Spine Research

Keywords

Coflex; Lumbar spinal stenosis; Fusion; Intervertebral height; Adjacent segment degeneration

Introduction

Lumbar spinal stenosis (LSS), one of the most common spinal disorders in the elderly, often results in low back pain, neurogenic claudication, and significant disability and impaired quality of life due to narrowing of the spinal canal and the pressure on nerves [1]. According to the literature, the incidence of LSS is as many as 38.8% of adults 60 years and older in the United States [2]. Traditionally, decompression with fusion and internal fixation has been the mainstay of surgical approaches to the management of symptomatic LSS [3-6]. However, some authors reported that it may be related to other problems such as serious trauma, transfusion requirement, pseudarthrosis as well as higher morbidity and mortality for elderly patients [7-10], especially adjacent segment degeneration [11-17]. In order to overcome these deficiencies associated with fusion surgery, an interspinous process device-Coflex system (Paradigm Spine, LLC, New York) was developed as a possible alternative to spinal decompression with posterolateral fusion and instrumentation [18-20]. Although the encouraging results of Coflex have been widely reported in the past a few years [21-24], there is still controversy of the long-term benefit of this procedure. High complication such as prosthesis loosening and spinous process fracture, reoperation rate, and costs with poor outcomes were also mentioned in the literature [25-27]. Is the interspinous Device-Coflex outdated in the treatment of LSS? The purpose of the present study is to evaluate whether Coflex implantation following spinal decompression provided better clinical outcomes compared with traditional decompression with pedicle screws fixation and fusion for symptomatic lumbar spinal stenosis through mid-term follow-up.

Materials and Methods

Clinical data

A prospective cohort study was conducted in our institute between June 2007 and June 2010. 100 consecutive patients with symptomatic degenerative LSS at L4/5 were recruited in the study. They were randomly divided into 2 groups: 50 patients were placed in the study group who were offered spinal decompression with Coflex implantation at the affected level, while 50 patients were placed in the comparison group who were treated decompression with pedicle screws fixation and interbody fusion. There were 29 males and 21 females with an average age of 57.6 ± 5.9 years (range, 48-70 years) in Coflex group. The ratio of males to females was 28:22 with an average age of 59.0 ± 6.7 years (range, 50-73 years) in fusion group. The preoperative data in the two groups is illustrated in Table 1.

Table 1: The general data of the present study.

Inclusion criteria: (1) Symptomatic LSS with obvious low back pain, intermittent claudication, or sciatica. (2) After 3 months’ conservative treatment still invalid. (3) Imaging examination confirmed to be LSS; (4) Affected segment (L4/5) with or without lumbar disc herniation or slight spondylolisthesis; (5) Without degeneration or instability of adjacent segments (L3/4, L5/S1).

Exclusion criteria: (1) Having a history of lumbar surgery. (2) Lumbar spine trauma, infection scoliosis, kyphosis, or ankylosing spondylitis. (3) Spondylolisthesis over II degrees or spondylolysis. (4) Adjacent segments (L3/4, L5/S1) degeneration or instability. (5) Severe osteoporosis.

Surgical technique

The Coflex group (decompression with Coflex implantation): Patients were operated under general anesthesia and in prone position. C-arm was used to determine L4/5 level before operation in everyone. A 4 cm-length-incision was chosen and paraspinal muscle separation was performed through a standard posterior midline approach in all the patients. Supraspinal Ligament was carefully separated to one side by sharp dissection. The interspinous ligament was dissected and excised. Partial laminotomy, excision of hypertrophic ligamentum flavum were performed to decompress the stenotic level with carefully protecting bilateral joint facet joints. Discectomy was also done if a herniation was confirmed. Then a suitable size Coflex was implanted at the interspinous of L4/5 after measurement as deep as possible so that the vertex of shape U was in the same line with the joint facet joints. The wings of the Coflex were clamped using the manufacturer’s forceps so that it was seated snugly. Satisfactory placement of the implant and adequate segmental sagittal alignment were ensured under C-arm image. Then the wound was closed routinely after placement of a closed suction drain.

The fusion group (decompression with pedicle screws fixation and interbody fusion): Anaesthesia and body position of the patients were the same as those of Coflex group. A posterior median incision of 4-5 cm long was chosen and paraspinal muscles were separated from the surface of spinous process and lamina, exposing both sides’ lamina and facet joints. Pedicle screws were placed in both sides of L4 and L5 under the monitoring of C-arm. Decompression was performed by bilateral laminectomy and hypertrophic ligamentum flavum resection, as well as enlargement of nerve root canal. After insertion of a cage with allograft bone, two rods were installed. A closed suction drain was placed routinely before the wound was closed.

Postoperative care

All the patients in both groups received similar postoperative care. They were allowed to ambulate as tolerated from the next postoperative day. Early return to activities was encouraged after surgery. The drainage was pulled out after 48 hours postoperative and the flow rate was less than 30 ml.

Clinical outcome assessment

Clinical outcome scores were assessed preoperative and at the last follow-up postoperative using the Japanese Orthopaedic Association (JOA) score, Oswestry disability index (ODI), 100 mm visual analogue scale (VAS) back pain and leg pain, and short form- 36 (SF-36). Operation time, intraoperative blood loss, ambulation time, and hospitalization days were also compared between the two groups. Complications were statistics and analysis in the two groups, respectively.

Radiological assessment

All the patients underwent lumbar spine radiographs including standardized, erect antero-posterior (AP), lateral, dynamic (hyperextension and flexion lateral) position and magnetic resonance imaging (MRI) examination preoperative and postoperative. The observer, who did not participate in surgeries, took all the measurements using the Carestream PACS system (Ver. 11.0, Carestream Health, Inc., Rochester, New York, 2008). Disc height was calculated by taking the mean of the anterior and poste rior disc heights at the level in question. Anterior disc height was calculated as the distance between the anterior inferior corner of the upper vertebral body and the an terior superior corner of the lower vertebral body. Like wise, posterior disc height was calculated as the distance between the posterior inferior corner of the upper verte bral body and the posterior superior corner of the lower vertebral body (Figure 1). Disc height loss was calculated by the difference between preoperative and the last follow-up postoperative disc heights. Sagittal angle was measured by determining the angle subtended between the lines drawn parallel to the inferior endplate of the cephalad vertebra and the superior endplate of the caudad vertebra. Intervertebral range of motion (ROM) was calculated by the difference between hyperextension and flexion sagittal angles (Figure 2). Increment of intervertebral ROM was calculated by the difference between the last follow-up postoperative and preoperative intervertebral ROMs. Intervertebral disc degeneration at L3/4 level and L5/ S1 level was also evaluated by Pfirrmann Classification [28] preoperative and at the last follow-up postoperative based on MRI.

Figure 1: Anterior disc height (ADH): The distance between the anterior inferior corner of the upper vertebral body and the an terior superior corner of the lower vertebral body. Posterior disc height (PDH): the distance between the posterior inferior corner of the upper verte bral body and the posterior superior corner of the lower vertebral body.

Figure 2: Sagittal angle: The angle between the lines drawn parallel to the inferior endplate of the cephalad vertebra and the superior endplate of the caudad vertebra.

Statistical analysis

Statistical analysis was performed using SPSS soft package (Ver. 16.0, SPSS Inc., Chicago, IL, USA). One-way ANOWA was performed to compare operation time, intraoperative blood loss, ambulation time and hospitalized days between the two groups. A paired t-test was performed to compare the last follow-up JOA, ODI, VAS (back pain and leg pain), and SF-36 scores with the respective preop erative scores in both groups. Student- Newman-Keuls (SNK) technique was used to adjust for multiple comparisons. Mixed model analysis was performed to compare the improvement in JOA, ODI, VAS-back pain and leg pain, and SF- 36 scores between Coflex group and fusion group. Preoperative and postopera tive radiological measurements including disc height loss and increment of intervertebral ROM were compared within the two groups by using repeated measures ANOVA. SNK technique was used to adjust for multiple comparisons. Chi square test was used to compare the difference of Pfirrmann grade changes and complication rates between Coflex group and fusion group. A p-value of <0.05 was considered as statistically significant.

Results

Clinical outcome assessment

All patients in the two groups were followed up. The average follow-up period was 7.02 ± 0.34 years in Coflex group and 7.62 ± 0.18 years in fusion group, respectively. There was no statistically significant difference between the two groups (P>0.05). The operation time, intraoperative blood loss, ambulation time and hospitalization days in the two groups are illustrated in Table 2. There were statistically significant differences between the two groups (P<0.01).

Table 2: The comparisons of the operation times, intraoperative blood loss, ambulation time, and inpatient days.

Clinical outcome scores

The clinical outcome scores are illustrated in Table 3. The mean JOA, ODI, VAS-leg pain, VAS-back pain and SF-36 scores in both Coflex group and fusion group showed significant improvement at the last follow-up as compared with preoperative scores (p<0.001). However, there were no statistically significant differences between Coflex group and fusion group in the mean improvement in JOA score (p=0.317), ODI score (p=0.159), VASleg pain score (p=0.295), VAS-back pain score (p=0.276), and SF- 36 score (p=0.603).

Table 3: The clinical outcomes scores of JOA, ODI, VAS and SF-36.

Radiological measurements

The mean height of adjacent segment disc was decrease in both Coflex group and fusion groups postoperatively. The mean height loss was 1.78 ± 0.70 mm at L3/4 level and 1.48 ± 0.38 mm at L5/ S1 level in Coflex group, while the mean height loss was 4.30 ± 0.87 mm at L3/4 level and 2.69 ± 0.49 mm at L5/S1 level in fusion group (Table 4). There was statistically significant difference between the two groups (P<0.01). The adjacent segment disc activities were increased in both Coflex group and fusion group. The mean sagittal angle showed an overall increase of 3.05 ± 1.30 degrees at L3/4 level and 3.04 ± 1.24 degrees at L5/S1 level in Coflex group. There was also a significant sagittal angle increase of 4.03 ± 0.34 degrees at L3/4 level and 4.01 ± 0.33 degrees at L5/S1 level in fusion group. There was statistically significant difference between the two groups (P<0.01) (Table 4).

Table 4: Radiological measurements of disc height decrease (mm) and adjacent segments ROM increment (degree).

At the last follow-up, the upper and lower adjacent segment degeneration was evaluated using Pfirrmann grading system in both Coflex group and fusion group (Table 5). There were 7 patients progressed to grade IV from grade II or grade III at L3/4 level, 11 patients progressed to grade IV and one patient progressed to grade V at L5/S1 level in Coflex group. There were 15 patients progressed to grade IV at L3/4 level, 19 patients progressed to grade IV and 6 patients progressed to grade V at L5/S1 level in fusion group. There were statistically significant differences between the two groups at L3/4 level (p=0.019<0.05) and L5/S1 level (p=0.008<0.05), respectively.

Table 5: Adjacent intervertebral disc degeneration according to Pfirrmann grading system.

Complications

Surgical complications were found 4 cases (8%) in Coflex group and 3 patients (6%) in fusion group, respectively. The incidence of complications was no statistically significant deferent between the two group (p=0.695). In Coflex group, there were two patients with spinous process fracture on L4, one patient with L4/5 recurrent stenosis and disc herniation, one patient with symptomatic L5/S1 disc herniation. Revision was performed on three patients with pedicle screws fixation and transforaminal interbody fusion except the one who was confirmed L4 spinous process fracture 6 months after surgery because of low back pain. After 3 months conservative therapy, the patient felt no longer pain and the radiological examination showed the fracture healed. During the follow-up period, there were still another 6 patients who were confirmed partial bone absorption of L4 spinous process, including 4 patients with Coflex loosening and slightly displacement. Nevertheless, observing without any treatment for the 6 patients because of no complaints at all. In fusion group, two patients were conformed to adjacent segment disease (ASD) at L3/4 level and one patient was occurred disc herniation and spinal stenosis at L5/S1 level. All the three patients underwent secondary revision surgery.

Discussion

Traditional decompression with posterior fusion is the primary procedure for the treatment of symptomatic LSS. The aim is to relieve clinical symptoms without considering the problem of fixed segment movement. Long-term follow-up reveals adjacent segment ROM increased to compensate for the lost ROM of the fixed segment, resulting in ASD [13-15,29-33]. Following improved knowledge of lumbar motion function, surgeons now consider how to treat lumbar degenerative disease while maintaining ROM, and dynamic stabilization has been developed and accepted. New materials and techniques have led to the development of many non-fusion techniques and devices, such as: nucleus replacement, artificial disc, interspinous process devices, and posterior dynamic stabilization. A systematic review comparing fusion with non-fusion techniques showed that nonfusion techniques-maintained ROM at the surgical level, had less side-effect on the adjacent level than fusion [34,35].

Coflex (Paradigm Spine, LLC, New York), a kind of dynamic interspinous Device, was first introduced by the French orthopedic surgeon Jacques Samani as an alternative to fusion in 1994. Since then, the device has been used in various degenerative spinal conditions [21-24,36-38]. Although it was initially developed as a motion-preserving alternative used to treat various lumbar degenerative disorders, long-term studies from Europe suggested that the subset of patients with spinal stenosis and Grade I spondylolisthesis experienced the most significant improvement. However, high level evidence on its clinical efficacy and indications remains limited. A multicenter randomized and controlled clinical research of Coflex has been approved by FDA as an adjunct to fusion but is not approved as a stand-alone spacer in USA [21].

In the present study, we compared the clinical results between Coflex implantation and fusion after spinal decompression in treatment of symptomatic LSS. It showed that Coflex group had the same good clinical efficacy as fusion group in JOA score, ODI, VAS-leg pain, VAS-back pain, and SF-36 score. There was no statistically significant difference between the two groups. However, Coflex group had the advantages of less trauma, less intraoperative blood loss, early ambulation and shorter hospitalization days compared with fusion group. The results of the present study were consistent with those of previous researches [21-23,36-39].

Based on radiological measurements, there was statistically significant difference between Coflex group and fusion group in the height loss of adjacent segment disc at the last follow-up. It showed that the mean height loss of adjacent segment disc in fusion group was much more than that in Coflex group at both L3/4 level and L5/S1 level. There was also statistically significant difference between the two groups in adjacent segment activity increase. There was more activity increase in fusion group than that in Coflex group at both L3/4 level and L5/S1 level. The stress in adjacent segment might increase much more in fusion group than that in Coflex group, which leading to postoperative ASD. Intervertebral disc degeneration in adjacent segments was observed in both groups by Pfirrmann classification at the last follow-up. However, there was significant difference between the two groups. Adjacent segment degeneration aggravation was found more cases and sever grade in fusion group than that in Coflex group. According to the results of this study, it can be concluded that decompression with Coflex implantation may have an advantage in preventing postoperative ASD compared with decompression with fixation and fusion in the treatment of symptomatic LSS.

The overall complication rate in the present study was lower than that in other researches [25-27]. One of the possible reasons was that the patient with instability or low-grade spondylolisthesis was excluded from Coflex group. Although there was seldom reported that the application of Coflex implantation developed significant improvement in the treatment of low-grade spondylolisthesis [21], we prefer to consider that Coflex is weak at stabling the intervertebral joint and cannot prevent intervertebral instability and further slipping. Therefore, no patient with intervertebral instability or low-grade spondylolisthesis was enrolled in Coflex group.

Among 4 cases of complications in Coflex group, there were 2 cases of spinous process fractures, which were all found at L4 and in early surgeries. The reasons for spinous process fracture might be that fenestration was a little bit larger, lamina near the base of L4 spinous process resection was a little bit more, and Colex implantation was not deep enough leading the supporting force acting on L4 spinous process increased. In the following surgeries, we paid more attention on fenestration, preserving lamina near the base of L4 spinous process, and implanting Coflex as deep as possible so that the arc vertex of the shape U was in the same line with joint facet joints. No spinous process fracture case was found in the following surgeries. Nevertheless, no complication of ADS was found in Colex group.

Conclusion

Previous research reported that additional Coflex implantation was safe but not beneficial in the treatment of symptomatic LSS [25]. In the present study, we found significant clinical improvements (JOA, ODI, VAS-back, VAS-leg and SF-36 scores) in patients of both groups after surgery. Although the improvements were not significantly different between the two groups, the implantation of Coflex had the advantage of less trauma, faster recovery and better lumbar function. It may play a role in reducing adjacent segments overactivity and ASD. Appropriate fenestration and lamina near the base of spinous process preservation may reduce complication as well as improve the effectiveness. Coflex implantation may be a better choice in avoiding fusion and its associated problem in the treatment of symptomatic LSS, and fusion surgery can still be a remedy for the failure of a non-fusion surgery. The limitation of this study is that the number of cases was small and the follow-up period was not long enough. Further research is needed prior to wide application.

Acknowledgements

The authors thank other members in Department of Orthopedics in Guangdong General Hospital, Guangdong Academy of Medical Sciences, Drs. Shiqiang Zhan, Shixing Zeng, Yongxiong Huang, Shuaihao Huang, Dan Xiao, and Yuhong Ke, who participated partly in this survey. Additionally, Dr. Liangze Wang made contributions to this study in data collection and statistics.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study, formal consent is not required.

Competing and Conflicting Interests

The authors declare no conflict of interests concerning the materials and methods used in this study or the findings specified in this paper.

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