Introduction

Degenerative lumbar canal stenosis (LCS) is a dynamic pathology where symptoms increase in extension (standing and walking) and relieved in flexion (standing flexion or sitting). Standing and walking narrows the foramina and spinal canal resulting in entrapment; whereas sitting increases the area relieving entrapment. The primary level affected is L4–L5, followed by L3–L4, L5–S1, L2–L3, and L1–L2.^{5,8,11,15,32,41} Patients with no motor deficits or sphincteric troubles are generally treated conservatively for an adequate time interval up to 3 months. Failure of conservative treatment is the indication of intervention. Depending on the pathological components in the affected motion segment, surgical decompressive options include laminectomy, laminotomy, foraminotomy, micro- or interlaminar decompression. In addition, fusion may be indicated in cases where the motion segment is seen to be unstable. Turner et al. (1992) analyzed the success rate of decompressive surgery for lumbar spinal stenosis of many studies and reported a mean rate of good to excellent outcomes of 64% in the first year.^{2-4,7,12,13,17,31,38}

The concept of motion segment preservation and soft tissue preservation and the increasing number of patients with degenerative spinal disease warrant the need of new approaches and devices. As an alternative to conservative treatment and decompressive surgery, other treatments have been developed for patients suffering from LCS, including micro-techniques and many interspinous devices.^{1,3,5,6,10,14,16,20,21,23,25,29,30,35,39,42} During the surgical micro-decompression, the thickened bones and ligaments are removed, in a minimally invasive approach called microlaminectomy, re-establishing the normal diameter of the spinal canal. Advantages of the decompression / microlaminectomy procedure include that it can be done under local anaesthesia (in risk patients), standing up and walking is possible few hours after surgery, and patients can go home after 1 or 2 days.^{3,14,25,26,33,35,39,42} In case of mild to moderate stenosis, as the 'minimallest' surgery, a coflex spacer can be implanted between the spinous process in height of the spinal stenosis. Because spacers allow for minimal tissue resection, making the procedure less invasive, their application is likely to be beneficial. Coflex device between the spinous process in height of the spinal stenosis can provide biomechanical strengths and dynamic stabilization without motion segment fixation, presenting a good alternative procedure. The augmentation of decompression / microlaminectomy procedure with a Coflex spacer leads to dilatation of the neural foramen & the diameter of the spinal canal, restriction of extension, reducing the pressure in the posterior annulus and can, thus, eliminate the complaints.^{5,6,10,16,21-25,30,32,34,36,37,40,43}

This study was conducted because over 35,000 people outside the U.S. have been implanted with the coflex device. Early clinical results for the coflex, in Germany reported 86 % relief in LBP that allowed patients to significantly increase their walking distance, together with reduced post-operative disability and pain scores as compared with pre-operative scores.^10,30,43 This study is a multi-center, prospective, controlled study that compares the 1-year clinical and radiological results of lumbar minimally invasive microdecompression / microlaminectomy augmented with the implantation of the coflex device as compared to the microdecompression / microlaminectomy approach alone in treating patients with LCS. We selected patients older than 40 years of age with degenerative segmental stenosis & neurogenic claudication.

Materials And Methods

Our study is a multi centre prospective, case controlled study, done in Egypt to evaluate the 1-year results of lumbar minimally invasive microdecompression microlaminectomy alone as compared to those augmented with the implantation of the coflex device in treating patients with LCS. The Coflex implant is a functionally dynamic interspinous implant (U-shaped titanium). From June 2008 until December 2009 we included 50 patients within this study. Median follow-up was 10.5 months. At the time of follow-up all patients had questionnaires, clinical examination and x-ray taken.

Patient Selection

Patient Population

Surgical Technique

Outcomes Assessment

Clinical Outcome

Radiological Outcome & Image Interpretation

Results

From June 2008 until December 2009, 50 patients with mild to moderate spinal stenosis were treated, 22 (44%) male, 28 (56%) female. The most prevalent diagnosis for intervention was segmental stenosis. Fourty six out of 50 patients in the study had a segmental form of stenosis, (discogenic, liganentous, bony, or mixtures), four cases had mild degree of degenerative retrololisthesis. All decompression alone group cases were segmental stenosis cases. The rest of the cases, including those with mild retrolithesis, were included in the Coflex group.

Clinical Results

Complications

Radiological Results

(Fig. 5, 6, and 7)

Radiologically, there were significant differences in anterior and posterior disc height and foraminal height between the two groups. Coronal and lordotic angles were reduced postoperatively in the device group but not in the micro-decompression alone group.

The radiological results could be concluded in the following:

1. Endplate Angles: in Group (B) in neither flexion nor extension was there any difference in the change in endplate angles after the decompression. No difference was seen above, below or at single or double level procedure. Endplate Angles in Group (A) that were acute preoperatively, always become less acute postoperatively; and the foraminal height always increases.

2. Maintained Dynamic Movements: no difference was noted in the level(s) treated in both groups. In Group (A), postoperative flexion and extension views showed maintenance of the dynamic movements at the operated level.

3. Disc Height: in Group (B) no significant changes in both anterior and posterior disc heights was noted. Group (A), showed significant changes after the procedure in both anterior and posterior disc heights.

Figure 1

Fig.1: Degenerative lumbar canal stenosis (LCS) in patients older than 40 years of age with neurogenic claudication, as demonstrated by narrowing of the lumbar spine, nerve root canal, or intervertebral foramina, at one or 2 levels.

Figure 2

Fig.2: Microlaminectomy/Microdecompression. Notice that not only is the skin incision small, but the incision in the muscle is small. The thickened ligaments and the stenotic rim of the lamina are only removed (arrows), leaving the main structural components of the segment intact, not violated. (Sp = spinous process)

Figure 3

Fig.3: Microlaminectomy/Microdecompression alone (A), Augmentation with interspinous Coflex device (B). Notice the distraction effect, the interlaminar, interspinous orientation of the device.

Figure 4

Fig.4: Minimally deviated coflex (A, B), posttraumatic, indicated the need for revision. The double level coflex devices removed due to traumatic fracture of the intervening spinous process. He needed no further management. Notice the dynamic deviation upon flexion and extension.

Figure 5

Fig.5: Microlaminectomy/Microdecompression as evidenced by postoperative x-rays (A1, A2, B2). Notice the decompressed foramen by the microprocedure (C3). However, unilateral disc space collapse (B1) and the end plate angel (C4) are not corrected.

Figure 6

Fig.6: Microlaminectomy augmented with Coflex as evidenced by postoperative x-rays. Notice the unilateral disc space collapse (A, B), the foraminal height and the end plate angels (C, D) are corrected.

Figure 7

Fig.7: The concept of motion segment preservation seen with microlaminectomy augmented with Coflex as evidenced by postoperative dynamic x-rays. Notice the maintained dynamic motion in flexion and extension, in both the disc space and the implant.

Discussion

Important questions to be answered rose from our previous preliminary study, done to assess the safety and effectiveness of Coflex® Dynamic Interlaminar-Interspinous Distraction Stabilization (DIDS) device (Paradigm Spine GmbH, Germany) (28). Our previous study was treating patients with degenerative diseases of the lumbar spine (DDLS), especially lumbar canal stenosis (LCS), to confirm indications for Coflex implantation, and to evaluate the short-term clinical outcomes of patients. The first inquiry was about the reported benefits and improvements, is it secondary to the decompression done or to the spacer implanted? The second inquiry was about declaration of the real benefits of the Coflex device over decompression alone.

Lumbar posterior decompressive surgery has many ways and different techniques, including formal wide laminectomy, laminotomy, partial laminectomy, hemilaminectomy, and interlaminar approaches.^{2-4,12-14,17,19,25,31,38,42} Lumbar canal stenosis is frequently accompanied by multilevel affection and concomitant disc problems. Moreover, traditional decompressive surgery does not always eliminate the patient's pain. We all know the incidence and the big problem of failed back syndrome. Moreover, iatrogenic instability 2ry to the invasive decompression may warrant a more aggressive fixation procedure and, as many authors have indicated, rigid fusion may have a chance of adjacent joints & segment degeneration, ending in an endless circle of pathological dynamic events causing more pain and disability.^7,13,27 That led us to the choice of micro-laminectomy as the decompressive procedure to be studied, sticking to the minimally invasive phenomenon we believe in.

MICRO-LAMINECTOMY: is a newer and preferred way of doing a lumbar decompression in mild to moderate stenosis, and in segmental discogenic stenosis. Micro-laminectomy accomplishes the same goal as traditional laminectomy, in properly selected cases. The herniated disc can still be removed from underneath the nerve root and decompression is done and patient's symptoms are relieved. The differences between a micro-laminectomy and traditional laminectomy include the size of the incision and the muscle separation required. Moreover, the amount of bony work done is minimal; leaving a functionally decompressed, near normal bony and joint anatomy, and at times, even ligament preserving microdecompression. A micro-laminectomy on a thin patient can usually be done with a 3 cm incision. With micro-laminectomy, postoperative recovery is generally much quicker. The statement that says “a very small back incision equals a much quicker recovery time” is a real fact. Postoperative pain is substantially less and recovery is dramatically quicker than with traditional lumbar laminectomy. Most people are up walking on the day of surgery and are back to light office work within one week. Micro-laminectomy may be done as an outpatient, or a one-day admission procedure. Micro-laminectomy is the safest and best way to obtain relief of discogenic and stenotic pain symptoms, in a minimally invasive way.^26,33,35,39

It is a fact that the success rate for micro-laminectomy and traditional laminectomy are the same. Generally, the success rate for one level herniation is over 95% in obtaining relief of most leg pain and associated symptoms. Avoiding the major mechanical sequelae of formal laminectomy, still small percentage of individuals does not improve substantially following micro-laminectomy. Katz et al, have noted deterioration of the early results of decompressive surgery over time. In Katz’s series, 17% of patients ultimately underwent a second procedure for instability or recurrent stenosis.^18,19 It was stated that this small percentage had nerve damage that was present prior to surgery due to pressure on the nerve, changing the pain into a neuropathic type of pain. Due to the fact that it is impossible to diagnose whether permanent nerve damage is present prior to surgery, and that curing a postoperative persistent pain syndrome after a failed laminectomy is a major unsolved problem. That explanation, to us, solved nothing of the real problem. These results pushed us to re-look, re-evaluate, and re-think of the cases again, looking for better solutions and good explanations. Microdecompressive surgery was used as the control in this study. Comparison with reported results of microlaminectomy, physical, functional and symptom severity improvements for patients treated with the Coflex are better. Despite a 1-year relatively short follow-up in the current study, it is clear that the performance of the Coflex patients compares favorably to that of patients undergoing surgical microdecompression alone.

Many spine surgeons don't recognize the fact that the facet joint is the corner stone of LCS pathological events. Despite removing the herniated disc fragment and surgically decompressing the nerve roots, the remainder of the pathology, the facet, remains loaded and arthropathic in place. That correlation explains the fact that some people do have periodic or continuous backache or leg pain, postoperatively. Augmenting the decompression with unloading of the facets should theoretically cure most of those people of their back and leg pains.

The Coflex is an axially compressible U-shaped device, made of titanium, which is interposed between the spinous processes. By implanting it in a somewhat compressed condition, the device can expand further with flexion thereby reducing the buckling of the ligamentum flavum and off-loading the facet joints. However, the results of its clinical application have rarely been reported.^{5,8,10,16,20,21,22,28,30,34,37,43} Tsai et al., assessed the motion segment after destabilization and insertion of the Coflex, and concluded that the Coflex offered nonrigid fixation and can return a partially destabilized specimen back to the intact condition in terms of motion in flexion/extension and axial rotation.³⁷ Kong et al., reported a favorable result with Coflex in spinal stenosis in terms of adjacent level degeneration when compared with a posterior interbody fusion group.²³ The author, in this study, assumed that interspinous implantation can be a good adjuvant augmenting microlaminectomy procedure for mild to moderate spinal stenosis. Moreover, it puts less stress on the adjacent levels than decompression surgery alone in which elements of disc space collapse or narrowing is present.

Radiologically, in our study, Coflex device insertion does induce a significant change in disc and foraminal heights, a finding that was not noticed with decompression alone. There was also an apparent difference in postoperative back pain and ADL score between the two groups. Of course, pain improvement has resulted from the effects of decompression by a way or another. However, the pain after surgical decompression alone would recur with time, as found in our results. So, long term follow-up is required. Changes of disc height or foraminal height require mechanical and structural transformation as distinct from motion changes. Changes in intervertebral angles with Coflex have also been reported using plain radiographs. An increase in the angles toward lordosis was noted in the erect posture from supine. The posterior disc height did show an increase irrespective of posture and number of operated levels. Postoperatively, the anterior disc height appeared to increase, albeit minimally, in single-level implantation. In double levels, the disc height expectedly reduced postoperatively. We also reported increases in the cross-sectional area of the dural sac and intervertebral foramina. Our study demonstrated that the Coflex, distracting the interspinous processes, increased the dimensions of the spinal canal and neural foramina at the implanted level in extension, but it did not alter the dimensions of the adjacent, intact levels in the extended, flexed, or neutral positions. These effects are expected to significantly reduce the pressure in the facet joints and posterior annulus and nucleus at the implanted disc level, without altering the mean pressures at adjacent levels. These effects produce a clinical benefit for LSS patients treated with the Coflex. The addition of these beneficial effects to the decompressive procedure should raise the good outcomes, clinical and radiological.

Clinically, the study confirmed the known positive effect of decompression of neural structures on claudication and leg pain. In addition, the moderate and/or severe LBP could be relieved in most of the patients. The decreased preoperative walking distance, partly due to LBP, partly due to claudication, improved significantly. Also, the patient satisfaction was extremely high and the majority would undergo surgery again. Therefore, we think that the decompression with additional coflex implantation can not only improve the claudication but also the accompanying LBP. The rate of complications in our study was very low.

Procedural aspects of Coflex implantation also compare favorably to those reported for decompressive surgery. The mean operative time for the Coflex procedure was more than that reported for microlaminectomy procedures by only 5-10 minutes, which is not a big issue. In addition, the mean blood loss of 60 ml during the microdecompression procedure did not increase in the coflex group.

Because group B served as a control in the current study, definitive comparisons between the Coflex and microdecompressive microlaminectomy could be made. The current study is one of the new comprehensive evaluations of LSS conducted to date. Care was taken in the current study to address the importance of protocol design, to clarify the new philosophy of LCS management, and to have solid comparative conclusions. Limitations only include a moderate sample size and a follow-up period of 1 year. A report will be published based on the late follow-up data for all patients. Despite these limitations, the current study provides evidence that immediate pain relief and increase in function can be provided by the Coflex with a low rate of morbidity. This clinical improvement is greater than that associated with microlaminectomy alone.

Conclusion

The Coflex device was helpful in alleviating pain and improving ADL performance in patients with lumbar spinal stenosis. It corrected segmental scoliosis and restricted extension. However, there should be careful selection to apply of this device in segmental canal stenosis patients, for better results to follow. The addition of coflex device to the micro-decompression procedure, improves the clinical and radiological outcomes much, in properly-selected cases. The addition of coflex as a method of dynamic stabilisation after neural decompression reduces low back pain without fusion. We could demonstrate that the implantation of coflex is safe and effective. Further prospective studies will be needed and are planned.