we retrospectively analyzed the outcomes of 19 patients ( mean age , 67.9 years ; 2 men and 17 women ) who were treated using the scd method for a lumbar spinal stenosis with degenerative spondylolisthesis from 2010 to 2013 . the average follow - up period was 37 months ( range , 25 to 56 months ) . all patients had radiating pain and neurologic intermittent claudication ( nic ) due to a spinal stenosis . magnetic resonance imaging showed central and lateral recess stenosis at the degenerative spondylolisthesis site in all patients . from 2010 to 2013 , there was one patient with meyerding grade ii spondylolisthesis and no patient with meyerding grade iii spondylolisthesis . the follow - up period of patients with meyerding grade ii spondylolisthesis was too short ( 5 months ) . single - level degenerative spondylolisthesis was observed at l4 on 5 in 13 of 19 patients , l3 on 4 in four patients , and l5 on s1 in one patient . double - level degenerative spondylolisthesis was observed at l3 on 4 and l4 on 5 in one patient . no instability was detected on a preoperative lumbar spine dynamic ( flexion / extension ) radiological study . a median skin excision was used , soft tissue was detached , and the supraspinous ligament was detached from the spinous process , and moved to the side with multifidus muscle . the inferior one - quarter of the upper - level vertebral spinous process was removed , if needed , to enhance vision . the ligamentum flavum was detached from the inferior one - third of the lamina using a currette . after thinning the lamina with a high speed burr , a partial laminectomy was performed using a kerrison rongeur . it is important that ligamentum flavum must not be removed before thinning the lamina with a high speed burr . by maintaining ligamentum flavum finally , the total ligamentum flavum was removed en - bloc by detaching the ligamentum flavum from the inner side of the lamina to the inner side of the posterior facet ( figs . 1 and 2 ) . the detached supraspinous ligament was returned to its original position , and sutured with surrounding fascia . ambulation was permitted beginning on postoperative day 1 , and patients were encouraged to use a corset for 6 weeks . preoperative and postoperative symptom relief was estimated using the visual analogue scale ( vas ) score and the oswestry disability index ( odi ) before surgery and at follow - up days . patients were evaluated for vas score and odi after 3 , 6 month post - surgery and every 1 year subsequently . these results were used to estimate slip percentage and slip angle and assess instability and progression of lumbar degenerative spondylolisthesis . slip percentage and slip angle we estimated dynamic slip percentage ( preoperative and postoperative change in the slip percentage ) and dynamic slip angle ( preoperative and postoperative change in the slip angle ) , and analyzed the occurrence of vertebral instability . the wilcoxon signed - rank test was performed to detect postoperative changes using ibm spss ver . a median skin excision was used , soft tissue was detached , and the supraspinous ligament was detached from the spinous process , and moved to the side with multifidus muscle . the inferior one - quarter of the upper - level vertebral spinous process was removed , if needed , to enhance vision . the ligamentum flavum was detached from the inferior one - third of the lamina using a currette . after thinning the lamina with a high speed burr , a partial laminectomy was performed using a kerrison rongeur . it is important that ligamentum flavum must not be removed before thinning the lamina with a high speed burr . by maintaining ligamentum flavum finally , the total ligamentum flavum was removed en - bloc by detaching the ligamentum flavum from the inner side of the lamina to the inner side of the posterior facet ( figs . 1 and 2 ) . the detached supraspinous ligament was returned to its original position , and sutured with surrounding fascia . ambulation was permitted beginning on postoperative day 1 , and patients were encouraged to use a corset for 6 weeks . preoperative and postoperative symptom relief was estimated using the visual analogue scale ( vas ) score and the oswestry disability index ( odi ) before surgery and at follow - up days . patients were evaluated for vas score and odi after 3 , 6 month post - surgery and every 1 year subsequently . these results were used to estimate slip percentage and slip angle and assess instability and progression of lumbar degenerative spondylolisthesis . slip percentage and slip angle we estimated dynamic slip percentage ( preoperative and postoperative change in the slip percentage ) and dynamic slip angle ( preoperative and postoperative change in the slip angle ) , and analyzed the occurrence of vertebral instability . the wilcoxon signed - rank test was performed to detect postoperative changes using ibm spss ver . 21.0 ( ibm co. , armonk , ny , usa ) . a p - value the mean vas score of back pain decreased from 6.3 to 4.3 , and the mean vas score for lower leg radiating pain also decreased from 8.3 to 2.5 ( p < 0.01 ) . the average odi score ( maximum , 45 points ) improved significantly from 25.3 preoperatively to 10.3 postoperatively ( p < 0.01 ) . the change in slip percentage increased from 10% to 12.2% postoperatively , but the difference was not significant . the dynamic slip percentage did not show significant change postoperatively ( 5.2% vs. 5.8% ) . slip angle in the scd group also did not change ( 3.2 vs. 3.6 ) at the last follow - up . the mean vas score of back pain decreased from 6.3 to 4.3 , and the mean vas score for lower leg radiating pain also decreased from 8.3 to 2.5 ( p < 0.01 ) . the average odi score ( maximum , 45 points ) improved significantly from 25.3 preoperatively to 10.3 postoperatively ( p < 0.01 ) . the change in slip percentage increased from 10% to 12.2% postoperatively , but the difference was not significant . the dynamic slip percentage did not show significant change postoperatively ( 5.2% vs. 5.8% ) . slip angle in the scd group also did not change ( 3.2 vs. 3.6 ) at the last follow - up . newman and stone8 ) described degenerative spondylolisthesis as a disease in which a vertebral body slips anteriorly with no neural arch abnormality . degenerative spondylolisthesis tends to be accompanied by spinal stenosis , and typically shows degeneration of the posterior facet or intervertebral disc , and ligament laxity . so far , decompression with fusion is reportedly better than decompression - only surgery.91011 ) in particular , a broad range of decompression techniques lead to poor outcomes , as compared to decompression with fusion.12 ) according to the spinal degeneration theory suggested by kirkaldy - willis , spinal segment stability is maintained in patients with degenerative spondylolisthesis,1314 ) and good surgical outcomes occur if sufficient decompression is performed preserving structures that affect posterior spinal stability . thus , studies on decompression - only surgery with minimal excision to treat patients with degenerative spondylolisthesis were recently conducted . weiner et al.5 ) reported a surgical procedure that restores the native position of the spinous process after a spinous process osteotomy and decompression to maintain stability by preserving the interspinous and supraspinous ligaments . recently , various techniques using unilateral approach and bilateral decompression have been used in an attempt to minimize postoperative vertebral instability.67 ) the scd technique has been introduced to prevent postoperative vertebral instability.15 ) collectively , ours and previous results suggested that scd technique could be applied for treatment of degenerative spondylolisthesis without instability and also for spondylolisthesis with instability preoperatively . if spinal segment stability is maintained postoperatively and sufficient decompression is achieved , surgical effect is well maintained . we carried out another study on the effect of scd technique for spondylolisthesis with segmental instability . the follow - up period was short yet , studies to evaluate the effect of scd technique for spondylolisthesis with instability after sufficient follow - up period are currently ongoing . anatomical research about ligamentum flavum by okuda et al.16 ) suggested that ligamentum flavum degenerate , ossify , and calcify in patients with degenerative spondylosis , and that these changes are more severe if spondylolisthesis is present . another research by okuda et al.17 ) showed that nerve root compression is most severe in the proximal portion of the ligamentum flavum because the ligamentum flavum is thickest in this area ( fig . the proximal border of the ligamentum flavum is attached to upper level vertebra at the inner surface of lamina almost horizontally and just below the pedicle ; thus nerve root is compressed continuously when the ligamentum flavum is not completely removed.17 ) however , we can determine whether decompression is sufficient by observing the ligamentum flavum removed by en - bloc resection . zander et al.18 ) reported that a unilateral medial hemifacetectomy can induce vertebral instability , and hamasaki et al.19 ) reported that a bilateral medial facetectomy for the medial one - third of the posterior facet could induce vertebral instability . actually , in patients who have spinal stenosis with degenerative spondylolisthesis , cause of nerve root compression is ligamentum flavum hypertrophy at lateral recess , and facet hypertrophy is not cause of nerve root compression . so medial facetectomy is unnecessary for decompression of nerve root , and scd technique can decompress nerve root sufficiently , maintaining spinal segmental stability . in addition , abumi et al.20 ) conducted a biomechanical study demonstrating that spinal instability does not develop when the posterior facet is preserved with only the interspinous and supraspinous ligaments detached . according to these studies , the scd technique , which decompress posteriorly by total excision of the ligamentum flavum with preservation of the supraspinous ligament and posterior facet , improves clinical outcomes and does not lead to spinal instability . thus , the scd technique can be applied to patients who have a spinal stenosis with degenerative spondylolisthesis ( fig . slip angle , we demonstrated that decompression through a total ligamentum flavectomy preserving the facet joint results in clinical improvement without causing vertebral instability . the limitation of scd technique is that this technique is not suitable for bilateral foraminal stenosis . there has been consensus that posterior lumbar interbody fusion is suitable for treatment of bilateral foraminal stenosis . however , the spinal stenosis with degenerative spondylolisthesis and unilateral foraminal stenosis can be treated using scd technique and lateral fenestration technique simultaneously . hence , degenerative spondylolisthesis without foraminal stenosis , in which especially nic is main symptom , is an absolute indication for scd , and degenerative spondylolisthesis with unilateral foraminal stenosis is a relative indication for scd . decompression alone can reduce preoperative back pain but some preoperative back pain remains because it usually results from degeneration of facet joint degeneration or intervertebral disc . long term follow - up observations to assess instability and radiological exacerbations of spondylolisthesis are needed . although a prospective randomized controlled clinical study is needed , our results showed that decompression surgery using the scd technique was effective and less invasive for patients with spinal stenosis and degenerative spondylolisthesis . in conclusion , the scd technique , which decompress posteriorly by en - bloc total ligamentum flavectomy and preserve posterior facet , was clinically effective and does not lead to postoperative spinal instability .
backgroundto describe and assess clinical outcomes of the semi - circumferential decompression technique for microsurgical en - bloc total ligamentum flavectomy with preservation of the facet joint to treat the patients who have a lumbar spinal stenosis with degenerative spondylolisthesis.methodswe retrospectively analyzed the clinical and radiologic outcomes of 19 patients who have a spinal stenosis with meyerding grade i degenerative spondylolisthesis . 
 they were treated using the " semi - circumferential decompression " method . 
 we evaluated improvements in back and radiating pain using a visual analogue scale ( vas ) and the oswestry disability index ( odi ) . 
 we also evaluated occurrence of spinal instability on radiological exam using percentage slip and slip angle.resultsthe mean vas score for back pain decreased significantly from 6.3 to 4.3 , although some patients had residual back pain . 
 the mean vas for radiating pain decreased significantly from 8.3 to 2.5 . 
 the odi score improved significantly from 25.3 preoperatively to 10.8 postoperatively . 
 no significant change in percentage slip was observed ( 10% preoperatively vs. 12.2% at the last follow - up ) . 
 the dynamic percentage slip ( gap in percentage slip between flexion and extension x - ray exams ) did not change significantly ( 5.2% vs. 5.8% ) . slip angle and dynamic slip angle did not change ( 3.2 and 8.2 vs. 3.6 and 9.2 , respectively).conclusionsthe results suggested that semi - circumferential decompression is a clinically recommendable procedure that can improve pain . 
 this procedure does not cause spinal instability when treating patients who have a spinal stenosis with degenerative spondylolisthesis .