conus medullaris is the cone - shaped terminal part of the spinal cord that is usually located between the 12th thoracic ( t12 ) vertebra and the 3rd lumbar ( l3 ) vertebra . tuffier 's line is a clinical landmark defined as a horizontal line connecting the superior aspect of the posterior iliac crests , used as a reference to localize 4th lumbar ( l4 ) vertebra body before performing a lumbar puncture . previous studies showed that trained anesthesiologists fail to correctly identify the lumbar interspaces through physical exam . also , mr imaging evidences a variable conus medullaris and tuffier 's line position according to age , gender , and race [ 35 ] . misidentification of l4 using tuffier 's line causes conus medullaris iatrogenic trauma during anesthesia and lumbar puncture procedures . therefore , the correct position of these anatomic landmarks is important to execute this procedure safely . moreover , there are several reports of damage to conus medullaris by lumbar puncture needle during lumbar anesthesia particularly in women [ 7 , 8 ] . the purpose of this study is to determine the level of the conus medullaris , tuffier 's line , and conus medullaris - tuffier 's line distance in an adult population with low back pain and its relation to their age and gender . from may 2008 to april 2009 , a total of 189 adult patients served by our hospital ( between 20 and 73 years old ) , who underwent lumbosacral spine mr imaging as part of workup for low back pain , were included . patients with kyphoscoliosis , history of previous spine surgery , spinal fracture , spinal collapse , congenital spinal anomalies , malignancy , and tethered cord were excluded from this study . the presence of thickened filum terminale was studied using axial images , and , if present , the patients were excluded . all patients were examined using a 1.5 t signa ( general electric , signa , usa ) superconducting magnet with a 5  11  cm surface coil . t1-weighted multiple sagittal images , t2-weighted mid - sagittal , and multiple axial images were routinely obtained in all patients . the section thickness was 4  mm , and interslice gap of sagittal sequences was 1  mm . each vertebra was divided into 3 equal segments ( upper , middle , and lower ) , and intervertebral disc space was also assumed as one segment . all segments were numbered consecutively from t12 upper segment to l5s1 intervertebral disc ( from 1 to 24 , resp . ) a horizontal line was drawn from the most distal part of the spinal cord on mid - sagittal mr images perpendicular to the longitudinal axis of the spine . the position of conus medullaris was determined by the corresponding vertebral segment or intervertebral disc space at the same level . tuffier 's line position was determined by a line intersecting the highest part of iliac crests on the anteroposterior ( ap ) lumbosacral x - ray . the same method used for defining the position of the conus on mri was used on x - ray images for tuffier 's line . all cases were evaluated by a single radiologist , and the presence of sacralization ( a developmental abnormality in which the first sacral vertebra becomes fused with the fifth lumbar vertebra ) and lumbarization ( nonfusion of the first and second segments of the sacrum so that there is one additional articulated vertebra , the sacrum consisting of one fewer segment ) was noted if present . tuffier 's line is actually found on physical examination , and we needed to validate our method of determination of tuffier 's line position . a radiopaque marker was left on the skin on tuffier 's line determined using physical exam . an ap lumbosacral x - ray was performed , and we compared the tuffier 's line determined by the two methods . on coronal mr images the iliolumbar ligament passes from l5 transverse process to the adjacent part of ilium . that ligament can be used for identification of l5 vertebra , and these images may also be useful for determination of the tuffier 's line position . to assess this possibility , we assumed the line connecting top of iliac crests on coronal mr images which include both iliac crests and vertebral bodies as the tuffier 's line . we compared position of this line with tuffier 's line on lumbosacral x - ray in 30 patients , and we encountered almost the same results ( figure 2 ) . the statistical package spss 16 for windows ( chicago , ill , usa ) was used for analysis . kolmogorov - smirnov test was employed to test the normality of the variables in each group . for comparison of variables between the groups , mann - whitney u test ( for continuous variables deviated from the normal distribution ) , independent sample t - test ( for normally distributed continuous variables ) , chi - square test ( for categorical variables ) were employed . studies have substantially noted age and sex differences in the position of conus medullaris and tuffier 's line . to study the role of age , the cut - off point of 50 years old was set . to provide a measure of association between conus medullaris position , conus - tuffier 's line distance , age , and sex , the patients were stratified into high conus ( conus medullaris position equal and higher than middle l1 vertebra ) and low conus ( conus medullaris position lower than middle l1 vertebra ) as well as short conus - tuffier 's line distance ( conus - tuffier 's distance equal and less than 14 segments ) and long conus - tuffier 's distance ( conus - tuffier 's distance more than 14 segments ) . the probability of a patient to have a low conus and a short conus - tuffier 's distance according to their age and sex was determined . pearson correlation was employed to study the correlation between conus - tuffier 's line and age . table 1 presents the primary characteristics of participants . there were 72 ( 38.1% ) males and 117 ( 61.9% ) females with the mean age of 50.1 and 52.3 years old . the median of conus medullaris position was l1 upper segment ( ranging from t12 upper segment to l2 middle segment ) . the median of tuffier 's line position was in l5 upper segment ( ranging from l3l4 intervertebral disc to l5s1 intervertebral disc ) . the median of conus - tuffier 's line distance was 15 vertebral segments ( ranging from 9 to 21 vertebral segments ) . the conus medullaris was significantly lower in females than in males ( from t12 upper segment to l2 middle segment ( median : l1 middle segment ) in females versus from t12 upper segment to l2 upper segment ( median : l1 upper segment ) in males ; p < .05 ) ( table 1 ) . the tuffier 's line was significantly higher in males than in females ( between l3l4 intervertebral disc to l5s1 intervertebral disc ( median : l4l5 intervertebral disc ) in males versus from l4 middle segment to l5s1 intervertebral disc ( median : l5 upper segment ) in females ; p < .001 ) . there was not any significant difference in conus - tuffier 's line between males and females ( from 9 to 21 ( median : 15 ) in males versus from 10 to 20 ( median : 15 ) in females ; p = .6 ) . there were significantly more women with low conus compared to men in patients older than 50 years old ( 56/77 , 72.7% in females versus 21/38 , 55.3% in males ; p < .05 ) when there was not such a sexual dimorphism in patients younger than 50 years old ( 15/40 , 37% in females versus 16/34 , 47% in males ; p = .43 ) . similarly short conus - tuffier 's line distance was more frequent among women than men in patients older than 50 years old ( 46/77 , 59.7% in females versus 15/38 , 39.5% in males ; p < .05 ) when there was not any gender difference in patients younger than 50 years old ( 15/40 , 37% in females versus 14/34 , 41% in males ; p = .65 ) . conus - tuffier 's line distance was negatively correlated with age ( r = 0.32 , p < .001 ) in our cases . lumbar spine degenerative joint disease was noted in 80 ( 42.3% ) cases . there was a slight lowering of the conus and decrease in conus - tuffier 's line distance in patients with degenerative joint disease . sacralization was noted in 34 ( 18% ) and lumbarization was noted in 10 ( 5.3% ) of our studied population . tuffier 's line in patients with sacralization ( from l5 lower segment to l3l4 intervertebral disc , median : l4l5 intervertebral disc ) was upper and in patients with lumbarization ( from l5s1 intervertebral disc to l4 middle segment , median : l5 lower segment ) was lower than those in healthy volunteers ( from l5s1 intervertebral disc to l3l4 intervertebral disc , median : l5 upper segment ) . our findings clearly demonstrated that both conus medullaris and the tuffier 's line were in a significantly lower position in females compared to males . there were a higher number of women with low conus and short conus - tuffier 's distance compared to men in patients older than 50 years old , whereas there was not such a sexual dimorphism in patients younger than 50 years old . both conus medullaris and tuffier 's line have been reported to be placed slightly lower down more frequently in females than in males . to date we are unaware of any study demonstrating gender differences in the conus - tuffier 's line distance . two other groups , thomson and demiryrek et al . showed that conus medullaris is lower in females than in males [ 10 , 11 ] . kim and collaborators showed a negative correlation between old age and the position of conus medullaris   however , they did not report any sexual dimorphism in old ages . we chose a cutpoint of 50 years old as it is the mean age of menopause in iran . it is known that postmenopausal women have a higher risk of osteoporosis and spinal fracture compared to men [ 1316 ] . so it was expected to observe a higher frequency of short conus - tuffier 's line among postmenopausal women . interestingly , we found these results despite excluding patients with spinal fracture and collapsed vertebra , which are usually women [ 17 , 18 ] .   on the other hand , women have a higher bmi compared to men . the identification of tuffier 's line requires palpation through a variable amount of subcutaneous fat and would be harder in obese individuals . hence , we suggest that clinicians should be more cautious in identifying tuffier 's line and appropriate site of puncture in postmenopausal women .   our results about the anatomical positions of conus medullaris and tuffier 's line are consistent   with previous studies [ 3 , we showed that there is a safe zone of at least 2 vertebral bodies and disc spaces ( 9 vertebral segments ) between conus medullaris and tuffier 's line . the median of conus medullaris position was l1 upper segment ( ranging from t12 upper segment to l2 middle segment ) . the median of tuffier 's line position was l5 upper segment ( ranging from l3l4 intervertebral disc to l5s1 intervertebral disc ) . thomson showed that the position of the conus medullaris is from the lower border of t12 and the upper border of l3 . consistently , saifuddin et al . showed that the tip of the conus medullaris is between middle segment of t12 and upper segment of l3 with a median position at the lower segment of l1 . in older patients with osteoporosis or age - related vertebral deformity , a reduced height of the vertebral body we also showed that there is a significant negative correlation between age and conus - tuffier 's line distance , irrespective of gender . the principal limitation of the present study is its cross - sectional nature , which precludes the determination of the direction of causality . however , we have relatively large sample size and close similarity between groups in most of the potentially confounding variables .   in conclusion , we showed that there should be more caution in using the tuffier 's line as a landmark during lumbar puncture in postmenopausal women .
aim . to determine the level of the conus medullaris - tuffier 's line , and conus medullaris - tuffier 's line distance using imaging and evaluate their relation to age and gender 
 . 
 methods . 
 we performed a cross - sectional study of 189 adult participants , who underwent mr imaging of lumbosacral spine . 
 each vertebra was divided into 3 equal segments ( upper , middle , and lower ) , and intervertebral disc space was also assumed as one segment . 
 all segments from t12 upper segment to l5s1 intervertebral disc were numbered consecutively . 
 the position of conus medullaris and tuffier 's line was determined by the vertebral segment or intervertebral disc space at the same level . 
 the patients were stratified into high / low conus medullaris position ( cutpoint : l1 middle segment ) and short / long conus - tuffier 's distance ( cutpoint : 14 segments ) . 
 results . 
 women with low conus were significantly more than men , in patients older than 50 years old ( 72.7% in females versus 55.3% in males ; p < .05 ) , whereas there was not such a sexual dimorphism in patients younger than 50 years old . 
 similarly , short conus - tuffier 's distance was more frequent among women than men in patients older than 50 years old ( 59.7% in females versus 39.5% in males ; p < .05 ) , whereas there was not any gender difference in patients younger than 50 years old . 
 conus - tuffier 's distance was negatively correlated with age ( r = 0.32 , p < 
 .001 ) in all studied population . 
 conclusion . 
 anatomical landmarks vary according to age and gender , with a lower end of conus medullaris in women , so clinicians should use more caution on the identification of the appropriate site for lumbar puncture , particularly in elderly women .