Les lyses isthmiques du rachis sont des pathologies fréquentes traitées habituellement par une prise en charge médicale simple.
Elles correspondent à une insuffisance osseuse qui peut être congénitale ou acquise par hypersolicitation de l’arc postérieur rachidien en particulier chez les sportifs ou chez les personnes agées. Cette insuffisance osseuse pouvant être une véritable fracture peut engendre un déséquilibre sagittal de la colonne vertebral et entrainer un glissement en avant de la vertebre sus-jacente : antélisthésis.
Les infiltrations sous guidage de l’imagerie permettent souvent de passer un cap en terme de douleur en particulier de lombalgie et de radiculalgie.
La chirurgie par réduction de l’antélisthésis avec fixation postérieure par vis transpédiculaire (PLIF) et greffe osseuse inter-somatique est le traitement de référence.

L’évolution technologique des scanners interventionnels permet de réaliser une fixation au niveau précis de la lyse isthmique (Pars defect fixation) sous anesthésie locale et micro-incision.

Les résultats obtenus sont excellent en terme de tolérance, de récupération immédiate post-opératoire et de nette amélioration de la symptomatologie. De nombreuses communications nationales et internationales ainsi que d’articles réalisés par le service du scanner interventionnel sur ce sujet ont connu un grand essor et une véritable évolution de cette prise en charge mini-invasive de la colonne vertebrale.

Computed tomography- and fluoroscopy-guided percutaneous screw fixation of low-grade isthmic spondylolisthesis in adults: a new technique

Abstract
Study design. Technical report.
Objective. We report on a new CT-guided percutaneous screw fixation of low-grade isthmic spondylolisthesis in adults.
Summary of Background Data. In general, low-grade isthmic spondylolisthesis has a favorable outcome, and surgery is rarely required. Patients with pars defects typically become symptomatic in adulthood. Even though posterolateral fusion in situ has been the most common technique, many controversies remain about the treatment of low-grade isthmic spondylolisthesis.
Methods. Ten consecutive adult patients with low-grade isthmic spondylolisthesis were prospectively treated under local anesthesia by percutaneous screw fixation of the pars defects of L5 using CT and fluoroscopy guidance.
Results. The VAS and ODI measurements ± standard deviations decreased from 7.8 ± 0.9 preoperatively to 1.5 ± 1.1 at the two-year follow-up, and from 62.3 ± 17.2 to 15.1 ± 6.0, respectively. There was no slip progression at two years. No screw failure or displacement was also noted.
Conclusion. This rapid, safe and effective procedure could allow to clearly improve the short- and long-term of low-grade isthmic spondylolisthesis.

Key Words: Isthmic spondylolisthesis. Screw fixation. CT and fluoroscopy guidance. Interventional radiology.

Key points:
1. Percutaneous screw fixation of adult low-grade isthmic spondylolisthesis was successfully performed under local anesthesia and using CT and fluoroscopy guidance.
2. This minimally invasive procedure of percutaneous screw fixation confirmed the crucial role of dual guidance, making the intervention rapid, safe and effective.
3. This minimally invasive procedure could allow to clearly improve the short- and long-term outcome of low-grade isthmic spondylolisthesis.

Mini-Abstract

We report on a new minimally invasive technique of screw fixation of low-grade isthmic spondylolisthesis in adults. Under local anesthesia, ten patients were successfully treated by percutaneous screw fixation of the pars defects of L5 using CT and fluoroscopy guidance. Short- and long-term outcome of these patients was clearly improved.

Introduction

Isthmic spondylolisthesis is the forward slippage of a vertebra on the caudad vertebra resulting from a defect in the pars interarticularis. It is most common at the L5–S1 segment.
Typically considered a pediatric condition, isthmic spondylolisthesis is more commonly symptomatic in adults. Although the pars defect develops before skeletal maturity,
skeletally immature individuals with pars defects with or without low-grade spondylolisthesis are typically asymptomatic. It is usually in adulthood when patients who become symptomatic seek medical attention and treatment.
Classifying an isthmic spondylolisthesis into low- versus high-grade has important implications regarding treatment decisions. Low-grade spondylolisthesis refers to slippage less than 50% according to the Meyerding classification [1] and high grade refers to slippage of greater than 50%.
In general, most patients with low-grade isthmic spondylolisthesis are asymptomatic. Even when symptoms develop, for example, low back pain, radiculopathy, or both, conservative treatment has favorable results, and surgery is rarely required. Conservative treatment consists of activity
modification, bracing, and a focused physical therapy program.
Therefore, the main indication for surgery is low back pain, with or without radiculopathy, that is unresponsive to a prolonged course of conservative treatment [2]. The most commonly used technique for adult patients with low-grade isthmic spondylolisthesis is posterolateral in situ fusion [2]. However, several points of controversy remain in the surgical treatment of isthmic spondylolisthesis, such as the need for decompression, instrumentation, reduction, and anterior column fusion [2, 3].
Recently, minimally invasive procedures performed under CT and fluoroscopy guidance have been described in various indications including the fixation of sacroiliac joint disruptions, posterior arthrodesis of spine or extraction of foreign bodies from soft tissues [4-6]. The role of dual guidance is crucial, making the interventions rapid, safe and effective. To the best of our knowledge, no study has ever been published about the percutaneous screw fixation of isthmic spondylolisthesis. The purpose of this technical report is to assess this new technique using computed tomography and fluoroscopy guidance for the treatment of low-grade isthmic spondylolisthesis in adult patients.

Materials and Methods

Patients

All procedures in this study were approved by the Institutional Review Board of our institution. Patients were enrolled after giving written informed consent. From January 2009 to January 2010, ten consecutive adult patients were prospectively treated in our department of radiology by percutaneous screw fixation under CT and fluoroscopy guidance for low-grade isthmic spondylolisthesis. There were four men and six women. The mean age ± standard deviation (SD) was 57,1 ± 9.5 years (range, 44 – 78 years). The level of spondylolisthesis was in all cases L5 with six grades 1 and four grades 2 (according to the Meyerding classification) [1].
The inclusion criteria were at least 1 year of disabling low back pain with or without sciatica, thta have not responded to conservative treatment (including focused physical therapy, bracing, class I or II analgesics, nonsteroidal anti-inflammatory medications, and at least two CT-guided para-isthmic steroïd injections).
The exclusion criteria were mild symptoms, neurologic deficit (greater than trace motor weakness), other lumbar deformity (such as scoliosis), previous spine surgery, psychiatric disorders, drug or alcohol abuse, a possibility of secondary gains from surgical fixation and workers’ compensation.
Preoperative outcome measures were performed in all patients, including the visual analog scale (VAS) for the severity of back pain and the Oswestry Disability Index (ODI) for functional disability [7].

Technique of percutaneous screw fixation

Procedures were decided only following an interdisciplinary meeting between interventional radiologists and orthopedic surgeons. The contraindication for facet screw fixation was bone quality unable to support a 4.0-mm diameter screw.
All patients were treated by a senior interventional radiologist (with ten years of experience).
After haemostatic control, procedures were performed under surgical conditions of aseptia in an interventional CT room using CT (GE Lightview 8-row MDCT scanner; GE Healthcare, Waukesha, Wis, USA) and lateral fluoroscopy (GE Stenescop C-arm) guidance. Patients were placed in a prone position on the CT table with a support optionnaly placed under abdomen to decrease lumbar lordosis and simplify the access to pars defect.
The first part of the intervention was a CT acquisition of lumbar spine with millimetric multiplanar reconstructions which were analyzed on a GE ADW 4.2 workstation to confirm the diagnosis and plan the approach. More precisely, this CT scan allowed to:
– analyze the anatomy of the posterior arch of the vertebra L5,
– determine the best approach so that the direction of screws can be perpendicular to the plane of the pars defect to be fixed. An imaginary line of the proper screw trajectory passing through the center of pars defect was drawn on the CT image for guidance. A skin entry point was determined, and the distance was measured from the midline.
– and calculate the optimal length of the screws
Radiopaque markers were put on the skin prior to the insertion of the material. Using a 20-gauge 20-cm Shiba needle, local anesthesia (lidocaïne 1% [Xylocaïne; Astra, Sodertalge, Sweden]) was administered from subcutaneous tissues to bone contact under fluoroscopy guidance according to the angle previously determined. A CT acquisition confirmed the correct positioning of the tip of the needle at the antero-inferior portion of the lamina of L5.
This needle was then used as a guide for an 13-gauge 10-cm Trocar t’am (Thiebaud, Thonon-les-Bains, France) which was inserted under fluoroscopy after the hub had been removed.
The cannula was inserted from the antero-inferior portion of the lamina of L5, crossed the pars interarticularis defect through its center and stopped at the ipsilateral pedicle of L5 vertebra.
The same procedure was repeated on the opposite side.
In both cases, a follow-up via axial CT scans (SmartStep system) confirmed the good progression of the Trocar.
In case of pain, a Shiba needle was inserted inside the Trocar to infuse 1 cc of lidocaïne 1%. A 2.0 mm Kirschner guidewire (Synthes, West Chester, PA, USA) was placed through the cannula.
Following the withdrawal of the Trocar, a 4.0 mm-diameter cannulated self-drilling/tapping screw (Asnis III; Stryker, Mahwah, New Jersey, United States) was placed over the Kirschner guidewire under CT and fluoroscopy guidance. Trans-isthmic screw fixation was performed using a hollow screwdriver. Once the good positioning of the screw was confirmed by a CT scan, the guidewire was withdrawn.
A CT scan of lumbar spine was performed at the end of the procedure to confirm the correct transfacet screw fixation and eliminate any locoregional complication.

Post-operative follow-up

Patients were followed at intervals for 2 years after the index surgery (1 month, 3 months, 6 months, 12 months, and 24 months) by an independent assessor, an orthopaedic surgeon.
The VAS for back pain was measured at the five follow-up examinations.
Preoperative radiographic assessment included plain radiographs, stress radiographs in flexion and extension, and CT scans for all the patients.
Radiographs (with anterior and posterior radiographs and standing lateral flexion and extension radiographs) and CT scans were performed to indicate:
– screw failure or displacement
– lucency adjacent to screws
– slip progression

Results

The mean procedure time for the screw fixation of two facet joints (from the positionning of the patient on the CT table to his leaving) ranged from 15 to 25 minutes.
Two screws were placed for each patient with a total of 20: in all cases, screws were successfully placed in only one attempt. The mean screw length was 27 mm long (range, 24 mm – 32 mm).
The intervention was well tolerated by patients. There was negligible intra-operative blood loss. No screw penetrated the spinal canal or the intervertebral foramen and injured the neural structures.
All patients had only an ambulatory care with immediate mobilization following percutaneous screw fixation.

The VAS measurements ± standard deviations (SD) were: 7.8 ± 0.9, preoperatively; 1.7 ± 2.0, at 1 month; 1.7 ± 1.2, at 3 months; 2.1 ± 1.2, at 6 months; and 1.5 ± 1.1, at 1 year and 2 years.
The ODI score ± SD decreased from 62.3 ± 17.2 (preoperatively) to 15.1 ± 6.0 (at the two-year follow-up).
There was no slip progression in particular on flexion/extension films at the last follow-up.
No evidence of screw failure, screw displacement or lucency adjacent to screws was also noted
No superficial or deep infection occurred.

Discussion

The results of our feasibility study showed that low-grade isthmic spondylolisthesis could be successfully treated by percutaneous screw fixation under CT and fluoroscopy guidance with an excellent short- and long-term clinical outcome and maintenance of radiographic stabilization.
Fredrickson et al. [8], in a landmark study on the natural history of spondylolysis and spondylolisthesis, reported the incidence of spondylolysis at L5 to be 4.4% in 6-year-old
children and increased to 5.8% in adulthood. Other studies on the natural history of isthmic spondylolisthesis have also confirmed a very low rate of slip progression [9, 10]. Saraste [10], in a large longitudinal study, demonstrated that the onset of symptoms tends to occur after childhood, with a mean age at presentation of 20 years. Many patients may not present to the spine surgeon until adulthood.
Low-grade isthmic spondylolisthesis has a benign clinical course in most patients, regardless of age. Slip progression is very rare in adults and has been estimated to occur in less than 4% of cases [10, 11]. If a low slip is symptomatic, most patients respond to conservative treatment consisting of activity modification, physical therapy, with or without bracing [12, 13]. Nonsteroidal anti-inflammatory medications and judicious use of narcotics and muscle relaxants are used for pain control. Injections (epidural steroids, selective nerve root blocks, and pars or facet joint injections) may also be helpful in a patient who has undergone a trial of physical therapy and activity modification without relief.
Patients who fail at least 6 months of conservative treatment should be considered for surgery. A prospective randomized study comparing posterolateral fusion with an exercise program in adult patients with primarily low-grade isthmic spondylolisthesis who had failed conservative
treatment showed improved function and pain relief with surgery [14].
Many surgical procedures have been described, and the literature shows conflicting results comparing various treatments. Lumbar fusion has become a widely accepted method for the management of low-grade isthmic spondylolisthesis in adults, including: anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF) and posterolateral fusion in situ.
Posterolateral fusion in situ has been the most common technique to treat low-grade isthmic spondylolisthesis. Points of controversy have been the need for decompression and/or instrumentation. Fusion rates are variable in adult patients, ranging from 33% to 100% depending on the study and the radiographic criteria used to evaluate the fusion mass [15-18].
The need for concomitant decompression is somewhat controversial. Stabilizing the olisthesed segment may relieve radicular symptoms if the cause of radiculopathy is dynamic foraminal compression caused by the unstable segment. However, studies have documented a lower fusion rate when decompression was performed at the time of fusion compared with fusion without decompression [19, 20]. Other authors have advocated formal decompression in the presence of an objective neurologic deficit but not necessarily leg pain or radiculopathy [21].
Despite the widespread use of instrumentation (such as pedicle screws), the literature does not provide ample evidence that instrumentation improves clinical outcomes. No benefits from instrumentation were found in four randomized trials that evaluated the role of instrumentation in posterolateral fusion for low-grade adult spondylolisthesis [22-25]. Other studies have highlighted the benefit of instrumentation in improving fusion rates and outcomes [26, 27].

Although rarely performed, there is evidence in the literature to support stand-alone anterior lumbar interbody fusion (ALIF) for isthmic spondylolisthesis. Studies have reported favorable clinical outcomes after stand-alone ALIF [54,55]. Kim and Lee [28] retrospectively compared 20 adults who underwent ALIF with 20 adults who underwent instrumented posterolateral fusion for isthmic spondylolisthesis and found no difference in clinical outcomes between the two groups. Moreover, the procedure relies on indirect decompression of the L5 nerve roots in adults who may have significant radicular symptoms. However, stand-alone ALIF remains rarely used for isthmic spondylolisthesis because of the compromised stability of the posterior column as a result of the pars defects. Removing the anterior longitudinal ligament and anterior annulus fibrosus will add to this instability and may result in extrusion of the graft and progression of the slip. If ALIF is performed, it should be supplemented by posterolateral fusion and instrumentation. Given that a circumferential fusion can be performed from a posterior-only approach (TLIF or PLIF), the need for a separate anterior approach is difficult to justify.
Circumferential fusion through either a PLIF/TLIF approach or a combined anteroposterior approach has become more common in recent years. TLIF is the most common method of fusing the anterior column in low-grade slips because the TLIF approach offers several advantages over the PLIF technique. Nerve root and dural retraction are minimized because of the lateral entry point, thereby reducing the risk of neural injury. In adults, there is some evidence that despite a solid posterolateral fusion, adults may develop further degenerative changes in the disc over time [29]. Barrick et al. [30] reported on patients who had solid posterolateral fusion but continued to complain of low back pain, which was successfully treated after subsequent ALIF.
In 2005, Kwon and Albert [3] reviewed the literature on the surgical management of low-grade adult spondylolytic spondylolisthesis. Combining the results of these studies, they found the highest fusion rate in patients who underwent a circumferential fusion as compared with a posterolateral alone or anterior approach alone. Clinical outcomes were more successful in the circumferential group. However, most of the studies were retrospective with a variety of surgical indications and techniques and inconsistent methods of evaluating fusion rate and clinical outcomes [3]. Moreover, they found no prospective randomized studies comparing one surgical approach versus another.
More recently, several studies have compared the different surgical approaches for low-grade isthmic spondylolisthesis. Swan et al. [31], in a nonrandomized prospective trial, compared posterolateral fusion with combined anterior and posterolateral fusion in low-grade isthmic spondylolisthesis. They found superior 2-year clinical outcomes in the combined antero-posterior group. Ekman et al. [32] compared posterolateral fusion alone with PLIF for adult low-grade isthmic spondylolisthesis and found no difference in the 2-year clinical outcome between the two
groups. The PLIF cohort of this study was prospectively enrolled, but the postero-lateral fusion group was historical controls. Kim et al. [67], in the only prospective randomized study comparing the three fusion methods (posterolateral fusion (PLF), posterior lumbar interbody fusion (PLIF), and PLIF combined with PLF) could not demonstrate a difference in outcome in a mixed group of patients that included both degenerative and isthmic spondylolisthesis.
In the absence of a well-designed prospective comparison study of the different surgical approaches for low-grade isthmic spondylolisthesis in any age population, Agabegi et al. [2] concluded in their recent review that it was difficult to make recommendations on the optimal approach. In most cases of low-grade isthmic spondylolisthesis adults, in situ instrumented posterolateral fusion (with or without decompression as indicated) has historically yielded a successful clinical outcome. The literature seems to suggest that a circumferential fusion (either a TLIF or combined anterior and posterior approaches) is associated with a higher fusion rate and improved clinical outcomes. Although we do not routinely advocate a circumferential fusion, it should be considered in adult patients with one or more risk factors for pseudarthrosis to increase the likelihood of fusion success. Although not corroborated by solid evidence, adults with large or hypermobile discs may also benefit from the addition of anterior column fusion as these discs may degenerate over time despite a solid posterolateral fusion.
Moreover, open lumbar fusion procedures require lengthy hospital admissions and are costly [25]. The long-term morbidity associated with these procedures is concerning. A significant proportion of this morbidity is iatrogenic and likely due to the extensive soft tissue and muscle dissection required to obtained adequate exposure of the spine for fusion. Therefore, minimal access spinal procedures were developed to limit the approach-related soft tissue dissection and thus to maintain the dynamic stability of the spine while accomplishing the intended goals of surgery [33]. More specifically, what distinguishes minimally invasive surgery (MIS) from traditional open surgery is its emphasis on the following: (1) decreasing muscle crush injuries during retraction; and (2) avoiding disruption of the osteotendinous complex of the paraspinal muscles, especially the multifidus attachments to the spinous process and superior articular processes. This is accomplished through the use of specialized instruments and refined surgical techniques where multiple smaller incisions are used to exploit known anatomic neurovascular and bone-tendon-muscle planes. Consequently, the reported advantages of MIS-LIF on open LIF include, but are not limited to, less intraoperative blood loss, less postoperative pain, decreased postoperative narcotic usage, early ambulation, and decreased length of stay in hospital.
Another minimally invasive method is direct fixation of the pars defect that is currently a treatment option in adolescents and young adults with a normal intervertebral disc (on magnetic resonance imaging). In other ways, this procedure is recommended if the pars defect is determined to be the source of pain. Consequently, this procedure is rarely indicated in adults who often have concomitant disc degeneration and, therefore, do not meet the criteria for pars repair. Several techniques of direct pars repair have been described, such as translaminar screw technique or the use of button wires [34, 35].
Currently, the most common technique of pars repair involves pedicle screws and sublaminar hooks connected with rods. This technique allows direct compression across the pars defect and compared with other techniques, has been shown to allow the least amount of motion across the defect under flexion loads in biomechanical evaluation [36]. High healing rates and good clinical results have been reported using this technique [37-39].
Faced with so many controversies in the surgical management of low-grade isthmic spondylolisthesis, we attempted to apply percutaneous screw fixation to the fixation of pars defect in adults even if this kind of procedure is usually performed in younger patients. Percutaneous screw fixation that was performed only under local anesthesia was guided by the combination of CT and fluoroscopy. Gangi et al. [40] showed in vertebroplasty procedures that this dual guidance could allow to facilitate needle placement and reduce complications. The crucial role of dual guidance, which made the intervention rapid, safe and effective, was confirmed in various percutaneous interventions including screw fixation of sacroiliac joint disruptions, posterior arthrodesis of spine or extraction of foreign bodies from soft tissues [4-6].
Using this technique, low back pain pain and functional disability were clearly improved at short- and long-term. Moreover, we attribute the absence of complications with this technique to the fact that insertion of the screws is technically easy under CT and fluoroscopy guidance, and the learning curve, therefore, is short. More precisely, it is critical to avoid violation of the facet joint capsules during exposure because a fusion is not being performed, which was the case in our study in which there was no screw malposition.
This study has some limitations. The main one is the small number of patients in this feasibility study. The second one is the absence of assessment of pars defect screw fixation on radiculopathy. Several studies have reported improvement or resolution of nerve root symptoms after posterior fusion alone [41, 42]. Even if several mechanisms – anterior translation of L5 on S1 causing stenosis of the neural foramen, disc degeneration with bulging and collapse of the disc space, and the pars defect inciting the development of fibrocartilaginous reparative tissue at the site of the defect – lead to nerve root compression in isthmic spondylolisthesis, this improvement presumably results from the improved stability imparted by fusion, eliminating the dynamic component of nerve root irritation that is caused by micromotion at the slipped level. The third one is the absence of pre-operative and post-operative MR imaging to evaluate the potential effect on Modic changes in case of disc degeneration. The fourth one is the absence of injection of lidocaïne into the pars defect to determine if the pars defect is the source of pain.
This preliminary study showed the accuracy of CT-guided percutaneous screw fixation of low-grade isthmic spondylolisthesis. Further studies remain to be done to define the place of such a technique in the therapeutic management of isthmic spondylolisthesis in collaboration with orthopedists who tend increasingly to give priority to less invasive procedures.