nontraumatic sacral fractures can be characterized as insufficiency fractures in elderly populations and fatigue fractures in younger populations and athletes 13 .
insufficiency fractures occur in osteoporotic patients or in patients who have undergone radiation therapy for pelvic malignancy .
fatigue fractures occur in physically active individuals , such as long - distance runners , in whom repetitive stress loads occur 4 .
several reports have described their occurrence in athletes who engage in vigorous exercise . however , sacral fatigue fractures in children are very uncommon 46 , especially in those younger than 10 years of age . here , we present two cases of 9-year - old children diagnosed with sacral fatigue fractures .
the authors obtained informed written consent from the patients parents to publish this case report . a 9-year - old baseball player presented with a 1-month history of right low back and buttock pain during baseball .
he had just returned to baseball after cessation of sports activity because of osteochondritis dissecans of the left knee .
he was referred to our department for further workup of his low back and buttock pain .
the patient had no paresthesia , weakness , fever , bowel or bladder dysfunction , or weight loss .
physical examination indicated local tenderness over the right iliac crest and slight limitation in the range of motion in the right hip ; however , no areas of decreased sensation or leg - length discrepancy were noted .
plain radiographs of the pelvis showed no abnormal findings such as osteolytic or sclerotic changes ( fig .
1 ) . mri showed a linear signal void in the right s1 ala on both t1-weighted and short tau inversion recovery ( stir ) coronal images .
further , there were low signal intensity changes on t1-weighted images and high signal changes on stir surrounding the linear signal void ( fig .
a linear sclerotic change was observed at the same area on computed tomography , and spina bifida occulta ( sbo ) was noted from s1 to s5 ( fig .
3 ) . a diagnosis of sacral fatigue fracture was made on the basis of both clinical and imaging data .
three months after symptom onset , pain was improved and signal changes in the right s1 ala had disappeared on mri ( fig . 2c and d ) .
coronal images showing ( a ) diffuse low marrow signals with a central linear signal void ( arrows ) in the t1-weighted image and ( b ) diffuse increased signals in the stir image at the right s1 ala ( arrows ) .
( c , d ) the low signals in the t1-weighted image , high signals in the stir image , and the linear signal void are no longer evident 3 months later .
( a ) coronal and ( b ) axial ct images showing linear medullar sclerosis in the right s1 ala ( arrows ) and sbo ( arrowhead ) .
( c ) three - dimensional - ct image showing sbo from s1 to s5 .
a 9-year - old male baseball player experienced pain in the left hip after playing baseball .
no history of paresthesia , weakness , fever , bowel or bladder dysfunction , or weight loss was noted .
his previous medical history and family history were nonspecific , and there was no history of trauma .
three weeks after symptom onset , he was referred to our department for further workup of the persistent left hip pain .
physical examination indicated no tenderness over the paraspinal region , buttocks , low back , or femoral head .
both his lower extremities showed full range of motion and full motor strength , and there were no areas of decreased sensation or leg - length discrepancy .
mri showed a linear signal void on the t2-weighted coronal image in the left s2 sacral ala ( fig .
4a ) . computed tomography indicated a linear band of medullary sclerosis at the same site and sbo was noted at s2 ( fig . 5 ) .
( b ) two months later . coronal mr images showing the linear signal void ( arrows ) in the t2-weighted image ( a ) .
the linear signal void in the t2-weighted image is no longer evident 2 months later ( b ) .
( a ) coronal and ( b ) axial ct images showing linear medullar sclerosis in the left s2 ala ( arrows ) and sbo ( arrowhead ) .
because his pain had already improved , he was allowed to resume sports activities as long as pain was tolerable .
two months later , t2-weighted coronal image showed the linear signal void at the fracture to be unclear and diffuse ( fig .
a 9-year - old baseball player presented with a 1-month history of right low back and buttock pain during baseball . he had just returned to baseball after cessation of sports activity because of osteochondritis dissecans of the left knee .
he was referred to our department for further workup of his low back and buttock pain .
the patient had no paresthesia , weakness , fever , bowel or bladder dysfunction , or weight loss .
physical examination indicated local tenderness over the right iliac crest and slight limitation in the range of motion in the right hip ; however , no areas of decreased sensation or leg - length discrepancy were noted .
plain radiographs of the pelvis showed no abnormal findings such as osteolytic or sclerotic changes ( fig .
1 ) . mri showed a linear signal void in the right s1 ala on both t1-weighted and short tau inversion recovery ( stir ) coronal images .
further , there were low signal intensity changes on t1-weighted images and high signal changes on stir surrounding the linear signal void ( fig .
a linear sclerotic change was observed at the same area on computed tomography , and spina bifida occulta ( sbo ) was noted from s1 to s5 ( fig .
a diagnosis of sacral fatigue fracture was made on the basis of both clinical and imaging data .
three months after symptom onset , pain was improved and signal changes in the right s1 ala had disappeared on mri ( fig . 2c and d ) .
coronal images showing ( a ) diffuse low marrow signals with a central linear signal void ( arrows ) in the t1-weighted image and ( b ) diffuse increased signals in the stir image at the right s1 ala ( arrows ) .
( c , d ) the low signals in the t1-weighted image , high signals in the stir image , and the linear signal void are no longer evident 3 months later .
( a ) coronal and ( b ) axial ct images showing linear medullar sclerosis in the right s1 ala ( arrows ) and sbo ( arrowhead ) .
( c ) three - dimensional - ct image showing sbo from s1 to s5 .
a 9-year - old male baseball player experienced pain in the left hip after playing baseball .
no history of paresthesia , weakness , fever , bowel or bladder dysfunction , or weight loss was noted .
his previous medical history and family history were nonspecific , and there was no history of trauma .
three weeks after symptom onset , he was referred to our department for further workup of the persistent left hip pain .
physical examination indicated no tenderness over the paraspinal region , buttocks , low back , or femoral head .
both his lower extremities showed full range of motion and full motor strength , and there were no areas of decreased sensation or leg - length discrepancy .
mri showed a linear signal void on the t2-weighted coronal image in the left s2 sacral ala ( fig .
computed tomography indicated a linear band of medullary sclerosis at the same site and sbo was noted at s2 ( fig . 5 ) .
coronal mr images showing the linear signal void ( arrows ) in the t2-weighted image ( a ) .
the linear signal void in the t2-weighted image is no longer evident 2 months later ( b ) .
( a ) coronal and ( b ) axial ct images showing linear medullar sclerosis in the left s2 ala ( arrows ) and sbo ( arrowhead ) .
because his pain had already improved , he was allowed to resume sports activities as long as pain was tolerable .
two months later , t2-weighted coronal image showed the linear signal void at the fracture to be unclear and diffuse ( fig .
fatigue fractures in children usually occur in the lower extremities , most commonly in the tibia , fibula , or metatarsals 7,8 .
fatigue fractures of the sacrum are less commonly reported , but may be encountered as the result of serious athletic training for long - distance running 9 . to our knowledge , there are only five case reports of fatigue fractures of the sacrum in children aged 12 years or younger in the literature .
sacral fatigue fractures are very uncommon in children and all published reports describe excellent clinical outcomes with conservative treatment ( table 1 ) 5,7,1012 .
previous studies on sacral fatigue fracture in children aged 12 years or younger symptoms of sacral fatigue fractures are low back pain of gradual onset , occasionally radiating to the hip or the groin .
most patients have normal results on neurological examination , and most show full range of motion of the back and lower extremities . with respect to radiological findings , plain radiographs
are usually normal as they are not sensitive enough to show sacral fatigue fractures , but may be useful in revealing other causes of back pain .
bone scintigraphy shows increased activity in the lateral part of the sacrum and mri shows bone marrow edema as an early sign of a stress fracture .
t1-weighted and t2-weighted and stir images show a linear signal void with surrounding diffuse decreased marrow signals on the t1-weighted images and surrounding high - intensity signals on the t2-weighted and stir images .
the radiological findings in our cases were consistent with these features . in both our patients ,
however , we could find no reports describing the presence of sbo in pediatric patients with sacral fatigue fractures ( table 1 ) 5,7,1012 .
in addition , athletes typically incur fatigue fractures , but neither patient was a highly enthusiastic athlete .
sakai et al . 
 13 reported a significantly higher incidence of lumbar spondylolysis among patients with sbo than in those without sbo ( 16.2 vs. 5.0% , respectively .
several studies in the literature have described a positive association between sbo and spondylolysis 1416 .
a recent finite element study showed a bifid arch in sbo and following laminectomy increases load across the isthmus , predisposing toward early fatigue fractures of the isthmus 17 .
similarly , sbo in the sacrum might affect the stress concentration on the sacral alae , predisposing toward stress fractures of the sacrum without repetitive stress .
we have presented two cases of sacral fatigue fractures in 9-year - old patients with sbo at each affected level .
sacral fatigue fracture is an important consideration in the differential diagnosis of lower back and pelvic pain in children and should be considered whenever a healthy , active child presents with unexplained persistent low back and buttock pain .
we have presented two cases of sacral fatigue fractures in 9-year - old patients with sbo at each affected level .
sacral fatigue fracture is an important consideration in the differential diagnosis of lower back and pelvic pain in children and should be considered whenever a healthy , active child presents with unexplained persistent low back and buttock pain .
 in this report , we present two cases of 9-year - old children with spina bifida occulta ( sbo ) of the sacrum , who were diagnosed with sacral fatigue fractures . in both 
 patients , mri showed a linear signal void and high signal in sacral ala on the short tau inversion recovery sequence . 
 sacral sbo at the same level of the sacral fracture was observed in each patient on computed tomography images . 
 these lesions healed with rest . 
 this is the first literature reporting cases with sacral stress fractures who had sbo at the same level of fracture . 
Introduction
Case reports
Case 1
Case 2
Discussion
Conclusion
Conflicts of interest