A Modified Method to Treat Severe Asymptomatic Pre-Existing Degeneration of Adjacent Segment: A Retrospective Case-Control Study

DOI: https://doi.org/10.21203/rs.3.rs-94518/v1

Abstract

Background: Pre-existing degeneration of adjacent segment is an important risk factor for adjacent segment degeneration (ASD), but limited and controversial studies have addressed its management.

Methods: Patients with symptomatic degeneration of the L5/S1 segment warranting surgical interference and severe asymptomatic degeneration of the L4/5 segment were retrospectively analyzed. Among them, those who underwent interbody fusion in the causative (L5/S1) segment and distraction of the intervertebral space and facet fusion in the adjacent L4/5 segment were included as Group A (n=103). Patients who underwent interbody fusion in both L5/S1 and L4/5 segments were included as Group B (n=81). Clinical and radiographic outcomes were evaluated.

Results: Mean follow-up was 58.5 months (range, 48-75 m). No significant difference in clinical outcomes or the incidence of adjacent segment degeneration in L3/4 segment was found between Groups A and B. Compared with Group B, less bleeding (315±84 vs. 532±105 ml), shorter operation time (107±34 vs. 158±55 min) and lower costs (13,830±2640 vs. 16,020±3380 US$) were found in Group A (P<0.05). In Group A, disc height ratio (DHR) of L4/5 segment was significantly increased from preoperative value of 0.40±0.13 to last follow-up value of 0.53±0.18 (P<0.05), while the degree of canal stenosis (DCS) was decreased from preoperative value of 34.3±11.2% to last follow-up value of 15.9±9.3% (P<0.05).

Conclusions: This modified method could be effective in treating severe asymptomatic pre-existing degeneration of adjacent segment in lumbar spine.

Background

Posterior lumbar interbody fusion (PLIF), which can provide posterior fusion concomitant with anterior column support, is an effective procedure for lumbar degenerative diseases such as lumbar disc herniation, degenerative spondylolisthesis, degenerative instability and spinal canal stenosis. However, with its wide applications, many complications emerge, including pseudarthrosis, loosening or breaking of the implant, and adjacent segment degeneration (ASD). Development of ASD has attracted increasing attention because it adversely affects long-term clinical outcome and sometimes requires surgery13. The exact cause of ASD remains controversial, yet some risk factors have been documented4, 5. Among them, pre-existing degeneration of the adjacent segment is one of the most important risk factors4, 1, 6. Studies concerning whether asymptomatic pre-existing degeneration of adjacent disc should be treated, and how to be treated are limited and controversial. If left untreated, clinical symptoms may appear, warranting a second operation, which was consistently associated with technical difficulties, poor outcomes, and psychological and economical burdens6, 7. A better therapeutic approach should be taken from the first surgery. Some surgeons may carry out a fusion of the causative segment and simultaneous extensive laminal or semi-laminal decompression surgery or augmenting the vertebral canal in a hidden-proceed manner without fusion at the adjacent segment with asymptomatic pre-existing degeneration, but this approach may not be so effective and may even induce symptomatic ASD4. Some suggest a complete PLIF at the adjacent level, which may increase not only the costs but also the surgical trauma8. Recently, some other surgeons prefer dynamic stabilization, but multiple studies showed that there is no significant advantages of dynamic stabilization on preventing ASD and many issues have been reported for the use of dynamic stabilization such as limited indications, dissatisfactory long-term results, and high incidence of reoperation911.

In this paper, we reported a modified method to treat severe asymptomatic pre-existing degeneration of adjacent segment by performing a distraction of the intervertebral space and facet fusions in the adjacent segment with significant degeneration. To evaluate the effectiveness of this approach, a retrospective case-control study was conducted.

Methods

Patient Characteristics

This study was approved by the Ethics Committee of Honghui Hospital (No. XAHHLLSP0901), and written consent was obtained from all of the patients. We retrospectively reviewed the records of all patients who underwent lumbar spinal fusion surgery in L4/5 and L5/S1 segments for lumbar disc herniation from September 2009 through November 2014. We included the patients who had received imaging examination and preoperative nerve electrophysiological test to confirm that S1 nerve root was causative of the neurological symptoms, and L5/S1 segment was the causative segment. And if confirmed diagnosis cannot be obtained in the above-mentioned examinations, nerve root block had been conducted.

Inclusion and Exclusion Criteria

Inclusion criteria were the following: 1) symptomatic degeneration of the L5/S1 segment warranting surgical interference; 2) asymptomatic degeneration of the L4/5 segment with equal or more than Pfirrmann Grade IV12 causing equal or more than 25% spinal canal stenosis (the degree of canal stenosis was evaluated and calculated on preoperative MRI according to the method introduced by Imagama et al13 as shown in Fig. 2b).

Exclusion criteria were the following: 1) symptomatic disc herniation in L4/5 segment; 2) equal or more than Pfirrmann Grade IV disc degeneration, spondylolisthesis, spinal instability or stenosis in L3/4 segment; 3) history of spinal operation.

The patients who underwent interbody fusion in the causative (L5/S1) segment, and a distraction of the intervertebral space and facet fusions in the adjacent L4/5 segment were included as Group A, and those who underwent interbody fusions in both L5/S1 and L4/5 segments were included as Group B.

Surgical Technique

For patients in Group A, standard PLIF was performed in the L5/S1 segment. For the distraction of the intervertebral space in L4/5 segment, disc space between L4 and L5 was moderately distracted using a distraction device with the L4 and L5 pedicle screw caps as fulcrums. As a reference for the distraction distance, the height of the adjacent intervertebral space was used, and excessive distraction should be avoided to prevent excessively increased nerve root tension. For the facet fusions in L4/5 segment, V-shape osteotomy was carried out on the L4 inferior articular facet and L5 superior articular facet from top to bottom using an osteotome to create a V-shape groove on the both sides of L4/5 segment (Fig. 1a, 1c). The autogenous bone chips from laminectomy were then implanted into the V-shape grooves (Fig. 1b, 1d).

For patients in Group B, standard PLIFs were performed in both L5/S1 and L4/5 segments.

Assessment of Outcome

Data Collection and Analysis

X-rays were obtained at 3, 6, 9, 12,18, and 24 months and every 1 year thereafter to evaluate the position of the internal fixation, presence of loosening or migration and change in the adjacent L3/4 segment. Symptomatic and functional recovery was evaluated using the Visual Analogue Scale (VAS) and the Oswestry Disability Index (ODI). At the most recent follow-up, X-rays, computed tomography (CT) and MRI were performed.

In Group A, disc height ratio (DHR) of the L4/5 segment was measured according to the Farfan’s method14 on lateral radiograph as shown in Fig. 2a. Briefly, DHR was defined as [anterior disc height (A) + posterior disc height (B)] / the distance between the anterior and posterior margins of the disc (C) [DHR=(A + B)/C]. The degree of disc degeneration in L3/4 and L4/5 segments was graded on MRI T2-weighted images according to the Pfirrmann grading system12. The degree of canal stenosis (DCS) in L3/4 and L4/5 segments was evaluated and calculated on MRI according to the method introduced by Imagama et al13 as shown in Fig. 2b. Briefly, DCS was defined as [the sagittal length of the spinal canal (A) - the maximal sagittal length of the hernia (B)] / the sagittal length of the spinal canal (A) × 100 [DCS=(A-B)/A × 100]. Measurements were performed twice by two observers independently, and interobserver and intraobserver reliabilities of these data were greater than a correlation of 0.80. Radiographic ASD in L3/4 segment was defined as: 1) development of spondylolisthesis or spinal instability; 2) disc degeneration equal to or more than Pfirrmann Grade IV.

Statistical analysis

Comparison between preoperative and postoperative values was performed using paired t-test. The independent sample t-test was conducted to compare the outcomes between Groups A and B. Statistical analyses were conducted using SPSS 20.0 (IBM, Armonk, NY, USA). Two-sided P < 0.05 was considered statistically significant.

Results

Follow-up of Patient Characteristics

A total of 103 patients (43 male and 60 female) were included in Group A, whose mean age was 61.5 years (range, 31–74 y). And 81patients (37 male and 44 female) were included in Group B, whose mean age was 59.7 years old (range, 34–72 y). The mean follow-up was 58.5 months (range, 48–75 m).

Clinical Results

As shown in Table 1, compared with Group B, less bleeding (315 ± 84 vs. 532 ± 105 ml), shorter operation time (107 ± 34 vs. 158 ± 55 min), and lower costs (13,830 ± 2640 vs. 16,020 ± 3380 US$) (all P < 0.05) were found in Group A. The preoperative and final follow-up VAS and ODI scores were presented also in Table 1, and the clinical symptoms in both groups were improved postoperatively (P < 0.05). But preoperatively or postoperatively there was no significant difference of VAS and ODI scores between Groups A and B (all P > 0.05). No implant loosening or breakage was found in all patients at the last follow-up.

Table 1

Clinical outcomes in Groups A and B

 

Group A

Group B

Bleeding (ml)#

315 ± 84

532 ± 105

Operation time (min)#

107 ± 34

158 ± 55

Total cost (US$)#

13,830 ± 2640

16,020 ± 3380

VAS*

   

Preoperative

7.7 ± 2.1

7.5 ± 1.6

Final Follow-Up

1.4 ± 0.7

1.6 ± 0.8

ODI*

   

Preoperative

65.3 ± 11.6

62.2 ± 8.2

Final Follow-Up

13.5 ± 5.7

14.7 ± 7.3

#P < 0.05 between Groups A and B
*P < 0.05 between preoperative score and final follow-up score in both Groups A and B
VAS: Visual Analog Scale; ODI: Oswestry Disability Index

Radiographic Findings

In Group A, disc height ratio (DHR) in L4/5 segment was significantly increased from preoperative value of 0.40 ± 0.13 to last follow-up value of 0.53 ± 0.18 (P < 0.05), while the degree of canal stenosis (DCS) was decreased from preoperative value of 34.3 ± 11.2% to last follow-up value of 15.9 ± 9.3% (P < 0.05) (Table 2). Radiographic ASD in L3/4 segment has been found in 13 of 103 (12.62%) patients in Group A and 9 of 81 (11.11%) patients in Group B at the final follow up, but there was no significant difference in the occurrence of radiographic L3/4 ASD between the two groups (P>0.05).

Table 2

Radiologic Outcomes of L4/5 Segment in Group A

 

Preoperative

Final Follow-Up

DHR#

0.40 ± 0.13

0.53 ± 0.18

DCS #

34.3 ± 11.2%

15.9 ± 9.3%

# P < 0.05 between preoperative score and final follow-up score
DHR: Disc Height Ratio
DCS: Degree of Canal Stenosis

Illustrative Case

A 54-years-old man with chief complaint of radiating pain to the left lower extremity was diagnosed as lumbar disc herniation. The causative segment had been confirmed to be L5/S1 segment by preoperative examination. Preoperative MRI demonstrated that 42.5% of spinal canal stenosis in L4/5 segment was caused by the degenerative disc (Pfirrmann Grade IV, Fig. 3c, d). We performed a standard PLIF in L5/S1 segment, and distraction of the intervertebral space and facet fusion in L4/5 segment. At the 5-year follow-up assessment, CT showed that complete facet fusion in L4-5 facets was achieved (Fig. 3a, 3b), and MRI demonstrated that the degree of spinal canal stenosis in L4/5 segment was decreased to 7.2% (Fig. 3e, f), indicating that the disc herniation was retracted.

Discussion

Our study demonstrated that a distraction of the intervertebral space and facet fusions in L4/5 segment with severe degeneration, could be effective in preventing ASD of L4/5 segment, and had several advantages over interbody fusions in both L5/S1 and L4/5 segments, including decreased bleeding, shorter operation time and lower costs.

The incidence of ASD varies from 8.2–18.5% among studies, and about 2.7–20% patients with symptomatic ASD need surgical intervention13, 5. Patients with pre-existing degenerative changes at an adjacent motion segment would have a worse long-term clinical outcome and experience a higher rate of sequelae4, 1, 6. Anandjiwala et al. found that adjacent segments with Pfirrmann Grade IV or V degeneration constitute a significant risk factor for ASD and suggested that adjacent segments with Grade IV or V degeneration should be included in the primary fusion procedure to prevent subsequent ASD15. But complete interbody fusion at the adjacent level, not only markedly increases the overall operation costs, but also leads to more surgical trauma with related consequences8. Meanwhile, some surgeons choose to augment the vertebral canal in a hidden-proceed manner without fusion at the adjacent segment, but Hikata et al. reported that simultaneous decompression surgery without fusion at the adjacent level may not be effective in reducing the incidence of symptomatic ASD4.

Interspinous distraction devices and dynamic stabilization across pedicle screws can theoretically prevent ASD by preserving some motion at the segment. Korovessis et al. recommended the use of the Wallis interspinous implant in the unfused vertebral segment cephalad to instrumentation with mild arthritic changes to protect the adjacent segments16. In the present study, significant disc degeneration and spinal stenosis in the adjacent segment (L4/5 segment) were present; therefore, distracting the interspinous process is far from enough to retract the herniated disc and decompress the spinal stenosis. Graf ligament and Dynesys device are the mostly used devices for dynamic stabilization. Since there was severe disc degeneration at L4/5 segment, the Graf ligament was unsuitable for our patients17. The Dynesys system can resist both tensile and compressive forces and control motion of the segment in all the directions, but this system has a high incidence of screw loosening18 and the incidence of ASD is similar to that of traditional method10, 19.

The present study has several limitations. It was a retrospective study that limited the data to those available in the medical charts. Only a single center was involved, and a small sample size of cases were included. Patients with significant L3/4 degeneration were excluded to lower interindividual and intergroup variability, but it could result in lower generalizability. Additional prospective studies are necessary to confirm these results.

Conclusion

Our outcomes indicate that distraction of the intervertebral space and facet fusions could be effective in treating severe asymptomatic pre-existing degeneration of adjacent segment in lumbar spine.

Abbreviations

ASD

adjacent segment degeneration; PLIF:posterior lumbar interbody fusion; VAS:Visual Analogue Scale; ODI:Oswestry Disability Index; MRI:magnetic resonance imaging; CT:computed tomography; DHR:disc height ratio; DCS:degree of canal stenosis.

Declarations

Acknowledgements

We thank the patients for their cooperation.

Funding

This study was supported by the Postdoctoral Science Foundation in Shaanxi Province of China (NO.2017BSHQYXMZZ15) and Young Teachers Fund of the Sun Yat-Sen University (NO.20ykpy94). The funding agency had no input in to the design of the study, the collection, analysis and interpretation of data, the writing of the manuscript, or the decision to publish, and the authors have no competing interests.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors’ contributions

All authors contributed to the analysis and interpretation of data. WJG and DJH has been involved in conception and design. XLZ and JWZ has been involved in drafting the manuscript. YBL contributed to the acquisition of data. All authors gave final approval of the version to be published.

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Honghui Hospital (No. XAHHLLSP0901), and written consent was obtained from all patients. 

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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