The Bryan Cervical Disc: wear properties and early clinical results

Assessing accuracy of measurement methods for bony fusion assessment after anterior cervical discectomy

BACKGROUND CONTEXT

Currently, there is no universally accepted method for assessing radiological fusion shortly after anterior cervical discectomy. Five-year follow-up radiological X-rays demonstrating solid fusion or absence of fusion provided a gold standard for comparison with various assessment methods.

PURPOSE

Establishing the most accurate diagnostic test for earlier bony fusion assessment by comparing different cut-off values for the difference in interspinous distance and the change in Cobb angle on dynamic radiological images against the established gold standard.

DESIGN

Post-hoc analysis from the NEtherlands Cervical Kinematics (NECK) trial (NTR1289).

PATIENT SAMPLE

A total of 40 patients with 1 level herniated disc that underwent anterior discectomy between 2010 and 2014 returned for a 5-year follow-up X-ray.

OUTCOME MEASURES

Radiological outcome was assessed quantitatively and qualitatively by fusion on radiographic images 5 years after surgery.

METHODS

Radiological dynamic X-rays were reviewed for fusion at 5-year follow-up by a senior spine surgeon. At this timepoint, bony continuity was indisputable and served as gold standard. Cobb angles and interspinous distances on flexion-extension images were measured independently by 2 investigators. Optimum agreement between the gold standard and the 2 methods was assessed, evaluating varying cut-off values, considering sensitivity, specificity, and area under the curve (AUC).

RESULTS

Dynamic radiographic assessments revealed fusion in 29 out of 40 patients (mean age: 49 years ± 8; 23 women). For Cobb angle (optimal cut-off: ≤3.0°), the AUC was 0.86 with 100% sensitivity and 72.7% specificity. For interspinous distance (optimal cut-off: ≤1.5 mm), the AUC was 0.89 with 96.6% sensitivity and 81.8% specificity. The highest AUC (0.91) was observed for combined cut-off values (Cobb angle ≤3.0° and interspinous distance ≤2.0 mm), yielding 100% sensitivity and 81.8% specificity.

CONCLUSION

The combination of cut-off values ≤3.0° difference for Cobb angle and ≤2.0 mm difference for interspinous distance on lateral flexion-extension X-rays was assessed to be an accurate diagnostic criterion for fusion evaluation. This tool provides a practical and easy applicable method for assessing fusion during follow-up after anterior discectomy.

Incidence and Risk Factor of Implant Dislocation After Cervical Disk Arthroplasty: A Retrospective Cohort Analysis of 756 Patients

BACKGROUND

Implant dislocation after cervical disk arthroplasty (CDA) is obviously a critical complication, but no information about the incidence and associated risk factor has been reported.

OBJECTIVE

To investigate the incidence and risk factor of implant dislocation after CDA by a retrospective cohort analysis.

METHODS

A retrospective review of a consecutive series of CDA performed between January 2009 and March 2021 at a single institution was conducted. Analyses of chart records and radiological data established the incidence and associated risk factor of implant dislocation after CDA. A Kaplan-Meier survival estimation of implant survival was performed.

RESULTS

A total of 756 consecutive patients were included in this analysis. Five patients (0.7%) had a migration and even dropout of the artificial disk. The overall cumulative survival rate of the implant reached approximately 99.3% of the 756 patients. Preoperative kyphosis was significantly related to implant dislocation ( P = .016), with an odds ratio of 15.013.

CONCLUSION

The incidence of implant dislocation after CDA is as low as 0.7% or 5/756 patients. Preoperative kyphosis significantly increases the risk of postoperative implant dislocation by a factor of 15. The migrating implants could be revealed on radiographs as early as 0.9 to 1.4 months postoperatively and were revised to anterior cervical diskectomy and fusion within half a year. No new event of implant dislocation occurred half a year postoperatively. The overall cumulative survival rate of the implant reached 99.3% of the 756 patients. In conclusion, CDA remains a safe and reliable procedure.

Long-Term Clinical and Radiographic Outcomes After Bryan Cervical Disk Arthroplasty: A Systematic Literature Review

Introductionː Cervical disk arthroplasty is a potential alternative procedure to anterior cervical decompression and fusion for the treatment of cervical disk disease. The aim of the study was to perform a systematic literature review on long-term clinical and radiological outcomes after Bryan cervical disk arthroplasty.Material and Methodsː A systematic literature review was performed according to PRISMA guidelines via PubMed and Embase, Scopus, and the Cochrane Library database by using the following keywords: "Bryan prosthesis"; "cervical disk arthroplasty"; "outcomes"; and "long-term follow-up." Eight articles with at least 10 years of follow-up were considered for eligibility.Resultsː In total, 481 patients were enrolled in the studies. Because of the occurrence of multiple treated levels, 588 arthroplasties were performed, divided as follows: 12 C3/4 cervical disk arthroplasties (2.01%), 63 C4/5 (10.71%), 325 C5/6 (55.27%), and 188 C6/7 (31.97%). The mean preoperative cervical lordosis was 13.6 ± 9.3°, whereas the last follow-up value was 12.8 ± 8.7°. In the last follow-up, the mean segmental range of motion was 8.2 ± 3.3°.Discussion: Recent studies have suggested that cervical disk arthroplasty should be safely performed in healthy young patients with disk degeneration who may need future revision surgery. The results suggest that this procedure preserves native cervical spinal biomechanics at long-term follow-up with acceptable adjacent segments disease and periprosthetic ossifications.Conclusionsː Cervical disk arthroplasty has good long-term device survival, motility, adjacent segment degeneration, and clinical outcomes. Therefore, it represents a valid alternative for the treatment of cervical spine degenerative pathologies, especially in young patients.

Clinical validity of the smallest oblique sagittal area of the neural foramen in patients with suspected cervical spondylotic radiculopathy

OBJECTIVE

To evaluate the smallest oblique sagittal area of the neural foramen in detecting cervical spondylotic radiculopathy (CSR) and to determine its potential significance for treatment decisions.

METHODS

The subjects of the study were patients with CSR who visited the spine surgery from 2016 to 2019. All patients were compared according to the minimum oblique sagittal area and the cut-off point value, and they were divided into positive and negative parameters. The changes in neck disability index (NDI), Japanese Orthopaedic Association score (JOA), and visual analog scale (VAS) during the two treatment groups from baseline to at least 24 months of follow-up were compared.

RESULTS

In the surgery group, there was no significant difference in symptom improvement between patients with positive and negative parameters. In the non-surgical group, for patients with positive parameters, NDI decreased by 2.35, JOA increased by 0.88, and neck VAS score improved by 0.42. For patients with negative parameters, NDI decreased by 10.32, JOA increased by 2.86 on average, and neck VAS score improved by 2.46 points on average (both p<0.01 on t test).

CONCLUSIONS

Patients with both positive and negative parameters showed significant improvement in their symptoms after surgery, and the smallest oblique sagittal area of the neural foramen seems to be unable to predict the outcome of the surgery. However, in non-surgical patients, symptomatic improvement was more limited in patients with positive parameters than in those with negative parameters. This suggests that patients with positive parameters may be more suitable for surgery and those with negative parameters are more suitable for conservative treatment.

Investigation into Cervical Spine Biomechanics Following Single, Multilevel and Hybrid Disc Replacement Surgery with Dynamic Cervical Implant and Fusion: A Finite Element Study

Cervical fusion has been a standard procedure for treating abnormalities associated with the cervical spine. However, the reliability of anterior cervical discectomy and fusion (ACDF) has become arguable due to its adverse effects on the biomechanics of adjacent segments. One of the drawbacks associated with ACDF is adjacent segment degeneration (ASD), which has served as the base for the development of dynamic stabilization systems (DSS) and total disc replacement (TDR) devices for cervical spine. However, the hybrid surgical technique has also gained popularity recently, but its effect on the biomechanics of cervical spine is not well researched. Thus, the objective of this FE study was to draw a comparison among single-level, bi-level, and hybrid surgery with dynamic cervical implants (DCIs) with traditional fusion. Reductions in the range of motion (ROM) for all the implanted models were observed for all the motions except extension, compared to for the intact model. The maximum increase in the ROM of 42% was observed at segments C5–C6 in the hybrid DCI model. The maximum increase in the adjacent segment’s ROM of 8.7% was observed in the multilevel fusion model. The maximum von Mises stress in the implant was highest for the multilevel DCI model. Our study also showed that the shape of the DCI permitted flexion/extension relatively more compared to lateral bending and axial rotation.

Acute Migration Following Dissociation of Components of Cervical Disc Arthroplasty

Cervical disc arthroplasty (CDA) is a newer alternative to the traditional fusion, in patients with prolapsed cervical disc in the younger eligible patient aiming to provide mobility similar to the native disc and by some ways preventing the adjacent segment disease. The rising popularity of its early success has seen emergence of a number of products in the market. In a country where cost remains an important constraint for the patients, local design products are available to cater to these lesser privileged patients. The present complication is an acute dissociation of components from such a product wherein the implant was retrieved and fusion was done. The patient was subsequently discharged uneventfully.

Revision Surgery for a Failed Artificial Disc

PURPOSE

This study aimed to present our experience with failures in C-TDR and revision surgery outcomes.

MATERIALS AND METHODS

We retrospectively examined patients who underwent revision surgery due to the failure of C-TDR between May 2005 to March 2019. Thirteen patients (8 males and 5 females) were included in this study. The mean age was 46.1 years (range: 22-61 years), and the average follow-up period was 19.5 months (range: 12-64 months). The outcome measures of pre- and post-operative neck and arm pain using a visual analogue scale (VAS) and functional impairment were assessed using a modified Japanese Orthopedic Association (JOA) scale and the Neck Disability Index (NDI).

RESULTS

The main complaints of patients were posterior neck pain (77%), radiculopathy (62%), and/or myelopathy (62%). The causes of failure of C-TDR were improper indications for the procedure, osteolysis and mobile implant use, inappropriate techniques, and postoperative infection. The most common surgical level was C5-6, followed by C4-5. After revision surgery, the neck and arm pain VAS (preoperative vs. postoperative: 5.46 vs. 1.31; 4.86 vs. 1.08), a modified JOA scale (14.46 vs. 16.69), and the NDI (29.77 vs. 9.31) scores were much improved.

CONCLUSION

C-TDR is good surgical option. However, it is very important to adhere to strict surgical indications and contraindications to avoid failure of C-TDR. The results of reoperations were good regardless of the approach. Therefore, various reoperation options could be considered in patients with failed C-TDR.

Comparison of adverse events between cervical disc arthroplasty and anterior cervical discectomy and fusion: a 10-year follow-up

BACKGROUND CONTEXT

Cervical disc arthroplasty (CDA) has been advocated as an alternative to anterior cervical discectomy and fusion (ACDF) with the added potential to reduce the risk of adjacent level disc degeneration and segmental instability. However, the long-term adverse events of arthroplasty have yet to be fully reported.

PURPOSE

To investigate the 10-year follow-up adverse events rates between CDA and ACDF.

STUDY DESIGN/SETTING

The study was a randomized, prospective, multicenter Investigational Device Exemption (IDE) trial and its continued follow-up as a postapproval study (PAS). Single level surgeries were performed for cervical disc pathologies between May 2002 and October 2004.

PATIENT SAMPLE

n=463 patients.

OUTCOME MEASURES

Adverse events comparison of CDA and ACDF from self-reported and physiologic measures.

METHODS

At each evaluation time point, subjects were queried for adverse events since their last visit; and all adverse events were documented, regardless of whether or not they appeared related to the surgery or device. Adverse events were recorded, categorized, and assessed for severity and relationship to the study device and/or surgical procedure. The 10-year cumulative rates for each type of adverse events were summarized using a life-table method for the time-to-event analysis. A log-rank test was used to compare the two treatment groups.

RESULTS

A total of 242 patients received CDA and 221 patients received ACDF. At 10-year follow-up, 54% (130/242) of CDA patients and 47% (104/221) of the ACDF subjects were evaluated. At up to 10-year follow-up, 231 patients in the CDA group (cumulative rate 98.4%) and 199 patients in the ACDF group (cumulative rate 98.7%) had at least one adverse event. Overall, the difference in the cumulative rate of all adverse events over 10 years was not statistically different (p=0.166). The cumulative rates of the following adverse events were not different between the two groups for cancer, cardiovascular, death, dysphonia/dysphagia, gastrointestinal, infection, urogenital, respiratory, implant displacement/loosening, implant malposition, neck and arm pain, neurological, other pain, spinal events, and intraoperative vascular injury. However, there were more adverse events in the CDA group resulting from trauma (p=.012) and more spinal events at the index level (p=.006). The ACDF group had significantly more nonunion events (p=.019), and nonunion outcome pending (p=.034), adjacent level spinal events (p=.033), and events that fell into the "other" category (p=.015).

CONCLUSIONS

The cumulative rates of patients who had any adverse events were not different between the artificial cervical disc and the anterior cervical arthrodesis groups. In addition, the cumulative rates were not different between the two groups for the majority of categories as well.

Comparing Heterotopic Ossification in Two Cervical Disc Prostheses

STUDY DESIGN

Retrospective analysis using data from randomized clinical trials.

OBJECTIVE

To compare the occurrence of heterotopic ossification (HO) between two cervical disc prostheses. Clinical outcome and range of motion (ROM) were also evaluated.

SUMMARY OF BACKGROUND DATA

Cervical arthroplasty was reported to be able to maintain the segmental ROM. However, controversy exists since the difference of the occurrence of HO concerning cervical prosthesis is still huge.

METHODS

Patients who underwent anterior cervical discectomy with arthroplasty for a cervical radiculopathy due to a herniated disc from the The Netherlands Cervical Kinematics (NECK) trial (activC; metal endplates with a polyethylene inlay and a keel for primary stability) and the PROCON trial (Bryan; metal-on-polymer with titanium coated endplates without a keel) were analyzed for HO at 12 and 24 months postoperatively. HO was scored according to the McAfee-Mehren classification. Segmental ROM was defined by a custom developed image analysis tool, and global cervical ROM was measured by Cobb's angle. Clinical outcome was evaluated by means of the neck disability index (NDI) as well as physical-component summary (PCS) and mental-component summary (MCS).

RESULTS

At 2-year follow-up, the occurrence of HO was 68% in patients treated with the activC prosthesis (severe HO 55%), which was comparable with 85% (P = 0.12) in patients with the Bryan disc (severe HO 44%; P = 0.43). The HO progression was similar between groups. Clinically, the patients had comparable NDI, PCS, and MCS at 2-year follow-up, and comparable improvement of clinical outcomes. The global ROM in the Bryan group (56.4 ± 10.8°) was significantly higher than in the activC group (49.5 ± 14.0, P = 0.044) at 2-year follow-up.

CONCLUSION

In comparison of two cervical disc prostheses the development of HO is independent on their architecture. Although global ROM was higher in the Bryan prosthesis group, this difference was not deemed clinically important, particularly because the clinical condition of patients with and without severe HO was comparable.

LEVEL OF EVIDENCE

2.

Cervical Disc Arthroplasty Migration Following Mechanical Intubation: A Case Presentation and Review of the Literature

BACKGROUND

Cervical arthroplasty has established itself as a safe and efficacious alternative to fusion in management of symptomatic cervical degenerative disease. Recent literature has indicated a trend toward decreased risk of reoperation with cervical arthroplasty, and reoperation in this subset commonly occurs secondary to recurrent pain and device-related complications. The instance of cervical arthroplasty migration, particularly in the setting of trauma, is particularly rare. Here, we report the first case of implant migration secondary to iatrogenic trauma following neck manipulation during direct laryngoscopy for mechanical intubation.

CASE DESCRIPTION

A 53-year-old smoker with cervical spondylosis underwent a cervical 3/4 arthroplasty with a ProDisc-C implant. About a month postoperatively, he was intubated via direct laryngoscopy for community acquired pneumonia and began experiencing new dysphonia and dysphagia after extubation. Delayed imaging revealed anterior migration of the implant. The patient immediately underwent removal of the implant and conversion to anterior cervical discectomy and fusion.

CONCLUSIONS

Supraphysiologic forces exerted through neck manipulation in mechanical intubation mimicked low-energy trauma, and in the setting of ligamentous resection necessary for cervical arthroplasty and inadequate osseous integration, led to migration of the implant. We recommend the integration of fiberoptic technique or video laryngoscopy with manual in line stabilization for intubation of post cervical arthroplasty patients when airway management is necessary within 10 months after cervical arthroplasty. Clinicians and anesthesiologists should have a high clinical suspicion for prompt and early workup with spine imaging in the setting of persistent postintubation symptoms such as dysphonia and/or dysphagia.

Ten-year Outcomes of Cervical Disc Replacement With the BRYAN Cervical Disc: Results From a Prospective, Randomized, Controlled Clinical Trial

STUDY DESIGN

A prospective, randomized multicenter IDE trial between May 2002 and October 2004.

OBJECTIVE

The aim of this study was to report on the 10-year safety and efficacy of BRYAN cervical disc arthroplasty (CDA).

SUMMARY OF BACKGROUND DATA

Cervical disc arthroplasty (CDA) is a potential alternative for anterior cervical decompression and fusion (ACDF) with the hope that maintenance of motion may decrease the likelihood of adjacent segment disease.

METHODS

This is an analysis of a US Food and Drug Administration (FDA) investigation comparing CDA with ACDF for single-level patients. Eligible patients were ≥ 21 years of age with symptomatic cervical disc disease who had failed conservative care. Patients were followed at regular intervals with the current data set at > 10 years. Protocol for overall success: ≥ 15-point improvement in NDI scores, maintenance or improvement in neurologic status, no serious adverse events related to implant or implant/surgical procedure, and no subsequent surgery or intervention classified as "failure."

RESULTS

At 10-year follow-up, 128 (CDA) and 104 (ACDF) patients were available for evaluation. Overall success rate was significantly higher for CDA group (81.3% vs. 66.3%; P = 0.005). The rate of second surgeries at adjacent levels was lower for CDA group (9.7% vs. 15.8%; P = 0.146). NDI scores improved significantly in CDA group (Δ38.3 vs. Δ31.1; P = 0.010). Visual Analog Scale (VAS) neck and arm improved in the CDA group (Δ54.3 vs. Δ49.2; P = 0.119), (Δ58.1 vs. Δ51.6; P = 0.0.60) respectively. About 4.1% of CDA patients and 4.9% of ACDF patients had serious adverse events related to study device. Mean angular motions at index level for BRYAN disc and ACDF were 8.69° and 0.60°, respectively.

CONCLUSION

CDA can preserve and maintain motion in the long term compared with ACDF. There was a trend toward fewer adjacent segment surgeries for BRYAN disc that did not reach significance. Significant improvement in CDA NDI scores may suggest better long-term success for CDA as compared to fusion.

LEVEL OF EVIDENCE

2.

A Comparison of Cervical Disc Arthroplasty and Anterior Cervical Discectomy and Fusion in Patients with Two-Level Cervical Degenerative Disc Disease: 5-Year Follow-Up Results

OBJECTIVE

To present a long-term clinical and radiographic comparison between the Prestige LP cervical disc replacement and the Zero-P spacer cervical disc fusion in the treatment of patients with symptomatic 2-level cervical degenerative disease.

METHODS

In total, 36 patients in the anterior cervical discectomy and fusion (ACDF) group and 24 patients in the cervical disc arthroplasty (CDA) group were analyzed before surgery and at 1 week and 3, 6, 12, 24, and 60 months after surgery. Clinical assessments included the Japanese Orthopaedic Association score, visual analog scale, and Neck Disability Index scores. Radiographic assessments included cervical lordosis, range of motion (ROM) of the total cervical spine, functional spinal unit (FSU), and superior and inferior adjacent segments. Complications including heterotopic ossification and adjacent-segment degeneration (ASD) at 5-year follow-up were collected as well.

RESULTS

Mean follow-up period was 65.6 months. Both the ACDF and CDA groups showed significant clinical improvements in terms of Japanese Orthopaedic Association score, visual analog scale, and Neck Disability Index (P < 0.05), but there was no significant difference between groups at the last follow-up period. A significant increase of cervical lordosis was observed in the CDA group after surgery whereas a significant difference was not observed between groups. ROM of the total cervical spine and FSU were maintained during the follow-up, and a significant decrease was observed in the ACDF group after surgery (P < 0.05). The ROM of the superior adjacent segment did not show any difference whereas the ROM of the inferior adjacent segment in the ACDF group presented a significant increase at 6 months and 1 year after surgery and a significant decrease at the last follow-up period. A total of 8 (33.3%) patients in the CDA group had an occurrence of heterotopic ossification. ASD was observed in 2 (8.3%) patients who underwent CDA surgery and 8 (22.2%) patients who underwent ACDF surgery.

CONCLUSIONS

The use of the Prestige-LP and ZERO-P Spacer implantations is safe and effective. At 5 years after surgery, CDA with Prestige-LP is superior in terms of ROM of the total cervical spine, FSU, and inferior adjacent segment. It also has a relatively low occurrence rate of ASD. This procedure may be a suitable choice for the treatment of contiguous 2-level CDDD.

Numerical Shape Optimization of Cervical Spine Disc Prosthesis Prodisc-C

Various ball and socket-type designs of cervical artificial discs are in use or under investigation. All these disc designs claim to restore the normal kinematics of the cervical spine. In this study, we are interested in the cervical prosthesis, which concerns the most sensitive part of the human body, given the movements generated by the head. The goal of this work is to minimize the constraints by numerical shape optimization in the prodisc-C cervical spine prosthesis in order to improve performance and bio-functionality as well as patient relief. Prodisc-C cervical spine prosthesis consists of two cobalt chromium alloy plates and a fixed nucleus. Ultra-high molecular weight polyethylene, on each plate there is a keel to stabilize the prosthesis; this prosthesis allows thee degrees of freedom in rotation. To achieve this goal, a static study was carried out to determine the constraint concentrations on the different components of the prosthesis. Based on the biomechanical behaviour of the spine discs, we totally fixed the lower metal plate; a vertical load of 73.6 N to simulate the weight of the head was applied to the superior metallic endplate. After a static study on this prosthesis, using a finite element model, we noticed that the concentration of the Von-Mises stress is concentrated on the peripheral edge core and the concave articulating surface of the superior metallic endplate the numerical. We use the module optimization for 3D SolidWorks for optimize our design, based on the criteria of minimizing stress value. Shape optimization concluded to minimize the equivalent stress value on both joint surface (concave and convex) from 11.3 MPa to 9.1MPa corresponding to a percentage decrease of 19.4% from the original geometry. We conclude that despite the fact that maximum Von Mises stresses are higher in the case of the dynamic load, remains that they are weak. Which is an advantage for the durability of the prosthesis and-also for the bone, because a low stress concentration on the prosthesis will reduce stress concentration generated by the implant on the bone, therefore its risk of fracture reduces.

Adjacent Level Degeneration: Bryan Total Disc Arthroplasty Versus Anterior Cervical Discectomy and Fusion

STUDY DESIGN

Prospective randomized, 2-center, clinical trial.

OBJECTIVE

To prospectively compare adjacent level degeneration between the Bryan Cervical Disc Prosthesis and anterior cervical discectomy and fusion (ACDF), and assess the reliability of our measurements utilizing a method not previously described.

SUMMARY OF BACKGROUND DATA

ACDF is a reliable and proven procedure for the treatment of radiculopathy and/or myelopathy. Despite a successful track record several limitations including adjacent segment degeneration/disease, loss of viscoelastic disc properties, perioperative immobilization, graft site morbidity, pseudarthrosis, and plating complications have been identified. An original driving force and theoretical basis for total disc arthroplasty was prevention of adjacent level degeneration.

MATERIALS AND METHODS

Seventy-nine patients were enrolled and followed prospectively at 2 centers in a multicenter, Food and Drug Administration Investigational Device Exemption trial for the Bryan Cervical Disc arthroplasty. Neutral lateral radiographs were obtained preoperatively and postoperatively, and at 1-, 2-, 4-, and out to 7-year follow-up after surgery. The cephalad, adjacent level above the blinded procedure level was analyzed for all patients and time points by measuring the anteroposterior distance and the vertical disc height. A ratio was created using disc height/anteroposterior distance.

RESULTS

Seventy patients (Bryan Cervical Disc N=34 and ACDF N=36) met inclusion criteria. Both fusion and arthroplasty groups showed a significant (P=0.001) decrease in disc height over time, indicative of adjacent level degeneration. Overall change in disc height between groups was not significantly different. Using our measurement technique, the overall interreviewer reliability was good [intrareviewer correlation coefficients (95% confidence interval)=0.77 (0.55-0.85)] and intrareviewer reliability was excellent [0.93 (0.91-0.94) and 0.85 (0.81-0.87)].

CONCLUSIONS

Adjacent level degeneration occurs in a similar manner in both the ACDF and total disc arthroplasty group. Our measurement technique is reliable and to the best of our knowledge not previously reported in the literature.

Cervical Disk Replacement With Discover Versus Fusion in a Single-Level Cervical Disk Disease: A Prospective Single-Center Randomized Trial With a Minimum 2-Year Follow-up

STUDY DESIGN

Prospective randomized study.

OBJECTIVE

To compare the clinical outcome after Discover arthroplasty versus anterior cervical discectomy and fusion (ACDF) in patients treated for symptomatic single-level cervical disk disease.

SUMMARY OF BACKGROUND DATA

ACDF is still the gold standard for surgical treatment of cervical spine degenerative disk disease. However, results of many studies suggest that it may cause degenerative changes at levels immediately above and below the fusion, known as adjacent segment degenerative disease. Cervical arthroplasty has recently been introduced as an alternative to standard procedure of ACDF. It showed decreased surgical morbidity, decreased complications from postoperative immobilization, and an earlier return to previous level of function.

MATERIALS AND METHODS

A total of 105 consecutive patients with single-level cervical disk disease, producing radiculopathy and/or myelopathy were randomly divided into groups to undergo ACDF or Discover arthroplasty. All patients were evaluated with preoperative and postoperative serial radiographic studies and clinically, using Neck Disability Index, Visual Analog Scale and neurological status at 3, 6, 12, and 24 months.

RESULTS

The results of our study indicate that cervical arthroplasty using Discover Artificial Cervical Disc provides favorable clinical and radiologic outcomes in a follow-up period of 24 months. There has been significant improvement in clinical parameters, Visual Analog Scale and Neck Disability Index, at 3, 6, 12, and 24 months in arthroplasty group comparing to control group.

CONCLUSION

The Discover artificial cervical disc replacement offers favorable outcome compared with ACDF for a single-level cervical disk disease at short-term and long-term follow-up.

Implant Migration in Cervical Disk Arthroplasty

OBJECTIVE

The purpose of this study is to discuss the causes of implant migration after cervical arthroplasty with clinical cases.

METHODS

The patients who underwent cervical arthroplasty operations in our department between 2006 and 2015 because of cervical disk disease were retrospectively analyzed. The patients who were determined to be symptomatic of implant migration were evaluated.

RESULTS

Symptomatic implant migration was detected in 5 of 163 (0.3%) patients who underwent cervical disk arthroplasty, and these patients also underwent reoperation. In 4 patients who underwent reoperation, the prosthesis was removed, and an anterior fusion was made. The prosthesis was only removed in 1 patient.

CONCLUSIONS

The following situations should be considered in the prevention of dislocation and migration of the implant in cervical arthroplasty: protection of the structure of the end plate, selection of the appropriate implant size, and proper surgical construction. In the preoperative period, computed tomography scan may be useful for determining the implant size and details of the bone structure. Foreign body reactions or postoperative trauma may be a rare and unpreventable reason for prosthesis dislocation despite all of the preoperative and perioperative measures and well-made prosthesis designs.

Traumatic Migration of the Bryan Cervical Disc Arthroplasty

Study Design Case study. Objective To describe a case of dislodgment and migration of the Bryan Cervical Disc (Medtronic Sofamor Danek, Memphis, Tennessee, United States) arthroplasty more than 6 months after implantation secondary to low-energy trauma. Methods The inpatient, outpatient, and radiographic medical records of a patient with traumatic migration of the Bryan Cervical Disc arthroplasty were reviewed. The authors have no relevant disclosures to report. Results A 36-year-old man with chronic left upper extremity radiculopathy underwent uncomplicated Bryan Cervical Disc arthroplasty at C5-C6, with complete resolution of his symptoms. Approximately 6 months after his index procedure, he sustained low-energy trauma to the posterior cervical spine, after being struck by a book falling from a shelf. The injury forced his neck into flexion, and though he did not have recurrence of his radiculopathy symptoms, radiographs demonstrated anterior migration of the arthroplasty device. He underwent revision to anterior cervical diskectomy and fusion. Conclusions Although extremely rare, it is imperative that surgeons consider the potential for failure of osseous integration in patients undergoing cervical disk arthroplasty, even beyond 3 to 6 months postoperatively. This concern is especially relevant to press-fit or milled devices like the Bryan Cervical Disc arthroplasty, which lack direct fixation into adjacent vertebral bodies. We are considering modification of our postoperative protocol to improve protection of the device after implantation, even beyond 3 months postoperatively.

Cervical spine alignment in disc arthroplasty: should we change our perspective?

PURPOSE

The alignment at the cervical spine has been considered a determinant of degeneration at the adjacent disc, but this issue in cervical disc replacement surgery is poorly explored and discussed in this patient population. The aim of this systematic review is to compare anterior cervical fusion and total disc replacement (TDR) in terms of preservation of the overall cervical alignment and complications.

METHODS

A systematic review of the current literature was performed, together with the evaluation of the methodological quality of all the retrieved studies.

RESULTS

In most of the retrieved studies, a tendency towards a more postoperative kyphotic alignment in TDR was reported. The reported mean complication rate was of 12.5 % (0-66.2 %). Complications associated with cervical prosthesis included heterotopic ossification, device migration, mechanical instability, failure, implant removal, reoperations and revision.

CONCLUSIONS

Even though cervical disc arthroplasty leads to similar outcomes compared to arthrodesis in the middle term follow-up, no evidence of superiority of cervical TDR is available up to date. We understand that the overall cervical alignment after TDR tends towards the loss of lordosis, but only longer follow-up can determine its influence on the clinical results.

Polyurethane on titanium unconstrained disc arthroplasty versus anterior discectomy and fusion for the treatment of cervical disc disease: a review of level I-II randomized clinical trials including clinical outcomes

PURPOSE

To contrast the clinical and radiologic outcomes and adverse events of anterior cervical discectomy and fusion (ACDF) with a single cervical disc arthroplasty design, the polyurethane on titanium unconstrained cervical disc (PTUCD).

METHODS

This is a systematic review of randomized clinical trials (RCT) with evidence level I-II reporting clinical outcomes. After a search on different databases including PubMed, Cochrane Central Register of Controlled Trials, and Ovid MEDLINE, a total of 10 RCTs out of 51 studies found were entered in the study. RTCs were searched from the earliest available records in 2005 to November 2014.

RESULTS

Out of a total of 1101 patients, 562 were randomly assigned into the PTUCD arthroplasty group and 539 into the ACDF group. The mean follow-up was 30.9 months. Patients undergoing arthroplasty had lower Neck Disability Index, and better SF-36 Physical component scores than ACDF patients. Patients with PTUCD arthroplasty had also less radiological degenerative changes at the upper adjacent level. Overall adverse events were twice more frequent in patients with ACDF. The rate of revision surgery including both adjacent and index level was slightly higher in patients with ACDF, showing no statistically significant difference.

CONCLUSIONS

According to this review, PTUCD arthroplasty showed a global superiority to ACDF in clinical outcomes. The impact of both surgical techniques on the cervical spine (radiological spine deterioration and/or complications) was more severe in patients undergoing ACDF. However, the rate of revision surgeries at any cervical level was equivalent for ACDF and PTUCD arthroplasty.

Comparison of Clinical Outcomes of 1- and 2-Level Total Disc Replacement: Four-Year Results From a Prospective, Randomized, Controlled, Multicenter IDE Clinical Trial

STUDY DESIGN

A prospective, randomized, multicenter Food and Drug Administration Investigation Device Exemption study using total disc replacement as surgical treatment of degenerative disc disease at 1 or 2 contiguous levels of the cervical spine.

OBJECTIVE

To evaluate the safety and effectiveness of total disc replacement at single or 2 contiguous levels through 48 months of follow-up.

SUMMARY OF BACKGROUND DATA

Cervical total disc replacement has been shown to be a safe and effective alternative to anterior cervical discectomy and fusion at 24 months. Its motion-preserving capabilities may avoid accelerating adjacent segment pathology and thereby lower the rate of associated complications.

METHODS

Patients were randomized in a 2:1 ratio (total disc replacement [TDR]: anterior cervical discectomy and fusion [ACDF]) at 24 sites. Ultimately, 164 patients received TDR at 1 level and 225 patients received TDR at 2 contiguous levels. An additional 24 patients (15 one-level, 9 two-level) were treated with TDR as training cases.Outcome measures included neck disability index, visual analogue scale neck and arm pain, Short Form 12-item Health Survey (SF-12) Mental Composite Score (MCS) and Physical Composite Score (PCS), range of motion, major complication rates, and secondary surgery rates. Patients received follow-up examinations at regular intervals through 4 years after surgery.

RESULTS

Preoperative characteristics were statistically similar for the 1- and 2-level patient groups. Four-year follow-up rates were 83.1% (1-level) and 89.0% (2-level). There was no statistically significant difference between 1- and 2-level TDR groups for all clinical outcome measures. Both TDR groups experienced significant improvement at each follow-up when compared with preoperative scores. One case of migration was reported in the 2-level TDR group.

CONCLUSION

A 4-year post hoc comparison of 1- and 2-level TDR patients concurrently enrolled in a 24-center, Food and Drug Administration Investigation Device Exemption clinical trial indicated no statistical differences between groups in clinical outcomes, overall complication rates, and subsequent surgery rates.

LEVEL OF EVIDENCE

1.

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

BACKGROUND CONTEXT

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

PURPOSE

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

STUDY DESIGN/SETTING

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Core herniation after implantation of a cervical artificial disc: case report

INTRODUCTION

Cervical artificial discs (CADs) represent an established surgical option in selected patients with cervical spinal disc degeneration. Though CADs have been available for many years, there is a lack of information concerning long-term safety, durability and implant-related failure rates.

MATERIALS AND METHODS

The authors describe the failure of a M6-C CAD (Spinal Kinetics, Sunnyvale, CA, USA).

RESULTS

Eight years after implantation of a CAD of the M6 type, a 39-year-old female presented with new clinical signs of cervical myelopathy. Radiologically, medullar compression due to posterior core herniation was the suspected cause. The damaged CAD was removed and the segment fused. During revision surgery, rupture of the posterior structures could be detected. Possible mechanisms leading to implant failure are discussed.

CONCLUSION

As there is no standard regarding clinical and radiological follow-up for patients with CADs, radiological long-term follow-up investigations seem to be justified for exclusion of implant failure.

Cervical arthroplasty: a critical review of the literature

BACKGROUND CONTEXT

Cervical disc arthroplasty (CDA) is a motion-preserving procedure that is an alternative to fusion. Proponents of arthroplasty assert that it will maintain cervical motion and prevent or reduce adjacent segment degeneration. Accordingly, CDA, compared with fusion, would have the potential to improve clinical outcomes. Published studies have varying conclusions on whether CDA reduces complications and/or improves outcomes. As many of these previous studies have been funded by CDA manufacturers, we wanted to ascertain whether there was a greater likelihood for these studies to report positive results.

PURPOSE

To critically assess the available literature on cervical arthroplasty with a focus on the time of publication and conflict of interest (COI).

STUDY DESIGN/SETTING

Review of the literature.

METHODS

All clinical articles about CDA published in English through August 1, 2013 were identified on Medline. Any article that presented CDA clinical results was included. Study design, sample size, type of disc, length of follow-up, use of statistical analysis, quality-of-life (QOL) outcome scores, COI, and complications were recorded. A meta-analysis was conducted stratifying studies by COI and publication date to identify differences in complication rates reported.

RESULTS

Seventy-four studies were included that investigated 8 types of disc prosthesis and 22 met the criteria for a randomized controlled trial (RCT). All Level Ib RCTs reported superior quality-of-life outcomes for CDA versus anterior cervical discectomy and fusion (ACDF) at 24 months. Fifty of the 74 articles (68%) had a disclosure section, including all Level Ib RCTs, which had significant COIs related to the respective studies. Those studies without a COI reported mean weighted average adjacent segment disease rates of 6.3% with CDA and 6.2% with ACDF. In contrast, the reverse was reported by studies with a COI, for which the averages were 2.5% with CDA and 6.3% with ACDF. Those studies with a COI (n=31) had an overall weighted average heterotopic ossification rate of 22%, whereas those studies with no COI (n=43) had a rate of 46%.

CONCLUSIONS

Associated COIs did not influence QOL outcomes. Conflicts of interest were more likely to be present in studies published after 2008, and those with a COI reported greater adjacent segment disease rates for ACDF than CDA. In addition, heterotopic ossification rates were much lower in studies with COI versus those without COI. Thus, COIs did not affect QOL outcomes but were associated with lower complication rates.

CASINO: surgical or nonsurgical treatment for cervical radiculopathy, a randomised controlled trial

Background

Cervical radicular syndrome (CRS) due to a herniated disc can be safely treated by surgical decompression of the spinal root. In the vast majority of cases this relieves pain in the arm and restores function. However, conservative treatment also has a high chance on relieving symptoms. The objective of the present study is to evaluate the (cost-) effectiveness of surgery versus prolonged conservative care during one year of follow-up, and to evaluate the timing of surgery. Predisposing factors in favour of one of the two treatments will be evaluated.

Methods/design

Patients with disabling radicular arm pain, suffering for at least 2 months, and an MRI-proven herniated cervical disc will be randomised to receive either surgery or prolonged conservative care with surgery if needed. The surgical intervention will be an anterior discectomy or a posterior foraminotomy that is carried out according to usual care. Surgery will take place within 2–4 weeks after randomisation. Conservative care starts immediately after randomisation. The primary outcome measure is the VAS for pain or tingling sensations in the arm one year after randomisation. In addition, timing of surgery will be studied by correlating the primary outcome to the duration of symptoms. Secondary outcome measures encompass quality of life, costs and perceived recovery. Predefined prognostic factors will be evaluated. The total follow-up period will cover two years. A sample size of 400 patients is needed. Statistical analysis will be performed using a linear mixed model which will be based on the ‘intention to treat’ principle. In addition, a new CRS questionnaire for patients will be developed, the Leiden Cervical Radicular Syndrome Functioning (LCRSF) scale.

Discussion

The outcome will contribute to better decision making for the treatment of cervical radicular syndrome.

Trial registration

NTR3504

Biomechanical effects of cervical arthroplasty with U-shaped disc implant on segmental range of motion and loading of surrounding soft tissue

PURPOSE

Various design concepts have been adopted in cervical disc prostheses, including sliding articulation and standalone configuration. This study aimed to evaluate the biomechanical effects of the standalone U-shaped configuration on the cervical spine.

METHODS

Based on an intact finite element model of C3-C7, a standalone U-shaped implant (DCI) was installed at C5-C6 and compared with a sliding articulation design (Prodisc-C) and an anterior fusion system. The range of motion (ROM), adjacent intradiscal pressure (IDP) and capsular ligament strain were calculated under different spinal motions.

RESULTS

Compared to the intact configuration, the ROM at C5-C6 was reduced by 90% after fusion, but increased by 70% in the Prodisc-C model, while the maximum percentage change in the DCI model was 30% decrease. At the adjacent segments, up to 32% increase in ROM happened after fusion, while up to 34% decrease occurred in Prodisc-C model and 17% decrease in DCI model. The IDP increased by 11.6% after fusion, but decreased by 5.6 and 6.3% in the DCI and Prodisc-C model, respectively. The capsular ligament strain increased by 147% in Prodisc-C and by 13% in the DCI model. The DCI implant exhibited a high stress distribution.

CONCLUSIONS

Spinal fusion resulted in compensatory increase of ROM at the adjacent sites, thereby elevating the IDP. Prodisc-C resulted in hyper-mobility at the operative site that led to an increase of ligament force and strain. The U-shaped implant could maintain the spinal kinematics and impose minimum influence on the adjacent soft tissues, despite the standalone configuration encountering the disadvantages of high stress distribution.

Cost-effectiveness analysis: comparing single-level cervical disc replacement and single-level anterior cervical discectomy and fusion: clinical article

OBJECT

In recent years, there has been increased interest in the use of cervical disc replacement (CDR) as an alternative to anterior cervical discectomy and fusion (ACDF). While ACDF is a proven intervention for patients with myelopathy or radiculopathy, it does have inherent limitations. Cervical disc replacement was designed to preserve motion, avoid the limitations of fusion, and theoretically allow for a quicker return to activity. A number of recently published systematic reviews and randomized controlled trials have demonstrated positive clinical results for CDR, but no studies have revealed which of the 2 treatment strategies is more cost-effective. The purpose of this study was to evaluate the cost-effectiveness of CDR and ACDF by using the power of decision analysis. Additionally, the authors aimed to identify the most critical factors affecting procedural cost and effectiveness and to define thresholds for durability and function to focus and guide future research.

METHODS

The authors created a surgical decision model for the treatment of single-level cervical disc disease with associated radiculopathy. The literature was reviewed to identify possible outcomes and their likelihood following CDR and ACDF. Health state utility factors were determined from the literature and assigned to each possible outcome, and procedural effectiveness was expressed in units of quality-adjusted life years (QALYs). Using ICD-9 procedure codes and data from the Nationwide Inpatient Sample, the authors calculated the median cost of hospitalization by multiplying hospital charges by the hospital-specific cost-to-charge ratio. Gross physician costs were determined from the mean Medicare reimbursement for each current procedural terminology (CPT) code. Uncertainty as regards both cost and effectiveness numbers was assessed using sensitivity analysis.

RESULTS

In the reference case, the model assumed a 20-year duration for the CDR prosthesis. Cervical disc replacement led to higher average QALYs gained at a lower cost to society if both strategies survived for 20 years ($3042/QALY for CDR vs $8760/QALY for ACDF). Sensitivity analysis revealed that CDR needed to survive at least 9.75 years to be considered a more cost-effective strategy than ACDF. Cervical disc replacement becomes an acceptable societal strategy as the prosthesis survival time approaches 11 years and the $50,000/QALY gained willingness-to-pay threshold is crossed. Sensitivity analysis also indicated that CDR must provide a utility state of at least 0.796 to be cost-effective.

CONCLUSIONS

Both CDR and ACDF were shown to be cost-effective procedures in the reference case. Results of the sensitivity analysis indicated that CDR must remain functional for at least 14 years to establish greater cost-effectiveness than ACDF. Since the current literature has yet to demonstrate with certainty the actual durability and long-term functionality of CDR, future long-term studies are required to validate the present analysis.

Does total disc arthroplasty in C3/C4-segments change the kinematic features of axial rotation?

We analyze how kinematic properties of C3/C4-segments are modified after total disc arthroplasty (TDA) with PRESTIGE(®) and BRYAN(®) Cervical Discs. The measurements were focused on small ranges of axial rotation (<0.8°) in order to investigate physiologic rotations, which frequently occur in vivo. Eight human segments were stimulated by triangularly varying, axially directed torque. By using a 6D-measuring device with high resolution the response of segmental motion was characterised by the instantaneous helical axis (IHA). Position, direction, and migration rate of the IHA were measured before and after TDA. External parameters: constant axially directed pre-load, constant flexional/extensional and lateral-flexional pre-torque. The applied axial torque and IHA-direction did not run parallel. The IHA-direction was found to be rotated backwards and largely independent of the rotational angle, amount of axial pre-load, size of pre-torque, and TDA. In the intact segments pre-flexion/extension hardly influenced IHA-positions. After TDA, IHA-position was shifted backwards significantly (BRYAN-TDA: ≈8mm; PRESTIGE-TDA: ≈6mm) and in some segments laterally as well. Furthermore it was significantly shifted ventrally by pre-flexion and dorsally by pre-extension. The rate of lateral IHA-migration increased significantly after BRYAN-TDA during rightward or leftward rotations. In conclusion after the TDA the IHA-positions shifted backwards with significant increase in variability of the IHA-positions after the BRYAN-TDA more than in PRESTIGE-TDA. The TDA-procedure altered the segment kinematics considerably. TDA causes additional translations of the vertebrae, which superimpose the kinematics of the adjacent levels. The occurrence of adjacent level disease (ALD) is not excluded after the TDA for kinematical reasons.

Implant failure of Bryan cervical disc due to broken polyurethane sheath: a case report

STUDY DESIGN

A case report.

OBJECTIVE

A rare case of Bryan disc implantation failure due to broken polyurethane sheath was reported. The bone ingrowth at implant-bone interface and wear debris leaking from broken Bryan disc were also observed.

SUMMARY OF BACKGROUND DATA

The Bryan disc is one of the most commonly used cervical prostheses and has shown satisfactory results compared with anterior cervical discectomy and fusion in short- and long-term follow-up. The complications, including neurological worsening, heterotopic ossification, kyphosis, and so forth, still occur, although infrequently. The broken polyurethane sheath is an extremely rare complication that has seldom been reported before.

METHODS

A 55-year-old female patient experienced progressive neck pain after 8 years of Bryan disc implantation because of cervical spondylotic myelopathy at C5-C6 level. The subsequent magnetic resonance imaging scan demonstrated a cystic mass in front of Bryan disc, with high-signal intensity on T2-weighted images. The Bryan disc was removed and segment (C5-C6) was fused with cage and plate. The bone ingrowth and wear debris of retrieved Bryan disc were studied. RESULTS.: In revision surgery, a cyst with thick pseudocapsule connecting the anterior part of Bryan disc was excised. A transverse crack (5 mm) was identified in the anterior part of polyurethane sheath. The bacteria test of fluid from the cyst showed a negative result. Micro-computed tomography and histological study both indicated abundant bone ingrowth at implant-bone interface. The metal wear debris could be observed around titanium alloy shells.

CONCLUSION

This case demonstrates the unique incident of broken Bryan disc after 8 years of implantation. Follow-up imaging shortly after the procedure should be mandatory to monitor such potential complication.

Do design variations in the artificial disc influence cervical spine biomechanics? A finite element investigation

Various ball and socket-type designs of cervical artificial discs are in use or under investigation. Many artificial disc designs claim to restore the normal kinematics of the cervical spine. What differentiates one type of design from another design is currently not well understood. In this study, authors examined various clinically relevant parameters using a finite element model of C3-C7 cervical spine to study the effects of variations of ball and socket disc designs. Four variations of ball and socket-type artificial disc were placed at the C5-C6 level in an experimentally validated finite element model. Biomechanical effects of the shape (oval vs. spherical ball) and location (inferior vs. superior ball) were studied in detail. Range of motion, facet loading, implant stresses and capsule ligament strains were computed to investigate the influence of disc designs on resulting biomechanics. Motions at the implant level tended to increase following disc replacement. No major kinematic differences were observed among the disc designs tested. However, implant stresses were substantially higher in the spherical designs when compared to the oval designs. For both spherical and oval designs, the facet loads were lower for the designs with an inferior ball component. The capsule ligament strains were lower for the oval design with an inferior ball component. Overall, the oval design with an inferior ball component, produced motion, facet loads, implant stresses and capsule ligament strains closest to the intact spine, which may be key to long-term implant survival.

The Latest Lessons Learned from Retrieval Analyses of Ultra-High Molecular Weight Polyethylene, Metal-on-Metal, and Alternative Bearing Total Disc Replacements

Knowledge regarding the in vivo performance and periposthetic tissue response of cervical and lumbar total disc replacements (TDRs) continues to expand. This review addresses the following four main questions: 1) What are the latest lessons learned from polyethylene in large joints and how are they relevant to current TDRs? 2) What are the latest lessons learned regarding adverse local tissue reactions from metal-on-metal, CoCr bearings in large joints and how are they relevant to current TDRs? 3) What advancements have been made in understanding the in vivo performance of alternative biomaterials, such as stainless steel and polycarbonate urethane, for TDRs in the past five years? 4) How has retrieval analysis of all these various artificial disc bearing technologies advanced the state of the art in preclinical testing of TDRs? The study of explanted artificial discs and their associated tissues can help inform bearing selection as well as the design of future generations of disc arthroplasty. Analyzing retrieved artificial discs is also essential for validating preclinical test methods.

Superiority of the Bryan(®) disc prosthesis for cervical myelopathy: a randomized study with 3-year followup

BACKGROUND

The current standard of care for cervical myopathy is anterior discectomy and fusion (ACDF). Although well tolerated in the short term, this treatment might ultimately result in progressive degeneration of adjacent motion segments. Artificial disc arthroplasty offers the theoretical advantage of preservation of motion at the operative level with consequent stress reduction at adjacent levels.

QUESTIONS/PURPOSES

We compared function, radiographic measures, and incidence of complications at 3-year followup after cervical disc arthroplasty with the Bryan(®) prosthesis and ACDF in patients with cervical myelopathy.

PATIENTS AND METHODS

Eighty-three patients with cervical myelopathy were randomized to undergo arthroplasty with implantation of a Bryan(®) cervical disc prosthesis (n = 41) or ACDF (n = 42). Patients were assessed preoperatively to 3 years postoperatively using the modified Odom's criteria, Japanese Orthopaedic Association scale, SF-36, and Neck Disability Index. ROM, stability, and subsidence of the prostheses were evaluated radiographically.

RESULTS

Patients who received the Bryan(®) prosthesis scored significantly better in three of the four functional assessment methods used (Japanese Orthopaedic Association scale, SF-36, and Neck Disability Index). ROM was retained by the patients in the Bryan(®) group but not in the patients in the ACDF group. Patients in the Bryan(®) group had fewer complications, primarily because dysphagia occurred in only one patient in the Bryan(®) group but in seven patients in the ACDF group. Other complications included pseudarthrosis in three patients in the ACDF group and one patient had spontaneous fusion, one had deep vein thrombosis, and one had heterotopic ossification in the Bryan(®) group.

CONCLUSIONS

Bryan(®) cervical disc arthroplasty appears reliable and effective in the treatment of cervical myelopathy.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of the levels of evidence.

Validity and responsiveness of the Core Outcome Measures Index (COMI) for the neck

PURPOSE

Patient-orientated outcome questionnaires are essential to evaluate treatment success. To compare different treatments, hospitals, and surgeons, standardised questionnaires are required. The present study examined the validity and responsiveness of the Core Outcome Measurement Index for neck pain (COMI-neck), a short, multidimensional outcome instrument.

METHODS

Questionnaires were completed by patients with degenerative problems of the cervical spine undergoing cervical disc arthroplasty before (N = 89) and 3 months after (N = 75) surgery. The questionnaires comprised the EuroQol-Five Dimension (EQ-5D), the North American Spine Society Cervical Spine Outcome Assessment Instrument (NASS-cervical) and the COMI-neck.

RESULTS

The COMI and NASS-cervical scores displayed no notable floor or ceiling effects at any time point whereas for the EQ-5D, the highest values [corrected] were reached in around 32.5% of patients at follow-up. With one exception (symptom-specific well-being), the individual COMI items and the COMI summary score correlated to the expected extent (R = 0.4-0.8) with the scores of the chosen reference questionnaires. The area under the curve (AUC) generated by ROC analysis was significantly higher for the COMI (0.96) than for any other instrument/subscale when self reported treatment outcome was used as the external criterion, dichotomised as "good" (operation helped a lot/helped) versus "poor" (operation helped only a little/didn't help/made things worse). The COMI had a high effect size (standardised response mean; SRM) (2.34) for the good global outcome group and a low SRM for the poor outcome group (0.34). The EQ-5D and the NASS-cervical lacked this ability to differentiate between the two groups, showing less distinct SRMs for good and poor outcome groups.

CONCLUSIONS

This study provides evidence that the COMI-neck is a valid and responsive questionnaire in the population of patients examined. Further investigations should examine its applicability in other patient groups with less severe neck pain or undergoing other treatment modalities.

A comparison of the shock-absorbing properties of cervical disc prosthesis bearing materials

Background Data

Cervical arthroplasty offers theoretical advantages over traditional spinal fusion, including elimination of adjacent segment disease and elimination of the risk of pseudoarthrosis formation. Initial studies of cervical arthroplasty have shown promising results, however, the ideal design characteristics for disc replacement constructs have not been determined. The current study seeks to quantify the differences in the shock absorption characteristics of three commonly used materials in cervical disc arthroplasty.

Methods

Three different nucleus materials, polyurethane (PU), polyethylene (PE) and a titanium-alloy (Ti) were tested in a humidity- and temperature-controlled chamber. Ten of each nucleus type underwent three separate mechanical testing protocols to measure 1) dynamic stiffness, 2) quasi-static stiffness, 3) energy absorption, and 4) energy dissipation. The results were compared using analysis of variance.

Results

PU had the lowest mean dynamic stiffness (435 ± 13 N/mm, P < .0001) and highest energy absorption (19.4 ± 0.1 N/mm, P < .0001) of all three nucleus materials tested. PU was found to have significantly higher energy dissipation (viscous damping ratio 0.017 ± 0,001, P < .0001) than the PE or TI nuclei. PU had the lowest quasi-static stiffness (598 ± 23 N/mm, P < .0001) of the nucleus materials tested. A biphasic response curve was observed for all of the PU nuclei tests.

Conclusions

Polyurethane absorbs and dissipates more energy and is less stiff than either polyethylene or titanium.

Level of Evidence

Basic Science/Biomechanical Study.

Clinical Relevance

This study characterizes important differences in biomechanical properties of materials that are currently being used for different cervical disc prostheses.

[Cervical arthroplasty using the Bryan Cervical Disc System]

OBJECTIVE

Treatment of radicular or myelopathic symptoms of the vertebral segments from C2 through Th1.

INDICATIONS

Discogenic and/or spondylotic radiculopathy. Acute myelopathy. Acute or progressive functional neurological deficit. Persistent pain resistant toward conservative treatment for > 6 weeks.

CONTRAINDICATIONS

Chronic myelopathy. Spondylotic myelopathy. Infection. Tumor in the vertebral segment. Ossification of the posterior longitudinal ligament (OPLL). Metabolic bone disease. Osteoporosis. Long-lasting steroid medication. Allergy to titanium, polyurethane and ethylene oxide. Bekhterev's disease. Bony segmental fusion. Instability.

SURGICAL TECHNIQUE

Using the Bryan Cervical Disc Template Set together with magnetic resonance or computer tomographic images, the exact size of the prosthesis will be selected. The patient is lying in a supine position and the level of surgery is verified fluoroscopically. Diskectomy and decompression are performed via an anterior approach. After preparation of the implant bed, the center of the disk space is established using a transverse centering tool and inserting the Bryan cervical distractor. Before the prosthesis can be inserted, the end plates have to be milled. The prosthesis is filled with sterile saline solution and inserted. Proper fitting is verified fluoroscopically.

POSTOPERATIVE MANAGEMENT

Depending on the clinical situation postoperatively, the patient is discharged. Wound clamps are distracted on day 8, support by a cervical collar is not necessary. Light physical manipulations for muscle relaxation can be performed.

RESULTS

Since 2002, 178 patients have received at least one Bryan Cervical Disc Prosthesis. 92 patients had a complete follow- up. Examinations were performed 8 and 12 weeks, respectively, as well as 6 up to 44 months postoperatively. 29 patients received a hybrid implantation. Cobb's angle and range of motion were determined radiologically, the degree of heterotopic ossification was classified according to McAfee. Disk prosthesis placement was measured in relation to the dorsal edge of the vertebral body, the center of the spine, as well as the body axes. For clinical evaluation, the Oswestry Neck Disability Index was used, and the neurostatus was determined.

Postoperative segmental malalignment after surgery with the Bryan cervical disc prosthesis: is it related to the mechanics and design of the prosthesis?

STUDY DESIGN

In a radiographic study, postoperative segmental alignment was compared between 2 cohorts of 20 consecutive patients operated with a Bryan Cervical Disc Prosthesis. In group 2, patients with severe preoperative kyphosis were excluded for disc replacement surgery and the surgical technique was slightly altered to avoid asymmetric overdrilling of the posterior part of the cranial endplate of the caudal vertebral body.

OBJECTIVE

The aim was to investigate whether this change in patient inclusion criteria and modification of the surgical technique had an influence on postoperative segmental alignment and whether postoperative kyphosis is related to the mechanical properties and/or the design of the prosthesis.

SUMMARY OF BACKGROUND DATA

Several research groups reported segmental kyphosis after treatment of degenerative disc disease with the Bryan Cervical Disc Prosthesis.

METHODS

On the basis of lateral radiographs, the disc insertion angle (as a postoperative estimate for the intraoperative angle of approach) and the angle of the functional spinal unit (FSU) and disc angle (both as measures for segmental alignment) were calculated.

RESULTS

In group 1, 80% of the patients had a kyphotic FSU angle and 40% had a kyphotic disc angle preoperatively. At follow-up, 65% of the patients had a kyphotic FSU angle, whereas 55% had a kyphotic disc angle. In group 2, 40% of the patients had a kyphotic FSU angle and 5% had a kyphotic disc angle preoperatively. At follow-up, 40% of the patients had a kyphotic FSU angle, whereas 5% had a kyphotic disc angle. Due to the change in patient inclusion criteria, there was a significant difference in preoperative FSU angle between groups 1 and 2; however, no significant difference in preoperative disc angle was found. Owing to the change in surgical technique, the disc insertion angle was significantly different between both the groups. A difference in postoperative FSU angle, however, nonsignificant, between both the groups was observed. There was a significant difference in postoperative disc angle between both the groups; group 1 showed significantly more kyphosis of the shells, than group 2.

CONCLUSIONS

This study shows that segmental malalignment with the Bryan Disc can be reduced and is therefore not device related. Proper patient selection and a modified surgical technique can prevent this adverse outcome.

Clinical outcomes of Bryan cervical disc arthroplasty a prospective, randomized, controlled, single site trial with 48-month follow-up

STUDY DESIGN

Prospective, randomized, controlled. Level 1 evidence.

OBJECTIVE

To report functional outcomes at 48 months follow-up on prospectively randomized patients to either the Bryan cervical disc prosthesis or anterior cervical discectomy and fusion (ACDF) at a single site.

SUMMARY OF BACKGROUND DATA

Surgical treatment of cervical disc pathology can involve discectomy and fusion (ACDF), the gold standard technique. The safety and effectiveness of this procedure has been established and demonstrated in the literature, however, limitations have evolved and alternatives such as disc replacement are being investigated. Intervertebral disc replacement is designed to preserve motion, both at affected and adjacent levels avoiding limitations of fusion such as adjacent level degeneration. New onset degenerative changes and possible recurring neurologic symptoms may be deferred or eliminated with cervical disc replacement. A recent multicenter trial with 24 months follow-up has shown the Bryan disc to compare favorably with ACDF. Continued follow-up is needed to further evaluate and compare functional outcomes in both these cohorts.

METHODS

A total of 47 patients were enrolled at our site as part of an ongoing multicenter prospectively randomized study investigating ACDF versus Bryan cervical disc prosthesis. Functional outcomes are now reported at 48 months follow-up for our cohort of participants. Neck disability index score (NDI), VAS neck and arm and SF-36 both physical and mental as well as complications and reoperations will be reported.

RESULTS

Functional outcome data collected at routine follow-up for 48-months has favorably demonstrated improved functional outcomes for NDI, neck/arm pain VAS scores, and the SF-36 physical/mental health component scores for the Bryan arthroplasty and ACDF cohorts. The NDI scores for the Bryan arthroplasty preoperatively was 51 and at 48 months 10. For ACDF preoperative NDI score was also 51 and at 48 months 16.7. At 48 months NDI success, measured by >or=15 points NDI improvement demonstrated a 93.3% success for Bryan arthroplasty and an 82.4% success for ACDF. VAS neck pain scores for the Bryan arthroplasty preoperatively was 76.2 and at 48 months was 13.6. VAS neck pain scores for ACDF preoperatively was 80.6 and at 48 months was 28.1. Arm Pain scores were also measured and for the Bryan arthroplasty preoperatively measured 78.8 and at 48 months 10.8. For ACDF arm pain scores preoperatively measured 77.1 and at 48 months 21.7. These outcomes have not been associated with any degradation of outcome measures from 2 to 4 years. During the 48 months of follow-up at our institution we also report 6 secondary surgeries in our control group (ACDF) and only 1 in our investigational group (Bryan). Of the 6 surgeries in the control group performed, 3 or 12% to date were for adjacent level degenerative disease and 1 or 4% for remote level degenerative disc disease. The remaining 2 surgeries were performed on the same patient for a pseudarthrosis. In the investigational group there was only 1 secondary surgery performed to date for adjacent level disease 5%.

CONCLUSIONS

At 48 months, cervical arthroplasty with the Bryan cervical disc prosthesis continues to compare favorably to ACDF at our institution. There has been no degradation of functional outcomes from 24 to 48 months for NDI, VAS of neck and arm, and SF-36. There has been a lower incidence of secondary surgeries for the Bryan arthroplasty cohort to date.

Update on cervical disc arthroplasty: where are we and where are we going?

Despite the very good results of anterior cervical discectomy and fusion, there are concerns of adjacent level degeneration. For this reason, interest has grown in the potential for motion sparing alternatives. Cervical disc arthroplasty is thus evolving as a potential alternative to fusion. Specific design characteristic and implants will be reviewed and outcomes summarized.

Fusion versus disk replacement for degenerative conditions of the lumbar and cervical spine: quid est testimonium?

This article compares the outcomes following spinal fusion and disk replacement for degenerative conditions of the lumbar and cervical spine. The short-term outcomes of lumbar and cervical total disk replacement are equivalent to that following spinal fusion. Long-term follow-up studies of total disk replacement are necessary to confirm its potential benefit in reducing or preventing adjacent level degeneration. Also discussed is the philosophy of the surgical management of degenerative conditions of the lumbar and cervical spine.

Surgical outcome of cervical arthroplasty using bryan(r)

OBJECTIVE

Recently, motion preservation has come to the forefront of emerging technologies in spine surgery. This is the important background information of the emergence of cervical arthroplasty as an alternative to arthrodesis that offers the promise of restoring normal spinal movement and reduces a kinematic strain on adjacent segments. The study was designed to evaluate early surgical outcome and radiological effects of Bryan(R) cervical disc prosthesis.

METHODS

The authors retrospectively reviewed radiographic and clinical outcomes in 52 patients who received the Bryan(R) Cervical Disc prosthesis, for whom follow-up data were available. Static and dynamic radiographs were measured by computer to determine the angles formed by the endplates of the natural disc preoperatively, those formed by the shells of the implanted prosthesis, the angle of functional spine unit (FSU), and the C2-7 Cobb angle. The range of motion (ROM) was also determined radiographically, whereas clinical outcomes were assessed using Odom's criteria, visual analogue pain scale (VAS) and neck disability index (NDI).

RESULTS

A total of 71 Bryan(R) disc were placed in 52 patients. A single-level procedure was performed in 36 patients, a two-level procedure in 13 patients, and a three-level procedure in 3. Radiographic and clinical assessments were made preoperatively. Mean follow-up duration was 29.2 months, ranging from 6 to 36 months. All of the patients were satisfied with the surgical results by Odom's criteria, and showed significant improvement by VAS and NDI score (p < 0.05). The postoperative ROM of the implanted level was preserved without significant difference from preoperative ROM of the operated level (p < 0.05). 97% of patients with a preoperative lordotic sagittal orientation of the FSU were able to maintain lordosis. The overall sagittal alignment of the cervical spine was preserved in 88.5% of cases at the final follow up. Interestingly, preoperatively kyphotic FSU resulted in lordotic FSU in 70% of patients during the late follow up, and preoperatively kyphotic overall cervical alignment resulted in lordosis in 66.6% of the patients postoperatively.

CONCLUSION

Arthroplasty using the Bryan(R) disc seemed to be safe and provided encouraging clinical and radiologic outcome in our study. Although the early results are promising, this is a relatively new approach, therefore long-term follow up studies are required to prove its efficacy and its ability to prevent adjacent segment disease.

A comparison of outcomes of cervical disc arthroplasty and fusion in everyday clinical practice: surgical and methodological aspects

Randomised controlled trials (RCTs) of cervical disc arthroplasty vs fusion generally show slightly more favourable results for arthroplasty. However, RCTs in surgery often have limited external validity, since they involve a select group of patients who fit very rigid admission criteria and who are prepared to subject themselves to randomisation. The aim of this study was to examine whether the findings of RCTs are verified by observational data recorded in our Spine Center in association with the Spine Society of Europe Spine Tango surgical registry. Patients undergoing fusion/stabilisation or disc arthroplasty for degenerative cervical spinal disease were selected for inclusion. They completed a questionnaire pre-operatively and at 12 and 24 months follow-up (FU). The questionnaire comprised the multidimensional Core Outcome Measures Index (COMI; 0-10 scale) and, at FU, questions on global outcome and satisfaction with treatment (5-point scales, dichotomised to "good" and "poor"), re-operation and patient-rated complications. The surgeon completed a Spine Tango Surgery form. The outcome data from 266 (208 fusion, 58 arthroplasty) out of 284 eligible patients who had reached 12 months FU, and 169 (139 fusion, 30 arthroplasty) out of 178 who had reached 24 months FU, were included. Patients with cervical disc arthroplasty were younger [46 (SD 8) years vs 56 (SD 11) years for fusion; P < 0.05], had less comorbidity (P < 0.05), more often had only mono-segmental pathology (69% arthroplasty, 47% fusion) and only one type of degenerative pathology (69% arthroplasty, 46% fusion). Surgical complication rates were similar in each group (arthroplasty, 1.5%; fusion, 2.6%). The reduction in the COMI score was significantly greater in the arthroplasty group (at 12 months, 4.8 (SD 3.0) vs 3.7 (SD 2.9) points for fusion, and at 24 months 5.1 (SD 2.8) vs 3.8 (SD 2.9) points; each P < 0.05). In the arthroplasty group, a "good" global outcome was recorded in 90% patients (at 12 months) and 93% (at 24 months); in the fusion group the figures were 80 and 82%, respectively (group differences at each timepoint, P > 0.09). Satisfaction with treatment was similar in both groups (89-93%), at each timepoint. In multiple regression analysis, treatment group was of borderline significance as a unique predictor of the change in COMI at FU (P = 0.059 at 12 months, P = 0.055 at 24 months) in a model in which known confounders (age, comorbidity, number of affected levels) were controlled for. Being in the arthroplasty group was associated with an approximately 1-point greater reduction in the COMI score at FU. The results of this observational study appear to support those of the RCTs and suggest that, in patients with degenerative pathology of the cervical spine, disc arthroplasty is associated with a slightly better outcome than fusion. However, given the small size of the difference, its clinical relevance is questionable, especially in view of the a priori more favourable outcome expected in the arthroplasty group due to the more rigorous selection of patients.

Sagittal balance influences range of motion: an in vivo study with the ProDisc-C

BACKGROUND CONTEXT

Cervical arthroplasty is designed to maintain cervical motion of the functional spinal unit after cervical discectomy. The impact of the ProDisc-C (Synthes Spine, Paoli, PA) on in vivo kinematics and sagittal alignment requires further assessment.

PURPOSE

The purpose of this study is to test the hypothesis that the ProDisc-C increases range of motion (ROM) in flexion and extension at the surgical level, and assess its impact on cervical alignment.

STUDY DESIGN

Clinical study.

PATIENT SAMPLE

Fifteen patients with a mean age of 49 years were included in this study. Each patient had a single-level arthroplasty. Patients with multilevel arthroplasty, previous cervical spine surgery, and length of follow-up less than 6 months were excluded from this study.

OUTCOME MEASURE

Lateral dynamic radiographs of the cervical spine were analyzed using quantitative measurement analysis (QMA) preoperatively and postoperatively. QMA software was also used to determine the ROM and sagittal translation at the surgical level.

METHODS

Flexion/extension lateral radiographs of the cervical spine were prospectively collected and reviewed in 15 patients preoperatively and at early (1-3 months) and late (6-14 months) follow-up after placement of the ProDisc-C. Shell angle (SA) and C2-C7 Cobb angles were measured. Sagittal translation and ROM were calculated at each time point. Preoperative values were compared with early and late follow-up values using paired Student t tests and Pearson's correlation.

RESULTS

The C2-C7 Cobb angle did not change significantly after surgery. Segmental ROM increased significantly from neutral to flexion (p=.02) and neutral to extension (p=.002) at late follow-up. SA correlated significantly with ROM from neutral to extension (Pearson's r=-0.55; p=.02) and translation from neutral to extension (Pearson's r=-0.58; p=.02).

CONCLUSIONS

The ProDisc-C increased overall segmental ROM. A lordotic SA may be associated with restricted segmental ROM and translation in extension. This study did not detect any change in overall cervical spinal alignment after insertion of the device.

Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial

STUDY DESIGN

A prospective, randomized, multicenter study of surgical treatment of cervical disc disease.

OBJECTIVE

To assess the safety and efficacy of cervical disc arthroplasty using a new arthroplasty device at 24-months follow-up.

SUMMARY OF BACKGROUND DATA

Cervical disc arthroplasty preserves motion in the cervical spine. It is an alternative to fusion after neurologic decompression, whereas anterior decompression and fusion provides a rigorous comparative benchmark of success.

METHODS

We conducted a randomized controlled multicenter clinical trial enrolling patients with cervical disc disease. Ultimately 242 received the investigational device (Bryan Cervical Disc), and 221 patients underwent a single-level anterior cervical discectomy and decompression and fusion as a control group. Patients completed clinical and radiographic follow-up examinations at regular intervals for 2 years after surgery.

RESULTS

Analysis of 12- and 24-month postoperative data showed improvement in all clinical outcome measures for both groups; however, 24 months after surgery, the investigational group patients treated with the artificial disc had a statistically greater improvement in the primary outcome variables: Neck disability index score (P = 0.025) and overall success (P = 0.010). With regard to implant- or implant/surgical-procedure-associated serious adverse events, the investigational group had a rate of 1.7% and the control group, 3.2%. There was no statistical difference between the 2 groups with regard to the rate of secondary surgical procedures performed subsequent to the index procedure. Patients who received the artificial cervical disc returned to work nearly 2 weeks earlier than the fusion patients (P = 0.015).

CONCLUSION

Two-year follow-up results indicate that cervical disc arthroplasty is a viable alternative to anterior cervical discectomy and fusion in patients with persistently symptomatic, single-level cervical disc disease.

Biomechanical studies on cervical total disc arthroplasty: a literature review

BACKGROUND

Many models of cervical disc prostheses are currently commercially available or under clinical trial, and are based on several design concepts and built employing different materials. This paper is targeted to the understanding of the possible relationships between the geometrical, mechanical and material properties of the various cervical disc prostheses and the restoration of a correct biomechanics of the implanted spine.

METHODS

Papers about cervical disc arthroplasty, based on ex vivo testing, mathematical models, and radiographic measurements, were included in the present review.

FINDINGS

Although disc arthroplasty was found to be generally able to preserve a nearly physiological motion in the cervical spine, several alterations in the spine biomechanics due to disc arthroplasty were reported in the literature. An increase of the range of motion at the implanted level was observed in some ex vivo studies. Loss of mobility and heterotopic ossification were reported in radiographic investigations. Loss of lordosis at the implanted level was detected as well. Wear debris was usually found very limited and device stability seemed not to be an actual problem.

INTERPRETATION

The possible relationships between the observed alterations in the spine biomechanics after disc arthroplasty and the properties of the various cervical disc prostheses have been reviewed. Clinical studies are needed to assess the validity of the considerations inferred from the biomechanical papers.