Following fusion surgery, various surgical interventions can be performed in cases where adjacent segment disease (ASD) develops. These interventions include extending the instrumentation with decompression, performing short-level stabilization at the adjacent segment after instrumentation removal, conducting minimally invasive decompression after instrumentation removal, or performing minimally invasive decompression without removing the instrumentation.1–11

In cases with fusion, removal of the instrumentation may positively affect lumbar pain syndrome.12,13 Moreover, in cases where fusion is applied with pedicular screw fixation, the most commonly encountered causes of lumbar pain syndrome include pseudoarthrosis, flatback deformity, ASD, painful disc due to posterolateral fusion as well as implant loosening or fracture.12–14

There is no consensus in the literature regarding the surgical technique that should be used in these cases. However, a positive effect on lumbar pain syndrome following the removal of instrumentation has been reported.12–14 Additionally, there is debate regarding what the subsequent intervention should be after the removal of instrumentation. One commonly used method is short-segment fixation-decompression (SSFD) with extensive decompression (laminectomy) at the segment with ASD, and the use of endoscopic or microscopic minimally invasive techniques is also becoming more common.15,16

Regardless of these cases, microsurgical bilateral decompression via unilateral approach (MBDU)ok is also a minimally invasive technique used in degenerative spinal stenosis.17–21

This study aimed to determine which method is more effective and safe in patients who developed ASD following fusion surgery by comparing SSFD and MBDU after the removal of instrumentation.

The study was started with ethics committee approval with protocol number.2024-TBEK 2024/07/11.

A total of 47 cases who had previously undergone lumbar fusion and subsequently developed ASD and underwent instrumentation removal followed by SSFD at the Neurosurgery Clinic of Yüksek İhtisas Training and Research Hospital, and a total of 29 cases with a similar history that underwent instrumentation removal followed by MBDU at the Neurosurgery Clinic of Bursa VM Medical Park Hospital between 2017 and 2021 were retrospectively examined.

Surgical procedure

Patients who had previously undergone lumbar fixation and developed ASD underwent posterior lumbar decompressive laminectomy and pedicle screw instrumentation at the single stenotic level after the removal of instrumentation under general anesthesia in the prone position.

MBDU; Patients who had previously undergone lumbar fixation and developed ASD underwent MBDU to decompress the central canal and bilateral lateral recesses under general anesthesia in the prone position. After the removal of instrumentation microscopic laminotomy was performed on the approach side using an air drill, Kerrison rongeur, and microcurette. Subsequently, decompression was performed on the contralateral side after rotating the operating table to the contralateral side.

While determining the effectiveness of the techniques, it was planned to make comparisons of radicular pain and low back pain in pre and postoperative follow-ups and to determine whether there was adequate decompression. Radicular Visual Analogue Scale (VAS), Owestry Disability Index (ODI) and ratios of canal diameters in pre and postoperative 3-month lumbar MRI imaging were used to make these comparisons.

In determining the safety of the techniques, we looked for complications that may develop secondary to instrumentation such as new ASD development, instability development in both groups; screw fracture-slippage, loosening in the SSFD group, which occurred in the follow-up after optimally performed surgery without perop complications; and radiologic examinations were used for this.

Patients with radiological evidence of instability, those with spinal deformities, those with ASD observed at the spinal transition zones and cases with peroperative complications were excluded from the study.

The surgical technique to be used for patients other than those excluded from the study was determined entirely according to the surgeons' preference.

In both groups, gender; age; preoperative symptom duration; duration of hospitalization; preoperative and postoperative 1-h, 10-day, 3-month, 1-year, and final follow-up radicular VAS scores; ratios of canal diameters in preoperative and postoperative 3-month lumbar MRI imaging (Fig. 1); ODI indices during postoperative intermittent follow-up periods were determined and documented. At the same time, postoperative complications that may develop secondary to instrumentation such as new ASD development, instability development in both groups; screw fracture-slippage, loosening in the SSFD group were evaluated and radiologic examinations such as MRI, CT and radiographs were utilized for this purpose. Late complications were noted.

Fig. 1.

Measurement of transverse canal diameter at the surgically treated segment in axial lumbar MRI sections.

The data were compared statistically, and inferences were made based on data analysis. As the length of skin incision, amount of bleeding, and operation times may vary based on the type and length of previous instrumentation, these parameters were not included in the study.

In the SSFD group, 55.40% of the patients were women and 44.60% were men. The age range was 55–69 years (mean age 67.06 years). In the MBDU group, 51.80% of the patients were women and 48.20% were men. The age range was 48–71 years (mean age 60.37 years). Moreover, there was no significant difference between the two groups in terms of gender distribution and age range (p = 0.4 and 0.3, respectively).

The mean follow-up period was 38.89 months (24–60 months) in the SSFD group and 37.48 months (32–54 months) in the MBDU group.

Preoperative symptom duration ranged between 3 and 12 months in the SSFD group (mean 5.20 months) and 3 and 8 months in the MBDU group (mean 4.80 months). No significant difference was observed between the groups in terms of symptom duration (p = 0.15).

The mean hospitalization duration was 66.38 hours in the SSFD group and 23.58 hours in the MBDU group. Statistical comparison revealed a significant difference (p < 0.001) (Table 1).

In terms of radicular pain assessment using VAS, the mean preoperative VAS score was 5.8 in the SSFD group and 1.4 at postoperative 1 hour, 1.2 at postoperative day 10, 0.8 at 3 months, and 0.2 at 1 year. In the MBDU group, the mean preoperative VAS score was 6.2 and 1.2 at postoperative 1 hour, 1.1 at postoperative day 10, 0.8 at 3 months, and 0.1 at 1 year. No significant difference was observed between the groups (Table 2) (Fig. 2).

Fig. 2.

VAS Scores in the Preop and Postop Period.

In the preoperative and postoperative 3-month lumbar MRI imaging, the mean ratio of transverse canal diameter at the segment that underwent decompression for ASD was 0.27 in the SSFD group and 0.43 in the MBDU group. A significant difference was observed between the groups in terms of this value (p = 0.03) (Table 3).

In terms of ODI assessment, in the SSFD group, the mean ODI score was observed as 42 on day 10, 38 at 3 months, 24 at 1 year, and 22 at the final follow-up. In the MBDU group, the mean ODI score was calculated as 18 on day 10, 12 at 3 months, 4 at 1 year, and 4 at the final follow-up. A statistically significant difference was found between the groups in terms of ODI scores (Table4) (Fig. 3).

Fig. 3.

ODI Index Values in the Postop Period.

In cases of lumbar degenerative diseases where conservative treatment fails to yield results, spinal fusion has commonly been used as a surgical method that can often produce satisfactory outcomes.22,23 However, this method may lead to ASD in some cases during the postoperative period due to increased biomechanical stress on the adjacent segments caused by lumbar arthrodesis.24 Symptomatic ASD often leads to worsened clinical outcomes and the need for new surgical interventions.24

The decision regarding additional surgical interventions in cases unresponsive to conservative treatment is contentious. In cases where ASD develops, various surgical interventions can be performed, including extending the instrumentation with decompression, performing short-level stabilization at the adjacent segment after instrumentation removal, conducting minimally invasive decompression after instrumentation removal, or performing minimally invasive decompression without removing the instrumentation.1–11 Since minimally invasive decompression of the adjacent segment without extending or removing the instruments would not eliminate lumbar pain syndrome secondary to instrumentation and would cause confusion in the comparison between SSFD and MBDU methods, the study was planned and conducted only in cases in which the instrumentation was removed and additional intervention was performed.

There have been studies in the literature regarding the development of ASD following short-segment fixation and decompression applied to the pathological segment.9–11 In the present study, during the 3-year follow-up period, new symptomatic ASD was observed in 6.80% of cases treated with SSFD and radiological ASD development was observed in 19.15% of cases. Conversely, no new symptomatic ASD was observed in the MBDU group, whereas radiological ASD was observed in 10.34% of the patients. In cases where ASD is the primary concern, SSFD surgery carrying the risk of new ASD development can lead to further issues in the future. Furthermore, it may include expected complications secondary to fixation surgery such as loosening, instrument fracture, and pull-out. As MBDU does not create additional biomechanical stress, symptomatic ASD is not expected in these cases. However, Telfeian et al. reported a failure rate of 33% at 2 years after transforaminal endoscopic surgery for L5-S1 ASD after fusion in a study published in 2022.1 In our study, although the radiologic ASD rate was not very low in patients who underwent MBDU, it was interesting that no symptomatic ASD was observed. This may be due to the fact that MBDU allows wider decompression compared to endoscopic interventions and does not create additional biomechanical stress on adjacent segments as in instrumentation.

In terms of the duration of hospitalization, it can be said that MBDU is more advantageous compared to SSFD. Since MBDU causes less tissue trauma, it was noted that patients treated with MBDU could be discharged earlier and mobilized on the same day, and this period was longer in the SSFD group (p < 0.001) (Table 1).

In terms of radicular pain, no significant difference was observed between the two groups during postoperative follow-up (Table 2, Fig. 2). Additionally, ODI scores were significantly lower in the MBDU group (Table 4). The fact that it is a minimally invasive method that causes less tissue trauma, does not cause biomechanical stress secondary to fixation, and eliminates the possibility of pseudoarthrosis or loosening may have minimized the occurrence and severity of lumbar pain syndrome in the MBDU group.

Canal diameter ratios measured in the decompressed segment in preoperative and postoperative lumbar MRI were observed to be low in the SSFD applied group. This data shows that more extensive decompression is performed in SSFD than in MBDU. These results were thought to be due to the opportunity to perform wider decompression with facet resection in SSFD. Protecting the facets in order to avoid instability in MBDU may have caused the decompression to appear to be more inadequate than in SSFD. However, no clinical symptoms secondary to inadequate decompression were observed in the MBDU group during the 3-year follow-up.

As authors, we are aware that our study has some limitations. One of the limitations may be the relatively small number of cases in the groups. However, the results are clear that MBDU seems to be much more advantageous than SSFD in both groups at postoperative follow-up, especially in terms of ODI index and new ASD development. Therefore, it can be assumed that the results would not have been essentially different if more patients had been included.

Secondly, the homogeneity of the groups and the retrospective nature of the study may be questioned due to the fact that only one technique was used in one of the centers and the other technique was used in the other. In this sense, we believe that new prospective studies to be performed in a single center and, if possible, with cases operated by the same surgical team may provide more detailed results.

This is the first comparison of these two techniques after instrument removal in ASD cases in the literature. In selected cases with ASD after fusion surgery, without signs of instability, spinal deformities, or ASD at the spinal transition zones, MBDU after instrumentation removal can be considered as a minimally invasive option that does not exacerbate postoperative lumbar pain syndrome or trigger the development of new ASD.

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  Study conception and design: TK, AK.

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  Data collection: TK, AK.

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  Analysis and interpretation of results: TK.

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  Draft manuscript preparation: AK & TK.

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  Critical revision of the article: TK, AK.

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  Other (study supervision, fundings, materials, etc…): TK.

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  All authors reviewed the results and approved the final version of the manuscript.

None.