Aims

People with severe, persistent low back pain (LBP) may be offered lumbar spine fusion surgery if they have had insufficient benefit from recommended non-surgical treatments. However, National Institute for Health and Care Excellence (NICE) 2016 guidelines recommended not offering spinal fusion surgery for adults with LBP, except as part of a randomized clinical trial. This survey aims to describe UK clinicians’ views about the suitability of patients for such a future trial, along with their views regarding equipoise for randomizing patients in a future clinical trial comparing lumbar spine fusion surgery to best conservative care (BCC; the FORENSIC-UK trial).

Aims

To report the outcome of spinal deformity correction through anterior spinal fusion in wheelchair-bound patients with myelomeningocele.

Aims

High-grade dysplastic spondylolisthesis is a disabling disorder for which many different operative techniques have been described. The aim of this study is to evaluate Scoliosis Research Society 22-item (SRS-22r) scores, global balance, and regional spino-pelvic alignment from two to 25 years after surgery for high-grade dysplastic spondylolisthesis using an all-posterior partial reduction, transfixation technique.

Aims

Chronic low back pain due to degenerative disc disease is sometimes treated with fusion. We compared the outcome of three different fusion techniques in the Swedish Spine Register: noninstrumented posterolateral fusion (PLF), instrumented posterolateral fusion (IPLF), and interbody fusion (IBF).

We evaluated the efficacy of Escherichia coli-derived recombinant human bone morphogenetic protein-2 (E-BMP-2) in a mini-pig model of spinal anterior interbody fusion. A total of 14 male mini-pigs underwent three-level anterior lumbar interbody fusion using polyether etherketone (PEEK) cages containing porous hydroxyapatite (HA). Four groups of cages were prepared: 1) control (n = 10 segments); 2) 50 μg E-BMP-2 (n = 9); 3) 200 μg E-BMP-2 (n = 10); and 4) 800 μg E-BMP-2 (n = 9). At eight weeks after surgery the mini-pigs were killed and the specimens were evaluated by gross inspection and manual palpation, radiological evaluation including plain radiographs and micro-CT scans, and histological analysis. Rates of fusion within PEEK cages and overall union rates were calculated, and bone formation outside vertebrae was evaluated. One animal died post-operatively and was excluded, and one section was lost and also excluded, leaving 38 sites for assessment. This rate of fusion within cages was 30.0% (three of ten) in the control group, 44.4% (four of nine) in the 50 μg E-BMP-2 group, 60.0% (six of ten) in the 200 μg E-BMP-2 group, and 77.8% (seven of nine) in the 800 μg E-BMP-2 group. Fusion rate was significantly increased by the addition of E-BMP-2 and with increasing E-BMP-2 dose (p = 0.046). In a mini-pig spinal anterior interbody fusion model using porous HA as a carrier, the implantation of E-BMP-2-loaded PEEK cages improved the fusion rate compared with PEEK cages alone, an effect that was significantly increased with increasing E-BMP-2 dosage. Cite this article: Bone Joint J 2013;95-B:217–23

Introduction. Recently published results suggest insertion of shorter screws in L5/S1 stand-alone anterior interbody fusion, fearing S1 nerve root violation. However, insertion of shorter screws led to screw fixation failure and new onset of S1 body fractures. Material and Methods. Retrospective review of patients with L5/S1 stand-alone anterior interbody fusion, focussing on screw length, radiological outcomes (especially metal work failure, screw fixation and S1 body fractures) and new onset of S1 nerve root irritation. Results. 38 patients were included (mean age 46.2±13.3 years, 21 females, 17 males). Fusion of the L5/S1 segment was performed in between 2003-2010; postoperative follow-up ranged from 2-24 months. 15 patients had multilevel surgery (7 multiple segmental fusion, 8 hybrid procedures). Screw length ranged from 20-30 mm. No patient had new postoperative S1 nerve root irritation. Interestingly, 2 patients out of the hybrid group had a new onset of L5 radiculopathy, concordant to the level of disc-replacement. Follow-up x-ray review showed no fracture of S1 body fractures in all patients. No evidence of screw loosening, migration or metal work failure was reported. Conclusion. In our opinion, this review showed that insertion of longer screws for stand-alone anterior interbody fusion in L5/S1 is safe. Longer screws offer better stabilization and seem to minimize risks like S1 body fractures. Short and long-term follow-ups were satisfactory regarding screw placement, migration and positioning of implants in all patients

The June 2012 Spine Roundup³⁶⁰ looks at: back pain; spinal fusion for tuberculosis; anatomical course of the recurrent laryngeal nerve; groin pain with normal imaging; the herniated intervertebral disc; obesity’s effect on the spine; the medicolegal risks of cauda equina syndrome; and intravenous lidocaine use and failed back surgery syndrome.

Introduction. Iatrogenic spondylolisthesis occurs infrequently after posterior decompression. Posterior surgery is challenging due to altered anatomy and scarring. Anterior lumbar interbody fusion (ALIF) allows indirect decompression, restoration of lordosis and fusion. Material and Methods. Retrospective review of 6 patients (5 female, 1 male, mean age 64±5.8 years) with iatrogenic spondylolisthesis (5 L4/L5; 1 L4/L5) treated with stand-alone ALIF (Synfix, BMP2). Assessment of pelvic incidence, listhesis, pre- and post-operative ODI, VAS, global lumbar lordosis and segmental lordosis as outcome measurements. Results. The slippage was grade II at L4/L5 in 3 patients and grade I in 2 patients at L4/L5 and 1 patient at L5/S1. Average ODI dropped from 49±11% pre-operatively to 30±9% at 6 and to 25±6% at 12 months follow-up. VAS average dropped from 7±1 to 3±1 at 6 and 12 months follow-up. Average pelvic incidence was 54.6±8.0°. Global lordosis of 44.6±5.2° increased to 49.0±8.6°; Segmental lordosis in L4/5 was increased from 12.1±8.2° to 22.4±3.7° at 6 and 20.5±7.9° at 12 months. Cage migration due to severe osteoporosis occurred in 1 case after 5 months. Conclusion. Anterior interbody fusion offers good stabilization and restoration of lordosis in iatrogenic spondylolisthesis. In our group, ODI and VAS scores were improved. These early results encourage further investigations regarding long-term follow-ups and prospective studies in larger patient groups

We do know that the use of stand-alone cage with no plate is prone to subsidence and segmental kyphosis. Cage and plate construct are prone to adjacent level ossification. Zero P (Synthes, UK) cage combines the functionality of spacer and anterior plate. Radiological evaluation of subsidence of cervical spine after anterior cervical interbody fusion using Zero P cage system. Method: Retrospective review of radiographic records of patients undergoing surgery between June 2008- Oct 2009. We evaluated lateral cervical standing radiographs before, after, 6 weeks, 3, 6 months of surgery. We measured subsidence (using Total Intervertebral Height (TIH). All measurements were done using Web 1000 (Impax Agfa). Two level was treated as single segment. Subsidence > 3mm was considered significant. 20 patients (11 male: 9 female) with median age of 51 yrs (40-65) underwent one (n=10) or two level (n= 10) cervical fusion. Immediately post-op there was increase in TIH in one and two level group by 1.74mm (1.61 and 4.25mm (1.48 respectively, which at 6 months reduced to 1.05mm (0.24 (p< 0.003) and 1.32mm (1.29 (p< 0.085) at 6 months respectively. Subsidence was seen in all cases and was rapid in first 3 months and then tailed off. It was significant (> 3mm) only in 2/20 (2%) patients at 6 months. Early results indicate that spine alignment is maintained radiologically with no associated complications as screw loosening, cage extrusion etc

A number of causes have been advanced to explain the destructive discovertebral (Andersson) lesions that occur in ankylosing spondylitis, and various treatments have been proposed, depending on the presumed cause. The purpose of this study was to identify the causes of these lesions by defining their clinical and radiological characteristics.

We retrospectively reviewed 622 patients with ankylosing spondylitis. In all, 33 patients (5.3%) had these lesions, affecting 100 spinal segments. Inflammatory lesions were found in 91 segments of 24 patients (3.9%) and traumatic lesions in nine segments of nine patients (1.4%). The inflammatory lesions were associated with recent-onset disease; a low modified Stoke ankylosing spondylitis spine score (mSASSS) due to incomplete bony ankylosis between vertebral bodies; multiple lesions; inflammatory changes on MRI; reversal of the inflammatory changes and central bony ankylosis at follow-up; and a good response to anti-inflammatory drugs. Traumatic lesions were associated with prolonged disease duration; a high mSASSS due to complete bony ankylosis between vertebral bodies; a previous history of trauma; single lesions; nonunion of fractures of the posterior column; acute kyphoscoliotic deformity with the lesion at the apex; instability, and the need for operative treatment due to that instability.

It is essential to distinguish between inflammatory and traumatic Andersson lesions, as the former respond to medical treatment whereas the latter require surgery.

Aim: To determine the clinical improvement and the radiological time to fusion as well as correction of the lordosis angle in patients undergoing anterior cervical interbody fusion with the use of a silicate substituted calcium phosphate ceramic (Si-CaP) (Actifuse™ Synthetic Bone Graft, ApaTech, Ltd., Elstree, UK) as the bone graft substitute in the cage. Design: We conducted a prospective clinical and radiological study to evaluate the use of Si-CaP as bone graft substitute in anterior cervical fusion for degenerative cervical spondylosis. Materials and methods: Thirty patients were selected prospectively by preoperative and postoperative clinical and radiological assessments. All patients were operated on by a single surgeon (D.A.J.). Neck disability index and visual analogue score were used for the clinical assessment. Radiological assessment included improvement in the lordosis angle and time to fusion. Patients were evaluated at three months, six months and one year post-surgery. Results: At present 14 patients with a total of 19 levels have completed their one year follow-up. The patients had an average of 50.4 years (range 34–69), with ratio of male to female of 6:7. Lordosis angle improved significantly from a mean lordosis angle of 0.31 preoperatively to 4.75 degree postoperatively (p< 0.05). All the levels had fused at the 1 year follow up and there was no radiological evidence of sinkage of the cage. Conclusion: Substitution of silicate ions into calcium phosphate ceramics has been shown to impart a negative surface charge, leading to greater protein absorption, increased osteoblast proliferation, and higher production of extracellular matrix. Our results show that Si-CaP has excellent clinical performance as a synthetic bone graft in anterior cervical discectomy and fusion. Postoperatively, patients demonstrate a good fusion with an excellent correction and maintenance of the lordosis angle

Introduction: Bone morphogenetic protein (BMP) has become widely used in the interbody space as part of a lumbar fusion. Complications can occur but are not completely understood or well documented. Methods: A prospective review of consecutive lumbar interbody fusions performed by a single surgeon was undertaken over a 2-year period. Early complications (defined as occurring within the first six weeks) were noted. The interbody cages (titanium Syncage, Synthes cages for ALIFs and PEEK Capstone, Medtronic cages for TLIFs) were filled with Infuse BMP-collagen sponge. Until early 2007, the amount of Infuse used was not strictly measured but after that time, only enough to fill the cage was used, with the volume assessed according to the manufacturer’s guidelines. Patients were routinely assessed preoperatively and at the six-week postoperative review using a visual analogue scale and the Oswestry disability score. Plain x-ray and MRI were obtained preoperatively, and plain x-ray was obtained postoperatively. In addition, if early problems developed, MRI scan was obtained. The incidence of complications was compared to that seen in similar procedures but where BMP was not used. Results: 114 patients, including 78 transforaminal inter-body fusions (TLIFs) and 36 anterior lumbar interbody fusions (ALIFs) were available for review. Early complications were noted in 10 of 114 patients. Two (both with TLIF) were not directly linked with BMP use: in the first, the cage migrated posteriorly and in the second, a deep infection developed. The remaining eight were associated with an exaggerated inflammatory response likely related to BMP use. Severe back pain associated with marked vertebral body inflammation seen on MRI was noted in two ALIF patients. The response occurred within 2 weeks of surgery, and settled with conservative treatment. Severe back pain and recurrence of leg pain developed in six TLIF patients. Fluid cyst formation within the spinal canal was seen on MRI in 4 of these. The cyst extended from the region of the posterior aspect of the cage into the canal and toward the area of the excised facet joint, resulting in compression of the exiting nerve root. In one case, the surgical site was re-explored and the cyst removed. In two cases, the cyst was aspirated under CT guidance and injected with steroid. In the final case a course of oral Prednisone was administered. In the remaining two TLIF cases, there was a diffuse inflammatory response in the region of the posterior aspect of the cage and adjacent epidural space but without discrete cyst formation. In one, oral Prednisone was prescribed. The second was treated expectantly. The majority of these complications were noted in 2007, after the dose of BMP was titrated in line with the manufacturer’s guidelines. In contrast, no such complications were seen when a similar technique but without BMP was undertaken in 33 posterior and 41 anterior interbody fusions. Discussion: The incidence of an exaggerated inflammatory response with BMP in the lumbar spine may be under-recognised. The majority of complications published to date relate to vertebral osteolysis and bony overgrowth, although a number of adverse responses to BMP reported to the FDA relate to fluid cyst formation or inflammation. With the rapid increase in BMP use, it is important that surgeons are aware of potential complications, and possible strategies to prevent and address them

We have reviewed our experience in managing 11 patients who sustained an indirect sternal fracture in combination with an upper thoracic spinal injury between 2003 and 2006. These fractures have previously been described as ‘associated’ fractures, but since the upper thorax is an anatomical entity composed of the upper thoracic spine, ribs and sternum joined together, we feel that the term ‘fractures of the upper transthoracic cage’ is a better description. These injuries are a challenge because they are unusual and easily overlooked. They require a systematic clinical and radiological examination to identify both lesions. This high-energy trauma gives severe devastating concomitant injuries and CT with contrast and reconstruction is essential after resuscitation to confirm the presence of all the lesions. The injury level occurs principally at T4–T5 and at the manubriosternal joint. These unstable fractures need early posterior stabilisation and fusion or, if treated conservatively, a very close follow-up.

Injury to the spinal cord and kyphosis are the two most feared complications of tuberculosis of the spine. Since tuberculosis affects principally the vertebral bodies, anterior decompression is usually recommended. Concomitant posterior instrumentation is indicated to neutralise gross instability from panvertebral disease, to protect the anterior bone graft, to prevent graft-related complications after anterior decompression in long-segment disease and to correct a kyphosis. Two-stage surgery is usually performed in these cases. We present 38 consecutive patients with tuberculosis of the spine for whom anterior decompression, posterior instrumentation, with or without correction of the kyphus, and anterior and posterior fusion was performed in a single stage through an anterolateral extrapleural approach. Their mean age was 20.4 years (2.0 to 57.0).

The indications for surgery were panvertebral disease, neurological deficit and severe kyphosis. The patients were operated on in the left lateral position using a ‘T’-shaped incision sited at the apex of kyphosis or lesion. Three ribs were removed in 34 patients and two in four and anterior decompression of the spinal cord was carried out. The posterior vertebral column was shortened to correct the kyphus, if necessary, and was stabilised by a Hartshill rectangle and sublaminar wires. Anterior and posterior bone grafting was performed.

The mean number of vertebral bodies affected was 3.24 (2.0 to 9.0). The mean pre-operative kyphosis in patients operated on for correction of the kyphus was 49.08° (30° to 72°) and there was a mean correction of 25° (6° to 42°). All except one patient with a neural deficit recovered complete motor and sensory function. The mean intra-operative blood loss was 1175 ml (800 to 2600), and the mean duration of surgery 3.5 hours (2.7 to 5.0). Wound healing was uneventful in 33 of 38 patients. The mean follow-up was 33 months (11 to 74). None of the patients required intensive care.

The extrapleural anterolateral approach provides simultaneous exposure of the anterior and posterior aspects of the spine, thereby allowing decompression of the spinal cord, posterior stabilisation and anterior and posterior bone grafting. This approach has much less morbidity than the two-stage approaches which have been previously described.

Purpose: To investigate the potential value of titanium anterior interbody cages compared to morselized rib graft for anterior interbody fusion in combination with posterior instrumentation, correction and fusion for Scheuermann’s kyphosis. Methods and Materials: A Non-Randomised historic cohort study of two surgical techniques in matched subjects was carried out.15 patients with identical pre-operative radiographic and physical variables (age, gender, height, weight, BMI ) were managed with combined anterior release, interbody fusion, posterior instrumentation, correction and fusion . Group A (n=8) had morsilized rib graft inserted into each intervertebral disc space. Group B (n=7) had titanium interbody cages packed with bone graft inserted at each level. The posterior instrumentation extended from T2 to L2 in both groups. Pre- and post-operative curve morphometry was studied on plain radiographs by two independent observers. The indices studied included Cobb angle, Ferguson’s angle(FA) , Voutsinas index(VI), Sagittal Vertical Axis (SVA), Sacral Inclination (SI) and Lumbar Lordosis (LL). Interbody Fusion was assessed at final follow up. Each patient was reviewed at 3, 6, 12, 24, 48 and 60 months following surgery with standing radiographs. Wilcoxon-matched pairs test and Mann-Whit-ney test were used for statistical analysis. Results: The average follow-up for groups A was 70 and Group B,66 months. For the whole group, the pre-operative : postoperative median Cobb angle, FA, VI, SVA and SI were 86: 42degrees, 50 : 28.4degrees, 28.7 :13, −3.5 : −4.0 centimetres and 40 : 34 degrees respectively. There were significant differences for all variables [p< 0.01] indicating good correction. At four-year follow-up, fusion criteria were satisfied in 12 / 15 cases (80%). Three patients had distal junctional kyphosis. There was no significant difference with respect to the variables between the two groups and both retained the post-operative correction achieved. Conclusion: There was no significant advantage in the use of anterior titanium interbody cages over the use of morselized rib graft in the surgical management of Scheuermann’s Kyphosis

Aim: To determine the incidence of adjacent level osteophytes in patients who have had anterior cervical fusion using an anterior cervical plate as compared to those who are fused without an anterior cervical plate. Design: We retrospectively reviewed the lateral radiograms of sixty two patients who have had an anterior cervical fusion with a minimum follow up of twelve months. Materials and methods: We looked for the development of adjacent level osteophytes in these patients at their final follow up, which was generally at the time radiological fusion. There were 27 patients in the first group who had an anterior cervical plate used to fix the vertebrae in addition to the Cervios cage, while the 35 patients in the second group in whom only a Rabea cage was used for the fusion. The mean follow-up was 20.6 months (range 12–48). Results: 64.3% of the patients who had an anterior cervical plate developed adjacent level osteophytes while none of the patients who have had the fusion without the cage developed the osteophytes. Conclusion: We found the patients who had an anterior cervical interbody fusion using a plate had a significant risk of developing adjacent level osteophytes while this is not seen in patients who do not have the plate for the fixation

Objective: To report a consecutive series of patients who underwent staged reduction and fusion with the Magerl External Fixator and 360° fusion for high grade slips and spondyloptosis. Design: Prospective observational study. Patients & methods: There were 11 patients, average age 17 years (range 9–25 years). All these patients had equal or greater than Meyerding grade III slips. Clinical presentation included severe back pain with disability and a severe cosmetic deformity (including flexed knees, proptotic abdomen and loin creases). The indications for surgery were pain relief and neurological symptoms/signs, and to improve the sagittal alignment. Surgery consisted of first stage Gill procedure, L5 root decompression, and insertion of Schanz pins into L4 pedicles and ilium, and application of the fixateur-externe. Second stage consisted of gradual correction of kyphosis and translation (average 1 week duration). Third stage entailed anterior interbody fusion, removal of fixator and instrumented fusion L5 to sacrum. Outcome measures: Functional out comes (pain scores [VAS], activities of daily living) cosmesis, complications (including neurologic status) and radiographic parameters. Results: Average follow-up was 3 years and 3 months. Postoperatively none of these patients developed a neurological deficit. Imaging confirmed solid fusion in all patients. In terms of reduction, 1 patient failed to reduce (fusion in-situ) and 1 patient developed subsequent L4 on L5 spondylolisthesis. There was no case of permanent neurologic deficit. Nine (82%) patients reported improved pain scores on the VAS, improved quality of life and cosmetic appearance. There was significant reduction of the translation (in most cases to grade II) and correction of the lumbosacral kyphosis. All patients went on to a solid arthrodesis and there was no late loss of correction. Conclusions: Staged reduction and Fusion not only improves a severe cosmetic deformity but also restores sagittal balance. We recommend this technique as there is negligible risk of neurological complications, and avoids fusion involving two motion segments

Spondylolytic spondylolisthesis is one of the common causes of mechanical low back pain in adults. Conservative treatment of such cases, particularly for the low grade slips, remains the mainstay of management. When patients’ symptoms are marked and not responsive to conservative therapy, the surgical option can be considered. Up to the time of writing this abstract [January 2003], arthrodesis of the affected motion segment with or without instrumentation is the standard surgical option for treating mechanical low back pain. Results of different types of arthrodesis for treating such condition had been reported in literature, including posterior fusion, posterolateral fusion, and posterior and anterior interbody fusion. Between 1993 and 1998, seventy- five adult patients with grade I or II lytic spondylolisthesis were treated by in situ posterolateral fusion and segmental instrumentation using the Oswestry Pedicle Screw System, with or without extended Gill’s procedure. The indications for surgical intervention in these cases were significant reduction in the quality of life with persistent low back pain and/or leg pain after a minimum of six months conservative therapy. Confirmatory imaging studies consistent with the clinical data should also be obtained before deciding the surgical option. The average operative time was 2.5 hours [range 2–4 hours). The average blood loss was 850 mls (range 300–2300 mls). After an average follow-up of 60.7 months (range 24–95 months) clinical results were excellent and good in 92%, and radiological union was achieved in 94% of patients. Complications included 2 cases with superficial wound infection, one case with deep wound infection, and four of the patients went to non-union. In conclusion, with a careful patient selection, patients with instrumental insitu posterolateral fusion gained a satisfactory clinical and radiological outcome and the results were maintained for an adequate postoperative period

There are few reports on the treatment of pyogenic lumbar spondylodiscitis through the posterior approach using a single incision. Between October 1999 and March 2003 we operated on 18 patients with pyogenic lumbar spondylodiscitis. All underwent posterior lumbar interbody fusion using an autogenous bone graft from the iliac crest and pedicle screws via a posterior approach. The clinical outcome was assessed using the Frankel neurological classification and the criteria of Kirkaldy-Willis. Under the Frankel classification, two patients improved by two grades (C to E), 11 by one grade, and five showed no change. The Kirkaldy-Willis functional outcome was excellent in five patients, good in ten and fair in three. Bony union was confirmed six months after surgery in 17 patients, but in one patient this was not achieved until two years after operation. The mean lordotic angle before operation was 20° (−2° to 42°) and the mean lordotic angle at the final follow-up was 32.5° (17° to 44°). Two patients had a superficial wound infection and two a transient root injury. Posterior lumbar interbody fusion with an autogenous iliac crest bone graft and pedicle screw fixation via a posterior approach can provide satisfactory results in pyogenic spondylodiscitis.

Objective: Retrospective analysis of consecutive paediatric patients treated surgically for high-grade spondylolisthesis by one of three circumferential surgical procedures with emphasis on complications and patient outcome measurements. Methods: Between 1980 and 1998 fourty patients underwent anterior-posterior correction for Meyerding Grade 3 or 4 isthmic dysplastic spondylolisthesis. Ten patients were treated with an anterior reduction according to Louis and anterior interbody fusion followed by posterior decompression and instrumented fusion (group A). Fourteen patients underwent posterior decompression followed by anterior reposition and fusion with tricortical iliac bone crest and posterior instrumented fusion (group B). Sixteen patients underwent progressive reduction by halopelvic traction followed by anterior and posterior fusion (group C). All patients completed the North American Spine Society (NASS) outcome questionnaire and the SF-36. The cosmetic assessment was performed by means of a VAS. The mean follow-up period for group A was 13,5 years, for group B 5,5 years and for group C 15,4 years, respectively. Results: The three groups were comparable with respect to age at operation, radiographic measurement of the slip, lumbosacral kyphosis and lumbar lordosis. The incidence of postoperative extensor hallucis longus weakness was 33% in group A, 50% in group C and 0% in group B (p< 0.001). Pearson correlation coefficient revealed a positive correlation between extensor hallucis longus weakness and the degree of correction of the lumbosacral kyphosis (P=0.56, p=0.024). Postoperative reduction of the sagittal slip (A: 64%, B: 44%, C: 50%) and lumbosacral kyphosis (A: 27°, B: 16°, C: 27°) was significant in all three groups. The incidence of pseudarthrosis was 10% in group A, 7% in group B and 6% in group C. SF-36 and NASS outcome questionnaire results have not been found statistically significant among the groups. Conclusion: Outcomes of function, satisfaction and cosmesis are satisfactory in all three surgical groups. Posterior decompression followed by anterior reduction and fusion using tricortical iliac crest bone graft and posterior instrumented fusion lack neurogenic complications. Therefore it is the standard surgical procedure for severe isthmic dysplastic spondylolisthesis at our department