Stabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression

Biomechanical analysis of the door-shaped titanium plate in single-level anterior cervical discectomy and fusion

BACKGROUND

Analyse and discuss the immediate stability of the cervical spine after anterior cervical discectomy and fusion using a door-shaped titanium plate and compare it with the traditional titanium plate, to provide biomechanical evidence for the rationality and effectiveness of the door-shaped titanium plate in clinical applications.

METHODS

Ten adult goat C4/5 vertebral bodies were obtained, and models were prepared using denture base resin. Biomechanical experiments were performed on the specimens before internal fixation. MTS was used to conduct non-destructive biomechanical loading tests in six directions, including flexion, extension, left-right bending, and left-right torsion, recording the range of motion (ROM) and neutral zone (NZ) of each specimen. The specimens were then randomly divided into two groups: the study group was fixed with a door-shaped titanium plate, and the control group was fixed with a traditional titanium plate. ROM and NZ in each direction were measured again. After measurements, both groups were subjected to 0.5 Hz torsion loading with a torque of 2 N m for a total of 3000 cycles, followed by measuring ROM and NZ in six directions once more.

RESULTS

Compared to before fixation, ROM and NZ in both groups significantly decreased in all six directions after fixation, with statistical significance (P < 0.05); after fixation, the study group showed slightly lower values for various mechanical reference parameters compared to the control group, with no statistical significance (P > 0.05); after 3000 torsional loads, both internal fixation groups showed increased ROM and NZ compared to after fixation but to a lower extent, and no screw or titanium plate loosening was observed. Compared to before fixation, the differences were still statistically significant (P < 0.05), with the study group having slightly lower ROM and NZ values in all directions compared to the control group, with no statistical significance (P > 0.05).

CONCLUSION

The door-shaped titanium plate exhibits mechanical properties similar to the traditional titanium plate in all directions, and its smaller size and simpler surgical operation can be used for anterior cervical endoscopic surgery, reducing surgical trauma. It is clinically feasible and deserves further research and promotion.

Finite element analysis of optimized novel additively manufactured non-articulating prostheses for cervical total disc replacement

Ball-and-socket designs of cervical total disc replacement (TDR) have been popular in recent years despite the disadvantages of polyethylene wear, heterotrophic ossification, increased facet contact force, and implant subsidence. In this study, a non-articulating, additively manufactured hybrid TDR with an ultra-high molecular weight polyethylene core and polycarbonate urethane (PCU) fiber jacket, was designed to mimic the motion of normal discs. A finite element (FE) study was conducted to optimize the lattice structure and assess the biomechanical performance of this new generation TDR with an intact disc and a commercial ball-and-socket Baguera^®C TDR (Spineart SA, Geneva, Switzerland) on an intact C5-6 cervical spinal model. The lattice structure of the PCU fiber was constructed using the Tesseract or the Cross structures from the IntraLattice model in the Rhino software (McNeel North America, Seattle, WA) to create the hybrid I and hybrid II groups, respectively. The circumferential area of the PCU fiber was divided into three regions (anterior, lateral and posterior), and the cellular structures were adjusted. Optimal cellular distributions and structures were A2L5P2 in the hybrid I and A2L7P3 in the hybrid II groups. All but one of the maximum von Mises stresses were within the yield strength of the PCU material. The range of motions, facet joint stress, C6 vertebral superior endplate stress and path of instantaneous center of rotation of the hybrid I and II groups were closer to those of the intact group than those of the Baguera^®C group under 100 N follower load and pure moment of 1.5 Nm in four different planar motions. Restoration of normal cervical spinal kinematics and prevention of implant subsidence could be observed from the FE analysis results. Superior stress distribution in the PCU fiber and core in the hybrid II group revealed that the Cross lattice structure of a PCU fiber jacket could be a choice for a next-generation TDR. This promising outcome suggests the feasibility of implanting an additively manufactured multi-material artificial disc that allows for better physiological motion than the current ball-and-socket design.

Comparison of the Postoperative Motion Stabilization Between Anterior Cervical Decompression and Fusion with a Zero-Profile Implant System and a Plate-Cage Construct

OBJECTIVE

Due to the lack of an additional anterior plate, the motion stability of a zero-profile device with an anchored cage (AC) may be inferior to that of a traditional plate-cage construct (PCC). However, the impact of this difference in motion stability on various outcomes has not been fully explored. Therefore, the aim of this study was to compare the motion stabilization features of an AC and a PCC and analyze their impact on postoperative outcomes and complications.

METHODS

A retrospective study of patients treated with single-level anterior cervical discectomy and fusion from January 2008 to May 2016 was performed. First, clinical and radiological outcomes, postoperative complications and time to achieve motion stabilization were compared between the AC and PCC groups. Then, based on the time to achieve motion stabilization, all patients were divided into group A (time to achieve motion stabilization <3 months), group B (time to achieve motion stabilization from 3-6 months), and group C (time to achieve motion stabilization >6 months). The early postoperative complications were compared across the 3 groups. Motion stabilization was measured on dynamic cervical radiographs using the interspinous process method and Cobb angle method according to previously published methods.

RESULTS

A total of 160 patients met the inclusion criteria, including 90 patients in the AC group and 70 patients in the PCC group. There were no significant differences between the AC and PCC groups in the clinical outcomes, C2-7 angle change, segmental angle change, final fusion rate or adjacent-level degeneration (P > 0.05). The disc height loss was 2.26 ± 1.00 mm in the AC group and 1.76 ± 1.13 mm in the PCC group (P = 0.004), and the incidence of implant subsidence was 24.44% in the AC group and 11.43% in the PCC group (P = 0.036). In addition, the PCC was more dynamically stable than the AC at 3 months post-surgery (P < 0.001), and at this time, the disc height loss and implant subsidence in motion-stable patients were significantly lower than those in motion-unstable patients (P < 0.05). Furthermore, our results also showed that when the arrival time of motion stabilization was prolonged, the loss of disc height and occurrence of subsidence gradually increased.

CONCLUSIONS

More attention should be given to minimizing the adverse impact of poor motion stability in the design and development of future zero-profile cervical implants, although this has little impact on clinical efficacy.

Dynamic Cervical Implants in Patients With Disc Degenerative Disease: A Single-Center Cohort From the Greek Population

Aim

The aim of this study was to review the safety and feasibility, clinical and radiological outcomes, and postoperative complications associated with the use of dynamic cervical implants (DCI).

Patients and methods

A prospective single-cohort study was performed of all consecutive patients who underwent DCI implantation as an adjunct to anterior cervical discectomy. We measured the anterior disc space height (ADH) and posterior disc space height (PDH), as well as the ADH/PDH ratio.

Results

In 11 patients, the ADH/PDH ratio averaged 0.98 (range: 0.7-1.125) postoperatively, from the initial 0.96 (range: 0.72-1.106).

Conclusion

DCI seems to be a viable alternative to anterior cervical discectomy and fusion. However, its role in motion preservation and protection against the degeneration of the adjacent segment is questioned.

Long-term Follow-Up Results of Dynamic Cervical Implant in Patients with Cervical Disc Diseases: Compared with Prestige LP

BACKGROUND AND STUDY AIMS

Prestige LP arthroplasty has been proven to be a safe and effective treatment for patients with cervical disc degenerative disease (DDD). Dynamic Cervical Implant (DCI) has emerged as a novel implantation device for cervical DDD. This study aimed to compare the outcomes of these procedures after 5 years of follow-up in the DCI and Prestige LP groups. Key words: cervical disc degenerative disease; cervical disc replacement; Dynamic Cervical Implant; Prestige LP Materials and Methods: This study retrospectively enrolled 79 consecutive cervical DDD patients with 41 DCI and 47 Prestige LP prostheses implanted. Radiographs were analyzed for intervertebral height and range of motion (ROM). Neural function of the participants was assessed using the Neck Disability Index score, Visual Analog Scale, Japanese Orthopaedic Association score and 36-Item Short Form Survey.

RESULTS

The DCI group had statistically lesser flexion/extension and bilateral bending ROM than the Prestige LP group at the operated level(s) (p<0.05). The DCI group showed improved lordotic alignment of C2-C7 and operated functional spinal unit than the Prestige LP group (p<0.05). No statistical difference was observed in the neural function of the two groups. Heterotopic ossification was found in 7 and 14 patients in the DCI and Prestige LP groups, respectively.

CONCLUSION

The 5 years follow-up results were comparable between the two groups. We believe that DCI implantation is a safe and effective procedure and could possibly become an alternative treatment for cervical DDD.

Biomechanical Analysis of Cervical Artificial Disc Replacement Using Cervical Subtotal Discectomy Prosthesis

Background: Anterior cervical discectomy and fusion (ACDF) sacrifices segmental mobility, which can lead to the acceleration of adjacent segment degeneration. The challenge has promoted cervical artificial disc replacement (CADR) as a substitute for ACDF. However, CADR has revealed a series of new issues that are not found in ACDF, such as hypermobility, subsidence, and wear phenomenon. This study designed a cervical subtotal discectomy prosthesis (CSDP) consisting of a cervical disc prosthesis structure (CDP structure), cervical vertebra fixation structure (CVF structure), link structure, and locking screw, aiming to facilitate motion control and reduce subsidence. The aim of this study was to assess the biomechanics of the CSDP using finite element (FE) analysis, friction-wear test, and non-human primates implantation study. Study Design: For the FE analysis, based on an intact FE C₂-C₇ spinal model, a CSDP was implanted at C₅-C₆ to establish the CSDP FE model and compare it with the Prestige LP prosthesis (Medtronic Sofamor Danek, Minneapolis, MN, United States). The range of motion (ROM), bone-implant interface stress, and facet joint force were calculated under flexion extension, lateral bending, and axial rotation. In addition, CSDP was elevated 1 mm to mimic an improper implantation technique to analyze the biomechanics of CSDP errors in the FE model. Moreover, the friction-wear test was conducted in vitro to research CSDP durability and observe surface wear morphology and total wear volume. Finally, the CSDP was implanted into non-human primates, and its properties were evaluated and verified by radiology. Results: In the FE analysis, the ROM of the CSDP FE model was close to that of the intact FE model in the operative and adjacent segments. In the operative segment, the CSDP error FE model increased ROM in flexion extension, lateral bending, and axial rotation. The maximum stress in the CSDP FE model was similar to that of the intact FE model and was located in the peripheral cortical bone region. The facet joint force changes were minimal in extension, lateral bending, and axial rotation loads in CSDP. In the friction-wear test, after the 150-W movement simulation, both the CVF-link-junction and the CDP-link-junction had slight wear. In the CSDP non-human primate implantation study, no subsidence, dislocation, or loosening was observed. Conclusion: In the FE analysis, the biomechanical parameters of the CSDP FE model were relatively close to those of the intact FE model when compared with the Prestige LP FE model. In terms of CSDP error FE models, we demonstrated that the implantation position influences CSDP performance, such as ROM, bone-implant interface stress, and facet joint force. In addition, we performed a friction-wear test on the CSDP to prove its durability. Finally, CSDP studies with non-human primates have shown that the CSDP is effective.

Clinical and radiological outcomes of dynamic cervical implant arthroplasty: A 5-year follow-up

BACKGROUND

Dynamic cervical implant (DCI) stabilization has been reported to have satisfactory clinical and radiological results with short- and mid-term follow-up in the treatment of cervical degenerative disc disease. However, few reports about the clinical and radiological outcome with more than 5-year follow-up exist.

AIM

To investigate the long-term clinical and radiological results of DCI arthroplasty.

METHODS

A total of 40 patients who received DCI arthroplasty were consecutively reviewed from May 2010 to August 2015. Visual analogue scale (VAS), neck disability index (NDI) score, Japanese Orthopaedic Association (JOA) score, and SF-36 items were used to assess neural function rehabilitation. Static and dynamic radiographs and 3-dimentional computed tomography were used to evaluate the radiological outcomes.

RESULTS

The scores of neck/arm VAS, NDI, JOA, and 8-dimensions of SF-36 were significantly improved at the 1-mo follow-up (P < 0.05) and maintained until the last follow-up (P < 0.05). The range of motion (ROM) of C2-C7, functional spinal unit (FSU), upper/lower adjacent level, C2-C7 lateral bending, and FSU lateral bending decreased at the 1-mo follow-up (P < 0.05), whereas they increased to the preoperative level at the later follow-up intervals (P > 0.05), except the ROM of FSU lateral bending (P < 0.05). The C2-C7 alignment and FSU angle kept more lordotic at the last follow-up (P < 0.05). The intervertebral height increased significantly at the 1-mo follow-up (P < 0.05) and decreased at later follow-ups (P > 0.05). At the last follow-up, 12 (26.1%) segments developed heterotopic ossification.

CONCLUSION

DCI arthroplasty is a safe and effective non-fusion technique to treat cervical degenerative disc disease in long-term follow-up.

Single level anterior cervical discectomy and fusion versus dynamic cervical implant: clinical and radiological outcome

Background

Although anterior cervical discectomy and fusion (ACDF) is considered a gold standard approach for surgical management of cervical disc herniation syndromes, the use of dynamic cervical implant (DCI) provided a novel technique that aims at reconstruction of the anterior column while facilitating controlled neck motion and reducing stress across the facet joints.

Aim of the work

The objective of this study is to evaluate the clinical and radiological outcome of the DCI surgery in comparison to that achieved with ACDF using a conventional polyethylethylketone (PEEK) cage.

Materials and methods

This is a retrospective comparative study of 30 patients, with single level cervical degenerative disc disease (DDD), managed by the authors, either by DCI (n = 15) or ACDF (n = 15). Clinical and radiologic outcomes were assessed at 1, 3, and 12 months postoperatively. Clinical scoring systems included the Visual Analog Scale for Neck (VAS-N) and Arm (VAS-A), the Neck Disability Index score (NDI), as well as the evaluation of incidence of complications and neurological deterioration postoperatively. Radiographic evaluation included the assessment of postoperative cervical implant fusion, as well as evaluating the incidence of implant migration. Study duration was for two years from October 2016 to October 2018.

Results

Both the ACDF and DCI groups showed significant clinical improvement at 12 months postoperatively regarding the clinical outcome including VAS-A, VAS-N, and NDI values (P = 0.001), while there was no significant difference on comparing between the two groups as regard the VAS-N, the VAS-A, and the NDI at 1,3 and 12 months after surgery. The ACDF group however showed better rate of implant fusion at 12 months postoperatively in contrast to the DCI group (80% and 26,7%, respectively) also, the ACDF group showed a lower rate of implant subsidence at 12 months after surgery (P = 0.002). Besides, the incidence of implant migration was relatively high in the DCI group (20%).

Conclusion

The clinical results for DCI arthroplasty for the management of single-level cervical DDD are equivalent to those for ACDF; however, though providing an immediate dynamic stability, DCI is associated with a low fusion rate, higher rates of implant subsidence, and relatively high implant migration rate. Larger series and further studies should be considered with longer follow-up periods giving special attention to these issues.

Resorbable plating system stabilizes tissue-engineered intervertebral discs implanted ex vivo in canine cervical spines

Total disc replacement using tissue-engineered intervertebral discs (TE-IVDs) may offer a biological alternative to treat radiculopathy caused by disc degeneration. A composite TE-IVD was previously developed and evaluated in rat tail and beagle cervical spine models in vivo. Although cell viability and tissue integration into host tissue were promising, significant implant displacement occurred at multiple spinal levels. The goal of the present study was to assess the effects of a resorbable plating system on the stiffness of motion segments and stability of tissue-engineered implants subjected to axial compression. Canine motion segments from levels C2/C3 to C5/C6 were assessed as intact (CTRL), after discectomy (Dx), with an implanted TE-IVD only (PLATE-), and with a TE-IVD combined with an attached resorbable plate (PLATE+). Segments under PLATE+ conditions fully restored separation between endplates and showed significantly higher compressive stiffness than segments under PLATE- conditions. Plated segments partially restored more than 25% of the CTRL motion segment stiffness. Plate attachment also prevented implant extrusion from the disc space at 50% compressive strain, and this effect was more significant in segments from levels C3/C4 when compared to segments from level C5/C6. These results suggest that stabilization of motion segments via resorbable plating assists TE-IVD retention in the disc space while allowing the opportunity for implants to fully integrate into the host tissue and achieve optimal restoration of spine biomechanics.

Clinical and radiographic outcome of dynamic cervical implant (DCI) arthroplasty for degenerative cervical disc disease: a minimal five-year follow-up

Background

To evaluate the mid- to long-term clinical and radiographic outcomes of anterior cervical discectomy and dynamic cervical implant (DCI) arthroplasty for degenerative cervical disc disease.

Methods

From April 2010 to October 2010, 38 patients with single- or double-level cervical disc herniation underwent anterior cervical discectomy and DCI arthroplasty. The clinical results and radiographic outcomes of these 38 patients (42 levels) were retrospectively evaluated. The clinical results included the visual analogue scale, Japanese Orthopaedic Association score, Neck Disability Index score, 36-item short form health survey questionnaire, and incidences of complications and neurological deterioration. Radiographic results including cervical alignment, intervertebral height, cervical range of motion (ROM), ROM of the functional spinal unit, adjacent intervertebral ROM, migration, subsidence, and heterotopic ossification (HO) were assessed on plain radiography, three-dimensional computed tomography, and magnetic resonance imaging.

Results

The mean follow-up period was 72.3 months (range 68–78 months). During follow-up, all patients showed significant improvements in the visual analogue scale score, Japanese Orthopaedic Association score, Neck Disability Index score, 36-item short form health survey physical component summary score and mental component summary score. The ROM of the functional spinal unit was partly reduced. The DCI migrated forward in 10 of 42 (23.8%) cases, and HO was detected in 24 of the 42 (57.1%) DCI segments. Subsidence was observed in 14 of 42 (33.3%) DCI segments. Two patients experienced symptom recurrence, and were treated conservatively.

Conclusions

The clinical efficacy of DCI arthroplasty was maintained during mid- to long-term follow-up. HO formation is a common phenomenon, leading to a substantial decrease in ROM at the index level and recurrence of neurological symptoms. The incidence of implant subsidence and migration is relatively high, leaving a potential risk of symptoms at the index level and adjacent segment degeneration. We consider that the first choice for patients with degenerative cervical disc disease should still be total disc replacement or anterior cervical discectomy and fusion, rather than DCI arthroplasty.

Biomechanical Analysis of Two-level Cervical Disc Replacement With a Stand-alone U-shaped Disc Implant

STUDY DESIGN

Biomechanical study using a three-dimensional nonlinear finite element model.

OBJECTIVE

To analyze biomechanical changes with three prostheses based on two-level arthroplasty and to verify the biomechanical efficiency of dynamic cervical implants (DCIs) with a stand-alone U-shaped structure.

SUMMARY OF BACKGROUND DATA

Few studies have compared biomechanical behavior of various prostheses as they relate with clinical results after two-level total disc replacement.

METHODS

Three arthroplasty devices Mobi-C, porous coated motion (PCM), and DCI were inserted at the C4-C6 disc space and analyzed. Displacement loading was applied to the center of the endplate at the C3 level to simulate flexion and extension motions.

RESULTS

The motion distributions in extension with DCI and in flexion with DCI and Mobi-C were relatively close to that in the intact model. Mobi-C and PCM obviously increased the combined extension range of motion at the index levels, but both resulted in about 45% decrease in extension moment. DCI showed a trend in strain energy similar to that of healthy discs. PCM exhibited a facet joint stress distribution almost similar to that of the intact model. DCI did not generate significant overloading at cartilage between the index levels, whereas the maximum facet joint stress increased with Mobi-C was about 39%. The maximum stress on a ultrahigh molecular-weight-polyethylene core was above the yield stress (42.43 MPa for Mobi-C and 30.94 MPa for PCM).

CONCLUSION

Each prosthesis shows its biomechanical advantages and disadvantages. However, DCI has the capacity to preserve motion and store energy under external loading, similar to the behavior of normal discs. Compared with Mobi-C, both DCI and PCM showed a lower stress at cartilage between index levels, which may avoid facet joint degeneration to some extent. Such a well-controlled arthroplasty device with a stand-alone structure may be a potential candidate and needs to be investigated in future studies.

LEVEL OF EVIDENCE

5.

The prevalence of heterotopic ossification among patients after cervical artificial disc replacement: A systematic review and meta-analysis

BACKGROUND

Prevalence estimates of heterotopic ossification (HO) following cervical artificial disc replacement (ADR) varied widely in previous studies. We conducted a systematic review and meta-analysis to summarize its point prevalence.

METHODS

Electronic searches of PubMed, Web of Science, Embase, and Cochrane Library databases were conducted to identify studies that reported prevalence of HO. Definitions of HO and severe HO were based on McAfee grading system. Random-effects model was used to estimate the pooled prevalence. We conducted subgroup analyses according to the different length of follow-up time, and performed univariate metaregression analyses to explore the effects of potential variables on the overall prevalence.

RESULTS

A total of 38 studies were included in this study. The pooled data showed that the prevalence of HO after cervical ADR within the 1 to 2 years, 2 to 5 years, and 5 to10 years of follow-up was 38.0% (95% confidence interval [CI], 30.2%-46.5%), 52.6% (95% CI, 43.1%-61.9%), and 53.6% (95% CI, 40.0%-66.7%), respectively, while the prevalence of severe HO was 10.9% (95% CI, 9.0%-13.2%), 22.2% (95% CI, 15.5%-30.7%), and 47.5% (95% CI, 30.0%-65.8%), respectively. Follow-up time was positively associated with the prevalence of severe HO (P < .01), and the 1-month growth of mean follow-up went with 0.63% increase of severe HO.

CONCLUSION

This meta-analysis reported data on the prevalence of HO and severe HO after cervical ADR, and provided information on its process of development. These should be useful to enable surgeons and patients to gain a better understanding of HO after cervical ADR.

Changes of proteoglycan and collagen II of the adjacent intervertebral disc in the cervical instability models

OBJECTIVE

Post-operation of cervical decompression fusion and internal fixation (CDF) accelerated adjacent segment disc degeneration (ASD). It is not clear that whether instability of one single segmental accelerates the degeneration of adjacent segment disc. This study aims to explore the effect of cervical instability on the change of morphology and biochemistry in adjective segment (above) in the L5/6 cervical instability rabbit models.

METHODS

Thirty-two mature New Zealand white rabbits (3000±250g) were randomly divided into two groups, control group (n=8) and model group (n=24). The animal models were established by destruction of partly annulus fibrosus and suction of nucleus pulposus. ASD was detected by X-ray after 4, 8 or 12 weeks surgery (8 model rabbits of each time). Animals were then euthanatized for cervical intervertebral disc tissue samples separation. Histomorphology, proteoglycan and collagen II of samples were detected.

RESULTS

Histomorphology data showed that notochord cells were decreased in C4/5 cervical nucleus pulposus and were replaced by fibroblast-like cells; a small amount cartilage cells were emerged; intervertebral disc anulus fibrosus becomes rough, disorganized, hyaline degeneration and pigmentation, in which contained fibrocartilage cells and cracks between the inner and outer layers. Proteoglycan content of nucleus pulposus was significantly decreased. Meanwhile, type II collagen of nucleus pulposus and annulus was also apparently reduced.

CONCLUSION

Cervical instability can alter morphology and reduce the content of proteoglycan and collagen II in adjacent intervertebral disc, thereby contributes adjacent intervertebral disc degeneration.

Adjacent segment degeneration and disease following cervical arthroplasty: a systematic review and meta-analysis

BACKGROUND CONTEXT

Cervical arthroplasty is an increasingly popular alternative for the treatment of cervical radiculopathy and myelopathy. This technique preserves motion at the index and adjacent disc levels, avoiding the restraints of fusion and potentially minimizing adjacent segment pathology onset during the postoperative period.

PURPOSE

This study aimed to identify all prospective studies reporting adjacent segment pathology rates for cervical arthroplasty.

STUDY DESIGN/SETTING

Systematic review and meta-analysis were carried out.

PATIENT SAMPLE

Studies reporting adjacent segment degeneration (ASDegeneration) and adjacent segment disease (ASDisease) rates in patients who underwent cervical arthroplasty comprised the patient sample.

OUTCOME MEASURES

Outcomes of interest included reported ASDegeneration and ASDisease events after cervical arthroplasty.

METHODS

We conducted a MEDLINE, SCOPUS, and Web of Science search for studies reporting ASDegeneration or ASDisease following cervical arthroplasty. A meta-analysis was performed to calculate effect summary values, 95% confidence intervals (CIs), Q values, and I(2) values. Forest plots were constructed for each analysis group.

RESULTS

Of the 1,891 retrieved articles, 32 met inclusion criteria. The patient incidence of ASDegeneration and ASDisease was 8.3% (95% CI 3.8%-12.7%) and 0.9% (95% CI 0.1%-1.7%), respectively. The rate of ASDegeneration and ASDisease at individual levels was 10.5% (95% CI 6.1%-14.9%) and 0.2% (95% CI -0.1% to 0.5%), respectively. Studies following patients for 12-24 months reported a 5.1% (95% CI 2.1%-8.1%) incidence of ASDegeneration and 0.2% (95% CI 0.1%-0.2%) incidence of ASDisease. Conversely, studies following patients for greater than 24 months reported a 16.6% (5.8%-27.4%) incidence of ASDegeneration and 2.6% (95% CI 1.0%-4.2%) of ASDisease. This identified a statistically significant increase in ASDisease diagnosis with lengthier follow-up. Additionally, 1- and 2-level procedures resulted in a 7.4% (95% CI 3.3%-11.4%) and15.6% (95 CI-9.2% to 40.4%) incidence of ASDegeneration, respectively. Although there was an 8.2% increase in ASDegeneration following 2-level operations (relative to 1-level), it did not reach statistical significance. We were unable to analyze ASDisease incidence following 2-level arthroplasty (too few cases), but 1-level operations resulted in an ASDisease incidence of 0.8% (95% CI 0.1%-1.5%).

CONCLUSIONS

This review represents a comprehensive estimation of the actual incidence of ASDegeneration and ASDisease across a heterogeneous group of surgeons, patients, and arthroplasty techniques. Our investigation should serve as a framework for individual surgeons to understand the impact of various cervical arthroplasty techniques, follow-up duration, and surgical levels on the incidence of ASDegeneration and ASDisease during the postoperative period.

In vitro investigation of a new dynamic cervical implant: comparison to spinal fusion and total disc replacement

PURPOSE AND METHODS

For the treatment of degenerative disc diseases of the cervical spine, anterior cervical discectomy and fusion (ACDF) still represents the standard procedure. However, long term clinical studies have shown a higher incidence of pathologies in the adjacent segments. As an alternative to spinal fusion, cervical total disc replacement (cTDR) or dynamically implants were increasingly used. This in vitro study analyzed the kinematics and intradiscal pressures in seven multi-segmental human cervical spine using hybrid multidirectional test method. The aim of our study was to compare the intact condition with a single-level dynamic stabilization with DCI(®), with cTDR (activC(®)) and with simulated ACDF (CeSPACE(®) cage and CASPAR plate).

RESULTS

No significant changes in the kinematics and pressures were observed in all segments after arthroplasty. The DCI(®) significantly decreased the motion of the treated segment in flexion/extension and lateral bending with some remaining residual mobility. Thereby the motion of the upper segment was increased significantly in flexion/extension. No significant changes of the intradiscal pressures were observed. With simulated fusion the motion of the indexed level was significantly decreased in flexion/extension and axial rotation with the greatest changes in the adjacent levels and the highest pressures.

CONCLUSION

Based on our biomechanical study the DCI(®) can pose an alternative to fusion, which has a lesser effect on adjacent levels. This might reduce the risk of long-term degeneration in those levels. In particular, the facet joint arthritis and kyphotic deformity, as a contraindication to the arthroplasty, could be a clinical application of the dynamic implant.