Segment-by-segment stabilization for degenerative disc disease: a hybrid technique

Finite element modelling of hybrid stabilization systems for the human lumbar spine

Intersomatic fusion is a very popular treatment for spinal diseases associated with intervertebral disc degeneration. The effects of three different hybrid stabilization systems on both range of motion and intradiscal pressure were investigated, as there is no consensus in the literature about the efficiency of these systems. Finite element simulations were designed to predict the variations of range of motion and intradiscal pressure from intact to implanted situations. After hybrid stabilization system implantation, L4-L5 level did not lose its motion completely, while L5-S1 had no mobility as a consequence of disc removal and fusion process. BalanC hybrid stabilization system represented higher mobility at the index level, reduced intradiscal pressure of adjacent level, but caused to increment in range of motion by 20% under axial rotation. Higher tendency by 93% to the failure was also detected under axial rotation. Dynesys hybrid stabilization system represented more restricted motion than BalanC, and negligible effects to the adjacent level. B-DYN hybrid stabilization system was the most rigid one among all three systems. It reduced intradiscal pressure and range of motion at the adjacent level except from motion under axial rotation being increased by 13%. Fracture risk of B-DYN and Dynesys Transition Optima components was low when compared with BalanC. Mobility of the adjacent level around axial direction should be taken into account in case of implantation with BalanC and B-DYN systems, as well as on the development of new designs. Having these findings in mind, it is clear that hybrid systems need to be further tested, both clinically and numerically, before being considered for common use.

Biomechanical Effects of Fixation of Different Segments of Goat Lumbar Spine on Adjacent Segmental Motion and Intradiscal Pressure Change

Background

The aim of this study was to investigate the biomechanical fixation effects of different segments of the goat spine on adjacent segmental motion and intradiscal pressure (IDP) change.

Material/Methods

Eighteen goat spine specimens were randomly divided into 3 groups: group A (single-segment fixation), group B (double-segment fixation), and group C (triple-segment fixation). The motion was tested on each specimen using a spinal motion simulation test system with rational pressure loading. The IDP was measured using a pinhole pressure sensor.

Results

Range of motion (ROM) and IDP of adjacent segments increased with increased external load. In comparison of the 3 groups, significant differences in ROM were found when the external force was more than 100 N (P<0.05). The differences in IDP of the adjacent segment were statistically significant (P<0.05) when external pressure was greater than or equal to 60 N. However, in comparison of group A with group B, no significant differences in ROM and IDP of the adjacent segments were noted for the motions of anterior flexion, posterior extension, and lateral bending (P>0.05). Moreover, upper adjacent segments had greater ROM than the lower adjacent segments (P<0.05). We found significant differences between IDPs of the upper adjacent segments and lower adjacent segments (P<0.05).

Conclusions

As the number of fixated lumbar segments increases, ROM and IDP of the adjacent segments increase. Multisegment fixation is most likely the main factor contributing to the development of adjacent segmental lesions after lumbar fixation.

The use of the DTO™ hybrid dynamic device: a clinical outcome- and radiological-based prospective clinical trial

Background

The purpose of this study was to assess the radiological and clinical outcome parameters following lumbar hybrid dynamic instrumentation with the focus on the adjacent segment degeneration (ASD) and adjacent segment disease (ASDi).

Methods

In this prospective trial all patients presenting with degenerative changes to the lumbar spine have been included. Precondition was a stable adjacent level with/without degenerative alteration. The elected patients underwent a standardised fusion procedure with hybrid instrumentation (DTO™, Zimmer Spine Inc., Denver, USA). Patients’ demographics have been documented and the follow-up visits were conducted after 6 weeks, and then stepwise after 6 up to 48 months. Each follow-up visit included assessment of quality of life and pain using specific questionnaires (COMI, SF-36, ODI) and the radiological evaluation with focus on the adjacent level alterations.

Results

At a mean follow up of 24 months an incidence of ASD with 10.91% and for ASDi with 18.18% has been observed. In 9% a conversion to standardised fusion was needed. There was a high rate of mechanical complication: (1) screw loosening (52.73%), (2) pedicle screw breakage (10.91%), and (3) rod breakage (3.64%) after a follow up of a maximum of 60 months. There were no significant difference of COMI, ODI and SF-36(v2) in comparison to all groups but all 55 patients showed a clinical improvement over the time.

Conclusion

The dynamic hybrid DTO™ device is comparable to the long-term results after standardised fusion procedure, while a high rate of mechanical complication decreased the initial benefit.

Trial registration

This trial was registered at the ClinicalTrials Register (#NCT03404232, 2018/01/18, registered retrospectively).

Pathoanatomic Risk Factors for Instability and Adjacent Segment Disease in Lumbar Spine: How to Use Topping Off?

PURPOSE

The goal of this review is to identify criteria indicating implantation of hybrid system into lumbar spine and to evaluate general benefits of use.

METHODS

A systematic review of literature was performed using current randomized clinical trials, reviews, and meta-analyses. Data sources included relevant literature of human studies identified through searches of Medline Library until May 2015.

RESULTS

Predisposing factors for Adjacent Segment Disease (ASDi) are discussed in literature: laminar horizontalization, insufficiency of fascia thoracolumbalis, facet tropism, and facet sagittalization. Currently there is no evidence for topping off. There are only 12 studies and these have no consistent statements about use of a hybrid system for avoidance of ASDi.

CONCLUSION

Hybrid instrumentation of lumbar spine, either with pedicle-based technique or additional spacer, might possibly prevent ASDi from developing in previously damaged segment adjacent to a fusion. Good clinical data proving effectiveness of this new implant technique is as yet unavailable. Thus, currently one must speak of an unevaluated procedure. Various radiological classifications can assist in making a reliable decision as to whether hybrid instrumentation is an appropriate choice of therapy. Pathoanatomical conditions of facet joints and laminae as well as preservation of sagittal balance must also be considered.

The influence of L4-S1 Dynesys® dynamic stabilization versus fusion on lumbar motion and its relationship with lumbar degeneration: a retrospective study

Background

The aim of this study is to evaluate the efficacy of Dynesys® posterior dynamic stabilization (PDS) in the treatment of L4–S1 degenerative diseases and to assess the influence of postoperative motion on lumbar degeneration.

Methods

Included in this retrospective study were patients with L4–S1 degenerative disease who underwent fusion or PDS from September 2010 to September 2014. Clinical outcomes were assessed by preoperative and postoperative visual analog scale (VAS) and Oswestry Disability Index (ODI). Preoperative and postoperative X-rays assessed range of motion (ROM) of the non-surgical and surgical levels and whole lumbar. MRI assessed degeneration of non-surgical levels.

Results

A total of 56 consecutive patients were divided into two groups: group A, PDS, and group B, fusion. Patient demographics and baseline characteristics were similar in the two groups. In both groups, there was a significant difference between preoperative and postoperative VAS and ODI scores (P < 0.05). However, there was a significant difference in a 6-month follow-up ODI between the two groups (P < 0.05). X-rays showed PDS patients partially maintained surgical level ROM and non-surgical level ROM increased less than in the fusion group. MRI showed adjacent segment degeneration (ASD) in both groups, and patients whose preoperative L3–4 Pfirrmann classification was higher than grade 2 had more ASD than lower than grade 2.

Conclusion

PDS can maintain surgical level ROM and had less influence on whole and non-surgical level ROM. Following PDS, patients recovered faster and had a better lumbar function. It may be a better choice for multi-level lumbar degenerative diseases.

In vitro oxidative degradation of a spinal posterior dynamic stabilization device

This study quantified the changes of the frequency-dependant viscoelastic properties of the BDyn (S14 Implants, Pessac, France) spinal posterior dynamic stabilization (PDS) device due to in vitro oxidation. Six polycarbonate urethane (PCU) rings and six silicone cushions were degraded using a 20% hydrogen peroxide/0.1 M cobalt (II) chloride hexahydrate, at 37°C, for 24 days. The viscoelastic properties of the individual components and the components assembled into the BDyn PDS device were determined using Dynamic Mechanical Analysis at frequencies from 0.01 to 30 Hz. Attenuated Total Reflectance Fourier Transform Infra-Red spectra demonstrated chemical structure changes, of the PCU, associated with oxidation while Scanning Electron Microscope images revealed surface pitting. No chemical structure or surface morphology changes were observed for the silicone cushion. The BDyn device storage and loss stiffness ranged between 84.46 N/mm to 99.36 N/mm and 8.13 N/mm to 21.99 N/mm, respectively. The storage and loss stiffness for the components and BDyn device increased logarithmically with respect to frequency. Viscoelastic properties, between normal and degraded components, were significantly different for specific frequencies only. This study demonstrates the importance of analyzing changes of viscoelastic properties of degraded biomaterials and medical devices into which they are incorporated, using a frequency sweep. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1237-1244, 2018.

Complications associated with the Dynesys dynamic stabilization system: a comprehensive review of the literature

The Dynesys dynamic stabilization system is an alternative to rigid instrumentation and fusion for the treatment of lumbar degenerative disease. Although many outcomes studies have shown good results, currently lacking is a comprehensive report on complications associated with this system, especially in terms of how it compares with reported complication rates of fusion. For the present study, the authors reviewed the literature to find all studies involving the Dynesys dynamic stabilization system that reported complications or adverse events. Twenty-one studies were included for a total of 1166 patients with a mean age of 55.5 years (range 39-71 years) and a mean follow-up period of 33.7 months (range 12.0-81.6 months). Analysis of these studies demonstrated a surgical-site infection rate of 4.3%, pedicle screw loosening rate of 11.7%, pedicle screw fracture rate of 1.6%, and adjacent-segment disease (ASD) rate of 7.0%. Of studies reporting revision surgeries, 11.3% of patients underwent a reoperation. Of patients who developed ASD, 40.6% underwent a reoperation for treatment. The Dynesys dynamic stabilization system appears to have a fairly similar complication-rate profile compared with published literature on lumbar fusion, and is associated with a slightly lower incidence of ASD.

Clinical efficacy and safety of a new flexible interbody spacer system

BACKGROUND

Patients with lumbar degenerative disk disease (DDD) often require an interbody fusion. Several spacer systems have been developed to achieve an adequate fusion. The newly developed flexible interbody spacer system (Luna®, Benvenue Medical Inc.) expands to the disk space and is adjustable to the patient's anatomy.

OBJECTIVE

Prospective monocentric evaluation of interbody fusions performed with the new system in patients with DDD to assess the device's efficacy and safety.

METHODS

The study includes patients with DDD of one or two contiguous lumbar levels. All patients were treated with the new flexible cage system. To evaluate the clinical outcome, examinations were conducted preoperatively, 6 weeks, 6 months and 12 months postoperatively. At each study visit possible implant loosening was assessed by plain radiography and any adverse events were documented. Furthermore, back pain was evaluated using the visual analogue scale (VAS), functional impairment using the Oswestry-Disability-Index (ODI) and quality of life using the SF36.

RESULTS

A total of 30 patients (age: 52.8 ± 11 years, gender: 53% male) were included. None of the patients showed signs of implant loosening and the total number of adverse events was low (3%). The VAS improved significantly from 81.2 ± 9.5 mm at baseline to 28 ± 26.2 mm after 12-months (p ≤ 0.0001). The ODI also improved significantly from 57.9 ± 9.6% at baseline to 20 ± 15.6% after 12-months (p ≤ 0.0001). The physical component score (PCS) of the SF36 improved significantly ongoing from 29.2 ± 9.3 at baseline to 56.1 ± 14.9 after 12-months (p = 0.0079) and the mental component score (MCS) improved significantly from 49.2 ± 20.7 at baseline to 62.8 ± 18.9 after 12 months (p = 0.013).

CONCLUSIONS

Minimal-invasive lumbar interbody fusion with the new flexible system is a safe and effective treatment method for patients with DDD. Complication rates are low and treatment leads to an improvement of pain, functional impairment and quality of life.

Viscoelastic properties of a spinal posterior dynamic stabilisation device

The purpose of this study was to quantify the frequency dependent viscoelastic properties of two types of spinal posterior dynamic stabilisation devices. In air at 37°C, the viscoelastic properties of six BDyn 1 level, six BDyn 2 level posterior dynamic stabilisation devices (S14 Implants, Pessac, France) and its elastomeric components (polycarbonate urethane and silicone) were measured using Dynamic Mechanical Analysis. The viscoelastic properties were measured over the frequency range 0.01-30Hz. The BDyn devices and its components were viscoelastic throughout the frequency range tested. The mean storage stiffness and mean loss stiffness of the BDyn 1 level device, BDyn 2 level device, silicone component and polycarbonate urethane component all presented a logarithmic relationship with respect to frequency. The storage stiffness of the BDyn 1 level device ranged from 95.56N/mm to 119.29N/mm, while the BDyn 2 level storage stiffness ranged from 39.41N/mm to 42.82N/mm. BDyn 1 level device and BDyn 2 level device loss stiffness ranged from 10.72N/mm to 23.42N/mm and 4.26N/mm to 9.57N/mm, respectively. No resonant frequencies were recorded for the devices or its components. The elastic property of BDyn 1 level device is influenced by the PCU and silicone components, in the physiological frequency range. The viscoelastic properties calculated in this study may be compared to spinal devices and spinal structures.

Short-term effects of a dynamic neutralization system (Dynesys) for multi-segmental lumbar disc herniation

PURPOSE

To determine the safety and short-term curative effects of internal fixation using a dynamic neutralization system (Dynesys) for multi-segmental lumbar disc herniation (ms-LDH) with the control group treated by posterior lumbar interbody fusion (PLIF).

METHODS

Forty-five patients with ms-LDH were selected as study group treated with Dynesys and 40 patients as control group with PLIF. The surgical efficacy was evaluated by comparing the visual analogue scale (VAS) scores, the Oswestry Disability Index (ODI) scores and the ROMs of the adjacent segment before and after surgery. The postoperative complications related to the implants were identified.

RESULTS

All patients were followed up for an average duration of over 30 months. Dynesys stabilization resulted in significantly higher preservation of motion at the index level (p < 0.001), and significantly less (p < 0.05) hypermobility at the adjacent segments. VAS for back and leg pain and ODI improved significantly (p < 0.05) with both the methods, but there was no significant difference between the groups.

CONCLUSIONS

The non-fusion fixation system Dynesys is safe and effective regarding short-term curative effects for the treatment of ms-LDH.

The use of polyurethane materials in the surgery of the spine: a review

BACKGROUND CONTEXT

The spine contains intervertebral discs and the interspinous and longitudinal ligaments. These structures are elastomeric or viscoelastic in their mechanical properties and serve to allow and control the movement of the bony elements of the spine. The use of metallic or hard polymeric devices to replace the intervertebral discs and the creation of fusion masses to replace discs and/or vertebral bodies changes the load transfer characteristics of the spine and the range of motion of segments of the spine.

PURPOSE

The purpose of the study was to survey the literature, regulatory information available on the Web, and industry-reported device development found on the Web to ascertain the usage and outcomes of the use of polyurethane polymers in the design and clinical use of devices for spine surgery.

STUDY DESIGN/SETTING

A systematic review of the available information from all sources concerning the subject materials' usage in spinal devices was conducted.

METHODS

A search of the peer-reviewed literature combining spinal surgery with polyurethane or specific types and trade names of medical polyurethanes was performed. Additionally, information available on the Food and Drug Administration Web site and for corporate Web sites was reviewed in an attempt to identify pertinent information.

RESULTS

The review captured devices that are in testing or have entered clinical practice that use elastomeric polyurethane polymers as disc replacements, dynamic stabilization of spinal movement, or motion limitation to relieve nerve root compression and pain and as complete a listing as possible of such devices that have been designed or tested but appear to no longer be pursued. This review summarizes the available information about the uses to which polyurethanes have been tested or are being used in spinal surgery.

CONCLUSIONS

The use of polyurethanes in medicine has expanded as modifications to the stability of the polymers in the physiological environment have been improved. The potential for the use of elastomeric materials to more closely match the mechanical properties of the structures being replaced and to maintain motion between spinal segments appears to hold promise. The published results from the use of the devices that are discussed show early success with these applications of elastomeric materials.

Kinematic and mechanical comparisons of lumbar hybrid fixation using Dynesys and Cosmic systems

STUDY DESIGN

The biomechanical effects of Dynesys and Cosmic fixators on transition and adjacent segments were evaluated using the finite-element method.

OBJECTIVE

This study investigated the load-transferring mechanisms of 2 dynamic fixators and the fixator-induced effects on the junctional problem of the adjacent segments.

SUMMARY OF BACKGROUND DATA

The mobility and flexibility of Dynesys screw-spacer and Cosmic screw-hinge joints preserve motion and share loads for the transition segment. However, the differences in tissue responses and fixator mechanisms among these 2 fixators have not been investigated extensively.

METHODS

A lumbosacral model from L1 to S1 levels was developed and subjected to muscular contraction, ligamentous interconnection, compressive force, and trunk moment. A static fixator was instrumented at the moderately degenerative L4-L5 segment to serve as a comparison baseline. Subsequently, the 2 fixators were instrumented at the mildly degenerative L3-L4 segment. The tissue responses of the adjacent segments and the load transmission at the screw-spacer and bone-screw interfaces were compared.

RESULTS

Both systems show the ability to protect the transition segment but deteriorate the adjacent segments. The screw-hinge joint and the stiffer rod of the Cosmic system significantly constrained the motion pattern of the transition segment. Comparatively, the Dynesys screw-spacer interfaces make contact with and depart from each other during motion; thus providing higher mobility to the transition segment. However, the highly stressed distribution at the Cosmic bone-screw causes the screw and hinge prone to pullout and fatigue failures.

CONCLUSION

Cosmic fixation can better protect the disc and facet joint of the transition segment than can the Dynesys. However, the screw-hinge joint strictly constrains intersegmental motion and deteriorates the junctional problem. The Cosmic system can be chosen to treat more severely degenerative transition segments. With higher flexibility, the Dynesys system is recommended for the transition segment that is healthy or mildly degenerative.

LEVEL OF EVIDENCE

N/A.

Pretension effects of the Dynesys cord on the tissue responses and screw-spacer behaviors of the lumbosacral construct with hybrid fixation

STUDY DESIGN

The pretension of the Dynesys cord was varied to evaluate its effects on both tissue responses and screw-spacer behaviors by the finite-element method.

OBJECTIVE

This study aimed to provide detailed information about the motion-preserving and load-shielding mechanisms of the Dynesys screw-spacer joint.

SUMMARY OF BACKGROUND DATA

Intuitively, higher cord pretension aims to ensure the occurrence of screw-spacer contact, thus making the spacer the transmitter of the vertebral loads. However, detailed investigations of the cord-pretension effects have not yet been carried out. METHODS.: Using a validated lumbosacral model, the moderately degenerative L4-L5 segment was instrumented by a static fixator and the Dynesys fixator was further used to bridge a mildly degenerative L3-L4 segment. The pre-tended cord was modeled as an elastic spring with 0- and 300-N pretensions. The disc range-of-motion, disc stress, facet force, bone-screw stress, and screw-spacer force were chosen as comparison indices. RESULTS.: At the transition and adjacent segments, the range-of-motion differences between the 2 pretensions were 7.7% and 2.0% on average, respectively. The mechanical differences at the transition and adjacent segments were 9.0% and 5.2% (disc stress) and 9.4% and 9.1% (facet force), respectively. The results indicated that the cord pretension has a minor effect on the adjacent segments in comparison with the transition segment. However, the stress at the screw hub and force of the screw-spacer contact of the 300-N pretension were increased by 33.7% and 316.5% on average than without pretension, respectively.

CONCLUSION

The moment arm from the screw-cord center to the fulcrum is significantly less than that of vertebral loads. This leads to the minor effect of increasing the cord pretension on the responses of the adjacent segments. However, the cord pretension can significantly affect both screw-spacer force and bone-screw stress.

LEVEL OF EVIDENCE

4.

Biomechanical effects of disc degeneration and hybrid fixation on the transition and adjacent lumbar segments: trade-off between junctional problem, motion preservation, and load protection

STUDY DESIGN

The biomechanical effects of disc degeneration and hybrid fixation on the transition and adjacent segments were evaluated using a numerical approach.

OBJECTIVE

This study aimed to evaluate the rigidity-rising effects of the dehydrated disc and bridged fixator on the kinematic and mechanical redistribution of the transition and adjacent segments.

SUMMARY OF BACKGROUND DATA

After static fixation, a dynamic fixator can be used to preserve motion and share loads for the transition segments. However, the hybrid use of both static and dynamic fixators and its effects on the biomechanical behavior of the transition and adjacent segments were not investigated extensively.

METHODS

A nonlinear and osseoligamentous lumbar model from L1 vertebra to S1 vertebrae was developed. Ligament interconnection, muscular contraction, and weight compression were all used to simulate lumbar flexion. The static fixator was instrumented at the degenerative L4-L5 segment and the dynamic fixators (Dynesys system) with different stiffness were subsequently applied to the degenerative or healthy L3-L4 segment. A healthy lumbar model was used as a reference point for further comparison and evaluation. The predicted results were validated with the cadaveric and numerical values of the literature studies. Among the 21 models, the junctional problem at the adjacent (L2/L3 and L5/S1) discs as well as the motion preservation and stress distribution at the transition (L3/L4) disc were compared.

RESULTS

Static fixation and the degenerative disc deteriorated the junctional problem at adjacent segments. On average, the hybrid fixation of the original Dynesys cord constrained the range of motion (ROM) by 65%. Furthermore, it shared 43% of the stress on the transition disc. However, this resulted in the adjacent discs increasing about 50% ROM and 40% stress. The term "trade-off stiffness" was used to express the concept that the decreased stiffness of the original cord could balance the junctional problem, motion preservation, and load protection of the transition and adjacent segments. The trade-off stiffness of the degenerative transition disc was higher than that of the healthy disc. Compared with the original design, the increased ROM and stress of the adjacent segments can be reduced by about 43% using the trade-off stiffness.

CONCLUSION

The use of the hybrid fixator should involve a certain trade-off between the protection of the transition segment and the deterioration of the adjacent segments. This trade-off stiffness, which largely depends on both fixator design and disc degeneration, provides the improved rigidity and flexibility of the transition and adjacent segments.

Late infections after dynamic stabilization of the lumbar spine with Dynesys

INTRODUCTION

Dynamic stabilization of the spine was developed as an alternative to rigid fusion in chronic back pain to reduce the risk of adjacent segment degeneration. Dynamic neutralization system (Dynesys, Zimmer CH) is one of the most popular systems available, but some midterm studies show revision rates as high as 30 %. Some late infectious complications in our patients prompted us to review them systematically. Propionibacterium recently has been shown to cause subtle infections of prosthetic material.

MATERIALS AND METHODS

Here, we report on a consecutive series of 50 Dynesys implants. In a median follow-up of 51 months (range 0-91), we identified 12 infectious and 11 non-infectious complications necessitating reoperation or removal of the implant in 17 patients.

RESULTS

Material infections occurred after a median of 52 months (2-77) and were due to Propionibacterium alone (n = 4) or in combination (n = 3) in seven out of 11 patients. Clinical presentation combines new or increasing pain associated with signs of screw loosening on conventional X-rays; however, as many as 73.5 % of patients present some degree of screw loosening without being at all symptomatic of infection.

CONCLUSION

The high rate of late infections with low-grade germs and the frequency of screw loosening signs made us suspect a lack of integration at the bone-screw interface. Surgeons should be suspicious if the patient presents a combination of new or increasing pain and signs of screw loosening, and aggressive revision is recommended in these cases.