Transdiscal L5-S1 screws for the treatment of adult spondylolisthesis

Biomechanical analysis of a trans-discal, multi-level stabilization screw (MLSS) at the upper instrumented vertebra (UIV) of long posterior thoracolumbar instrumentations

PURPOSE

To evaluate proximal junctional biomechanics of a MLSS relative to traditional pedicle screw fixation at the proximal extent of T10-pelvis posterior instrumentation constructs (T10-p PSF).

METHODS

A previously validated three-dimensional osseoligamentous spinopelvic finite element (FE) model was used to compare proximal junctional range-of-motion (ROM), vertebral body stresses, and discal biomechanics between two groups: (1) T10-p with a T10-11 MLSS ("T10-11 MLSS") and (2) T10-p with a traditional T10 pedicle screw ("Traditional T10-PS").

RESULTS

The T10-11 MLSS had a 5% decrease in T9 cortical bone stress compared to Traditional T10-PS. Conversely, the T10 and T11 bone stresses increased by 46% and 98%, respectively, with T10-11 MLSS compared to Traditional T10-PS. Annular stresses and intradiscal pressures (IDP) were similar at T9-T10 between constructs. At the T10-11 disc, T10-11 MLSS decreased annular stresses by 29% and IDP by 48% compared to Traditional T10-PS. Adjacent ROM (T8-9 & T9-10) were similar between T10-11 MLSS and Traditional T10-PS. T10-11 MLSS had 39% greater ROM at T10-11 and 23% less ROM at T11-12 compared to Traditional T10-PS.

CONCLUSIONS

In this FE analysis, a T10-11 MLSS at the proximal extent of T10-pelvis posterior instrumentation resulted in increased T10 and T11 cortical bone stresses, decreased discal annular stress and IDP and increased ROM at T10-11, and no change in ROM at the adjacent level. Given the complex and multifactorial nature of proximal junctional kyphosis, these results require additional biomechanical and clinical evaluations to determine the clinical utility of MLSS on the proximal junctions of thoracolumbar posterior instrumented fusions.

Use of L5-S1 transdiscal screws in the treatment of isthmic spondylolisthesis: a technical note

Surgical treatment of L5-S1 isthmic spondylolisthesis consists of a combination of decompression and fusion. One previously discussed mode of fusion is via transdiscal screws. Biomechanical studies of transdiscal screws have demonstrated greater rigidity than traditional pedicle screw fixation, which theoretically translates to a higher fusion rate. Furthermore, when compared to pedicle screw fixation, transdiscal screw fixation also demonstrates improved functional and radiographic outcomes. However, transdiscal screw placement can be technically difficult. At this time, a detailed surgical technique has yet to be reported in the literature. Our surgical technique for transdiscal screw placement using intraoperative C-arm at L5-S1 is described. We include considerations for preoperative planning including necessary imaging and appropriate patient selection. We also discuss intraoperative concerns such as setup, surgical approach, proper screw trajectory, and our method for achieving indirect decompression. The results of thirteen consecutive patients treated with transdiscal screw fixation are described. One patient had subcutaneous seroma requiring reoperation (7.7%), three patients had implant failure (23.1%), and one patient had nonunion (7.7%). Our results suggest that transdiscal screw fixation is a safe and acceptable alternative for stabilization and indirect decompression of L5-S1 isthmic spondylolisthesis. Recent innovation in intraoperative navigation and robotic surgery may lessen the technical difficulty of transdiscal screw placement and make it even more effective.

The role of femoral obliquity angle and T1 pelvic angle in predicting quality of life after spinal surgery in adult spinal deformities

BACKGROUND

Adult spinal deformities (ASD) represent a growing clinical condition related to chronic pain, disability and reduction in quality of life (QoL). A strong correlation among spinal alignment, spinopelvic parameters and QoL after spinal fusion surgery in ASD patients was thoroughly investigated over the last decade, However, only few studies focused on the relationship between lumbo-pelvic-femoral parameters - such as Femoral Obliquity Angle (FOA), T1 Pelvic Angle (TPA) and QoL.

METHODS

Radiological and clinical data from 43 patients surgically treated with thoracolumbar posterior spinal fusion for ASD between 2015 and 2018 were retrospectively analyzed. The primary outcomes were the correlation between preoperative spino-pelvic-femoral parameters and postoperative clinical, functional outcomes and QoL. Secondary outcomes were: changes in sagittal radiographic parameters spino-pelvic-femoral, clinical and functional outcomes and the rate of complications after surgery.

RESULTS

Using Spearman's rank correlation coefficients, spinopelvic femoral parameters (FOA, TPA, pre and post-operative) are directly statistically correlated to the quality of life (ODI, SRS-22, pre and post-operative; > 0,6 strong correlation, p <  0.05). Stratifying the patients according pre preoperative FOA value (High FOA ≥ 10 and Normal/Low FOA <  10), those belonging to the first group showed worse clinical (VAS: 5.2 +/- 1.4 vs 2.9 +/- 0.8) and functional outcomes (ODI: 35.6+/- 6.8 vs 23.2 +/- 6.5) after 2 years of follow-up and a greater number of mechanical complications (57.9% vs 8.3% p <  0.0021).

CONCLUSION

Based on our results, preoperative FOA and TPA could be important prognostic parameters for predicting disability and quality of life after spinal surgery in ASD patients and early indicators of possible spinal sagittal malalignment. FOA and TPA, like other and better known spinopelvic parameters, should always be considered when planning corrective surgery in ASD patients.

Epidemiology and aetiology of male and female sexual dysfunctions related to pelvic ring injuries: a systematic review

INTRODUCTION

Pelvic ring injuries, frequently caused by high energy trauma, are associated with high rates of morbidity and mortality (5-33%), often due to significant blood loss and disruption of the lumbosacral plexus, genitourinary system, and gastrointestinal system. The aim of the present study is to perform a systematic literature review on male and female sexual dysfunctions related to traumatic lesions of the pelvic ring.

METHODS

Scopus, Cochrane Library MEDLINE via PubMed, and Embase were searched using the keywords: "Pelvic fracture," "Pelvic Ring Fracture," "Pelvic Ring Trauma," "Pelvic Ring injury," "Sexual dysfunction," "Erectile dysfunction," "dyspareunia," and their MeSH terms in any possible combination. The following questions were formulated according to the PICO (population (P), intervention (I), comparison (C), and outcome (O)) scheme: Do patients suffering from pelvic fracture (P) report worse clinical outcomes (C), in terms of sexual function (O), when urological injury occurs (I)? Is the sexual function (O) influenced by the type of fracture (I)?

RESULTS

After screening 268 articles by title and abstract, 77 were considered eligible for the full-text analysis. Finally 17 studies that met inclusion criteria were included in the review. Overall, 1364 patients (902 males and 462 females, M/F ratio: 1.9) suffering from pelvic fractures were collected.

DISCUSSION

Pelvic fractures represent challenging entities, often concomitant with systemic injuries and subsequent morbidity. Anatomical consideration, etiology, correlation between sexual dysfunction and genitourinary lesions, or pelvic fracture type were investigated.

CONCLUSION

There are evidences in the literature that the gravity and frequency of SD are related with the pelvic ring fracture type. In fact, patients with APC, VS (according Young-Burgess), or C (according Tile) fracture pattern reported higher incidence and gravity of SD. Only a week association could be found between GUI and incidence and gravity of SD, and relationship between surgical treatment and SD. Electrophysiological tests should be routinely used in patient suffering from SD after pelvic ring injuries.

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.

Biomechanical comparison of 3 types of transdiscal fixation implants for fixing high-grade L5/S1 spine spondylolisthesis

BACKGROUND CONTEXT

There are several options for the stabilization of high-grade lumbosacral spondylolisthesis including transdiscal screws, the Bohlman technique (transdiscal fibular strut) and the modified Bohlman technique (transdiscal titanium mesh cage). The choice of an optimum construct remains controversial; therefore, we endeavoured to study and compare the biomechanical performance of these 3 techniques.

PURPOSE

The aim of this study was to compare 3 types of transdiscal fixation biomechanically in an in vitro porcine lumbar-sacral spine model.

STUDY DESIGN/SETTING

Porcine cadaveric biomechanical study.

METHODS

18 complete lumbar-sacral porcine spines were split into 3 repair groups, transdiscal screws (TS), Bohlman technique, and a modified Bohlman technique (MBT). Range of motion (L3 - S1) was measured in an intact and repaired state for flexion, extension, left/right lateral bending, and left/right torsion. To recreate a high-grade lumbosacral spondylolisthesis a bilateral L5/S1 facetectomy, removing the intervertebral disc completely, and the L5 body was displaced 50%-60% over the sacral promontory. Results were analyzed and compared to intact baseline measurements. Standard quasi-static moments (5 Nm) were applied in all modes.

RESULTS

All range of motion (ROM) were in reference to intact baseline values. TS had the lowest ROM in all modes (p=.006-.495). Statistical difference was found only in extension for TS vs. BT (p=.011) and TS vs. MBT (p=.014). No bone or implant failures occurred.

CONCLUSION

TS provided the lowest ROM in all modes of loading compared to Bohlman technique and MBT. Our study indicates that TS results in the most biomechanically stable construct.

CLINICAL SIGNIFICANCE

Knowledge of the biomechanical attributes of various constructs could aid physicians in choosing a surgical construct for their patients.

Screws Fixation for Oblique Lateral Lumbar Interbody Fusion (OL-LIF): A Finite Element Study

Background

The combination of screw fixation and cage can provide stability in lumbar interbody fusion (LIF), which is an important technique to treat lumbar degeneration diseases. As the narrow surface cage is developed in oblique lateral lumbar interbody fusion (OL-LIF), screw fixation should be improved at the same time. We used the finite element (FE) method to investigate the biomechanics response by three different ways of screw fixation in OL-LIF.

Methods

Using a validated FE model, OL-LIF with 3 different screw fixations was simulated, including percutaneous transverterbral screw (PTVS) fixation, percutaneous cortical bone trajectory screw (PCBTS) fixation, and percutaneous transpedical screw (PPS) fixation. Range of motion (ROM), vertebral body displacement, cage displacement, cage stress, cortical bone stress, and screw stress were compared.

Results

ROM in FE models significantly decreased by 84-89% in flexion, 91-93% in extension, 78-89% in right and left lateral bending, and 73-82% in right and left axial rotation compared to the original model. The maximum displacement of the vertebral body and the cage in six motions except for the extension of model PTVS was the smallest among models. Meanwhile, the model PTVS had the higher stress of screw-rods system and also the lowest stress of cage. In all moments, the maximum stresses of the cages were lower than their yield stress.

Conclusions

Three screw fixations can highly restrict the surgical functional spinal unit (FSU). PTVS provided the better stability than the other two screw fixations. It may be a good choice for OL-LIF.

High-Grade Spondylolisthesis in Adults: Current Concepts in Evaluation and Management

Background

Information regarding the treatment of high-grade spondylolisthesis (HGS) in adults has been previously described; however, previous descriptions of the evaluation and surgical management of HGS do not represent more recent and now established approaches. The purpose of the current review is to discuss current concepts in the evaluation and management of patients with HGS.

Methods

Literature review.

Results

HGS is diagnosed in up to 11.3% of adults with spondylolisthesis and typically presents as nonspecific lower back pain. Regarding evaluation, a thorough history and physical examination should be performed, which may help predict the presence of HGS. Diagnostic imaging, and specifically the use of spino-pelvic parameters, are now commonly implicated in guiding treatment course and prognosis. When surgical intervention is indicated, surgical approaches include in situ fusion variations, reduction and partial reduction with fusion, and vertebrectomy. Although the majority of studies suggest improvements with these approaches, the literature is limited by a low level of evidence with regards to the superiority of one technique when compared with others.

Conclusions

HGS is a unique cause of low back pain in adults that carries considerable morbidity, but rarely presents with neurologic symptoms. Although the definitions, classifications, and methods of diagnosis of this spinal deformity have been established and accepted, the ideal surgical management of this deformity remains highly debated. Fusion in situ techniques are often technically easier to perform and provide lower risk of neurologic complications, whereas reduction and fusion techniques offer greater restoration of global spino-pelvic balance. Preoperative spino-pelvic parameters may have utility in assisting in procedural selection; however, future, higher-quality and longer-term studies are warranted to determine the optimal surgical intervention among the widely available techniques currently used, and to better define the indications for these interventions.

Symptomatic vertebral hemangioma during pregnancy period: A case series and systematic literature review

Vertebral Hemangioma (VH) is a benign tumor usually symptomless and discovered incidentally. Pregnancy, because of several hormonal and physiologic changes, is a recognized risk factor coinciding with the development of a rapid onset of neurological symptoms in patients affected by VH. In the Literature, sporadic cases of neurological symptoms have been described, which occurred during pregnancy, but only rarely the onset of symptoms was reported after pregnancy and childbirth. Usually surgical treatment is reserved for severe cases with rapid onset of neurological symptoms. However, the use of conservative treatments is still a topic of debate In the present study, we report a series of patients affected by VH become symptomatic during or after pregnancy along with a systematic review of the Literature.

Biomechanical evaluation of traditional posterior versus anterior spondylolisthesis reduction in a cadaveric grade I slip model

OBJECTIVE

Posterior reduction with pedicle screws is often used for stabilization of unstable spondylolisthesis to directly reduce misalignment or protect against micromotion while fusion of the affected level occurs. Optimal treatment of spondylolisthesis combines consistent reduction with a reduced risk of construct failure. The authors compared the reduction achieved with a novel anterior integrated spacer with a built-in reduction mechanism (ISR) to the reduction achieved with pedicle screws alone, or in combination with an anterior lumbar interbody fusion (ALIF) spacer, in a cadaveric grade I spondylolisthesis model.

METHODS

Grade I slip was modeled in 6 cadaveric L5-S1 segments by creation of a partial nucleotomy and facetectomy and application of dynamic cyclic loading. Following the creation of spondylolisthesis, reduction was performed under increasing axial loads, simulating muscle trunk forces between 50 and 157.5 lbs, in the following order: bilateral pedicle screws (BPS), BPS with an anterior spacer (BPS+S), and ISR. Percent reduction and reduction failure load-the axial load at which successful reduction (≥ 50% correction) was not achieved-were recorded along with the failure mechanism. Corrections were evaluated using lateral fluoroscopic images.

RESULTS

The average loads at which BPS and BPS+S failed were 92.5 ± 6.1 and 94.2 ± 13.9 lbs, respectively. The ISR construct failed at a statistically higher load of 140.0 ± 27.1 lbs. Reduction at the largest axial load (157.5 lbs) by the ISR device was tested in 67% (4 of 6) of the specimens, was successful in 33% (2 of 6), and achieved 68.3 ± 37.4% of the available reduction. For the BPS and BPS+S constructs, the largest axial load was 105.0 lbs, with average reductions of 21.3 ± 0.0% (1 of 6) and 32.4 ± 5.7% (3 of 6) respectively.

CONCLUSIONS

While both posterior and anterior reduction devices maintained reduction under gravimetric loading, the reduction capacity of the novel anterior ISR device was more effective at greater loads than traditional pedicle screw techniques. Full correction was achieved with pedicle screws, with or without ALIF, but under significantly lower axial loads. The anterior ISR may prove useful when higher reduction forces are required; however, additional clinical studies will be needed to evaluate the effectiveness of anterior devices with built-in reduction mechanisms.

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

Transdiscal screw fixation is generally performed in the treatment of high-grade L5-S1 spondylolisthesis. The main thought of the study is that the biomechanical performances of the transdiscal pedicle screw fixation can be identical to standard posterior pedicle screw fixations with or without transforaminal lumbar interbody fusion cage insertion. Lumbosacral portions and pelvises of 45 healthy lambs' vertebrae were dissected. Animal cadavers were randomly and equally divided into three groups for instrumentation. Three fixation systems, L5-S1 posterior pedicle screw fixation, L5-S1 posterior pedicle screw fixation with transforaminal lumbar interbody fusion cage insertion, and L5-S1 transdiscal pedicle screw fixation, were generated. Axial compression, flexion, and torsion tests were conducted on test samples of each system. In axial compression, L5-S1 transdiscal fixation was less stiff than L5-S1 posterior pedicle screw fixation with transforaminal lumbar interbody fusion cage insertion. There were no significant differences between groups in flexion. Furthermore, L5-S1 posterior fixation was stiffest under torsional loads. When axial compression and flexion loads are taken into consideration, transdiscal fixation can be alternatively used instead of posterior pedicle screw fixation in the treatment of L5-S1 spondylolisthesis because it satisfies enough stability. However, in torsion, posterior fixation is shown as a better option due to its higher stiffness.

Image guidance in transdiscal fixation for high-grade spondylolisthesis in adults with correct spinal balance

OBJECTIVE Spondylolisthesis is a prevalent spine disease that recent studies estimate could be detected in 9% of the population. High-grade spondylolisthesis (HGS), however, is much less frequent, which makes it difficult to develop a general recommendation for its treatment. Posterior transdiscal fixation was proposed in 1994 for HGS, and the use of spine navigation could make this technique more accessible and reduce the morbidity associated with the procedure. The purpose of this study was to present a case series involving adult patients with HGS and correct spinal alignment who were treated with transdiscal pedicle screw placement guided with neuronavigation and compare the results to those achieved previously without image guidance. METHODS The authors reviewed all cases in which adult patients with correct spinal alignment were treated for HGS with posterior transdiscal instrumentation placement guided with navigation between 2014 and 2016 at their institution. The authors compared preoperative and postoperative spinopelvic parameters on standing radiographs as well as Oswestry Disability Index (ODI) scores and visual analog scale (VAS) scores for low-back pain. Follow-up CT and MRI studies and postoperative radiographs were evaluated to identify any screw malplacement or instrumentation failure. Any other intraoperative or postoperative complications were also recorded. RESULTS Eight patients underwent posterior transdiscal navigated instrumentation placement during this period, with a mean duration of follow-up of 16 months (range 9-24 months). Six of the patients presented with Meyerding grade III spondylolisthesis and 2 with Meyerding grade IV. In 5 cases, L4-S1 instrumentation was placed, while in the other 3 cases, surgery consisted of transdiscal L5-S1 fixation. There was no significant difference between preoperative and postoperative spinopelvic parameters. However, there was a statistically significant improvement in the mean VAS score for low-back pain (6.5 ± 1.5 vs 4 ± 1.7) and the mean ODI score (49.2 ± 19.4 vs 37.7 ± 22) (p = 0.01 and p = 0.012, respectively). Six patients reduced their use of pain medication. There were no intraoperative or postoperative complications during the hospital stay, and as of the most recent follow-up, no complications related to pseudarthrosis or hardware failure had been observed. CONCLUSIONS Treatment with posterior transdiscal pedicle screws with in situ fusion achieved good clinical and radiological outcomes in patients with HGS and good sagittal spinal balance. The use of navigation and image guidance was associated with improved results in this technique, including a reduction in postoperative and intraoperative complications related to screw malplacement, pseudarthrosis, and instrumentation failure.

Biomechanical properties of posterior transpedicular-transdiscal oblique lumbar screw fixation with novel trapezoidal lateral interbody spacer: an in vitro human cadaveric model

PURPOSE

To investigate biomechanical properties of posterior transpedicular-transdiscal (TPTD) oblique lumbar screw fixation whereby the screw traverses the inferior pedicle across the posterior disc space into the super-adjacent body and lateral trapezoidal interbody spacer.

METHODS

Eight fresh-frozen osteoligamentous human cadaveric spines (L1-S1) were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR), with pure bending moment set at 7.5 Nm. Surgical constructs included (1) intact spine; (2) bilateral pedicle screw (BPS) fixation at L3-L4; (3) TPTD screw fixation at L3-L4; (4) lateral L3-L4 discectomy; (5) TPTD screw fixation with lateral interbody spacer (TPTD+S); and (6) BPS fixation with lateral interbody spacer (BPS+S). Peak range of motion (ROM) at L3-L4 was normalized to intact for statistical analysis.

RESULTS

In FE and LB, all posterior fixation with or without interbody spacers significantly reduced motion compared with intact and discectomy. BPS and BPS+S provided increased fixation in all planes of motion; significantly reducing FE and LB motion relative to TPTD (p = 0.005, p = 0.002 and p = 0.020, p = 0.004, respectively). In AR, only BPS significantly reduced normalized ROM to intact (p = 0.034); BPS+S provided greater fixation compared with TPTD+S (p = 0.005).

CONCLUSIONS

Investigators found less stiffness with TPTD screw fixation than with BPS regardless of immediate stabilization with lateral discectomy and spacer. Clinical use should be decided by required biomechanical performance, difficulty of installation, and extent of paraspinal tissue disruption.

Transdiscal screw versus pedicle screw fixation for high-grade L5-S1 isthmic spondylolisthesis in patients younger than 60 years: a case-control study

PURPOSE

To compare outcomes between transdiscal and conventional pedicle fixation for high-grade L5-S1 spondylolisthesis.

METHODS

This was a retrospective case-control study with patients prospectively followed. Twenty-five consecutive patients with mean age of 36.7 years underwent transdiscal fixation, and 31 other with mean age of 42.0 years to pedicle fixation were clinically and radiographically compared. Clinical assessments were performed using Oswestry Disability Index (ODI), Core Outcomes Measures Index (COMI), Short-Form 12 (SF-12), and pain visual analog scale (VAS). Radiographic spinopelvic parameters were also evaluated. The mean follow-up was 2.7 years (range 2.0-5.3).

RESULTS

Preoperative data were comparable between groups. Surgery time, blood loss, and hospital stay were similar between groups. At last follow-up, clinical and radiographic outcomes were significantly improved in both groups. Postoperatively, both lumbar and leg pain VAS were similar between groups, but ODI (20.2 vs. 31.6, p = 0.010), COMI (1.6 vs. 2.8, p = 0.012), and SF-12 physical (84.3 vs. 61.5, p = 0.004) and mental (81.5 vs. 69.4, p = 0.021) scores were significantly better in the transdiscal group. The neurologic complication rate was similar in both groups. There were 4 pseudoarthroses in the pedicle group, and none in the transdiscal group.

CONCLUSION

L5-S1 transdiscal screw fixation provided better functional and radiographic outcomes at medium-term than conventional pedicle fixation for high-grade spondylolisthesis, although transdiscal sacral screws are difficult to place in correct position.

Biomechanics of transvertebral screw fixation in the thoracic spine: an in vitro study

OBJECTIVE Transvertebral screws provide stability in thoracic spinal fixation surgeries, with their use mainly limited to patients who require a pedicle screw salvage technique. However, the biomechanical impact of transvertebral screws alone, when they are inserted across 2 vertebral bodies, has not been studied. In this study, the authors assessed the stability offered by a transvertebral screw construct for posterior instrumentation and compared its biomechanical performance to that of standard bilateral pedicle screw and rod (PSR) fixation. METHODS Fourteen fresh human cadaveric thoracic spine segments from T-6 to T-11 were divided into 2 groups with similar ages and bone quality. Group 1 received transvertebral screws across 2 levels without rods and subsequently with interconnecting bilateral rods at 3 levels (T8-10). Group 2 received bilateral PSR fixation and were sequentially tested with interconnecting rods at T7-8 and T9-10, at T8-9, and at T8-10. Flexibility tests were performed on intact and instrumented specimens in both groups. Presurgical and postsurgical O-arm 3D images were obtained to verify screw placement. RESULTS The mean range of motion (ROM) per motion segment with transvertebral screws spanning 2 levels compared with the intact condition was 66% of the mean intact ROM during flexion-extension (p = 0.013), 69% during lateral bending (p = 0.015), and 47% during axial rotation (p < 0.001). The mean ROM per motion segment with PSR spanning 2 levels compared with the intact condition was 38% of the mean intact ROM during flexion-extension (p < 0.001), 57% during lateral bending (p = 0.007), and 27% during axial rotation (p < 0.001). Adding bilateral rods to the 3 levels with transvertebral screws decreased the mean ROM per motion segment to 28% of intact ROM during flexion-extension (p < 0.001), 37% during lateral bending (p < 0.001), and 30% during axial rotation (p < 0.001). The mean ROM per motion segment for PSR spanning 3 levels was 21% of intact ROM during flexion-extension (p < 0.001), 33% during lateral bending (p < 0.001), and 22% during axial rotation (p < 0.001). CONCLUSIONS Biomechanically, fixation with a novel technique in the thoracic spine involving transvertebral screws showed restoration of stability to well within the stability provided by PSR fixation.

Feasibility and biomechanical performance of a novel transdiscal screw system for one level in non-spondylolisthetic lumbar fusion: an in vitro investigation

BACKGROUND CONTEXT

The bilateral pedicle screw system (BPSS) is currently the "gold standard" fusion technique for spinal instability. A new stabilization system that provides the same level of stability through a less invasive procedure will have a high impact on clinical practice. A new transdiscal screw system is investigated as a promising minimally invasive device.

PURPOSE

To evaluate the feasibility of a novel transdiscal screw in spinal fixation as an alternative to BPSS, with and without an interbody cage, in non-spondylolisthesis cases.

STUDY DESIGN

An in vitro biomechanical study in lumbar cadaveric spines.

METHODS

Twelve lumbar cadaveric segments (L4-S1) were tested under flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Six treatments were simulated as follows: (1) intact, (2) bilateral facetectomy at L4-L5, (3) transdiscal screw system, (4) BPSS, (5) BPSS with transforaminal lumbar interbody cage, and (6) transdiscal screws with transforaminal interbody cage. Specimens were randomly divided into two testing groups: Group 1 (n=6) was tested under the first five conditions, in the order presented, whereas Group 2 (n=6) was tested under the first, second, third, fourth, and sixth conditions, with the fourth condition preceding the third. Range of motion (ROM) and neutral zone stiffness (NZS) were estimated and normalized with respect to the intact condition to explore statistical differences among treatments using non-parametric approaches.

RESULTS

Significant differences in FE ROM were observed in the pedicle screws-cage condition with respect to the facetectomy (p<.01), the pedicle screw (p=.03), and the transdiscal screw (p<.02) conditions. All fixation constructs significantly restricted LB and AR ROM (p<.01) with respect to facetectomy. In terms of stiffness, the pedicle screw and the transdiscal screw systems increased (p<.01) LB and AR NZS with respect to facetectomy. The pedicle screws-cage condition significantly increased flexion and extension stiffness with respect to all other conditions (p<.05). However, LB NZS for the pedicle screws-cage and the transdiscal screws-cage condition could not be explored due to a testing order bias effect. There was not enough evidence to state any difference between the pedicle and transdiscal screw conditions in terms of ROM or NZS.

CONCLUSIONS

Transdiscal and pedicle screw systems showed comparable in vitro biomechanical performance in the immediate stabilization of a complete bilateral facetectomy. The pedicle screws-cage condition was the most stable in FE motion; however, comparison with respect to the transdiscal screws-cage condition could not be investigated.