the supratrochlear foramen ( stf ) is an important and relatively common anatomic variation in the lower end of the humerus in humans . the supratrochlear foramen ( stf ) of the humerus has been neglected in standard anatomy and orthopedics books . in recent years it has become clear that stf should be emphasized because anatomical knowledge of stf is useful for anatomists , anthropologists , orthopedic surgeons , and radiologists . a thin plate of compact bone known as supratrochlear septum , which is lined by a synovial membrane , usually separates the olecranon fossa and coronoid fossa in the supratrochlear area of the distal part of the humerus [ 15 ] . this bony septum is opaque or translucent and septum in some cases may become perforated to form a foramen called as supratrochlear aperture , septal aperture , intercondylar foramen , or epitrochlear foramen , but is most commonly referred to as supratrochlear foramen ( stf ) [ 68 ] . the perforation lies between the lateral and the medial epicondyle . the supratrochlear foramen was first described by meckel in 1825 . although it may have different shapes , stf are mainly oval , round , triangular , sieve - like , and irregular . the septum is present until 7 years of age , after which it is occasionally absorbed to form stf . the significance of the presence of coronoid - olecranon septal perforation was not clinically an atypical fracture pattern of distal humerus in teenaged boys . it is of some clinical significance that it may predispose to low - energy fractures of the distal humerus . the septal aperture is located along the narrow medullary humeral canal and extreme anterior angulation at the distal part of the humerus . studies have shown that the distal portion of the medullary canal in humeri with septal aperture was narrower and shorter at the entry point of a retrograde nail than in humeri without a septal aperture . features of the intramedullary canal are important in the treatment of supracondylar fractures , especially following traumatic injuries and pathologic fractures and also in intramedullary nailing procedures [ 11,13,1719 ] . nayak et al . observed in plain radiographs that the sa was located closer to the medial epicondyle , resulting in difficult intramedullary nailing . in the literature , the supratrochlear foramen of the humerus has been defined as coexistent with the supracondylar process in the same humerus . additionally , the sa is a relatively radiolucent area , commonly described as a  pseudo lesion  in an x - ray of the upper limb and can be mistaken as an osteolytic or cystic lesion . the osteochondritis dissecans of the septum supratrochlear is the result of an incomplete resolution of the septum in the development of the elbow joint . it remains unclear as to what degree the various factors contribute to the formation of the aperture . the goal of this study was to describe supratrochlear foramen of the humerus in the turkish population . a total of 166 dried humeri ( 83 right side and 83 left side ) , of which 78 belong to males and 88 to females , were examined to determine the presence of supratrochlear foramen in the turkish population . these bones were obtained from the department of anatomy , faculty of medicine and department of antrophology , university of mustafa kemal , hatay , turkey . an osteometric board was used to measure the epicondylar breadth ( eb ) for the sex determination of the humerus . digital vernier calipers were used to measure the transverse ( width ) diameter ( td ) and vertical ( height ) diameter ( vd ) of the stf , the distance of the medial epicondyle to the medial aspect of the stf ( mb ) , and that of the lateral epicondyle to the lateral border of the stf ( lb ) . the shape of the stf was also imaged . in bones where the foramen was not present , opacity and translucency of the supratrochlear septum were noted with the help of transmitted light from posterior to anterior . all measurements are expressed in millimeters . by using these measurements , we calculated minimum , maximum , mean , and standard deviation . the supratrochlear foramen was studied in 166 unpaired turkish humeri with sex and side known . stf was observed in 4 ( 4.8% ) cases on the right side and 14 ( 16.9% ) on the left side . in males , it was seen in 16.7% of cases on the left side and 2.1% of cases on the right side . in females , stf was present on the left side in 17.0% of humeri and 8.6% on the right side ( table 1 , figure 1 ) . in this study , we found most stf were on the left side of both sexes . in the current study , the vertical diameter for supratrochlear foramen was 4.120.98 mm ( range 2.74.9 mm ) on the right side and 4.040.9 mm ( range 2.15.1 mm ) on the left side . transverse diameter was 5.630.97 mm ( range 4.36.5 mm ) on the right side and 6.011.86 mm ( range 2.78.9 mm ) on the left side . in males , the vertical diameter ( vd ) was 2.720.0 mm ( range 2.72.7 mm ) on the right side and 4.260.0 mm ( range 2.95.1 mm ) on the left side . transverse diameter ( td ) was 6.520.0 mm ( range 6.76.7 mm ) on the right side and 6.72.2 mm ( range 4.18.9 mm ) on the left side . in females , the vertical diameter was 4.590.36 mm ( range 4.24.9 mm ) on the right side and 3.920.93 mm ( range 2.15 mm ) on the left side . the transverse diameter ( td ) was 5.340.95 mm ( range 4.36.2 mm ) on the right side and 5.641.66 mm ( range 2.77.9 mm ) on the left side ( table 2 ) . the mean distance from medial epicondyle to medial edge of the stf ( mb ) was 26.13.33 mm ( range 22.630.5 mm ) on the right and 25.733.37 mm ( range 18.930.7 mm ) on the left side . the mean distance from lateral epicondyle to lateral border of the stf ( lb ) was 27.31.54 mm ( range 25.829.5 mm ) on the right and 27.51.5 mm ( range 24.930.1 mm ) on the left side . we observed the position of the stf to be located nearer to the medial epicondyle ( table 2 ) . the epicondylar breadth ( eb ) was 604.36 mm ( range 50.769.1 mm ) on the right and 58.14.07 mm ( range 49.768 mm ) on the left side . the epicondylar breadth was significantly larger in males ( 62.72.46 mm ) than in females ( 55.8 mm2.75 ) ( table 2 ) ] . the stf was oval , round , triangular , and sieve - like in shape in 13 ( 7.8% ) , 2 ( 1.2% ) , 2 ( 1.2% ) , and 1 ( 0.6% ) , respectively , and the oval shape was common on the left side and in females ( table 3 ) . translucent septum was found in 34 ( 20.5% ) humeri and opaque septum was seen in 114 ( 68.7% ) humeri . translucent septum was found in 17 ( 20.5% ) on both sides of the humeri and was very similar in both sexes ( table 1 , figure 2 . ) the sa is a foramen of the bony septum that separates the olecranon from the coronoid fossae at the distal end of the humerus [ 2426 ] . the supratrochlear foramen is of great interest to anthropologists , who claim it as important in establishing relationships between humans and lower animals , including cattle , rats , dogs , hyenas , and other primates . lamb observed that the formation of the stf was more common in ancient peoples and occurs more frequently on the left side and in adolescents , as well as in mature individuals . the supratrochlear foramen has , apart from its evolutionary significance , much clinical and surgical importance . there is a wide variation in the rate of the stf occurrence in various human populations . its incidence varies from close to 0% to almost 60% among different human populations globally . studies on stf in different populations showed an incidence of 58% in arkansas indians , 21.7% of african negroes , 32.5% of south africans , 47% in tellem , 4.3% in white americans , 18.4% in american negroes , 18.1% in japanese , 17.5% in chinese , 6.9% in americans , and 43.6% in egyptians . incidence in european populations was 0.304% in greeks , 6.1% in netherlands , 9.4% in italians . incidence in indian populations showed 27.4% in eastern indians , 32% in central indians , 27.56% in north indians , 28% in south indians   and 34.4% in overall indians   ( table 4 ) . the few previous studies in turkey reported incidence at 7.9% , 8.6% , and 12% . we found this ratio was 10.8% , which is similar to the previous turkish reports ( table 4 ) . prevalence of septal aperture has been reported to be higher in indians and africans than in europeans and turks ( table 4 ) . the frequency of supratrochlear foramen in our study was higher in females and more common on the left side ( table 1 ) . in contrast , blakely et al . reported that incidence of stf was higher on the left side and in males . in the present study , the prevalence of stf was higher on the left side than the right side ( table 1 ) . conversely , nayak et al . found the presence of stf in 44.5% of cases on the right side . singhal and rao found the incidence on both sides was very similar : 27.9% of the right and 27.8% of the left humeri . a number of studies have reported that humeral septal aperture was associated with supracondylar process and there are reports of a greater incidence in males . in our study the shape of stf was predominantly oval and it was more common on the left side , similar to previous reports   ( table 3 ) . translucent septum was found in 17 ( 20.5% ) on both sides of the humeri in the turkish population ( table 1 ) . found the translucency in 69 ( 82.14% ) humeri and chiefly on the left side . krishnamurthy et al . reported an incidence of 66.6% , mostly on the left side . vasantbhai observed the translucency of septum in 126 ( 55.8% ) on the right side   and veerappan et al . reported 50% . conversely , according to many authors , incidence of translucency of the septum and stf was higher on the right side . in the present study , the vertical diameter of the supratrochlear foramen was 4.120.98 mm on the right side and 4.040.9 mm on the left side , and the transverse diameter was 5.630.97 mm on the right side and 6.011.86 mm on the left side ( table 2 ) . table 5 contains comparative statistical data of supratrochlear foramen of humerus in various studies . in our study we observed that the mean transverse diameter of the stf on the left side is larger than on the right side . this finding was similar to previous reports of ozturk et al . . in our study , the epicondylar breadth was significantly larger in males ( 62.72.46 mm ) than in females ( 55.82.75 mm ) . reported a mean 56.15.5 mm , significantly larger in males ( 60.5 mm ) than in females ( 53.4 mm ) . the mean distance from medial epicondyle to medial edge of the stf ( mb ) was 26.13.33 mm on the right side and 25.733.37 mm on the left side , thus the position of stf is located near to the medial epicondyle , especially on the left side . nayak et al . found 28 mm on the right and 26.1 mm on the left side , which agrees with veereppan et al . . the mean distance from lateral epicondyle to lateral border of the stf ( lb ) was 27.31.54 mm on the right and 27.51.5 mm on the left side . ndou et al . found 26.32.9 mm between the stf and the tip of the lateral epicondyle . some of the mechanisms explaining the cause of stf in the humerus are : it may be an atavistic character . it may be worthwhile to investigate this trait in families , with the idea that it may represent an epigenetic character . it was suggested that the generally greater degree of joint hypermobility in females than in males , and in the left than the right upper limb joints , may be a factor behind the greater prevalence of septal aperture in left humeri and in females . hirsh mentioned that the pressure of olecranon process may decrease the blood supply , leading to septal aperture formation . usual mechanism of injury is by hyperextension load on the elbow from falling on an outstretched arm it has often been noticed that populations which have a high frequency of septum perforation tend also to have a low robusticity of the bones . a septal aperture is associated with decreased robustness , smaller humeral diameter , and a narrower canal diameter . the possible reason for the presence of the stf in animals is the posture adapted by them during tearing of food . hirdlika pointed out that intermittent pressure would cause hyperemia , resulting in the strengthening of the bony plate ( fossa ) rather than adsorption . it can be explained that it is a phylogenetic characteristic feature frequently found in primates and is suppressed by the stronger limb and exhibited in the weaker limb . a septal aperture is thought to occur early in childhood from excessive cancellous bone resorption in the distal humerus . mall suggested that the higher occurrence of stf in females may be due to inward curvature of the female elbow angle . it represents evolutionary aspects of the foramen in addition to its surgical and orthopedic significance . the knowledge of presence of stf may be important for preoperative planning for treatment of supracondylar fractures , especially following traumatic injuries and pathologic fractures , and call for performing antegrade medullary nailing rather than retrograde medullary nailing . the supracondylar fracture of the distal humerus is the most common pediatric fracture in the elbow . 5 . awareness of the various shapes and dimensions such as the transverse ( td ) and vertical ( vd ) distance in which this foramen occurs may help avoid misinterpretation of radiographs . , stf presents as radiolucent areas simulating an osteolytic or cystic lesion , hence knowledge of stf may prevent misinterpretation of x - rays by radiologists . 10 . measurements of the epicondylar breadth ( eb ) will be obtained to shed some light on the gracility of these bones , as the stf is known to be more prevalent in gracile bones than in robust ones . a number of studies have suggested that stf may be a hereditary phylogenetic trait with evolutionary significance . 13 . prevalence of septal aperture , which is higher in populations from india and africa than in europeans . the present study showed 10.8% stf incidence in the turkish population , with the left side predominant . prevalence of septal aperture has been reported to be higher in india and in africa than in europeans and turks ( table 5 ) . we believe that this study will contribute to the literature ; anatomical knowledge of stf is beneficial for anatomists , anthropologists , forensic practice , orthopedic surgeons , and radiologists .
backgroundthe supratrochlear foramen ( stf ) is an important and relatively common anatomic variation in the lower end of the humerus in humans . 
 its structure has received increased attention in recent years . 
 anatomical knowledge of stf is useful for anatomists , anthropologists , orthopedic surgeons , and radiologists . 
 this aperture is of great interest to anthropologists who claim it as one of the points in establishing a relationship between humans and lower animals . 
 the goal of this study was to describe the features of stf of the humerus in the turkish population.material/methodsall bones were obtained from the department of anatomy , faculty of medicine and department of antrophology , university of mustafa kemal , hatay . 
 a total of 166 dried humeri ( 83 right side and 83 left side ) , of which 78 belonged to males and 88 to females , were examined to determine the presence of supratrochlear foramen . 
 digital vernier calipers were used to measure the maximum width ( transverse ) and height ( vertical ) of the stf.resultsout of 166 bones , the foramen was present in 18 humeri ( 4 right side and 14 left side ) , showing the incidence as 10.8% with unpaired humeri . 
 we observed 4 types of shape : oval , round , triangular , and sieve - like . 
 the average diameter of the long ( transverse ) axis was 5.931.68 mm and the short ( vertical ) axis was 4.060.89 mm . 
 some of the bones showed translucency of the bony septum , found in 17 ( 20.5% ) on both sides of the humeri.conclusionsthere are few studies about stf in the turkish population . 
 knowledge of supratrochlear foramen in the distal humerus in humans is important in diagnostic orthopedics , in intramedullary nailing of the humerus , and in possibly increasing the risk of future low - energy fractures . 
 in addition , stf is a radiolucent area in radiographs and may be misinterpreted as an osteolytic or cystic lesion .