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bilateral pedicle stress fractures in the spine are uncommon and are generally associated with previous spine surgery or stress - related activities3 - 5,7,9,12 ) .
bilateral pedicle stress fractures as well as defects due to congenital aplasia are quite rare etiologies for spondylolisthesis . to the authors ' knowledge ,
only one case of spondylolisthesis has been previously described in the literature4 ) . here , we report a rare case of spondylolisthesis accompanying a bilateral pedicle stress fracture in two levels not associated with major trauma , previous spine surgery , or stress - related activity .
a 70-year - old woman with progressively worsening of lower back and leg pain for 2 years is presented .
she had a history of mild back pain over the past several years but the leg pain had progressively increased without any traumatic episodes or spinal surgery .
a review of the patient 's past medical history showed that she had suffered from severe osteoporosis for 2 years and had taken bisphosphonate drug ( fosamax ) 70 mg once a week .
her condition worsened to the extent that she had not been able to walk for 3 weeks prior to admission .
the back pain was worse with activites , and the patient experienced relief of pain by sitting or lying down .
she had no paresthesia or muscle weakness of the legs , no bowel or bladder symptoms , and was able to straighten and raise her leg .
bone densitometry results indicated that her spine density as below average , and the mean t - score of the lumbar spine was -3.67 .
she had undergone menopause 20 years ago , and the patient had been healthy without prior medical concerns before admission except severe osteoporosis .
plain radiographs showed severe degenerative changes and grade i spondylolisthesis at the l5-s1 vertebrae according to the meyerding classification , but bilateral pedicle fractures were not clearly observed ( fig .
1 ) . in the dynamic simple radiographs the instability at l4-l5 level was not evident . computed tomographic ( ct ) scans and magnetic resonance imaging ( mri ) confirmed the presence of a bilateral pedicle stress fracture of the l4 and l5 vertebrae , and an intact isthmus as well as a foraminal stensosis compressing the right l5 nerve root ( fig .
after posterior segment removal and l5-s1 discectomy , interbody fusion using peek cages packed with autologous local bone chips were performed to provide anterior column support and bone cement - augmented screw fixation was done at l5-s1 level ( fig .
her pain markedly decreased immediately after operation . at 12 months follow - up , she was pain free .
during the past century , the etiology of spondylolisthesis has been extensively discussed in the literature .
this can be categorized into several types : congenital , isthmic , degenerative , traumatic , and pathologic with alteration of the bone structure ( e.g. , osteoporosis , paget 's disease , osteolytic tumors , and iatrogenic spondylolisthesis)11 ) .
repetitive mechanical stress fractures in the posterior elements are usually located in the pars interarticularis or , to a substantially lesser extent , in the pedicle .
the pedicle has greater intrinsic strength and a shorter moment arm from the vertebral body , and can therefore resist greater cyclic shear forces 3 ) . as a result ,
rather , they are more frequently observed in the isthmus , corresponding to the weakest zone .
bilateral pedicle stress fractures in the lumbar spine are quite rare and very few cases have been reported in the literature .
most of these fractures are associated with underlying causative factors , such as previous spine surgery or stress - related activities7,11 ) . to the best of our knowledge ,
there has not been a previously reported case of spondylolisthesis accompanying a bilateral pedicle stress fracture involving two vertebrae .
currently , only five cases of bilateral pedicle stress fractures have been described occurring independent of the above - mentioned etiologies1,2,4,6,8 ) . among these , only one case was accompanied by spondylolisthesis ( table 1 ) .
our patient did not have any predisposing risk factors for pedicle fractures except severe osteoporosis .
osteoporotic bone loss resulting in material and structural changes of the bone leads to an increased risk of stress fractures due to the weaken structure of the spinal bones .
tabrizi and bouchard10 ) reported axial osteoporosis caused stress fractures of the pedicles and produce a spondylollisthesis in the 73-year old female patient .
stress fractures can develop after minor trauma or even in the absence of any specific trauma6 ) . in our patient , the pedicle fracture appeared to be old given the sclerosis observed at the fracture margins along with pseudoarthosis .
thus , we speculate that continuous fatiguing stresses caused the microfractures on the osteoporotic pedicles .
the three cases of bilateral stress pedicle fractures reported in the literature were treated with surgery , and two patients underwent conservative treatment . our patient presented with spondylolisthesis with foraminal stenosis , and was treated with bone cement - augmented screw fixation and interbody fusion .
we report a unique case of spondylolisthesis accompanying a bilateral pedicle stress fracture in two vertebrae occurring in the absence of major trauma , previous spine surgery , or stress - related activity .
there has been no report of bilateral pedicle stress fractures involving two vertebrae . 
 the authors describe a unique case of spondylolisthesis accompanying a bilateral pedicle stress fracture involving two vertebrae . 
 de novo development of spondylolisthesis at the l5-s1 vertebrae accompanying a bilateral pedicle stress fracture at l4 and l5 was observed in a 70-year - old woman . 
 the patient 's medical history was unremarkable and she did not have any predisposing factors except severe osteoporosis . 
 interbody fusion with bone cement augmented screw fixation was performed . 
 surgical treatment resulted in good pain management and improved functional recovery .