European Journal of Cardiovascular Medicine

The supratrochlear foramen (STF) is a significant and relatively atypical anatomical variation noticed in the distal end of humerus Generally, foramen transmits blood vessels and nerves, in the case of Supratrochlear foramen, no significant structure is transmitted and in the rare case, there may be a probability of entry of the median nerve, which may produce symptoms such as pain and weakness in the hand. A bony septum separates the olecranon and coronoid fossae at the lower end of the humerus, between the two epicondyles. The thickness of the bony septum determines its opacity or translucency. This translucent or opaque septum may have massive perforations, and in severe cases, it may be perforated to form a narrow orifice known as a 'supratrochlear orifice' or 'supratrochlear foramen'. The Supratrochlear foramen has been designated by a variety of names such as intercondylar foramen, olecranon foramen, and epitrochlear foramen4.

The Supratrochlear foramen observed in a variety of shapes, and their morphometry varies depending on gender and race. The delicate and translucent Supratrochlear septum (STS) is not observed in newborns and appears later in life, persists until the age of seven years, and later, for a variety of reasons, Supratrochlear septum undergoes degeneration or absorption only in some individuals, which may lead to the formation of Supratrochlear foramen and some referred to Supratrochlear foramen as the septal aperture¹.  Hence the present study describes incidence and various shapes of the STF among population of East Godavari, Andhra Pradesh which is quite useful in pre operative planning for orthopaedic surgeons and radiologists in daily practice.

The current study was done on a total of 400 dried adult human humerii (200 right& 200 left) of unknown age and gender which were obtained from the bone bank of Department of Anatomy, Rangaraya Medical College, Kakinada,East Godavari district. Bones with pathology and damaged ones were discarded. Presence of STF and its various shapes like round, oval, triangular and sieve was observed by visual examination. All observations were recorded in tabular form and results were interpreted.

side (15.75%) compared to left side (15.25%). The STF was further categorized according to its shapewith moreprevalenceof oval (20.5%) Fig - 3, followed by round (10%) Fig - 2and sieve (1%) Fig - 4. Triangular shape STF was not seen.

Table 1: Distribution of total number of humerii according to presence of the STF.

Table 2: Distribution of humerii with STF according to its shape.

1. IV. Figures

Figure 1.Humeri Showing STF Out of 400 Humeri            Figure 2.Humeri showing Round STF

Figure 3.Humeri showing oval  STF                                      Figure 4.Humeri showing sieve like  STF

The medial and lateral epicondyles of the humerus are the origins of the flexor and extensor groups of forearm muscles. They have three fossae, the radial, olecranon, and coronoid, and articulate with the radius and ulna to form the elbow joint. The function and formation of supratrochlear foramen is largely obscure. No anatomical structure is known to pass through the Supratrochlear foramen and thus it does fit the definition of foramina, as normally foramina serve as conduits for vessels and nerves, while apertures are merely openings in bones with no structure passing through them.

STF is more common finding and prominent structure in the lower animals such as cats.In the lower animals,the foramen forms the safe passage for the median nerve and brachial artery¹².Darwin considered this foramen in humans,as one of the characteristics to show the evolutionary aspect of humans from primates⁴.

Various theories have been proposed by different authors for the formation of STF in the lower end of humerus. According to the mechanical theory, propounded by Glanville the foramen is formed as a result of articulations between the humerus and ulna during extremes of flexion and extension¹¹The foramen usually develops during adolescence,or more frequently adulthood due to incomplete ossification,due to intralamellar space enlargement and gradual septum absorption¹². The genetic theory states that STF is an inherited trait.Frequencies of occurrence in different populations favour this theory².

Incidence:-

The STF in the present study exhibited different shapes, which included oval, round, irregular, and triangular. The oval shape was observed in the highest percentage, and the triangular shape was the least common. Similar observations were reported in some studies in India. Many studies in different regions also observed the oval shape to be the most common shape. However, in a few studies the round shape outnumbered the oval shape. Incidence of STF varies from 6% to 60% in different races¹⁴.Anthropologist suggested rather argued that the incidence of the STF is more in the ancient population as compared to the modern world. The suggested cause in the ancestral population was that they used to perform heavy load work such as agriculture and lifting of heavy tools. The intermittent pressure of the two processes of the ulna may gradually result in the absorption of the septum between them and lead to the formation of the foramen¹².Studies in Greek population having revealed prevalence as low as 1% and the highest of 52 % have reported in Arkansas Indians. Some of the other populations on which the STF has been studied include American 6.9%, Egyptians 7.9 % and Japanese 18.8%. This wide variation favours the genetic basis of development.

Table No 3: Comparative study of Incidence of STF in Indian Population

The studies done on Indian population have shown regional variations. The highest of 32 % was seen in Central Indian population³ while South Indian population recorded 28% ¹⁵  and North Indians and East Indians were 27.4% and 27% respectively(16,17)and31.4% were seen in  Telangana population¹⁸  35.95% were seen in Rajasthan ¹, 28.75% were seen in North East India ¹⁹.

In the present study, out of the 400 humeri studied STF was observed in 124 of the 400 accounting for prevalence of 31 % which is supported by Singhal S. Rao et al and comparatively lower than the findings of D. Naga jyothi et al.

Sidedness of STF:-

If mechanical stress is the causative agent,then the STF should be more frequent on the right side.This is due to the fact that the STF is a phylogenetic and atavistic feature found in primates and is suppressed by the stronger limb and exhibited in the weaker limb²⁰.The side frequency of STF can be explained on the basis of handedness.

Table No4: Comparative study of sidedness of STF

In the present study, the frequency of STF on right side has been reported which is supported by S R Nayak et al and it is contrary to remaining authors shown in table no 4.

Shape of STF:-

Some authors have suggested that more frequent STF in left bones and in female groups is a result of ligamentousand/or muscle laxity that can lead to greater joint laxity, jointhypermobility, impingement of ulnar processes on the humeral laminaand finally to perforation of the lamina²¹.Its presence therefore can be attributed to the functional development of the elbow joint and its variable shapes to the morphometry of the articulating surfaces²

Table No 5: Comparative study of various shapes of STF

In the present study, oval shape of STF (65.32%) was more common followed by round shape (31.45%) and sieve like is (3.2%). These findings were correlated to most of the authors in the table no 5.

The study of the STF in the east Godavari  part Andhra pradesh is still a rarity. The present study sheds light on the prevalence of STF in Andhra pradesh a state in t India. A comprehensive knowledge of the occurrence, shapes, side predisposition of supratrochlear foramen may help in the treatment of supracondylar fractures. We believe that this study will contribute to the literature. The STF of humerus is the very important anatomical variation of lower end of the humerus which is often neglected. For Anthropologists, STF is one of the nonmetrical skeletal traits to play an important role analysis of familial inheritance and population migrations. For orthopaedicians, presence of STF is associated with decreased robustness ,smaller humeral diameter and a narrow medullary canal which predisposes to increased tendency of atypical fractures following low energy impact. Knowledge about this is important for pre operative planning in intra medullary nailing surgeries to prevent secondary fractures.For radiologists, to differentiate psudolesions.

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