Cervical disc prosthesis versus arthrodesis using one-level, hybrid and two-level constructs: an in vitro investigation

The effects of setup parameters on the measured kinetic output of cervical disc prostheses

Mechanical testing machines are used to evaluate kinematics, kinetics, wear, and efficacy of spinal implants. The simulation of "physiological" spinal loading conditions necessitates the simultaneous use of multiple actuators. The challenge in achieving a desired loading profile lies in achieving close synchronization of these actuators. Errors in load application can be attributed to both the control system and the intrinsic sample response. Moreover, the presence of friction in the setup can have an impact on the measured outcome. The optimization of setup parameters can substantially improve the ability to simulate spinal loading conditions and obtain reliable data on implant performance. In this study, a reproducible kinematic test protocol was developed to evaluate the sensitivity of the kinetic response (i.e., measured loads, moments, and stiffnesses) of a cervical disc prosthesis to several testing parameters. In this context, five ceramic ball and socket sample implants were mounted in a 6 DOF material testing machine and tested with a constant axial compressive force of 100 N in two motion modes: 1) flexion-extension (±7.5°) and 2) lateral bending (±6°). Parameters including rotation rate, slider friction, friction between the samples' articulating surfaces, and moment arm were considered to determine their effects on measured kinetic parameters. The sensitivity analysis indicated that all setup parameters except friction between the samples' articulating surfaces had a substantial effect on the results. The findings were then compared to predictions from a free body diagram to determine the optimal setup parameters. Consequently, the setup with the lowest rotation rate and employing passive sliders yielded results that were consistent with the free body diagram. This study demonstrated the significance of a comprehensive setup evaluation for reliable and reproducible testing of spinal implants, also for comparison between labs.

Is Posterior Cervical Foraminotomy Better Than Fusion for Warfighters?: A Biomechanical Study

INTRODUCTION

Cervical spondylosis in the warfighter is a common musculoskeletal problem and can be career-ending especially if it requires fusion. Head-mounted equipment and increased biomechanical forces on the cervical spine have resulted in accelerated cervical spine degeneration. Current surgical gold standard is anterior cervical discectomy and fusion (ACDF). Posterior cervical foraminotomy (PCF) is a nonfusion surgical alternative, and this can be effective in alleviating radiculopathy from foraminal stenosis caused by disc-osteophyte complex. Biomechanical studies have not been done to analyze motion associated with military aircrew personnel following PCF. The aim of this study was to compare the biomechanical responses of the effects of ACDF and PCF with different grades of facet resection under simulated military aircrew conditions using range of motion, disc pressure, and facet loads at the index and adjacent levels.

MATERIALS AND METHODS

A validated 3D finite element model of the human cervical spinal column was used to simulate various graded PCF and ACDF. All surgical simulations were performed at the most commonly operated level (C5-C6) in warfighters. Pure moment loading under flexion, extension, and lateral bending, and in vivo follower force of 75 N were applied to the intact spine. Hybrid loading protocol was used to achieve 134 degrees of combined flexion-extension and 83 degrees of lateral bending in intact and surgical models to reflect military loading conditions. Segmental motions, disc pressure, and facet load were obtained and normalized with respect to the intact model to quantify the biomechanical effect.

RESULTS

Anterior cervical discectomy and fusion decreased range of motion at the index and increased motion at the adjacent levels, while all graded PCF responses had an opposite trend: increased motion at the index and decreased motion at adjacent levels. The magnitude of changes depended on the level of resection, spinal level, and loading mode. Disc pressure increased at the index level and decreased at the adjacent levels after PCF. These changes were exaggerated with increasing extent of facet resection. Facet load increased at the index level after PCF especially with extension and right (contralateral) lateral bending. Complete facetectomy led to facet load increases greater than ACDF at the adjacent levels in both flexion and extension.

CONCLUSIONS

Posterior cervical foraminotomy is a motion-preserving implant-free surgical alternative to ACDF for warfighters with cervical radiculopathy after failure of conservative management. The treating surgeon must pay close attention to the extent of facet resection to avoid potential spinal instability and future disc and facet degeneration after PCF. Posterior cervical foraminotomy can be more advantageous than ACDF in terms of adjacent segment degeneration, motion preservation, reoperation rate, surgical cost, and retention of warfighters.

Comparison of Load-Sharing Responses Between Graded Posterior Cervical Foraminotomy and Conventional Fusion Using Finite Element Modeling

Following the diagnosis of unilateral cervical radiculopathy and need for surgical intervention, anterior cervical diskectomy and fusion (conventional fusion) and posterior cervical foraminotomy are common options. Although patient outcomes may be similar between the two procedures, their biomechanical effects have not been fully compared using a head-to-head approach, particularly, in relation to the amount of facet resection and internal load-sharing between spinal segments and components. The objective of this investigation was to compare load-sharing between conventional fusion and graded foraminotomy facet resections under physiological loading. A validated finite element model of the cervical spinal column was used in the study. The intact spine was modified to simulate the two procedures at the C5-C6 spinal segment. Flexion, extension, and lateral bending loads were applied to the intact, graded foraminotomy, and conventional fusion spines. Load-sharing was determined using range of motion data at the C5-C6 and immediate adjacent segments, facet loads at the three segments, and disk pressures at the adjacent segments. Results were normalized with respect to the intact spine to compare surgical options. Conventional fusion leads to increased motion, pressure, and facet loads at adjacent segments. Foraminotomy leads to increased motion and anterior loading at the index level, and motions decrease at adjacent levels. In extension, the left facet load decreases after foraminotomy. Recognizing that foraminotomy is a motion preserving alternative to conventional fusion, this study highlights various intrinsic biomechanical factors and potential instability issues with more than one-half facet resection.

Segment selection for fusion and artificial disc replacement in the hybrid surgical treatment of noncontiguous cervical spondylosis: a finite element analysis

Introduction: The treatment of skip-level cervical degenerative disease (CDD) with no degenerative changes observed in the intervening segment (IS) is complicated. This research aims to provide a reference basis for selecting treatment approaches for noncontiguous CDD. Methods: To establish accurate finite element models (FEMs), this study included computed tomography (CT) data from 21 patients with CDD (10 males and 11 females) for modeling. The study primarily discusses four cross-segment surgical approaches: upper (C3/4) anterior cervical discectomy and fusion (ACDF) and lower (C5/6) cervical disc arthroplasty (CDA), FA model; upper CDA (C3/4) and lower ACDF (C5/6), AF model; upper ACDF (C3/4) and lower ACDF (C5/6), FF model; upper CDA (C3/4) and lower CDA (C5/6), AA model. An initial axial load of 73.6 N was applied at the motion center using the follower load technique. A moment of 1.0 Nm was applied at the center of the C2 vertebra to simulate the overall motion of the model. The statistical analysis was conducted using STATA version 14.0. Statistical significance was defined as a p value less than 0.05. Results: The AA group had significantly greater ROM in flexion and axial rotation in other segments compared to the FA group (p < 0.05). The FA group consistently exhibited higher average intervertebral disc pressure in C2/3 during all motions compared to the AF group (p < 0.001); however, the FA group displayed lower average intervertebral disc pressure in C6/7 during all motions (p < 0.05). The AA group had lower facet joint contact stresses during extension in all segments compared to the AF group (p < 0.05). The FA group exhibited significantly higher facet joint contact stresses during extension in C2/3 (p < 0.001) and C6/7 (p < 0.001) compared to the AF group. Discussion: The use of skip-level CDA is recommended for the treatment of non-contiguous CDD. The FA construct shows superior biomechanical performance compared to the AF construct.

Biomechanical evaluation of the novel assembled internal fixed system in C2-C3 anterior cervical discectomy and fusion: a finite element analysis

BACKGROUND

To analyze and compare the biomechanical characteristics of the new combined cervical fusion device (NCCFD) and the traditional cage-plate construct (CPC) to ascertain its effectiveness in anterior cervical discectomy and fusion (ACDF) using finite element analysis.

METHODS

A finite element model of the cervical spine, inclusive of the occipital bone was created and validated. In the ACDF model, either CPC or NCCFD was implanted at the C2-C3 segment of the model. A pure moment of 1.0 Nm combined with a follower load of 50 N was directed onto the superior surfaces of the occipital bone to determine flexion, extension, lateral bending (left and right), and axial rotation (left and right). The range of motion (ROM), stress distribution at the bone-implant interface, and facet joint forces were investigated and compared between CPC and NCCFD systems.

RESULT

The results showed that the ROMs of the fused levels in both models were nearly zero, and the motions of the unfused segments were similar. In addition, the maximum displacement exhibited nearly identical values for both models. The maximum stress of NCCFD screws in lateral bending and rotational conditions is significantly higher than that of the CPC, while the NCCFD model's maximum stress remains within an acceptable range. Comparing the maximum fusion stress, it was found that the CPC experiences much lower fusion stress in anterior flexion and extension than the NCCFD, with no significant difference between the two in lateral bending and rotational states. Stress on the cage was mainly concentrated on both sides of the wings. Comparing the maximum IDP in the CPC and NCCFD, it was observed that maximum stresses rise in extension and lateral bending for both models. Lastly, stress distributions of the facet joints were generally similar across the two devices.

CONCLUSION

NCCFD not only provides the same level of biomechanical stability as CPC but also avoids postoperative complications associated with uneven force damage to the implant. The device offers a novel surgical alternative for ACDF in C2-C3 level.

Cervical Disc Arthroplasty for the Treatment of Noncontiguous Cervical Degenerative Disc Disease: Results of Mid- to Long-Term Follow-up

OBJECTIVE

The long-term results of cervical disc arthroplasty (CDA) for noncontiguous cervical degenerative disc disease (CDDD) are still uncertain. Moreover, it is unclear whether CDA delays or avoids the degeneration of the intermediate segment (IS), leading to controversy in the field. Therefore, this study aimed to investigate the mid- to long-term clinical and radiographic outcomes of CDA in treating noncontiguous CDDD and to explore whether the IS degenerated faster after CDA than other non-surgically treated adjacent segments.

METHODS

We retrospectively analyzed patients with noncontiguous CDDD who underwent CDA in our department between January 2008 and July 2018. The patients were divided into the CDA and hybrid surgery (HS) groups, and clinical and radiographic outcomes were evaluated at routine postoperative intervals. Clinical outcomes were assessed using the Japanese Orthopaedic Association (JOA), neck disability index (NDI), and visual analogue scale (VAS), while radiographic outcomes included cervical lordosis (CL), C2-C7 range of motion (ROM), segmental ROM, and disc angle (DA) at the arthroplasty level. Complications were also evaluated.Pre- and postoperative values were compared using paired t-tests or Wilcoxon rank-sum tests. Independent Student t-tests or Mann-Whitney U tests analyzed continuous data between CDA and HS groups, while chi-square or Fisher exact tests assessed categorical data.

RESULTS

Sixty-four patients with noncontiguous CDDD, with 31 in the CDA group and 33 in the HS group, were evaluated. The mean follow-up time was over 70 months. The most frequently involved levels were C4/5 and C5/6. Both groups showed significant improvements in JOA, NDI, and VAS values after surgery. Although CL was maintained, the CL in the CDA group was consistently lower than that in the HS group (p < 0.05). There was a significant decrease in C2-C7 ROM (p < 0.05), but at the last follow-up, the C2-C7 ROM in the CDA group was greater than that in the HS group (p < 0.05). At the last follow-up, 44.3% of arthroplasty levels had developed heterotopic ossification (HO), and 48.45% had developed anterior bone loss (ABL). In addition, adjacent segment degeneration (ASDeg) was observed in the IS (22.7%), superior adjacent segment (20.6%)and inferior adjacent segment (21.9%).

CONCLUSION

CDA or CDA combined with fusion are viable treatments for noncontiguous CDDD, with satisfactory outcomes after mid-to-long-term follow-up. ASDeg is similar in non-surgical segments after 70 months of follow-up. ROM of the IS issimilar to preoperative levels, indicating CDA does not increase the risk of IS degeneration.

Biomechanical evaluation of a novel biomimetic artificial intervertebral disc in canine cervical cadaveric spines

Background Context

Cervical disc replacement (CDR) aims to restore motion of the treated level to reduce the risk of adjacent segment disease (ASD) compared with spinal fusion. However, first-generation articulating devices are unable to mimic the complex deformation kinematics of a natural disc. Thus, a biomimetic artificial intervertebral CDR (bioAID), containing a hydroxyethylmethacrylate (HEMA)-sodium methacrylate (NaMA) hydrogel core representing the nucleus pulposus, an ultra-high-molecular-weight-polyethylene fiber jacket as annulus fibrosus, and titanium endplates with pins for primary mechanical fixation, was developed.

Purpose

To assess the initial biomechanical effect of the bioAID on the kinematic behavior of the canine spine, an ex vivo biomechanical study in 6-degrees-of-freedom was performed.

Study Design

A canine cadaveric biomechanical study.

Methods

Six cadaveric canine specimens (C3-C6) were tested in flexion-extension (FE), lateral bending (LB) axial rotation (AR) using a spine tester in three conditions: intact, after C4-C5 disc replacement with bioAID, and after C4-C5 interbody fusion. A hybrid protocol was used where first the intact spines were subjected to a pure moment of ±1 Nm, whereafter the treated spines were subjected to the full range of motion (ROM) of the intact condition. 3D segmental motions at all levels were measured while recording the reaction torsion. Biomechanical parameters studied included ROM, neutral zone (NZ), and intradiscal pressure (IDP) at the adjacent cranial level (C3-C4).

Results

The bioAID retained the sigmoid shape of the moment-rotation curves with a NZ similar to the intact condition in LB and FE. Additionally, the normalized ROMs at the bioAID-treated level were statistically equivalent to intact during FE and AR while slightly decreased in LB. At the two adjacent levels, ROMs showed similar values for the intact compared to the bioAID for FE and AR and an increase in LB. In contrast, levels adjacent to the fused segment showed an increased motion in FE and LB as compensation for the loss of motion at the treated level. The IDP at the adjacent C3-C4 level after implantation of bioAID was close to intact values. After fusion, increased IDP was found compared with intact but did not reach statistical significance.

Conclusion

This study indicates that the bioAID can mimic the kinematic behavior of the replaced intervertebral disc and preserves that for the adjacent levels better than fusion. As a result, CDR using the novel bioAID is a promising alternative treatment for replacing severely degenerated intervertebral discs.

Hybrid Implants in Anterior Cervical Spine Surgery: The State of the Art and New Trends for Multilevel Degenerative Disc Disease

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) still represents the first surgical option in the treatment of cervical degenerative disc disease (DDD) but is still burdened by several complications secondary to the loss of mobility at the treated segment and adjacent segment diseases (ASDs). To overcome those complications, hybrid surgery (HS) incorporating ACDF and cervical disc arthroplasty (CDA) is increasingly performed for DDD.

METHODS

We retrospectively reviewed the clinical, surgical, and outcome data of 85 consecutive patients (M/F, 41/44) harboring cervical disc herniation with or without osteophytes, with radiculopathy and with or without myelopathy, who underwent the anterior approach to a cervical discectomy on two or more levels with at least one disc prosthesis, along with a cage and plate or an O Profile screwed plate.

RESULTS

All the patients improved regardless of the cervical construct used. No significant relationship between different kinds of prosthesis and their surgical level; the number of cages; and the site of the cages (screwed and/or plated) was found concerning immediate stability, dynamic prosthesis effectiveness, and clinical improvement in all the patients up to the maximum follow-up time.

CONCLUSIONS

Although the optimal surgical technique for cervical DDD remains controversial, HS represents a safe and effective procedure in select patients with multilevel cervical DDD, as demonstrated by biomechanical and clinical studies and the present series.

Comparison of clinical efficacy between retention and removal of the vertebral bony endplate in anterior cervical discectomy and fusion for the treatment of cervical spondylotic myelopathy

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) have a history of more than 60 years to treat cervical spondylotic myelopathy. This study is based on the original classic surgical procedure to remove the bony endplate to expand the range of vertical decompression to analyze and compare the clinical efficacy of two different ACDF in treating cervical spondylotic myelopathy.

METHODS

The inpatients in hospital were randomly divided into two groups A and B. Patients in Group A received ACDF surgery with bony endplates preserved, and patients in group B received ACDF surgery with bony endplates removed. All patients were followed-up for three years, and then compared the clinical efficacy from the following aspects, blood loss statistics during and after the operation, Japanese Orthopedic Association's scoring (JOA) standard for cervical spondylotic myelopathy, Cervical curvature index, cervical flexion and extension range, intervertebral bone graft fusion time and fusion rate.

RESULTS

1. The operative time and intraoperative (postoperative) blood loss in group A were significantly better than that in group B, with statistical significance (P < 0.05)0.2. There was no significant difference in postoperative neurological function recovery, cervical curvature index, cervical flexion and extension activity, and Intervertebral fusion time between two groups (P > 0.05), while group A was superior to group B in terms of bone graft fusion rate (P < 0.05). 3. Four patients (6.7%) in group B suffered from dyspnea due to neck hematoma caused by drainage tube blockage, but all of them were cured immediately and no death occurred.

CONCLUSIONS

During the 3-year follow-up period after the operation, six patients in group B have subsidence and loosening of the internal fixator due to bone subsidence around the implant. Although immediate surgical treatment is not required, renovation surgery is inevitable in the long term.

Spinal Cord Stress After Anterior Cervical Diskectomy and Fusion: Results from a Patient-Specific Finite Element Model

Degenerative cervical myelopathy (DCM) is the commonest cause of cervical spinal cord dysfunction in older adults and is characterized by spinal cord compression and stress during neck motion. Although surgical decompression eliminates static spinal cord compression, cord stress resulting from flexion-extension motion of the spinal column has not been determined for single and multi-level surgical interventions. The effect of surgery on spinal cord stress is expected to change with the number of surgical levels as well as patient-specific anatomy. Using a MRI-derived patient-specific finite element model, we simulated 1-, 2- and 3-level anterior cervical diskectomy and fusion (ACDF) surgery for DCM. A substantial decrease in spinal cord stress at the level of spinal cord decompression was noted in all simulations. This was associated with a considerable increase in spinal cord stress rostral to the surgical level, and the magnitude of stress was higher in multi-level surgery. Increased spinal cord stress at the rostral adjacent segment correlated with increased segmental range of motion (r = 0.69, p = 0.002) and disk pressure (r = 0.57, p = 0.05). Together, these results indicate that ACDF for DCM is associated with adverse spinal cord stress patterns adjacent to the fusion construct, and further research is needed to determine if the altered stress is associated with clinical outcomes after surgery for DCM.

Kinematics of a cervical disc prosthesis implanted above or below one- and two-level fusions

Background

The theoretical advantages of hybrid constructs over multi-level fusion have been illustrated in clinical and biomechanical studies. However, there is no biomechanical data on hybrid constructs using load control analyses. There is also no clear data on whether there is a biomechanical difference if the arthroplasty is below or above a 1- or 2-level fusion. This work investigated the effect on segmental motion of having a cervical total disc arthroplasty implanted above or below a 1- or 2-level fusion.

Methods

Segmental motions of 16 C2-T1 cervical spine specimens were measured as the specimens were tested to 1.5Nm in axial rotation and in flexion-extension under compressive preload. Tests were conducted on intact specimens, and then after arthroplasty with a 1-level and 2-level fusion. 8 specimens were in test Group 1, where the hybrid configuration had a total disc arthroplasty above a 1- or 2-level fusion. The arthroplasty was below the 1- and 2-level fusion in Group 2. Load control and displacement control analyses were conducted to determine the effect of the hybrid configurations on segmental motion.

Results

In load control, compensatory motion increases were found at all non-instrumented cervical spine segments in flexion-extension and axial rotation. Flexion-extension and axial rotation ranges of motion at the total disc arthroplasty level were less than 1° different than intact.

In displacement control, there was no consistent pattern of compensatory motion. Range of motion at the arthroplasty level was within 3.5° of intact.

Conclusions

The total disc arthroplasty segmental level in a hybrid construct has similar amounts of motion as intact. This may shield the arthroplasty level and adjacent levels from supra-physiological motion and loading. These results suggest that a hybrid construct may be protective of adjacent segments, whether the total disc arthroplasty is above or below the fusion.

Incorporating strategy in hybrid surgery for continuous two-level cervical spondylosis from a biomechanical perspective

BACKGROUND AND OBJECTIVE

Hybrid surgery, incorporating cervical disc replacement and anterior cervical discectomy and fusion, has shown good clinical results in the treatment of multilevel cervical spondylosis according to early follow-ups. This study investigated the surgical strategy of hybrid surgery for two-level cervical spondylosis by distinguishing the biomechanical characteristics with different incorporating modes.

METHOD

A finite element model of a healthy cervical spine including C2-T1 was developed, and hybrid surgery was simulated by replacing at one level with Prestige-LP and fusion at another level with the anterior plate in C3-C5 (Hybrid-S1: replaced at C3-C4, Hybrid-S2: replaced at C4-C5), and in C4-C6 (Hybrid-M1: replaced at C4-C5, Hybrid-M2: replaced at C5-C6) and in C5-C7 (Hybrid-U1: replaced at C5-C6, Hybrid-U2: replaced at C6-C7). The motion of C2 vertebrae in flexion, extension, axial rotation, and lateral bending was imposed on all hybrid models following the displacement control testing protocol.

RESULTS

The largest range of motion (ROM) in a healthy spine was observed at C5-C6, followed by C3-C4, C4-C5 and C6-C7. On average, the ROM at the replaced segment increased by 175.7%, 202.7%, 176.3%, 117.1%, 139.4%, and 236.0% in Hybrid-S1, Hybrid-S2, Hybrid-M1, Hybrid-M2, Hybrid-U1, and Hybrid-U2, respectively. The facet joint stress at the replaced segment increased by 186.9%, 124.4%, 111.1%, 60.3%, 62.7%, and 144.7%, and the adjacent intradiscal pressure (IDP) increased by 45.2%, 38.7%, 2.7%, 2.1%, 13.9%, and 20.1%.

CONCLUSIONS

Incorporating mode in hybrid surgery affects cervical biomechanics. Hybrid surgery with replacement at a segment with a greater ROM and fusion at a segment with a lower ROM can results in fewer changes in terms of overall cervical stiffness, ROM at the operative level, facet joint stress, and adjacent IDP. In hybrid surgery, it is better to implement disc replacement at a level with a greater ROM and fusion of another segment.

Instrumentation Across the Cervicothoracic Junction Does Not Improve Patient-reported Outcomes in Multilevel Posterior Cervical Decompression and Fusion

STUDY DESIGN

This was a retrospective cohort.

OBJECTIVE

The objective of this study was to determine if instrumentation across the cervicothoracic junction (CTJ) in elective multilevel posterior cervical decompression and fusion (PCF) is associated with improved patient-reported outcome measures (PROMs).

SUMMARY OF BACKGROUND DATA

Fusion across the CTJ may result in lower revision rates at the expense of prolonged operative duration. However, it is unclear whether constructs crossing the CTJ affect PROMs.

MATERIALS AND METHODS

Standard Query Language (SQL) identified patients with PROMs who underwent elective multilevel PCF (≥3 levels) at our institution. Patients were grouped based on anatomic construct: crossing the CTJ (crossed) versus not crossing the CTJ (noncrossed). Subgroup analysis compared constructs stopping at C7 or T1. Independent t tests and χ 2 tests were utilized for continuous and categorical data, respectively. Regression analysis controlled for baseline demographics. The α was set at 0.05.

RESULTS

Of the 160 patients included, the crossed group (92, 57.5%) had significantly more levels fused (5.27 vs. 3.71, P <0.001), longer operative duration (196 vs. 161 min, P =0.003), greater estimated blood loss (242 vs. 160 mL, P =0.021), and a decreased revision rate (1.09% vs. 10.3%, P =0.011). Neither crossing the CTJ (vs. noncrossed) nor constructs spanning C3-T1 (vs. C3-C7) were independent predictors of ∆PROMs (change in preoperative minus postoperative patient-reported outcomes) on regression analysis. However, C3-C7 constructs had a greater revision rate than C3-T1 constructs (15.6% vs. 1.96%, P =0.030).

CONCLUSION

Crossing the CTJ in patients undergoing elective multilevel PCF was not an independent predictor of improvement in PROMs at 1 year, but they experienced lower revision rates.

LEVEL OF EVIDENCE

Level III.

Biomechanical Effects of a Novel Anatomic Titanium Mesh Cage for Single-Level Anterior Cervical Corpectomy and Fusion: A Finite Element Analysis

Background: The traditional titanium mesh cage (TTMC) has become common as a classical instrument for Anterior Cervical Corpectomy and Fusion (ACCF), but a series of complications such as cage subsidence, adjacent segment degeneration (ASD), and implant-related complications by using the TTMC have often been reported in the previous literature. The aim of this study was to assess whether a novel anatomic titanium mesh cage (NTMC) could improve the biomechanical condition after surgery.

Methods: The NTMC model consists of two spacers located on both sides of the TTMC which match the anatomic structure between the endplates by measuring patient preoperative cervical computed tomography (CT) data. The ranges of motion (ROMs) of the surgical segments and the stress peaks in the C6 superior endplates, titanium mesh cage (TMC), screw–bone interface, anterior titanium plate, and adjacent intervertebral disc were compared.

Results: Compared with the TTMC, the NTMC reduced the surgical segmental ROMs by 89.4% postoperatively. The C6 superior endplate stress peaks were higher in the TTMC (4.473–23.890 MPa), followed by the NTMC (1.923–5.035 MPa). The stress peaks on the TMC were higher in the TTMC (47.896–349.525 MPa), and the stress peaks on the TMC were lower in the NTMC (17.907–92.799 MPa). TTMC induced higher stress peaks in the screw–bone interface (40.0–153.2 MPa), followed by the NTMC (14.8–67.8 MPa). About the stress peaks on the anterior titanium plate, the stress of TTMC is from 16.499 to 58.432 MPa, and that of the NTMC is from 12.456 to 34.607 MPa. Moreover, the TTMC induced higher stress peaks in the C3/4 and C6/7 intervertebral disc (0.201–6.691 MPa and 0.248–4.735 MPa, respectively), followed by the NTMC (0.227–3.690 MPa and 0.174–3.521 MPa, respectively).

Conclusion: First, the application of the NTMC can effectively decrease the risks of TMC subsidence after surgery. Second, in the NTMC, the stresses at the anterior screw-plate, bone–screw, and TMC interface are much less than in the TTMC, which decreased the risks of instrument-related complications after surgery. Finally, increases in IDP at adjacent levels are associated with the internal stresses of adjacent discs which may lead to ASD; therefore, the NTMC can effectively decrease the risks of ASD.

Biomechanical Analysis of 3-Level Anterior Cervical Discectomy and Fusion Under Physiologic Loads Using a Finite Element Model

Objective

Pseudarthrosis and adjacent segment degeneration (ASD) are 2 common complications after multilevel anterior cervical discectomy and fusion (ACDF). We aim to identify the potential biomechanical factors contributing to pseudarthrosis and ASD following 3-level ACDF using a cervical spine finite element model (FEM).

Methods

A validated cervical spine FEM from C2 to C7 was used to study the biomechanical factors in cervical spine intervention. The FEM model was used to simulate a 3-level ACDF with intervertebral spacers and anterior cervical plating with screw fixation from C4 to C7. The model was then constrained at the inferior nodes of the T1 vertebra, and physiological loads were applied at the top vertebra. The pure moment load of 2 Nm was applied in flexion, extension, and lateral bending. A follower axial force of 75 N was applied to reproduce the weight of the cranium and muscle force, was applied using standard procedures. The motion-controlled hybrid protocol was utilized to comprehend the adjustments in the spinal biomechanics.

Results

Our cervical spine FEM demonstrated that the cranial adjacent level (C3–4) had significantly more increase in range of motion (ROM) (+90.38%) compared to the caudal adjacent level at C7–T1 (+70.18%) after C4–7 ACDF, indicating that the cranial adjacent level has more compensatory increase in ROM than the caudal adjacent level, potentially predisposing it to earlier ASD. Within the C4–7 ACDF construct, the C6–7 level had the least robust fixation during fixation compared to C4–5 and C5–6, as reflected by the smallest reduction in ROM compared to intact spine (-71.30% vs. -76.36% and -77.05%, respectively), which potentially predisposes the C6–7 level to higher risk of pseudarthrosis.

Conclusion

Biomechanical analysis of C4–7 ACDF construct using a validated cervical spine FEM indicated that the C3–4 has more compensatory increase in ROM compared to C7–T1, and C6–7 has the least robust fixation under physiological loads. These findings can help spine surgeons to predicate the areas with higher risks of pseudarthrosis and ASD, and thus developing corresponding strategies to mitigate these risks and provide appropriate preoperative counseling to patients.

In-vitro Biomechanics of the Cervical Spine: a Systematic Review

In-vitro testing has been conducted to provide a comprehensive understanding of the biomechanics of the cervical spine. This has allowed a characterization of the stability of the spine as influenced by the intrinsic properties of its tissue constituents and the severity of degeneration or injury. This also enables the pre-clinical estimation of spinal implant functionality and the success of operative procedures. The purpose of this review paper was to compile methodologies and results from various studies addressing spinal kinematics in pre- and post-operative conditions so that they could be compared. The reviewed literature was evaluated to provide suggestions for a better approach for future studies, to reduce the uncertainties and facilitate comparisons among various results. The overview is presented in a way to inform various disciplines, such as experimental testing, design development, and clinical treatment. The biomechanical characteristics of the cervical spine, mainly the segmental range of motion (ROM), intradiscal pressure (IDP), and facet joint load (FJL), have been assessed by testing functional spinal units (FSUs). The relative effects of pathologies including disc degeneration, muscle dysfunction, and ligamentous transection have been studied by imposing on the specimen complex load scenarios imitating physiological conditions. The biomechanical response is strongly influenced by specimen type, test condition, and the different types of implants utilized in the different experimental groups.

Study on biomechanical analysis of two-level cervical Mobi-C and arthrodesis

OBJECTIVE

To investigate the range of motion (ROM) index of a two-level cervical arthroplasty.

METHODS

Seven human cadaveric spines were biomechanically examined from C2 level to T1 level under intact status and the following conditions: 2-level arthroplasty (C4-C6) employing Mobi-C devices (MM group), 2-level anterior cervical discectomy and fusions (2-ACDFs) (FF group), and both as a hybrid surgery (HS) (MF group and FM group). Multidirectional flexibility examination was conducted according to the Panjabi hybrid testing protocol. Unconstrained intact moments of ±1.5 NM were performed for axial rotation (AR) flexion/extension (FE), and lateral bending (LB).

RESULTS

No statistical differences were found between the intact spine and MM group at the operative- and adjacent-level kinematics in the three loading conditions, except that C4-C5 ROM significantly increased in the axial rotation loading (P<0.05). Compared with the intact spine, MF group led to a significant decrease at the arthrodesis segment ROM C5-C6 in the three loading (P<0.05), with corresponding significantly increased at C4-C5 in FE and AR (P<0.05). FM group resulted in a significant decrease in ROM C4-C5 (P<0.05) with corresponding significantly increased at C5-C6 in FE, AR and LB (P<0.05). There was not any difference for non-operative level kinematics between MF group and FM group and intact spine. Compared with the intact spine, FF group led to a significant decrease at the arthrodesis-levels (P<0.05) and marked increase at the non-operative level kinematics.

CONCLUSION

A two-level Mobi-C and Hybrid construct generated better biomechanical conditions. This study suggested that two-level cervical total disc replacement or HS could become an alternative approach for therapy of two-level consecutive cervical spondylosis.

Biomechanical effects of uncinate process excision in cervical disc arthroplasty

BACKGROUND

Studies on the role of uncinate process have been limited to responses of the intact spine and patient's outcomes, and procedures to perform the excision. The aim of this study was to determine the role of uncinate process on the biomechanical response at the index and adjacent levels in three artificial discs used in cervical disc arthroplasty.

METHODS

A validated finite element model of cervical spine was used. Flexion, extension, and lateral moments and follower load were applied to Bryan, Mobi-C, and Prestige LP artificial discs at C5-C6 level with and without uncinate process. Ranges of motion at index level and adjacent caudal and cranial segments, intradiscal pressures at adjacent segments, and facet loads at index level and adjacent segments were obtained. Data were normalized with respect to the preservation of uncinate process.

FINDINGS

Uncinate process removal increased motions up to 27% at index and decreased up to 10% at adjacent levels, decreased disc pressures up to 14% at adjacent segments, decreased facet loads at adjacent segments up to 14%, while at index level, change in loads depended on mode and arthroplasty, with Mobi-C responding with up to 51% increase and Bryan disc up to 11% decrease, while Prestige LP increased loads by 17% in extension and decreased by 9%% in lateral bending.

INTERPRETATION

As surgical selection is based on morphology and surgeon's experience, the present computational findings provide quantitative information for an optimal choice of the device and procedure, while further studies (in vitro/clinical) would be required.

Anterior hybrid construction of multilevel cervical disc disease and spondylotic spinal stenosis: surgical results and factors affecting adjacent segment problems

Objective

We aimed to evaluate reliability, radiological outcomes, and the impacts of anterior cervical hybrid construction on the adjacent segments for the multilevel cervical degenerative disc disease (mCDDD) and spondylotic spinal stenosis (SSS).

Methods

A retrospective analysis was performed using data extracted from the medical files of 195 patients (105 males, 90 females; mean age: 47.7 years). From 2008 to 2018, these patients underwent anterior cervical hybrid construction for symptomatic contiguous at least 2-level cervical degenerative disc diseases and cervical spondylosis. Clinical and radiological data including Neck Disability Index (NDI), visual analogue scale (VAS), local cervical degenerative disk disease in adjacent segments on magnetic resonance imaging (MRI) views, and complications were reviewed.

Results

The mean clinical and radiological follow-up was 45.2 months (range 24 to 102). Radiculopathy and/or myelopathy were the main clinical problems in all patients. The mean VAS scores of HC for arm pain were 7.4 ± 0.8 preoperatively; 2.8 ± 0.6, 1 month after surgery; 2.3 ± 0.6, 6 months after surgery; 1.8 ± 0.6, 12 month after surgery; and 1.6 ± 0.6, 24 months after surgery. The mean NDI scores (mean ± SD) of HC significantly improved after surgery (on admission, 57.2 ± 5.5%; 1 month after surgery, 27.35 ± 5.3%; 6 month after surgery, 21.43 ± 2.8%; 12 months after surgery, 21.9 ± 2.3%; 24 months after surgery, 20.6 ± 2.6%, p = 0.006). Hoarseness and dysphagia were the most common complications and osteophyte formation was the most frequent radiographic change.

Conclusion

Anterior cervical hybrid construction appears to be an acceptable option in the management of multilevel cervical degenerative disc diseases and spondylotic spinal stenosis.

Hybrid implants in anterior cervical decompressive surgery for degenerative disease

Background:

Anterior cervical discectomy and fusion (ACDF) still represent the mainstream surgical approach in the treatment of degenerative cervical Degenerative Disc Disease (DDD), being a loss of mobility at the treated segment and adjacent segment diseases well-known complications. To overcome those complications, hybrid surgery (HS) incorporating ACDF and cervical disk arthroplasty is increasingly performed for DDD.

Methods:

We retrospectively reviewed the clinical, surgical, and outcome data of 62 consecutive patients (male/female, 29/37) harboring cervical disk herniation with or without osteophytes, with radiculopathy with or without myelopathy, who underwent a cervical discectomy on two or more levels with the anterior approach with at least one disk prosthesis along with cage and plate or O Profile screwed plate.

Results:

All the patients improved regardless of the cervical construct used. No significant relationship between different kind of prostheses as well as their surgical level, the number and the site of the cages (screwed and/or plated) was found out concerning immediate stability, dynamic prosthesis effectiveness, and clinical improvement in all the patients up to the maximum follow-up.

Conclusions:

Although the optimal surgical technique for cervical DDD remains controversial, HS represents a safe and effective procedure in selected patients with multilevel cervical DDD, as demonstrated by biomechanical and clinical studies and the present series. Some technical aspects should be considered when dealing with this procedure, like the drilling of the endplate, and some radiological findings have to be detected because potentially predictive of future misplacement.

Viscoelastic cervical total disc replacement devices: Design concepts

Cervical disc replacement (CDR) is a motion-preserving surgical procedure for treating patients with degenerative disorders. Numerous reports of first generation CDR "ball-and-socket" articulating devices have shown satisfactory clinical results. As a result, CDR devices have been safely implemented in the surgeon's armamentarium on a global scale. However, only minor design improvements have been made over the last few years, as first generation CDRs devices were based on traditional synovial joint arthroplasty designs. As a consequence, these articulating designs have limited resemblance to the complex kinematic behavior of a natural disc. This has driven the development of deformable viscoelastic CDR devices to better mimic the biomechanical behavior of a natural disc. As a result, several viscoelastic CDR devices have been developed in recent years that vary in terms of materials, design and clinical outcomes. Since these viscoelastic CDR devices are fairly new, their weaknesses and strengths, which are related to their design characteristics, have not been well described. Therefore, this literature review discusses design related advantages and disadvantages of deformable viscoelastic CDR devices. As such, this paper can provide insight for surgeons and engineers on specific design characteristics of several viscoelastic devices and could potentially help to develop and design future implants. Eleven viscoelastic CDR devices were identified. An extensive database search on the devices' tradenames in Medline and PubMed was performed next. The devices were categorized based on common design characteristics to give an overview of both category and device specific complications and advantages. Overall, literature shows that most of these viscoelastic CDR devices can provide motion in all six degrees-of-freedom and have a variable center of rotation. Nevertheless, the viscoelastic materials used do not have an extensive history in orthopedics, so the long-term material behavior in vivo is still unknown. Although the viscoelastic devices have common benefits and risks, each specific design and category also has its own design related advantages and drawbacks that are described in this review. Altogether, viscoelastic total disc replacements seem to be a promising option for the future of cervical arthroplasty, but long-term clinical outcome is needed to confirm the advantages of mimicking the viscoelasticity of a natural disc.

External and internal responses of cervical disc arthroplasty and anterior cervical discectomy and fusion: A finite element modeling study

Surgical treatment for spinal disorders, such as cervical disc herniation and spondylosis, includes the removal of the intervertebral disc and replacement of biological or artificial materials. In the former case, bone graft is used to fill the space, and this conventional procedure is termed anterior cervical discectomy and fusion (ACDF). The latter surgery is termed as artificial disc replacement ADR) or cervical disc arthroplasty (CDA). Surgeries are most commonly performed at one or two levels. The present study was designed to determine the external (range of motion, ROM) and internal (anterior and posterior load sharing) responses of the spines with one-level and two-level surgeries in both models (ACDF and CDA) using a previously validated finite element model (FEM) of the subaxial cervical spinal column. The FEM simulated the vertebra (cancellous core and cortical shell of the body, posterior elements - laminae, pedicles and spinous processes), discs (anulus fibers, ground substance, and nucleus pulposus), anterior and posterior ligaments of the disc and facet joints, and interspinous and supraspinous ligaments. Appropriate material properties were assigned to the spinal components. The United States Food Drug Administration-approved Mobi-C was used for the CDA option. The FEM was exercised under pure flexion and extension moment loading of 2 Nm in the intact state. The overall ROM of the column was obtained. The hybrid loading protocol applied moments that matched the ROM in the intact spine for both one-level (C5-C6) and two-level (C5-C7) ACDF and CDA surgeries. ROM at the level(s) of surgery, termed the index level was obtained. These data along with anterior column load (ACL) and posterior column load (PCL) sharing were obtained for all surgical options at superior and inferior segments (termed adjacent segment outputs). Results for both one-level and two-level surgeries showed that ACDFs decreases ROM at the index level, while CDAs increase motions compared to the intact normal spine. The ROM, ACL, and PCL increased at both adjacent levels for the ACDF while CDA showed a decrease. Although two-level surgeries resulted in increased these biomechanical variables, greater changes to adjacent segment biomechanics in ACDF may accelerate adjacent segment disease. Decreased ROM and lower load sharing in CDAs may limit adjacent segment effects such as accelerated degeneration. Their increased posterior load sharing, however, may need additional attention for patients with suspected facet joint disease.

Comprehensive Analysis of Hybrid Surgery and Anterior Cervical Discectomy and Fusion in Cervical Diseases: A Meta-Analysis

To investigate the outcomes and reliability of hybrid surgery (HS) versus anterior cervical discectomy and fusion (ACDF) for the treatment of multilevel cervical spondylosis and disc diseases.Hybrid surgery, combining cervical disc arthroplasty (CDA) with fusion, is a novel treatment to multilevel cervical degenerated disc disease in recent years. However, the effect and reliability of HS are still unclear compared with ACDF.To investigate the studies of HS versus ACDF in patients with multilevel cervical disease, electronic databases (Medline, Embase, Pubmed, Cochrane library, and Cochrane Central Register of Controlled Trials) were searched. Studies were included when they compared HS with ACDF and reported at least one of the following outcomes: functionality, neck pain, arm pain, cervical range of motion (ROM), quality of life, and incidence of complications. No language restrictions were used. Two authors independently assessed the methodological quality of included studies and extracted the relevant data.Seven clinical controlled trials were included in this study. Two trials were prospective and the other 5 were retrospective. The results of the meta-analysis indicated that HS achieved better recovery of NDI score (P = 0.038) and similar recovery of VAS score (P = 0.058) compared with ACDF at 2 years follow-up. Moreover, the total cervical ROM (C2-C7) after HS was preserved significantly more than the cervical ROM after ACDF (P = 0.000) at 2 years follow-up. Notably, the compensatory increase of the ROM of superior and inferior adjacent segments was significant in ACDF groups at 2-year follow-up (P < 0.01), compared with HS.The results demonstrate that HS provides equivalent outcomes and functional recovery for cervical disc diseases, and significantly better preservation of cervical ROM compared with ACDF in 2-year follow-up. This suggests the HS is an effective alternative invention for the treatment of multilevel cervical spondylosis to preserve cervical ROM and reduce the risk of adjacent disc degeneration. Nonetheless, more well-designed studies with large groups of patients are required to provide further evidence for the benefit and reliability of HS for the treatment of cervical disk diseases.

Influence of Fusion on the Behavior of Adjacent Disc Arthroplasty in Contiguous 2-Level Hybrid Surgery In Vivo

OBJECTIVE

To investigate whether the behavior of disc arthroplasty in 2-level hybrid surgery (HS) was affected by adjacent fusion in vivo compared with cervical disc arthroplasty (CDA) alone.

METHODS

Seventy-nine patients undergoing either a 1-level CDA or contiguous 2-level HS were retrospectively reviewed. Radiologic assessments included segmental lordosis (SL), intervertebral disc height (IDH), changes in SL and IDH, range of motion (ROM) of the disc replacement and its adjacent segments, migration and subsidence of the prosthesis, heterotopic ossification (HO), and adjacent segment degeneration (ASD) adjacent to the arthroplasty level. Clinical features and outcome scores were also recorded.

RESULTS

Compared with 1-level CDA, the increased SL and IDH immediately after surgery in 2-level HS were more likely to be lost throughout the follow-up period. However, both groups generally maintained the SL and IDH of the arthroplasty segment postoperatively. Two-level HS did not exhibit hypermobility of the disc prosthesis and preserved preoperative ROM of the adjacent segment of the device. The HS group showed adverse effects on the prosthesis stability, but there was no significant difference in the number of cases of obvious migration or subsidence between the groups. The differences in HO, ASD, and clinical outcomes between the groups were not significant at the final follow-up.

CONCLUSIONS

Although the fusion in 2-level HS partially affected the behavior of adjacent disc arthroplasty compared with CDA alone, it did not cause severe complications and adverse clinical outcomes. However, large-scale and long follow-up trials are warranted.

Biomechanical effects on the intermediate segment of noncontiguous hybrid surgery with cervical disc arthroplasty and anterior cervical discectomy and fusion: a finite element analysis

BACKGROUND CONTEXT

Surgery for cervical degenerative disc disorder (CDDD) at two noncontiguous segments is infrequent. Few studies have explored the biomechanical effects on the intermediate adjacent segment of anterior cervical discectomy and fusion (ACDF) or cervical disc arthroplasty (CDA) in this situation. No study has examined biomechanical differences between ACDF and hybrid surgery (HS) constructs for noncontiguous CDDD. Differences in the biomechanical changes between the intermediate and adjacent segments are unknown.

PURPOSE

This study was conducted to compare the biomechanical changes resulting from noncontiguous ACDFs and HS.

STUDY DESIGN

A finite element analysis study.

METHODS

A finite element model of a healthy cervical spine (C2-C7) was constructed. Three surgical models were developed: (1) ACDF at C3/4 and C5/6 (FF), (2) ACDF at C3/4 and CDA at C5/6 (FA) and (3) CDA at C3/4 and ACDF at C5/6 (AF). A 75-N follower load with 1.0 N·m moments was applied to the top of the C2 vertebra in the intact model to simulate flexion, extension, lateral bending, and axial rotation. Surgical models achieved identical motion angles of the intact model in each direction following the displacement-control protocols.

RESULTS

The FF model required much higher moments than did the AF and FA models to achieve the same amount of motion. In the FF model, the motion contributions of the unfused segments were unevenly increased. The magnitude of the increased motion in the intermediate segment was larger than those in the supra- or infra-adjacent segments. The facet contact force (FCF) and intradiscal pressure (IDP) at the intermediate segment were also more susceptible to impact. In the FA and AF models, the motion contributions of the untreated levels were evenly changed, and the intermediate segment did not experience additive motion, FCF, or IDP. The segment adjacent to the level of ACDF had greater FCF and IDP than did the segment adjacent to the level of CDA in the two HS constructs.

CONCLUSIONS

HS constructs resulted in less altered biomechanics and kinematics of the untreated levels and showed no additive biomechanical effects on the intermediate segments compared with ACDF at noncontiguous levels. However, the effects were associated with the relative location of the ACDF and CDA levels.

CLINICAL SIGNIFICANCE

This study provides a biomechanical rationale for the use of HS to treat patients with noncontiguous CDDD.

Radiological exploration on adjacent segments after total cervical disc replacement with Prodisc-C prosthesis

Purpose

The relationship between upper or lower adjacent segments (UAS/LAS) and the cervical spine parameters was not clear yet. So, the purpose was to analyze range of motion (ROM), lordosis (LOR), and intervertebral disc height (IDH) of UAS and LAS before and after total cervical disc replacement (TDR) and to explore the influencing factors of cervical spine radiological parameters on adjacent segments.

Methods

A single-center retrospective study was performed on patients completing 10-year follow-up undergone TDR. As the primary outcomes, radiological parameters included UAS-ROM/LAS-ROM, UAS-LOR/LAS-LOR, and UAS-IDH/LAS-IDH. The secondary outcomes were ROM and LOR of C2–C7 and surgical levels, IDH of surgical segments, prosthesis migration, subsidence, heterotopic ossification (HO), and adjacent segment degeneration (ASD), which were measured on X-ray.

Results

UAS-ROM and LAS-ROM remained stable in follow-up periods. There was no significance on UAS-LOR or LAS-LOR between pre- and post- operation, so was UAS-IDH or LAS-IDH. UAS-ROM was larger in the segments with ASD (P < 0.001), the same to LAS-ROM (P < 0.001), and UAS-LOR was larger in segments with ASD (P = 0.02). UAS-ROM was positively correlated with C2–C7 ROM and LOR (both P < 0.001). UAS-LOR was correlated with operated-segmental LOR while LAS-LOR were in correlation with surgical segment ROM. The influencing factors of UAS-ROM were the surgical segment ROM and C2–C7 LOR. The influencing factors of UAS-LOR and LAS-LOR were LAS-ROM and UAS-ROM, respectively. The influencing factors of UAS-IDH were LAS-IDH, surgical segment IDH, and HO while that of LAS-IDH were UAS-IDH and surgical segment IDH.

Conclusions

TDR has only a little effect on the adjacent segments. There is an interaction between UAS and LAS. The maintenance on surgical segments ROM and reconstruction of IDH will benefit to adjacent segments.

Biomechanical analysis of cervical range of motion and facet contact force after a novel artificial cervical disc replacement

An ideal implantation of artificial cervical disc replacement (ACDR) prosthesis should preserve the cervical biomechanics and maintain normal cervical biomechanics. In this study, we designed a novel prosthesis based on the physiological curvature of the cervical endplate, and conducted an in vitro test with cadaveric cervical specimens to study its effect on cervical range of motion (ROM) and facet contact force. Eighteen cadaveric cervical specimens (C2-C7) were evaluated with a 50 N follower load and a moment of ± 2.0 N-m. Testing conditions were as follows: control (group 1), C5-C6 ACDR with a novel prosthesis (group 2), C5-C6 ACDR with the Prestige LP prosthesis (group 3) and C5-C6 cervical discectomy and fusion (ACDF) with cage internal fixation (group 4). The range of motion (ROM) of all segments and facet joint contact force were measured and analyzed. The results showed that there was no significant difference among the group 1, 2 and 3 in terms of ROM (P>0.05). The ROM of C5-C6 in the group 4 showed a significant decrease compared with the group 1, 2, and 3 (P<0.05). The group 2 had a similar facet joint force with the group 1, and there is no statistical difference among the group 1, 2 and 3 (P>0.05). The facet joint force of C5-C6 in the group 4 reduced significantly compared with the other groups (P<0.05). In conclusion, both novel cervical prosthesis and Prestige LP could better preserve the normal cervical ROM and maintain facet joint force than ACDF.

Factors predicting adjacent segment disease after anterior cervical discectomy and fusion treating cervical spondylotic myelopathy: A retrospective study with 5-year follow-up

The purpose of this study is to explore perioperative factors predicting symptomatic adjacent segment disease (ASD) after anterior cervical discectomy and fusion (ACDF) for patients with cervical spondylotic myelopathy (CSM) at 5-year follow-up.This study included 356 patients who underwent ACDF for CSM from Jan.2011 to Jan.2013. Up to Jan. 2018, 39 patients suffered from ASD and 317 did not. Assessments include: age, sex, body mass index (BMI), diabetes, smoking, alcohol, duration of symptoms, preoperative Cobb angle of C2 to 7, T1 slope, C2 to 7 range of motion (C2-7 range of motion [ROM]), C2 to 7 sagittal vertical axis (C2-7 SVA), fusion level involved, superior fusion segment, high signal intensity on T2-WI of magnetic resonance imaging (MRI), preoperative visual analogue scale (VAS)-neck, VAS-Arm, Neck Disability Index (NDI) and Japanese Orthopaedic Association (JOA). Factors were processed by univariate analysis and multivariate linear regression.Data analyzed by univariate and multivariate analysis shows that age (68.9 years old), duration of symptoms (18.8 months), superior fusion segment, more fusion level involved (2.7), high signal intensity on T2-WI (17 of 39 patients), Cobb angle of C2 to C7 (18.7°), C2 to C7 SVA (31.0 mm), T1 slope (28.4°), preoperative VAS-neck (5.2), VAS-Arm (5.6) and NDI (36.7) in ASD group are significantly higher than those in non-ASD group, however, preoperative JOA (8.2 vs 11.2, P < .001) has an opposite trend in 2 groups.The rate of ASD after ACDF is 10.9% in 5-year follow up. Patients with cervical sagittal imbalance, advanced age and sever state of CSM, which have a positive relation with ASD before surgery should be paid attention for surgeons.

Anterior cervical discectomy and fusion versus hybrid surgery in multilevel cervical spondylotic myelopathy: A meta-analysis

OBJECTIVE

A meta-analysis was performed to compare the radiographic and surgical outcomes between anterior cervical discectomy and fusion (ACDF) and hybrid surgery (HS, corpectomy combined with discectomy) in the treatment for multilevel cervical spondylotic myelopathy (mCSM).

SUMMARY OF BACKGROUND DATA

Both ACDF and HS are used to treat mCSM, however, which one is better treatment for mCSM remains considerable controversy.

METHODS

An extensive search of literature was searched in PubMed/Medline, Embase, the Cochrane library, CNKI, and WANFANG databases on ACDF versus HS treating mCSM from January 2011 to December 2017. The following variables were extracted: blood loss, operation time, fusion rate, Cobb angles of C2-C7, total complications, dysphagia, hoarseness, C5 palsy, infection, cerebral fluid leakage, epidural hematoma, and graft subsidence. Data analysis was conducted with RevMan 5.3 and STATA 12.0.

RESULTS

A total of 4 studies including 669 patients were included in our study. The pooled analysis showed that there were no significant difference in the operation time, fusion rate, Cobb angles of C2-C7, dysphagia, hoarseness, C5 palsy, infection, cerebral fluid leakage, epidural hematoma, and graft subsidence. However, there were significant difference between 2 groups in blood loss [P < .00001, SMD = -30.29 (-45.06, -15.52); heterogeneity: P = .38, I = 0%= and total complications [P = .04, OR = 0.66 95%CI (0.44, 0.98); heterogeneity: P = .37, I = 4%].

CONCLUSIONS

Based on our meta-analysis, except for blood loss and total complications, both ACDF and hybrid surgery are effective options for the treatment of multilevel cervical spondylotic myelopathy.

Comparison of Multilevel Cervical Disc Replacement and Multilevel Anterior Discectomy and Fusion: A Systematic Review of Biomechanical and Clinical Evidence

OBJECTIVE

The aim of this study was to comprehensively compare the clinical and biomechanical efficiency of anterior cervical discectomy and fusion (ACDF) with anterior cervical disc replacement (ACDR) for treatment of multilevel cervical disc disease using a meta-analysis and systematical review.

METHODS

A literature search was performed using PubMed, MEDLINE, EMBASE, and the Cochrane Library for articles published between January 1960 and December 2017. Both clinical and biomechanical parameters were analyzed. Statistical tests were conducted by Revman 5.3. Nineteen studies including 10 clinical studies and 9 biomechanical studies were filtered out.

RESULTS

The pooled results for clinical efficiency showed that no significant difference was observed in blood loss (P = 0.09; mean difference [MD], 7.38; confidence interval [CI], -1.16 to 15.91), hospital stay (P = 0.33; MD, -0.25; CI, -0.76 to 0.26), Japanese Orthopaedic Association scores (P = 0.63; MD, -0.11; CI, -0.57 to 0.34), visual analog scale (P = 0.08; MD, -0.50; CI, -1.06 to 0.05), and Neck Disability Index (P = 0.33; MD, -0.55; CI, -1.65 to 0.56) between the 2 groups. Compared with ACDF, ACDR did show increased surgical time (P = 0.03; MD, 31.42; CI, 2.71-60.14). On the other hand, ACDR showed increased index range of motion (ROM) (P < 0.00001; MD, 13.83; CI, 9.28-18.39), lower rates of adjacent segment disease (ASD) (P = 0.001; odds ratio [OR], 0.27; CI, 0.13-0.59), complications (P = 0.006; OR, 0.62; CI, 0.45-0.87), and rate of subsequent surgery (P < 0.00001; OR, 0.25; CI, 0.14-0.44). As for biomechanical performance, ACDR maintained index ROM and avoided compensation in adjacent ROM and tissue pressure.

CONCLUSIONS

Multilevel ACDR may be an effective and safe alternative to ACDF in terms of clinical and biomechanical performance. However, further multicenter and prospective studies should be conducted to obtain a stronger and more reliable conclusion.

Biomechanical evaluation of cervical disc replacement with a novel prosthesis based on the physiological curvature of endplate

Background

Most of the current available cervical disc prostheses present a flat surface instead of an arcuate surface which is most similar to the morphology of cervical endplate. Therefore, we designed a novel prosthesis (Pretic-I, Trauson) based on the physiological curvature of the cervical endplate. Biomechanical evaluation of cervical disc replacement (CDR) with this novel prosthesis was performed and compared with the Prestige LP prosthesis.

Methods

Three motion segments of 18 cadaveric cervical specimens (C2-C7) were evaluated with a 75 N follower load. Overall, the biomechanics of three models, intact specimen, CDR with the novel prosthesis and CDR with the Prestige LP prosthesis, were studied to gain insight into the effective function of the novel prosthesis. The range of motion (ROM) of all three segments and intradiscal pressure (IDP) on adjacent levels were measured and analysed.

Results

Compared to the intact condition, the ROM of all three segments showed no significant difference in the replacement group. Moreover, there was also no significant difference in the ROM between the two prostheses. Besides, the IDP on the cranial adjacent level showed no obvious difference between the two prostheses; nevertheless, the IDP on the caudal adjacent level of the novel prosthesis was significantly less than the Prestige LP prosthesis.

Conclusions

In summary, the novel disc prosthesis was effective to maintain the ROM at the target segment and adjacent segments. Besides, CDR with the novel prosthesis could reduce the IDP on the caudal adjacent level to a certain extent, compared with the Prestige LP prosthesis.

Electronic supplementary material

The online version of this article (10.1186/s13018-018-0748-7) contains supplementary material, which is available to authorized users.

Clinical and Radiologic Features of 3 Reconstructive Procedures for the Surgical Management of Patients with Bilevel Cervical Degenerative Disc Disease at a Minimum Follow-Up Period of 5 Years: A Comparative Study

OBJECTIVE

To assess the mid-long-term follow-up of the safety and efficacy of anterior cervical discectomy and fusion (ACDF), cervical artificial disc replacement (CADR) and hybrid surgery (HS) for bilevel cervical degenerative disc disease (cDDD).

METHODS

77 patients who underwent ACDF, HS, and CADR were retrospectively reviewed. Clinical effects were evaluated based on Neck Disability Index (NDI), Visual Analog Scale (VAS), and Japanese Orthopedic Association (JOA) scores and the Odom criteria. Radiographic outcomes were evaluated, including cervical range of motion (ROM), ROM in the operative and adjacent segments, incidence of degeneration in the adjacent segments (ASD), and heterotopic ossification (HO).

RESULTS

NDI, VAS, and JOA scores significantly improved in all patients after surgery without significant differences between groups. The excellent-to-good ratio in the Odom scale was 28/30 for the HS group, 30/33 for the ACDF group, and 13/14 for the CADR group. No significant differences in clinical outcomes or complication were found between groups (P > 0.05). Furthermore, the HS and CADR groups had less decreased ROM in the cervical and operative segments and less compensatory ROM in adjacent segments (P < 0.05). By contrast, the ACDF group had decreased ROM in the cervical and operative segments and significantly increased ROM in adjacent segments (P < 0.05). Moreover, the incidence of ASD was higher in the ACDF group, but the difference was not statistically significant (P > 0.05). HO was found in 10 patients (33.3%) in the HS group and 5 patients (35.7%) in the CADR group.

CONCLUSION

HS was superior to ACDF with regard to equivalent clinical outcomes in the mid-long-term follow-up. Furthermore, HS was superior in the maintenance of ROM and had less impact on its adjacent segments. The efficacy of HS is similar to that of CADR.

A comparison of anterior cervical discectomy and fusion combined with cervical disc arthroplasty and cervical disc arthroplasty for the treatment of skip-level cervical degenerative disc disease: A retrospective study

Anterior cervical discectomy and fusion (ACDF) has been widely performed for the treatment of multilevel cervical degenerative disc disease (CDDD). In recent decades, cervical disc arthroplasty (CDA) and hybrid surgery (HS) have been developed to overcome the shortcomings of ACDF. Controversy still remains with regard to the optimal surgical procedure for skip-level CDDD.A total of 55 patients who received surgical treatment for skip-level CDDD in our department were reviewed. The patients were divided into the HS group (n = 29) and the CDA group (n = 26). The collected data included Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), and Visual Analog Scale (VAS) scores, and cervical lordosis (CL), range of motion (ROM), and intervertebral disc height (IDH). Radiological changes at the intermediate segment (IS) were also collected. All data were collected preoperatively and at routine postoperative intervals of 1 week and 3, 6, and 12 months and at the last follow-up period.Compared with preoperative values, mean JOA, NDI, and VAS scores significantly improved after surgery in both the HS and CDA groups (P < .05). However, there were no significant differences between the groups (P > .05). The HS group had better CL recovery than the CDA group after surgery (P < .05). There was no significant difference in the ROM of C2-C7 between the 2 groups (P > .05). A significant difference in the ROM of the IS was found at the last follow-up between the 2 groups (P < .05). At the last-follow-up, 4 discs (14.29%) in the CDA group and 6 discs (19.36%) in the HS group had adjacent segment degeneration (ASD) without symptoms.Both HS and CDA might be considered safe and effective surgical strategies for the treatment of skip-level CDDD. Although the clinical outcomes were similar in the 2 groups, CDA altered the ROM of the IS to a lesser degree.

Artificial Disk Replacement Combined With Fusion Versus 2-Level Fusion in Cervical 2-Level Disk Disease With a 5-Year Follow-up

STUDY DESIGN

Prospective study.

OBJECTIVE

The purpose of this study was to compare the long-term clinical and radiologic outcomes of hybrid surgery (HS) and 2-level anterior cervical discectomy and fusion (2-ACDF) in patients with 2-level cervical disk disease.

SUMMARY OF BACKGROUND DATA

In a previous study with a 2-year follow-up, HS was shown to be superior to 2-ACDF, with a better Neck Disability Index (NDI) score, less postoperative neck pain, faster C2-C7 range of motion (ROM) recovery, and less adjacent ROM increase.

MATERIALS AND METHODS

Between 2004 and 2006, 40 patients undergoing 2-level cervical disk surgery at our hospital were identified as 2-level degenerative disk disease. Forty patients were included in the previous study; 35 patients were followed up for 5 years. Patients completed the NDI and graded their pain intensity before surgery and at routine postoperative until 5 years. Dynamic cervical radiographs were obtained before surgery and at routine postoperative intervals and the angular ROM for C2-C7 and adjacent segments was measured.

RESULTS

The HS group had better NDI recovery until 3 years after surgery (P<0.05). Postoperative neck pain was lower in the HS group at 1 and 3 years after surgery (P<0.05), but arm pain relief was not differently relieved. The HS group showed more angular ROM for C2-C7 at 2 and 3 years after surgery. The superior adjacent segment ROM showed hypermobility in the 2-ACDF group and hypomobility in the HS group at all follow-up periods without statistically significance, but the inferior adjacent segment ROM differed significantly (P<0.05).

CONCLUSION

HS is superior to 2-ACDF; it leads to better NDI recovery, less postoperative neck pain, faster C2-C7 ROM recovery, and less adjacent ROM increase over a 2-year follow-up, but these benefits of HS become similar to those of 2-ACDF with 5 years of follow-up.

Multilevel cervical disc replacement versus multilevel anterior discectomy and fusion: A meta-analysis

BACKGROUND

Cervical disc replacement (CDR) has been developed as an alternative surgical procedure to anterior cervical discectomy and fusion (ACDF) for the treatment of single-level cervical degenerative disc disease. However, patients with multilevel cervical degenerative disc disease (MCDDD) are common in our clinic. Multilevel CDR is less established compared with multilevel ACDF. This study aims to compare the outcomes and evaluate safety and efficacy of CDR versus ACDF for the treatment of MCDDD.

METHODS

A meta-analysis was performed for articles published up until August 2016. Randomized controlled trials (RCTs) and prospective comparative studies associated with the use of CDR versus ACDF for the treatment of MCDDD were included in the current study. Two reviewers independently screened the articles and data following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement.

RESULTS

Seven studies with 702 enrolled patients suffering from MCDDD were retrieved. Patients who underwent CDR had similar operative times, blood loss, Neck Disability Index (NDI) scores, and Visual Analog Scale (VAS) scores compared to patients who underwent ACDF. Patients who underwent CDR had greater overall motion of the cervical spine and the operated levels than patients who underwent ACDF. Patients who underwent CDR also had lower rates of adjacent segment degeneration (ASD). The rate of adverse events was significantly lower in the CDR group.

CONCLUSION

CDR may be a safe and effective surgical strategy for the treatment of MCDDD. However, there is insufficient evidence to draw a strong conclusion due to relatively low-quality evidence. Future long-term, multicenter, randomized, and controlled studies are needed to validate the safety and efficacy of multilevel CDR.

Minimum four-year subsequent surgery rates of cervical disc replacement versus fusion: A meta-analysis of prospective randomized clinical trials

INSTRUCTION

Anterior cervical discectomy and fusion (ACDF) is a well-accepted surgical management strategy for radiculopathy and/or myelopathy. However, complications sometimes required subsequent surgery at the operated and adjacent levels. Artificial cervical disc replacement (ACDR) has been accepted as the most extensive non-fusion procedure and is designed to preserve motion. However, some specific complications can result in subsequent surgery, thus, attracting the attention of investigators.

HYPOTHESIS

Compared with ACDF, ACDR had a lower subsequent surgery rates at both operated and adjacent levels after a minimum of four-years of follow-up.

MATERIAL AND METHODS

A meta-analysis was performed with articles published prior to February 2016. Only randomized controlled trials that reported a minimum of 4 years of follow-up with regard to the rates of subsequent surgeries after ACDR compared with ACDF were included in this study. Two reviewers independently screened the articles and data following the PRISMA statement.

RESULTS

Our data showed that the pooled overall rate of subsequent surgery at the operated level and adjacent levels was lower in the ACDR group (7.4%) than in the ACDF group (16.8%) (P=0.0006). For subsequent surgery at the operated level, patients who received ACDR had a lower rate of subsequent surgery than patients who received ACDF (P<0.0001). With respect to the adjacent level, ACDR also had fewer subsequent surgeries compared with ACDF (P<0.0001).

CONCLUSION

ACDR had significantly fewer subsequent surgical interventions compared with ACDF, However, a review of the literature showed that there were an insufficient number of studies with respect to subsequent surgery with a minimum of 4 years of follow-up. Hence, longer-term, multicenter studies are needed for better evaluation of the rate of subsequent surgery after ACDR.

LEVEL OF EVIDENCE

Level I, meta-analysis of high-powered prospective randomized trials.

Anterior cervical discectomy and fusion versus anterior cervical corpectomy and fusion in multilevel cervical spondylotic myelopathy: A meta-analysis

BACKGROUND

Both anterior cervical discectomy and fusion (ACDF) and anterior cervical corpectomy and fusion (ACCF) are used to treat multilevel cervical spondylotic myelopathy (mCSM); however, which one is better treatment for mCSM remains considerable controversy. A meta-analysis was performed to compare clinical outcomes, radiographic outcomes, and surgical outcomes between ACDF and ACCF in treatment for mCSM.

METHODS

An extensive search of literature was performed in Pubmed/MEDLINE, Embase, the Cochrane library, CNKI, and WANFANG databases on ACDF versus ACCF treatment for mCSM from January 2011 to August 2016. The following variables were extracted: length of hospital stay, blood loss, operation time, Japanese Orthopedic Association (JOA) scores, Neck Disability Index (NDI) score, fusion rate, Cobb angles of C2 to C7, dysphagia, hoarseness, C5 palsy, infection, cerebral fluid leakage, donor site pain, epidural hematoma, graft subsidence, graft dislodgment, pseudoarthrosis, and total complications. Data analysis was conducted with RevMan 5.3 and STATA 12.0.

RESULTS

A total of 8 studies containing 878 patients were included in our study. The results showed that ACDF is better than ACCF in the angle of C2 to C7 at the final follow-up (P < 0.00001, standardized mean difference = 4.76 [3.48, 6.03]; heterogeneity: P = 0.17, I = 43%), C5 plasy (P = 0.02, odds ratio [OR] 0.42, 95% confidence interval [CI] 0.21, 0.86; heterogeneity: P = 0.52, I = 0%), blood loss (P < 0.00001, standardized mean difference = -53.12, 95% CI -64.61, -41.64; heterogeneity: P = 0.29, I = 20%), fusion rate (P = 0.04, OR 2.54, 95% CI 1.05, 6.11; heterogeneity: P = 0.29, I = 20%), graft subsidence (P = 0.004, OR 0.11, 95% CI 0.02, 0.48; heterogeneity: P = 0.94, I = 0%), and total complications (P = 0.0009, OR 0.56, 95% CI 0.40, 0.79; heterogeneity: P = 0.29, I = 18%).However, there are no significant differences in length of hospital stay, operation time, JOA scores, NDI scores, preoperative angle of C2 to C7, dysphagia, hoarseness, infection, cerebral fluid leakage, donor site pain, epidural hematoma, graft dislodgment, and pseudoarthrosis (all P > 0.05).

CONCLUSIONS

Based on our meta-analysis, our results suggest that both ACDF and ACCF are good plans in clinical outcomes; however, ACDF is a better choice in radiographic outcomes and total complications for the treatment of multilevel CSM.

Comparisons of Safety and Clinical Outcomes Between Multiple-level and Single-level Cervical Disk Replacement for Cervical Spondylosis: A Systematic Review and Meta-analysis

STUDY DESIGN

This is a systematic review and meta-analysis.

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of multiple-level cervical disk replacement (CDR) over single-level CDR for the treatment of cervical spondylosis.

SUMMARY OF BACKGROUND DATA

Some authors advocate for the multiple-level CDR instead of anterior decompression and fusion in cervical multiple-level spondylosis. However, whether the efficacy and safety of multi-level CDR are as favorable as that of single-level CDR remains controversial.

METHODS

MEDLINE, EMBASE, and Cochrane library databases were searched up to November 2015 for controlled studies that compared the clinical outcomes of single-level and multiple-level CDR for the treatment of cervical spondylosis. The following outcomes were extracted and analyzed: prevalence of heterotopic ossification and reoperation, preoperative and postoperative Neck Disability Index scores, preoperative and postoperative Visual Analog Scale scores, and success rate using the Odom grading system.

RESULTS

Ten studies involving 1402 patients were included: including 3 randomized controlled trials, 5 prospective studies, and 3 retrospective studies. No significant differences between single-level and multiple-level groups were found in terms of the prevalence of heterotopic ossification and reoperation rate, Neck Disability Index score, Visual Analog Scale score, and success rate using the Odom grading system.

CONCLUSIONS

On the basis of this meta-analysis, clinical outcomes of multiple-level CDR are similar to those of single-level CDR for cervical spondylosis, which suggests the multiple-level CDR is as effective and safe as the single-level CDR. Nonetheless, more well-designed studies are needed for further evaluation.

A PARAMETRIC INVESTIGATION OF THE EFFECTS OF CERVICAL DISC PROSTHESES WITH UPWARD AND DOWNWARD NUCLEI ON SPINE BIOMECHANICS

This work aimed at investigating the influence of Baguera and Discocerv cervical disc prostheses, with mobile downward center of rotation (COR) and fixed upward COR, respectively, on the biomechanical behavior of C4–C6 cervical spine. For this purpose, using computed tomography (CT) data, a parametric nonlinear finite element (FE) model of intact C4–C6 spinal segments was developed, and an artificial disc was implanted at C5–C6 level. To assess the influence of implants on the biomechanics of cervical spine, the FE models were analyzed in flexion, extension, lateral bending, and axial rotation, and the results were presented in the range of motion (ROM) curves, and torsional stiffness. Results of this study, in agreement with the literature, suggested that both Baguera and Discocerv implants might be able to preserve the motion, and limit the alteration of the biomechanics of adjacent levels. Except for the possible confliction of adjacent vertebrae at the implanted level with Baguera implant in lateral bending, results of this study also indicated that the movability and downward COR of Baguera disc prosthesis caused ROMs of the implanted segment to be more similar to the intact model than Discocerv implant. Moreover, the upward COR of Discocerv implant may result in over-distraction on facets in the maximal flexion, with the ratio of 1.22 versus 1.36, and consequently facet syndrome during extension for Bageura and Discocerv disc prostheses, respectively.

Biomechanical consideration of prosthesis selection in hybrid surgery for bi-level cervical disc degenerative diseases

PURPOSE

Hybrid surgery (HS) coupling total disc replacement and fusion has been increasingly applied for multilevel cervical disc diseases (CDD). However, selection of the optimal disc prosthesis for HS in an individual patient has not been investigated. This study aimed to distinguish the biomechanical performances of five widely used prostheses (Bryan, ProDisc-C, PCM, Mobi-C, and Discover) in HS for the treatment of bi-level CDD.

METHODS

A finite element model of healthy cervical spine (C3-C7) was developed, and five HS models using different disc prostheses were constructed by arthrodesis at C4-C5 and by arthroplasty at C5-C6. First, the rotational displacements in flexion (Fl), extension, axial rotation, and lateral bending in the healthy model under 1.0 Nm moments combined with 73.6 N follower load were achieved, and then the maximum rotations in each direction combined with the same follower load were applied in the surgical models following displacement control testing protocols.

RESULTS

The range of motion (ROM) of the entire operative and adjacent levels was close to that of the healthy spine for ball-in-socket prostheses, that is, ProDisc-C, Mobi-C, and Discover, in Fl. For Bryan and PCM, the ROM of the operative levels was less than that of the healthy spine in Fl and resulted in the increase in ROMs at the adjacent levels. Ball-in-socket prostheses produced similar reaction moments (92-99 %) in Fl, which were close to that of the healthy spine. Meanwhile, Bryan and PCM required greater moments (>130 %). The adjacent intradiscal pressures (IDPs) in the models of ball-in-socket prostheses were close to that of the healthy spine. Meanwhile, in the models of Bryan and PCM, the adjacent IDPs were 25 % higher than that of the ball-in-socket models. The maximum facet stress in the model of Mobi-C was the greatest among all prostheses, which was approximately two times that of the healthy spine. Moreover, Bryan produced the largest stress on the bone-implant interface, followed by PCM, Mobi-C, ProDisc-C, and Discover.

CONCLUSION

Each disc prosthesis has its biomechanical advantages and disadvantages in HS and should be selected on an individual patient basis. In general, ProDisc-C, Mobi-C, and Discover produced similar performances in terms of spinal motions, adjacent IDPs, and driving moments, whereas Bryan and PCM produced similar biomechanical performances. Therefore, HS with Discover, Bryan, and PCM may be suitable for patients with potential risk of facet joint degeneration, whereas HS with ProDisc-C, Mobi-C, and Discover may be suitable for patients with potential risk of vertebral osteoporosis.

Five-year clinical results of cervical total disc replacement compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled, multicenter investigational device exemption clinical trial

OBJECTIVE

The purpose of this study was to report the outcome of a study of 2-level cervical total disc replacement (Mobi-C) versus anterior cervical discectomy and fusion (ACDF). Although the long-term outcome of single-level disc replacement has been extensively described, there have not been previous reports of the 5-year outcome of 2-level cervical disc replacement.

METHODS

This study reports the 5-year results of a prospective, randomized US FDA investigational device exemption (IDE) study conducted at 24 centers in patients with 2-level, contiguous, cervical spondylosis. Clinical outcomes at up to 60 months were evaluated, including validated outcome measures, incidence of reoperation, and adverse events. The complete study data and methodology were critically reviewed by 3 independent surgeon authors without affiliation with the IDE study or financial or institutional bias toward the study sponsor.

RESULTS

A total of 225 patients received the Mobi-C cervical total disc replacement device and 105 patients received ACDF. The Mobi-C and ACDF follow-up rates were 90.7% and 86.7%, respectively (p = 0.39), at 60 months. There was significant improvement in all outcome scores relative to baseline at all time points. The Mobi-C patients had significantly more improvement than ACDF patients in terms of Neck Disability Index score, SF-12 Physical Component Summary, and overall satisfaction with treatment at 60 months. The reoperation rate was significantly lower with Mobi-C (4%) versus ACDF (16%). There were no significant differences in the adverse event rate between groups.

CONCLUSIONS

Both cervical total disc replacement and ACDF significantly improved general and disease-specific measures compared with baseline. However, there was significantly greater improvement in general and disease-specific outcome measures and a lower rate of reoperation in the 2-level disc replacement patients versus ACDF control patients.

Clinical trial registration no. NCT00389597 (clinicaltrials.gov)

A Biomechanical Analysis of an Artificial Disc With a Shock-absorbing Core Property by Using Whole-cervical Spine Finite Element Analysis

STUDY DESIGN

A biomechanical comparison among the intact C2 to C7 segments, the C5 to C6 segments implanted with fusion cage, and three different artificial disc replacements (ADRs) by finite element (FE) model creation reflecting the entire cervical spine below C2.

OBJECTIVE

The aim of this study was to analyze the biomechanical changes in subaxial cervical spine after ADR and to verify the efficacy of a new mobile core artificial disc Baguera C that is designed to absorb shock.

SUMMARY OF BACKGROUND DATA

Scarce references could be found and compared regarding the cervical ADR devices' biomechanical differences that are consequently related to their different clinical results.

METHODS

One fusion device (CJ cage system, WINNOVA) and three different cervical artificial discs (Prodisc-C Nova (DePuy Synthes), Discocerv (Scient'x/Alphatec), Baguera C (Spineart)) were inserted at C5-6 disc space inside the FE model and analyzed. Hybrid loading conditions, under bending moments of 1 Nm along flexion, extension, lateral bending, and axial rotation with a compressive force of 50 N along the follower loading direction, were used in this study. Biomechanical behaviors such as segmental mobility, facet joint forces, and possible wear debris phenomenon inside the core were investigated.

RESULTS

The segmental motions as well as facet joint forces were exaggerated after ADR regardless of type of the devices. The Baguera C mimicked the intact cervical spine regarding the location of the center of rotation only during the flexion moment. It also showed a relatively wider distribution of the contact area and significantly lower contact pressure distribution on the core than the other two devices. A "lift off" phenomenon was noted for other two devices according to the specific loading condition.

CONCLUSION

The mobile core artificial disc Baguera C can be considered biomechanically superior to other devices by demonstrating no "lift off" phenomenon, and significantly lower contact pressure distribution on core.

LEVEL OF EVIDENCE

N/A.

Biomechanical Analysis of a Novel Prosthesis Based on the Physiological Curvature of Endplate for Cervical Disc Replacement

STUDY DESIGN

Biomechanical analysis of a novel prosthesis based on the physiological curvature of endplate was performed.

OBJECTIVE

To compare the biomechanical differences between a novel prosthesis based on the physiological curvature of the endplate and the Prestige LP prosthesis after cervical disc replacement (CDR).

SUMMARY OF BACKGROUND DATA

Artificial disc prostheses have been widely used to preserve the physiological function of treated and adjacent motion segments in CDR, while most of those present a flat surface instead of an arcuate surface which approximately similar to anatomic structures in vivo. We first reported a well-designed artificial disc prosthesis based on the physiological curvature of the endplate.

METHODS

Three motion segments of 24 ovine cervical spines (C2-5) were evaluated in a robotic spine system with axial compressive loads of 50N. Testing conditions were as follows: 1) intact, 2) C3-4 CDR with artificial disc prosthesis based on the physiological curvature of the endplate, and 3) C3-4 CDR with the Prestige LP prosthesis. The range of motion (ROM) and the pressures on the inferior surface of the two prostheses were recorded and analyzed.

RESULTS

As compared to the intact state, the ROM of all three segments had no significant difference in the replacement group. Additionally, there was no significant difference in ROM between the two prostheses. The mean pressure on the novel prosthesis was significantly less than the Prestige LP prosthesis.

CONCLUSION

ROM in 3 groups (intact group, CDR group with novel prosthesis and CDR group with Prestige LP) showed no significant difference. The mean pressure on the inferior surface of the novel prosthesis was significantly lower than the Prestige LP prosthesis. Therefore, the novel artificial disc prosthesis is feasible and effective, and can reduce the implant-bone interface pressure on the endplate, which may be one possible reason of prosthesis subsidence.

The M6-C Cervical Disk Prosthesis: First Clinical Experience in 33 Patients

STUDY DESIGN

Retrospective study.

OBJECTIVE

To determine the short-term clinical succesrate of the M6-C cervical disk prosthesis in primary and secondary surgery.

SUMMARY OF BACKGROUND DATA

Cervical disk arthroplasty (CDA) provides an alternative to anterior cervical decompression and fusion for the treatment of spondylotic radiculopathy or myelopathy. The prevention of adjacent segment disease (ASD), a possible complication of anterior cervical decompression and fusion, is its most cited--although unproven--benefit. Unlike older arthroplasty devices that rely on a ball-and-socket-type design, the M6-C cervical disk prosthesis represents a new generation of unconstrained implants, developed to achieve better restoration of natural segmental biomechanics. This device should therefore optimize clinical performance of CDA and reduce ASD.

MATERIALS AND METHODS

All patients had preoperative computed tomography or magnetic resonance imaging and postoperative x-rays. Clinical outcome was assessed using the Neck Disability Index, a Visual Analog Scale, and the SF-36 questionnaire. Patients were asked about overall satisfaction and whether they would have the surgery again.

RESULTS

Thirty-three patients were evaluated 17.1 months after surgery, on average. Nine patients had a history of cervical interventions. Results for Neck Disability Index, Visual Analog Scale, and SF-36 were significantly better among patients who had undergone primary surgery. In this group, 87.5% of patients reported a good or excellent result and 91.7% would have the procedure again. In contrast, all 4 device-related complications occurred in the small group of patients who had secondary surgery.

CONCLUSIONS

The M6-C prosthesis appears to be a valuable addition to the CDA armatorium. It generates very good results in patients undergoing primary surgery, although its use in secondary surgery should be avoided. Longer follow-up is needed to determine to what measure this device can prevent ASD.

Hybrid Surgery Versus Anterior Cervical Discectomy and Fusion in Multilevel Cervical Disc Diseases: A Meta-Analysis

To investigate the outcomes and reliability of hybrid surgery (HS) versus anterior cervical discectomy and fusion (ACDF) for the treatment of multilevel cervical spondylosis and disc diseases.Hybrid surgery, combining cervical disc arthroplasty (CDA) with fusion, is a novel treatment to multilevel cervical degenerated disc disease in recent years. However, the effect and reliability of HS are still unclear compared with ACDF.To investigate the studies of HS versus ACDF in patients with multilevel cervical disease, electronic databases (Medline, Embase, Pubmed, Cochrane library, and Cochrane Central Register of Controlled Trials) were searched. Studies were included when they compared HS with ACDF and reported at least one of the following outcomes: functionality, neck pain, arm pain, cervical range of motion (ROM), quality of life, and incidence of complications. No language restrictions were used. Two authors independently assessed the methodological quality of included studies and extracted the relevant data.Seven clinical controlled trials were included in this study. Two trials were prospective and the other 5 were retrospective. The results of the meta-analysis indicated that HS achieved better recovery of NDI score (P = 0.038) and similar recovery of VAS score (P = 0.058) compared with ACDF at 2 years follow-up. Moreover, the total cervical ROM (C2-C7) after HS was preserved significantly more than the cervical ROM after ACDF (P = 0.000) at 2 years follow-up. Notably, the compensatory increase of the ROM of superior and inferior adjacent segments was significant in ACDF groups at 2-year follow-up (P < 0.01), compared with HS.The results demonstrate that HS provides equivalent outcomes and functional recovery for cervical disc diseases, and significantly better preservation of cervical ROM compared with ACDF in 2-year follow-up. This suggests the HS is an effective alternative invention for the treatment of multilevel cervical spondylosis to preserve cervical ROM and reduce the risk of adjacent disc degeneration. Nonetheless, more well-designed studies with large groups of patients are required to provide further evidence for the benefit and reliability of HS for the treatment of cervical disk diseases.

Biomechanics of Artificial Disc Replacements Adjacent to a 2-Level Fusion in 4-Level Hybrid Constructs: An In Vitro Investigation

Background

The ideal procedure for multilevel cervical degenerative disc diseases remains controversial. Recent studies on hybrid surgery combining anterior cervical discectomy and fusion (ACDF) and artificial cervical disc replacement (ACDR) for 2-level and 3-level constructs have been reported in the literature. The purpose of this study was to estimate the biomechanics of 3 kinds of 4-level hybrid constructs, which are more likely to be used clinically compared to 4-level arthrodesis.

Material/Methods

Eighteen human cadaveric spines (C2–T1) were evaluated in different testing conditions: intact, with 3 kinds of 4-level hybrid constructs (hybrid C3–4 ACDR+C4–6 ACDF+C6–7ACDR; hybrid C3–5ACDF+C5–6ACDR+C6–7ACDR; hybrid C3–4ACDR+C4–5ACDR+C5–7ACDF); and 4-level fusion.

Results

Four-level fusion resulted in significant decrease in the C3–C7 ROM compared with the intact spine. The 3 different 4-level hybrid treatment groups caused only slight change at the instrumented levels compared to intact except for flexion. At the adjacent levels, 4-level fusion resulted in significant increase of contribution of both upper and lower adjacent levels. However, for the 3 hybrid constructs, significant changes of motion increase far lower than 4P at adjacent levels were only noted in partial loading conditions. No destabilizing effect or hypermobility were observed in any 4-level hybrid construct.

Conclusions

Four-level fusion significantly eliminated motion within the construct and increased motion at the adjacent segments. For all 3 different 4-level hybrid constructs, ACDR normalized motion of the index segment and adjacent segments with no significant hypermobility. Compared with the 4-level ACDF condition, the artificial discs in 4-level hybrid constructs had biomechanical advantages compared to fusion in normalizing adjacent level motion.