Clinical Experiences of Non-fusion Dynamic Stabilization Surgery for Adjacent Segmental Pathology after Lumbar Fusion

Biomechanical Study of Minimally Invasive Nonfusion Surgery for Treatment of Disc Herniation Associated with Adjacent Segment Disease: A Finite Element Analysis

OBJECTIVE

We explored the biomechanical changes of 2 conventional minimally invasive nonfusion surgical methods for treating disc herniation in adjacent segment disease using 3-dimensional finite element analysis.

METHODS

A model comprising L3 to the sacrum was validated and used to establish an L4-L5 fusion model, and an adjacent segment disease (ASD) model was developed by modifying the material properties of the intervertebral discs. The ASD model was used to simulate 2 conventional minimally invasive nonfusion surgical methods, which resulted in the creation of 2 postoperative models (M1 and M2). The range of motion and the equivalent stress for each model were recorded under 6 different working conditions. The data are descriptive and were analyzed comparatively under a normal load.

RESULTS

Compared with the ASD group, the range of motion of the adjacent segment in the M1 and M2 groups remained unaffected. However, significant Von-Mises stress changes were found in the annulus fibrosus and nucleus pulposus (NP), especially during extension, ipsilateral bending, and rotation. Stress in the NP also shifted toward the surgical incision in the annulus fibrosus during these movements. The maximum Von-Mises stress in the NP of the cephalic segment increased more than did that of the caudal segment.

CONCLUSIONS

Minimal nonfusion surgery for ASD might not affect adjacent segment stability significantly. Nonetheless, it can lead to segmental degeneration deterioration and postoperative recurrence. The cephalic segment is affected more than the caudal segment. Therefore, consideration of disc degeneration and appropriate selection of surgical methods for ASD are crucial.

Medium and long-term radiographic and clinical outcomes of Dynesys dynamic stabilization versus instrumented fusion for degenerative lumbar spine diseases

BACKGROUND

Dynesys stabilization (DS) is utilized to preserve mobility at the instrumental segments and prevent adjacent segment pathology in clinical practice. However, the advantages of DS method in medium and long-term follow-up remain controversial.

OBJECTIVE

To compare the radiographic and clinical outcomes between DS and instrumented fusion in the treatment of degenerative lumbar spine disease with or without grade I spondylolisthesis with a minimum follow-up period of 2 years.

METHODS

We conducted a comprehensive search of PubMed, EMBASE, Cochrane, and Web of Science databases, Chinese National Knowledge Databases, and Wanfang Database for potentially eligible articles. Clinical outcomes were assessed in terms of VAS and ODI scores, screw loosening and breakage, and surgical revision. Radiographic outcomes were assessed in terms of postoperative range of movement (ROM) and disc heigh. Moreover, adjacent segment degeneration (ASDeg) and adjacent segment disease (ASDis) were evaluated.

RESULTS

Seventeen studies with 1296 patients were included in the meta-analysis. The DS group was associated with significantly lower postoperative VAS scores for low-back and leg pain, and lower rate of surgical revision than the fusion group. Moreover, the Dynesys group showed significantly less ASDeg than the fusion group but showed no significant advantage over the fusion group in terms of preventing ASDis. Additionally, the ROM at the stabilized segments of the fusion group decreased significantly and that at the adjacent segments increased significantly compared with those of the DS group.

CONCLUSION

DS showed comparable clinical outcomes and provided benefits in preserving the motion at the stabilized segments, thus limiting the hypermobility at the adjacent segments and preventing ASDeg compared with the fusion method in degenerative disease with or without grade I spondylolisthesis.

Adjacent segment disease following Dynesys stabilization for lumbar disorders: A case series of mid- and long-term follow-ups

BACKGROUND

Radiologic adjacent segment degeneration (ASDeg) can occur after spinal surgery. Adjacent segment disease (ASDis) is defined as the development of new clinical symptoms corresponding to radiographic changes adjacent to the level of previous spinal surgery. Greater pre-existing ASDeg is generally considered to result in more severe ASDis; nonetheless, whether the ASDeg status before index surgery influences the postoperative risk of revision surgery due to ASDis warrants investigation.

AIM

To identify possible risk factors for ASDis and verify the concept that greater preexisting ASDeg leads to more severe ASDis.

METHODS

Data from 212 patients who underwent posterior decompression with Dynesys stabilization from January 2006 to June 2016 were retrospectively analyzed. Patients who underwent surgery for ASDis were categorized as group A (n = 13), whereas those who did not were classified as group B (n = 199). Survival analysis and Cox proportional hazards models were used to compare the modified Pfirrmann grade, University of California-Los Angeles grade, body mass index, number of Dynesys-instrumented levels, and age.

RESULTS

The mean time of reoperation was 7.22 (1.65–11.84) years in group A, and the mean follow-up period was 6.09 (0.10–12.76) years in group B. No significant difference in reoperation risk was observed: Modified Pfirrmann grade 3 vs 4 (P = 0.53) or 4 vs 5 (P = 0.46) for the upper adjacent disc, University of California-Los Angeles grade 2 vs 3 for the upper adjacent segment (P = 0.66), age of < 60 vs > 60 years (P = 0.9), body mass index < 25 vs > 25 kg/m² (P = 0.3), and sex (P = 0.8).

CONCLUSION

Greater preexisting upper ASDeg was not associated with a higher rate of reoperation for ASDis after Dynesys surgery. Being overweight tended to increase reoperation risk after Dynesys surgery for ASDis.

Dynesys® dynamic stabilization outcomes in degenerative spine surgery

Dynesys® is a dynamic device used for posterior stabilization of the lumbar spine. The objective of this study was to analyze the clinical and radiological outcomes at a 2-year minimum follow-up. In this retrospective study, patients operated between 2009 and 2016 with Dynesys® stabilization were included. 5 different etiologies were included: disc herniation, lumbar stenosis, revision for adjacent seg- ment disease (ASD), spondylolisthesis, and scoliosis. Clinical and radiological evaluations were performed. Postoperative complications and revisions were recorded. 136 patients were included: 34 for lumbar spinal stenosis, 19 for disc herniation, 29 degenerative spon- dylolisthesis, 41 revisions for ASD, and 13 scoliosis. Mean age was 64.8. Average clinical follow-up was 46 months. Postoperative clinical results showed a mean lumbar VAS of 3.07, a mean radicular VAS of 3.01 and an ODI score of 31.8%. The ASD rate was 16.2%, and overall revision rate was 11.8%. 2 cases (1.5%) of screw loosening were identified. Clinical outcomes, ASD rate and revision rate were more favorable in the spondylolisthesis and disc herniation groups. This study has one of the largest Dynesys® cohort in literature. Spinal dynamic stabilization by Dynesys® presents good long-term clinical and radiological out- comes with a lower rate of complications than pre- viously published cohorts and lumbar fusions. Best indications seem to be degenerative spondylolisthesis.

Clinical efficacy and radiographic K-rod stabilization for the treatment of multilevel degenerative lumbar spinal stenosis

Background

This study compares the use of radiographic K-Rod dynamic stabilization to the rigid system for the treatment of multisegmental degenerative lumbar spinal stenosis (MDLSS).

Methods

A total of 40 patients with MDLSS who underwent surgical treatment using the K-Rod (n = 25) and rigid systems (n = 15) from March 2013 to March 2017 were assessed. The mean follow-up period was 29.1 months. JOA, ODI, VAS and modified Macnab were assessed. Radiographic evaluations included lumbar lordosis angle, ISR value, operative and proximal adjacent ROM. Changes in intervertebral disc signal were classified according to Pfirrmann grade and UCLA system.

Results

JOA, ODI and VAS changed significantly after the operation to comparable levels between the groups. However, the lumbar lordosis significantly decreased at final follow-up between both groups. The ROM of the proximal adjacent segment increased at final follow-up, but the number of fixed segment ROMs in the K-Rod group were significantly lower at the final follow-up than observed prior to the operation. In both groups, the ISR of the proximal adjacent segment decreased, most notably in the rigid group. The ISR of the non-fusion fixed segments in the K-Rod group increased post-operation and during final follow-up. The levels of adjacent segment degeneration were higher in the rigid group vs. the K-Rod group according to modified Pfirrmann grading and the UCLA system.

Conclusions

Compared with the rigid system for treatment of MDLSS, dynamic K-Rod stabilization achieves improved radiographic outcomes and improves the mobility of the stabilized segments, minimizing the influence on the proximal adjacent segment.

Clinical validity of two different grading systems for lumbar central canal stenosis: Schizas and Lee classification systems

OBJECTIVE

To assess the learnability of two magnetic resonance imaging (MRI) grading systems for lumbar central canal stenosis based on inter-observer agreement and test-retest reliability of doctors with no prior knowledge of the two systems.

MATERIALS AND METHODS

Two clinical fellows, one novice radiology resident, one neurosurgeon, and one orthopedic surgeon, who were unaware of the two qualitative MRI grading systems prior to this study, acquainted themselves with the teaching files. All five observers independently assessed the LCCS grade of 70 patients using T2-weighted axial magnetic resonance images at the L2-3, L3-4, L3-4, and L5-S1 disc levels. Analysis was performed twice at an interval of two months.

RESULTS

The inter-observer agreement among all five readers was excellent and test-retest reliability was moderate to excellent for both the Schizas and Lee systems. Positive percentage agreements were found to be over 0.8 in almost all observers with relatively narrow 95% confidence limits.

CONCLUSION

Both Schizas and Lee MRI grading systems for LCCS are reliable grading systems, and can be used as a learnable method for both clinicians and radiologists.

Analysis of clinical effect and radiographic outcomes of Isobar TTL system for two-segment lumbar degenerative disease: a retrospective study

Background

Nonfusion fixation is an effective way to treat lumbar degeneration. In the present study, we analyzed the clinical effects and radiographic outcomes of the Isobar TTL system used to treat two-segment lumbar degenerative disease.

Method

Forty-one patients diagnosed with two-segment lumbar degenerative disease underwent surgical implantation of the Isobar TTL dynamic stabilization system (n = 20) or a rigid system (n = 21) from January 2013 to June 2017. The mean follow-up time was 23.6 (range 15–37) months. Clinical results were evaluated with the Oswestry Disability Index (ODI), modified Macnab criteria, and the visual analog score (VAS). Radiographic evaluations included the height of the intervertebral space and the range of motion (ROM) of the treated and adjacent segments. The intervertebral disc signal was classified using the modified Pfirrmann grading system and the University of California at Los Angeles (UCLA) system.

Results

The clinical results, including the ODI and VAS, showed that there was significant improvement in the two groups after implantation and that the difference between the two groups was not significant. In addition, the clinical efficacy indicated by the modified Macnab criteria for the two groups was similar. Radiological outcomes included the height of the intervertebral space, lumbar mobility, and intervertebral disc signal. The height of the intervertebral space of the upper adjacent segment L2/3 in the rigid group was significantly lower than that in the Isobar TTL group at the last follow-up. Furthermore, the number of ROMs of the fixed-segment L3/4 in the Isobar TTL group was significantly less than that before implantation, suggesting that the fixed-segment ROMs in the Isobar TTL group were limited. In addition, the ROM of the upper adjacent segment L2/3 in the last follow-up of the rigid group increased significantly, while that of the Isobar TTL group did not change after implantation. Finally, the incidence of adjacent-segment degeneration (ASD) was significantly greater in the rigid group than in the Isobar TTL group according to the UCLA system.

Conclusion

The Isobar TTL system can be clinically effective for treating two-segment lumbar degenerative disease. Compared with rigid fixation, the Isobar TTL system yielded better radiographic outcomes and maintained the mobility of the treated segments with less impact on the proximal adjacent segment.