Posterolateral versus Posterior Interbody Fusion in Isthmic Spondylolisthesis

Abstract

Spondylolisthesis is a heterogeneous disorder characterized by subluxation of a vertebral body over another in the sagittal plane. Its most common form is isthmic spondylolisthesis (IS). This study aims to compare clinical outcomes of posterolateral fusion (PLF) with posterior lumbar interbody fusion (PLIF) with posterior instrumentation in the treatment of IS. We performed a randomized prospective study in which 80 patients out of a total of 85 patients with IS were randomly allocated to one of two groups: PLF with posterior instrumentation (group I) or PLIF with posterior instrumentation (group II). Posterior decompression was performed in the patients. The Oswestry low back pain disability (OLBP) scale and Visual Analogue Scale (VAS) were used to evaluate the quality of life (QoL) and pain, respectively. Fisher's exact test was used to evaluate fusion rate and the Mann-Whitney U test was used to compare categorical data. Fusion in group II was significantly better than in group I (p=0.012). Improvement in low back pain was statistically more significant in group I (p=0.001). The incidence of neurogenic claudication was significantly lower in group I than in group II (p=0.004). In group I, there was no significant correlation between slip Meyerding grade and disc space height, radicular pain, and low back pain. There was no significant difference in post-operative complications at 1-year follow-up. Our data showed that PLF with posterior instrumentation provides better clinical outcomes and more improvement in low back pain compared to PLIF with posterior instrumentation despite the low fusion rate.

Introduction

S pondylolisthesis is a heterogeneous disorder characterized by the subluxation of a vertebral body over another in the sagittal plane (Le Roux and Winn, 2003). It represents a particular and relatively frequent mechanism of intervertebral instability, and occurs most frequently at the L4–L5 and L5–S1 interspaces (Fischgrund et al., 1997; Ganju, 2002). The first case of lumbosacral spondylolisthesis was described by Herbinaux (1782) in 1772. Spondylolisthesis has been classified into five types, among which isthmic spondylolisthesis (IS) is the most common form (Ganju, 2002). This failure is caused by a defect in the pars interarticularis; it occurs in 4–8% of the general population in individuals of all ages (Fredrickson et al., 1984; Ganju, 2002; Jones and Rao, 2009; La Rosa et al., 2003).

A majority of patients with spondylolisthesis are asymptomatic. Neurological symptoms are common with spondylolisthesis (Fischgrund et al., 1997; McCulloch, 1998). Symptoms are usually related to axial back pain and the sequelae of neural compression (McCulloch, 1998). The nerve root deficits and leg pains involve foraminal stenosis caused by a combination of a fibrocartilaginous mass at the isthmic defect, disc, and osteophyte of the slipped body (Ming-li et al., 2009). Complete decompression of nerve roots is essential to obtain a better prognosis and a good surgical outcome, as is the need for stabilization (Wenger et al., 2005).

The initial treatment for patients with low-grade spondylolisthesis is nonsurgical, and consists of a combination of pain medications, bracing, and physical therapy. The surgical treatment of spondylolisthesis is indicated for failure of conservative management (Zdeblick, 1993). It typically consists of a fusion procedure with or without neural decompression (McCulloch, 1998). Orthopedic spinal surgeons and neurosurgeons use instrument-assisted posterolateral fusion (PLF), and posterior lumbar interbody fusion (PLIF) as two common techniques to treat IS. PLF using a pedicle screw system is the most popular spinal fusion technique to treat IS (Dehoux et al., 2004; Ekman et al., 2005; Lamberg et al., 2005).

We have found a few studies comparing the use of PLF and PLIF, both with posterior instrumentation, for the treatment of IS (Dehoux et al., 2004; Ekman et al., 2007; La Rosa et al., 2003; Madan and Boeree, 2002; Müslüman et al., 2011). Because each of these techniques has different clinical outcomes, functional improvements, and neurological complications, the ideal surgical treatment for IS is still controversial (Dai et al., 2001). This randomized prospective study aims to evaluate the clinical outcomes of PLF with posterior instrumentation and PLIF with posterior instrumentation in patients with IS, and to compare the efficacy and complications of these techniques.

Methods

Study design

We performed a randomized prospective study, in which 80 patients out of a total of 85 patients, 18 men and 62 women aged 18–65 years with lumbar IS were eligible to participate, and were enrolled from September 2008 to March 2010. A 1-year follow-up was planned from March 2010 to March 2011. A general practitioner not only assessed 85 patients for eligibility, but also evaluated baseline characteristics of eligible patients before randomization. Eligible participants were randomly assigned to two groups by opening sealed envelopes. The envelopes were prepared beforehand and sorted randomly by using random allocation software (computerized random number generators). Forty patients were operated on with PLF with posterior instrumentation (group I) and 40 were operated on with PLIF with posterior instrumentation (group II). The surgeon was aware of the procedure and all patients were followed by two radiologists who were unaware of the study. A rater, who was likewise unaware of the study, verified the results. The radiologists and the rater were not involved in the care of the patients. Written informed consent was obtained from all patients, and the medical research ethics committee of Shiraz University of Medical Sciences approved the study on March 18, 2009 with approval number 2732.

Patients and evaluations

During the period from September 2008 to March 2010, 85 patients were selected for participation, and 80 patients with lumbar IS were randomized. We excluded 5 patients in accordance with the exclusion criteria. Of the 80 remaining patients, 40 were assigned to undergo PLF with posterior instrumentation and 40 to be operated on with PLIF with posterior instrumentation. The population consisted of 10 men and 30 women in group I, and 9 men and 31 women in group II. Mean ages for groups I and II were 49.66±9.01 year and 50.35±11.30 year, respectively. Mean weight was 72±12.55 kg in group I and 73.47±12 kg in group II. Isthmic form was confirmed by lateral and oblique simple and dynamic graphs of the lumbosacral area and computed tomography (CT) scans of the pars interarticularis. Other specified forms with no fracture in the pars interarticularis were regarded as non-isthmic. Neurogenic claudication was one of the symptoms related to this disease in our patients. The patients had mild to severe hamstring spasms.

Inclusion criteria

The inclusion criteria were: (1) IS; (2) no previous spine operation; (3) age between 18 and 65 years; (4) failed conservative therapy including rest and pain medication, lumbosacral orthosis, and physical therapy, at least for 6 months; and (5) hamstring spasm.

Exclusion criteria

The exclusion criteria were: (1) non-isthmic spondylolisthesis; (2) the need for performing discectomy in group I patients; (3) infection; (4) generalized bone disease; and (5) osteoporosis.

Radiological evaluation

The patients' complete neurological examinations, personal data, and radiological findings were added to the pre-operative part of the questionnaire. Pre-operative radiological evaluation included static and functional lumbar spine plain x-rays, four views: anteroposterior (AP), and lateral, right, and left obliques, in which features relevant to spondylolisthesis, including percentage of subluxation, severity of slip, slippage angle, and height of intervertebral disc space were evaluated. CT scans and magnetic resonance imaging (MRI) scans of the lumbosacral area without gadolinium injection were used to assess narrowing intervertebral foramens, and the presence or absence of lumbar spinal stenosis. If the disc space height reduction was the same as that detected in the upper level, this was considered to be normal disc space narrowing; 25% reduction was considered to be mild disc space narrowing, 25–49% reduction was considered to be moderate disc space narrowing, and a reduction of height more than 50% was considered to be severe disc space narrowing.

Operative technique

The patients were carefully placed prone, a one skin incision about 11 cm in length was made in the midline. Spinous processes, laminae, and the bilateral facets were exposed. Posterior decompression, consisting of the removal of the spinous process, bilateral laminectomy, partial bilateral facetectomy, and foraminotomy, was performed. Complete discectomy and total disc resection was performed with preservation of both vertebral endplates only in group II. Fluoroscopically-guided transpedicular fixation was performed at the involved level and its caudal vertebra as a standard technique. The nerve root release procedure was the same in both groups. In group I, after performing neural decompression, the osseous surfaces of the transverse processes and facets were decorticated using a high-speed drill to expose cancellous bone and facet joints. Intertransverse fusion was performed by using bone chips from the resected lamina, mixed with synthetic bone substitute granules (Medical Biomate Inc., Warsaw, IN).

In both groups, medfield spine system II (MSS II) was used for posterior pedicular fixation. We used autologous bone graft from the excised loose lamina and spinous process mixed with synthetic bone substitute granules to achieve fusion. Fusion rate was qualitatively measured after 1 year. Constant solid ossification, segmental ossification, and lack of ossification were considered good, fair, and bad, respectively. In addition, the subluxation in dynamic post-operative radiographies was considered to be bad fusion. Successful fusion was defined as the integrated ossification at the fusion bed without motion in a dynamic graph.

Outcome measures

The degree of spondylolisthesis and severity of slip was determined according to the Meyerding classification (Meyerding, 1932). All 80 patients completed a questionnaire regarding pain and lower back pain (LBP)-related disability. Evaluation measures were performed before randomization and 1 year after the operation. Quality of life (QoL) or functional daily activity and severity of LBP were evaluated using a questionnaire based on the Oswestry LBP disability scale (Fairbank et al., 1980), and the severity of radicular pain was evaluated by using the Huskisson Visual Analogue Scale (VAS), with scores ranging from 1 (no pain) to 10 (excruciating pain) at the first week and 1 year after the surgery.

Statistical analysis

Statistical analysis was conducted using the paired Student's t-test to compare continuous intragroup data (percentage of subluxation, foraminal area, disc height, and slippage angle), and the unpaired t-test was used to compare intergroup data. Fisher's exact test was used to evaluate fusion rate, and the Mann-Whitney U test was used to compare categorical data (VAS and OLBP). Statistical significance was set at p<0.05.

Results

In our study, 18 men (22.5%) and 62 women (77.5%) were assigned to either group I or group II. Distribution of age, weight, height, and body mass index was measured, but there was no statistically significant difference between the two groups. In all, 70% of patients had mild hamstring spasms, 25% had moderate hamstring spasms, and 5% had severe hamstring spasms. Major complaints were neurogenic claudication, radicular pain, and low back pain.

In both men and women, the number of patients who had IS at the L5–S1 level was more than for the other levels. The most involved levels in decreasing order were L5–S1 (36 cases, 45%), L4–L5 (28 cases, 35%), and L3–L4 (10 cases, 12.5%). In cases of involvement at more than one level, the involvement of L3–L4 and L4–L5 levels (5 cases, 6.25%) was more than the involvement of L4–L5 and L5–S1 levels (1 case, 1.25%), especially in women. Preoperative patient family history revealed a 21.1% incidence of IS in first-degree relatives.

We observed preoperative neurogenic claudication in 38 (95%) in the PLF group, and in 36 (90%) in the PLIF group. There was no statistically significant difference in the prevalence of preoperative neural symptoms such as neurogenic claudication in the two groups (p=0.183). Table 1 shows preoperative QoL and severity of radicular pain in groups I and II. The patients' preoperative MRI scans showed no statistically significant difference for the presence of intervertebral foraminal stenosis, improvement in radicular pain (p=0.242), and LBP (p=0.416) in the two groups.

Table 1.

Preoperative Quality of Life and Severity of Radicular Pain in Groups I and II

Groups	Radicular pain (VAS)	QoL (OLBP)
I (n=40)
Mean	5.6	47.7
SD	2.23	1.85
Median	6.00	44
II (n=40)
Mean	5.8	43.3
SD	2.01	1.17
Median	6.00	43
Total
Mean	5.7	43.8
SD	2.12	1.03
Median	6.00	43

QoL, quality of life; VAS, Visual Analogue Scale; OLBP, Oswestry low back pain disability; SD, standard deviation.

There was no statistically significant difference in improvement of radicular pain in both groups 3 days after surgery, but LBP in group I was statistically lower than in group II (Table 2). Over a 3-day hospitalization period, group II patients received more narcotic doses than group I patients, and this was statistically significant (p=0.016).

Table 2.

Radicular Pain and Low Back Pain in Groups I and II 3 Days Post-Surgery

Parameters	Groups	Mean rank (median)	Mean±SD	p Value
Low back pain	I	35.41	2.25±1.34	0.0001
	II	54.09	3.52±1.76
Radicular pain	I	42.43	1±0.98	0.504
	II	45.85	1.2±1.58

SD, standard deviation.

Other clinical parameters were measured 1 year after surgery. The percentage of patients who had complaints of neurogenic claudication 1 year after the operation was significantly higher in group II than in group I (33.3% versus 7.3%; p=0.004).

The difference of OLBP score of low back pain was obtained by subtracting the pre-operative OLBP score from the OLBP score 1 year after the operation. Improvement in QoL in group I was statistically significantly more than in group II (25±9.36 versus 17.10±12.98; p=0.001; Table 3).

Table 3.

Improvement in Low Back Pain in Groups I and II According to the Oswestry Low Back Pain Scale 6 Months after Surgery

Parameters	Groups	Mean rank	Mean±SD	p Value
Low back pain	I	51.00	25.34±9.36	0.001
	II	33.11	17.10±12.98

SD, standard deviation.

One of the other clinical symptoms was the presence of tenderness in the surgical field at 1 year after the operation. It was significantly more prevalent in group II patients (42.5%) than group I patients (20%; p=0.025).

There was no correlation between blood group, job, and underlying diseases in the patients and improvement in radicular pain and LBP.

Radiological results

In our patients, 17.6% had normal disc space narrowing, 34.1% had mild disc space narrowing, 32.9% had moderate disc space narrowing, and 15.3% had severe disc space narrowing. In group I, there was no significant correlation between slip Meyerding grade and disc space height, radicular pain, and LBP. It seemed that an increase of the slip and more reduction of disc height decreased the improvement of radicular pain and LBP in group II, but the difference was not statistically significant.

There was no significant correlation between number of fusion levels (2 vertebrae at one-level listhesis and 3 vertebrae at two-level listhesis) and functional outcome of the patients in groups I and II. Table 4 shows the frequency of the patients with good, fair, and bad fusion in both groups after 1 year.

Table 4.

Frequency of the Patients with Good, Fair, and Bad Fusion in Groups I and II after 6 Months

	Fusion
Groups	Fair+bad	Good	p Value
I	33.3%	66.7%	0.012
II	10.9%	89.1%
Total	21.2%	78.8%

Intraoperative blood loss in group II was significantly more than in group I (Table 5). Surgical duration in the PLIF group was more than in the PLF group, but there was no statistically significant difference between the two groups (p=0.707).

Table 5.

Comparison of Intraoperative Blood Loss in Groups I and II

Parameters	Groups	Mean rank	Mean±SD (mL)	p Value
Intraoperative blood loss	I	38.51	747.87±439	0.04
	II	49.51	873.07±370.24

SD, standard deviation.

There was no significant difference between post-operative complications in the short-term 1-year follow-up period in the two groups (Table 6).

Table 6.

Prevalence of Postoperative Complications in Groups I and II

Complications	Group I (%)	Group II (%)	p Value
Cerebrospinal fluid leak	4.3	5	0.999
Infection	2.1	2.5	0.699
Permanent motor impairment	4.3	5	0.999

Discussion

Instrument-assisted PLF and instrument-assisted PLIF are the two most common techniques for the surgical treatment of IS. Various other minimally-invasive techniques such as extreme lateral interbody fusion/direct lateral interbody fusion (XLIF/DLIF), and transforaminal lumbar interbody fusion (TLIF) are also commonly used for fusion in IS, but there are few concise studies available on these techniques and their comparison to PLF or PLIF (Gong et al., 2010; Goyal et al., 2009; Harms and Jeszenszky, 1998; Kwon et al., 2003; Oliveira et al., 2010). In this study, our findings suggest that PLF with posterior instrumentation provides better clinical outcomes, and improvement in low back pain and QoL, despite the low fusion rate compared to PLIF with posterior instrumentation.

There was no significant difference in the improvement in radicular pain immediately after the operation in the two groups, but the improvement in LBP 3 days after the operation in the patients who were operated on using PLF with posterior instrumentation was significantly more than in the patients who were operated on with PLIF with posterior instrumentation. It seems that foraminotomy without discectomy is sufficient to reduce radicular pain. More LBP was seen in the patients of group II immediately after the operation and 1 year post-operatively, and this may be due to end-plate injury during discectomy and manipulation of the dura, which can also be the cause of the mild tenderness seen in the patients who underwent PLF compared to those with PLIF. The need for careful and gentle release and retraction of the nerve roots and dura in discectomy and appropriate interbody fusion in PLIF patients were the reasons why the procedure was longer in the PLIF group than in the PLF group. Re-assessment of the improvement in radicular pain 1 year after the operation showed that there was no significant difference between the two groups. In contrast with the findings reported by Dantas and associates (2007), who reported that the improvement in radicular pain was 82% in the PLF group and 85.5% in the PLIF group, no statistically significant difference was found between the two groups. Inamdar and colleagues (2006) reported that PLF with posterior instrumentation provides more improvement in radicular pain than PLIF with posterior instrumentation. Our study showed that the improvement of LBP in group I was more significant than in group II. Inamdar's group strongly supported our findings and reported that the improvement of low back pain was 100% in the patients who were operated on with PLF with posterior instrumentation and 80% in the patients who were operated on with PLIF with posterior instrumentation. Madan and Boeree (2002) showed that clinical outcome was good in 81% of patients who underwent PLF with posterior instrumentation, and 69.5% of patients who underwent PLIF with posterior instrumentation. Our finding that PLF with posterior instrumentation provides better clinical outcomes than PLIF with posterior instrumentation replicates the findings of these studies (Inamdar et al., 2006; Madan and Boeree, 2002).

Neurogenic claudication is a clinical syndrome due to lumbar spinal stenosis, or inflammation of the nerves emanating from the spinal cord. Neurogenic means that the problem originates from a nerve, and claudication, from the Latin for limp, describes the painful cramping or weakness in the legs (Comer et al., 2009). Dantas and associates (2007) observed neurogenic claudication in 19 patients (63.3%) in the PLF group, and in 11 patients (36.6%) in the PLIF group, and reported that it was improved in all cases. However, in our study, despite posterior decompression of spinal canal and nerve roots that was performed completely in both groups, the number of the patients who had complaints of neurogenic claudication 1 year after the operation was significantly more in the PLIF group with posterior instrumentation than in the PLF group with posterior instrumentation. As there was no significant difference between the two groups before the operation, the complaints might be because of the performed discectomy, and an increased risk of more extensive epidural fibrosis formation.

Some studies state that the use of narcotics in most cases with IS may be appropriate for managing pain (Agabegi and Fischgrund, 2010; O'Brien, 2003). Over the hospitalization period, the higher rate of narcotic use in group II patients for the reduction of post-operative pain showed that PLIF with posterior instrumentation is a more painful procedure than PLF with posterior instrumentation.

Similarly to the findings of most recent studies (Dehoux et al., 2004; Kim et al., 2010; Tsirikos and Garrido, 2010), except Inamdar and associates (2006), who reported the same fusion rate in both groups, we found significantly higher fusion rates in patients who underwent PLIF rather than PLF with posterior instrumentation. It could be due to more fusion bed and performing fusion under compression (Wolff's law), which was closer to the normal physiology of load-bearing of the anterior spinal column. We believe a 1-year follow-up period is inadequate to evaluate fusion, and fusion rates should be determined at a later time period than 1 year, because the PLF technique probably requires more time to achieve fusion.

Similarly to Kho and Chen (2008), we used the bone chips obtained from laminectomy and posterior decompression mixed with synthetic bone substitute granules to achieve fusion. Farrokhi and colleagues (2010) reported that regarding fusion with either autologous bone or tricalcium phosphate granules, and whether or not decompressive laminectomy had been performed, there were no significant differences. Because the amount of the material used for fusion in groups I and II was substantially different, it was not possible to find a prognostic statistical difference. However, the use of more material was associated with better fusion rates and more improvement in LBP in both groups at 1 year after the operation.

Excessive bleeding, often requiring multiple blood transfusions, can cause not only hemodynamic changes, but also fever and complications following the injection of allogenic blood (Farrokhi et al., 2011; Rhine and Menard, 1991). Möller and Hedlund (2000) showed that supplementary pedicle screw fixation in adult IS increased the total blood loss. Cloward (1985) reported that despite increased the fusion rate of the PLIF technique, it was associated with complications related to blood loss. Yehya (2010) reported that the intraoperative blood loss among the patients undergoing either transforaminal lumbar interbody fusion or PLIF was not significantly different. In our study, intraoperative blood loss in the patients who underwent PLIF was significantly more than those who were operated on with PLF with posterior instrumentation, and there was a significant difference between intraoperative blood loss in the two groups. Our data conflicted with the findings of the study conducted by Ohtori and associates (2011), in which they reported more blood loss in the PLF patients. However, similarly to our findings, Ming-li and colleagues (2009) found that PLF gives rise to less blood loss.

The prevalence of multiple-level spondylolisthesis, that is spondylolisthesis in more than one level, is rare. Only a few articles have reported on multiple-level spondylolysis in the lumbar spine and its treatment (Al-khawashki and Al-sebai, 2001; Al-sebai and Al-khawashki, 1999; Chang et al., 2000; Eingorn and Pizzutillo, 1985; Mathiesen et al., 1984). Wong (2004) reported a rare multi-level IS in a patient following an acute onset of low back pain. Al-sebai and Al-khawashki (1999) reported a case with a combination of multiple bilateral spondylolyses at L2, L3, and L4, spondylolisthesis at L3–L4, spondyloptosis at L4–L5, and sacralization of L5. In our study, the most involved level was L5–S1, and the involvement of L3–L4 and L4–L5 levels was more than the involvement of L4–L5 and L5–S1 levels. Although most of our patients had pars interarticularis defects at L5, the number of the patients with involvement at L4 was remarkable, perhaps because of our patients' spinal anatomy, and the difference in the force exerted on the spine. Wiltse and Winter (1983) reported that the site of IS was at L5 in 90% of cases and L4 in 5%. They showed less involvement at the L4 vertebra compared to our study.

Although the genetic basis of IS is unknown, one possibility can be inferred from the increased incidence of the disease in first-degree relatives of patients with IS (Meyerding, 1932). Wynne-Davies and Scott (1979) showed that the close relatives of patients with IS had a 15% chance of having a similar lesion. Some studies have reported that the incidence in close relatives is about 25–30% (Al-sebai and Al-khawashki, 1999; Ganju, 2002; Wiltse and Rothman, 1989). In our study, preoperative patient family history revealed a 21.1% incidence of IS in first-degree relatives of the patients, unrelated to the degree of improvement in LBP. Family history can help us predict the predisposition of a patient to IS. These findings necessitate further investigation of IS in close relatives of the patients.

Conclusions

Compared with PLIF, the improvement in LBP and QoL was better in patients who underwent PLF with posterior instrumentation. In this study, PLF with posterior instrumentation is recommended for patients with IS, because the procedure is simple, has fewer neurological deficits and less blood loss, as well as better clinical outcomes, especially in patients in whom most complaints are about LBP rather than radicular pain. Our results extend only 1 year, and other conclusions about the advantages of each procedure will require longer follow-up.

Footnotes

Acknowledgments

The authors would like to thank Ms. Hosseini of the Shiraz Neurosciences Research Center (SNRC) for her kind assistance, and the Vice-Chancellor for Research Affairs of Shiraz University of Medical Sciences and Apadana Tajhizgostar Co. for their financial support. We also wish to thank Ms. Gholami of SNRC for translating the manuscript, and Dr. Sedighi for improving the English in the manuscript.

Author Disclosure Statement

No competing financial interests exist.

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