Posterior lumbar interbody fusion for revision disc surgery: review of 50 cases in which carbon fiber cages were implanted

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1 J Neurosurg (Spine 2) 95: , 2001 Posterior lumbar interbody fusion for revision disc surgery: review of 50 cases in which carbon fiber cages were implanted BHUPAL CHITNAVIS, F.R.C.S.(SN), GIUSEPPE BARBAGALLO, M.D., RICHARD SELWAY, F.R.C.S.(SN), RONAN DARDIS, F.R.C.S.(I), AHMED HUSSAIN, F.R.C.S.(SN), AND RICHARD GULLAN, M.R.C.P., F.R.C.S. Department of Neurosurgery, King s College Hospital, London, United Kingdom Object. The authors undertook a study to assess the value of posterior lumbar interbody fusion (PLIF) in which carbon fiber cages (CFCs) were placed in patients undergoing revision disc surgery for symptoms suggesting neural compression with low-back pain. Methods. The authors followed their first 50 patients for a maximum of 5 years and a minimum of 6 months after implantation of the CFCs. Patients in whom magnetic resonance (MR) imaging demonstrated simple recurrent herniation did not undergo PLIF. Surgery was performed in patients with symptoms of neural root compression, tension signs, and back pain with focal disc degeneration and nerve root distortion depicted on MR imaging compatible with clinical signs and symptoms. In 40 patients (80%) pedicle screws were not used. Clinical outcome was assessed using the Prolo Functional Economic Outcome Rating scale. Fusion outcome was assessed using an established classification. Symptoms in 46 patients (92%) improved after surgery, and given their outcomes, 45 (90%) would have undergone the same surgery again. Two thirds of patients experienced good or excellent outcomes (Prolo score 8) at early and late follow up. There was no difference in clinical outcome between those in whom pedicle screws were and were not implanted (p = 0.83, Mann Whitney U-test). The fusion rate at 2 years postsurgery was 95%. There were minimal complications, and no patients fared worse after surgery. No patient has undergone additional surgical treratment of the fused intervertebral space. Conclusions. In this difficult group of patients the aim remains to improve symptoms but not cure the disease. A high fusion rate is possible when using the CFCs. Clinical success depends on selecting patients in whom radiological and clinical criteria accord. Pedicle screws are not necessary if facet joints are preserved, and high fusion rates and clinical success are possible without them. KEY WORDS posterior lumbar interbody fusion carbon fiber cage revision disc surgery R Abbreviations used in this paper: CFC = carbon fiber cage; MR = magnetic resonance; PLIF = posterior interbody fusion. EVISION lumbar disc surgery is reputed to follow a law of diminishing returns. 11 Advocates of primary fusion have argued for a more definitive and permanent treatment of the intervertebral space at first surgery to prevent recurrent disc herniation. Fusion, however, is technically challenging and increases operative time and blood loss. These increased disadvantages must be weighed against the majority of favorable outcomes following simple discectomy. Nevertheless, a significant number of patients, ranging from 6 to 11% 5,12 reported in recent publications, experience additional difficulty from recurrent disc herniation following simple discectomy. In the established view it is held that the chance of good outcome following further surgery in this group, particularly those with epidural fibrosis, is low. Lumbar fusion in revision surgery is less controversial than primary fusion, but it is technically more demanding and its use has not been supported by evidence from randomized clinical trials. A few surgeons have reported excellent results following PLIF in which autologous bone was used, 4,8,9 but the majority of surgeons have not been successful with this treatment, and their experiences remain largely unpublished. The principal reason for this lack of technical success is thought to be graft failure. The grafted bone is often unable to fulfill both structural and biological roles simultaneously. New materials, in particular the CFC, have been reported to improve fusion rates 1,2 by acting as a structural support while biological fusion occurs. We report experience with CFCs in our first 50 patients who underwent follow up for up to 5 years. 190 J. Neurosurg: Spine / Volume 95 / October, 2001

2 Carbon fiber cages for PLIF FIG. 1. Left: Photograph showing the Brantigan cage packed with autologous bone prior to implantation. Note the serrated edges that prevent retropulsion. Right: Computerized tomography scan demonstrating preserved facet joints with paired cages in situ. Patient Population Clinical Material and Methods There were 27 women and 23 men who ranged in age from 19 to 58 years (median 42 years) at the time of surgery. Our regional neurosurgical service receives referrals from neurosurgeons and orthopedic surgeons. All patients had previously undergone one or more discectomies at the same now-symptomatic spinal level with good but unsustained improvement. In cases in which MR imaging demonstrated simple recurrent disc herniation compatible with symptoms, the patients were offered simple discectomy and were excluded from the study. In general, patients with multilevel degenerative disc disease were excluded. All patients suffered sciatica with definite tension signs, namely diminished straight-leg raising ability and back pain. Patients with back pain alone were also excluded from the study. Preoperative neuroimaging demonstrated entrapment/distortion of the nerve root by scar, disc, or both at the previously operated level, and the findings were compatible with the clinical features. Furthermore, all patients underwent at least 3 months of conservative treatment prior to PLIF. Patients in whom radiologically documented instability was present were excluded. Surgical Treatment Three surgeons performed all operations: 44 (88%) by the senior surgeon (R.G.) and the remainder under his direct supervision. A standard midline laminectomy was performed in all cases. The dura was decompressed, including that within the intervertebral foramen, and the facet joints were preserved as much as possible. Paired Brantigan cages, packed with autologous bone (Fig. 1) obtained from the iliac crest or spinous process, were inserted into the intervertebral space. In patients treated early in the series or in those in whom instability was demonstrated intraoperatively, pedicle screws (DePuy Acromed, Cincinnati, OH) were placed (see Discussion). Use of postoperative spinal bracing was avoided, although in some patients a fabric corset was used for 6 weeks to provide comfort, and early ambulation has been the rule. J. Neurosurg: Spine / Volume 95 / October, 2001 Patients returned for outpatient assessment at regular intervals following surgery. Radiographs including shoot-through views parallel to the vertebral endplates were acquired to assess the success of fusion (Fig. 2). The angle of the shoot-through was calculated based on examination of the plain lateral lumbar radiograph obtained first. Clinical outcome was assessed using the Prolo Functional Economic Outcome Rating Scale 13 (Table 1). Good and excellent outcomes are reflected by a combined (Economic and Functional Status) score of 8 or above. Fusion outcome was assessed using criteria used by Brantigan and Steffee 2 (Table 2). Results Of the 50 patients, 49 underwent single-level operations; in nine of these pedicle screw augmentation was performed. One patient underwent a two-level fusion in which pedicle screws were placed. In one patient interspinous wiring was required. All patients had previously undergone at least one discectomy at the level currently requiring fusion. Five patients had previously undergone three discectomies and seven patients two discectomies at the same level. Thirty-two CFCs were implanted at the L5 S1 level and 16 at the L4 5 level (Table 3). A single procedure was undertaken at the L3 4 level and another involving L4 5 and L5 S1 (Fig. 3). The mean time from previous surgery was 46 months, and patients had experienced recurrent symptoms for a mean of 30 months prior to undergoing PLIF and CFC implantation. All patients complained of back pain and sciatica prior to surgery, although one patient had a fixed neural deficit with numbness and weakness of the L-5 nerve root. Radiological Outcome Of 45 patients expected to undergo 2-year radiological follow-up assessment, 39 patients completed the course; in 37 (95%) of these patients, fusion was judged, based on the criteria given in Table 2, to be Grade 5 (Fig. 2). The fusion status remains uncertain in two (5%) of the 39 patients, as radiographs demonstrated lucent lines at the 191

3 B. Chitnavis, et al. TABLE 1 Prolo Functional Economic Outcome Rating Scale Score Criteria economic status 1 complete invalid 2 no gainful occupation, including ability to do housework or retirement activities 3 ability to work but not at previous occupation 4 working at previous occupation part time or w/ limited status 5 able to work at previous occupation w/ no restrictions functional (social) status 1 total incapacity (worse than preop) 2 mild to moderate level of low-back pain &/or sciatica (or pain same as preop but able to perform all daily tasks of living) 3 low level of pain & able to perform all activities except sports 4 no pain, but 1 or more recurrences of low-back pain or sciatica 5 complete recovery, no episodes of recurrent low-back pain, & able to perform all previous sports activities FIG. 2. Plain radiograph obtained through the level of the intervertebral space, demonstrating solid fusion (Grade 5) between vertebral bodies and across the facet joints. center of the fusion mass. One of these patients has experienced an excellent outcome, and the other reported no improvement, although she remains at work on the beat as a policewoman. In both patients weight-bearing lateral lumbar radiographs have demonstrated the absence of spinal instability. There have been no screw or hardware breakages. Only five patients have yet to reach the 2-year assessment. An additional patient had, for social reasons, difficulty making the journey to the hospital, and another was hospitalized elsewhere for unrelated reasons at the time writing. Of four patients lost to follow up, all reported excellent/good results at their last follow-up evaluation. If we assume that fusion was not achieved in all those who were lost to follow up, then our poorest anticipated fusion rate would be 82%. Clinical Outcomes Thirty-six (72%) of the 50 patients attended clinical assessment sessions at 2 or more years. Five patients have yet to reach a 2-year postoperative marker. Seven patients (14%) were lost to follow up by the 2-year postoperative date; four of these patients, who earlier had reported good or excellent outcomes, were previously mentioned in the Radiological Outcomes section. At early (6-month) follow up, 46 patients (92%) reported improved symptoms. Ninety-four percent of those who were assessed at late follow up expressed their belief that surgery had improved their symptoms (Table 4). Of those who attended the early and late follow-up session, 66% were classified into the good or excellent outcome group on the Prolo scale (score 8). Only four patients (8%) did not exhibit improvement at late follow up, and 45 patients (90%) indicated they would undergo the same surgery again given the level of improvement achieved. Of significance, no patients felt they were worse after surgery. Overall 43 patients (86%) were free of sciatica at last assessment, although 24 (48%) suffered some persistent back pain. Of the 13 patients who experienced fair improvement at 1 year, in 10 (77%) complete resolution of sciatica occurred. There was no difference (p = 0.83 Mann Whitney U-test) in clinical outcomes between those in whom pedicle screws were and were not implanted. Of 11 patients who had undergone two or more procedures at the same level prior to referral, nine (82%) experienced good or excellent outcomes. There was no significant difference in clinical outcome between patients who had undergone a single procedure compared with those who had undergone several previous operations (p = 0.49 Mann Whitney U-test). Intraoperative Findings Pure scarring with thecal distortion and nerve root entrapment was observed in 14 patients, of whom seven (50%) experienced good or excellent results, four (29%) experienced fair results, and three (21%) reported no improvement at 1-year follow up. Scar- and disc-related nerve entrapment was encountered in 36 patients, of whom 26 (72%) experienced good or excellent outcomes, and only one claimed no improvement. Significantly fewer good outcomes were achieved in patients with pure scar compared with those with scar and disc entrapment of the nerve root (p = 0.02, Mann Whitney U-test). Pedicle Screw Augmentation In the first five patients it was a routine practice to perform screw and rod augmentation. The subsequent five pedicle screw procedures were performed for a variety of reasons. Intraoperative vertebral instability was demonstrated in one case; in another case a two-level graft was placed, and augmentation was thought necessary to provide support. In two patients, slower than expected bone formation was demonstrated at 6- and 9-month assessment, and because they continued to complain of pain, it was believed that fusion and their symptoms would improve after pedicle screw augmentation. After pedicle screw fixation, for- 192 J. Neurosurg: Spine / Volume 95 / October, 2001

4 Carbon fiber cages for PLIF TABLE 2 Description of fusion result Grade Criteria 1 obvious radiographic pseudarthrosis based on vertebral slippage, resorption of bone graft, displacement of carbon cage, broken screws, or construct collapse 2 probable radiographic pseudarthrosis based on significant resorption of bone, or a major lucency gap visible in the fusion area ( 2 mm around the entire periphery of graft or cage) 3 radiographic status uncertain: bone graft is visible in the fusion area at approximately the density originally achieved surgically; a small lucency or gap may be visible, involving just a portion of the fusion area w/ at least 50% of graft area showing no lucency between graft bone & vertebral bone 4 probable radiographic fusion: bone bridges the entire fusion area w/ at least the same density achieved at surgery; there should be no lucency between donor bone and vertebral bone 5 radiographic fusion: bone in the fusion area is radiographically more dense and mature than originally achieved in surgery; optimally, there is no interface betw/ donor bone and vertebral bone, but a sclerotic line betw/ the graft & vertebral bone indicates fusion; other signs of solid fusion include mature osseous trabeculae bridging the fusion area, fusion of facet joints, & anterior progression of graft w/in the disc space mation of new bone was observed to be much more rapid and Grade 5 fusion (Table 2) was achieved in both patients 6 months postoperatively. The fifth patient had undergone four previous surgeries, including an anterior and posterior fusion at the intervertebral level below, and we believed from the outset that very firm fixation was required. Of the 10 patients in whom the augmentation procedure was performed, good to excellent outcomes were achieved in seven (70%), fair outcomes in two (20%), and no improvement was demonstrated in one patient (10%). Treatment-Related Complications There were no cases of infection. At 3-month follow-up evaluation one pair of cages was found to be broken. We suspect this may have occurred at the time of implantation, as the lumbosacral disc space was narrow and very stiff. This patient s clinical outcome has remained excellent, and solid fusion was demonstrated on flexion extension radiographs. None of the cages has become displaced. There was one case of partial foot drop in a woman in whom a delayed postoperative hematoma developed, which resolved after reexploration. She, unfortunately, has experienced no amelioration of preoperative symptoms overall. Four patients have complained of occasional muscle spasms and heaviness of their legs, and in one of them paresthesia was demonstrated. One patient complained of altered sensation in the nerve root adjacent to the fusion level. One patient failed to disclose that he was suing a third party prior to undergoing fusion surgery; he has experienced no improvement following surgery. Other than two patients who underwent pedicle screw augmentation and the aforementioned case, no patient has undergone surgical reexploration. Discussion Choice of Procedure The posterior approach allows direct visualization of neural elements, optimizes their safe decompression, allows access for a total discectomy, and addresses the anterior column, which is the principle load-bearing apparatus. Carbon fiber has advantages over metal implants, because it is radiolucent, which permits visualization of J. Neurosurg: Spine / Volume 95 / October, 2001 fusion, and its modulus of elasticity is similar to cortical bone. 3 A previous study 2 reported improved fusion rates when using impacted CFCs compared with donor or autologous bone alone. Case Selection We chose to exclude patients with simple recurrent disc herniations as a high rate of good outcomes has been shown in this group when simple repeated discectomy is performed. 6 Our group underwent a prolonged period of nonoperative management. The mean period of conservative therapy prior to surgery extended beyond 2 years. During this period, many patients attended pain clinics and sought help from alternative practitioners, including osteopaths, chiropractors, and acupuncturists, but no improvement was sustained. Preoperative MR imaging demonstrated a mixture of predominantly epidural scarring and herniated disc or epidural scarring that caused distortion of the nerve root, accounting for sciatica in each case. Our results compare favorably with those of other series. 1,6,7,10,11,14 In a recent study 1 the authors found no difference among their three groups (Group 1, patients who had previously undergone discectomy; Group 2, those without a history of surgery but with spondylolisthesis; and Group 3, those without a history of surgery but with monosegmental degenerative disc disease) in whom PLIF and CFC implantation were performed. The authors gave little information on case selection criteria for patients who had previously undergone discectomy and few details of intraoperative findings, which makes comparison with our series difficult. Patients with multilevel degenerative disc disease were excluded from this study (apart from one patient who underwent a two-level fusion) principally to obtain as discrete a surgical target but also to avoid placing additional strain on already affected adjacent levels. The majority of patients felt they had improved postoperatively and would opt for the same surgery again. Pedicle Screw Augmentation At the outset of this study the senior author (R.G.) chose to augment all fusions with instrumentation. His practice subsequently evolved and use of pedicle screw fixation was 193

5 B. Chitnavis, et al. TABLE 3 Vertebral levels at which PLIF and CFC placement were performed Fusion Level No. of Patients L5 S1 32 L L3 4 1 L4 5 & L5 S1 1 no longer routine. We have always attempted to preserve the facet joints but have chosen more recently to insert pedicle screws only if a careful intraoperative assessment demonstrates vertebral instability. Facet joint preservation has not, in our experience, hindered the placement of cages, and there have been no cases of spondylolisthesis to date. We also view as counterproductive the extensive exposure and strong retraction required to insert pedicle screws. Because of this policy, operating time, expense, and risk have been reduced. We do not routinely use spinal bracing and have encouraged early ambulation. There were two cases in which grafts were slow to incorporate, with only minimal new bone formation observed at 6 and 9 months postoperatively. In neither case was radiological instability documented. Both of these patients underwent a second procedure at a later date to insert pedicle screws and rapid radiologically demonstrated fusion was achieved in both patients, with good corresponding clinical results. Although unscientific, this lends credence to the view that pedicle screw augmentation may hasten fusion. Overall fusion rates in patients with and without pedicle screws remain high. Given our selective approach toward pedicle screw fixation, meaningful analysis is not possible between patients with and without pedicle screws. We have demonstrated, however, that routine insertion of pedicle screws is not mandatory. Operative Failures and Complications Intraoperative difficulties, which were not always predictable prior to surgery, led us to abandon CFC placement in a number of cases. These patients underwent simple nerve root/dural decompressive procedures. There were two categories of difficulty: 1) excessive scarring that made mobilization and retraction of dura hazardous; and 2) high take off of nerve roots that made their retraction hazardous. There were few complications in our series. In particular there were no cases of infection. Other than the patient who underwent early reexploration for treatment of a postoperative hematoma (previously mentioned) and the two patients who underwent pedicle screw augmentation, no patients underwent further lumbar spinal surgery during the follow-up period. Importantly, none of our patients has felt she/he was made worse by surgery. We believe the low complication rate was achieved, at least partly, because of an early descision to avoid placing CFCs where scarring was very dense and extensive or in cases in which a high take off of nerve roots has indicated their retraction would be hazardous. Fusion Outcomes Brantigan and Steffee 2 reported a 100% fusion rate FIG. 3. Radiograph revealing two-level fusion with pedicle screws and rods. when using CFCs. Our experience, similar to that of others, 1 has yielded as high a success rate. In two cases in this study the grafts showed lucent lines on the shoot-through radiographs. Postoperative flexion extension radiography demonstrated that these locked in fusions were stable after a follow-up period of more than 2 years. Clinical Outcome Patients in whom pure scarring caused nerve root distortion formed the worst prognosis group, with favorable outcomes being achieved in 50%. Other authors have reported similar results, and our results reflect this. It emerged later that one of the four patients who did not improve after surgery was seeking compensation following a road traffic accident that was claimed to have aggravated back pain and sciatica. Nevertheless, the intraoperative finding in his case was pure scarring. Although we accept that preexisting litigation may play an important role in determining a patient s outcome we did not exclude patients on this basis alone. Our inclusion criteria were based on clinical history (especially that involving a good result following previous surgery, albeit unsustained), clinical findings, and radiological features. In one of the patients who did not improve (the case in which evacuation of a postoperative hematoma was required), a mixture of scar and disc was found intraoperatively; in the other three in whom no improvement occurred dense scarring was found intraoperatively. In the majority of patients (82%) who had undergone two or more discectomies prior to enrollment in this series, good or excellent outcomes were achieved after PLIF and placement of CFCs; there was no statistical difference when results obtained in these patients were compared with those obtained in patients who had undergone just one prior surgery. Multiple previous surgeries alone, therefore, is not an exclusion criterion from fusion surgery. 194 J. Neurosurg: Spine / Volume 95 / October, 2001

6 Carbon fiber cages for PLIF TABLE 4 Clinical outcomes after PLIF and CFC placement* No. of Patients (%) Result 6 Mos 1 Year 2 Years excellent & good 33 (66) of (64) of (66) of 36 fair 13 (26) of (29) of (28) of 36 no improvement 4 (8) of 50 3 (7) of 45 2 (6) of 36 worse * Excellent and good: Prolo scores of 8, 9, or 10; fair: Prolo scores of 5, 6, or 7; no improvement: Prolo score of 2, 3, or 4. Analysis of patients with fair improvement showed the majority experienced relief from sciatica; however, back pain persisted, despite the presence of solid fusion and reasonably normal-looking adjacent discs observed on MR imaging. Miscellaneous Issues A potential disadvantage of the CFC is that it cannot be remodeled. This means cage placement must be accurate. We suspect that in one of our patients, who experienced altered sensation in the distribution of the nerve root adjacent to a fusion level, the cage may have caused compression, but she is pleased with the surgery-related result, and her symptoms of sciatica and back pain have improved. Our experience suggests that CFCs may bed in over time, causing progressive loss of intervertebral height, and therefore, also loss of intervertebral foraminal dimensions, but this phenomenon has yet, in our experience, to induce symptoms. Although excellent results were initially achieved in one patient in whom a solid fusion mass formed, by 2 years postoperatively further back pain led to deterioration. Her symptoms may be caused by degenerative disease present at an undisclosed level on MR imaging. Although disappointing, we anticipate others in this study will experience additional future problems, as the natural history of lumbar disc degeneration is generally multifocal and progressive. Conclusions In treating this difficult group of patients the aim remains to improve rather than cure. Our experience of more than 5 years suggests the Brantigan CFC is reliable, safe, and effective. Fusion rates are good but not as high as initially reported. Clinical success is good. Pedicle screws are not routinely required if facet joints are preserved. Ultimate fusion and clinical success is probably unaffected by the absence of pedicle screws, but they may hasten fusion. We have tried to establish clear criteria as indications for fusion in revision disc surgery and have assessed outcomes by using established fusion and clinical scales. Our hope is that this will aid comparison with future studies and allow for refinement of indications for this procedure. We support the wider use of CFCs for the more complex cases in which revision lumbar disc surgery is required. Financial Disclosure None of the authors has any financial interest in the products cited in the study. No funding from grant-giving organizations or other sources has been or will be received for any aspect of this work. References 1. Agazzi S, Reverdin A, May D: Posterior lumbar interbody fusion with cages: an independent review of 71 cases. J Neurosurg (Spine 2) 91: , Brantigan JW, Steffee AD: A carbon fiber implant to aid interbody lumbar fusion. Two-year clinical results in the first 26 patients. Spine 14: , Christel PS: The applications of carbon fiber-reinforced carbon composites (CRFC) in orthopaedic surgery. CRC Crit Rev Biocompatibility 2: , Cloward RB: Posterior lumbar interbody fusion updated. Clin Orthop 193:16 19, Davis RA: A long-term outcome analysis of 984 surgically treated herniated lumbar discs. J Neurosurg 80: , Finnegan WJ, Fenlin JM, Marvel JP, et al: Results of surgical intervention in the symptomatic multiply-operated back patient. Analysis of sixty-seven cases followed for three to seven years. J Bone Joint Surg (Am) 61: , Law JD, Lehman RAW, Kirsch WM: Reoperation after lumbar intervertebral disc surgery. J Neurosurg 48: , Lin PM: Posterior lumbar interbody fusion technique: complications and pitfalls. Clin Orthop 183:90 102, Ma GW: Posterior lumbar interbody fusion with specialized instruments. Clin Orthop 193:57 63, North RB, Campbell JN, James CS, et al: Failed back surgery syndrome: 5-year follow-up in 102 patients undergoing repeated operations. Neurosurgery 28: , O Sullivan MG, Connolly AE, Buckley TF: Recurrent lumbar disc protrusion. Br J Neurosurg 4: , Pappas CTE, Harrington T, Sonntag VKH: Outcome analysis in 654 surgically treated lumbar disc herniations. Neurosurgery 30: , Prolo DJ, Oklund SA, Butcher M: Toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to posterior lumbar interbody fusions. Spine 11: , Waddell G, Kummel EG, Lotto WN, et al: Failed lumbar disc surgery and repeat surgery following industrial injuries. J Bone Joint Surg (Am) 61: , 1979 Manuscript received March 6, Accepted in final form June 5, Address reprint requests to: Richard W. Gullan, M.R.C.P., F.R.C.S.(SN), Department of Neurosurgery, Kings College Hospital, London SE5 9RS, United Kingdom. J. Neurosurg: Spine / Volume 95 / October,