diffuse idiopathic skeletal hyperostosis ( dish ) is non - inflammatory systemic disease which leads to ossification of ligaments and entheses . especially ossification of longitudinal ligaments causes the ankylosing spine .
according to utsinger , dish is diagnosed when radiographs present the ossification of at least four contiguous vertebral bodies . spinal fractures and following spinal cord injuries are easily caused by low - energy trauma in patients with dish because of immobilized spinal column [ 3 , 4 ] .
the pathogenesis is unknown and the prevalence of spinal dish varies depending on region and ethnic differences ; however , recently an age - related increase in prevalence is undisputed .
several studies suggested that delayed neurological deterioration tends to occur in the fracture caused by hyperextension injury .
here we report three cases of those who developed delayed leg paraplegia after hyperextension injuries of the thoracolumbar spine with dish .
a 68-year - old male presented with back pain and no neurological deficits after the traffic accident .
plain radiographs showed ankylosing spine at t1 to l2 level ; however , no fractures were identified at the first time visit to the hospital ( fig .
1b ) , computed tomography ( ct ) scan revealed the hyperextension fracture at t12 ( fig .
magnetic resonance image ( mri ) also showed hyperextension fracture and epidural hematoma compressing spinal cord ( fig .
figure 1:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at t12 ; mri t2-weighted image ( d , e ) showing the epidural hematoma compressing the dura matter .
plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at t12 ; mri t2-weighted image ( d , e ) showing the epidural hematoma compressing the dura matter . a 77-year - old female presented with lower back pain and no neurological deficit after  falling down .
about 11 days after the injury , severe lower back pain and incomplete leg paraplegia of frankel grade b appeared .
ct scan revealed ankylosing spine at t1 to l2 and the hyperextension fracture at l1 ( fig . 2c ) .
figure 2:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at l1 level . 

table 1:summary of three casescasemechanism of injuryinjury levelcause of paraplegiaduration from injury to paraplegiafrankel grade alteration1high energyt12epidural hematoma<24 hc to d2low energyl1dislocation10 daysb to c3low energyl1dislocation14 daysa to b plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at l1 level .
summary of three cases a 79-year - old female presented with lower back pain after falling down .
about 14 days after the injury , she developed complete leg paraplegia of frankel grade a and she was admitted to our hospital .
second plain radiographs showed no major change , but ct revealed ankylosing spine at t5 to l2 and the hyperextension fracture at l1 ( fig .
figure 3:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at t12 level .
plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at t12 level .
a 68-year - old male presented with back pain and no neurological deficits after the traffic accident .
plain radiographs showed ankylosing spine at t1 to l2 level ; however , no fractures were identified at the first time visit to the hospital ( fig .
1b ) , computed tomography ( ct ) scan revealed the hyperextension fracture at t12 ( fig .
magnetic resonance image ( mri ) also showed hyperextension fracture and epidural hematoma compressing spinal cord ( fig .
figure 1:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at t12 ; mri t2-weighted image ( d , e ) showing the epidural hematoma compressing the dura matter .
plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at t12 ; mri t2-weighted image ( d , e ) showing the epidural hematoma compressing the dura matter .
a 77-year - old female presented with lower back pain and no neurological deficit after  falling down .
about 11 days after the injury , severe lower back pain and incomplete leg paraplegia of frankel grade b appeared .
ct scan revealed ankylosing spine at t1 to l2 and the hyperextension fracture at l1 ( fig . 2c ) .
figure 2:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at l1 level . 
 table 1:summary of three casescasemechanism of injuryinjury levelcause of paraplegiaduration from injury to paraplegiafrankel grade alteration1high energyt12epidural hematoma<24 hc to d2low energyl1dislocation10 daysb to c3low energyl1dislocation14 daysa to b plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at l1 level .
about 14 days after the injury , she developed complete leg paraplegia of frankel grade a and she was admitted to our hospital .
second plain radiographs showed no major change , but ct revealed ankylosing spine at t5 to l2 and the hyperextension fracture at l1 ( fig .
figure 3:plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at t12 level .
plain radiographs on initial assessment ( a ) and on admission ( b ) ; sagittal ct image ( c ) showing the hyperextension fracture at l1 and dislocation of it ; mri t2-weighted image ( d , e ) showing the severely compressed spinal cord at t12 level .
dish and ankylosing spondylitis are known as ankylosing spinal disorders , which lead to ankylosis of spinal column .
the prevalence of dish is different between races ranging from 2.9% to 25% [ 6 , 7 ] , and its etiology is unclear .
however , several studies showed association with advancing age , obesity and type 2 diabetes mellitus .
dish patients are susceptible to spinal fracture with trivial trauma due to immobilization of vertebrae .
the previous studies reported that most fractures are localized in cervical spine , uncommon at thoracolumbar junction [ 3 , 4 , 8 ] .
hyperextension fracture is the most frequent type of fractures with dish patients ( 51.2% ) and induces the anterior distraction of vertebral bodies
upper and lower fused vertebral bodies make the stress concentration on fracture level , so spinal cord injury due to dislocation of fracture or epidural hematoma is easy to occur after an interval from first injury . therefore secondary deterioration of neurological status is observed [ 3 , 4 , 8 ] .
however , it is difficult to diagnose the hyperextension fracture at the initial assessment only with plain radiograph .
patients with unrecognized fractures commonly complain of only lower back pain until abrupt neurological deterioration occurs .
once after the neurological deficits occur , surgical treatment does not have the great influence to the clinical outcome .
we analyzed the mechanism of injury , fracture level , direct cause of leg paraplegia , the duration from onset to paralysis , surgical procedure , and neurological deficits before and after treatment .
the mechanism of injury was high - energy trauma in case 1 , and low - energy trauma in case 2 and case 3 .
only a few reports mentioned the epidural hematoma causing spinal cord injury . to the best of our knowledge ,
the cause of leg paraplegia was epidural hematoma within 24 h in case 1 , and dislocation of fracture over 1 week in case 2 and case 3 .
a delay in diagnosis often occurs in hyperextension fractures with dish [ 3 , 4 ] because it is difficult to diagnose the fractures in plain radiographs due to ankylosing spine .
the absence of major trauma may also mislead the diagnosis , this leads to second neurological deterioration .
all cases were treated conservatively at an initial treatment , because the hyperextension injuries in dish were not recognized only with plain photographs .
we can find only a few reports that neurological deficits improved by more than two frankel grade after surgical treatment , again , the definitive treatment should be performed before the second neurological deterioration appears .
we here reported three cases of the thoracolumbar hyperextension injuries in patients with dish , those who developed delayed leg paraplegia .
the spinal fracture with dish is difficult to diagnose only with plain radiograph , therefore screening of spinal column with ct and/or mri should be recommended even if the fractures are not detected .
 abstractdiffuse idiopathic skeletal hyperostosis ( dish ) is characterized by calcifications and ossification of ligaments and tendon insertions . 
 the patients with dish are susceptible to spinal column injury with trivial trauma due to immobilization of vertebrae and this easily leads to spinal cord injury . 
 however , only few reports on hyperextension injuries of the thoracolumbar spine with dish exist . here 
 we report three cases of those who developed delayed leg paraplegia after hyperextension injuries of the thoracolumbar spine with dish . 
 all cases complained only lower back pain without neurological deficits and plain radiographs showed no fractures at an initial assessment . 
 the spinal fracture caused by hyperextension injury was diagnosed with computed tomography ( ct ) and magnetic resonance image ( mri ) after delayed leg paraplegia occurred . 
 many of the fractures caused by hyperextension injuries are not detected only with plain radiographs in patients with dish . 
 further investigations using ct and/or mri should be recommended . 
INTRODUCTION
CASE DESCRIPTION
Case 1
Case 2
Case 3
DISCUSSION
CONCLUSION
CONFLICT OF INTEREST STATEMENT