Minimum Four-Year Follow-up of Spinal Stenosis With Degenerative Spondylolisthesis Treated With Decompression and Dynamic Stabilization

Minimum Four-Year Follow-up of Spinal Stenosis With Degenerative Spondylolisthesis Treated With Decompression and Dynamic Stabilization SPINE Volume 33, Number 18, pp E636 E642 2008, Lippincott Williams & Wilkins Stefan Schaeren, MD,* Ivan Broger, MD, and Bernhard Jeanneret, MD* Study Design. Prospective clinical study. Objective. To test whether posterior dynamic stabilization in situ with Dynesys (Zimmer Spine, Minneapolis, MN) can maintain enough stability to prevent progression of spondylolisthesis in long-term follow-up. Summary of Background Data. In spinal stenosis with degenerative spondylolisthesis, decompression and fusion are widely recommended. However, drawbacks of fusion remain length of surgery, blood loss, possible adjacent segment disease, errant instrumentation, nonunion, and pain at the bone donor site. The Dynesys system was introduced to stabilize the spine without adding bone graft for fusion. Excellent 2 years results have been reported. Methods. Twenty-six consecutive patients (mean age, 71 years) with symptomatic lumbar spinal stenosis and degenerative spondylolisthesis underwent interlaminar decompression and stabilization with Dynesys. Patients were evaluated clinically and radiologically after a minimum follow-up of 4 years. Results. Nineteen of 26 patients could be evaluated with a mean follow-up of 52 months (range, 48 57 months). Pain on VAS and walking distance improved significantly (P 0.001) at 2 years and remained unchanged at 4 years followup. Radiographically, spondylolisthesis did not progress and the motion segments remained stable, even in the 3 patients who showed slight screw-loosening at 2 and 4 years follow-up. One patient showed screw breakage with low back pain and motion at the instrumented level in flexion/extension views. At 4 years follow-up, 47% of the patients showed some degeneration at adjacent levels. Overall, patient satisfaction remained high as 95% would undergo the same procedure again. Conclusion. In elderly patients with spinal stenosis and degenerative spondylolisthesis, decompression and dynamic stabilization lead to excellent clinical and radiologic results. It maintains enough stability to prevent progression of spondylolisthesis. Because no bone grafting is necessary, donor site morbidity, which is one of the main drawbacks of fusion is eliminated. However, the From the *Center for Musculoskeletal Diseases/Spine, University Hospital, Basel, Switzerland; and Clinic of Orthopedic Surgery, Kantonsspital, St. Gallen, Switzerland. Acknowledgment date: September 19, 2007. Revision date: January 17, 2008. Acceptance date: March 12, 2008. The device(s)/drug(s) that is/are the subject of this manuscript is/are being evaluated as part of an ongoing FDA-approved investigational protocol (IDE) or corresponding national protocol to stabilize the lumbar motion segment in degenerative spondylolisthesis without adding bone graft for fusion. No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Stefan Schaeren, MD, Center for Musculoskeletal Diseases/Spine, University Hospital, Spitalstrasse 21, CH-4031 Basel, Switzerland; E-mail: sschaeren@uhbs.ch degenerative disease still is progressive and degeneration at adjacent motion segments remains a problem. Key words: spinal stenosis, degenerative spondylolisthesis, dynamic stabilization, dynesys, decompression. Spine 2008;33:E636 E642 Degenerative lumbar spondylolisthesis can be encountered in the degeneration of the lumbar motion segment. 1 Typically, it causes spinal stenosis leading to neurogenic claudication or pain in the buttock, thigh, and leg. 2 Surgery is indicated if conservative treatment fails and quality of life is progressively impaired. 3,4 The classic surgical treatment is decompression to relieve radicular symptoms and neurogenic claudication. 5 7 Fusion is added to prevent progression of spondylolisthesis. Several studies showed that decompression and fusion significantly improved patient outcome compared with decompression alone. 8 12 The value of instrumentation is still a matter of debate. 13,14 Instrumentation improves fusion rate. 15 In short-term follow-up no difference between noninstrumented and instrumented fusion could be demonstrated. 16 However, good results in noninstrumented fusion deteriorate over time due to the higher nonunion rate. 17 The benefit of instrumentation and fusion comes with the price of higher complication rate because of the bigger and longer surgery, significant donor site morbidity, and accelerated degeneration of adjacent segments. 18 20 Dynamic stabilization has been introduced in 1994 as a motion preserving device in an attempt to overcome the disadvantages of fusion and provide sufficient stability to restore normal segmental kinematics, prevent instability, and avoid adjacent segment degeneration. 21,22 In the few existing studies, dynamic stabilization was used for various indications and results were contradictory not allowing to conclude if dynamic stabilization can meet the high expectations. 23 25 We conducted a prospective study to investigate the role of dynamic stabilization in the surgical treatment of single level degenerative spondylolisthesis. Two years results reported earlier were promising. 26 The most important advantage of dynamic stabilization compared with fusion with or without instrumentation appeared to be that there is no donor site morbidity. We performed the current study to answer the question whether dynamic stabilization in situ with the Dynesys System (Zimmer Spine, Minneapolis, MN) without bone grafting provides enough stability to maintain sig- E636

Dynesys in Degenerative Spondylolisthesis Schaeren et al E637 nificant clinical improvement and prevent progression of spondylolisthesis in a long-term follow-up. To our knowledge, there are no articles that examine the surgical results of dynamic stabilization at a minimum 4 years follow-up. Materials and Methods Between November 1999 and November 2000, a total of 26 consecutive patients were selected for the current study. Inclusion criteria were symptomatic lumbar spinal stenosis associated with degenerative spondylolisthesis grade I and II at a single level unresponsive to adequate trial of nonoperative treatment. Patients with lytic spondylolisthesis, patients with degenerative spondylolisthesis of more than 1 level and patients with prior lumbar fusion were excluded. Informed written consent was obtained from each participant. All patients suffered from spinal claudication with leg pain with or without back or buttock pain. All patients underwent preoperative functional myelography and/or magnetic resonance imaging. In all patients decompression was performed and the olisthetic segment was stabilized in situ with Dynesys (Zimmer Spine, Minneapolis, MN) without adding any bone grafting material. Operative Technique Patients were operated under general anesthesia in prone position. Decompression of the stenotic levels was performed through a midline open approach removing the supraspinal and interspinal ligament as well as the ligamentum flavum. The dura was exposed and a laminotomy was carried out as far as needed to achieve proper decompression of the spinal canal itself. In no case a laminectomy was necessary and the bony continuity of the lamina from left to right was always preserved. Most of the decompression was performed by undercutting the lamina and the articular masses. Usually, the medial part of the facet joints was removed up to the pedicles to decompress the lateral recess. If needed, foraminotomy was performed as well without resecting the isthmus. After adequate decompression, Dynesys pedicle screws were introduced under fluoroscopic control. The olisthetic segment was slightly distracted and the Dynesys system was placed under compression as described by Dubois et al. 21 No attempt was made to reduce the spondylolisthesis. All patients were allowed to get up the first day after surgery and wore a lumbar orthosis for 12 weeks. After 3 months, patients were allowed to return to their normal activities without restriction. Clinical Outcome Measures The patients were reviewed after a minimum follow-up of 4 years by an independent surgeon (I.B.) The following data were collected and compared with preoperative and 2 years follow-up data: location of pain, intensity of pain according to the VAS 0 to100, neurologic symptoms, walking distance, fingertoe distance to assess lumbar mobility, pain medication, complications caused by the operation, subsequent spinal surgery, occupation, and activity status according to the Prolo Economic Scale. 27 The NASS Patient Satisfaction Index was used to asses treatment satisfaction: patients were asked would you have the same treatment again for the same outcome? and they could answer: definitely yes, probably yes, not sure, probably not, or definitely not. 28 Radiologic Outcome Measures Plain radiographs (AP and lateral standing) and functional radiographs with flexion and extension views were obtained. On plain radiographs, the following variables were measured: spondylolisthesis (%), the segmental angle, and the anterior and posterior disc height. On flexion-extension radiographs, the segmental angle of the stabilized segment was measured according to Cobb. In addition, any anterior or posterior translation was noted to detect instability. Changes of more than 5 or 3 mm were stated as significant. 29 Implant failure, such as screw loosening or breakage, was noted. Finally, degenerative changes at adjacent levels were evaluated. Four years results were compared with preoperative, postoperative, and 2-year follow-up data. Statistical Evaluation The clinical and radiologic results were analyzed using Student t test and Pearson correlation coefficient (r). Statistical significance was accepted at 0.5. All analyses were carried out with SPSS 13.0 (SPSS, Inc., Chicago, IL). Results Preoperative Data A total of 26 patients (18 females, 8 males) with a mean age of 71 years (range, 47 87 years) were included. On average, patients had symptoms for 35 months (range, 2 180 months) with a mean pain of 80 on the VAS Scale (range, 55 100). Eighteen patients (69%) were on pain medication, 6 (23%) of these needed opiates. The mean walking distance was 250 m (range, 10 2000 m). Three patients had a spine operation before (2 decompressions, 1 discectomy). One patient suffered from multiple sclerosis (MS) and had a gait disorder with a strong left sided limping. Nine patients (35%) had diffuse paresthesia at 1 or both legs. All patients had a radiologic spinal stenosis as seen in the magnetic resonance imaging and/or myelography. Twenty-two patients (85%) had degenerative spondylolisthesis at the L4/L5 level, 4 patients (15%) at L3/4. The mean value of spondylolisthesis measured 16% (range, 5% 29%). Mean segmental motion on flexion/extension views was 11 (range, 5 18 ). Perioperative Data The perioperative data were reported with the 2 years results. 26 Mean surgery time was 137 minutes (range, 90 210 minutes.). Mean blood loss was 415 cc (range, 100 700 cc). Dural tears occurred in 3 patients (12%). They were sutured and healed without sequelae. One patient (no. 18) had to be reoperated after 2 weeks because of insufficient decompression. Clinical Follow-up A total of 19 patients (73%) could be evaluated after 4 years, 14 women and 5 men (Table 1). There were 7 patients who had to be excluded: 1 patient (no. 13) died because of an unrelated pathology, 1 patient (no. 6) moved out of the country, 1 patient (no. 1) suffered from severe chronic obstructive pulmonary disease being bedridden at the time of the follow-up, 1 patient (no. 5)

E638 Spine Volume 33 Number 18 2008 Table 1. List of Patients 4-yr Follow-up Data Patient Age (yr) Gender Stabilized Level Preoperative Walking Distance (m) Complications Lost to Follow-up Walking Distance (m) Implant Failure/Stability Adjacent Segment Degeneration 1 71 Male L3/4 100 Dural tear Severe pulmonary disease 2 76 Male L4/5 200 5000 Screw loosening, stable 3 79 Female L4/5 80 5000 Stable 4 47 Female L4/5 300 5000 Screw loosening, stable 5 87 Female L4/5 50 Dementia 6 56 Male L4/5 50 Moved out of country 7 76 Female L4/5 15 200 Stable 8 71 Female L4/5 500 Osteoporotic fracture of L4 at 18 mo; fusion L3/L5 9 74 Male L3/4 150 300 Stable 10 52 Female L4/5 100 100 Screw breakage, unstable 11 76 Male L4/5 100 900 Stable 12 76 Female L4/5 2000 Osteoporotic fracture of L5 at 30 mo; fusion L4/S1 13 81 Female L4/5 NA Death caused by unrelated pathology 14 69 Male L4/5 10 5000 Stable 15 77 Male L4/5 500 1000 Screw loosening, stable 16 73 Female L4/5 50 1000 Stable 17 78 Female L3/4 10 Dural tear 600 Stable 18 71 Female L4/5 100 NA Stable 19 72 Female L4/5 40 700 Stable 20 65 Male L4/5 500 Reoperation due to adjacent level instability at 24 mo 21 52 Female L4/5 500 1000 Stable 22 58 Female L4/5 20 1000 Stable 23 84 Female L4/5 100 250 Stable 24 73 Female L3/4 50 1000 Stable 25 73 Female L4/5 500 1000 Stable 26 73 Female L4/5 100 Dural tear 700 Stable NA indicates not applicable. developed severe dementia and was in a nursing home and 3 patients had subsequent lumbar surgery. Patient no. 8 had an osteoporotic fracture of the upper endplate of L4 because of a fall 18 months after surgery. Dynesys at L4/5 was removed and instrumented fusion L3/L5 was performed. Patient no. 12 also suffered an osteoporotic fracture of the lower endplate of L5 30 months after surgery. She was treated with removal of Dynesys at L4/5 and instrumented fusion L4/S1. Patient no. 20 developed instability at the adjacent level L3/4 24 months after surgery and was subsequently stabilized. Mean follow-up was 52 months (range, 48 57 months). Mean pain on VAS Scale decreased significantly from 80 to 25 (range, 0 80) (P 0.001). Mean walking distance improved significantly from 250 to 1000 m (range, 100 to infinite) (P 0.003). Patient no. 10 with a walking distance of 100 m suffered from MS and was still limited by her limping gait. Mean finger-toe distance was 9.8 cm (range, 0 40 cm). There were 16 patients (84%) who had no more claudication (P 0.001), and 6 of them (32%) were completely free of back and leg pain whereas 11 patients (58%) had intermittent back pain. Three patients (16%) still suffered from some claudication, but only one of them had no benefit from the operation at all. Fourteen patients (68%) did not use pain medication any more (P 0.002), 6 patients needed nonsteroidal antiinflammatory drugs and no patient was in need of opiates. According to the Prolo Economic Scale 8 patients (42%) were more active than before the onset of their symptoms and 6 patients (32%) were active at their pre-

Dynesys in Degenerative Spondylolisthesis Schaeren et al E639 Figure 1. A 69-year-old man (no. 14) presented with neurogenic claudication. Lateral lumbar myelography shows degenerative spondylolisthesis at L4/5 with compression of the dural sack (A). He was treated by decompression and dynamic stabilization at L4/5. Two years postoperative lateral view demonstrates stable implants and no progression of spondylolisthesis but narrowing of disc space at L3/4 without clinical symptoms (B). At 4 years follow-up lateral radiograph shows stable situation at L4/5 and progressive degeneration at L3/4 (C). Clinically the patient had some minor back pain not requiring treatment. vious level without restriction. There were 3 patients (16%) who stated their activity was at their previous level with limitation and 2 patients (11%) were active but not at premorbid level. There were 15 patients (79%) who would definitely and 3 (16%) who would probably undergo the same operative procedure again. The patient suffering from MS stated that she would probably not undergo the same operation again because her walking distance had not improved. Radiologic Follow-up Plain and flexion-extension radiographs of 19 patients could be obtained at the 4 years follow-up. Overall postoperative progression of spondylolisthesis measured 0.5% (with a maximum of 3%) and was not significant (P 0.43). Implant failure was seen in 4 patients (21%). There were 3 screws in 3 patients (no. 2, 4, 15) showing radiolucent lines in terms of possible loosening without radiologic instability. The patient (no. 10) with MS had obvious screw loosening and a screw breakage. This patient showed translation of more than 3 mm and an angular motion of 10 during flexion/extension. These 4 cases were already recorded at 2 years follow-up. No radiologic changes between 2 and 4 years were observed and no new case of implant failure occurred. Neither screw breakage (r 0.268, P 0.267) nor loosening (r 0.037, P 0.884) was related to patient s satisfaction or back pain. The average height of anterior intervertebral discs was not significantly increased from preoperative 5.9 to postoperative 6.4 mm (P 0.07) whereas the height of posterior intervertebral discs was significantly increased from 2.9 to 3.5 mm (P 0.02). At the 2-year follow-up anterior and posterior disc height had significantly decreased to preoperative values (P 0.02 and 0.05). From 2 to 4 years anterior and posterior disc height showed no significant alteration (P 0.2 and 0.7). The average segmental angle was reduced from 19.7 before surgery to 17.7 at the 2 years follow-up (P 0.72) to 15.9 at 4 years (P 0.001). Mean segmental motion of the instrumented segment on flexion/ extension views was 3 (range, 0 10 ). Three patients had more than 5 and therefore were considered to show mobility at the instrumented level. One of them was associated with the screw breakage afore mentioned above, and the other 2 had stable implants. Segmental motion at follow-up did not correlate with preoperative values (r 0.29, P 0.46). The average anterior or posterior vertebral slip of the stabilized segment was 0.4 mm (range, 0 2 mm). At the 4 years follow-up 9 of 19 patients (47%, P 0.004) showed new signs of degeneration at the adjacent motion segment (Figure 1). Eight patients (42%) had degeneration at the level above and 1 (5%) at the level below. Furthermore progressive degeneration at the level next to the adjacent segment was seen in 8 patients (P 0.002) (Figure 2). Discussion Our 4-year results demonstrate that the combination of decompression and dynamic stabilization for the treatment of lumbar spinal stenosis in the presence of degenerative spondylolisthesis gives long lasting clinical improvement. The excellent clinical results after 2 years reported earlier remained stable. 26 Clinical Follow-up Pain and the use of pain medication were still significantly reduced, walking distance and neurologic symptoms significantly improved. At 4 years follow-up 74% of the patients had either maintained or even increased their daily activity level compared with preoperative. Patient satisfaction remained high as 95% would undergo the same operative procedure for the same condition again.

E640 Spine Volume 33 Number 18 2008 Figure 2. The postoperative AP and lateral control in a 72-year-old woman (no. 19) with neurogenic claudication show dynamic stabilization at L4/5 (A and B). The AP and lateral radiographs at 4 years follow-up depict stable implants at L4/5, clear loss of disc height at L2/3, 2 levels above dynamic stabilization and minimal loss at the adjacent level (C and D). Clinically the patient was asymptomatic. A review of the literature on dynamic stabilization reveals contradictory results. Stoll et al 25 investigated the use of dynamic stabilization in 83 patients with various forms of lumbar instability and showed significant improvement in pain scale and Oswestry disability index. Grob et al 23 reported less favorable 2 years results and a high reoperation rate in 50 consecutive patients with different indications. Only half of the patients declared that the operation had helped and had improved their overall quality of life. In a comparative study between dynamic stabilization and anterior-posterior fusion for the treatment of degenerative instability Cakir et al 24 described similar results for both groups after 1 year. Surgical indications for dynamic stabilization have been poorly defined. Thus, no definitive conclusion can be drawn from these studies. In contrast, the current study clearly defined degenerative spondylolisthesis as surgical indication for dynamic stabilization. Our data match favorably with the results of decompression and instrumented fusion published in the literature. In a retrospective study, Nork et al 11 used the SF-36 survey and a functional questionnaire to assess patient satisfaction and found a 93% satisfaction rate at an average follow-up of 37 months. Booth et al 30 reported an 83% satisfaction rate after a minimum follow-up of 5 years; 77% of patients would have undergone the same procedure again. Better clinical outcome has been reported in the longterm follow-up with instrumentation over noninstrumented fusion because of the higher incidence of nonunion in the latter group. Kornblum et al 17 showed that at 5 to 14 years of follow-up clinical outcome was good or excellent in 86% of patients with successful fusion and in 56% of patients with a nonunion. The difference was significant. Therefore they recommended instrumentation to achieve a better fusion rate and long-term outcome. Our data indicate that Dynesys provides enough stability even without fusion to maintain clinical improvement over time. Radiologic Follow-up The radiologic results show that dynamic stabilization may maintain enough stability to prevent instability or further translation of the slipped vertebra without fusion. Neither spondylolisthesis nor vertebral slip significantly changed during follow-up time. To our knowledge, no comparable long-term data for Dynesys are available in the current literature. Results with Graf ligamentoplasty are contradictory. Guigui and Chopin 31 reported destabilization of the operated segment in 27% of 26 patients at 29 month follow-up. In a retrospective study, Kanayama et al 32 reviewed 64 patients with Graf artificial ligament stabilization for degenerative spondylolisthesis at a mean follow-up period of 67 months. They found that the Graf system did not improve the vertebral slip but maintained lordosis and preserved segmental motion in 80%. Implant Failure. Screw loosening in 3 patients observed after 2 years remained radiologically unchanged not showing any instability at the last follow-up. Moreover no new case of screw loosening was detected between 2-year and 4-year follow-up. Clinically 2 of these patients were asymptomatic and one had some back pain. No patient had to be reoperated. Stoll et al 25 reported screw loosening in 8 of 73 patients (11%) with Dynesys

Dynesys in Degenerative Spondylolisthesis Schaeren et al E641 occurring mostly within the first 6 months and none later than 1 year after surgery. We saw 1 instability because of a screw breakage in a patient with MS and abnormal gait at 2 years. No other instabilities were documented. Radiologically, the broken screw and the instability remained unchanged. One verified instability in 19 patients corresponds to a nonunion rate of 5%. This is a very low figure if compared with the nonunion rate seen after fusion surgeries with autologous bone graft. 17,33 Overall our results suggest that dynamic stabilization can stabilize the olisthetic segment sufficiently. This corroborates the data of biomechanical studies of Schmoelz et al 34 who investigated the behavior of Dynesys compared with a rigid pedicle system. The authors concluded that Dynesys provides substantial stability in cases of degenerative spinal pathologies and can therefore be considered as an alternative method to fusion surgery. Motion Preservation and Adjacent Level Degeneration. Some authors have mentioned that a dynamic stabilization system preserves motion at the stabilized level and prevents degeneration of the adjacent segment. 25,35 At follow-up, some motion (more than 5 ) was preserved at the stabilized segment in 2 patients. In the other patients, however, no measurable motion was seen (except in the patient with 1 broken screw). Furthermore, we found new signs of degeneration adjacent to the stabilized segment in 9 patients (47%) after 4 years. The rate of degeneration at adjacent motion segments is similar to the rate seen after fusions. 36 Booth et al reported transition zone syndrome in 12 of 41 (29%) patients after 5 years. Rahm and Hall 36 described adjacent segment degeneration in 35% of 49 patients after instrumented lumbar fusion. We also observed progressive degeneration at the second level above dynamic stabilization in 8 patients (42%). Several authors also report degeneration at the second level above lumbar fusion with a frequency at least equal to that at the first level. 37,38 Our data show that dynamic stabilization cannot prevent adjacent segment degeneration either. This may be due to the high intrinsic stability 34,39 of the system which probably acts similarly to a rigid pedicle screw system and can overload the adjacent motion segments. Not all authors share the theory of adjacent segment degeneration. In a recent prospective study after instrumented posterior lumbar fusion Pellise et al 40 found that disc degeneration appeared homogeneously at several levels cephalad to fusion and seemed to be more determined by individual characteristics than by fusion itself. Considering the relatively high average age of 71 years in our patients, we feel it ultimately remains unclear whether adjacent segment degeneration is due to dynamic stabilization or merely a consequence of the natural aging process. Reoperations. During the follow-up period 4 (12%) of the initial 26 patients had reoperations. There was no reoperation because of implant-related complications at the instrumented level. One patient required early revision because of insufficient decompression and 2 patients suffered osteoporotic fractures after falls, which had to be stabilized. However, only 1 patient (4%) needed revision because of adjacent segment instability. In a 10- year cost-effectiveness analysis of fusion with and without instrumentation Kuntz et al 41 reported a reoperation rate of 2.3% per year. Booth et al 30 showed 12% revisions because of transition zone syndrome after 5 years. We cannot exclude that the 2 osteoporotic fractures and the 1 instability at an adjacent level are related to the increased rigidity provided by the Dynesys system and consequently are possible failures of the technique. However, with a rigid system the risk for fracture or instability would even have been higher as in a biomechanical study the Dynesys System was shown to be more flexible than a rigid pedicle system. 34 Limitations Our data are restricted by the small number of patients and by the fact that it is not a comparative study. However, the surgical indication for the use of dynamic stabilization is clearly defined. Generalizablity of our data may also be limited by the relatively high average age in our patients. Therefore results in terms of implant failure cannot be transferred to younger and more active patients. However, degenerative spondylolisthesis typically occurs in patients older than 50 years, as represented in our study. Conclusion The results of our long-term study are encouraging. In elderly patients with spinal stenosis and degenerative spondylolisthesis, decompression and dynamic stabilization can maintain clinical improvement and radiologic stability over time. Dynamic stabilization therefore can be advocated as an effective alternative to fusion. Because of no fusion bed has to be prepared and no bone grafting is necessary, dynamic stabilization is less invasive and eliminates donor site morbidity. Dynamic stabilization, however, neither preserves motion at the instrumented level in most of the patients nor does it prevent from degeneration at adjacent motion segments. Key Points At 52-month follow-up, dynamic stabilization for degenerative spondylolisthesis with spinal stenosis maintains clinical improvement and radiologic stability. The long-term results of dynamic stabilization in degenerative spondylolisthesis are similar to instrumented fusion reported in the literature. Stabilization with Dynesys seems to be less invasive than fusion, because donor site morbidity is avoided.

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