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Year : 2017  |  Volume : 65  |  Issue : 6  |  Page : 1358--1365

Minimally invasive lateral foraminotomy with partial lateral facetectomy for lumbar radiculopathy—An evaluation of facet integrity and description of the procedure

Akshay Hari, Murali Krishna, Santosh Rajagandhi, Ankit Sharma, Rajakumar V Deshpande 
 Department of Neurosurgery, Fortis Hospital, Bannerghatta Road, Bengaluru, Karnataka, India

Correspondence Address:
Dr. Rajakumar V Deshpande
Department of Neurosurgery, Fortis Hospital, #154/9, Opposite IIM-B, Bannerghatta road, Bengaluru - 560 076, Karnataka
India

Abstract

Foraminal stenosis causing nerve root compression and radiculopathy is a relatively common pathology in the lumbar spine. The treatment of choice, when surgery is indicated, is foraminal decompression at the affected level, usually through a conventional midline open foraminotomy. Minimally invasive lateral foraminotomy with partial lateral facetectomy is a potentially effective surgical alternative when such a surgery is warranted. The evaluation of the efficacy and benefits of this approach for treatment of radiculopathy; an assessment of facet integrity; and, a detailed description of the procedure are also provided. Patients with predominantly unilateral lower limb radiculopathy, who had persistent symptoms despite conservative therapy, underwent a minimally invasive lumbar lateral foraminotomy (through tubular retractors) with partial lateral facetectomy. The Oswestry disability index (ODI) and the visual analog scale (VAS) for back and leg pain were evaluated preoperatively, postoperatively, and at the latest follow-up. Facet integrity was evaluated with postoperative computed tomography (CT) scans. Between 2013 and 2014, in the 12 patients who underwent this procedure and were evaluted after a minimum follow up of 1 year, there was significant improvement in the ODI, VAS based back pain, and VAS based leg pain. A minimally invasive, lateral foraminotomy with partial lateral facetectomy is an effective alternative technique for treatment of radiculopathy due to foraminal stenosis in a carefully selected subgroup of patients. A larger study would possibly highlight the effectiveness of this procedure.



How to cite this article:
Hari A, Krishna M, Rajagandhi S, Sharma A, Deshpande RV. Minimally invasive lateral foraminotomy with partial lateral facetectomy for lumbar radiculopathy—An evaluation of facet integrity and description of the procedure.Neurol India 2017;65:1358-1365


How to cite this URL:
Hari A, Krishna M, Rajagandhi S, Sharma A, Deshpande RV. Minimally invasive lateral foraminotomy with partial lateral facetectomy for lumbar radiculopathy—An evaluation of facet integrity and description of the procedure. Neurol India [serial online] 2017 [cited 2019 Oct 19 ];65:1358-1365
Available from: http://www.neurologyindia.com/text.asp?2017/65/6/1358/217932


Full Text

Key Message:

Patients with predominantly unilateral lower limb radiculopathy due to lateral recess or foraminal stenosis (as a result of facetal hypertrophy, osteophytes, and/or disc herniation), who have persistent symptoms despite conservative therapy, may get a considerable benefit utilizing the minimally invasive lumbar lateral foraminotomy through tubular retractors with partial lateral facetectomy. The procedure provides a safe, rapid, and direct localization of the intervertebral foramen with excellent visualization of the lateral spinal structures, without the need for significant muscle retraction or potentially destabilizing bony resection. However, patients with significant mechanical back pain; with etiologies such as a facet joint cyst, a spinal tumor, or traumatic fractures; as well as those with significant instability due to spondylolisthesis should not be subjected to this procedure.

Lumbar radiculopathy or sciatica is a commonly encountered pathology in clinical practice.[1] Studies report an incidence of 8–11% as a consequence of lateral recess or foraminal stenosis.[2] The notion of a herniated disc fragment causing neural compression in the lumbar spinal canal was first reported by Mixter and Barr in 1934.[3] Putti first described the role of facet joint “arthritis” in causing foraminal stenosis.[4] Since then, various causative factors have been identified, such as hypertrophy of the superior facets, buckling of the ligamentum flavum, osteophyte formation, far lateral disc herniation, as well as a decrease in the intervertebral disc height, which lead to impingement of the exiting nerve root due to narrowing of the neural foramen.[5],[6]

Surgical intervention is recommended for patients whose symptoms persist despite conservative management.[7] The treatment of choice in such cases is foraminal decompression. Several different techniques have been described including the conventional midline open foraminotomy, facetectomy, partial pediculectomy, distraction instrumentation, far lateral intertransverse approaches, and percutaneous transforaminal endoscopic surgeries.[8],[9],[10],[11] We report the use of partial lateral facetectomy for lumbar foraminal stenosis with minimally invasive tubular retractors from a paramedian lateral approach. Very few reports of such techniques have been described in the literature.[12],[13],[14],[15],[16]

Minimally invasive access to the posterior spine using tubular retractors has become increasingly popular since its inception by Foley et al.[17] Routine microdiscectomies and central decompressions are regularly being performed at most institutions using such minimally invasive approaches. Advantages of a minimally invasive technique include less tissue dissection, decreased blood loss, decreased postoperative pain, shorter hospital stay, and earlier ambulation.[18],[19],[20],[21]

While most authors have recommended a posterior approach, either midline open or minimally invasive,[9],[10] the posterolateral approach has certain benefits. Originally described by Watkins [22] and Wiltse [23] for lumbar fusion, it provides a safe, rapid, and direct localization of the intervertebral foramen with excellent visualization of the lateral spinal structures without the need for significant muscle retraction or potentially destabilizing bony resection.

Our initial experience in a small cohort of patients who underwent minimally invasive lateral foraminotomy with partial lateral facetectomy is being presented, along with a description of the procedure. The goal was to ensure sufficient visualization of the anatomy and obtain adequate decompression of the foramen, while maintaining the integrity of the facet joint.

 Surgical Technique



Patient demographics

In a prospective cohort experience of 12 carefully selected patients with predominantly unilateral lower extremity radicular pain, a minimally invasive lateral foraminotomy through tubular retractors with lateral partial facetectomy was performed from 2013 to 2014 at a single center by a single surgeon. The inclusion criteria were the presence of unilateral radicular symptoms, evidence of foraminal stenosis on the preoperative magnetic resonance imaging (MRI) corresponding to the side and severity of symptoms, and failure of conservative management for a minimum of 6 to 12 weeks. Etiologies considered were degenerative foraminal stenosis, due to facet hypertrophy or osteophyte, and disc herniation. Patients were excluded if they presented with significant mechanical back pain. Etiologies such as facet joint cysts, tumor, or trauma, as well as significant instability due to spondylolisthesis were also excluded. The study included the L3–L4 to L5–S1 levels. Demographic and perioperative data collected were age, gender, medication status, preoperative diagnosis, number and levels of surgery, estimated blood loss, operative time, and length of hospital stay.

Operative steps

Under general anesthesia and in prone position, the appropriate level was identified with a draped C arm. A small skin incision (18–20 mm) was made overlying the desired level, approximately 3.5 cm lateral to the midline on the ipsilateral side. This incision was slightly more lateral in obese patients, and was carried deep through to the lumbosacral fascia. The next steps involved the use of MetRx tissue dilator system (MetRx; Medtronic Sofamor Danek, Memphis, TN, USA) [Figure 1].{Figure 1}

Using fluoroscopic guidance, the first (smallest) tubular dilator was inserted and docked to the bone at the junction of the transverse process (TP) of the superior vertebra with the pars interarticularis. It was then manipulated to dissect the soft tissues off the bone. The subsequent dilators with an increasing diameter were sequentially inserted between the paraspinal muscles and used to dissect the muscles off the underlying bony surfaces. An 18 mm diameter working port was introduced and secured to the operative table with a special arm. The dilators were then removed and fluoroscopy was repeated to confirm the positioning and level [Figure 2]. The next steps were performed under a surgical microscope.{Figure 2}

Monopolar cautery was used to remove the remaining soft tissue overlying the pars and the base of the TP. The ipsilateral facet joint, pars, and TP were identified. The superior articular process of the inferior vertebra, which forms the lateral facet joint, was then drilled, and the lateral aspect of the neural foramen was opened by drilling at the most lateral edge of the pars. Further enlargement of the foramen was accomplished by drilling or employing a Kerrison rongeur to cut the protruding edges of the inferior facet and removing the attached redundant ligamentum flavum.

Drilling the superolateral aspect of the facet joint along with the lateral 2 to 3 mm of the pars was usually sufficient to expose a 15–18 mm circular operative window. Importantly, the amount of facet joint resection should not exceed 50% [Figure 3].{Figure 3}

The intertransverse fascia and ligamentum flavum were gently resected, exposing the adipose tissue surrounding the exiting nerve root, the outer part of the foraminal disc, and the extraspinal portion, if any, of the disc herniation. Once the anatomical relationship between the nerve root and the disc herniation was clear, the disc was incised and then removed.

At this stage, if further medial compression of the traversing nerve root was suspected, either due to central disc herniation or ligamentum flavum hypertrophy, midline decompression could also be achieved. For proper visualization of the midline sublaminar structures, the operating table was tilted away from the surgeon and the tubular retractor was angled medially. Next, the base of the lamina was undercut using the drill and rongeurs and the ligamentum flavum was exposed. During the drilling, the ligamentum flavum was preserved in order to protect the dura. Next, the ligamentum flavum was carefully removed using Kerrison rongeurs. Dural exposure and decompression was achieved after complete removal of the ligamentum flavum. These techniques minimize the risk of injury to the dura. The central canal and the traversing nerve root were also completely decompressed. Sufficient decompression was confirmed with a microinstrument such as a nerve hook.

The advantage of this approach is the ability to remove even the medial part of the superior articular process allowing for excellent visualization of both nerve roots related to the disc space, thereby permitting decompression of the traversing ipsilateral nerve root, in addition to decompression of the ipsilateral lateral recess.

Hemostasis was then secured, surgical site irrigated, and the working port removed. Wound closure was achieved with a subcutaneous stitch and the skin was closed with an intradermal suture. The various intraoperative steps are highlighted in [Figure 4].{Figure 4}

Clinical evaluation

Clinical outcomes were evaluated preoperatively, postoperatively at first visit after surgery, and at the latest follow-up. Oswestry disability index (ODI)[24] and the visual analog scale (VAS) for back and leg pain were used to assess the outcomes. Score improvements were then calculated and statically analyzed. Functional outcome was evaluated using MacNab's criteria.[25]

Statistics

Clinical outcomes were analyzed using Student's paired sample t-test. Descriptive statistics were used for the patient demographics and data. The significance level was defined to be 0.001. Statistical analyses were conducted using QuickCals (GraphPad software Inc, USA).

 Patient Spectrum



Patient data

A total of 12 patients with a mean (± SD) age of 49.3 ± 13.5 years underwent minimally invasive lateral foraminotomy using tubular retractors with partial lateral facetectomy from 2013 to 2014 [Table 1]. There were 10 male and 2 female patients. Foraminal stenosis was documented in all patients [Figure 5].{Table 1}{Figure 5}

A total of 14 levels were operated upon; 2 patients had bi-level surgery. The most common level of surgery was L4–L5 (58.3% of the levels), followed by the L5–S1 (50%) and L3–L4 (8.3%) levels. The mean estimated blood loss for single level surgery was 30 ml, and the mean operative time was 45 min. The average length of hospital stay was 1.5 days.

Clinical outcome

There were significant improvements in the ODI (63 vs. 30, P < 0.001), VAS back pain (7.4 vs. 2.5, P < 0.001), and VAS leg pain (7.0 vs. 1.8, P < 0.001) [Table 2]. No statistically significant differences were found between the extent of improvement in the VAS between the first postoperative follow-up and the latest follow-up. The functional outcome assessed by Macnab's criteria was excellent and good in 91.7% of the patients [Table 3].{Table 2}{Table 3}

There were no intraoperative and/or perioperative complications, such as dural tear, CSF leak, or wound infection. At the latest follow-up, there were no sensory and/or motor deficits. No patient required additional surgery.

Facet integrity

Postoperatively, three-dimensional thin section reconstructed CT scan of the lumbar spine showed preservation of the main portion of the facet joints. The superolateral part of the facets were noted to have been partially resected along with a portion of the adjoining pars. Not more than 50% of the facets were removed [Figure 6].{Figure 6}

 Discussion



Indications and concepts of the approach

Nerve root compression due to canal stenosis is a common cause of radiculopathy, which can occur as a result of various pathologies of the spine including spondylosis, osteophytes, and disc herniation.[26],[27] When indicated, surgical decompression of the nerve root canal has been the intervention of choice for treatment of radiculopathy. The primary aim of this study was to describe the lateral minimally invasive partial lateral facetectomy approach as an effective alternative method for the treatment of radiculopathy caused by various pathologies impinging on the intervertebral foramen. Utilizing this approach, nerve root decompression is facilitated without causing significant destabilization of the facet joint.

Foraminal stenosis

Postacchini [28] classified spinal stenosis, on the basis of location of the compression within the lumbar spine, into 3 forms: central stenosis—referring to medial compression of the canal often affecting the cauda equina; lateral recess stenosis—involving part of the nerve root from the thecal sac to the entrance of the intervertebral foramen; and foraminal stenosis—narrowing of the neural foramen, which is further categorized into intraforaminal and extraforaminal stenosis.

The pathophysiology of foraminal stenosis was explained by Jenis and An.[2] Lumbar spondylosis causes reduction in the intervertebral disc height and foraminal stenosis through the anterior and superior migration of the superior facet, thereby decreasing the anteroposterior dimension of the neural foramen. In addition, hypertrophy of the ligamentum flavum and osteophyte formation worsen the compression. The craniocaudal dimension may also be compromised by vertebral endplate osteophytes, bulging annulus fibrosus, or a herniated disc. This combination of changes causes circumferential narrowing around the exiting nerve root leading to back pain and radicular symptoms.

Concept of the lateral approach

While the original concept of a lateral paraspinal approach was initially described by Wiltse and Spencer in 1988 as an open lumbar spinal approach,[29] it has not become popular as a standard treatment method for foraminal stenosis. The present approach gives the most direct access to the lateral recess and the foramen. There is also minimum tissue damage with reduced chances of muscle denervation. This approach can, thus, be applied to many forms of stenotic pathologies of the lumbar foramen including disc herniation, osteophyte formation or bony hypertrophy, and ligamentum flavum hypertrophy.

With this approach, the foramen as well as the lateral recesses can be accessed and decompressed with a single incision with preservation of mechanical stability due to minimum bony resection. Combined with partial lateral facetectomy, with partial resection of the lateral aspect of the pars, undercutting of the lamina, removal of any hypertrophied ligamentum flavum medially, as well as the release of the intertransverse structures laterally, it is possible to achieve maximum decompression of the dura and both the exiting and traversing nerve roots at a given level.

While this approach appears good for central canal decompression as well, our experience is limited to two patients only; hence, substantial conclusions cannot be drawn from this study based on the limited evidence available with us.

The minimally invasive approach versus the other approaches

The gold standard for treatment of radiculopathy, as described by Briggs and Krause in 1945, is open decompression with medial foraminotomy.[30] The contemporary open methods are based around either a midline or a paraspinal approach. However, they have been associated with tissue damage, muscle denervation, and increased blood loss.[31],[32]

The minimally invasive approach using tubular retractors aims to overcome these disadvantages and is already in vogue for various procedures such as standard discectomies and laminotomies. Nevertheless, its role in lateral foraminotomies has not been frequently reported.

Far-lateral and intertransverse approaches, while being effective for treating extraforaminal disc herniation, may not be suitable if the compression extends more centrally.[10] Conventional midline approaches, which are widely used for a range of routine interventions, such as foraminotomy, laminectomy, and laminotomy, have been traditionally used for all forms of spinal stenosis. The major limitations of the conventional approaches include the performance of a partial medial or complete facetectomy to access the foramen, which may cause instability, poor visualization of intraforaminal content, and increased surgical blood loss.[21],[33]

Fully-endoscopic interlaminar and transforaminal approaches have also been recently introduced for treatment of central and foraminal stenosis; however, no significantly better long-term outcomes were obtained utilizing these approaches when compared to the traditional ipsilateral open technique.[17],[34],[35] While theoretically, the endoscopic approach is least invasive, there are certain key challenges that remain a setback, including the limited mobility of instruments, the difficulties in carrying out repair of any iatrogenic dural injury, and the demanding learning curve.[36],[37]

Although minimally invasive procedures also required a learning curve, studies showed a decline in the operative time with more experience.[38]

Facetectomy—role and integrity of the facet joint

The role of facet joints in foraminal stenosis was first described by Putti in 1927.[4] The concept is that the superior articular process of the inferior vertebra (lateral facet) impinges on the exiting nerve root in an already compromised foramen. The notion of partial undercutting facetectomies for treating foraminal stenosis was introduced by Getty et al.,[39] in 1981. However, much of the procedure involves a medial facetectomy, through which it may not be possible to completely address the compression at the foraminal level without causing significant facetal resection, leading to instability.

A theoretical advantage of this minimally invasive, partial lateral facetectomy approach over the conventional midline open procedures is the ability to maintain biomechanical stability. As it is the inferior articular process of the superior vertebra (medial facet), which is in continuity with the pars and is responsible for stability of the joint, partial resection of the lateral facet should, ideally, not destabilize the joint. A number of studies have shown that minimally invasive bilateral undercutting of the lamina using a unilateral approach results in maintenance of lumbar stability, whereas a full facetectomy and laminectomy led to instability.[40],[41] As bony removal in this minimally invasive lateral approach is equal to or less than that described in the biomechanical studies, stability of the lumbar spine is presumably maintained.

Clinical results of our study also seem to suggest that at mid-term follow-up, the procedure does not appear to affect the integrity of the facet joint, as evaluated by the presence of new onset of any significant backache or by the Macnab's criteria. This further correlates well with the radiological evidence of preservation of majority of the more important medial facet joint. A brief review of the available international literature regarding this technique is summarized in a tabular format [Table 4].{Table 4}

Limitations

There are certain limitations in this study. The small number of cases, as well as lack of comparable control group within the same study are the major drawbacks. Second, the relatively short duration of follow-up for clinical assessment of iatrogenic instability is a major limitation. Further, bilateral radicular involvement cannot be addressed utilizing this technique through the same incision.

 Conclusion



This minimally invasive, lateral foraminotomy approach with partial lateral facetectomy is a novel approach. It is a safe and effective technique to treat patients with radicular pain due to foraminal compression. It allows for approach-related advantages including a direct foraminal access, minimal tissue dissection along with maximum decompression of the lumbar spinal canal, lateral recess as well as foramen, with preservation of facet integrity, through a single incision. Accompanied by the benefits of minimally invasive spinal approaches that utilize tubular retractors, such as low infection rates, minimal blood loss, and faster postoperative recovery rates, minimal blood loss, and fast postoperative recovery, this approach emerges as a good alternative to conventional treatments for radiculopathy due to foraminal stenosis in a carefully selected subgroup of patients. The initial results were encouraging. A larger study would possibly highlight the effectiveness of this procedure.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

[MULTIMEDIA:1]

Acknowledgement

We would like to acknowledge Clare Claiton, M. Sc., for her help in preparation of the manuscript.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.[46]

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