Heterotopic ossification, osteolysis and implant failure following cervical total disc replacement with the M6-C™ artificial disc.

INTRODUCTION: A recent study reported a 34% mid-term revision rate after M6-C™ cervical total disc replacement (CTDR) for wear-related osteolysis. Here, we aim to investigate the prevalence, risk factors, and radiographic characteristics of periprosthetic bony changes and implant failure of the M6-C™ artificial disc. METHODS: We retrospectively analysed radiographic (conventional X-ray, CT scan) and clinical outcomes (EQ-5D-5L, Neck Disability Index (NDI), and Visual Analog Scale (VAS) for neck and arm pain) data collected during routine follow-up of patients who underwent CTDR with the M6-C™ between 2011 and 2015. RESULTS: In total, 85 patients underwent CTDR with the M6-C™. Follow-up data were available for 43 patients (54% female, mean age 44 years) with 50 implants and a mean follow-up of 8.1 years (6.5-11 years). Implant failure with the presence of severe osteolysis was identified in 5 (12%) patients who were all male (p = 0.016) and implanted at the C5/6 level (p = 0.11). All failed implants required revision surgery. The overall prevalence of osteolysis was 44% (22/50 implants) and 34% (17/50 implants) for significant heterotopic ossification. Patients with high-grade osteolysis showed higher VAS arm pain (p = 0.05) and lower EQ-5D-VAS health VAS (p = 0.03). CONCLUSION: We report a lower reoperation rate for failed M6-C™ implants than previously published, but confirmed that osteolysis and heterotopic ossification are common following CTDR with the M6-C™ and may be asymptomatic. Therefore, we strongly recommend ongoing clinical and radiographic monitoring after CTDR with the M6-C™, particularly for male patients implanted at the C5/6 level.

Trends in use, outcomes, and revision procedures of anterior cervical disc replacement in the United States: a premiere database analysis from 2006-2019.

PURPOSE: We sought to characterize trends in demographics, comorbidities, and postoperative complications among patients undergoing primary and revision cervical disc replacement (pCDR/rCDR) procedures. METHODS: In this retrospective database study, the Premier Healthcare database was queried from 2006 to 2019. Annual proportions or medians were calculated for patient and hospital characteristics, comorbidities, and postoperative complications associated with CDR surgery. Trends were assessed using linear regression analyses with year of service as the sole predictor. RESULTS: A total of 16,178 pCDR and 758 rCDR cases were identified, with a median (IQR) age of 46 (39; 53) and 51 (43; 60) years among patients, respectively. The annual number of both procedures increased between 2006 and 2019, from 135 to 2220 for pCDR (p < 0.001), and from 17 to 49 for rCDR procedures (p < 0.001), with radiculopathy being the main indication for surgery in both groups. Mechanical failure was identified as a major indication for rCDR procedures with an increase over time (p = 0.002). Baseline patient comorbidity burden (p = 0.045) and complication rates (p < 0.001) showed an increase. For both procedures, an increase in outpatient surgeries and procedures performed in rural hospitals was seen (pCDR: p = 0.045; p = 0.006; rCDR: p = 0.028; p = 0.034). CONCLUSION: PCDR and rCDR procedures significantly increased from 2006 to 2019. At the same time, comorbidity burden and complication rates increased, while procedures were more often performed in an outpatient and rural setting. The identification of these trends can help guide future practice and lead to further areas of research.

A real-world analysis of hybrid CDA and ACDF compared to multilevel ACDF.

BACKGROUND: Multilevel anterior cervical discectomy and fusion (mACDF) is the gold standard for multilevel spinal disease; although safe and effective, mACDF can limit regular spinal motion and contribute to adjacent segment disease (ASD). Hybrid surgery, composed of ACDF and cervical disc arthroplasty, has the potential to reduce ASD by retaining spinal mobility. This study examined the safety of hybrid surgery by utilizing administrative claims data to compare real-world rates of subsequent surgery and post-procedural hospitalization within populations of patients undergoing hybrid surgery versus mACDF for multilevel spinal disease. METHODS: This observational, retrospective analysis used the MarketScan Commercial and Medicare Database from July 2013 through June 2020. Propensity score matched cohorts of patients who received hybrid surgery or mACDF were established based on the presence of spinal surgery procedure codes in the claims data and followed over a variable post-period. Rates of subsequent surgery and post-procedural hospitalization (30- and 90-day) were compared between hybrid surgery and mACDF cohorts. RESULTS: A total of 430 hybrid surgery patients and 2,136 mACDF patients qualified for the study; average follow-up was approximately 2 years. Similar rates of subsequent surgery (Hybrid: 1.9 surgeries/100 patient-years; mACDF: 1.8 surgeries/100 patient-years) were observed for the two cohorts. Hospitalization rates were also similar across cohorts at 30 days post-procedure (Hybrid: 0.67% hospitalized/patient-year; mACDF: 0.87% hospitalized/patient-year). At 90 days post-procedure, hybrid surgery patients had slightly lower rates of hospitalization compared to mACDF patients (0.23% versus 0.42% hospitalized/patient-year; p < 0.05). CONCLUSIONS: Findings of this real-world, retrospective cohort study confirm prior reports indicating that hybrid surgery is a safe and effective intervention for multilevel spinal disease which demonstrates non-inferiority in relation to the current gold standard mACDF. The use of administrative claims data in this analysis provides a unique perspective allowing the inclusion of a larger, more generalizable population has historically been reported on in small cohort studies.

Cervical disc prostheses need a variable center of rotation for flexion / extension below disc level, plus a separate COR for lateral bending above disc level to more closely replicate in-vivo motion: MRI-based biomechanical in-vivo study.

BACKGROUND: Cervical disc prostheses are used to preserve motion after discectomy, but they should also provide a near-physiological qualitative motion pattern. Nevertheless, they come in many completely different biomechanical concepts. This caused us to perform an in-vivo MR-based biomechanical study to further investigate cervical spine motion with the aim to gain new information for improving the design of future cervical arthroplasty devices. METHODS: Fifteen healthy volunteers underwent MRI-investigation (in order to avoid radiation exposure) of their cervical spines from C3 to C7; for each segment centers of rotation (COR) for flexion / extension were determined from 5 different positions, and CORs for lateral bending from 3 different positions. The motion path of the COR is then described and illustrated in relation to the respective COR for maximum flexion / extension or lateral bending, respectively, and the findings are translated into implications for a better biomechanical prosthesis-design. RESULTS: The COR for flexion / extension does not remain constant during motion. The CORs for the respective motion intervals were always found at different positions than the COR for maximum flexion /extension showing that the COR moves both along the x- and the y-axis throughout flexion / extension. For lateral bending a completely independent COR was found above disc-level. CONCLUSION: Flexion / extension is not a simple circular motion. Disc prostheses need a variable COR for flexion / extension below disc level with the capability to move both along the x- and the y-axis during motion, plus a second completely independent COR for lateral bending above disc level to closely replicate in-vivo motion. These findings are important for improving the biomechanical design of such devices in the future.

Spinal cord compression due to nucleus migration from Mobi-C total disc replacement.

Cervical disc replacement is an alternative option to an anterior cervical discectomy and fusion for cervical spine degenerative disease. We present the first reported case of a progressively worsening symptomatic spinal cord compression secondary to migration of the nucleus from a Mobi-C total disc replacement.

Anterior cervical discectomy and fusion is more effective than cervical arthroplasty in relieving atypical symptoms in patients with cervical spondylosis.

BACKGROUND AND PURPOSE: Patients with cervical spondylosis often present with concurrent 'atypical symptoms' of unknown etiology that have been associated with cervical spondylotic disease, including dizziness, headache, nausea, tinnitus, blurred vision, palpitations, and memory and gastrointestinal disturbances. Few studies have addressed whether surgical intervention to treat classic symptoms of cervical spondylosis can also effectively alleviate atypical symptoms. Accordingly, the purpose of this study is to compare the ability of cervical arthroplasty (CA) and anterior cervical discectomy and fusion (ACDF) to alleviate atypical symptoms associated with cervical spondylosis. MATERIALS AND METHODS: A retrospective analysis of 140 patients with cervical spondylosis and associated atypical symptoms was performed. Atypical symptoms were defined vertigo, headache, nausea and vomiting, tinnitus, blur vision, palpitation, hypomnesia, and gastroenteric disturbances not otherwise explained by medical comorbidities. Seventy-eight patients (55.7%) underwent ACDF and 62 (44.3%) patients underwent CA. Demographics, surgical characteristics, patient reported outcome measures (PROMs), radiographs, complication rates, and resolution in atypical symptoms were recorded and compared between groups. Atypical symptoms were assessed using a 20-point system. All the patients had a minimum of five years follow-up. RESULTS: VAS, SF-36, JOA, and NDI scores improved significantly in all the patients (p < 0.001). At the last follow-up, the fusion rate was 97% in the ACDF group. Atypical symptoms improved in both groups (p < 0.001), although the ACDF group demonstrated greater improvement in headache and vertigo resolution compared to the CA group (p < 0.0001). CONCLUSIONS: While both ACDF and CA are effective in alleviating atypical symptoms associated with cervical spondylosis, ACDF demonstrated greater improvements in atypical symptoms.

Does neck pain as chief complaint influence the outcome of cervical total disc replacement?

PURPOSE: We investigated whether outcomes after cervical total disc replacement (cTDR) are influenced by preoperative neck pain as the chief complaint. METHODS: This was a retrospective study using data in our local spine surgery outcomes database, linked to EUROSPINE Spine Tango Registry. Patients completed questionnaires at baseline enquiring about the "chief complaint" [neck pain (NP), arm/shoulder pain (AP) or neurological deficits (ND)] and including the Core Outcome Measures Index (COMI); these were completed again at 24 months postoperatively, along with a rating of "global treatment outcome" (on a five-point scale, later dichotomized as "good" or "poor"). Differences in outcomes between the groups were examined using ANOVA. Multivariable regression analysis examined the effect of the chief pain location on 24-month outcomes, controlling for age, gender, comorbidity, baseline pain and COMI scores. RESULTS: One hundred and fifty-nine consecutive patients were included, with a chief complaint of NP in 31%, AP in 38% and ND in 31%. The chief complaint groups did not differ in relation to their baseline COMI scores or their reductions in score from before surgery to 24 months after surgery (reduction: NP group, 4.4 ± 2.9 points; AP group, 4.7 ± 2.7; ND group, 4.3 ± 2.9; p = 0.78). Similarly, the percentage of patients reporting a "good global treatment outcome" at 24 months postoperatively did not differ between the groups (NP, 79%; AP, 77%; ND, 85%; p = 0.64). The findings were consistent when controlling for possible confounders in multiple regression. CONCLUSIONS: Having neck pain as opposed to arm pain or neurological deficits as preoperative chief complaint had no significant impact on clinical outcome after cTDR. These slides can be retrieved under Electronic Supplementary Material.

Unique biomechanical signatures of Bryan, Prodisc C, and Prestige LP cervical disc replacements: a finite element modelling study.

PURPOSE: The purpose of the study is to examine the biomechanical alterations in the index and adjacent levels of the human cervical spine after cervical arthroplasty with Bryan, Prodisc C, or Prestige LP. METHODS: A previously validated C2-T1 osteoligamentous finite element model was used to perform virtual C5-6 arthroplasty using three different FDA-approved artificial cervical discs. Motion-controlled moment loading protocol was used. Moment was varied until Bryan, Prodisc C, and Prestige LP models displayed the same total range of motion across C3-C7 as the intact spine model at 2 Nm of pure moment loading. Range of motion (ROM) and facet force (FF) were recorded at the index level. ROM, FF, and intradiscal pressure (IDP) were recorded at the adjacent levels. RESULTS: Prodisc C and Prestige LP led to supraphysiologic ROM and FF at the index level while decreasing ROM and FF at the adjacent levels. In contrast, Bryan reduced ROM and FF at the index level. Bryan increased ROM and FF at the adjacent levels in flexion, but decreased ROM and FF in the adjacent levels in extension. Prodisc C decreased IDP at the adjacent levels. Bryan reduced IDP in extension only. Prestige LP increased adjacent-level IDP. CONCLUSIONS: The distinct designs and material compositions of the three artificial discs result in varying biomechanical alterations at the index and adjacent levels in the cervical spine after implantation. The findings confirm the design and material influence on the spine biomechanics, as well as the advantages and contraindications of cervical arthroplasty in general. These slides can be retrieved under Electronic Supplementary Material.

Osteolysis after cervical disc arthroplasty.

PURPOSE: Cervical disc arthroplasty (CDA) has become an increasingly popular treatment for cervical degenerative disc disease. One potential complication is osteolysis. However, current literature on this topic appears limited. The purpose of this study is to elucidate the incidence, aetiology, consequence, and subsequent treatment of this complication. METHODS: A systematic literature review was performed according to the PRISMA guidelines. Studies discussing the causes, incidence and management of osteolysis after a CA were included. RESULTS: A total of nine studies were included. We divided these studies into two groups: (1) large case series in which an active radiological evaluation for osteolysis was performed (total = six studies), (2) case report studies, which discussed symptomatic cases of osteolysis (total = three). The incidence of asymptomatic osteolysis ranged from 8 to 64%; however, only one study reported an incidence of < 10% and when this case was excluded the incidence ranged from 44 to 64%. Severe asymptomatic bone loss (exposure of the implant) was found in less than 4% of patients. Bone loss from osteolysis appeared to occur early (< 1 year) after surgery and late (> 1 year) as well. Symptomatic patients with osteolysis often required revision surgery. These patients required removal of implant and conversion to fusion in the majority of the cases. CONCLUSIONS: Osteolysis after CDA is common; however, the majority of cases have only mild or asymptomatic presentations that do not require revision surgery. The timing of osteolysis varies significantly. This may be due to differences in the aetiology of osteolysis.

Evidence-based use of arthroplasty in cervical degenerative disc disease.

INTRODUCTION: Cervical disc arthroplasty (CDA) was developed to decrease the rate of symptomatic adjacent-level disease while preserving motion in the cervical spine. METHODS: The objectives of this paper are to provide criteria for proper patient selection as well as to present a comprehensive literature review of the current evidence for CDA, including randomized studies, the most recent meta-analysis findings, and long-term follow-up clinical trials as well. RESULTS: Currently, there are several prospective randomized controlled studies of level I of evidence attesting to the safety and efficacy of CDA in the management of cervical spondylotic disease (CSD) for one- or two-level degenerative diseases. These as well as recent meta-analyses suggest that CDA is potentially similar or even superior to anterior cervical discectomy and fusion (ACDF) when considering several outcomes, including dysphagia and re-operation rate over medium-term follow-up. Less robust studies have also reported satisfactory clinical and radiological outcomes of CDA for hybrid procedures (ACDF combined with CDA), non-contiguous disease, and even for multilevel disease (more than 2 levels). CONCLUSIONS: Based on this evidence we conclude that CDA is a safe and effective alternative to ACDF in properly selected patients for one- or two-level diseases. Defining superiority of specific implants and detailing optimal surgical indications will require further well-designed long-term studies.

Does design matter? Cervical disc replacements under review.

The present article reviews the design rationale of currently available cervical disc replacements. Recent prospective randomized control trials comparing cervical disc replacement and anterior fusion have demonstrated safety as well as equal or superior clinical results. Increasingly, more devices are becoming available on the market. Understanding design rationale will provide context for the surgeon to optimize decision making for the most appropriate prosthesis. Cervical arthroplasty is a technique that is undergoing rapid design refinement and development. Further improvements in device design will enable patient-specific device selection. Understanding the design rationale and complication profile of each device will improve clinical and radiographic outcomes.

Two-level cervical arthroplasty using a "no-distraction" technique.

Cervical arthroplasty is being recognized as an emerging alternative to anterior cervical fusion with comparable or superior outcomes. The authors describe the surgical nuances of 2-level cervical arthroplasty in a case of 2-level degenerative disease. In this surgical technique, conventional vertebral body distraction has been avoided to prevent facet distraction, which can be a cause of persistent postoperative neck pain. Good motion preservation was observed at the 1-year follow-up examination. The video can be found here: https://youtu.be/YTpRVRXuZZk .

Cervical arthroplasty: what does the labeling say?

OBJECTIVE The aim of this paper was to comprehensively review each of the Food and Drug Administration (FDA)-approved labels of 7 total cervical disc replacements, assess the exact methodology in which the trial was conducted, and provide a broad comparison of these devices to allow each surgeon to determine which disc best suits his or her specific treatment goals based on the specific labels and not the studies published. METHODS The FDA-approved labels for each of the 7 artificial discs were obtained from the official FDA website. These labels were meticulously compared with regard to the statistical analysis performed, the safety and efficacy data, and the randomized controlled trial that each artificial disc was involved in to obtain the FDA approval for the product or device. Both single-level and 2-level approvals were examined, and primary and secondary end points were assessed. RESULTS In the single-level group, 4 of the 7 artificial discs-Prestige LP, Prestige ST, Bryan, and Secure-C-showed superiority in overall success. Prestige ST showed superiority in 3 of 4 outcome measures (neurological success, revision surgery, and overall success), while the other aforementioned discs showed superiority in 2 or fewer measures (Prestige LP, neurological and overall success; Bryan, Neck Disability Index [NDI] and overall success; Secure-C, revision surgery and overall success; Pro-Disc C, revision surgery). The PCM and Mobi-C discs demonstrated noninferiority across all outcome measures. In the 2-level group, Prestige LP and Mobi-C demonstrated superiority in 3 outcome measures (NDI, secondary surgery, and overall success) but not neurological success. CONCLUSIONS This paper provides a comprehensive analysis of 7 currently approved and distributed artificial discs in the United States. It compares specific outcome measures of these devices against those following the standard of care, which is anterior cervical discectomy and fusion. This information will provide surgeons the opportunity to easily answer patients' questions and remain knowledgeable when discussing devices with manufacturers.

Multilevel cervical arthroplasty: current evidence. A systematic review.

OBJECTIVE Cervical disc arthroplasty (CDA) has been demonstrated to be an effective treatment modality for single-level cervical radiculopathy or myelopathy. Its advantages over an anterior cervical discectomy and fusion (ACDF) include motion preservation and decreased reoperations at the index and adjacent segments up to 7 years postoperatively. Considering the fact that many patients have multilevel cervical disc degeneration (CDD), the authors performed a systematic review of the clinical studies evaluating patients who underwent multilevel CDA (2 or more levels). METHODS A systematic review in the MEDLINE database was performed. Clinical studies including patients who had multilevel CDA were selected and included. Case reports and literature reviews were excluded. Articles were then grouped according to their main study objective: 1) studies comparing multilevel CDA versus ACDF; 2) studies comparing single-level CDA versus multilevel CDA; and 3) multilevel CDA after a previous cervical spine surgery. RESULTS Fourteen articles met all inclusion criteria. The general conclusions were that multilevel CDA was at least as safe and effective as ACDF, with preservation of cervical motion when compared with ACDF and potentially with fewer reoperations expected in most of the studies. Multilevel CDAs are clinically effective as single-level surgeries, with good clinical and radiological outcomes. Some studies reported a higher incidence of heterotopic ossification in multilevel CDA when compared with single-level procedures, but without clinical relevance during the follow-up period. A CDA may be indicated even after a previous cervical surgery in selected cases. CONCLUSIONS The current literature supports the use of multilevel CDA. Caution is necessary regarding the more restrictive indications for CDA when compared with ACDF. Further prospective, controlled, multicenter, and randomized studies not sponsored by the device manufactures are desirable to prove the superiority of CDA surgery over ACDF as the treatment of choice for CDD in selected cases.

Adjacent segment pathology: natural history or effect of anterior cervical discectomy and fusion? A 10-year follow-up radiological multicenter study using an evaluation scale of the ageing spine.

PURPOSE: Aim of this study is to compare late degenerative MRI changes in a subset of patients operated on with ACDF to a second subset of patients presenting indication to ACDF but never operated on. METHODS: Patients from both subgroups received surgical indication according to the same criteria. Both subgroups underwent a cervical spine MRI in 2004-2005 and 10 years later in 2015. These MRI scans were retrospectively evaluated with a cervical spine ageing scale. RESULTS: Comparing the two subset of patients both suffering from clinically relevant single-level disease returns no statistically significant difference in the degenerative condition of posterior ligaments, presence of degenerative spondylolisthesis, foraminal stenosis, diameter of the spinal canal, Modic alteration, and intervertebral discs degeneration at 10-year follow-up. CONCLUSIONS: The adjacent segment degeneration represents, in the present cohort, a result of the natural history of cervical spondylosis rather than a consequence of fusion.

Clinical and radiological analysis of Bryan cervical disc arthroplasty: eight-year follow-up results compared with anterior cervical discectomy and fusion.

PURPOSE: Bryan cervical disc arthroplasty has been reported with satisfactory short- and medium-term clinical results. However, the long-term clinical and radiographic outcomes are seldom reported. The purpose of this study was to compare the eight-year follow-up results in patients who underwent Bryan disc arthroplasty with patients received ACDF, and assess the incidence of heterotopic ossification (HO) and its effect on clinical outcome and mobility of the device. METHODS: Thirty-one patients underwent Bryan disc arthroplasty, and 35 patients underwent ACDF were included in the study. The Japanese Orthopedic Association (JOA) scores, neck disability index (NDI), visual analogue scale (VAS) of neck and arm pain, and the radiographs were used to evaluate the outcomes. The heterotopic ossification (HO) was determined by CT scan and was classified into three subgroups to compare the related effect. Adjacent segment degeneration (ASD) was also observed. RESULTS: At final follow-up, there were no significant differences in JOA scores between two groups, but the improvement in NDI and neck or arm VAS were significantly greater in the Bryan disc cohort. The range of motion at the index level was 7.0° in Bryan group, while 100 % bone fusion were achieved in ACDF group. HO was observed in 18 (51.4 %) levels. There were more restricted movement of the prosthesis and slight higher rate of axial pain in patients with severe-HO (grade III and IV). Fourteen (28.6 %) levels developed ASD in Bryan group, which was significantly lower than that (58.6 %) in ACDF group. CONCLUSIONS: At eight year follow-up, the clinical and radiographic outcomes of Bryan cervical disc arthroplasty compared favorably to those of ACDF. It avoided accelerated adjacent segment degeneration by preserving motion. However, severe HO restricted the ROM of the index levels and maybe associated with post-operative axial pain.

Dynamic cervical stabilization: a multicenter study.

PURPOSE: The dynamic cervical implant (DCI) is a novel motion-preserving concept for the treatment of degenerative cervical disorders. The aim of this prospective clinical study was to validate the concept and analyse clinical and radiological performance of the implant. MATERIALS/METHODS: One hundred seventy-five consecutive patients with degenerative cervical disorders, median age, 47 years, were treated with discectomy and DCI, and followed for 2 years. Clinical outcome was evaluated with the Neck Disability Index (NDI), the SF-12, and visual analogue scale (VAS) assessment of arm and neck pain. Range of motion (ROM) and cervical alignment were analysed using radiographic imaging. RESULTS: All clinical outcome measures--VAS neck and arm pain, NDI, and SF-12 mental and physical component summaries--improved significantly after surgery (each p < 0.001) and remained stable over the whole observation period. The ROM (flexion/extension) at the level treated with DCI was slightly reduced, but no significant changes could be verified at the adjacent levels. Six surgery or device-related adverse events were documented during the study. CONCLUSIONS: Good clinical and excellent radiological outcomes demonstrate that DCI is a safe and efficient treatment option in patients with degenerative cervical disorders.

Anterior cervical hybrid constructs reduce superior adjacent segment burden compared to multilevel anterior cervical discectomy and fusion.

Background: Traditional surgical treatment for symptomatic cervical degenerative disc disease is anterior cervical discectomy and fusion (ACDF), yet the increased risk of adjacent segment degeneration (ASD) requiring additional surgery exists and may result in limiting long-term surgical success when it occurs. Disc arthroplasty can preserve or restore physiologic range of motion (ROM), decreasing adjacent level stress and subsequent surgery. For patients with multilevel pathology requiring at least a 1-level fusion, interest is growing in anterior cervical hybrid (ACH) surgery as a partial motion-preserving procedure to decrease the adjacent level burden. This radiographic study compares postoperative superior adjacent segment motion between ACH and ACDF. Secondarily, total global motion, construct motion, inferior adjacent segment motion, and sagittal alignment parameters were compared. Methods: This is a single-center, multi-surgeon, retrospective cohort study of 2- and 3-level ACH and ACDF cases between 2013 and 2021. Degrees of motion were analyzed on flexion/extension views using Cobb angles to measure global (C2-C7) construct and adjacent segment lordosis. Neutral lateral X-rays were analyzed for alignment parameters, including global lordosis, cervical sagittal vertical axis (cSVA), and T1 slope (T1S). Differences were determined by independent t-test and Fisher's exact test. Results: Of 100 patients, 38% were 2-level cases (47% ACH, 53% ACDF) and 62% were 3-level cases: (52% ACH, 48% ACDF). Postoperatively, superior adjacent segment motion increased with ACDF and decreased with ACH (-1.3°±5.3° ACH, 1.6°±4.6° ACDF, P=0.005). Postoperatively, the ACH group had greater ROM across the construct (16.3°±8.7° ACH, 4.7°±3.3° ACDF, P<0.001) and total global ROM (38.0°±12.8° ACH, 28.0°±11.1° ACDF, P<0.001). ACH resulted in a significant reduction of motion loss across the construct (-10.0°±11.7° ACH, -18.1°±10.8° ACDF, P<0.001). Postoperative alignment restoration was similar between both cohorts (-2.61°±8.36° ACH, 0.04°±12.24° ACDF, P=0.21). Conclusions: Compared to ACDF, hybrid constructs partially preserved motion across operative levels and had greater postoperative global ROM without increasing superior adjacent segment mobility or sacrificing alignment restoration. This supports the consideration of ACH in patients with multilevel degenerative cervical pathology requiring at least a 1-level fusion and suggests a propensity for long-term success by reducing the superior adjacent segment burden.

Validation of Neck Disability Index Severity among Patients Receiving One or Two-Level Anterior Cervical Surgery.

STUDY DESIGN: Retrospective cohort. PURPOSE: To evaluate the validity of established severity thresholds for Neck Disability Index (NDI) among patients undergoing anterior cervical discectomy and fusion (ACDF) or cervical disc arthroplasty (CDA). OVERVIEW OF LITERATURE: Few studies have examined the validity of established NDI threshold values among patients undergoing ACDF or CDA. METHODS: A surgical database was reviewed to identify patients undergoing cervical spine procedures. Demographics, operative characteristics, comorbidities, NDI, Visual Analog Scale (VAS), and 12-item Short Form (SF-12) physical and mental composite scores (PCS and MCS) were recorded. NDI severity was categorized using previously established threshold values. Improvement from preoperative scores at each postoperative timepoint and convergent validity of NDI was evaluated. Discriminant validity of NDI was evaluated against VAS neck and arm and SF-12 PCS and MCS. RESULTS: All 290 patients included in the study demonstrated significant improvements from baseline values for all patient-reported outcome measures (PROMs) at all postoperative timepoints (p<0.001) except SF-12 MCS at 2 years (p =0.393). NDI showed a moderate- to-strong correlation (r≥0.419) at most timepoints for VAS neck, VAS arm, SF-12 PCS, and SF-12 MCS (p<0.001, all). NDI severity categories demonstrated significant differences in mean VAS neck, VAS arm, SF-12 PCS, and SF-12 MCS at all timepoints (p<0.001, all). Differences between NDI severity groups were not uniform for all PROMs. VAS neck values demonstrated significant intergroup differences at most timepoints, whereas SF-12 MCS showed significantly different values between most severity groups. CONCLUSIONS: Neck disability is strongly correlated with neck and arm pain, physical function, and mental health and demonstrates worse outcomes with increasing severity. Previously established severity categories may be more applicable to pain than physical function or mental health and may be more uniformly applied preoperatively for cervical spine patients.

Biomechanical analysis of single- and double-level cervical disc arthroplasty using finite element modeling.

Recently, many different types of artificial discs have been introduced to persevere the biomechanical behavior of the cervical spine. This study compares the biomechanical behavior of single- and double-level cervical disc arthroplasty, that is "Prestige LP and Mobi-C" on the index and adjacent segment. A three-dimension finite element model of C2-C7 was developed and validated. In single-level prostheses, the Prestige LP or Mobi-C was implanted in the segment C5-C6, while the double-level arthroplasty was integrated at both segments C4-C5 and C5-C6 in the FE model. The intact FE and prosthesis-modified models were constrained from the inferior endplate of the vertebra C7 and applied a compressive load of 73.6 N with a moment load of 1 Nm on the odontoid process of the vertebra C2 to produce flexion/extension, lateral bending, and axial rotation. The prosthesis-modified model's range of motion and intradiscal pressure were determined and compared to the intact model. Also examined the impact of the prostheses on the stress at the bone-implant interface. The range of motion of the implanted segments in both single- and double-levels arthroplasty was increased while that of the adjacent segment of implanted segments decreased. The intradiscal pressure in both levels of arthroplasty was greater than in the intact model. In conclusion, Mobi-C's cervical prostheses could better preserve the normal range of motion and maintain intradiscal pressure than the Prestige LP.