it is generally recommended to perform surgical treatment in lumbar disc herniation ( ldh ) for patients who suffer from cauda equina syndrome or intractable radicular pain , with or without neurological sensory / motor deficit21 ) . however , in numerous non - fatal cases , conservative treatment such as a nerve block could be effective92024 ) . in patients with ldh , a nerve block is generally performed before considering surgery for radicular pain as well3101320 ) . recent randomized clinical trials show some evidence that the nerve block is cost - effective in the majority of cases compared to other operative interventions2223 ) . furthermore , potential complications associated with surgery such as revision , cerebrospinal fluid leakage , hematoma , and infection make spine physicians and patients prefer conservative treatments17141725 ) . in contrast , many spine surgeons claim that early surgery should be considered an appropriate approach for those patients who have lower thresholds for pain , those who demonstrate lower compliance with multiple nerve blocks for several months , and those who are more likely to fail with long - term pain control . they argue that early surgery in carefully selected patients with radicular pain can achieve more rapid pain relief than prolonged non - operative treatment14172028 ) . in addition , there is some evidence that time loss due to delayed surgery following the failure of conservative treatment can lead to unwanted results , such as development of the neuropathic pain , which can be refractory to usual or conventional treatments . there are numerous studies comparing the clinical results between surgery and nerve blocks , but hardly any studies have suggested decision algorithm and none of them analyzed radiographic data as predicting factors20222329 ) . selecting appropriate treatment modalities for ldh requires thorough considerations of all aspects in order to make balanced decisions which are based on cost - effectiveness as well as possible side effects and complications . thus , establishing radiological criteria as the prognostic factor for success of treatment between surgery and nerve blocks would be helpful in choosing an optimal treatment option . authors in this paper have performed a quantitative analysis of radiological factors to determine the correlation of multiple factors with successful outcomes . a retrospective review was performed to 64 adult patients who were treated with surgery or nerve blocks for single level ldh at our institution from january 2012 to december 2014 , and they were followed up for at least a year . all of the patients were considered to be surgical candidates by two spine surgeons with more than 15 years of experience , and all of them had initially been recommended for surgery . the surgery group ( sg ) included 34 patients , and the nerve blocks group ( ng ) included 30 patients who initially refused the surgery . the inclusion criteria of this study were as follows : patients with 1 ) unilateral or bilateral intractable radicular leg pain and back pain with or without sensory / motor deficit after conservative treatment ; 2 ) l45 level ldh confirmed by magnetic resonance imaging ( mri ) , and 3 ) organized medical records including both clinical and mri data ( pre- and post - treatment ) . in contrast , the following patients were excluded : 1 ) those with cauda equina syndrome ; 2 ) those with progressive motor deficit ; 3 ) those with previous histories of lumbar surgery ; 4 ) those with histories of psychological disorder ; and 5 ) those with radiological evidence of other pathologies correlated with symptoms such as spinal stenosis . the clinical outcomes were investigated in the medical records of patients using a visual analogue scale ( vas ) score for leg pain and back pain . motor deficit was graded according to the medical research council ( mrc ) scale8 ) . these clinical factors were evaluated pre - procedurally and were repeated at 1 month , 6 months , and 12 months in the outpatient clinic . a successful outcome was defined as excellent or good based on the macnab classification18 ) . the data of the patients ' baseline demographic characteristics , comorbidities , and clinical factors are summarized in table 1 . the disc herniation length , disc herniation area , canal cross - section length , canal cross - section area , canal length - occupying ratio , and canal area - occupying ratio were measured with imagej software , version 1.49 ( nih , bethesda , md , usa ) , obtained from an axial plane scan at the foraminal level pre - procedurally ( fig . carlisle et al.4 ) published predictive values of the need for surgical intervention by mri analysis , and we used this model for radiological analysis . canal area boundary tracing was performed from neural arch posteriorly , 4 mm from the anterior surface of the superior facet on both sides anteriorly . the 4-mm antero - posterior ( ap ) distance in the foramen was estimated as sufficient to allow for normal nerve root function . the measured interpedicular distance was used as the canal width on the foraminal axial image of the same vertebra . we performed a transforaminal epidural steroid injection ( tfesi ) to relieve radicular pain with or without a nerve block of medial branch of posterior ramus ( so called medial branch block : mbb ) to relieve additional low back pain . in particular , the tfesi solution consisted of 1% lidocaine , dexamethasone ( 10 mg ) , and hyaluronidase ( 1500 iu ) as an adjunct . a 23-gauge spinal needle was introduced to the target point , which was a so - called " safe triangle , " i.e. , above the nerve root and below the pedicle until bony contact was encountered . after verifying the correct needle positioning under ap fluoroscopic control , contrast solution was injected to confirm that the material was passing the selected nerve root and was not administered intravascularly . then , 3 ml of mixed solution was injected into each targeted point . following the procedure , the needle was withdrawn , the site was sealed with a sterile dressing , and the patients were monitored for 30 minutes for any untoward side effects . each patient was evaluated 1 , 6 , and 12 months after the second nerve block . for patients with associated low back pain , it was done in usual fashion with injection of additional 2 ml of mixed solution ( without hyaluronidase ) to each site . under general anesthesia , the patient was placed prone on the operating table , and the thorax was supported on a wilson frame ( mdt corp . , torrance , ca , usa ) . a tubular retractor was inserted over the interlaminar area with the blade of the retractor medially . following partial laminectomy under the microscope , after identifying the disc material compressing the nerve root and dural sac , the disc fragment was then removed . we removed disc material from the disc space when the disc was poorly hydrated . in well - hydrated discs , the non - herniated disc was preserved because it was beneficial for the preservation of the vitality of the motion segment in well - hydrated discs2 ) . a nerve hook was used to explore the remnant disc material and to check for foraminal clearance . patients were discharged on the 1-week postoperative day , and the clinical outcome measurements were performed 1 month after surgery . the mann - whitney u test was used for an analysis of the differences between the clinical and radiological factors of the sg and ng . a receiver operating characteristic ( roc ) curve was obtained to determine the optimal cutoff values of radiological factors by plotting every possible cutoff value 's sensitivity on the y axis against 1-specificity on the x axis26 ) . sensitivity was defined as the proportion of patients who were correctly classified in the successful outcome group , whereas specificity was defined as the proportion of patients who were correctly classified in the non - successful outcome group . the area under the roc curve ( auc ) , which reflects the overall performance of diagnostic accuracy , was also analyzed with medcalc software , version 16.4 ( medcalc software , mariakerke , belgium ) . general guidelines have been suggested for interpreting the auc : 0.50.7 represents no to low discriminatory power ; 0.70.9 represents moderate discriminatory power ; and > 0.9 represents high discriminatory power111227 ) . with these cutoff values of radiological factors , multivariate logistic regression analysis was performed using the multiple clinical and radiological factors as independent variables and the successful outcome of the procedure as the dependent variable . statistical calculations were performed using spss software , version 23.0 ( ibm corporation , armonk , ny , usa ) . a retrospective review was performed to 64 adult patients who were treated with surgery or nerve blocks for single level ldh at our institution from january 2012 to december 2014 , and they were followed up for at least a year . all of the patients were considered to be surgical candidates by two spine surgeons with more than 15 years of experience , and all of them had initially been recommended for surgery . the surgery group ( sg ) included 34 patients , and the nerve blocks group ( ng ) included 30 patients who initially refused the surgery . the inclusion criteria of this study were as follows : patients with 1 ) unilateral or bilateral intractable radicular leg pain and back pain with or without sensory / motor deficit after conservative treatment ; 2 ) l45 level ldh confirmed by magnetic resonance imaging ( mri ) , and 3 ) organized medical records including both clinical and mri data ( pre- and post - treatment ) . in contrast , the following patients were excluded : 1 ) those with cauda equina syndrome ; 2 ) those with progressive motor deficit ; 3 ) those with previous histories of lumbar surgery ; 4 ) those with histories of psychological disorder ; and 5 ) those with radiological evidence of other pathologies correlated with symptoms such as spinal stenosis . the clinical outcomes were investigated in the medical records of patients using a visual analogue scale ( vas ) score for leg pain and back pain . motor deficit was graded according to the medical research council ( mrc ) scale8 ) . these clinical factors were evaluated pre - procedurally and were repeated at 1 month , 6 months , and 12 months in the outpatient clinic . a successful outcome was defined as excellent or good based on the macnab classification18 ) . the data of the patients ' baseline demographic characteristics , comorbidities , and clinical factors are summarized in table 1 . the disc herniation length , disc herniation area , canal cross - section length , canal cross - section area , canal length - occupying ratio , and canal area - occupying ratio were measured with imagej software , version 1.49 ( nih , bethesda , md , usa ) , obtained from an axial plane scan at the foraminal level pre - procedurally ( fig . carlisle et al.4 ) published predictive values of the need for surgical intervention by mri analysis , and we used this model for radiological analysis . canal area boundary tracing was performed from neural arch posteriorly , 4 mm from the anterior surface of the superior facet on both sides anteriorly . the 4-mm antero - posterior ( ap ) distance in the foramen was estimated as sufficient to allow for normal nerve root function . the measured interpedicular distance was used as the canal width on the foraminal axial image of the same vertebra . we performed a transforaminal epidural steroid injection ( tfesi ) to relieve radicular pain with or without a nerve block of medial branch of posterior ramus ( so called medial branch block : mbb ) to relieve additional low back pain . in particular , the tfesi solution consisted of 1% lidocaine , dexamethasone ( 10 mg ) , and hyaluronidase ( 1500 iu ) as an adjunct . a 23-gauge spinal needle was introduced to the target point , which was a so - called " safe triangle , " i.e. , above the nerve root and below the pedicle until bony contact was encountered . after verifying the correct needle positioning under ap fluoroscopic control , contrast solution was injected to confirm that the material was passing the selected nerve root and was not administered intravascularly . then , 3 ml of mixed solution was injected into each targeted point . following the procedure , the needle was withdrawn , the site was sealed with a sterile dressing , and the patients were monitored for 30 minutes for any untoward side effects . each patient was evaluated 1 , 6 , and 12 months after the second nerve block . for patients with associated low back pain , it was done in usual fashion with injection of additional 2 ml of mixed solution ( without hyaluronidase ) to each site . under general anesthesia , the patient was placed prone on the operating table , and the thorax was supported on a wilson frame ( mdt corp . , torrance , ca , usa ) . a tubular retractor was inserted over the interlaminar area with the blade of the retractor medially . following partial laminectomy under the microscope , the ligamentum flavum was detached from the lamina and removed . after identifying the disc material compressing the nerve root and dural sac , we removed disc material from the disc space when the disc was poorly hydrated . in well - hydrated discs , the non - herniated disc was preserved because it was beneficial for the preservation of the vitality of the motion segment in well - hydrated discs2 ) . a nerve hook was used to explore the remnant disc material and to check for foraminal clearance . after meticulous hemostasis , saline irrigation was performed . patients were discharged on the 1-week postoperative day , and the clinical outcome measurements were performed 1 month after surgery . the mann - whitney u test was used for an analysis of the differences between the clinical and radiological factors of the sg and ng . a receiver operating characteristic ( roc ) curve was obtained to determine the optimal cutoff values of radiological factors by plotting every possible cutoff value 's sensitivity on the y axis against 1-specificity on the x axis26 ) . sensitivity was defined as the proportion of patients who were correctly classified in the successful outcome group , whereas specificity was defined as the proportion of patients who were correctly classified in the non - successful outcome group . the area under the roc curve ( auc ) , which reflects the overall performance of diagnostic accuracy , was also analyzed with medcalc software , version 16.4 ( medcalc software , mariakerke , belgium ) . general guidelines have been suggested for interpreting the auc : 0.50.7 represents no to low discriminatory power ; 0.70.9 represents moderate discriminatory power ; and > 0.9 represents high discriminatory power111227 ) . with these cutoff values of radiological factors , multivariate logistic regression analysis was performed using the multiple clinical and radiological factors as independent variables and the successful outcome of the procedure as the dependent variable . statistical calculations were performed using spss software , version 23.0 ( ibm corporation , armonk , ny , usa ) . there were no significant differences between the sg and ng in any of the clinical characteristics , including age , sex , comorbidities , duration and neurologic symptoms ( table 1 ) . there were no severe complications , including nerve root injuries , infections , or bleeding events , in both groups . vas leg at 1 month ( sg : 1.500.68 , ng : 2.180.83 , p<0.01 ) , 6 months ( sg : 0.930.64 , ng : 1.711.00 , p<0.01 ) and 12 months ( sg : 0.670.66 , ng : 1.240.74 , p<0.01 ) showed significant differences between two groups ( fig . however , vas back at 6 months ( sg : 0.530.63 , ng : 0.880.81 , p=0.08 ) and 12 months ( sg : 0.370.49 , mrc grade was also improved ; however no significant differences were identified between the two groups at 1 month ( sg : 4.570.97 , ng : 4.790.41 , p=0.65 ) and 6 months ( sg : 4.670.84 , ng mrc grade at 12 months was significantly higher in the ng than in the sg ( sg : 4.670.84 , ng : 4.970.17 , p=0.03 ) . changes in radiological factors before and 12 months after the procedure were calculated ( table 3 ) . the disc herniation length and canal length - occupying ratio were significantly decreased in the sg compare to the ng after 12 months from baseline ( p=0.01 ) . changes in the disc herniation area and in the canal area - occupying ratio were also larger in the sg than in the ng ; however , the results were not statistically significant . the roc curve for successful leg pain relief at 12 months showed an auc ( 95% ci ) for the disc herniation length of the sg of 0.66 ( 0.460.82 ) and that of the ng of 0.64 ( 0.460.80 ) ( fig . 3 ) . the cutoff values ( sensitivity , specificity ) to distinguish between success and failure with the disc herniation length at 12 months were 6.31 mm ( 0.82 , 0.54 ) for the sg and 6.23 mm ( 0.68 , 0.58 ) for the ng . clinical outcomes was evaluated according to the macnab classification . in the sg , the 22 patients ( 94% ) at 1 month , 29 patients ( 97% ) at 6 months and 29 patients ( 97% ) at 12 months experienced excellent or good leg pain relief ( fig . the 23 patients ( 68% ) at 1 month , 30 patients ( 88% ) at 6 months and 32 patients ( 94% ) at 12 months experienced excellent or good leg pain relief ( fig . , the 25 patients ( 83% ) at 1 month , 26 patients ( 87% ) at 6 months and 27 patients ( 90% ) at 12 months responded that they have experienced excellent or good back pain relief ( fig . , the 24 patients ( 70% ) at 1 month , 29 patients ( 85% ) at 6 months and 32 patients ( 94% ) at 12 months responded that they have experienced excellent or good back pain relief ( fig . the odds ratio ( or ) of the clinical and radiological factors for the successful outcomes of procedures were analyzed by multivariate logistic regression analysis . the disc herniation length [ or 2.35 ; confidence interval ( ci ) 1.213.98 ] was a predictor for successful outcomes in the sg at 12 months , and the results in the ng revealed 2 independent predictors : disc herniation length ( or 0.05 ; ci 0.0030.89 ) and baseline vas leg ( or 12.63 ; ci 1.6497.45 ) . no significant radiological predictors were found of successful back pain relief in the two groups . however , high baseline vas back predicted successful outcomes in the ng at 12 months ( or 11.13 ; ci 1.9463.80 ) . there were no significant differences between the sg and ng in any of the clinical characteristics , including age , sex , comorbidities , duration and neurologic symptoms ( table 1 ) . there were no severe complications , including nerve root injuries , infections , or bleeding events , in both groups . vas leg at 1 month ( sg : 1.500.68 , ng : 2.180.83 , p<0.01 ) , 6 months ( sg : 0.930.64 , ng : 1.711.00 , p<0.01 ) and 12 months ( sg : 0.670.66 , ng : 1.240.74 , p<0.01 ) showed significant differences between two groups ( fig vas back at 1 month ( sg : 0.670.71 , ng : 1.291.12 , p=0.02 ) also showed significant differences between two groups ( fig . however , vas back at 6 months ( sg : 0.530.63 , ng : 0.880.81 , p=0.08 ) and 12 months ( sg : 0.370.49 , mrc grade was also improved ; however no significant differences were identified between the two groups at 1 month ( sg : 4.570.97 , ng : 4.790.41 , p=0.65 ) and 6 months ( sg : 4.670.84 , ng mrc grade at 12 months was significantly higher in the ng than in the sg ( sg : 4.670.84 , ng : 4.970.17 , p=0.03 ) . changes in radiological factors before and 12 months after the procedure were calculated ( table 3 ) . the disc herniation length and canal length - occupying ratio were significantly decreased in the sg compare to the ng after 12 months from baseline ( p=0.01 ) . changes in the disc herniation area and in the canal area - occupying ratio were also larger in the sg than in the ng ; however , the results were not statistically significant . the roc curve for successful leg pain relief at 12 months showed an auc ( 95% ci ) for the disc herniation length of the sg of 0.66 ( 0.460.82 ) and that of the ng of 0.64 ( 0.460.80 ) ( fig . 3 ) . the cutoff values ( sensitivity , specificity ) to distinguish between success and failure with the disc herniation length at 12 months were 6.31 mm ( 0.82 , 0.54 ) for the sg and 6.23 mm ( 0.68 , 0.58 ) for the ng . the 22 patients ( 94% ) at 1 month , 29 patients ( 97% ) at 6 months and 29 patients ( 97% ) at 12 months experienced excellent or good leg pain relief ( fig . the 23 patients ( 68% ) at 1 month , 30 patients ( 88% ) at 6 months and 32 patients ( 94% ) at 12 months experienced excellent or good leg pain relief ( fig . , the 25 patients ( 83% ) at 1 month , 26 patients ( 87% ) at 6 months and 27 patients ( 90% ) at 12 months responded that they have experienced excellent or good back pain relief ( fig . , the 24 patients ( 70% ) at 1 month , 29 patients ( 85% ) at 6 months and 32 patients ( 94% ) at 12 months responded that they have experienced excellent or good back pain relief ( fig . 4d ) . the odds ratio ( or ) of the clinical and radiological factors for the successful outcomes of procedures were analyzed by multivariate logistic regression analysis . the disc herniation length [ or 2.35 ; confidence interval ( ci ) 1.213.98 ] was a predictor for successful outcomes in the sg at 12 months , and the results in the ng revealed 2 independent predictors : disc herniation length ( or 0.05 ; ci 0.0030.89 ) and baseline vas leg ( or 12.63 ; ci 1.6497.45 ) . no significant radiological predictors were found of successful back pain relief in the two groups . however , high baseline vas back predicted successful outcomes in the ng at 12 months ( or 11.13 ; ci 1.9463.80 ) . we found that leg and back pain improvement was better in the sg during the follow - up period initially ; however , the differences in the vas leg between the two groups decreased from 6 months to 12 months , and vas back at 12 months showed no significant difference . based on these results , it is possible to assume that these differences could be further reduced over a longer - term follow - up period , although recurrence of disc herniation with the return of pain is also possible . surgery showed significant reductions in the disc herniation length and in the canal length - occupying ratio at 12 months after the procedure . however , nerve blocks also showed a decreasing tendency in radiological factors subsequent to the procedure . matsubara et al.19 ) reported that more degenerated discs and larger initial herniation had larger sizes of herniated fragments , which decreased in 32 patients treated conservatively with ldh . in this study , there is no evidence of nerve block effect for natural regression of disc herniation neither in positive nor negative ways . in studies evaluating the efficacy of surgery versus conservative treatment for ldh , radiological predictors have been suggested561630 ) . carlisle et al.4 ) also showed a trend for patients treated with surgery toward having larger disc herniation area , corresponding to a larger percentage canal compromise than the conservatively treated group . however , the nerve block was not included in conservatively treated group on the above - mentioned studies . therefore , authors have performed a comparative analysis between surgery and nerve blocks focusing on the radiological data which was not proposed elsewhere . from our study results , the patients with disc herniation length of l45 larger than 6.31 mm could be considered as candidates for surgical treatment , whereas those with disc herniation length less than 6.23 mm could be treated with nerve blocks . the radiological factors as cutoff values at 12 months had close to moderate discriminatory power . while the study is still promising , it has limitations as well . it was performed retrospectively and the number of patients involved in this study was relatively small especially in the elderly population . thus , further investigations with a greater number of patients will be needed for the general application of suggested cutoff values . a regression of the disc herniation could be important in correlation with improvement of symptoms and this could be also examined as a predictor . single level ldh , which does not represent the entire level of ldh , was selected for the study , although l45 was the most common prolapsed level15 ) . in addition , the patients sample were not randomly selected and rather patients chose the preferred treatment modality . despite these limitations , to the best to our knowledge , this is the first report to demonstrate the radiological criteria for the ldh treatment options between surgery and nerve block . disc herniation length was a good predictor for clinical outcome and could be considered as radiological criteria for choosing optimal treatment options for ldh .