orthopaedic surgeons, radiologists, and anatomists alike.

Aim and Objectives: This study was conducted to analyze the morphology and morphometry of the supratrochlear foramen in humeri from the Bihar population and to explore its clinical relevance.

In this cross-sectional study, adult dry humerus bones of unknown gender and age were studied in the Department of Anatomy, Bhagwan Mahavir Institute of Medical Sciences, Pawapuri, Bihar.

Sample Size Calculation:

Sample size was calculated using G*Power 3.0.1 at α = 0.05, 80% power, and an effect size of 60% based on prior literature [14]. A total of 100 dry humeri (50 right, 50 left) was deemed sufficient to detect significant morphometric differences and provide reliable data for the Bihar population.

Inclusion and Exclusion Criteria:

The study included dry, macerated adult human humeri with intact distal ends, obtained from the population of Bihar to ensure regional relevance. Only bones from individuals aged 18 years and above were analyzed, and both male and female humeri were considered. Specimens with a preserved supratrochlear septum, septal perforations, or a fully formed supratrochlear foramen (STF) were included. Bones showing fractures, pathological changes, congenital anomalies, surgical alterations, or developmental immaturity were excluded, as were fragmented or non-human specimens. These criteria ensured that only well-preserved, relevant adult humeri were analyzed for accurate morphological and morphometric evaluation.

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: PQ-Transverse diameter and RS-Vertical diameter.

Statistical Analysis:

The collected data were analyzed using Microsoft Excel and analyzed using Statistical Package for the Social Sciences (SPSS), version 25.0. Linear measurements were recorded using a digital vernier caliper with 0.01 mm sensitivity. Each parameter was measured twice, and the mean value was used for analysis. Data were expressed as mean ± standard deviation, and a p-value of less than 0.05 was considered statistically significant

Out of 100 humeri examined, the supratrochlear foramen (STF) was present in 31 specimens (31%), while 69 humeri (69%) did not show the foramen. On the right side, STF was observed in 13 humeri (13%) and absent in 37 (37%), whereas on the left side, STF was found in 18 humeri (18%) and absent in 32 (32%). Although the incidence of STF was slightly higher on the left side compared to the right side, this difference was not statistically significant (p = 0.279) (Table 1).

Three distinct shapes of the supratrochlear foramen (STF) were observed in this study: round, oval, and irregular. Among the 31 humeri exhibiting a supratrochlear foramen (STF), the most common shape observed was round, accounting for 16 specimens (51.62%), followed by oval in 11 specimens (35.48%) and irregular in 4 specimens (12.90%). On the right side, STF was round in 6 humeri (19.35%), oval in 5 (16.13%), and irregular in 2 (6.45%). On the left side, STF was round in 10 humeri (32.27%), oval in 6 (19.35%), and irregular in 2 (6.45%). Although the left side showed a slightly higher frequency of round and oval foramina compared to the right side, the difference between sides was not statistically significant (p = 0.864) (Table 2).

The transverse diameter of the supratrochlear foramen (STF) was significantly greater on the right side (mean = 4.88 ± 1.18 mm) compared to the left side (mean = 3.41 ± 1.00 mm), with the difference being statistically significant (p < 0.0001). In contrast, the vertical diameter showed no significant side difference, with mean values of 3.93 ± 1.33 mm on the right and 4.03 ± 1.31 mm on the left (p = 0.700) (Table 3 and Figure 2).

Table 1: Incidence of Supratrochlear Foramen (STF) in Right and Left Humeri.

[STF: Supratrochlear Foramen]

Table 2: Distribution of shapes of supratrochlear foramen (STF) in right and left humeri.

Table 3: Comparison of the diameters of the supratrochlear foramen (STF) on the right and left sides

[STF: Supratrochlear Foramen]

Figure 2: Comparison of the diameters of the supratrochlear foramen (STF) on the right and left sides

Foramina are generally defined as openings that transmit nerves and blood vessels, whereas apertures are simple bony openings without any conduit function [15]. Since the supratrochlear foramen (STF) does not carry neurovascular structures, the use of the term “foramen” is technically imprecise. Its exact origin and functional role remain uncertain. Two major hypotheses exist regarding its formation. The most widely accepted explanation attributes STF to mechanical factors such as pressure from prominent olecranon or coronoid processes, or from repetitive flexion-extension movements at the elbow joint [15]. Support for this view comes from evidence in prehistoric and Neolithic populations, where STF was observed more frequently. Hirsch proposed that if a relationship between STF and enhanced elbow mobility could be demonstrated, it might reflect a functional adaptation. This adaptation, however, may have diminished over time as modern humans typically exhibit a reduced range of motion compared to their prehistoric counterparts.

From an embryological perspective, STF is absent in early development and tends to appear later, usually in adolescence or adulthood, likely due to incomplete ossification or resorption of the thin septum. Historical data indicate that STF was more frequent in ancient populations, particularly in late Europeans, with a gradual decline since the Paleolithic and Neolithic eras, suggesting evolutionary regression. Some researchers also believe that poor vascularity of the septum may lead to resorption and formation of the foramen [16]. Its frequency and morphological variability may therefore be influenced by both developmental and mechanical factors. The slightly higher prevalence on the left side, reported in several studies, could be related to handedness, as the non-dominant arm tends to be less robust and thus more prone to STF formation [15,17].

In the present study, STF was identified in 31% of humeri. Reported global prevalence varies widely, ranging from 0.3% to nearly 60% (Table 4). Macalister documented a prevalence of 57% in Libyan skeletons [18]. In the absence of trauma or pathology, communication between the olecranon and coronoid fossae is considered a rare congenital variant. Although no genetic disorders linked to distal humeral perforations were identified in the OMIM database, it is speculated that genetic or biomechanical factors—such as exaggerated bony processes or increased joint laxity—might predispose to STF formation. Increased laxity, more common in females, could also account for its bilateral occurrence and higher prevalence in women. On the other hand, Papaloucas et al. reported only 0.3% prevalence in a Greek sample [19]. Consistent with earlier studies from Korean, Egyptian, and Eastern Indian populations, our results also showed a higher frequency of STF on the left side [2,20,21]. Prevalence data across populations, as reported by various authors, are summarized in Table 4 [22–25]. Hrdlicka noted that STF was more frequent among Australians, non-European groups (excluding Lapps), and African populations compared to European whites [26]. Benfer and McKern reported 6.9% in American samples [27].

Regarding shape, round foramina were most frequent in this study (51.62%), followed by oval (35.48%) and irregular (12.90%). These results are comparable with Veerappan et al. [28], who found oval foramina in 42.85%, round in 37.71%, triangular in 14.28%, and sieve-like in 7.14%. Nayak et al. reported septal translucency in 56.7% of humeri, while Veerappan et al. observed it in 50% [12,28].

Morphometric evaluation revealed that the mean transverse diameter measured 3.41 mm on the left and 4.88 mm on the right, whereas the vertical diameter was 4.03 mm on the left and 3.93 mm on the right. These values are in close agreement with the findings of Mathew et al. [29]. The transverse diameter showed a significant side difference (p < 0.0001), while the vertical diameter did not. Our results were compared with those reported by Nayak et al. [12], Krishnamurthy et al. [25], and Veerappan et al. [28] (Table 5).

From a clinical standpoint, STF is relevant in paediatric orthopedics, where supracondylar fractures constitute nearly 17% of traumatic cases. Retrograde intramedullary nailing is commonly performed [30]. Since the presence of STF may narrow the medullary canal, an antegrade approach may sometimes be preferable. On radiographs, STF may also appear as a radiolucent area and mimic osteolytic or cystic lesions. Beyond clinical relevance, STF shows considerable racial variation, serving as a valuable anthropological marker. Its evolutionary implications further support its use by anthropologists in dating and identifying 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: This study provides valuable baseline data on the supratrochlear foramen; future research incorporating age and sex information of the humeri could offer deeper insights into population-specific variations.

The supratrochlear foramen (STF), though well recognized in anatomical and anthropological studies, is often underemphasized in clinical literature. As it does not transmit neurovascular structures, the term ‘supracondylar aperture’ may serve as a more appropriate description. Awareness of this variation is important for orthopaedic surgeons during distal humerus surgeries and for radiologists to avoid misinterpreting it as a pathological lesion. A clear understanding of STF thus holds significance in both clinical practice and academic research.

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