degenerative lumbar canal stenosis is progressive narrowing of the spinal canal in the lumbar region and leads to compression of the thecal sac and nerves , eventually resulting in symptomatic neurogenic claudication .
however , patients with moderate to severe symptomatic stenosis often require surgical decompression of the spinal canal .
decompressive procedures for lumbar canal stenosis historically involved bilateral wide laminectomy with extensive disruption of the paravertebral muscles , ligaments and vertebral posterior arches including the spinous processes and intervertebral facet joints .
however , the microscopic interlaminar decompression is a procedure which involves a smaller midline incision , minimal disruption of posterior muscle and ligamentous complexes , followed by interlaminar fenestration and ligamentum flavectomy to microscopically decompress the compressed nerves .
our present study aims to assess the short - term and long - term postoperative outcomes of microscopic interlaminar decompression in patients diagnosed with symptomatic degenerative lumbar spinal stenosis , using a standardized functional outcome assessment tool .
this study is a retrospective review of prospectively collected patient - based outcomes in patients who underwent a standard interlaminar decompression at the aga khan university hospital between january 2007 and may 2009 .
all patients undergoing elective posterior lumbar spinal decompression for symptomatic single level or multilevel degenerative lumbar spinal stenosis were prospectively enrolled in a database with a minimum of 2 years of follow - up and complete outcome assessment . the decision for surgery
was based on a comprehensive assessment based on history , clinical examination and magnetic resonance imaging ( mri ) scans ; all patients enrolled in the study had moderate to severe symptomatic stenosis .
patients with associated pathologies such as instability , infection , malignancy , or a previous history of surgery for lumbar stenosis or lumbar spinal fusion were excluded from the study . also , those patients that required a discectomy in addition to interlaminar decompression were excluded from the final analysis .
all decompressive procedures were performed by the same surgeon ( sae ) . with the patient in a prone position under general anesthesia and all bony prominences well - padded ,
a midline skin incision was made centered at the interspinous level to be decompressed ( e.g. l4/l5interspinous level in case of l4-l5 decompression ) .
once this was exposed , a kocher clamp was placed , and a localizing cross table x - ray confirmed the interspace between the spinous processes .
the lamina ( e.g. the l4 lamina in case of l4-l5 decompression ) was exposed bilaterally followed by exposure of the upper edge of the lower adjacent lamina ( l5 lamina in case of l4-l5 decompression ) .
this was followed by a bilateral laminotomy ( lower edge of l4 lamina ) and bilateral medial factectomy of the concerned facets under the operating microscope .
subsequently , a ligamentum flavectomy was done , the thecal sac was decompressed , and the lateral recess and formaminal stenosis was relieved by undercutting of facet joints .
decompression was done bilaterally if stenosis was observed on both sides . the oswestry disability index ( odi ) assessment scale was used for preoperative , 2 weeks postoperative and 2 years follow - up assessment .
the odi is a self - completed questionnaire by the patient that examines perceived level of disability in 10 everyday activities of daily living to assign a subjective score of the level of function .
it is a standardized , and validated assessment tool with easy comprehension and hence can be used to determine a wide domain of the function , pain , and limitation in health status before and after back surgery .
demographic data collected included age , gender , comorbidities and body mass index ( bmi ) , prior history of physiotherapy and duration of symptoms . statistical analysis was performed to assess the outcome of patients in terms of preoperative , 2 weeks and 2 years follow - up odi assessment .
a change in odi score of at least 10 has been reported in literature to result in a minimum clinically important difference ( mcid ) .
this threshold value was used to determine the percentage of patients with clinical improvement at the 2 weeks and 2 years follow - up respectively .
moreover , data was analyzed with repeated measure analysis of variance to compare odi scores at the three different intervals ( preoperative vs. 2 weeks follow - up , preoperative vs. 2 years follow - up , 2 weeks vs. 2 years follow - up ) .
linear regression modelling was used to determine the effect of preoperative odi , bmi , age , prior physiotherapy , duration of symptoms , and single or multiple level decompression on the change in odi at 2 weeks and 2 years follow - up compared to the preoperative odi assessment .
this study is a retrospective review of prospectively collected patient - based outcomes in patients who underwent a standard interlaminar decompression at the aga khan university hospital between january 2007 and may 2009 .
all patients undergoing elective posterior lumbar spinal decompression for symptomatic single level or multilevel degenerative lumbar spinal stenosis were prospectively enrolled in a database with a minimum of 2 years of follow - up and complete outcome assessment . the decision for surgery
was based on a comprehensive assessment based on history , clinical examination and magnetic resonance imaging ( mri ) scans ; all patients enrolled in the study had moderate to severe symptomatic stenosis .
patients with associated pathologies such as instability , infection , malignancy , or a previous history of surgery for lumbar stenosis or lumbar spinal fusion were excluded from the study . also , those patients that required a discectomy in addition to interlaminar decompression were excluded from the final analysis .
all decompressive procedures were performed by the same surgeon ( sae ) . with the patient in a prone position under general anesthesia and all bony prominences well - padded ,
a midline skin incision was made centered at the interspinous level to be decompressed ( e.g. l4/l5interspinous level in case of l4-l5 decompression ) .
once this was exposed , a kocher clamp was placed , and a localizing cross table x - ray confirmed the interspace between the spinous processes .
the lamina ( e.g. the l4 lamina in case of l4-l5 decompression ) was exposed bilaterally followed by exposure of the upper edge of the lower adjacent lamina ( l5 lamina in case of l4-l5 decompression ) .
this was followed by a bilateral laminotomy ( lower edge of l4 lamina ) and bilateral medial factectomy of the concerned facets under the operating microscope .
subsequently , a ligamentum flavectomy was done , the thecal sac was decompressed , and the lateral recess and formaminal stenosis was relieved by undercutting of facet joints
the oswestry disability index ( odi ) assessment scale was used for preoperative , 2 weeks postoperative and 2 years follow - up assessment .
the odi is a self - completed questionnaire by the patient that examines perceived level of disability in 10 everyday activities of daily living to assign a subjective score of the level of function .
it is a standardized , and validated assessment tool with easy comprehension and hence can be used to determine a wide domain of the function , pain , and limitation in health status before and after back surgery .
demographic data collected included age , gender , comorbidities and body mass index ( bmi ) , prior history of physiotherapy and duration of symptoms . statistical analysis was performed to assess the outcome of patients in terms of preoperative , 2 weeks and 2 years follow - up odi assessment .
a change in odi score of at least 10 has been reported in literature to result in a minimum clinically important difference ( mcid ) .
this threshold value was used to determine the percentage of patients with clinical improvement at the 2 weeks and 2 years follow - up respectively .
moreover , data was analyzed with repeated measure analysis of variance to compare odi scores at the three different intervals ( preoperative vs. 2 weeks follow - up , preoperative vs. 2 years follow - up , 2 weeks vs. 2 years follow - up ) .
linear regression modelling was used to determine the effect of preoperative odi , bmi , age , prior physiotherapy , duration of symptoms , and single or multiple level decompression on the change in odi at 2 weeks and 2 years follow - up compared to the preoperative odi assessment .
a total of 71 consecutive patients initially satisfied our inclusion criteria and were incorporated into a database .
however , 60 of the 71 patients had an eventual follow - up of 2 years with complete outcomes assessment and were therefore included in the study for further analysis .
there were 40 males ( 67% ) and 20 females ( 33% ) , with a mean age of 55.7  13.6 years and an average bmi of 28.9  5.6
comorbids included diabetes ( n = 8) , hypertension ( n = 17 ) and ischemic heart disease ( n = 3 ) .
all patients had back pain and/or clear symptoms of neural claudication / radiculopathy with a corresponding radiological correlation on mri . the average duration of symptoms before surgery was 3.7 years ( range : 1 - 15 years ) .
a total of 58 patients ( 96.7% ) had a prior history of conservative management while 39 patients ( 65% ) had undergone physiotherapy for relief of symptoms .
the mean length of stay in the hospital after a standard microscopic interlaminar decompression was 3.2  1.4 days .
all patients were discharged with standard postoperative precautions to avoid heavy lifting and nonnarcotic analgesics ( nuberol forte , brufen ) to be tapered gradually over the ensuing 2 weeks ; none of the patients were recommended any postoperative physical therapy other than gradual return to routine physical activity as tolerated .
patients demographics ( mean  sd where applicable ) a repeated measures anova with a greenhouse - geisser correction determined that mean odi score differed significantly between time points ( f [ 1.578 , 118 ] = 244.392 , p < 0.0005 ) .
post - hoc tests using the bonferroni correction revealed that significant change in mean odi scores occurred between preoperative and 2 weeks postoperative assessments ( 29.5  7.1 vs. 12.9  4.6 , respectively ) with a p < 0.0005 , and between preoperative and 2 years follow - up assessments ( 29.5  7.1 vs. 11.50  6.2 respectively ) with p < 0.0005 [ figures 1 - 3 ] .
however , although the 2 years follow - up odi score was reduced to a mean of 11.5  6.2 , it was not found to be statistically significantly different to the 2 weeks postoperative odi score ( p = 0.204 ) .
trend of oswestry disability index scores at 2 weeks and 2 years scatter plot showing correlation between change in oswestry disability index scores at 2 weeks with preoperative oswestry disability index scores scatter plot showing correlation between change in oswestry disability index scores at 2 years with preoperative oswestry disability index scores linear regression analysis showed that the preoperative odi score was an independent predictor of change in odi score at 2 weeks and 2 years respectively ( p < 0.0005 ) ; patients with worse preoperative odi scores achieved greater odi postoperative improvement with a regression coefficient of 0.81 .
preoperative bmi , age , comorbids , duration of symptoms , physiotherapy and extent of decompression ( single vs. multiple ) were not significant predictors of change in odi at either the 2 weeks or 2 years follow - up .
interestingly , the duration of symptoms prior to surgery was found to predict the change in odi at 2 years follow - up after having adjusted for all other variables ( p = 0.04 ) ; patients with a greater duration of symptoms prior to surgery had a smaller change in odi with a regression coefficient of 0.20 [ figure 4 and table 2 ] .
scatter plot showing correlation between change in oswestry disability index scores at 2 years with duration of symptoms prior to surgery association between predictors and change in odi scores at 2 weeks and 2 years the percentage of patients with mcid , using an odi threshold value of 10 , was 86.7% ( n = 52 ) at the 2 weeks
follow - up and 83.3% ( n = 50 ) at the 2 years follow - up compared to the preoperative assessment . at the 2 years follow - up , 3.3% ( n = 2 ) of patients who had earlier not reached mcid did so ,
78.3% ( n = 47 ) of patients were assessed to have a change on odi score of < 10 or no change compared to the 2 weeks postoperative assessment while18.3% ( n = 11 ) reported a deterioration in their odi scores .
degenerative lumbar canal stenosis has become a common disease entity with our increasingly aging population ; spinal stenosis is the most common reason for lumbar spine surgery in adults over the age of 65 years .
the goal of surgical treatment of lumbar stenosis is sufficient decompression of the spinal canal with minimal operation - induced trauma .
the spine patient outcomes research trial , the largest study of its kind , showed that patients with symptomatic spinal stenosis compared to those treated nonoperatively maintained greater improvement in pain and function through 4 years .
traditionally , standard decompressive procedures involve total laminectomies and extensive removal of the accompanying spinous processes and posterior arches . however , microscopic interlaminar decompression involves focused decompression between adjacent laminae , with the spinous processes , and their attaching muscles kept intact .
the facet joints are also spared , midline structures including the ligaments and fascia are preserved , and the supporting lumbar musculature is not disrupted .
overall , this reduces surgical trauma , protects the dura from epidural scarring and keeps the integrity of the spine intact .
microsurgical interlaminar decompression has been repeatedly shown to produce comparable clinical results to standard laminectomies , with the added advantage of limited resection .
caspar et al . reported a favorable outcome rate of 71% in a series of 56 consecutive patients treated with interlaminar decompression .
further demonstrated that less invasive and more limited interlaminar decompression resulted in an increase in interface diameter measured on postoperative neuroradiological images as well as in gross pathological specimens .
the odi scores for our patients improved significantly after surgery , with 86.7% and 83.3% of all patients achieving mcid at the 2 weeks and 2 years follow - up assessment respectively , compared to the preoperative odi assessment .
however , the rate of decrease in the odi score decreased by the 2 years follow - up assessment , with only 3.3% ( n = 2 ) of patients achieving the threshold for mcid while 78.3% of patients did not have a significant decrease in their odi scores at the 2 years follow - up compared to the 2 weeks assessment .
further , 18.3% of patients at the 2 years assessment were found have worsened odi scores compared to the 2 weeks postoperative assessment .
the radiology and preoperative odi scores of the patients that reported a deterioration in their scores were reviewed to explain the relative difference in their outcome compared to the rest of the patients , but no confounding or association could be determined ( statistical analysis and results not shown ) .
six of the 11 patients reported that their routine activities did not cause pain in spite of the increased odi at , while 5 patients complained that the immediate improvement after surgery had worn off and that they would consider a repeat decompressive surgery .
our results show that functional improvement between the 2 weeks and 2 years follow - up in terms of odi scores was not significant .
however , the odi scores recorded at the 2 years follow - up were still significantly less than the preoperative odi scores ( p < 0.0005 ) . such time - related deterioration in surgical results in patients undergoing spinal canal decompression has been previously reported and long - term outcome reviews report slowly decreasing levels of patient satisfaction with time , possibly secondary to bone regrowth in some cases .
we employed regression analysis to determine any possible determinants for the short - term and long - term functional outcome of our patients .
however , after having adjusted for all other confounding factors , we only found preoperative odi scores to be significant predictors of change in odi both for short - term and long - term outcomes .
other studies have also shown that postsurgical outcomes correlate with the severity of preoperative stenosis . moreover ,
analysis of the 2 years odi scores in our study revealed a negative association between duration of symptoms prior to surgery and change in odi between the 2 weeks and 2 years odi score , depicting that a longer duration of symptoms of stenosis is likely to result in poor long - term outcome . a similar
ng et al . reported that symptom duration of more than 33 months in patients undergoing lumbar decompression surgery had a less favorable functional outcome at the 1-year and 2 years follow - up assessments .
similarly , studies in patient with sciatica indicated unfavorable outcomes if the pain had lasted longer than 6 - 8 months prior to surgery .
nevertheless , we stress cautious interpretation of our results until future studies with larger sample populations confirm a definitive association between the duration of symptoms and long - term outcomes .
perhaps , such an association could be used to define the optimum time for surgical intervention in patients with symptomatic lumbar canal stenosis .
a valid criticism of this study is the small sample size and lack of comparison with other standard decompression techniques .
nevertheless , the evidence regarding the long - term and short - term efficacy of interlaminar decompression on the basis of improvement in odi scores is overwhelming .
we conclude that microsurgical interlaminar decompression is an effective intervention in improving functional outcome in patients with degenerative lumbar canal stenosis .
further , none of the patient characteristics and the level and extent of decompression predict short - term and long - term outcome in these patients , with the exception of preoperative odi scores and duration of symptoms prior to surgery .
 objectives : our present study aims to assess the short and long - term postoperative outcome of microscopic interlaminar decompression from a neurosurgical center in a developing country and also aims to further determine any predictors of functional outcome.materials and methods : all patients with moderate to severe symptomatic stenosis undergoing elective posterior lumbar spinal decompression were prospectively enrolled in a database . 
 preoperative , 2 weeks and 2 years postoperative oswestry disability index ( odi ) scores were determined for all patients . 
 these scores were retrospectively compared using repeated measures analysis of variance . 
 further , linear regression modelling was applied to determine the effect of preoperative odi , body mass index , age , prior physiotherapy , duration of symptoms , and single or multiple level decompression on the change in odi at 2 weeks and 2 years follow - up respectively.results:a total of 60 consecutive patients ( 40 males , 20 females ) were included for statistical analysis . 
 the percentage of patients with a minimum clinically important difference ( mcid ) , using an odi threshold value of 10 , was 86.7% ( n = 52 ) at the 2 weeks postoperative follow - up . 
 at the 2 years follow - up assessment , 3.3% ( n = 2 ) patients who had earlier not achieved mcid did so , 78.3% ( n = 47 ) of patients were found to have a change in odi score of < 10 or no change , while 18.3% ( n = 11 ) reported a deterioration in their odi scores . 
 the preoperative odi score was an independent predictor of change in odi score at 2 weeks and 2 years respectively ( p < 0.0005 ) . 
 the duration of symptoms prior to surgery was found to predict the change in odi at 2 years follow - up ( p = 0.04).conclusion : the evidence regarding the long - term and short - term efficacy of microscopic interlaminar decompression in symptomatic lumbar stenosis is overwhelming . 
 preoperative odi scores and duration of symptoms prior to surgery can predict postoperative outcomes . 
INTRODUCTION
MATERIALS AND METHODS
Study design
Study intervention
Study measures
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION
Financial support and sponsorship
Conflicts of interest