Cervical Total Disc Arthroplasty Research Articles

The footprint mismatch of cervical disc arthroplasty comes from degenerative factor besides ethnic factor

A mismatch in footprints of cervical total disc arthroplasty (CTDA) implants occasionally occurred in Asian population and it had been attributed solely to ethnic factor. Yet, cervical degeneration process may play a role. Our purpose was to compare the cervical vertebra morphometric data with and without degeneration. The study included patients with CT scans of cervical spine from our hospital between January, 2019, and September, 2021. The total cervical degenerative index (TCDI) of each patient were collected by adding CDI score for 5 disc-levels. Patients were categorized into normal (TCDI 0–5) and degeneration groups (TCDI 6–60). Various measurements of the C3–C7 vertebral body and endplate were taken. Forty-nine patients in the normal group and 55 in the degeneration group were included. No significant difference was noted in gender, BH, BW, or BMI except age and TCDI (p < .001). During degeneration, disproportional endplate size changes were observed, with an increment ratio of 12–20% in the anteroposterior and 5–17% in the mediolateral plane throughout C3–C7, while vertebral body height remained constant. In conclusion, degeneration process, besides ethnic factor, causes the endplate size and shape mismatch. This information can help spine surgeon choose appropriate implants in CTDA surgery.

Adaptive core cervical total disc arthroplasty device replicates biomechanical instantaneous center of rotation in cadaver model

Adaptive core cervical total disc arthroplasty device replicates biomechanical instantaneous center of rotation in cadaver model

Cervical disc arthroplasty with the Baguera C prosthesis: clinical and radiological results of a 10-year follow-up study

PurposeWe evaluated the long-term safety, mobility and complications of cervical total disc arthroplasty with the Baguera®C prosthesis over 10 years.MethodsWe included 91 patients treated by arthroplasty for cervical degenerative disc disease. A total of 113 prostheses were implanted (50 one-level, 44 two-level and 19 hybrid constructs). They were assessed for complications, clinically, with NDI and SF-12 questionnaires and by independent radiologists for ROM, HO, disc height and adjacent level degeneration.ResultsNo spontaneous migration, loss of fixation, subsidence, vascular complication or dislocation were observed. The reoperation rate was 1%. About 82.7% of the patients were pain free. About 9.9% were taking occasional grade I painkillers. Motricity and sensitivity were preserved in 98.8% and 96.3%. The NDI showed an average functional disability of 17.58%, 26% lower than preoperatively. The SF-12 scores were close to normal health. The average ROM at the treated level was 7.4°. Motion was preserved in 86.6%. Lack of motion was observed in 13.4%. Grades II and III H0 were present in 53.7% and 31.7%, respectively, Grade IV was present in 13.4%. Motion was preserved in 100% of the grades 0–III. The preoperative adjacent level disc height of 4.3 mm remained stable during all the follow-ups at 4.4 mm and 4.2 mm, respectively, at 5 and 10 years.ConclusionsAfter 10 years, cervical arthroplasty with the Baguera®C prosthesis presents excellent safety and functional results and low complications. Motion was preserved in 86.6%, with a 7.4° ROM. Although common, HO did not hinder motion. Adjacent disc height preservation confirms some adjacent level degeneration protection.

Does disc distraction after cervical total disc arthroplasty impact range of motion and patient-reported outcomes?

Total disc arthroplasty (TDA) has been established as a safe and effective alternative to anterior cervical discectomy and fusion for the treatment of cervical spine pathology. However, there remains a paucity of studies in the literature regarding the amount of disc height distraction that can be tolerated, as well as its impact on kinematic and clinical outcomes. Patients who underwent 1- or 2-level cervical TDA with a minimum follow-up of 1 year with lateral flexion/extension and patient-reported outcome measures (PROMs) were included. Middle disc space height was measured on preoperative and 6-week postoperative lateral radiographs to quantify the magnitude of disc space distraction, and patients were grouped into < 2-mm distraction and > 2-mm distraction groups. Radiographic outcomes included operative segment lordosis, segmental range of motion (ROM) on flexion/extension, cervical (C2-7) ROM on flexion/extension, and heterotopic ossification (HO). General health and disease-specific PROMs were compared at the preoperative, 6-week, and final postoperative time points. The independent-samples t-test and chi-square test were used to compare outcomes between groups, while multivariate linear regression was used to adjust for baseline differences. Fifty patients who underwent cervical TDA at 59 levels were included in the analysis. Distraction < 2 mm was seen at 30 levels (50.85%), while distraction > 2 mm was observed at 29 levels (49.15%). Radiographically, after adjustment for baseline differences, C2-7 ROM was significantly greater in the patients who underwent TDA with < 2-mm disc space distraction at final follow-up (51.35° ± 13.76° vs 39.19° ± 10.52°, p = 0.002), with a trend toward significance in the early postoperative period. There were no significant postoperative differences in segmental lordosis, segmental ROM, or HO grades. After the authors controlled for baseline differences, < 2-mm distraction of the disc space led to significantly greater improvement in visual analog scale (VAS)-neck scores at 6 weeks (-3.68 ± 3.12 vs -2.24 ± 2.70, p = 0.031) and final follow-up (-4.59 ± 2.74 vs -1.70 ± 3.03, p = 0.008). Patients with < 2-mm disc height difference had increased C2-7 ROM at final follow-up and significantly greater improvement in neck pain after controlling for baseline differences. Limiting differences in disc space height to < 2 mm affected C2-7 ROM but not segmental ROM, suggesting that less distraction may result in more harmonious kinematics between all cervical levels.

Relative Efficacy of Cervical Total Disc Arthroplasty Devices and Anterior Cervical Discectomy and Fusion for Cervical Pathology: A Network Meta-Analysis.

Systematic Review and Meta Analysis. This study sought to compare patient-reported outcomes, success, complications, and radiographic outcomes directly and indirectly between different cervical total disc arthroplasty (TDA) devices and anterior cervical discectomy and fusion (ACDF). Patients of prospective randomized controlled trials of 1-level cervical TDA with a minimum of 2years follow up were identified in the literature. A frequentist network meta-analysis model was used to compare each outcome across the different TDA devices included and ACDF using the mixed effect sizes. 15 studies were included for quantitative analysis, reporting the outcomes of 2643 patients with an average follow-up was 67.3months (range: 24-120months), 1417 of whom underwent TDA and 1226 of whom underwent ACDF. Nine TDA devices were compared to ACDF, including the Bryan, Discover, Kineflex, M6, Mobi-C, PCM, Prestige ST, ProDisc-C, and Secure-C cervical prostheses. Several devices outperformed ACDF for certain outcomes, including Visual Analog Scale (VAS) Arm, Physical Component Score of the Short-Form Health Survey (SF PCS), neurological success, satisfaction, index-level secondary surgical interventions (SSI), and adjacent level surgeries. Cumulative ranking of each intervention assessed demonstrated the highest performance with the M6 prosthesis (P = .70), followed by Secure-C (P = .67), PCM (P = .57), Prestige ST (P = .57), ProDisc-C (P = .54), Mobi-C (P = .53), Bryan (P = .49), Kineflex (P = .49), Discover (P = .39), and ACDF (P = .14). Cervical TDA was found to be superior on most outcomes assessed in the literature of high-quality clinical trials. While most devices demonstrated similar outcomes, certain prostheses such as the M6 were found to outperform others across several outcomes assessed. These findings suggest that the restoration of near-normal cervical kinematics may lead to improved outcomes.

Complications in cervical total disc arthroplasty

Cervical total disc arthroplasty (CTDA) is an alternative to cervical fusion when addressing single level cervical disc disease and attempts to restore normal disc height and preserve motion, theoretically decreasing rates of adjacent segment disease (ASD) and symptomatic pseudoarthrosis. Although safe and effective, CTDA has a unique complication profile particularly in regard to long-term complications. Approach related complications are similar to anterior cervical discectomy and fusion (ACDF) and include injury to surrounding vascular, digestive, and neurologic structures. To achieve anatomic positioning, CTDA requires vertebral endplate cartilage removal and osseous preparation which can lead to endplate fracture, salvage fusion, or component malpositioning. Long term complications include heterotopic ossification (HO), implant subsidence, ASD requiring surgical intervention, and implant migration or translation. Although HO reduces motion at the prosthesis site, it does not appear to worsen clinical outcomes in most cases. Evidence is still conflicting regarding ASD when comparing ACDF to CTDA, however, the most recent evidence suggests a lower rate of development with CTDA.

Segmental range of motion after cervical total disc arthroplasty at long-term follow-up: a systematic review and meta-analysis.

As an alternative procedure to anterior cervical discectomy and fusion, total disc arthroplasty (TDA) facilitates direct neural decompression and disc height restoration while also preserving cervical spine kinematics. To date, few studies have reported long-term functional outcomes after TDA. This paper reports the results of a systematic review and meta-analysis that investigated how segmental range of motion (ROM) at the operative level is maintained with long-term follow-up. PubMed and MEDLINE were queried for all published studies pertaining to cervical TDA. The methodology for screening adhered strictly to the PRISMA guidelines. All English-language prospective studies that reported ROM preoperatively, 1 year postoperatively, and/or at long-term follow-up of 5 years or more were included. A meta-analysis was performed using Cochran's Q and I2 to test data for statistical heterogeneity, in which case a random-effects model was used. The mean differences (MDs) and associated 95% confidence intervals (CIs) were reported. Of the 12 studies that met the inclusion criteria, 8 reported the long-term outcomes of 944 patients with an average (range) follow-up of 99.86 (60-142) months and were included in the meta-analysis. There was no difference between preoperative segmental ROM and segmental ROM at 1-year follow-up (MD 0.91°, 95% CI -1.25° to 3.07°, p = 0.410). After the exclusion of 1 study from the comparison between preoperative and 1-year ROM owing to significant statistical heterogeneity according to the sensitivity analysis, ROM significantly improved at 1 year postoperatively (MD 1.92°, 95% CI 1.04°-2.79°, p < 0.001). However, at longer-term follow-up, the authors again found no difference with preoperative segmental ROM, and no study was excluded on the basis of the results of further sensitivity analysis (MD -0.22°, 95% CI -1.69° to -1.23°, p = 0.760). In contrast, there was a significant decrease in ROM from 1 year postoperatively to final long-term follow-up (MD -0.77°, 95% CI -1.29° to -0.24°, p = 0.004). Segmental ROM was found to initially improve beyond preoperative values for as long as 1 year postoperatively, but then ROM deteriorated back to values consistent with preoperative motion at long-term follow-up. Although additional studies with further longitudinal follow-up are needed, these findings further support the notion that cervical TDA may successfully maintain physiological spinal kinematics over the long term.

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

BackgroundThe 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. MethodsSegmental 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. ResultsIn 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. ConclusionsThe 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.

P75. Range of motion on flexion and extension at long term followup after cervical total disc arthroplasty: a systematic review and meta-analysis

<h3>BACKGROUND CONTEXT</h3> As an alternative procedure to anterior cervical discectomy and fusion (ACDF), total disc arthroplasty (TDA) facilitates direct neural decompression and disc height restoration while also preserving cervical spine kinematics. To date, few studies have reported long-term functional outcomes following TDA. <h3>PURPOSE</h3> This study sought to perform a systematic review and meta-analysis investigating how range of motion (ROM) at the operative level is maintained with long-term followup. <h3>STUDY DESIGN/SETTING</h3> Systematic review and meta-analysis <h3>PATIENT SAMPLE</h3> Patients in the literature of prospective studies of 1-level cervical TDA with a minimum of 5 years followup. <h3>OUTCOME MEASURES</h3> Segmental ROM at the preoperative, 1 year postoperative, and final (>5 years) postoperative time points. <h3>METHODS</h3> PubMed and MEDLINE were queried for all published studies pertaining to cervical TDA. The methodology for screening adhered strictly to the PRISMA guidelines. All English language prospective studies reporting ROM preoperatively, one year postoperatively, and/or at long-term follow-up of 5 or more years were included. A meta-analysis was performed using Cochran's Q and I2 to test data for statistical heterogeneity, in which case a random-effects model was used. The mean difference (MD) and associated 95% confidence intervals (CI) were reported. <h3>RESULTS</h3> After an initial search yielding 2,309 results, 12 studies met the inclusion criteria and 8 were included for meta-analysis. Overall, 1,158 patients were enrolled across the 8 studies and 944 (81.52%) were available for long-term followup. Of the patients who followed up, 163 (17.27%) were implanted with PCM, 131 (13.88%) with Mobi-C, 184 (19.49%) with Secure-C, 230 (24.36%) with Prestige LP, 229 (24.26%) with Bryan, and 27 (2.86%) with ProDisc-C prostheses. There was no difference found between operative segment ROM on flexion and extension preoperatively and at 1-year followup (MD = -0.91, CI: -3.07 to 1.25, p = .410). However, after excluding one study identified to contribute significantly to statistical heterogeneity via sensitivity analysis, ROM was found to significantly improve at 1-year postoperatively (MD = 1.92, CI: -2.79 to -1.04, p < .0001). There was no difference between ROM preoperatively and at long-term followup (MD = 0.52, CI: -0.98 to 2.03, p = .500). However, there was a significant decrease in ROM from 1-year postoperatively to final long-term followup (MD = 0.77, CI: 0.24 to 1.29, p = .004). <h3>CONCLUSIONS</h3> Operative segment ROM on flexion and extension was found to significantly deteriorate with long-term followup after TDA when compared to the early postoperative period. However, ROM on flexion and extension in the long-term following TDA remained similar to baseline function. While additional studies with further longitudinal follow-up investigating how much are needed, these findings further support the notion that cervical TDA may be successful in maintaining physiological spinal kinematics over the long-term. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Minimally Invasive Posterior Cervical Foraminotomy Versus Anterior Cervical Fusion and Arthroplasty: Systematic Review and Meta-Analysis.

Study DesignSystematic review and meta-analysis.ObjectivesPatients with lateral cervical disc and foraminal pathology can be treated with anterior and posterior approaches including anterior cervical discectomy and fusion(ACDF), cervical total disc arthroplasty(TDA), and minimally invasive posterior cervical foraminotomy(MIS-PCF). Although MIS-PCF may have some advantages over the anterior approaches, few comparative studies and meta-analyses have been done to assess superiority.MethodsThis study includes a systematic review of the literature and meta-analysis of studies directly comparing minimally invasive posterior cervical foraminotomy to either anterior cervical discectomy and fusion or cervical total disc arthroplasty.ResultsIn comparing patients undergoing ACDF and MIS-PCF, operative time ranged from 68 to 97.8 minutes in the ACDF group compared to 28 to 93.9 minutes in the MIS-PCF group. Mean postoperative length of stay ranged from 33.84 to 112.8 hours in the ACDF group compared to 13.68 to 83.6 hours in the MIS-PCF group. The total complication rates were 3.72% in the ACDF group and 3.73% in the MIS-PCF group. A random-effects model meta-analysis was carried out which failed to show a statistically significant difference in the complication rate between the two procedures(OR .91; 95% CI 0.13, 6.43; P = .92, I2 = 59%). The total reoperation rate was 3.5% in the ACDF group and 5.4% in the MIS-PCF group. A random-effects model meta-analysis was carried out which failed to show a statistically significant difference in the reoperation rate between the two procedures(OR .66; 95% CI 0.33, 1.33; P = .25, I2 = 0). In comparing patients undergoing TDA and MIS-PCF, operative time ranged from 90.3 to 106.7 minutes in the TDA group compared to 77.4 to 93.9 minutes in the MIS-PCF group. Mean postoperative length of stay ranged from 103.2 to 165.6 hours in the TDA group and 93.6 to 98.4 hours in the MIS-PCF group. The complication rate ranged from 23.5 to 28.6% in the TDA group and 0 to 14.3% in the MIS-PCF group. The overall reoperation rates were 2.6% in the TDA group and 10.2% in the MIS-PCF group.ConclusionsThere is no clear superiority between MIS-PCF and ACDF/TDA in terms of operative time, postoperative length of stay, or rate of complications/reoperations. Further studies with increased follow-up intervals >48 months, and higher sample sizes are necessary to determine the true superiority of MIS-PCF and anterior neck approaches in treatment of lateral disc and foraminal pathology.

Numerical wear study of metal‐on‐ultrahigh molecular weight polyethylene‐based cervical total disc arthroplasty by coupling finite element analysis and multi‐body dynamics

In this study, the effects of in vivo (head flexion-extension, lateral bending, and axial rotation) and in vitro (ISO 18192-1) working conditions on the wear of ultrahigh molecular weight polyethylene (UHWMPE)-based cervical disc prosthesis were studied via numerical simulation. A finite-element-based wear prediction framework was built by using a sliding distance and contact area dependent Archard wear law. Moreover, a pre-developed cervical spine multi-body dynamics model was incorporated to obtain the in vivo conditions. Contact mechanic analysis stated that in vitro conditions normally led to a higher contact stress and a longer sliding distance, with oval or crossing-path-typed sliding track. In contrast, in vivo conditions led to a curvilinear-typed sliding track. In general, the predicted in vivo wear rate was one order of magnitude smaller than that of in vitro. According to the yearly occurrence of head movement, the estimated total in vivo wear rate was 0.595 mg/annual. While, the wear rate given by the ISO standard test condition was 3.32 mg/annual. There is a significant impact of loading and kinematic condition on the wear of UHMWPE prosthesis. The work conducted in the present study provided a feasible way for quantitatively assessing the wear of joint prosthesis.

Failure in cervical total disc arthroplasty: single institution experience, systematic review of the literature, and proposal of the RUSH TDA failure classification system

BACKGROUND CONTEXTCervical total disc arthroplasty (TDA) is an alternative procedure to anterior cervical discectomy and fusion that facilitates neural decompression while both preserving motion of the spinal unit and decreasing the risk for degenerative changes at adjacent segments. However, due to its more recent introduction in clinical practice and low complication rates, the modes by which TDA may fail remain to be described. PURPOSEThis study sought to identify the modes and frequencies of cervical TDA failure in order to propose a novel classification system. STUDY DESIGNRetrospective cohort and systematic review. PATIENT SAMPLEPatients who underwent single or two-level TDA for cervical radiculopathy or myelopathy at a single institution and in the literature of medium and large prospective studies. OUTCOME MEASURESCervical TDA failure, defined as subsequent surgical intervention at the index segment. METHODSThis study retrospectively reviewed patients who underwent single or two-level TDA for cervical radiculopathy or myelopathy at a single institution to identify the potential implant failure modes. A systematic review and meta-analysis of prospective data in the literature was then performed to further supplement failure mode identification and to describe the rates at which the various failure types occurred. Statistical analysis included between-group comparisons of Non-Failed and Failed patients and frequencies of each failure type among Failed patients. RESULTSA retrospective review at our institution of 169 patients (201 levels) identified eight failures, for a failure rate of 4.7%. Additionally, seven patients were revised who had the primary surgery at an outside institution. The systematic review of 3976 patients (4525 levels) identified 165 (4.1%) additional failures. Using this data, six primary failure types were classified, with several subtypes. These include recurrent or persistent index-level stenosis (Type I); migration (Type II) presenting as gross extrusion (A) or endplate failure with subsidence/acute fracture (B); instability (Type III) due to mechanical loosening (A), septic loosening (B), or device fracture (C); device motion loss (Type IV) such as “locking” of the device in kyphosis; implantation error (Type V) due to malposition (A) or improper sizing (B); and wear (Type VI) either without osteolysis (A) or with wear-particle-induced osteolysis (B). Stenosis (Type I) was the most common mode of failure found both through retrospective review and in the literature. CONCLUSIONSCervical TDA fails through six primary mechanisms. While rates of certain failures requiring subsequent surgical intervention are low, it is possible that these complications may become more prevalent upon further longitudinal observation. Thus, future application and validation of this classification system is warranted to evaluate how failure frequencies change over time and with larger patient samples.

Periprosthetic Osteolysis in Cervical Total Disc Arthroplasty: A Single Institutional Experience

ABSTRACT BACKGROUND Cervical disc arthroplasty (CDA) affords an excellent alternative to cervical fusion for the treatment of symptomatic patients with degenerative disc disease. As more surgeons perform CDAs, an understanding of the complications associated with this technique is crucial. Periprosthetic osteolysis (PO) is a rare potential complication associated with CDA. OBJECTIVE To highlight potential complications associated with CDA. METHODS A retrospective chart review of patients who underwent CDA at our institution was performed. Patient outcomes and relevant clinical and radiographical data were analyzed in addition to associated complications. Explanted devices were subjected to macroscopic and microscopic analyses. RESULTS A total of 88 patients were included: 68 patients underwent 1-level CDA and 20 patients had 2-level CDA. Implants used in this series included Mobi-C (Zimmer Biomet), Prestige LP (Medtronic), Secure C (Globus), Advent (Orthofix), and ProDisc C (DePuy). One patient demonstrated symptoms of myeloradiculopathy that correlated with radiographical periprosthetic osteolysis and required surgical intervention in the form of disc explantation, corpectomy, and cervical instrumented fusion. Device retrieval analysis demonstrated evidence of elevated oxidation levels and increased wear in the presence of high concentrations of metal ions and debris in the surrounding tissue. The tissue did not exhibit any immune response, infection, or acute inflammation. CONCLUSION PO is a potential complication of CDA that occurs irrespective of the type of implant used. We describe its occurrence and management and highlight the importance of being aware of this understated phenomenon.

112. Changes in flexion/extension range of motion due to oversizing of cervical total disc arthroplasty

BACKGROUND CONTEXT Total disc arthroplasty (TDA) is a popular treatment for cervical degenerative disc because it preserves motion, decreasing the potential for adjacent level disease. However, oversizing the disc may occur due to limited options in artificial disc height and may diminish this motion preservation. In this study, 1- and 2-level disc arthroplasties with mobile core devices (MCD) at C5-C6 and C4-C5 were compared to oversized devices and 2-level fusions. METHODS Eight cadaveric cervical (C2-T1) spine specimens (average age: 43 ± 12 years) were prepared with cranial and caudal ends embedded in bone cement. Each vertebra was instrumented with optoelectronic markers for motion capture. Each specimen was tested using a six degree-of-freedom kinematic spinal simulator up to 2 Nm in three cycles of flexion/extension. All specimens were tested at four intervention points: intact, ALL resection, 1-level TDA @ C5-C6 with an MCD (Mobi-C, Zimmer Biomet), and 2-level TDA @ C4-C6 with MCDs. After these interventions, the specimens were separated into two equal groups (A and B) with two additional interventions: 2-level TDA with overstuffing or increasing the height of the MCD by 1 mm at C5-C6 (Group A) or C4-C5 (Group B), and 2-level fusion @ C4-C6. All moment and motion capture data were imported into Matlab, and the 3rd test cycle was analyzed. Maximum ranges of motion, normalized as percent of intact, were analyzed for the index (C4-C5 and C5-C6) and adjacent (C3-C4 and C6-C7) levels. Two-way ANOVA with one way repeated-measures was performed with post-hoc Tukey's tests to measure changes in maximum ranges of motion. RESULTS Flexion/Extension, Interventions 1-4: No significant differences were observed between all four interventions at C3-C4 and C4-C5. At C5-C6, significantly greater flexion/extension was measured with ALL resection compared to intact and 1-level TDA interventions. Finally, at C6-C7, ALL resection produced significantly higher range of motion vs 2-level TDA. Flexion/Extension, Group A, Interventions 1,3-6: At C3-C4 and C6-C7, no significant differences were measured between any of the interventions. At C4-C5, intactROM was significantly larger than 2-level TDA, overstuffed TDA @ C5-C6, and 2-level fusion @ C4-C6. In addition, 1-level TDAROM was significantly larger than 2-level TDA and 2-level fusion. Finally, ROM for 2-level TDA and overstuffed TDA @ C5-C6 were both significantly larger than 2-level fusion. At C5-C6, intact, 1-level, and 2-level TDA ROM were significantly larger than the overstuffed TDA @ C5-C6 and the 2-level fusion interventions. Also, the overstuffed TDA @ C5-C6 ROM was significantly larger than the 2-level fusion. Flexion/Extension, Group B, Interventions 1,3-6: At C3-C4 and C6-C7, no significant differences were measured between any of the interventions. At C4-C5, Intact ROM was significantly larger than 2-level TDA, overstuffed TDA @ C4-C5, and 2-level fusion. 1- and 2-level TDA ROM were both significantly larger than overstuffed TDA @ C4-C5 and 2-level fusion. Finally, overstuffed TDA @ C4-C5 ROM was significantly larger than 2-level fusion. At C5-C6, ROM of all interventions was significantly larger than 2-level fusion. CONCLUSIONS Mobile-core disc arthroplasty device maintained range of motion at the index levels, and did not increase motion in adjacent levels in both 1- and 2-level disc arthroplasty implantations. In addition, implanting with oversized devices caused significant decreases in range of motion. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

Does index level sagittal alignment determine adjacent level disc height loss?

The authors sought to compare the effect of index level sagittal alignment on cephalad radiographic adjacent segment pathology (RASP) in patients undergoing cervical total disc arthroplasty (TDA) or anterior cervical discectomy and fusion (ACDF). This was a retrospective study of prospectively collected radiographic data from 79 patients who underwent TDA or ACDF and were enrolled and followed prospectively at two centers in a multicenter FDA investigational device exemption trial of the Bryan cervical disc prosthesis used for arthroplasty. Neutral lateral radiographs were obtained pre- and postoperatively and at 1, 2, 4, and up to 7 years following surgery. The index level Cobb angle was measured both pre- and postoperatively. Cephalad disc degeneration was determined by a previously described measurement of the disc height/anteroposterior (AP) distance ratio. Sixty-eight patients (n = 33 ACDF; n = 35 TDA) had complete radiographs and were included for analysis. Preoperatively, there was no difference in the index level Cobb angle between the ACDF and TDA patients. Postoperatively, the ACDF patients had a larger segment lordosis compared to the TDA patients (p = 0.002). Patients who had a postoperative kyphotic Cobb angle were more likely to have undergone TDA (p = 0.01). A significant decrease in the disc height/AP distance ratio occurred over time (p = 0.035), by an average of 0.01818 at 84 months. However, this decrease was not influenced by preoperative alignment, postoperative alignment, or type of surgery. In this cohort of patients undergoing TDA and ACDF, the authors found that preoperative and postoperative sagittal alignment have no effect on RASP at follow-up of at least 7 years. They identified time as the only significant factor affecting RASP.

Motion response of a polycrystalline diamond adaptive axis of rotation cervical total disc arthroplasty

BackgroundCervical fusion is associated with adjacent segment degeneration. Cervical disc arthroplasty is considered an alternative to reduce risk of adjacent segment disease. Kinematics after arthroplasty should closely replicate healthy in vivo kinematics to reduce adjacent segment stresses. The purpose of this study was to assess the kinematics of a polycrystalline diamond cervical disc prosthesis. MethodsNine cadaveric C3–T1 spines were tested intact and after one (C5–C6) and two level (C5–C7) arthroplasty (Triadyme-C, Dymicron Inc., Orem, UT, USA). Kinematics were evaluated in flexion-extension, lateral bending, and axial rotation. FindingsProsthesis placement at C5–C6 and C6–C7 was 0.5 mm anterior and 0.6 mm posterior to midline respectively. C5–C6 flexion-extension motion was 12.8° intact and 10.5° after arthroplasty. C6–C7 flexion-extension motion was 10.0 and 11.4° after arthroplasty.C5–C6 lateral bending reduced from 8.5 to 3.7° after arthroplasty and at C6–C7 from 7.5 to 5.1°. C5–C6 axial rotation decreased from 10.4 to 6.2° after arthroplasty and at C6–C7 from 7.8 to 5.3°.Segmental lordosis increased by 4.2°, and middle disc height by 1.4 mm after arthroplasty. Change in center of rotation from intact to arthroplasty averaged 0.9 mm posteriorly and 0.1 mm caudally at C5–C6, and 1.4 mm posteriorly and 0.3 mm cranially at C6–C7. InterpretationThe cervical disc arthroplasty evaluated restored flexion-extension motion to intact levels and moderately increased segmental stiffness. Disc height increased by up to 1.5 mm and segmental lordosis by 4.2°. The unique prosthesis design allowed the axis of rotation after arthroplasty to closely mimic the native location.

Kinematic assessment of an elastic-core cervical disc prosthesis in one and two-level constructs.

IntroductionAnterior cervical discectomy and fusion has been associated with the development of adjacent segment degeneration (ASD), with clinical incidence of approximately 3% per year. Cervical total disc arthroplasty (TDA) has been proposed as an alternative to prevent ASD.HypothesesTDA in optimal placement using an elastic‐core cervical disc (RHINE, K2M Inc., Leesburg, Virginia) will replicate natural kinematics and will improve with optimal vs anterior placement.MethodsSeven C3‐T1 cervical cadaver spines were tested intact first, then after one‐level TDA at C5‐C6 anterior placement, after TDA at C5‐C6 optimal placement, after two‐level TDA at C5‐C6 and C6‐C7 optimal placement, and finally after two‐level TDA at C5‐C6 lateral placement and C6‐C7 optimal placement. The specimens were subjected to: Flexion‐Extension moments (+1.5 Nm) with compressive preloads of 0 N and 150 N, lateral bending (LB) and axial rotation (AR) (+1.5 Nm) without preload.Results C5‐C6 TDA in optimal placement resulted in a non‐significant increase in flexion‐extension ROM compared to intact under 0 N and 150 N preload (P > 0.05). Both LB and AR ROM decreased with arthroplasty (P < 0.01). Optimal placement of C6‐C7 TDA resulted in an increase in flexion‐extension ROM with preload compared to intact (P < 0.05) while LB and AR ROM decreased with arthroplasty (P < 0.01).ConclusionThis six degree of freedom elastic‐core disc arthroplasty effectively restored flexion‐extension motion to intact levels. In LB the TDA maintained 42% ROM at C5‐C6 and 60% at C6‐C7. In AR 57% of the ROM was maintained at C5‐C6 and 70% at C6‐C7. These findings are supported by literature which shows cervical TDA results in restoration of approximately 50% ROM in LB and AR, which is a multifactorial phenomenon encompassing TDA design parameters and anatomical constraints. Anterior placement of this viscoelastic TDA device shows motion restoration similar to optimal placement suggesting its design may be less sensitive to suboptimal placement.

Thursday, September 27, 2018 3:35 PM–5:05 PM Section on Motion Technology Abstract Presentations: 135. Influence of preoperative segmental range of motion on postoperative motion after cervical disc arthroplasty using fixed-core, mobile-core and restrained compressible-core prostheses

Thursday, September 27, 2018 3:35 PM–5:05 PM Section on Motion Technology Abstract Presentations: 135. Influence of preoperative segmental range of motion on postoperative motion after cervical disc arthroplasty using fixed-core, mobile-core and restrained compressible-core prostheses

Cervical Total Disc Arthroplasty

Cervical Total Disc Arthroplasty

Does Resection of the Posterior Longitudinal Ligament Affect the Stability of Cervical Disc Arthroplasty?

The need for posterior longitudinal ligament (PLL) resection during cervical total disc arthroplasty (TDA) has been debated. The purpose of this laboratory study was to investigate the effect of PLL resection on cervical kinematics after TDA. Eight cadaveric cervical spine specimens were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) to moments of ±1.5 Nm. After testing the intact condition, anterior C5-C6 cervical discectomy was performed followed by PLL resection and implantation of a compressible, 6-degrees-of-freedom disc prosthesis (M6-C, Spinal Kinetics Inc, Sunnyvale, California). Next, a second prosthesis was implanted at C6-C7 with PLL intact. Finally, the C6-C7 PLL was resected while the disc prosthesis remained in place. Segmental range of motion (ROM) and stiffness in the high flexibility zone around the neutral posture were analyzed using repeated measures ANOVA. At C5-C6, following TDA and PLL resection, FE, LB, and AR ROMs decreased significantly. Anterior and posterior disc height, segmental lordosis, and flexion stiffness increased significantly. At C6-C7, TDA with the PLL intact resulted in a significant increase in anterior disc height and segmental lordosis with no change in posterior disc height. FE, LB, and AR ROMs all decreased significantly, while flexion stiffness increased significantly compared to intact. PLL resection at C6-C7 did not result in a notable change compared to TDA with PLL intact. At the same level, flexion stiffness decreased following PLL resection compared to TDA with a value closer to intact. Two-level TDA (C5-C7) with PLL resection did not result in a loss of segmental stability. PLL resection did not significantly affect motion segment kinematics following cervical TDA using a prosthesis with inherent stiffness. Motion segment stiffness loss after PLL resection can be compensated for by a TDA design that can provide resistance to angular motion.