Background/aims: To assess the revision rate at L5-S1 when only posterior fixation with pedicle screws is done with multi-level spinal fixation.
Patients and Methods: The Retrospective quasi experimental study was conducted at the Combined Military Hospital, Rawalpinidi and comprised data from 2009 to 2014 of patients in whom multi-level posterior decompression including lumbosacral junction (L5-S1) with laminectomy and posterior fixation with pedicle screws was done till L3 and higher. Those with known cause of implant failure like osteoporosis, osteomalacia and infection were excluded. Patients were followed up and need for revision at L5-S1 level was assessed.
Result: Of the 22 cases, 5(23%) were males and 17(77%) were females with an overall mean age of 64±10.38 years (range 48-84 years). Mean number of levels fixed was 5.22±1.15 the highest level of fixation being T11. Mean follow-up was 08±3.22 months and focused only at the failure of fixation at L5-S1. Two (9%) cases showed implant loosening and required revision at L5-S1 because of screw cut out.
Conclusion: Properly placed pedicle screws were adequate with fusion for multilevel spinal fixations.
Keywords: Lumbosacral junction, Posterior fixation, Pedicle screws, Spinal fixations. (JPMA 65: S-152 (Suppl. 3); 2015).
Adult deformity is one the most common disorders which a spine surgeon is faces in the developed world. The reported prevalence has a wide range of 8.3 to 68%.1-3 Moreover elderly population has a much higher prevalence of scoliosis of 68% at mean age of 70 years.1 As the quality of health care improves and life expectancy increases in our part of the world these disorders will be more frequently encountered and operated upon here as well. Adult deformity is a combination of spinal stenosis, instability, disc degeneration facet joint arthropathy and idiopathic scoliosis.4
Surgical procedures performed in adult deformity range from simple decompression to complex fixation. Usually it is a combination of both the procedures. More extensive decompression requires extensive fixation to hold the spine in place till the time the bony fusion occurs. The combined fusion and decompression procedures have been reported to have a good outcome in this population.5
When a patient is fixed beyond L3 there is an increased failure rate at the S1 pedicle screw.6 Various strategies have been suggested to improve the survival of fixation at the base. Commonly suggested are a 360 degree fusion at L5-S17-8 or extending the fixation to iliac wing is recommended in cases when performing fixation beyond L3.9 Both these approaches lead to an increased operating time, increased incidence of complication and not to mention the increased morbidity especially associated with iliac fixation.
Our population is leading a much more sedentary life in advanced ages as compared to Western population and in our clinical observation we did not see an increase in the complication in the base when fixation was only carried till S1 without doing either discectomy and fusion or iliac wing fixation. In this study we followed our cases in which extensive fixation without doing discectomy and fusion or including ilium in fixation.
The current study was planned to assess the revision rate at L5-S1 when only posterior fixation with pedicle screws was done with multi-level spinal fixation.
Patients and Methods
The retrospective quasi experimental study was conducted at the Combined Military Hospital (CMH), Rawalpindi and comprised data from January 1, 2009 to June 30, 2014 of patients in whom multi-level posterior decompression, including lumbosacral junction (L5-S1) with laminectomy and posterior fixation with pedicle screw, was done till L3 and higher. Those included were cases who underwent long surgery was carried out for spinal stenosis, degen scoliosis and instability only.
Cases where discectomy of L5-S1 was performed along with bone grafting; patients in whom fixation was carried till Ilium; those who had poor bone quality because of osteoporosis or other metabolic conditions; patients developing post operative deep wound infection; those in whom screw augmentation was done using bone cement; patient having surgical fixation other than those mentioned in the inclusion criteria; those with neurological deficit; and patients who were lost to follow-up or having a follow-up less than 6 months.
Patients records were analyzed and demographic data was collected about gender, age, co-morbids. Dual energy absorptionmetry (DEXA) scan was used to determine bone density. Surgical records were reviewed for levels fused, decompression type and type of fusion performed. Last follow-up X-rays were analysed for evidence of fusion. These patients were further analysed for any revision surgery. Any revision surgery carried out at L5-S1 due to any kind of failure was recorded. Extension of fixation cranially was disregarded as failure of fixation. Solid fusion and asymptomatic pseudarthrosis was regarded as adequate treated case.
Pre-operative radiographs and magnetic resonance imaging (MRI) scan followed by pedicle screw fixation were reviewed. The spine was instrumented from T11 till S1. The fixation was stopped at Sq and no anterior discectomy was done. Posterolateral fusion was attempted and the deformity was corrected (Figure-1).
Preoperative images of the spine with decompression from L2-S1 by posterior laminectomy and fixation by pedicle screws were also recorded. Correction has been achieved by applying contoured rods (Figure-2).
In terms of fixation management the fixation was carried till ilium and the additional screws were cement augmented. To prevent the collapse of the top vertebrae it has been cement augmented to make it more rigid (Figure-3).
Mean and standard deviation was calculated for age, levels fixed, while frequencies and percentages were calculated for gender. The revision rate was measured for L5-S1 fixation.
Of the 22 cases, 5(23%) were males and 17(77%) were females with an overall mean age of 64±10.38 years (Range 48-84 years) Decade wise frequency was plotted and most patients were found to be in 6th and 8th decade of life (Figure-4).
The mean number of levels fixed was 5.27 (± 1.16) the highest level of fixation being T11. Eight (36%) patients had 6 or more levels fixed. The number of patients at L3-S1 was the same as the number of patients in the study (Figure-5).
Mean follow-up was 8±3.22 months and focused only at the failure of fixation at L5-S1. Two (9%) cases showed implant loosening and required revision at L5-S1 because of screw cutout. These were managed by extension of fixation.
The decision to include L5-S1 joint in a fixation is a major undertaking. Every effort is usually made to spare this segment as it is the most mobile joint. When this is included in the fixation the stress on the construct is increased manifold and chances of pseudarthosis are high.10,11 If we spare L5-S1 to preserve mobility we may be faced with a revision later as there is usually disc degeneration at this level in most cases,4 so stopping at L5 enhances the degeneration at that level.12 This situation is further complicated by the presence of spondylolisthesis at this level in many cases.13
The researchers have used various techniques to improve the fusion at L5-S1. The pseudarthosis at this level is marked by the presence of rod breakage.6 Birdwell et al14 looked at the various ways employed to this fixation which included anterior grafting, extension of fixation till ilium6,15 and extension of fixation till sacral 2.16,17 The aim of all these strategies is to increase the rigidity at L5-S118 and hence even in the presence of pseudarthosis at L5-S1 there was no case reported for fixation failure in as series.14 It was further confirmed by other researchers.19 This comes at the price of increased blood loss, increased operating time, increased incidence of complication of surgery20 and hardware placement complications.21
In our study we looked at the failures in our cases which had no major risk factor to cause hardware problems so as to isolate the complications arising due to limitation of fixation till S1 without doing anterior discectomy or extending till ilium.
The failure rates in our study is not as high as reported by other researches.5,13,15,21 The possibility is that we aimed to remove all those cases that had host factors for hardware-related complication like decreased bone density. Another reason can be due to the fact that our population is leading a much more sedentary life style compared to Western population especially in the later part of life. This causes decreased loading to the construct leading to better survival of fixation.
Even those cases in which we had to revise the psuedarthosis at L5-S1 caused rod breakage which is a common indication for revision in studies reported above. However, our indications for revision were screw cutouts, which would be ascribed to the fact that either the screw at L5-S1 was malplaced or failed to achieve anterior cortical fixation by sacral pedicle at sacral promontory.22
Therefore it can be stated that in our low-demand population there was very little clinical indication to undertake the fixation till ilium or to do anterior fusion at L5-S1 while performing long fixation. Further good-quality muliticentre prospective randomised clinical trials are needed to better answer this issue.
In low-demand patients without major risk factors to hardware failures long lumbar fixation can be started from S1 without performing anterior discectomy or ilium fixation.
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