Orthopedics

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Short-term Outcome of Bilateral Decompression via a Unilateral Paramedian Approach for Transforaminal Lumbar Interbody Fusion With Unilateral Pedicle Screw Fixation

Zhen-Zhou Feng, MD, PhD; Yuan-Wu Cao, MD, PhD; Chun Jiang, MD, PhD; Xiao-Xing Jiang, MD, PhD

Abstract

The purpose of this study was to evaluate the clinical and radiologic outcomes of bilateral decompression via a unilateral paramedian approach for transforaminal lumbar interbody fusion. Forty consecutive patients satisfying the inclusion criteria were divided randomly into groups 1 and 2. Patients were treated with unilateral (group 1) or bilateral (group 2) pedicle screw fixation and bilateral decompression via 1-sided (group 1) or bilateral (group 2) paramedian approach. Perioperative parameters (operation time, blood loss, hospital stay, complications, and implant cost), clinical outcome parameters (Japanese Orthopedic Association [JOA] scores, visual analog scale [VAS] scores, and Oswestry Disability Index [ODI] preoperatively and at 1 week and 3 months postoperatively), and radiologic parameters (radiograph and computed tomography [CT] scan preoperatively and at 1 week postoperatively) were compared.

No differences were seen between groups 1 and 2 with respect to operation time, blood loss, or hospital stay. No complications were observed in either group. The ODI, JOA, and VAS values of both groups showed significant differences between the preoperative and 1-week or 3-month postoperative values. No significant differences were seen in the improvements of the ODI, JOA, and VAPS values between groups 1 and 2 at any postoperative time point. Postoperative CT indicated that the contralateral decompression was sufficient in both groups.

The short-term results indicate that bilateral decompression via a unilateral paramedian approach for transforaminal lumbar interbody fusion with unilateral pedicle screw fixation is safe, feasible, and effective over the short-term and is more cost-efficient than a bilateral paramedian approach.

In 1982, Harms and Rolinger1 described an innovative improvement to posterior surgical approaches to the disk space for interbody arthrodesis, designated transforaminal lumbar interbody fusion. Use of the transforaminal lumbar interbody fusion technique with a bilateral pedicle screw has since been widely accepted as a standard operation for lumbar fusion, achieving fusion rates as high as 90% to 100%.2 The technique was further improved by Salehi et al3 in 2004, with the development of the minimally invasive transforaminal lumbar interbody fusion technique. In the latter method, a paramedian approach is used to expose the neural scute and articular processes by splitting the sacrospinalis, leaving the spinous processes and supraspinous/interspinous ligament complex intact.

However, a 1-sided paramedian approach allows only unilateral pedicle screw fixation, and bilateral pedicle screw fixation seems to require a bilateral paramedian approach. Although in vitro studies have shown that unilateral pedicle screw fixation is less stable than bilateral fixation,4,5 the clinical fusion rate does not appear to encounter the same stability problems.6-9 The use of unilateral fixation could reduce the surgical time, blood loss, and implant cost of performing transforaminal lumbar interbody fusion.

When treating bilateral nerve root compression, most surgeons take a back-to-midline approach or use a bilateral paramedian approach for the complete decompression of both sides. Although McCulloch10 achieved bilateral decompression through unilateral laminotomy as early as 1991, and other groups11-14 have since performed bilateral microdecompression using a unilateral approach, each of these studies was performed via a midline approach. Unilateral transforaminal lumbar interbody fusion via a paramedian approach and bilateral decompression via a midline incision were described in various studies,10,15-19 but to our knowledge, bilateral decompression with unilateral pedicle screw fixation via a unilateral paramedian approach incision has not been reported.

Accordingly, we integrated these initial techniques and describe a novel procedure in which a unilateral pedicle screw instrument was used and bilateral decompression was accomplished via a unilateral paramedian approach. The short-term objective of this prospective randomized study was to evaluate the feasibility, safety, and efficacy of bilateral decompression via a unilateral paramedian approach. The long-term objective was to evaluate the fusion rate of transforaminal lumbar…

Abstract

The purpose of this study was to evaluate the clinical and radiologic outcomes of bilateral decompression via a unilateral paramedian approach for transforaminal lumbar interbody fusion. Forty consecutive patients satisfying the inclusion criteria were divided randomly into groups 1 and 2. Patients were treated with unilateral (group 1) or bilateral (group 2) pedicle screw fixation and bilateral decompression via 1-sided (group 1) or bilateral (group 2) paramedian approach. Perioperative parameters (operation time, blood loss, hospital stay, complications, and implant cost), clinical outcome parameters (Japanese Orthopedic Association [JOA] scores, visual analog scale [VAS] scores, and Oswestry Disability Index [ODI] preoperatively and at 1 week and 3 months postoperatively), and radiologic parameters (radiograph and computed tomography [CT] scan preoperatively and at 1 week postoperatively) were compared.

No differences were seen between groups 1 and 2 with respect to operation time, blood loss, or hospital stay. No complications were observed in either group. The ODI, JOA, and VAS values of both groups showed significant differences between the preoperative and 1-week or 3-month postoperative values. No significant differences were seen in the improvements of the ODI, JOA, and VAPS values between groups 1 and 2 at any postoperative time point. Postoperative CT indicated that the contralateral decompression was sufficient in both groups.

The short-term results indicate that bilateral decompression via a unilateral paramedian approach for transforaminal lumbar interbody fusion with unilateral pedicle screw fixation is safe, feasible, and effective over the short-term and is more cost-efficient than a bilateral paramedian approach.

In 1982, Harms and Rolinger1 described an innovative improvement to posterior surgical approaches to the disk space for interbody arthrodesis, designated transforaminal lumbar interbody fusion. Use of the transforaminal lumbar interbody fusion technique with a bilateral pedicle screw has since been widely accepted as a standard operation for lumbar fusion, achieving fusion rates as high as 90% to 100%.2 The technique was further improved by Salehi et al3 in 2004, with the development of the minimally invasive transforaminal lumbar interbody fusion technique. In the latter method, a paramedian approach is used to expose the neural scute and articular processes by splitting the sacrospinalis, leaving the spinous processes and supraspinous/interspinous ligament complex intact.

However, a 1-sided paramedian approach allows only unilateral pedicle screw fixation, and bilateral pedicle screw fixation seems to require a bilateral paramedian approach. Although in vitro studies have shown that unilateral pedicle screw fixation is less stable than bilateral fixation,4,5 the clinical fusion rate does not appear to encounter the same stability problems.6-9 The use of unilateral fixation could reduce the surgical time, blood loss, and implant cost of performing transforaminal lumbar interbody fusion.

When treating bilateral nerve root compression, most surgeons take a back-to-midline approach or use a bilateral paramedian approach for the complete decompression of both sides. Although McCulloch10 achieved bilateral decompression through unilateral laminotomy as early as 1991, and other groups11-14 have since performed bilateral microdecompression using a unilateral approach, each of these studies was performed via a midline approach. Unilateral transforaminal lumbar interbody fusion via a paramedian approach and bilateral decompression via a midline incision were described in various studies,10,15-19 but to our knowledge, bilateral decompression with unilateral pedicle screw fixation via a unilateral paramedian approach incision has not been reported.

Accordingly, we integrated these initial techniques and describe a novel procedure in which a unilateral pedicle screw instrument was used and bilateral decompression was accomplished via a unilateral paramedian approach. The short-term objective of this prospective randomized study was to evaluate the feasibility, safety, and efficacy of bilateral decompression via a unilateral paramedian approach. The long-term objective was to evaluate the fusion rate of transforaminal lumbar interbody fusion with unilateral pedicle screw fixation after 2-year follow-up.

Materials and Methods

Approval for this study was obtained from the Institutional Review Board of Zhongshan Hospital. Consecutive patients who satisfied the following inclusion criteria were considered eligible: an age of 20 to 75 years and 1-level lumbar stenosis or spondylolisthesis (grade I or II) with bilateral nerve root compression symptoms. Exclusion criteria included any prior lumbar surgery or unilateral nerve root compression symptoms.

Enrolled patients were randomized into 2 groups using a computer-generated random number program. Group 1 was treated via 1-sided paramedian approach for transforaminal lumbar interbody fusion with unilateral pedicle screw fixation and bilateral decompression. Group 2 was treated with bilateral pedicle screw fixation and bilateral decompression via bilateral paramedian approach. A single surgeon (X.X.J.) performed all surgeries and was blinded to the patient group until the start of the surgery.

Surgical Technique

After general endotracheal anesthesia was induced, patients were placed in a prone position on a radiolucent table. The pedicles of the vertebral arch of the operating level were marked on the skin with a C-arm machine. A paramedian incision was made between the pedicle skin markers on the severe side in both groups. Through the posterior lumbar fascia, the sacrospinalis was split to expose the ipsilateral facet joint, transverse processes, and vertebral lamina. According to the standard transforaminal lumbar interbody fusion procedure, the inferior and superior articular processes and part of the vertebral lamina were removed with high-speed drills, curettes, and Kerrison rongeurs. These bones were kept for use as an autograft during interbody fusion. The underlying disk space was exposed. The nerve root was decompressed by removal of the ligamentum flavum and bone spur. A sharp knife was used to create a rectangular window on the annulus fibrosus. The disk materials and endplate cartilage were completely removed. The local autograft was implanted, and 1 Capstone cage implant (Medtronic Sofamor Danek, Memphis, Tennessee) and 2 pedicle screws (Legacy; Medtronic Sofamor Danek) were inserted and fixed on the ipsilateral side.

In group 1, the standard transforaminal lumbar interbody fusion procedure was performed. The more ipsilateral lamina was removed to the midline under the spinous process. The space between the contralateral dural and ligamentum flavum was divided. While protecting the nerve retractor, the contralateral ligamentum flavum and osteophytes that had proliferated on the medial margin of the contralateral lamina and facet joint were ground and removed using high-speed drills, curettes, and Kerrison rongeurs through the spinal canal inside.

In group 2, in addition to the standard transforaminal lumbar interbody fusion procedure, the same pedicle screw incision was also made on the other side (for a total of 1 cage implant and 4 pedicle screws). As on the first side, the sacrospinalis was split to expose the articular and transverse processes, laminotomy was performed to decompress the nerve root, and the system was fixed with pedicle screw.

Finally, the wound was irrigated with saline, and drains were placed as needed. Patients wearing a lumbar corset were able to leave the bed as soon as the drain was removed (ie, 1 or 2 days postoperatively).

Perioperative parameters included sex, age, hospital stay, blood loss, operation time, implant cost, and complications. These data were compared to evaluate safety and feasibility.

Clinical outcome parameters included Japanese Orthopedic Association (JOA) scores, visual analog scale (VAS) scores for the lumbar and leg, and Oswestry Disability Index (ODI). Scores were obtained preoperatively and at 1 week and 3, 6, 12, and 24 months postoperatively. These data were compared to evaluate efficacy.

Radiologic parameters included anteroposterior (AP) and lateral radiographs preoperatively and at 1 week and 3, 6, 12, and 24 months postoperatively, additional flexion–extension radiographs preoperatively and at 6, 12, and 24 months postoperatively, and 3-D computed tomography (CT) preoperatively and at 1 week and 12 and 24 months postoperatively. Radiographic analyses mainly evaluated the fusion rate and will be reported in a future article after all follow-ups are completed. The efficacy of the contralateral decompression was judged by comparing the preoperative CT scan with that obtained 1 week postoperatively.

Statistical analysis was performed using SPSS 17.0 for Windows (SPSS Inc, Chicago, Illinois). The Wilcoxon rank-sum and t test were used for statistical analysis of the differences in noncategorical variables between the unilateral and bilateral groups. A P value <.05 was considered statistically significant.

Results

From March 2008 to December 2008, a total of 40 patients were included in the study. Group 1 included 8 men and 12 women with a mean age of 53.8 years (range, 37-72 years). The vertebral levels involved included L3-4 (1 patient), L4-5 (11 patients), and L5-S1 (8 patients). Diagnoses included lumbar canal stenosis (11 patients), spondylolisthesis grade I (6 patients), and spondylolisthesis grade II (3 patients). Group 2 included 10 men and 10 women with a mean age of 53.2 years (range, 25-73 years). The vertebral levels involved included L3-4 (2 patients), L4-5 (12 patients), and L5-S1 (6 patients). Diagnoses included lumbar canal stenosis (10 patients), spondylolisthesis grade I (6 patients), and spondylolisthesis grade II (4 patients). No significant differences in age, sex, or surgical level were observed between the 2 groups.

No neurological injuries, dural tears, or infections were seen in either group. Blood loss, operation time, hospital stay duration, and implant costs are shown in Table 1. No differences were seen between the 2 groups with respect to operation time, blood loss, or hospital stay, although both blood loss and operation time are slightly lower in group 1. Group 1 used 2 pedicle screws plus 1 cage implant, and group 2 used 4 pedicle screws plus 1 cage implant. Accordingly, significant differences in implant cost were observed between the 2 groups.

Table 1

Data from the 3-month postoperative follow-up were received for all 40 patients (Table 2). Postoperative ODI, JOA, and VAS values were significantly different at all times from the preoperative values in both groups. No significant differences in either group were seen in the results at 1 week and 3 months postoperatively. To counteract interference by the basal condition among the 40 patients, groups were compared with the data calculated by the mean robustness regression. These statistics revealed no significant difference in the improvement of ODI, JOA, or VAS values between the 2 groups at any postoperative time point (Table 3).

Table 2


Table 3

Results of CT scans preoperatively and at 1 week postoperatively indicated that the contralateral decompression was sufficient in group 1 (Figure 1). Sufficient decompression was seen, and no osteophyma or disk material in the vertebral canal or bilateral recesses were seen. Radiographic results at 3 months postoperatively revealed no cage collapse, broken drafts, loose pedicle screws, or pseudoarticulation formation (Figure 2). We will continue collecting data through the 24-month follow-up visit, at which time we will compare differences in the fusion rates between the 2 groups.

Figure 1A Figure 1B
Figure 1C Figure 1D
Figure 1: Pre- (A, B) and postoperative (C, D) CT scans in group 1. The contralateral decompression appears sufficient.

Figure 2A Figure 2B
Figure 2: AP (left) and lateral (right) radiographs of group 1 patients preoperatively (A) and at 3 months postoperatively (B).

Discussion

The short-term objective of this prospective randomized study was to evaluate the feasibility, safety, and efficacy of bilateral decompression via a unilateral paramedian approach. No significant differences were seen in terms of hospital stay, blood loss, operation time, or complication rate between groups 1 and 2 (Table 1), indicating that the surgical procedure is feasible and safe. As surgeons become familiar with this technique, we believe blood loss and operation time can be lower. The ODI, JOA, and VAS values differed at all postoperative time points when compared with the preoperative values in both groups, with no significant difference between groups 1 and 2 (Tables 2, 3). These results indicate the efficacy of the surgical procedure. Computed tomography scan also showed that the contralateral decompression was sufficient (Figure 1). Therefore, the most important advantage of the unilateral procedure is that it can substantially reduce implant cost.

Degenerative lumbar spinal stenosis is a common disease worldwide, with the number of surgeries performed for lumbar stenosis increasing each year. Since its first description in 1982,1 transforaminal lumbar interbody fusion has become widely accepted as a standard surgical treatment for lumbar fusion. The standard transforaminal lumbar interbody fusion procedure includes a midline incision, bilateral pedicle screw fixation, and 1 or 2 cages for interbody fusion. The minimally invasive approach with transforaminal lumbar interbody fusion was first reported in 2004.3 Since that time, some surgeons have opted to use a paramedian approach incision, which facilitates pedicle screw insertion and diminishes muscle stripping.8,20 Compared to a midline incision, a paramedian approach incision can preserve the spinous processes and supraspinous/interspinous ligament complex and avoid the atrophy of paravertrebral muscles. In 26 patients who underwent transforaminal lumbar interbody fusion via a median approach on 1 side and a paramedian approach on the other, muscular atrophy was more serious on the side with the median incision, according to postoperative CT.21

Alternatively, some surgeons attempt to use unilateral pedicle screw fixation as a substitute for bilateral pedicle screw. Bilateral pedicle screw fixation requires bilateral pedicle screws, and unilateral fixation seems more suited for minimally invasive surgery. However, in addition to reducing blood loss and operation time, unilateral fixation also reduces implant cost. Therefore, unilateral fixation is the preferred method, assuming that the stability is sufficient. Using in vitro, model, and animal experiments, Goel et al4 observed that unilateral fixation is less stable than bilateral fixation to support interbody fusion. The stability of the unilateral pedicle screw fixation group was 18% to 57% of those in the bilateral fixation group. Similar results were also obtained from vitodynamic measurements on cadavers.5

In contrast, in a clinical study of 87 patients undergoing posterolateral lumbar interbody fusion of 1 or 2 levels, treatment with unilateral or bilateral pedicle screw fixation achieved statistically similar fusion rates (91.5% or 97.5%, respectively).9 In a study by Fernández-Fairen et al,6 eighty-two patients who accepted either unilateral or bilateral pedicle screw fixation were followed up for 3 years, at which time lateral flexion and extension radiographs were taken and the motion between the fusion segments was measured. The fusion rates in the unilateral and bilateral groups were statistically similar (92.7% and 90%, respectively). Thus, although the stability of unilateral pedicle screw fixation seems to be less than that with bilateral fixation, this change is not reflected clinically or in the fusion rate. The stability and fusion rates in the current study will be discussed in a later article, as part of the long-term analysis after 2-year follow-up.

Young et al18 first reported the use of contralateral decompression via the vertebral canal in 1988. A few years later, McCulloch10 used endoscopy to accomplish ipsilateral decompression, expose the contralateral vertebral structure by removing part of ligamenta interspinalia and vertebral lamina, separate the ligamentum flavum and dura, and remove the ligamentum flavum and osteophytes that compressed the nerve root. After finishing these procedures, the bilateral nerve roots were decompressed and free. With the increasing use of endoscopic surgery, numerous studies have addressed the clinical outcomes of unilateral laminotomy for bilateral decompression,11-12,14,22-25 with clinical success rates ranging from 87% to 100%. In contrast to the present study, most previous studies have used a midline incision with the aid of endoscopy. However, previous results suggest the feasibility, efficacy, and safety of using decompression from inside the lumbar canal.

The novelty of our procedure was combining decompression with minimally invasive transforaminal lumbar interbody fusion and unilateral pedicle screw. Because of the pedicle screw fixation, we do not need to consider iatrogenic instability. Because a paramedian approach incision is used and the transforaminal lumbar interbody fusion procedure requires that the facet joint be cut, it is easier to perform contralateral decompression under direct vision, even without endoscopic assistance. Our short-term results indicate that the procedure is safe (no complications), feasible (hospital stay, blood loss, and operation time are not prolonged, and the operation time may be able to be shortened), and effective (improved VAS, JOA, and ODI values). Computed tomography also showed that the contralateral decompression was sufficient. The main benefit to this approach is that it can substantially reduce implant cost.

References

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Authors

Drs Feng, Cao, Jiang (Chun), and Jiang (Xiao-Xing) are from the Department of Orthopedics, Zhongshan Hospital, Fudan University, Shanghai, China.

Drs Feng, Cao, Jiang (Chun), and Jiang (Xiao-Xing) have no relevant financial relationships to disclose.

Correspondence should be addressed to: Xiao-Xing Jiang, MD, PhD, Department of Orthopedics, Zhongshan Hospital, Fudan University, 130 Yixueyuan Rd, Shanghai, 20032 China (jiang.xiaoxing@zs-hospital.sh.cn).

doi: 10.3928/01477447-20110317-05

10.3928/01477447-20110317-05

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