Effect of intervertebral disc height on postoperative motion and clinical outcomes after Prodisc-C cervical disc replacement

Optimal Implant Sizing Using Machine Learning Is Associated With Increased Range of Motion After Cervical Disk Arthroplasty

BACKGROUND AND OBJECTIVES

Cervical disk arthroplasty (CDA) offers the advantage of motion preservation in the treatment of focal cervical pathology. At present, implant sizing is performed using subjective tactile feedback and imaging of trial cages. This study aims to construct interpretable machine learning (IML) models to accurately predict postoperative range of motion (ROM) and identify the optimal implant sizes that maximize ROM in patients undergoing CDA.

METHODS

Adult patients who underwent CDA for single-level disease from 2012 to 2020 were identified. Patient demographics, comorbidities, and outcomes were collected, including symptoms, examination findings, subsidence, and reoperation. Affected disk height, healthy rostral disk height, and implant height were collected at sequential time points. Linear regression and IML models, including bagged regression tree, bagged multivariate adaptive regression spline, and k-nearest neighbors, were used to predict ROM change. Model performance was assessed by calculating the root mean square error (RMSE) between predicted and actual changes in ROM in the validation cohort. Variable importance was assessed using RMSE loss. Area under the curve analyses were performed to identify the ideal implant size cutoffs in predicting improved ROM.

RESULTS

Forty-seven patients were included. The average RMSE between predicted and actual ROM was 7.6° (range: 5.8-10.1) in the k-nearest neighbors model, 7.8° (range: 6.5-10.0) in the bagged regression tree model, 7.8° (range: 6.2-10.0) in the bagged multivariate adaptive regression spline model, and 15.8° (range: 14.3-17.5°) in a linear regression model. In the highest-performing IML model, graft size was the most important predictor with RMSE loss of 6.2, followed by age (RMSE loss = 5.9) and preoperative caudal disk height (RMSE loss = 5.8). Implant size at 110% of the normal adjacent disk height was the optimal cutoff associated with improved ROM.

CONCLUSION

IML models can reliably predict change in ROM after CDA within an average of 7.6 degrees of error. Implants sized comparably with the healthy adjacent disk may maximize ROM.

Does Baseline Facet Arthropathy Influence Early Clinical and Radiographic Outcomes After Cervical Disc Replacement?

BACKGROUND AND OBJECTIVES

Severe facet arthropathy is generally a contraindication to undergoing cervical disc replacement (CDR) due to associated instability and potentially limited improvement in neck pain caused by arthropathy. This study evaluates the influence of facet arthropathy on radiographic/early clinical outcomes after CDR.

METHODS

One/two-level CDR patients from a single surgeon's prospectively maintained database created 2 cohorts based on facet arthropathy: grade 0-1 or 2-3 (milder/moderate arthropathy). Patient-reported outcome measures for neck disability, neck/arm pain, depressive burden, mental/physical health/function were obtained preoperatively and through final follow-up (average follow-up: 8.5 ± 6.5 months). Preoperative/postoperative radiographs measured segmental lordosis and C2-C7/segmental range of motion (ROM) and determined facet grade for each operative level. Demographic differences, perioperative variables, baseline patient-reported outcomes, and intercohort differences/changes for postoperative patient-reported/radiographic outcomes were determined.

RESULTS

Of 161 patients, 100 were in the milder arthropathy group. There were no differences in baseline patient-reported outcomes. Patients with moderate arthropathy reported superior 6-week 12-Item Veterans Rand Mental/Physical Composite Scores (P ≤ .047, all). By final follow-up, moderate patients reported better 12-Item Veterans Rand Mental/Physical Composite Scores/Patient-Reported Outcome Measurement Information System-Physical Function/Patient-Health Questionnaire-9 (P ≤ .049, all). Cohorts reported similar improvements in all patient-reported outcomes by 6 weeks/final follow-up. Those with more severe facet arthropathy had significantly shorter preoperative disc heights (P < .001). Accounting for baseline disc height differences, by final follow-up, moderate patients had lower segmental ROM (P = .036). There were no significant differences in radiographic measurement changes (P ≥ .264, all).

CONCLUSION

Postoperatively, patients with moderate facet arthropathy reported lower depressive burden, better mental health/physical function, and lower segmental ROM. However, this did not translate to inferior short-term clinical outcomes. Further study should be conducted on the relationship between clinical/radiographic outcomes in CDR patients with facet arthropathy.

Predictive Value of Cervical Degenerative Quantitative Scoring System on Postoperative Disc Height Loss After Cervical Disc Replacement

STUDY DESIGN

A retrospective study.

OBJECTIVE

In this study, a cervical degenerative quantitative scoring system was used to identify the risk factors for disc height loss after cervical disc replacement (CDR) and to verify their accuracy.

BACKGROUND

Disc height loss after CDR is drawing much attention. Preoperative cervical degeneration has been proven related to postoperative disc height loss but lacked quantitative verification.

PATIENTS AND METHODS

A total of 160 patients who underwent CDR with the Prestige-LP disc at our hospital between January 2011 and December 2016 were retrospectively reviewed. Disc height loss was defined as a reduction of more than 2 mm from postoperative to the final follow-up. A quantitative scoring system was used to evaluate preoperative degeneration on radiographs. Multivariate logistic regression was applied to determine predictive factors and calculate the logistic regression formula. Moreover, receiver operating characteristic curve analysis was conducted to obtain the optimal cutoff value and the area under the receiver operating characteristic curve [areas under the curve (AUC)].

RESULTS

Study subjects had a mean age of 43.51 ± 8.51 years, with a mean follow-up time of 60.14 ± 12.75 months. The overall incidence rate of disc height loss was 65.62%. Multivariate logistic regression analysis showed that endplate sclerosis ( P = 0.000) and low preoperative disc height ( P = 0.000) were independent risk factors for postoperative disc height loss. In addition, the calculated optimal cutoff point was 1 point of endplate sclerosis (AUC = 0.768) and 4.5 mm of preoperative disc height (AUC = 0.795). The regression formula established by multivariate logistic regression analysis was composed of preoperative disc height (odds ratio: 2.995, P = 0.000) and endplate sclerosis (odds ratio: 18.131, P = 0.000), with an AUC of 0.879.

CONCLUSIONS

Our findings suggest that a comprehensive preoperative assessment is essential when patients with apparent endplate sclerosis and low preoperative disc height are being considered for CDR.

One-Year Follow-Up Study on Assessing the Range of Segmental Motion and Clinical Outcomes Following Cervical Disc Arthroplasty for Treatment of Severe Cervical Disc Degeneration

BACKGROUND

Though previous studies have documented various clinical outcomes after cervical arthroplasty for degenerative cervical disc disease, none of them reported the impact of cervical arthroplasty on severe cervical disc degeneration (CDD).

METHODS

This retrospective cohort study included severe 40 CDD (C3-C7) patients who underwent single-level cervical arthroplasty using ProDisc-C between January 2017 and December 2019. After surgical intervention, the range of motion (ROM) was determined, whereas clinical outcomes were measured in terms of the Visual Analogue Scale (VAS) and Neck Disability Index (NDI) to evaluate neck pain and disability, respectively.

RESULTS

Compared to the mean preoperative ROM (6.57 ± 4.85°), the cervical dynamic ROM was increased 3 months after cervical arthroplasty, and the increment was maintained for at least 1 year. The increased ROM is attributed to the extension and not flexion components. The mean preoperative ROM of 6.57 ± 4.85° significantly increased to 11.67 ± 4.98° (P = 0.0005), 10.05 ± 5.18° (P = 0.0426) and 10.46 ± 4.73° (P = 0.0247) after 3 months, 6 months and 1 year, respectively. The extension ROM also revealed a similar trend. VAS for neck and arm decreased from 7.4 and 6.6 to 1.4 and 1.2, respectively. Consistently, the preoperative mean Neck Disability Index (NDI) score of 27.6 decreased to 14.6. We recorded a case of device subsidence, but without extrusion.

CONCLUSIONS

Cervical arthroplasty can improve clinical outcomes and restore ROM in severe CDD patients.

Does the sizing of current cervical disc arthroplasty systems match Chinese cervical anatomic dimensions?

Objective: The objectives of this study were to analyze the computed tomography (CT) scan imaging data of the cervical spine from healthy volunteers and to correlate the measurements to the dimensions of current cervical disc arthroplasty systems. Methods: A total of 130 participants (78 males and 52 females) with a mean age of 41.0 years (range 18.0-66.0 years) who had undergone computed tomography scans of the cervical spine were included. The linear parameters of the C3 to C7 levels, including anterior-posterior diameter (AP), middle disc height (DH), anterior disc height (ADH), posterior disc height (PDH) and center mediolateral diameter (ML), were measured. The analysis was conducted comparing different cervical levels, sexes, and age groups. Known dimensions from eight cervical disc arthroplasty systems were compared with the morphologic data. Results: A total of 520 vertebral segments were measured. The mean values for the measured parameters were as follows: anterior-posterior diameter 16.08 ± 1.84 mm, mediolateral diameter 16.13 ± 1.99 mm, anterior disc height 3.88 ± 1.11 mm, disc height 5.73 ± 1.00 mm, posterior disc height 2.83 ± 0.94 mm, and mediolateral diameter/anterior-posterior diameter 1.01 ± 0.13. All parameters except for posterior disc height were significantly different across the different cervical levels (p < 0.05). There were also significant sex differences in terms of the linear parameters. No differences were found in the majority of parameters among the different age groups (p > 0.05), except for anterior-posterior diameter at the C6/7 level. A comparison of the bone dimensions from the study data and the dimensions of the implants indicated the presence of a size mismatch in the currently available cervical disc prostheses. Conclusion: There is a large discrepancy between the cervical anatomical data of Chinese patients and the sizes of currently available prostheses. The dimensions collected in this study could be used to design and develop appropriate disc prostheses for Chinese patients.

Effect of Facet Tropism on Postoperative Cervical Range of Motion After Single-Level Cervical Disc Arthroplasty

STUDY DESIGN

Retrospective analysis.

OBJECTIVES

Cervical disc arthroplasty (CDA) was designed to replace the degenerated disc with the prosthesis to preserve cervical motion. The commonly used artificial discs are designed symmetric, whereas the facet joints were reported to be asymmetric in many people. This study aimed to evaluate the effect of facet tropism on the cervical range of motion (ROM) after single-level CDA using Prestige LP.

METHODS

A total of 90 patients who underwent single-level CDA using Prestige LP from 2012 to 2017 were retrospectively reviewed. Radiographs were taken at each time point to measure the C2-C7 ROM and the ROM at the surgical segment. The pre-operation CT scans were utilized to reconstruct and calculate the angular direction of facet joints with respect to transverse, coronal, and sagittal reference planes. Facet tropism above 7° was defined as facet joint asymmetry.

RESULTS

No significant difference was found in flexion-extension C2-C7 ROM or ROM at the surgical segment between patients with symmetric and asymmetric fact joints regarding the sagittal plane. Patients with coronal asymmetric facet joints had lower flexion-extension ROM at the surgical level. Patients with transverse asymmetric facet joints had both lower flexion-extension C2-C7 ROM and ROM at the surgical level. After CDA surgery, patients obtained good clinical outcomes including increased Japanese Orthopedic Association (JOA) and decreased Neck Disability Index (NDI) as well as Visual Analogue Scale (VAS).

CONCLUSION

The coronal and transverse tropism seemed to be correlated with decreased flexion-extension ROM after CDA using Prestige LP.

Comparison of Radiographic Reconstruction and Clinical Improvement between Artificial Cervical Disc Replacement and Anterior Cervical Discectomy and Fusion

Background

The surgical management of cervical degenerative disc degeneration (CDDD) has not reached a consensus. Artificial cervical disc replacement (ACDR) has been shown to be efficient in reducing symptoms after CDDD, although the topic remains highly controversial in this field. This study aimed to evaluate the effectiveness of ACDR on the treatment of CDDD on the aspect of radiographic reconstruction and clinical improvement compared with anterior cervical discectomy and fusion (ACDF).

Methods

This was a retrospective comparative study with 47 patients who underwent single-level ACDR and 46 patients who underwent single-level ACDF. The radiographic reconstruction was assessed by the cervical sagittal alignment parameters, consisting of two aspects, distance and angle, such as cervical sagittal vertical axis (cSVA), cervical lordosis (CL), T1 slope (T1s), and intervertebral space height (ISH). The clinical improvement was assessed by patient-related outcomes (PROs), consisting of two aspects, relief of axial neck pain and recovery of cervical dysfunction, measured through the Visual Analogue Scale (VAS), Neck Disability Index (NDI), and Japanese Orthopedic Association (JOA).

Results

Significant variations were achieved on aspects of radiographic reconstruction and clinical improvement after ACDR (P < 0.05), which were similar to that of the ACDF group (P < 0.05). A significantly larger postoperative range of motion (ROM) was found in patients less than 45 years of age in the ACDR group (P < 0.05). In addition, a significantly better postoperative JOA was found in patients with a preoperative ISH less than 4 mm in the ACDF group than that in the ACDR group (P < 0.05). Other than that mentioned above, no significant variations in radiographic and clinical outcomes were found between the two groups (P > 0.05).

Conclusions

Overall, this study showed that a similar capability in terms of radiographic reconstruction and clinical improvement was found between the two methods. Specific concerns should be analyzed while choosing between an ACDR and an ACDF. It should be pointed out that, based on our experience, if the patient is younger, ACDR is recommended; for patients with preoperative ISH less than 4 mm, ACDF is more recommended.

Effect of preoperative segmental range of motion on patient outcomes in cervical disc arthroplasty

Background

Cervical disc arthroplasty (CDA) has been demonstrated, in clinical trials, as an effective and safe treatment for patients diagnosed with radiculopathy and/or myelopathy. However, the current CDA indication criteria, based on the preoperative segmental range of motion (ROM), comprises a wide range of variability. Although the arthroplasty level preserved ROM averages 7°-9° after CDA, there are no clear guidelines on preoperatively limited or excessive ROM at the index level, which could be considered as suitable for CDA.

Methods

This was a retrospective study of patients who underwent CDA between January 2008 and October 2018 using Prestige-LP discs in our hospital. They were divided into the small-ROM (≤5.5°) and the large-ROM (> 12.5°) groups according to preoperatively index-level ROM. Clinical outcomes, including the Japanese Orthopedics Association (JOA), Neck Disability Index (NDI), and Visual Analogue Scale (VAS) scores, were evaluated. Radiological parameters, including cervical lordosis, disc angle (DA), global and segmental ROM, disc height (DH), and complications were measured.

Results

One hundred and twenty six patients, with a total of 132 arthroplasty segments were analyzed. There were 64 patients in the small-ROM and 62 in the large-ROM group. There were more patients diagnosed with cervical spondylosis in the small-ROM than in the large-ROM group (P = 0.046). Patients in both groups had significantly improved JOA, NDI, and VAS scores after surgery, but the intergroup difference was not significant. Patients in the small-ROM group had dramatic postoperative increase in cervical lordosis, global and segmental ROM (P < 0.001). However, there was a paradoxical postoperative decrease in global and segmental ROM in the large-ROM group postoperatively (P < 0.001). Patients in the small-ROM group had lower preoperative DH (P = 0.012), and a higher rate of postoperative heterotopic ossification (HO) (P = 0.037).

Conclusion

Patients with preoperatively limited segmental ROM had severe HO, and achieved similar postoperative clinical outcomes as patients with preoperatively excessive segmental ROM. Patients with preoperatively limited segmental ROM showed a postoperative increase in segmental mobility, which decreased in patients with preoperatively excessive segmental ROM.

A Retrospective Review of Radiographic and Clinical Findings from the M6 Cervical Prosthesis

Study Design

Retrospective clinical study.

Purpose

To evaluate clinical results of the M6 cervical prosthesis.

Overview of Literature

Cervical disk prostheses have been developed to preserve motion and reduce degeneration in adjacent segments in degenerative disk diseases.

Methods

A retrospective evaluation was performed on 43 patients who received the M6 cervical disk prosthesis between 2012 and 2016. Standard and dynamic radiographs, computed tomography, and magnetic resonance imaging were used to evaluate all the patients preoperatively and postoperatively. The Neck Disability Index (NDI) and Visual Analog Scale (VAS) scores were examined in evaluating the clinical and functional results of patients with collapsed disk herniation who had received the M6 cervical prosthesis and to evaluate whether the core structure of the prosthesis protects motion.

Results

The mean follow-up period was 34.12±6.70 months. Radiologically, the preoperative cervical segment ROM was measured as a mean of 5.77°±2.19° preoperatively and 8.49°±2.37° at the inal postoperative follow-up examination. In the patients with a preoperative disk height of <4 mm, the segmental ROM increased from 4.53°±2.79° preoperatively to 7.2°±3.18° postoperatively. In the patients with a preoperative disk height of >4 mm, the cervical segment ROM increased from 6.4°±1.45° preoperatively to 8.6°±2.02° at the inal postoperative follow-up examination. The NDI scores reduced from 53.86±9.77 preoperatively to 22.69±7.26 postoperatively and the VAS scores reduced from 8.74±0.58 to 1.88±1.14. During follow-up in any patient, no collapse of the levels at which surgery was performed was observed. No heterotopic ossiication or implant failure was recorded in any patient during the follow-up period.

Conclusions

The M6 new-generation cervical disk prosthesis had few complications. No heterotopic ossiication was observed in any patient, and lexion-extension ROM was maintained in all the patients, indicating the M6 prosthesis as a promising alternative.

Cervical disc arthroplasty with Prestige-LP for the treatment of contiguous 2-level cervical degenerative disc disease: 5-year follow-up results

The objective of this study is to present the long-term results and to evaluate the safety and effectiveness of the Prestige-LP cervical disc replacement in treatment of patients with symptomatic 2-level cervical degenerative disc disease.Twenty-four patients with 48 Prestige-LP disc were analyzed before surgery and at 1 week, 3 months, 6 months, 12 months, 24 months, and 60 months after surgery. Clinical assessments included 36-Short Form (SF-36), Japanese Orthopedic Assessment (JOA), visual analog scale (VAS), and Neck Disability Index (NDI) scores. Radiographic assessments included cervical lordosis (CL), disc height (DH), range of motion (ROM) of the total cervical spine, functional spinal unit (FSU) as well as upper and lower operated segment. Complications at the 5-year follow-up were collected as well.Mean follow-up period was 64.22 months. There was clinical improvement in terms of SF-36, JOA, NDI, and VAS from the preoperative to the final follow-up (P < .05). Overall, ROM of the total cervical spine, FSU, and upper and lower operated segment were maintained during the follow-up. Statistically significant (P < .05) improvements in the trend of CL and DH were noted at the follow-up. Eight patients were observed an appearance of heterotopic ossification at the 5-year follow-up, with 6 patients appeared at Class II and 2 patients at Class III. Adjacent segment degeneration assessed by radiographic evidence was found in 2 patients.Two-level cervical disc arthroplasty with Prestige-LP showed significant improvement in clinical outcomes at 5 years. It not only effectively preserves the motion of both total cervical spine and operated segments, but also restores normal CL and DH up to 5 years postoperation.

Long-term Evaluation of Cervical Disc Arthroplasty with the Mobi-C© Cervical Disc: A Randomized, Prospective, Multicenter Clinical Trial with Seven-Year Follow-up

Background

Cervical total disc replacement (TDR) is an increasingly accepted procedure for the treatment of symptomatic cervical degenerative disc disease. Multiple Level I evidence clinical trials have established cervical TDR to be a safe and effective procedure in the short-term. The objective of this study is to provide a long-term assessment of TDR versus anterior discectomy and fusion for the treatment of one- and two-level disc disease.

Methods

This study was a continuation of a prospective, multicenter, randomized, US FDA IDE clinical trial comparing cervical TDR with the Mobi-C^© Cervical Disc versus ACDF through 7 years follow-up. Inclusion criteria included a diagnosis of symptomatic cervical degenerative disc disease at one or two cervical levels. TDR patients were treated using a Mobi-C^© artificial disc (Zimmer Biomet, Austin TX, USA). ACDF with allograft and anterior plate was used as a control treatment. Outcome measures were collected preoperatively and postoperatively at 6 weeks, at 3, 6, 12, 18 months, annually through 60 months, and at 84 months. Measured outcomes included Overall success, Neck Disability Index (NDI), VAS neck and arm pain, segmental range of motion (ROM), patient satisfaction, SF-12 MCS/PCS, major complications, and subsequent surgery rate. The primary endpoint was an FDA composite definition of success comprising clinical improvement and an absence of major complications and secondary surgery events.

Results

A total of 599 patients were enrolled and treated, with 164 treated with one-level TDR, 225 treated with two-level TDR, 81 treated with one-level ACDF, and 105 treated with two-level ACDF. At seven years, follow-up rates ranged from 73.5% to 84.4% (overall 80.2%).The overall success rates of two level TDR and ACDF patients were 60.8% and 34.2%, respectively (p<0.0001). The overall success rates of one level TDR and ACDF patients were 55.2% and 50%, respectively (p>0.05). Both the single and two level TDR and ACDF groups showed significant improvement from baseline NDI scores, VAS neck and arm pain scores, and SF-12 MCS/PCS scores (p<0.0001). In the single level cohort, there was an increased percentage of TDR patients who reported themselves as "very satisfied" (TDR 90.9% vs ACDF 77.8%; p= 0.028). There was a lower rate of adjacent level secondary surgery in the single level TDR patients (3.7%) versus the ACDF patients (13.6%; p = 0.007).In the two level TDR group, the NDI success rate was significantly greater in the TDR group (TDR: 79.0% vs. ACDF: 58.0%; p=0.001). There was significantly more improvement in NDI change score at 7 years in the TDR patients versus ACDF. The TDR group had a significantly higher rate of patients who were "very satisfied" with their treatment compared to the ACDF group (TDR: 85.9% vs. ACDF: 73.9%). The rate of subsequent surgery at the index level was significantly lower in the TDR group compared to the ACDF group (TDR: 4.4% vs. ACDF: 16.2%; p=0.001). The rate of adjacent level secondary surgery was significantly lower in the two level TDR (4.4%) patients compared to the ACDF (11.3%; p=0.03) patients. In both single and two level cohorts, the percentage of patients with worse NDI (2.5%-3.8% of two level surgeries and 1.2%-2.5% of single level surgeries) or worse neck pain (5%-6.8% of the two level surgeries and 1.3% - 3.8% of the single level surgeries) was strikingly low in both groups but trended lower in the TDR patients.

Conclusions

At seven years, the composite success analysis demonstrated clinical superiority of two level TDR over ACDF and non-inferiority of single level TDR versus ACDF. There were lower rates of secondary surgery and higher adjacent level disc survivorship in both groups. Both surgeries were remarkably effective in alleviating pain relative to baseline and the rate of patients with worse disability or neck pain was surprisingly low. Overall, greater than 95% of patients (from both groups) who underwent TDR and 88% of patients who underwent ACDF were "very satisfied" at seven years. The differences in clinical effectiveness of TDR versus ACDF becomes more apparent as treatment increases from one to two levels, indicating a significant benefit for TDR over ACDF for two-level procedures.

Ethical Standards

The Mobi-C Clinical Trial (ClinicalTrials.gov registration number: NCT00389597) was conducted at 24 sites in the US and was approved by the Institutional Review Board, Research Ethics Committee, or local equivalent of each participating site.

Level of Evidence

1.

How to choose when implants of adjacent height both fit the disc space properly in single-level cervical artificial disc replacement

In cervical artificial disc replacement (C-ADR), sometimes we encountered with such cases that implants of adjacent height both fit the target disc space properly. No study was available discussing the choice of implant height and the clinical outcomes under such circumstance. The purpose of this study was to evaluate the impact of different implant heights on the clinical outcomes and radiographic results when the implants of adjacent height both fit the disc space properly. This retrospective study included 34 patients underwent single-level C-ADR at the C5-C6 level at our institution. In these 34 patients, implant with either 5 mm height or 6 mm height fit the surgical level properly without overstretching the disc space or the facet joint space. Clinical outcomes were evaluated using the Japanese Orthopedic Association score, visual analog scale (VAS), and Neck Disability Index. Radiographic assessments were conducted on static and dynamic radiographs for the determination of the disc space height, intersegmental range of motion (ROM), and the ROM of the functional spinal unit (FSU) at the surgical level. The baseline information of the patients, such as age, gender, weight, follow-up time, and diagnosis, was similar between the 2 groups (P > .05). Postoperative mean VAS in group B was significantly lower than that in group A (2.1 ± 0.7 vs. 2.7 ± 1.0, P < .05). The mean VAS decrease in group B was significantly larger than that in group A (5.3 ± 0.8 vs. 4.6 ± 1.1, P < .05). Significant difference was found in the postoperative disc height of the surgical segment between the 2 groups (6.4 ± 0.4 mm vs. 7.5 ± 0.5 mm, P < .05). No significant differences were noted in the intersegmental ROM and ROM of the FSU between the 2 groups both before the surgery and at the last follow-up (P > .05). No hypermobility or instability was observed in these patients. Our results suggested that when implants of adjacent height both fit the disc space properly, using the larger implant could result in better pain relief without the risk of segmental hypermobility in patients underwent single-level C-ADR at the C5-C6 level.

Analysis of the Factors That Could Predict Segmental Range of Motion After Cervical Artificial Disk Replacement: A 7-Year Follow-up Study

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

To identify the potential preoperative factors and surgical technique factors that are associated with long-term range of motion (ROM) after surgery. Further, this article aimed to guide selection of patients with cervical artificial disk replacement and a fine surgical technique.

SUMMARY OF BACKGROUND DATA

Segmental ROM is the most important parameter concerning cervical kinematics after a cervical artificial disk replacement. There are few researches regarding the influencing factors on postoperative ROM, and consistent results have not yet been reported.

METHODS

The cohort comprised a total of 68 disks implanted into 57 patients who were retrospectively analyzed. The mean follow-up period was 84.1 months. Segmental ROM and other useful parameters were measured using lateral neutral, extension, and flexion radiographs, which were obtained preoperatively, 3 months after surgery, and at last follow-up. Preoperative CT and clinical assessment were also used. To find out associated factors, the patients were divided into 2 groups according to the segmental ROM at last follow-up.

RESULTS

After surgery, the clinical outcomes were satisfactory. The segmental ROM at last follow-up (7.8±4.3 degrees) was preserved without significant change from preoperative ROM (8.8±3.8 degrees). The patients who had a better segmental ROM after surgery were found to have a higher preoperative segmental ROM, a younger age, a better disk insertion angle, and disk insertion depth. These 4 factors were identified as independent risk factors (P=0.027, 0.017, 0.036, and 0.046, respectively) for long-term ROM.

CONCLUSIONS

The postoperative long-term, segmental ROM was well preserved and found to be affected by the preoperative segmental ROM, patient's age, disk insertion angle, and disk insertion depth.

Are Collapsed Cervical Discs Amenable to Total Disc Arthroplasty?: Analysis of Prospective Clinical Data With 2-Year Follow Up

STUDY DESIGN

Analysis of prospectively collected radiographic data.

OBJECTIVE

To investigate the influence of preoperative index-level range of motion (ROM) and disc height on postoperative ROM after cervical total disc arthroplasty (TDA) using compressible disc prostheses.

SUMMARY OF BACKGROUND DATA

Clinical studies demonstrate benefits of motion preservation over fusion; however, questions remain unanswered as to which preoperative factors have the ability to identify patients who are most likely to have good postoperative motion, which is the primary rationale for TDA.

METHODS

We analyzed prospectively collected data from a single-arm, multicenter study with 2-year follow up of 30 patients with 48 implanted levels. All received compressible cervical disc prostheses of 6 mm-height (M6C, Spinal Kinetics, Sunnyvale, CA). The influence of index-level preoperative disc height and ROM (each with two levels: below-median and above-median) on postoperative ROM was analyzed using 2 x 2 ANOVA. We further analyzed the radiographic outcomes of a subset of discs with preoperative height less than 3 mm, the so-called "collapsed" discs.

RESULTS

Shorter (3.0 ± 0.4 mm) discs were significantly less mobile preoperatively than taller (4.4 ± 0.5 mm) discs (6.7° vs. 10.5°, P = 0.01). The postoperative ROM did not differ between the shorter and taller discs (5.6° vs. 5.0°, P = 0.63). Tall discs that were less mobile preoperatively had significantly smaller postoperative ROM than short discs with above-median preoperative mobility (P < 0.05). The "collapsed discs" (n = 8) were less mobile preoperatively compared with all discs combined (5.1° vs. 8.6°, P < 0.01). These discs were distracted to more than two times the preoperative height, from 2.6 to 5.7 mm, and had significantly greater postoperative ROM than all discs combined (7.6° vs. 5.3°, P < 0.05).

CONCLUSION

We observed a significant interaction between preoperative index-level disc height and ROM in influencing postoperative ROM. Although limited by small sample size, the results suggest discs with preoperative height less than 3 mm may be amenable to disc arthroplasty using compressible disc prostheses.

LEVEL OF EVIDENCE

2.

A Comparison of Zero-Profile Devices and Artificial Cervical Disks in Patients With 2 Noncontiguous Levels of Cervical Spondylosis

STUDY DESIGN

A prospective randomized and controlled study of 30 patients with 2 noncontiguous levels of cervical spondylosis.

OBJECTIVE

To compare the clinical outcome between zero-profile devices and artificial cervical disks for noncontiguous cervical spondylosis.

SUMMARY OF BACKGROUND DATA

Noncontiguous cervical spondylosis is an especial degenerative disease of the cervical spine. Some controversy exists over the choice of surgical procedure and fusion levels for it because of the viewpoint that the stress at levels adjacent to a fusion mass will increase. The increased stress will lead to the adjacent segment degeneration (ASD). According to the viewpoint, the intermediate segment will bear more stress after both superior and inferior segments' fusion. Cervical disk arthroplasty is an alternative to fusion because of its motion-preserving. Few comparative studies have been conducted on arthrodesis with zero-prolife devices and arthroplasty with artificial cervical disks for noncontiguous cervical spondylosis.

METHODS

Thirty patients with 2 noncontiguous levels of cervical spondylosis were enrolled and assigned to either group A (receiving arthroplasty using artificial cervical disks) and group Z (receiving arthrodesis using zero-profile devices). The clinical outcomes were assessed by the mean operative time, blood loss, Japanese Orthopedic Association (JOA) score, Neck Dysfunction Index (NDI), cervical lordosis, fusion rate, and complications.

RESULTS

The mean follow-up was 32.4 months. There were no significant differences between the 2 groups in the blood loss, JOA score, NDI score, and cervical lordosis except operative time. The mean operative time of group A was shorter than that of group Z. Both the 2 groups demonstrated a significant increase in JOA score, NDI score, and cervical lordosis. The fusion rate was 100% at 12 months postoperatively in group Z. There was no significant difference between the 2 groups in complications except the ASD. Three patients had radiologic ASD at the final follow-up in group Z, and none in group A.

CONCLUSIONS

Both zero-prolife devices and artificial cervical disks are generally effective and safe in the treatment of 2 noncontiguous levels of cervical spondylosis. However, in view of occurrence of the radiologic ASD and operative time, we prefer to artificial cervical disks if indications are well controlled.

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.

Clinical and radiographic outcomes of cervical disc replacement with a new prosthesis

BACKGROUND CONTEXT

Anterior cervical discectomy and interbody fusion was a classical treatment for cervical degenerative disc disease (CDDD). However, the rigid fusion also leads to a reduction in normal cervical spine motion and to increased biomechanical stress at adjacent levels, which in turn accelerates degenerative changes of the discs at these levels. Cervical disc replacement (CDR) is a new technology with the aim of addressing the limitations of fusion procession and preserving motion at the treated level. Discover prosthesis (DePuy Spine, Raynham, MA, USA) is a new type artificial disc and there are few reports about it.

PURPOSE

The purpose of this study was to analyze the primary clinical and radiographic outcomes of CDR with Discover prosthesis to treat mono- or bi-segment CDDD in a Chinese population.

STUDY DESIGN

The study design was prospective and single-center clinical trial of the Discover prosthesis in the treatment of patients with mono- or bi-segment CDDD.

PATIENTS SAMPLE

Seventy-nine patients with 102 Discover prosthesis arthroplasty performed (56 mono-segment and 23 bi-segment) were evaluated.

OUTCOME MEASURES

Clinical outcomes based on Japanese Orthopaedic Association (JOA), visual analog scale (VAS) pain score, and Odom's scale and radiographic outcomes including the anterior disc heights (ADH), posterior disc heights (PDH), range of motion, and performance of heterotopic ossification (HO) of the operative segment were assessed.

METHODS

Clinical and radiographic follow-up was performed. Preoperative and postoperative ADH, PDH, and range of motion were measured from lateral and flexion-extension radiographs. The paired t test was used to assess the difference of clinical and radiographic outcomes before and after operation. The performance of HO was observed by two independent MD.

RESULTS

The mean follow-up time for all the patients was 31.6 months, ranging from 24 to 43 months. Mean preoperative JOA score was 9.5, and VAS overall pain score was 7.2. At 2-, 6-, 12-, and 24-month follow-up, the mean JOA score was 14.1, 14.7, 15.3, and 14.9, whereas the mean VAS overall pain score was 1.9, 1.7, 1.8, and 1.4, respectively. Mean JOA and VAS scores showed statistical improvements in the postoperative period. Seven patients had mild dysphagia within the first month after operation. According to Odom's scale, 52 patients had excellent outcomes, 25 patients had good outcomes, and 2 patients had fair outcomes at 2-year follow-up. The Mean preoperative ADH and PDH of the operative segment were 4.9 mm and 3.1 mm. Compared with preoperative, there were significantly increased and maintenance well at 2- (7.5 mm, 5.1 mm), 6- (7.5 mm, 5.0 mm), 12- (7.4 mm, 4.9 mm) and 24-month (7.2 mm, 5.0 mm) follow-up. Range of motion of the operative segment in the postoperative follow-up was slightly increased than the preoperative follow-up but not statistically significant. Heterotopic ossification was presented in six replaced levels at 1-year follow-up including 4 Grade I and 2 Grade II and 18 replaced levels at the follow-up more than 2 years including 8 grade I and 10 grade II. No prosthesis subsidence or excursion was identified.

CONCLUSIONS

The use of Discover prostheses in our study resulted in satisfactory clinical and radiographic outcomes. The prostheses can restore and maintain interbody height, while preserve the motion of the treated segment. Although the results of this study demonstrate initial safety and effectiveness in a Chinese population, we need further studies to know more about the impact of CDR with Discover prosthesis, especially on HO and adjacent segment degeneration.

Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients

Object

Cervical arthroplasty with an artificial disc (AD) has emerged as an alternative to anterior cervical discectomy and fusion (ACDF) for the management of cervical spondylosis. This study aims to provide 3D motion analysis data comparing patients after ACDF and AD replacement.

Methods

Ten patients who underwent C5–6 ACDF and 7 who underwent C5–6 AD replacement were enrolled. Using biplanar fluoroscopy and a model-based track technique (accurate up to 0.6 mm and 0.6°), motion analysis of axial rotation and flexion-extension of the neck was performed. Three nonoperative segments (C3–4, C4–5, and C6–7) were assessed for both intervertebral rotation (coronal, sagittal, and axial planes) and facet shear (anteroposterior and mediolateral).

Results

There was no difference in total neck motion comparing ACDF and AD replacement for neck extension (43.3° ± 10.2° vs 44.3° ± 12.6°, p = 0.866) and rotation (36.0° ± 6.5° vs 38.2° ± 9.3°, p = 0.576). For extension, when measured as a percentage of total neck motion, there was a greater amount of rotation at the nonoperated segments in the ACDF group than in the AD group (p = 0.003). When comparing specific motion segments, greater normalized rotation was seen in the ACDF group at C3–4 (33.2% ± 4.9% vs 26.8% ± 6.6%, p = 0.036) and C6–7 (28.5% ± 6.7% vs 20.5% ± 5.5%, p = 0.009) but not at C4–5 (33.5% ± 6.4% vs 31.8% ± 4.0%, p = 0.562). For neck rotation, greater rotation was observed at the nonoperative segments in the ACDF group than in the AD group (p = 0.024), but the differences between individual segments did not reach significance (p ≥ 0.146). Increased mediolateral facet shear was seen on neck extension with ACDF versus AD replacement (p = 0.008). Comparing each segment, C3–4 (0.9 ± 0.5 mm vs 0.4 ± 0.1 mm, p = 0.039) and C4–5 (1.0 ± 0.4 mm vs 0.5 ± 0.2 mm, p = 0.022) showed increased shear while C6–7 (1.0 ± 0.4 mm vs 1.0 ± 0.5 mm, p = 0.767) did not.

Conclusions

This study illustrates increased motion at nonoperative segments in patients who have undergone ACDF compared with those who have undergone AD replacement. Further studies will be required to examine whether these changes contribute to adjacent-segment disease.

Cervical arthroplasty with Discover prosthesis: clinical outcomes and analysis of factors that may influence postoperative range of motion

PURPOSE

The aim of this current study was to analyze the clinical outcomes after Discover cervical disc replacement and its effects on maintaining cervical lordosis and range of motion (ROM). The possible factors influencing postoperative ROM were analyzed.

METHOD

27 men and 28 women with a mean age of 46.4 ± 8.7 years were prospectively followed up for 2 years. Clinical outcomes were assessed using Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), visual analog scale (VAS) and Odom's criteria. Radiographic information including segment and overall alignment, functional spinal unit (FSU) and overall ROM, and disc heights were prospectively collected during the follow-up. The correlations between the postoperative FSU ROM at last follow-up and influencing factors were analyzed.

RESULTS

Mean NDI, JOA and VAS scores showed statistical improvements at last follow-up. Anterior migration of the prosthesis was detected in six cases. Heterotopic ossification was observed in ten patients. Mean FSU angle, endplate angle of the treated level and mean overall cervical alignment were all improved significantly at last follow-up (P < 0.001). However, mean FSU ROM of the treated segment significantly decreased postoperatively (P = 0.008), while mean overall ROM showed no significant differences. A significant correlation was found between preoperative FSU ROM and postoperative FSU ROM by the Pearson correlation coefficient (r = 0.325, P = 0.034). Multiple linear regression analysis confirmed that preoperative FSU ROM contributed independently to a model with a coefficient of determination of 0.37 (P = 0.034).

CONCLUSIONS

In the 2 years follow-up, the Discover cervical disc arthroplasty has provided satisfactory clinical outcomes. It was able to substantially restore segment and overall cervical alignment while partially maintaining segment and overall cervical ROM. Additionally, we found that postoperative FSU ROM positively correlated with preoperative FSU ROM.

Cervical intervertebral disc replacement

Symptomatic adjacent-level disease after cervical fusion has led to the development and testing of several disc-replacement prostheses. Randomized controlled trials of cervical disc replacement (CDR) compared with anterior cervical discectomy and fusion (ACDF) have demonstrated at least equivalent clinical results for CDR with similar or lower complication rates. Biomechanical, kinematic, and radiographic studies of CDR reveal that the surgical level and adjacent vertebral level motion and center of rotation more closely mimic the native state. Lower intradiscal pressures adjacent to CDR may help decrease the incidence of adjacent spinal-level disease, but long-term follow-up is necessary to evaluate this theory.

Hybrid surgery of multilevel cervical degenerative disc disease : review of literature and clinical results

Objective

In the present study, we evaluated the effect, safety and radiological outcomes of cervical hybrid surgery (cervical disc prosthesis replacement at one level, and interbody fusion at the other level) on the multilevel cervical degenerative disc disease (DDD).

Methods

Fifty-one patients (mean age 46.7 years) with symptomatic multilevel cervical spondylosis were treated using hybrid surgery (HS). Clinical [neck disability index (NDI) and Visual Analogue Scale (VAS) score] and radiologic outcomes [range of motion (ROM) for cervical spine, adjacent segment and arthroplasty level] were evaluated at routine postoperative intervals of 1, 6, 12, 24 months. Review of other similar studies that examined the HS in multilevel cervical DDD was performed.

Results

Out of 51 patients, 41 patients received 2 level hybrid surgery and 10 patients received 3 level hybrid surgery. The NDI and VAS score were significantly decreased during the follow up periods (p<0.05). The cervical ROM was recovered at 6 and 12 month postoperatively and the mean ROM of inferior adjacent segment was significantly larger than that of superior adjacent segments after surgery. The ROM of the arthoplasty level was preserved well during the follow up periods. No surgical and device related complications were observed.

Conclusion

Hybrid surgery is a safe and effective alternative to fusion for the management of multilevel cervical spondylosis.

Motion analysis of single-level cervical total disc arthroplasty: a meta-analysis

OBJECTIVE

The purpose of this review was to investigate whether cervical total disc arthroplasty (CTDA) preserves motion of the treated level and what its effect is on adjacent segments.

METHODS

Relevant published reports were collected from PubMed, Medline and Cochrane library. The original studies were considered eligible only if the range of motion (ROM) of the index or adjacent level had been investigated. A meta-analysis was then performed on the collected data. Statistical heterogeneity across the various trials was tested using Cochran's Q statistic and I (2) ; in the case of heterogeneity, a random effect model was used.

RESULTS

The weighted mean differences (WMDs) of the index level were 0.34 (95% confidence interval [CI], -0.53∼1.21, P = 0.440) and 0.23 (95% CI, -1.92∼2.38, P = 0.834) in all included studies and randomized control trials (RCTs), respectively. The WMDs of the cranial adjacent levels, caudal adjacent levels and whole cervical spines were 1.01 (95% CI, 0.55∼1.47, P = 0.000), 1.10 (95% CI, 0.61∼1.59, P = 0.000) and 3.40 (95% CI, -6.02∼12.82, P = 0.479), respectively.

CONCLUSION

These findings suggest that the protective effect against adjacent segment degeneration provided by cervical arthroplasty might not be as good as has been believed. Long-term supporting evidence is still needed.

The effect of remodeling on the kinematics of the malpositioned disc allograft transplantation

STUDY DESIGN

A postoperative biomechanical study.

OBJECTIVE

This study aimed to assess whether the mal-alignment of the intervertebral disc (IVD) allograft during transplantation would negatively affect the biomechanics of the spinal segment.

SUMMARY OF BACKGROUND DATA

Studies of human IVD allograft transplantation have observed remodeling of the allograft implant, suggesting that the remodeling of the allograft may be able to restore the natural mechanics of the IVD.

METHODS

Eighteen male goats (age: 6-12 months; weight: 25-30 kg) were randomly assigned into control (n = 5), aligned (n = 5), or malpositioned (n = 5) groups. Transplantation of a size-matched cryopreserved IVD allograft was performed in the lumbar region (L4-L5) after disc excision. In the aligned group, the IVD allografts were placed aligned and flush with the anterior vertebral margin. In the malpositioned group, the allografts were placed proud anteriorly by 25% of the anterior-posterior diameter of the allograft. The lumbar spines were harvested at 6 months after transplantation. Three-dimensional kinematic assessment of the lumbar spines was performed using an MTS testing machine and an optoelectronic camera system. The range of motion, neutral zone, and instantaneous axis of rotation were calculated.

RESULTS

No significant difference in range of motion was noted between the groups in flexion, axial rotation, and lateral bending. Significance was noted with extension range of motion as detected in both the aligned (17.51 ± 1.97 degrees; P = 0.019) and malpositioned groups (16.61 ± 2.35 degrees; P = 0.027) compared with the control (10.11 ± 1.03 degrees). No significant difference was detected in the neutral zone between the groups. Significant difference in the instantaneous axis of rotation orientation between the malpositioned and control groups was detected in the sagittal plane during lateral bending motion (P = 0.036).

CONCLUSION

Kinematic parameters in both the aligned and malpositioned allograft were similar to those of the intact spine. This suggests that precise positioning of the IVD allograft may not be an essential factor affecting the biomechanics of the spinal segment after transplantation.

Cervical disc arthroplasty versus fusion for single-level symptomatic cervical disc disease: a meta-analysis of randomized controlled trials

OBJECTIVE

To evaluate the safety and effectiveness of cervical disc arthroplasty (CDA) versus anterior cervical discectomy and fusion (ACDF) for single-level symptomatic cervical disc disease.

METHODS

We identified eligible randomized controlled trials (RCTs) in PubMed (April 2011), EMBASE (April 2011) and Cochrane Central Register of Controlled Trials (April 2011). Data were collected and extracted by two reviewers independently. The methodological quality and clinical relevance of the included studies were assessed. Data analysis was conducted with RevMan 5.0.

RESULTS

Six RCTs involving 1,745 patients were included. The pooled analysis showed a higher prevalence of neurological and overall success [(P = 0.004, RR = 1.06, 95% CI = 1.02-1.10), (P = 0.0005, RR = 1.14, 95% CI = 1.06-1.22)], and a lower incidence of dysphagia and reoperation related to adjacent-segment degeneration [(P = 0.04, RR = 0.30, 95% CI = 0.09-0.97), (P = 0.03, RR = 0.46, 95% CI = 0.23-0.91)] with CDA compared to ACDF. However, there was no statistical difference in neck disability index (P = 0.92, SMD = 0.01, 95% CI = -0.25 to 0.27), neck and arm pain scores[(P = 0.33, SMD = -0.12, 95% CI = -0.37 to 0.13), (P = 0.54, SMD = 0.17, 95% CI = -0.36 to 0.70)], incidence of complications related to the implant or surgical procedure and reoperation related to primary surgery [(P = 0.32, RR = 0.76, 95% CI = 0.45-1.30), (P = 0.09, RR = 0.48, 95% CI = 0.20-1.12)].

CONCLUSION

Compared with ACDF, CDA carry a lower incidence of dysphagia complications and reoperation related to adjacent-segment degeneration, and a higher prevalence of neurological and overall success at 2 years postoperatively. As the poor quality of the included studies, it is still uncertain whether CDR is more effective and safer than ACDF treating single-level symptomatic cervical disc disease. Future large-scale RCTs with long-term follow-up are needed to provide clear evidence.

The development of a model for translation of the Neck Disability Index to utility scores for cost-utility analysis in cervical disorders

BACKGROUND CONTEXT

The Neck Disability Index (NDI) is a commonly used disease-specific instrument for cervical spine disorders with good responsiveness and psychometric properties compared with general health status measures. However, NDI scores are unitless and do not have an intrinsic value that is comparable to other health status measures, and these scores have limited value in cost-utility analysis. The translation of disease-specific measures to Short Form-6 Dimensions (SF-6D) utility scores may be useful in cost-utility analysis.

PURPOSE

The purpose of this study is to present a model for translating the NDI to SF-6D utility scores, permitting the use of NDI scores in the cost-utility analysis of cervical disorders.

STUDY DESIGN/SETTING

A secondary analysis of a multicenter prospective clinical trial of the Synthes ProDisc-C (Synthes, West Chester, PA, USA) was performed.

PATIENT SAMPLE

Patients included were randomized to receive either a total disc arthroplasty or anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease involving one vertebral level between C3 and C7. All subjects completed NDI and 36-Item Short Form Health Survey (SF-36) self-assessments at preoperative and postoperative follow-ups of 6 weeks, 3, 6, 12, 18, and 24 months.

OUTCOME MEASURES

The NDI is a validated and widely used self-reported questionnaire designed to assess patient-determined disability resulting from neck pain, including pain level and effects on activities of daily living. The SF-6D is a preference-based health state classification system derived from six health dimensions of the SF-36 self-reported questionnaire, including the domains of physical functioning, role limitation, social functioning, bodily pain, mental health, and vitality.

METHODS

The collected data points were divided into two cohorts: one for model formation and one for the assessment of model validity. SF-36 scores were converted to SF-6D utilities via three previously published methods. Correlation analyses and linear regression modeling between SF-6D and NDI created the models for translating scores. For validation, Spearman and Pearson correlations were calculated between the observed and predicted SF-6D utilities, and prediction errors were calculated.

RESULTS

Four hundred thirty patients with 2,137 time points were used for creation and validation of the model. Pearson and Spearman correlation coefficients between the NDI and the SF-6D derived from each conversion method were found to be between -0.8255 and -0.8504 (p<.01). R(2) values ranged from 0.68 to 0.71 and root mean squared error (RMSE) from 0.092 to 0.084. Correlations between estimated and observed SF-6D scores ranged from 0.8325 to 0.8372 (p<.01). The mean prediction error was less than 0.006, with standard deviation (SD) between 0.082 and 0.093.

DISCUSSION

Correlations between NDI and SF-6D utility scores are strong and statistically significant. The model has a large R(2) and small RMSE. The prediction models produce a small mean prediction error, but the SD of the prediction errors is large. High correlations between NDI and SF-6D permit these models to be used to calculate overall utilities, changes in utilities, and quality-adjusted life-years for large data samples. However, the relatively large observed prediction error SDs may limit the accuracy of translation of individual data points or small sample sizes.

Early follow-up outcomes after treatment of degenerative disc disease with the discover cervical disc prosthesis

BACKGROUND CONTEXT

Although anterior cervical decompression and fusion has been used successfully in the treatment of symptomatic radiculopathy and/or myelopathy, biomechanical studies have suggested possible deleterious effects of cervical fusion on adjacent level kinematics. The emergence of cervical arthroplasty as an alternative to arthrodesis may restore a more normal spinal movement and reduces a kinematic strain on adjacent segments. To date, with existing prostheses, the risk adjacent segment disease has not been proven to be reduced using artificial disc replacement.

PURPOSE

The study was designed to investigate the surgical techniques and clinical effects of the Discover artificial cervical disc prosthesis in a Chinese population and observe the stability and range of movement in the early and immediate postoperative period.

STUDY DESIGN/SETTING

Our clinical study design was prospective, concurrently enrolled, and single-center trial of the artificial cervical disc prosthesis (DePuy Spine, Raynham, MA, USA) in the treatment of patients with single- and two-level degenerative disc disease of the cervical spine.

PATIENT SAMPLE

Procedure was performed in 25 patients.

OUTCOME MEASURES

The functional spinal unit (FSU) and global angles, segmental and overall range of motion, FSU heights, and clinical parameters checked with Neck Disability Index (NDI), Japanese Orthopedic Association (JOA), Odom's scale, and visual analog scale (VAS) pain score were assessed.

METHODS

Twenty-five patients (26 discs) consecutively underwent cervical arthroplasty using the Discover artificial cervical disc in our hospital. Clinical and radiologic follow-up was performed. The radiographic parameters evaluated included the treated segments and the overall curvature of the cervical spine.

RESULTS

All the patients were assessed between 12 months and 18 months after surgery (average 15.3 months). According to Odom's scale, all 25 patients (26 levels) had good to excellent outcomes by independent assessment. Mean NDI, JOA, and VAS scores showed statistical improvements in the early and immediate postoperative period. The range of movement recovered to the preoperative value during the follow-up. The treated segment ultimately showed preservation of movement when compared with preoperative levels. No prosthesis subsidence or excursion was identified, and no heterotopic ossification was found in the replaced levels.

CONCLUSION

These early results from a small cohort demonstrate that cervical arthroplasty with the Discover artificial cervical disc for the treatment of degenerative cervical disc disease may provide a good clinical outcome and preserves some motion postoperatively. Although early outcomes are promising, this is also a relatively new technology and prosthesis, long-term follow-up studies with larger patient numbers are required to assess safety and efficacy compared with alternative treatments.

Kinematics of progressive circumferential ligament resection (decompression) in conjunction with cervical disc arthroplasty in a spondylotic spine model

STUDY DESIGN

Benchtop biomechanics study examining kinematic effects of progressive resection in a human cadaveric spine model.

OBJECTIVE

To determine the effects of posterior longitudinal ligament (PLL) resection, unilateral and bilateral foraminotomy, and laminectomy on cervical intervertebral rotation and translation after cervical disc arthroplasty (CDA).

SUMMARY OF BACKGROUND DATA

Although the clinical results after CDA have been studied, there remain unanswered questions regarding the surgical techniques used at the time of device insertion. For example, it is unclear whether a surgeon should retain or resect the PLL and uncinate processes at the time of primary surgical intervention. Further, the effect of a subsequent posterior decompression (foraminotomy or laminectomy) on the stability of a motion segment containing a disc arthroplasty is unknown.

METHODS

Three-dimensional intervertebral motion was measured by biplanar videography in human cadaveric spines at C4-C5 or at C5-C6 subjected to a 1.5-Nm moment applied to induce motion in the sagittal plane. Coupled motions were not constrained. After measuring intact spine motion, disc arthroplasty with bilateral ventral foraminotomy was performed without PLL resection. Sequentially, rotations and translations were measured after PLL resection, unilateral foraminotomy, bilateral foraminotomy, and laminectomy.

RESULTS

CDA with bilateral ventral foraminotomy increased sagittal rotation by 0.4 degrees (16%) compared with the intact spine. The addition of PLL resection increased rotation by 0.5 degrees (14% increase). Unilateral and bilateral foraminotomy had negligible effects on sagittal rotation or anteroposterior (AP) translation. Laminectomy resulted in an additional sagittal plane rotation of 2 degrees. The sagittal-plane interverterbal rotation resultant after all interventions was 6 degrees , with 1.5 mm of AP translation occurring only.

CONCLUSION

Given that a greater degree of motion was seen with PLL resection combined with ventral foraminotomy, we recommend that PLL resection be performed when performing CDA. In our benchtop model, unilateral and bilateral posterior foraminotomies were not associated with the creation of significant sagittal rotational or AP translational instability.

The factors that influence the postoperative segmental range of motion after cervical artificial disc replacement

BACKGROUND CONTEXT

Advantages of cervical artificial disc replacement (ADR) are to preserve segmental range of motion (ROM) and avoid adjacent segmental disease. To achieve successful outcome after cervical ADR, ROM maintenance is important, but few authors have investigated the factors that influence the postoperative segmental ROM.

PURPOSE

To evaluate the factors that influence the postoperative segmental ROM after cervical ADR.

STUDY DESIGN/SETTING

A retrospective clinical study.

PATIENT SAMPLE

Forty-one consecutive cervical ADR cases were analyzed.

OUTCOME MEASURES

Disc height, segmental and overall ROM, and clinical parameters checked with Neck Disability Index (NDI) and visual analog scale (VAS) in neck and arm pain were assessed.

METHODS

There were 21 men and 20 women with a mean age of 45 years (range, 27-61 years). All cases were followed up for more than 2 years (range, 24-54 months; average, 31 months). Angles of the inserted implant on the immediate postoperative lateral radiographs, segmental and overall ROM (full flexion angle-full extension angle), disc height increment (immediate postoperative disc height-preoperative disc height), and adjacent segment changes at cephalad and caudal disc space were measured. Correlations between the factors and segmental ROM at last follow-up were analyzed.

RESULTS

Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 at last follow-up, and mean VAS in the neck pain decreased from 56.8 preoperatively to 11.8 postoperatively and arm pain decreased from 68.1 to 18.0. The mean preoperative segmental ROM changed from 7.4+/-3.2 degrees preoperatively to 10.4+/-5.9 degrees at last follow-up, and mean preoperative disc height increased from 6.4+/-1.0 (4.1-8.4) mm preoperatively to 7.9+/-1.0 (6.3-9.9) mm postoperatively. The segmental ROM at last follow-up was not significantly correlated with preoperative segmental and overall ROM, angle of inserted implant, VAS, or age (p>.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p=.046, r=0.374) and preoperative NDI (p=.026, r=0.412). The patient group with the postoperative segmental ROM greater than 10 degrees had a significantly lower mean preoperative disc height than the group with the segmental ROM less than 10 degrees (p=.050).

CONCLUSIONS

At a minimum of 2 years after cervical ADR, clinical outcomes were satisfactory in terms of function and pain scores. Within our results, the segmental ROM was not affected by preoperative ROM but postoperative disc height increment positively and preoperative disc height negatively.