Dynamic versus rigid stabilization for the treatment of disc degeneration in the lumbar spine

ABSTRACT

 

Study design: Retrospective cohort study.

Clinical question: This study aimed to describe the outcome of stabilization surgery with dynamic instrumentation for degenerative disc disease. The results were compared with age- and gender-matched peers treated with traditional fusion with rigid instrumentation. If necessary, additional nerve elements decompression was undertaken in both groups.

Methods: This study analyzed the success rates of 25 patients aged 47.4 years (mean 95% confidence interval: 43.1 – 51.7) treated with stabilization of the involved vertebral dynamic unit(s) with either dynamic or rigid instrumentation with or without additional decompression. Clinical outcome was assessed with Oswestry disability index (ODI) and visual analogue scale (VAS) for back pain, leg pain, and activity level. Satisfaction outcome was measured with Stauffer and Coventry overall satisfaction criteria and VAS for satisfaction. Health-related quality of life was estimated with Short Form-36 (SF-36) questionnaires. Fusion rate and adjacent level(s) was checked with x-ray. Complications recorded in patients’ files were evaluated and revision surgeries were stated as treatment failures.

Results: At the 4-year follow-up (range, 2 – 5 years) significant improvement was noted on some subjective parameters in both groups. No statistical differences were seen between the groups at final follow-up. Five patients (42%) in the rigid group and two patients (20%) in the dynamic group were rated good or excellent according to the overall Stauffer and Coventry satisfaction criteria. Radiologically, seven patients (58%) in the rigid group were undoubtedly fused and all the involved discs in the dynamic group continued to degenerate. Adjacent segments showed loss of disc height in both groups but only loss of upper adjacent discs in the rigid group was statistically significant. Two patients in the dynamic group and one patient in the rigid group required reoperation because of the pedicle screw misplacement.

Conclusion: The results of this study indicate no significant difference between dynamic and rigid stabilization of the lumbar spine for patients with degenerative disc disease (DDD). However, the study is underpowered and further studies on larger and homogeneous group of patients should be undertaken.

None of the authors or the department with which they are affiliated has received anything of value from or owns stock in a commercial company or institution related directly or indirectly to the subject of this article.
Device(s) status: Approved.

REFERENCES

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EDITORIAL PERSPECTIVE

The reviewers congratulated Fokter and Strahovnik on tackling an interesting and controversial subject with a well-designed study. They make a good effort to compare the two groups clinically and radiographically. Dealing with degenerative lumbar spine conditions notoriously opens the door for a myriad of variables and confounding factors, which make real-life research in this area so very challenging.

(1) The reviewers joined the authors in noting that this retrospective study comparing 12 patients in one arm with 13 patients in another arm was underpowered due to lack of sample size. However, with the lack of a power, it is not accurate to conclude that there is no difference or even that „there does not appear to be a clear clinical advantage“ of one technique over the other. Therefore, to conclude a null hypothesis is inaccurate. Rather, the findings simply support that the authors did not observe a significant difference between the two techniques, while acknowledging that the study is underpowered.

(2) The inclusion criteria are patients with „degenerative disc disease [DDD] requiring decompressive surgery with additional stabilization of the degenerated segment(s).“ Fokter and Strahovnik list the number of patients with DDD only and DDD with herniated disc, stenosis, and prior disc surgery. This inclusion, however, is broad and includes many variables, and does not exclude deformity such as scoliosis or spondylolisthesis. The study group includes patients who underwent „decompression“ for presumptive neurocompressive pathology. It is impossible to point to how much the improvement of symptoms in both groups is attributable to decompression of the neural elements versus function of the implants. In the future, they may want to consider the two groups in patients with DDD who did not require decompression. Thus, the effect of these implants without a concurrent decompression can better be assessed.

(3) The fusion rate as x-ray outcomes remains controversial—fusions may have occurred in the dynamic group and may not have been identified. Conversely, the 58 % fusion rate in the rigid group after more than 2 years seems very low and raises questions about the surgical techniques.

(4) An interesting biomechanical observation involved the levels of instrumentation. The consequences of a L5-S1 and a L4-L5 stabilization are not comparable. Because after a lumbosacral stabilization, there is one adjacent segment left compared with two adjacent segments for all other segments.

(5) Finally, one of the reviewers challenged the indication for dynamic stabilization shown in Figure 3.

In light of a degenerated and extruded disc, with significant decrease of the disc height in L4 / 5 and a degenerated disc in L5/S1, the reviewer believed that the L4 / 5 was too unstable for dynamic stabilization and would have recommended a rigid fusion.

These points are helpful in advancing our understanding toward creating better future studies. Fokter and Strahovnik deserve praise for an excellent effort and simulating valuable further discussions on this surgical technique, and how we can improve our research efforts.