Dynamic stabilization of the spine: a new classification system

Current concepts of spondylosis and posterior spinal motion preservation for radiologists

Spinal fusion is performed to eliminate motion at a degenerated or unstable segment. However, this is associated with loss of motion at the fused levels and increased stress on adjacent levels. Motion-preserving implants have been designed in effort to mitigate the limitations of fusion. This review will focus on posterior spinal motion-preserving technologies. In the cervical spine, laminoplasty is a posterior motion-preserving procedure used in the management of myelopathy/cord compression. In the lumbar spine, motion-sparing systems include interspinous process devices (also referred to as interspinous process spacers or distraction devices), posterior dynamic stabilization devices (also referred to as pedicle screw/rod fixation-based systems), and posterior element replacement systems (also referred to as total facet replacement devices). Knowledge of the intended physiologic purpose, hardware utilized, and complications is important in the assessment of imaging in those who have undergone posterior motion preservation procedures.

A minimum 8-year follow-up comparative study of decompression and coflex stabilization with decompression and fusion

The current study aimed to compare the outcomes of decompression and interlaminar stabilisation with those of decompression and fusion for the treatment of lumbar degenerative disease (LDD) at a minimum 8-year follow-up. The current study also aimed to analyse the risk factors of radiographic adjacent segment degeneration (ASD). A total of 82 consecutive patients with LDD who underwent surgery between June 2007 and February 2011 were retrospectively reviewed. Of these patients, 39 underwent decompression and Coflex interspinous stabilisation (Coflex group) and 43 underwent decompression and posterior lumbar interbody fusion (PLIF) (PLIF group). All patients had a minimum of 8-years of follow-up data. Radiographic and clinical outcomes were compared between the groups, and the risk factors of developing radiographic ASD were also evaluated. The Oswestry disability index and visual analogue scale leg and back pain scores of both groups significantly improved compared with the baseline (all P<0.05), and no difference were indicated between the two groups at each follow-up time point (P>0.05). The Coflex group exhibited preserved mobility (P<0.001), which was associated with a decreased amount of blood loss (P<0.001), shorter duration of surgery (P=0.001), shorter duration of hospital stay and a lower incidence of ASD (12.8 vs. 32.56%; P=0.040) compared with the fusion group. The current study indicated that coflex and fusion technologies are safe and effective for the treatment of LDD, based on long-term follow-up data. However, Coflex interspinous stabilisation was revealed to reduce ASD incidence. Under strict indications, Coflex interspinous stabilisation is an effective and safe treatment method.

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.

Durability and Biological Response of a New Posterior Dynamic Stabilization System Using Polyethylene with Vitamin E

Objective

The purpose of this study was to evaluate the durability and biological response of a new Posterior Dynamic Stabilization system using polyethylene with vitamin E on the sliding surface.

Summary of Background Data

The use of polyethylene with vitamin E on the sliding surface in Posterior Dynamic Stabilization has not been reported previously.

Methods

A developed pedicle screw-based Posterior Dynamic system consists of four parts: a set screw, a rod, a ball, and a pedicle screw. The rod is inserted into the through hole of the ball, and the ball is sandwiched by the set screw. (1) Fatigue Wear Test. Testing was conducted under a dynamic compressive load of 50N at a speed of 1 Hz for 1 million cycles. We examined the loss of polyethylene due to abrasion in 3 units. (2) Biological Response in Pigs. In two pigs, a new pedicle screw and a conventional pedicle screw were inserted in L2 and L3/4, and L4 and L2/3, respectively. After breeding for 6 months, autopsies were performed. CT imaging was used to evaluate bone union of the facet joint. Abrasive specimens were prepared, and abrasion powder and inflammatory cell infiltration were evaluated microscopically.

Results

The average loss of polyethylene due to abrasion was -0.01 mg. In all units, polyethylene showed a decrease of 0.1 mm or less at the contact point with the set screw. The facet joints between the conventional screws exhibited bone fusion, but the facet joint between the conventional and the new screw retained mobility with no bony fusion. No abrasion powder was found and inflammatory cell infiltration was only minimally observed.

Conclusion

The new Posterior Dynamic Stabilization system exhibited a high level of durability and biological safety.

Does the Addition of a Dynamic Pedicle Screw to a Fusion Segment Prevent Adjacent Segment Pathology in the Lumbar Spine?

Study Design

Retrospective clinical cohort study.

Purpose

To investigate whether the combined use of dynamic pedicle screws and polyaxial pedicle screws was effective on adjacent segment pathology (ASP).

Overview of Literature

Various screw and rod models have been recently developed for preventing adjacent segment disease, and hybrid systems have been described along with posterior instrumentation in the fusion segment. In the literature, although the success of dynamic systems has been demonstrated in non-fusion posterior instrumentation, it remains unclear whether the addition of a screw-based dynamic system to a fusion segment would successfully prevent ASP in the long term.

Methods

The study included 101 patients who underwent surgery for degenerative spine diseases between 2007 and 2014 with lumbar stabilization that used either polyaxial pedicle screws alone or polyaxial pedicle screws plus dynamic stabilization screws (with hinged screw heads). These two patient groups were compared using retrospectively obtained postoperative new clinical findings, Oswestry disability index (ODI) scores, visual analog scale (VAS) scores, and radiological data.

Results

The proportion of patients with ASP who were radiologically assessed was low (p <0.01) in the group that underwent lumbar stabilization along with dynamic screws. Treatment outcomes were clinically successful in both groups according to ODI and VAS scores, and no significant difference was determined between the groups in terms of clinical ASP (p >0.05).

Conclusions

Although the combined use of dynamic screws and the static system was radiologically found to be effective for preventing ASP in patients who underwent lumbar fusion with posterior instrumentation, it did not completely eliminate ASP or result in a significant improvement in clinical ASP.

Biomechanical evaluation of a new pedicle screw-based posterior dynamic stabilization device (Awesome Rod System)--a finite element analysis

Background

Pedicle-screw-based posterior dynamic stabilization devices are designed to alleviate the rate of accelerated degeneration of the vertebral level adjacent to the level of spinal fusion. A new pedicle- screw-based posterior dynamic stabilization device- the Awesome Dynamic Rod System was designed with curve cuts on the rods to provide flexibility. The current study was conducted to evaluate the biomechanical properties of this new device.

Methods

Finite element models were developed for the intact spine (INT), the Awesome Dynamic Rod Implanted at L4-L5 (AWE), a traditional rigid rod system implanted at L4-L5 along with an interbody cage (FUS), and the Awesome Dynamic Rod System implanted at L4-L5 along with an interbody cage as an adjunct to fusion procedures and extension of dynamic fixation to L3-L4 (AWEFUS). The models were subjected to axial loads and pure moments and evaluated by a hybrid method on range of motion (ROM)s, disc stresses, pedicle screws stresses, and facet joint contact forces.

Results

FUS sustained the lowest L4-L5 ROM decrement in flexion and torsion. AWE demonstrated the lowest adjacent level ROM increment in all moments except for extension at L3-L4, and AWEFUS showed the greatest ROM increment at L2-L3. AWE demonstrated lowest adjacent segment disc stress in flexion, lateral bending and torsion at L3-L4. AWEFUS showed the highest disc stress increment in flexion, extension, and lateral bending, and the lowest disc stress decrement in torsion at L2-L3. AWE sustained greater adjacent facet joint contact forces than did FUS in extension and lateral bending at L3-L4, and AWEFUS demonstrated the greatest contact forces concentrating at L2-L3.

Conclusion

The results demonstrate that the Awesome Dynamic Rod System preserved more bridged segment motion than did the traditional rigid rod fixation system except in extension. However, the Awesome Dynamic Rod System bore a greater facet joint contact force in extension. The Awesome Dynamic Rod System did protect the adjacent level of fusion segments, but led to much greater ROM, disc stresses, and facet joint contact forces increasing at the adjacent level of instrumented segments.

Early clinical effects of the Dynesys system plus transfacet decompression through the Wiltse approach for the treatment of lumbar degenerative diseases

Background

This study investigated early clinical effects of Dynesys system plus transfacet decompression through the Wiltse approach in treating lumbar degenerative diseases.

Material/Methods

37 patients with lumbar degenerative disease were treated with the Dynesys system plus transfacet decompression through the Wiltse approach.

Results

Results showed that all patients healed from surgery without severe complications. The average follow-up time was 20 months (9–36 months). Visual Analogue Scale and Oswestry Disability Index scores decreased significantly after surgery and at the final follow-up. There was a significant difference in the height of the intervertebral space and intervertebral range of motion (ROM) at the stabilized segment, but no significant changes were seen at the adjacent segments. X-ray scans showed no instability, internal fixation loosening, breakage, or distortion in the follow-up.

Conclusions

The Dynesys system plus transfacet decompression through the Wiltse approach is a therapeutic option for mild lumbar degenerative disease. This method can retain the structure of the lumbar posterior complex and the motion of the fixed segment, reduce the incidence of low back pain, and decompress the nerve root.

Dynamic stabilization for challenging lumbar degenerative diseases of the spine: a review of the literature

Fusion and rigid instrumentation have been currently the mainstay for the surgical treatment of degenerative diseases of the spine over the last 4 decades. In all over the world the common experience was formed about fusion surgery. Satisfactory results of lumbar spinal fusion appeared completely incompatible and unfavorable within years. Rigid spinal implants along with fusion cause increased stresses of the adjacent segments and have some important disadvantages such as donor site morbidity including pain, wound problems, infections because of longer operating time, pseudarthrosis, and fatigue failure of implants. Alternative spinal implants were developed with time on unsatisfactory outcomes of rigid internal fixation along with fusion. Motion preservation devices which include both anterior and posterior dynamic stabilization are designed and used especially in the last two decades. This paper evaluates the dynamic stabilization of the lumbar spine and talks about chronologically some novel dynamic stabilization devices and thier efficacies.

Posterior Transpedicular Dynamic Stabilization versus Total Disc Replacement in the Treatment of Lumbar Painful Degenerative Disc Disease: A Comparison of Clinical Results

Study Design. Prospective clinical study. Objective. This study compares the clinical results of anterior lumbar total disc replacement and posterior transpedicular dynamic stabilization in the treatment of degenerative disc disease. Summary and Background Data. Over the last two decades, both techniques have emerged as alternative treatment options to fusion surgery. Methods. This study was conducted between 2004 and 2010 with a total of 50 patients (25 in each group). The mean age of the patients in total disc prosthesis group was 37,32 years. The mean age of the patients in posterior dynamic transpedicular stabilization was 43,08. Clinical (VAS and Oswestry) and radiological evaluations (lumbar lordosis and segmental lordosis angles) of the patients were carried out prior to the operation and 3, 12, and 24 months after the operation. We compared the average duration of surgery, blood loss during the surgery and the length of hospital stay of both groups. Results. Both techniques offered significant improvements in clinical parameters. There was no significant change in radiologic evaluations after the surgery for both techniques. Conclusion. Both dynamic systems provided spine stability. However, the posterior dynamic system had a slight advantage over anterior disc prosthesis because of its convenient application and fewer possible complications.

A short history of posterior dynamic stabilization

Interspinous spacers were developed to treat local deformities such as degenerative spondylolisthesis. To treat patients with chronic instability, posterior pedicle fixation and rod-based dynamic stabilization systems were developed as alternatives to fusion surgeries. Dynamic stabilization is the future of spinal surgery, and in the near future, we will be able to see the development of new devices and surgical techniques to stabilize the spine. It is important to follow the development of these technologies and to gain experience using them. In this paper, we review the literature and discuss the dynamic systems, both past and present, used in the market to treat lumbar degeneration.

Which radiographic parameters are linked to failure of a dynamic spinal implant?

BACKGROUND

Knowledge about factors leading to failure of posterior dynamic stabilization implants is essential to design future implants and establish surgical indications. Therefore, we analyzed an implant for single-level or hybrid configuration (adjacent to spondylodesis), which was recalled due to high failure rates.

QUESTIONS/PURPOSES

We asked: (1) Were postoperative radiographic changes linked to implant failure? (2) Were radiographic parameters different between the two configurations? And (3) was implant failure related to inferior clinical scores?

METHODS

The implant was used in 18 patients with lumbar single-level spinal stenosis or with (recurrent) disc herniation and concurrent degenerative disc disease and in 22 patients with an initially degenerated segment adjacent and superior to a fusion site. We prospectively obtained preoperative and postoperative (immediate, 6-, 12- and 24-month) clinical and radiographic evaluations; 37 of the 40 patients completed the 24-month followup. Using plain and extension-flexion radiographs, we compared implant failure rates and their association with postoperative implant translation, anterior and posterior disc height, and ROM for each configuration and between configurations. We assessed associations between clinical scores (VAS pain scores for back and leg, Oswestry Disability Index) and implant failure.

RESULTS

Implant failure occurred in 10 of the 37 implants and corresponded to greater posterior disc height (single-level only) and implant translation. Adjacent-segment ROM increases and posterior disc height decreases over time were greater with the hybrid configuration. Implant failure rate related to higher Oswestry Disability Index (single-level only) and higher back pain scores.

CONCLUSIONS

Implant translation is associated with failure likely due to insufficient resistance to shear forces. Load transfer may cause progressive degeneration in the dynamic and adjacent segments, especially in the hybrid configuration.