Biomechanical comparison of transdiscal fixation and posterior fixation with and without transforaminal lumbar interbody fusion in the treatment of L5-S1 lumbosacral joint

Transdiscal instrumentation in single-level lumbosacral fusion for high-grade isthmic pediatric spondylolisthesis: Technical note and review of the literature

Pediatric spondylolisthesis is a common cause of back pain in children, typically managed conservatively with bracing and non-steroidal anti-inflammatory drugs. When posterolateral fusion is performed for refractory pain, pseudarthrosis and implant failure may occur, necessitating reoperation. To improve patient outcomes, there is a need for alternative surgical techniques to effectively manage high-grade isthmic slips. Here, the authors report the case of a child with Meyerding grade III anterolisthesis of L5 on S1 who was treated with a single-level, instrumented fusion using bilateral S1-L5 transdiscal screws, supported with L5-S1 posterolateral instrumentation and arthrodesis. Postoperatively, there was improvement in the patient's symptoms with good clinical and radiographic outcomes. The patient continues to be symptom free with radiographic evidence of hardware stability and bony fusion across the segment. The authors detail a novel surgical technique in children as well as a review of lumbosacral transdiscal screw fixation. Further evidence is required to definitively establish the safety, outcomes, and biomechanical strength of this technique.

The effects of pre-stressed rods contoured by different bending techniques on posterior instrumentation of L4-L5 lumbar spine segment: A finite element study

Posterior pedicle screw instrumentation (PPSI) is a well-known method in lumbar spine surgery. Understanding how PPSI affects the biomechanics of the lumbar spine is an important issue. In particular, during PPSI operations, surgeons bend rods according to the patients’ spinal curvatures based on their own experiences. As a result, residual stresses develop on the rods due to this bending. Although many finite element-based biomechanical studies have been performed for PPSI, studies comparing the effects of residual stresses arising from rod contouring on the construct stresses are lacking. Thus, this study aimed to investigate the effects of residual stress in PPSI using rods contoured with a French bender and an in-situ bender, as well as comparing the differences in stress increment with straight and contoured rods for different physiological motions. Accordingly, a finite element (FE) model of the L4-L5 lumbar spine segment was developed for PPSI and the effects of residual stresses on rods were investigated by using different bending methods. In the simulations, it was found that rods contoured with a French bender with residual stress resulted in significantly more increased stress in PPSI compared to those contoured with an in-situ bender. The results of this study emphasize that increased stress in PPSI due to the residual stresses for different physiological motions may increase the risk of PPSI failures. Additionally, the finite element modeling approach employed here could be used as a fundamental tool for further investigations of topics such as PPSI fatigue life and failure studies.

Influence of posterior pedicle screw fixation at L4-L5 level on biomechanics of the lumbar spine with and without fusion: a finite element method

Background

Posterior pedicle screw (PS) fixation, a common treatment method for widespread low-back pain problems, has many uncertain aspects including stress concentration levels, effects on adjacent segments, and relationships with physiological motions. A better understanding of how posterior PS fixation affects the biomechanics of the lumbar spine is needed. For this purpose, a finite element (FE) model of a lumbar spine with posterior PS fixation at the L4–L5 segment level was developed by partially removing facet joints (FJs) to imitate an actual surgical procedure. This FE study aimed to investigate the influence of the posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion by determining which physiological motions have the most increase in posterior instrumentation (PI) stresses and FJ loading.

Results

It was determined that posterior PS fixation increased FJ loading by approximately 35% and 23% at the L3–L4 adjacent level with extension and lateral bending motion, respectively. This increase in FJ loading at the adjacent level could point to the possibility that adjacent segment disease has developed or progressed after posterior lumbar interbody fusion. Furthermore, analyses of peak von Mises stresses on PI showed that the maximum PI stresses of 272.1 MPa and 263.7 MPa occurred in lateral bending and flexion motion before fusion, respectively.

Conclusions

The effects of a posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion were investigated for all physiological motions. This model could be used as a fundamental tool for further studies, providing a better understanding of the effects of posterior PS fixation by clearing up uncertain aspects.

Long term outcome and fusion rate of transdiscal fixation for L5-S1 high grade spondylolisthesis

OBJECTIVE

High grade spondylolisthesis (HGS) is a quite rare entity and many techniques are available to address this condition. In 1994 Abdu et al. proposed a transdiscal fixation approach that achieved a good clinical outcome. We analyse outcome and fusion achieved in patients treated by transdiscal fixation after 1-year follow-up.

METHODS

We reviewed patients operated through transdiscal fixation since 2014 with a follow-up of at least 1 year, and compared preoperative and postoperative clinical measures (ODI, VAS and EQ-5D) and postoperative complications. Also, we analyzed the degree of fusion on CT scan with Lenke and Birdwell criteria.

RESULTS

Twelve patients were included in the study with a mean follow-up of 49.4 months (range 12.8-84.1 months). Three cases presented a Meyerding grade IV spondylolisthesis and 9 cases grade III. At 1-year follow-up mean postoperative ODI, VAS and EQ5D scores improved (ODI 13.2 (range 0-30) vs 49.83 (range 15-71.1); p = .005). Equally this improvement was seen in the last follow-up (ODI 9.28 (range 0-35) vs 49.83 (range 15-71.1); p = .005). CT scan showed fusion grade A in 5 patients (41.6%), another 5 as grade B (41.6%) in Lenke classification. According to the Birdwell criteria 4 patients were classified as grade I (33.3%), 7 patients grade II (58.3%). None showed complications postoperatively or radiolucency in follow-up.

CONCLUSIONS

Transdiscal fixation shows a good clinical outcome that is maintained throughout a long time period and provides a reliable and suitable fusion.

rhBMP in lumber fusion for lumbar spondylolisthesis: A systematic review and meta-analysis

PURPOSE

To compare the efficacy and safety of recombinant human bone morphogenetic protein (rhBMP) and iliac crest autograft in the fusion treatment of lumbar spondylolisthesis.

METHODS

The studies using randomized controlled trials to compare the rhBMP with iliac crest autograft in the treatment of lumbar spondylolisthesis were retrieved from Embase, Pubmed, ProQuest dissertations & theses (PQDT), China national knowledge infrastructure (CNKI), Chinese Biomedical Database, Wanfang Data, Cochrane Library (from March 1998 to March 2018). Postoperative fusion rate, clinical success rate, postoperative intervertebral height, complications, operation time, blood loss and duration of hospitalization were chosen as the outcome indicators. Methodological quality of the trials was critically assessed, and relevant data were extracted. Statistical software Revman 5.3 was used for data-analysis.

RESULTS

Eleven articles were included in the meta-analysis. The results showed that, comparing the efficacy of rhBMP with iliac crest autograft, statistical significance was found in the 24-month fusion rate post operation [95% CI (1.38, 24.70), p = 0.02] and operation time [95% CI (-14.22, -2.08), p = 0.008]. There is not sufficient evidence for statistical differences in the remaining indicators.

CONCLUSION

The current literature shows rhBMP is a safe and effective grafting material in the treatment of lumbar spondylolisthesis. Further evidence is dependent on the emergence of more randomized controlled trials with higher quality and larger sample sizes in the future.