Cervical arthroplasty: a critical review of the literature

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

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

Cervical Column and Cord and Column Responses in Whiplash With Stenosis: A Finite Element Modeling Study

Spine degeneration is a normal aging process. It may lead to stenotic spines that may have implications for pain and quality of life. The diagnosis is based on clinical symptomatology and imaging. Magnetic resonance images often reveal the nature and degree of stenosis of the spine. Stenosis is concerning to clinicians and patients because of the decreased space in the spinal canal and potential for elevated risk of cord and/or osteoligamentous spinal column injuries. Numerous finite element models of the cervical spine have been developed to study the biomechanics of the osteoligamentous column such as range of motion and vertebral stress; however, spinal cord modeling is often ignored. The objective of this study was to determine the external column and internal cord and disc responses of stenotic spines using finite element modeling. A validated model of the subaxial spinal column was used. The osteoligamentous column was modified to include the spinal cord. Mild, moderate, and severe degrees of stenosis commonly identified in civilian populations were simulated at C5-C6. The column-cord model was subjected to postero-anterior acceleration at T1. The range of motion, disc pressure, and cord stress-strain were obtained at the index and superior and inferior adjacent levels of the stenosis. The external metric representing the segmental motion was insensitive while the intrinsic disc and cord variables were more sensitive, and the index level was more affected by stenosis. These findings may influence surgical planning and patient education in personalized medicine.

Cervical Disc Arthroplasty Usage Has Leveled Out From 2010 to 2021

STUDY DESIGN

Descriptive epidemiologic study.

OBJECTIVE

To compare trends in utilization and predictive factors for single-level cervical disc arthroplasty (CDA) relative to anterior cervical discectomy and fusion (ACDF) over the years.

BACKGROUND

CDA is an alternative to ACDF for the treatment of cervical spine pathologies. With both procedures performed for similar indications, controversy on best practices exists.

MATERIALS AND METHODS

Patients who underwent single-level CDA or ACDF were identified in the 2010 through 2021 PearlDiver M151Ortho data set. The yearly number of CDAs performed and proportionality was assessed. Predictive patient factors for undergoing CDA as opposed to ACDF were determined. Kaplan Meyer survival analysis with an endpoint of cervical spine reoperation compared 5-year outcomes between CDA and ACDF.

RESULTS

From 2010 to 2021, 19,301 single-level CDAs and 181,476 single-level ACDFs were identified. The proportional utilization of CDA relative to ACDF increased from 4.00% in 2010 to 14.15% in 2018 ( P < 0.0001), after which there was a plateau between 2018 and 2021 where proportional utilization was 14.47% ( P = 0.4654). Multivariate analysis identified several predictors of undergoing CDA rather than ACDF, including: younger age [odds ratio (OR) per decade decrease: 1.72], having surgery performed in the Midwest, Northeast, or West (relative to South, OR: 1.16, 1.13, 2.26, respectively), having Commercial insurance (relative to Medicare, OR: 1.75), and having surgery performed by an orthopedic surgeon (relative to a neurological surgeon, OR: 1.54) ( P < 0.0001 for each). There was no statistically significant difference in 5-year survival to further cervical spine surgery between CDA and ACDF at 5 years (97.6% vs. 97.7%, P = 0.4249).

CONCLUSIONS

Although the use of CDA relative to ACDF rose from 2010 to 2018, its use has subsequently plateaued between 2018 and 2021 and remained a relatively low percentage of the single-level anterior cervical surgeries performed (14.47% in 2021). The causes for such changes in the trend are unclear.

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.

Comparison of anterior cervical discectomy and fusion versus artificial disc replacement for cervical spondylotic myelopathy: a meta-analysis

OBJECTIVE

Anterior cervical discectomy and fusion (ACDF) has long been regarded as a gold standard in the treatment of cervical myelopathy. Subsequently, cervical artificial disc replacement (c-ADR) was developed and provides the advantage of motion preservation at the level of the intervertebral disc surgical site, which may also reduce stress at adjacent levels. The goal of this study was to compare clinical and functional outcomes in patients undergoing ACDF with those in patients undergoing c-ADR for cervical spondylotic myelopathy (CSM).

METHODS

A systematic literature review and meta-analysis were performed using the Embase, PubMed, and Cochrane Central Register of Controlled Trials databases from database inception to November 21, 2021. The authors compared Neck Disability Index (NDI), SF-36, and Japanese Orthopaedic Association (JOA) scores; complication rates; and reoperation rates for these two surgical procedures in CSM patients. The Mantel-Haenszel method and variance-weighted means were used to analyze outcomes after identifying articles that met study inclusion criteria.

RESULTS

More surgical time was consumed in the c-ADR surgery (p = 0.04). Shorter hospital stays were noted in patients who had undergone c-ADR (p = 0.04). Patients who had undergone c-ADR tended to have better NDI scores (p = 0.02) and SF-36 scores (p = 0.001). Comparable outcomes in terms of JOA scores (p = 0.24) and neurological success rate (p = 0.12) were noted after the surgery. There was no significant between-group difference in the overall complication rates (c-ADR: 18% vs ACDF: 25%, p = 0.17). However, patients in the ACDF group had a higher reoperation rate than patients in the c-ADR group (4.6% vs 1.5%, p = 0.02).

CONCLUSIONS

At the midterm follow-up after treatment of CSM, better functional outcomes as reflected by NDI and SF-36 scores were noted in the c-ADR group than those in the ACDF group. c-ADR had the advantage of retaining range of motion at the level of the intervertebral disc surgical site without causing more complications. A large sample size with long-term follow-up studies may be required to confirm these findings in the future.

Development of an Intervertebral Disc for Cervical Spondylosis Composed of Seeded Biomaterials

Most of the current artificial disc prosthesis presented a restricted range of motion. Here we propose the design of a novel intervertebral disc composed of carbon fiber, hyaluronic methylcellulose hydrogel loaded with mesenchymal stem cells and polycaprolactone. The prosthesis was biomechanically evaluated under two static physiological conditions to study the mechanical influence of the material on the device. The results obtained in the simulations showed a not only a congruent behavior with preclinical condition, but also that the proposed materials met the desired biomechanical properties Clinical Relevance- Cervical spondylosis is a degenerative disease of the human spine that causes wear and tear of the cervical intervertebral discs. Nowadays, the proposed surgical solutions do not allow fully recovery of normal movement because the surgical intervention do not emulate the natural range of motion, may lack shock absorption mechanisms, show signs of fatigue over time affecting its durability, and do not have good bone adhesion. Therefore, hypermobility and problems of heterotopic ossification may restrict the range of motion.

Anterior Cervical Discectomy and Fusion Versus Cervical Disc Arthroplasty: A Comparison of National Trends and Outcomes

OBJECTIVE

Anterior cervical discectomy and fusion (ACDF) has been considered the standard treatment for degenerative cervical disc disease; however, recent trials have shown comparable outcomes with cervical disc arthroplasty (CDA). This study aimed to observe disparities in treatment paradigms of single-level cervical disc diseases and compare inpatient outcomes between procedures.

METHODS

A retrospective cohort of patients treated for single-level cervical disc herniation or degeneration without myelopathy was queried from the Nationwide Inpatient Sample spanning 2012-2015. Multivariate logistic regression was performed to assess the effects of demographics, temporality of admission, and hospital characteristics on odds of receiving CDA versus ACDF. Propensity-score matching was performed to compare cost, length of stay (LOS), non-home discharge, and inpatient complications.

RESULTS

In total, 1028 CDAs and 44,374 ACDFs were performed for single-level cervical disc disease during 2012-2015. Matched comparison showed that while non-home discharges were not different between CDA and ACDF (P = 0.248), patients who received CDA had a 0.19-day shorter LOS (P < 0.001) and $4694 greater total cost (P < 0.001). There were no statistically significant differences in inpatient complication rates. Multivariate analysis showed that patients in the 26th-50th percentile, 51st-75th percentile, and 76th-100th percentile of median household income had greater odds of CDA compared with patients in the 0-25th percentile (odds ratio [OR] 1.35, P = 0.003; OR 1.31, P = 0.013; OR 1.34, P = 0.011, respectively). Patients with private insurance had greater odds of receiving CDA compared with patients on Medicare (OR 1.91, P < 0.001).

CONCLUSIONS

CDA was associated with shorter LOS but greater costs compared with ACDF. Patients with greater median income and private insurance were more likely to receive CDA.

Biomechanical effects of uncinate process excision in cervical disc arthroplasty

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

Biomechanical Study of Cervical Disc Arthroplasty Devices Using Finite Element Modeling

Many artificial discs for have been introduced to overcome the disadvantages of conventional anterior discectomy and fusion. The purpose of this study was to evaluate the performance of different U.S. Food and Drug Administration (FDA)-approved cervical disc arthroplasty (CDA) on the range of motion (ROM), intradiscal pressure, and facet force variables under physiological loading. A validated three-dimensional finite element model of the human intact cervical spine (C2-T1) was used. The intact spine was modified to simulate CDAs at C5-C6. Hybrid loading with a follower load of 75 N and moments under flexion, extension, and lateral bending of 2 N·m each were applied to intact and CDA spines. From this work, it was found that at the index level, all CDAs except the Bryan disc increased ROM, and at the adjacent levels, motion decreased in all modes. The largest increase occurred under the lateral bending mode. The Bryan disc had compensatory motion increases at the adjacent levels. Intradiscal pressure reduced at the adjacent levels with Mobi-C and Secure-C. Facet force increased at the index level in all CDAs, with the highest force with the Mobi-C. The force generally decreased at the adjacent levels, except for the Bryan disc and Prestige LP in lateral bending. This study demonstrates the influence of different CDA designs on the anterior and posterior loading patterns at the index and adjacent levels with head supported mass type loadings. The study validates key clinical observations: CDA procedure is contraindicated in cases of facet arthroplasty and may be protective against adjacent segment degeneration.

Comparative Finite Element Modeling Study of Anterior Cervical Arthrodesis Versus Cervical Arthroplasty With Bryan Disc or Prodisc C

INTRODUCTION

Cervical disc arthroplasty (CDA), a motion-preserving alternative to anterior cervical discectomy and fusion (ACDF), is used in military patients for the treatment of disorders such as spondylosis. Since 2007, the FDA has approved eight artificial discs. The objective of this study is to compare the biomechanics after ACDF and CDA with two FDA-approved devices of differing designs under head and head supported mass loadings.

MATERIALS AND METHODS

A previously validated osteoligamentous C2-T1 finite element model was used to simulate ACDF and two types of CDA (Bryan and Prodisc C) at the C5-C6 level. The hybrid loading protocol associated with in vivo head and head supported mass was used to apply flexion and extension loading. First, intact spine was subjected to 2 Nm of flexion extension and the range of motion (ROM) was measured. Next, for each surgical option, flexion-extension moments duplicating the same ROM as the intact spine were determined. Under these surgery-specific moments, ROM and facet force were obtained at the index level, and ROM, facet force, and intradiscal pressure at the rostral and caudal adjacent levels.

RESULTS

ACDF led to increased motion, force and pressures at the adjacent levels. Prodisc C led to increased motion and facet force at the index level, and decreased motion, facet force, and intradiscal pressure at both adjacent levels. Bryan produced less dramatic biomechanical alterations compared with ACDF and Prodisc C. Numerical results are given in the article.

CONCLUSIONS

Recognizing that ROM is a clinical measure of spine stability/performance, CDA demonstrates a more physiological biomechanical response than ACDF, although the exact pattern depends on the implant design. Anterior and posterior column load-sharing patterns were different between the two implants and may affect implant selection based on the anatomical and pathological state at the index and adjacent levels.

A Comparison Study of Four Cervical Disk Arthroplasty Devices Using Finite Element Models

Study Design

The study examined and compared four artificial cervical disks using validated finite element models.

Purpose

To compare and contrast the biomechanical behavior of four artificial cervical disks by determining the external (range of motion) and internal (facet force and intradiscal pressure) responses following cervical disc arthroplasty (CDA) and to elucidate any device design effects on cervical biomechanics.

Overview of Literature

Despite CDA’s increasing popularity most studies compare the CDA procedure with anterior cervical discectomy and fusion. There is little comparative evaluation of different artificial disks and, therefore, little understanding of how varying disk designs may influence spinal biomechanics.

Methods

A validated C2–T1 finite element model was subjected to flexion-extension. CDAs were simulated at the C5–C6 level with the Secure-C, Mobi-C, Prestige LP, and Prodisc C prosthetic disks. We used a hybrid loading protocol to apply sagittal moments. Normalized motions at the index and adjacent levels, and intradiscal pressures and facet column loads were also obtained.

Results

The ranges of motion at the index level increased after CDA. The Mobi-C prosthesis demonstrated the highest amount of flexion, followed by the Secure-C, Prestige LP, and Prodisc C. The Secure-C demonstrated the highest amount of extension, followed by the Mobi-C, Prodisc C, and Prestige LP. The motion decreased at the rostral and caudal adjacent levels. Facet forces increased at the index level and decreased at the rostral and caudal adjacent levels following CDA. Intradiscal pressures decreased at the adjacent levels for the Mobi-C, Secure-C, and Prodisc C. Conversely, the use of the Prestige LP increased intradiscal pressure at both adjacent levels.

Conclusions

While all artificial disks were useful in restoring the index level motion, the Secure-C and Mobi-C translating abilities allowed for lower intradiscal pressures at the adjacent segments and may be the driving mechanism for minimizing adjacent segment degenerative arthritic changes. The facet joint integrity should also be considered in the clinical decision-making process for CDA selection.

The Assessment of Paravertebral Ossification Progression After Cervical Disc Arthroplasty Based on CT Images: A Long-term Follow-up

Objective

This study focused on the assessment of paravertebral ossification (PO) after cervical disc arthroplasty (CDA) using computed tomography (CT) images.

Methods

In this retrospective study, 52 patients (from 2004 to 2010) who received CDA at a single center were included (32 males). Preoperative and follow‐up X‐ray and CT images of all patients who underwent single‐level CDA were collected. PO from the C2/3 to C7/T1 in each patient was graded based on a CT grading system. Each segment was divided into operative level, adjacent level, or non‐adjacent level. The McAfee' classification system was used to grade PO using X‐ray plain film. The range of motion (ROM) and scores of neurological symptoms (Japanese Orthopaedic Association [JOA] score and Neck Disability Index [NDI]) at both preoperative and final follow‐up time were acquired. Progression and classification of PO in each group was compared using the chi‐square test. ROM between groups were compared using independent t‐test. JOA score and NDI between groups were compared using Mann–Whitney U test.

Results

The average follow‐up time was 81.2 months. In comparison with the preoperative status, the progression of PO development in left and right areas (the Luschka joints areas) in the operative level groups was significantly more severe (area L,χ² value = 36.612, P < 0.001; area R, χ² value = 39.172, P < 0.001) than the non‐adjacent level groups. In contrast, although the prevalence of PO in all areas of the adjacent level groups was higher than that of the non‐adjacent level group in the same segments, there was no significant difference (P > 0.05) in the progression of PO development. The follow‐up high‐grade (grades III and IV) PO incidence rate using X‐ray grading system (3.85%) was significantly lower than that using CT grading system in area L (42.31%) and R (38.46%), but close to that in area A (5.77%) and P (1.92%). The final follow‐up ROM was not significantly different with preoperative ROM in patients with low‐grade PO (9.47° ± 4.12° vs. 9.76° ± 3.69°, P = 0.794). However, in patients with high‐grade PO, the final follow‐up ROM was significantly lower than preoperative ROM (5.77° ± 3.32° vs. 9.28° ± 4.15°, P < 0.001). There was no significant difference for JOA score and NDI at follow‐up between patients with high‐grade and low‐grade PO (JOA, 16.2 ± 1.1 vs. 16.8 ± 0.9, P = 0.489; NDI, 8.9 ± 6.1 vs. 8.0 ± 7.3, P = 0.317).

Conclusion

High‐grade PO was observed in the areas of the Luschka joints at the operative level after CDA, which was difficult to observe using X‐ray plain film. The PO formation at adjacent segments was not significant.

Implant complications after one-level or two-level cervical disc arthroplasty: A retrospective single-centre study of 105 patients

The aim of study was to investigate the complications of cervical disc arthroplasty (CDA) and to discuss the factors affecting the mobility of the prosthesis and the measures to prevent these complications. Hundred and five patients who underwent CDA between 2009 and 2016 were enrolled. The clinical and radiographic outcomes were used to assess and the complications were recorded as well.All the patients were followed-up with an average of 41.30 ± 16.90 months with an average age of 47.90 ± 9.22 years. The visual analogue scale (VAS), neck disability index (NDI), and Japanese Orthopaedic Association (JOA) scores improved significantly at the final follow-up (FU) compared with the preoperative values. At the final FU, the overall incidence of heterotopic ossification (HO) was 51.42%. The distribution of different grades of HO was low-level HO (53.7%) and high-level HO (46.3%). No significant differences were found in the NDI, VAS, or JOA scores between patients with HO and those without HO (P > .05). In the high-level HO patients, the range of mobility (ROM) was significantly reduced compared with the low-level HO patients and those without HO (P < .05). The anterior displacement, subsidence, and instability were observed in 1 patient respectively and the segmental kyphosis, adjacent segment degeneration in 3 patients respectively. The patient of CDA instability also suffered severe neck pain and the revision surgery was performed.Postoperative complications in CDA such as HO, segmental kyphosis, and prosthesis displacement are prone to occur, affecting prosthesis mobility. Surgical indications should be strictly controlled, and intraoperative and postoperative treatments should be given great attention in order to reduce prosthesis-related complications.

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

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

NuNec™ Cervical Disc Arthroplasty Improves Quality of Life in Cervical Radiculopathy and Myelopathy: A 2-yr Follow-up

BACKGROUND

Anterior cervical disc replacement is an alternative to fusion for the treatment of selected cases of radiculopathy and myelopathy. We report clinical and radiological outcomes after disc replacement with the NuNec™ artificial cervical disc (Pioneer® Surgical Technology, Marquette, Michigan) with subgroup analysis.

OBJECTIVE

To review clinical and radiological outcomes after anterior cervical disc replacement with the NuNec™ artificial cervical disc.

METHODS

A consecutive case series of patients undergoing cervical disc replacement with the NuNec™ artificial disc was conducted. Clinical outcomes were assessed by questionnaires preoperatively and up to 2 yr postoperatively including neck and arm pain, Neck Disability Index, Euroqol 5-dimensions, and Short Form-36; x-rays from the same period were analyzed for range of movement and presence of heterotopic ossification.

RESULTS

A total of 44 NuNec™ discs were implanted in 33 patients. Clinical improvements were seen in all outcomes; significant improvements on the Neck Disability Index, Euroqol 5-dimensions, and physical domain of the Short Form-36 were maintained at 2 yr. There was a mean of 4° range of movement at the replacement disc level at 2 yr, a significant reduction from baseline; there was also progression in levels of heterotopic ossification. Complications included temporary dysphagia (10%) and progression of disease requiring foraminotomy (6%); no surgery for adjacent level disease was required. There was no significant difference in the outcomes of the radiculopathy and myelopathy groups.

CONCLUSION

Clinical outcomes using the NuNec™ disc replacement are comparable with other disc replacements. Although the range of movement is reduced, the reoperation rate is very low.

A Comparative in vivo Study of Semi-constrained and Unconstrained Cervical Artificial Disc Prostheses

PURPOSE

The objective of this study is to directly compare different types of cervical artificial disc implants using an in vivo model capable of simulating the axial load on a neck that is similar to the human neck.

METHODS

Cervical arthroplasty was performed at C3-4 in 14 healthy female adult Alpine goats. The goats were divided into three groups. Group A received Bryan (unconstrained one-piece design); Group B received ProDisc-C (semi-constrained two-piece design); and Group C received Mobi-C (unconstrained three-piece design) artificial discs. The goats were monitored in a veterinary unit for 6 months with radiography at regular intervals.

RESULTS

Each goat tolerated cervical arthroplasty well and had satisfactory placement of their implant per intra-operative radiography. Implants monitored in Group A demonstrated no migration. One out of five implants in Group B experienced anterior migration at 3 months. In Group C, anterior migration and disintegration occurred in all four implants, with migration occurring during the first postoperative week in three implants and after 5 weeks in the fourth.

CONCLUSIONS

Unconstrained multi-piece artificial cervical discs may be prone to anterior migration and extrusion out of the disc space. This outcome deserves attention in individuals with a hypermobile neck and/or an occupation involving the use of a head-supported mass, such as helmets.

Artificial disc replacement versus fusion in patients with cervical degenerative disc disease with radiculopathy: 5-year outcomes from the National Swedish Spine Register

OBJECTIVE: The long-term efficacy of artificial disc replacement (ADR) surgery compared with fusion after decompression for the treatment of cervical degenerative disc disease and radiculopathy has not previously been investigated in a population-based setting. METHODS: All patients with cervical degenerative disc disease and radiculopathy who were in the national Swedish Spine Registry (Swespine) beginning in January 1, 2006, were eligible for the study. Follow-up information was obtained up to November 15, 2017. The authors compared, using propensity score matching, patients treated with anterior decompression and insertion of an ADR with patients who underwent anterior decompression combined with fusion surgery. The primary outcome was the Neck Disability Index (NDI), a patient-reported function score ranging from 0% to 100%, with higher scores indicating greater disability and a minimum clinically important difference of > 15%. RESULTS: A total of 3998 patients (2018:1980 women/men) met the inclusion criteria, of whom 204 had undergone arthroplasty and 3794 had undergone fusion. After propensity score matching, 185 patients with a mean age of 49.7 years remained in each group. Scores on the NDI were approximately halved in both groups after 5 years, but without a significant mean difference in NDI (3.0%; 95% CI -8.4 to 2.4; p = 0.28) between the groups. There were no differences between the groups in EuroQol-5 Dimensions or in pain scores for the neck and arm. CONCLUSIONS: In patients with cervical degenerative disc disease and radiculopathy, decompression plus ADR surgery did not result in a clinically important difference in outcomes after 5 years, compared with decompression and fusion surgery.

Cervical Disk Arthroplasty

Anterior cervical diskectomy and fusion has been and remains the benchmark surgical management of cervical degenerative disk disease. However, an increased use of cervical disk arthroplasty (CDA) has been found in the past few years. The purported benefits of CDA included preserved motion, less adjacent-level degeneration, and less morbidity. Short-term results from randomized control trials clearly showed noninferiority of CDA compared with fusion. With long-term comparison data becoming available, results are equivalent and superior in many metrics compared, favoring CDA. Concerns remain regarding the best way to manage CDA failures. Nonetheless, appropriate patient selection and adherence to strict surgical technique make CDA a viable treatment.

Cervical disc herniation: which surgery?

PURPOSE

Cervical disc herniation is a common pathology. It can be treated by different surgical procedures. We aimed to list and analyzed every available surgical option. We focused on the comparison between anterior cervical decompression and fusion and cervical disc arthroplasty.

RESULTS

The anterior approach is the most commonly used to achieve decompression and fusion by the mean of autograft or cage that could also be combined with anterior plating. Anterior procedures without fusion have shown good outcomes but are limited by post-operative cervicalgia and kyphotic events. Posterior cervical foraminotomy achieved good outcomes but is not appropriate in a case of a central hernia or ossification of the posterior ligament. Cervical disc arthroplasty is described to decrease the rate of adjacent segment degeneration. It became very popular during the last decades with numerous studies with different implant device showing encouraging results but it has not proved its superiority to anterior cervical decompression and fusion. Anterior bone loss and heterotopic ossification are still to be investigated.

CONCLUSION

Anterior cervical decompression and fusion remain the gold standard for surgical treatment of cervical disc herniation.

Progressive Bone Formation After Cervical Disc Replacement: Minimum of 5-Year Follow-up

STUDY DESIGN

Retrospective review.

OBJECTIVE

Our objective was to examine the prevalence, clinical significance, ramifications, and possible etiology of postoperative bone formation at the index level after cervical disc replacement (CDR) with a minimum of 5 years of follow-up.

SUMMARY OF BACKGROUND DATA

CDR can be complicated by postoperative ossification and unwanted ankylosis at the index level, which some authors have termed "heterotopic ossification." This terminology may be inaccurate as it assumes the postoperative bone formation is unnatural and a consequence of the CDR surgery. We advocate that this phenomenon has more to do with individual patient factors rather than the surgery.

METHODS

Patients who underwent Bryan CDR for cervical myelopathy or radiculopathy between 12/2003 and 8/2008 with a minimum of 5-years follow-up were analyzed. They were divided into two groups, those with and without postoperative bone formation. Patient-reported outcomes (Japanese Orthopaedic Association score, Neck Disability Index, Visual Analogue Scale for neck and arm pain) and radiographic parameters were collected pre- and postoperatively and compared between groups.

RESULTS

Sixty-one patients (76 levels) were identified (mean follow-up 94.2 mo). The overall incidence of postoperative ossification was 50%. Both groups had sustained significant improvements across all patient-reported outcome measures at final follow-up. Notably, patients with more severe preoperative cervical spondylosis had higher rates of postoperative ossification (P = 0.036) and adjacent segment degeneration (P = 0.010).

CONCLUSION

Although the long-term incidence of postoperative bone formation after CDR was relatively high, this did not adversely affect patient outcomes. Patients with more severe preoperative spondylosis had higher rates of postoperative ossification, suggesting that postoperative ossification at the CDR segment is likely one of progressive bone formation in individuals already predisposed to forming bone rather than one of alleged heterotopic ossification as a consequence of the surgery.

LEVEL OF EVIDENCE

3.

Anterior cervical discectomy and fusion: review and update for radiologists

OBJECTIVES

The goals of this article are to describe the various types of interbody grafts and anterior cervical plating systems, techniques for optimizing evaluation of cervical spine metallic implants on CT and MR imaging, expected appearance and complications of ACDF on postoperative imaging and imaging assessment of fusion. Optimization for optimizing metal induced artifacts.

CONCLUSION

Currently, ACDF is the most commonly performed surgical procedure for degenerative cervical spine disease. Interbody fusion is performed with bone grafts or interbody spacers, and may be supplemented with anterior cervical plating. Compressive pathologies at the vertebral body level may be addressed by simultaneous corpectomy. Postoperatively, imaging plays an integral role in routine screening of asymptomatic individuals, fusion assessment and evaluation of complications.

Preoperative T1 Slope as a Predictor of Change in Cervical Alignment and Range of Motion After Cervical Disc Arthroplasty

BACKGROUND This study analyzed the effect of preoperative T1 slope on cervical alignment and range of motion (ROM) after cervical disc arthroplasty (CDA) in patients with cervical degenerative disease. MATERIAL AND METHODS This retrospective study included 32 patients with single-level symptomatic cervical disc disease who underwent CDA with the Mobi-C cervical disc prosthesis and had a mean follow-up of 26.8±6.4 months. Standing lateral, flexion, and extension X-rays of the cervical spine were obtained preoperatively and postoperatively at 24-month follow-up. Simple linear regression analysis was used to assess the impact of preoperative T1 slope on changes from preoperative values in radiologic parameters. RESULTS Compared to preoperative values, at 24-month follow-up, there was a significant increase in mean functional spinal unit (FSU) angle (+7.4°), upper adjacent segment (UAS) angle (+3.1°), and overall cervical alignment (C2-C7 angle) (+6.3°), and a significant decrease in mean lower adjacent segment (LAS) angle (-2.4°). Mean ROM of the FSU (-3.6°), LAS (-3.0°), and overall cervical spine (-11.5°) significantly decreased, and mean ROM of the UAS (+1.6°) significantly increased. There were significant correlations between preoperative T1 slope and mean change from preoperative value in FSU angle, C2-C7 angle, and ROM of the overall cervical spine (C2-C7). CONCLUSIONS T1 slope is useful for evaluating changes in the FSU angle, C2-C7 angle, and ROM of the overall cervical spine following CDA with the Mobi-C disc. Patients with a large preoperative T1 slope may be good candidates for CDA with the Mobi-C prosthesis due its motion maintenance and the fact that it has little adverse impact on sagittal alignment. It also could be a good option in terms of sagittal alignment improvement or motion maintenance for patients with kyphosis.

Trends in the Treatment of Single and Multilevel Cervical Stenosis: A Review of the American Board of Orthopaedic Surgery Database

BACKGROUND

In order to identify any changes in the utilization of new and old techniques, we investigated trends in the operative management of cervical stenosis by orthopaedic surgeons applying for board certification.

METHODS

We queried the American Board of Orthopaedic Surgery database from 1998 to 2013 to identify all of the cervical spine procedures for stenosis that had been performed by candidates taking Part II of the licensing examination. Longitudinal trends were determined for the utilized approach, the individual procedures that had been performed, and whether a motion-preserving technique had been employed.

RESULTS

There were 5,068 cervical spine procedures performed by 1,025 candidates. Procedure totals remained relatively constant until 2011, when a sudden increase of 280% (202 to 768 procedures) was noted. This trend continued, reaching a 460% increase (202 to 1,131 procedures) compared with 2010. The number of candidates only rose by 150% (42 to 105) over the entire study period. The proportion of procedures performed via an anterior approach saw a bimodal distribution; early on, this approach predominated over posterior procedures and was largely driven by the number of corpectomies that were performed. From 2004 to 2011, posterior procedures became more prevalent, but there was a sharp decline in 2011, driven by the large number of anterior cervical discectomies and fusions that were performed. This remained constant through 2013. Lastly, motion-preserving techniques, which included total disc replacement and laminoplasty, had modest increases in utilization from 2005 to 2007. This increased prevalence was short-lived, and it steadily declined through 2014 to <5% utilization.

CONCLUSIONS

The number of candidates performing cervical spine procedures increased more than twofold over a 16-year period. This reflects a larger proportion of the orthopaedic graduates who subspecialize in spine surgery. While the number of surgeons performing spine surgery has increased, the sheer number of procedures that each surgeon performed greatly outpaced the increased number of surgeons. Motion-preserving techniques had their peak utilization in 2007, and have since decreased to <5%, in contrast to fusion techniques, which predominate, comprising >90% of the performed procedures.

Adjacent Segment Disease in the Cervical and Lumbar Spine

Adjacent segment disease (ASD) is disappointing long-term outcome for both the patient and clinician. In contrast to adjacent segment degeneration, which is a common radiographic finding, ASD is less common. The incidence of ASD in both the cervical and lumbar spine is between 2% and 4% per year, and ASD is a significant contributor to reoperation rates after spinal arthrodesis. The etiology of ASD is multifactorial, stemming from existing spondylosis at adjacent levels, predisposed risk to degenerative changes, and altered biomechanical forces near a previous fusion site. Numerous studies have sought to identify both patient and surgical risk factors for ASD, but a consistent, sole predictor has yet to be found. Spinal arthroplasty techniques seek to preserve physiological biomechanics, thereby minimizing the risk of ASD, and long-term clinical outcome studies will help quantify its efficacy. Treatment strategies for ASD are initially nonoperative, provided a progressive neurological deficit is not present. The spine surgeon is afforded many surgical strategies once operative treatment is elected. The goal of this manuscript is to consider the etiologies of ASD, review its manifestations, and offer an approach to treatment.

An Analysis of Paravertebral Ossification in Cervical Artificial Disc Replacement: A Novel Classification Based on Computed Tomography

OBJECTIVE

Cervical artificial disc replacement (CADR) is a new technology in cervical spine surgery. However, CADR may result in paravertebral ossification (PO) after surgery and affect the mobility of the related spinal segments. The present widely used assessment method based on X-ray tomography cannot provide the position information of PO, and also PO detection rates by X-ray are low. The incidence of PO varies dramatically between studies. This study built a novel classification system based on cervical computer tomography (CT) scan to re-evaluate the incidence of PO and its influence on CADR, and also analyzed the predisposing factors of PO.

METHODS

In this retrospective study, 71 patients (from January 2004 to December 2009) who received cervical artificial disc replacement in our hospital were enrolled, and 82 cervical segments were replaced by Bryan discs. The range of motion (ROM) of the related cervical segments and scores of neurological symptoms (neck disability index [NDI] and Japanese Orthopaedic Association [JOA] scores) for both pre-surgery and last follow-up were acquired, respectively. After the establishment of a novel grading system for PO based on CT scan, we analyzed the CT images acquired before surgery and at the last time follow-up. Occurrence and distribution of PO at both time points were calculated. ROM between pre-surgery and post-surgery was compared by paired t-test stratified by PO stages. One-way ANOVA was used to compare NDI and JOA scores between high-grade and low-grade PO groups after surgery. The χ² -test was used to evaluate the risk (odds ratio) of predisposing factors in developing high-grade PO after surgery.

RESULTS

The CT-based classification system has good inter-observer and intra-observer reliability. The detection rate of PO by CT scan is higher than for traditional X-ray examination. The incidence of low-grade PO in all 82 segments at last follow-up is 32.9%. The occurrences of high-grade PO at preoperational and last follow-up time are 15.9% and 67.1%, respectively. The high-grade PO is mainly distributed around the uncovertebral joint. The pre-surgery and post-surgery ROM are similar in patients with low-grade PO at last follow-up time (9.80° ± 3.65° vs 10.03° ± 3.73°, P = 0.801); however, in patients with high-grade PO the post-surgery ROM decreases significantly compared to the pre-surgery ROM (9.73° ± 4.03° vs 6.63° ± 4.21°, P < 0.001). There is no statistical difference for JOA and NDI scores after surgery between high-grade and low-grade PO patients at final follow-up (P = 0.264, P = 0.703). The χ² -test indicates that patients with preoperational existence of PO have a high risk of high-grade PO after surgery (OR = 4, P = 0.012).

CONCLUSIONS

The novel CT image-based PO classification system has good intra-observer reliability. The incidence of PO after Bryan cervical disk replacement is relative high, and the high-grade PO is mainly distributed at the uncovertebral joint. The high-grade PO will affect the ROM after surgery; however, it does not affect the neurologic symptoms.

The Norwegian Cervical Arthroplasty Trial (NORCAT): 2-year clinical outcome after single-level cervical arthroplasty versus fusion-a prospective, single-blinded, randomized, controlled multicenter study

PURPOSE

Standard surgical treatment for symptomatic cervical disc disease has been discectomy and fusion, but the use of arthroplasty, designed to preserve motion, has increased, and most studies report clinical outcome in its favor. Few of these trials, however, blinded the patients. We, therefore, conducted the Norwegian Cervical Arthroplasty Trial, and present 2-year clinical outcome after arthroplasty or fusion.

METHODS

This multicenter trial included 136 patients with single-level cervical disc disease. The patients were randomized to arthroplasty or fusion, and blinded to the treatment modality. The surgical team was blinded to randomization until nerve root decompression was completed. Primary outcome was the self-rated Neck Disability Index. Secondary outcomes were the numeric rating scale for pain and quality of life questionnaires Short Form-36 and EuroQol-5Dimension-3 Level.

RESULTS

There was a significant improvement in the primary and all secondary outcomes from baseline to 2-year follow-up for both arthroplasty and fusion (P < 0.001), and no observed significant between-group differences at any follow-up times. However, linear mixed model analyses, correcting for baseline values, dropouts and missing data, revealed a difference in Neck Disability Index (P = 0.049), and arm pain (P = 0.027) in favor of fusion at 2 years. The duration of surgery was longer (P < 0.001), and the frequency of reoperations higher (P = 0.029) with arthroplasty.

CONCLUSION

The present study showed excellent clinical results and no significant difference between treatments at any scheduled follow-up. However, the rate of index level reoperations was higher and the duration of surgery longer with arthroplasty.

TRIAL REGISTRATION

http://www.clinicaltrials.gov NCT 00735176.19.

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.

Comparison of 2 Zero-Profile Implants in the Treatment of Single-Level Cervical Spondylotic Myelopathy: A Preliminary Clinical Study of Cervical Disc Arthroplasty versus Fusion

Objectives

Cervical disc arthroplasty (CDA) with Discover prosthesis or anterior cervical discectomy and fusion (ACDF) with Zero-P cage has been widely used in the treatment of cervical spondylotic myelopathy (CSM). However, little is known about the comparison of the 2 zero-profile implants in the treatment of single-level CSM. The aim was to compare the clinical outcomes and radiographic parameters of CDA with Discover prosthesis and ACDF with Zero-P cage for the treatment of single-level CSM.

Methods

A total of 128 consecutive patients who underwent 1-level CDA with Discover prosthesis or ACDF with Zero-P cage for single-level CSM between September 2009 and December 2012 were included in this study. Clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) score and Neck Disability Index (NDI). For radiographic assessment, the overall sagittal alignment (OSA), functional spinal unit (FSU) angle, and range of motion (ROM) at the index and adjacent levels were measured before and after surgery. Additionally, the complications were also recorded.

Results

Both treatments significantly improved all clinical parameters (P < 0.05), without statistically relevant differences between the 2 groups. The OSA and FSU angle increased significantly in both groups (P <0.05). Compared with Zero-P group, ROMs at the index levels were well maintained in the Discover group (P < 0.05). However, there were no statistical differences in the ROMs of adjacent levels between the 2 groups (P > 0.05). Besides, no significant differences existed in dysphagia, subsidence, or adjacent disc degeneration between the 2 groups (P > 0.05). However, significant differences occurred in prosthesis migration in CDA group.

Conclusions

The results of this study showed that clinical outcomes and radiographic parameters were satisfactory and comparable with the 2 techniques. However, more attention to prosthesis migration of artificial cervical disc should be paid in the postoperative early-term follow-up.

Four-year results of a prospective single-arm study on 200 semi-constrained total cervical disc prostheses: clinical and radiographic outcome

OBJECTIVE Recent studies have described encouraging outcomes after cervical total disc replacement (cTDR), but there are also critical debates regarding the long-term effects of heterotopic ossification (HO) and the prevalence of adjacent-level degeneration. The aim in this paper was to provide 4-year clinical and radiographic outcome results on the activ C disc prosthesis. METHODS A total of 200 subjects underwent single-level activ C (Aesculap AG) implantation between C-3 and C-7 for the treatment of symptomatic degenerative disc disease. Clinical and radiographic assessments were performed preoperatively, intraoperatively, at discharge, and again at 6 weeks, 6 months, 1 year, 2 years, and 4 years. Radiographic evaluations were done by an independent core laboratory using a specific software for quantitative motion analysis. RESULTS Neck Disability Index (NDI) and visual analog scale (VAS) score for neck and arm pain decreased significantly from baseline to the 4-year follow-up. The mean improvement for NDI was 20, for VAS severity and frequency of neck pain 26.4 and 28, and for VAS severity and frequency of arm pain 30.7 and 35.1, respectively. The neurological situation improved for the majority of patients (86.4%); 76.1% of cases were asymptomatic. Subsequent surgical interventions were reported in 7% of the cases, including device removals in 3%. In 2.5% a subsidence greater than 3 mm was recorded; 1 of these cases also had a migration greater than 3 mm. No device displacement, expulsion, disassembly, loose or fractured device, osteolysis, or facet joint degeneration at the index level was observed. Segmental lordotic alignment changed from -2.4° preoperatively to -6.2° at 4 years, and postoperative height was maintained during the follow-up. Advanced HO (Grade III and IV) was present in 27.1% of the cases; 82.4% showed segmental mobility. A progression of radiographic adjacent-segment degeneration occurred in 28.2%, but only 4.5% required surgical treatment. CONCLUSIONS The activ C is a safe and effective device for cervical disc replacement confirming the encouraging results after cTDR. Clinical trial registration no.: NCT02492724 ( clinicaltrials.gov ).

Wear simulation of a polyethylene-on-metal cervical total disc replacement under different concentrations of bovine serum lubricant

Metal-on-polyethylene total disc replacements have been an alternative to spinal fusion in the lumbar spine under certain indications for more than a decade. Recently, cervical total disc replacement has also become an alternative to cervical fusion. Knowledge acquired from years of in vitro simulator studies on other joint replacements has highlighted the risks associated with premature wear due to unforeseen adverse clinical conditions and the effect of particulate debris on surrounding natural tissues. Having no evidence of the type and composition of the lubricating fluid that will result after spinal arthroplasty, a study on the effects of lubricant serum concentration was undertaken. The wear rate was shown to be inversely proportional to protein content of the serum over a range of 50%-3% bovine serum to water concentration.

Complications of Anterior and Posterior Cervical Spine Surgery

Cervical spine surgery performed for the correct indications yields good results. However, surgeons need to be mindful of the many possible pitfalls. Complications may occur starting from the anaesthestic procedure and patient positioning to dura exposure and instrumentation. This review examines specific complications related to anterior and posterior cervical spine surgery, discusses their causes and considers methods to prevent or treat them. In general, avoiding complications is best achieved with meticulous preoperative analysis of the pathology, good patient selection for a specific procedure and careful execution of the surgery. Cervical spine surgery is usually effective in treating most pathologies and only a reasonable complication rate exists.

Effect of mechanical loading on heterotopic ossification in cervical total disc replacement: a three-dimensional finite element analysis

The development of heterotopic ossification (HO) is considered one of the major complications following cervical total disc replacement (TDR). Even though previous studies have identified clinical and biomechanical conditions that may stimulate HO, the mechanism of HO formation has not been fully elucidated. The objective of this study is to investigate whether mechanical loading is a biomechanical condition that plays a substantial role to decide the HO formation. A finite element model of TDR on the C5-C6 was developed, and HO formation was predicted by simulating a bone adaptation process under various physiological mechanical loadings. The distributions of strain energy on vertebrae were assessed after HO formation. For the compressive force, most of the HO formation occurred on the vertebral endplates uncovered by the implant footplate which was similar to the Type 1 HO. For the anteriorly directed shear force, the HO was predominantly formed in the anterior parts of both the upper and lower vertebrae as the Type 2 HO. For both the flexion and extension moments, the HO shapes were similar to those for the shear force. The total strain energy was reduced after HO formation for all loading conditions. Two distinct types of HO were predicted based on mechanically induced bone adaptation processes, and our findings were consistent with those of previous clinical studies. HO formation might have a role in compensating for the non-uniform strain energy distribution which is one of the mechanical parameters related to the bone remodeling after cervical TDR.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Strategies to improve the credibility of meta-analyses in spine surgery: a systematic survey

BACKGROUND CONTEXT

Meta-analyses are powerful tools that can synthesize existing research, inform clinical practice, and support evidence-based care. These studies have become increasingly popular in the spine surgery literature, but the rigor with which they are being conducted has not yet been evaluated.

PURPOSE

Our primary objectives were to evaluate the methodological quality (credibility) of spine surgery meta-analyses and to propose strategies to improve future research. Our secondary objectives were to evaluate completeness of reporting and identify factors associated with higher credibility and completeness of reporting.

STUDY DESIGN

This study is based on a systematic survey of meta-analyses.

OUTCOME MEASURES

We evaluated credibility according to the Users' Guide to the Medical Literature and completeness of reporting according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist.

METHODS

We systematically searched MEDLINE, EMBASE, and The Cochrane Library, and two reviewers independently assessed eligibility, credibility, and completeness of reporting. We used multivariable linear regression to evaluate potential associations. Interrater agreement was quantified using kappa and intraclass correlation (ICC) coefficients.

RESULTS

We identified 132 eligible meta-analyses of spine surgery interventions. The mean credibility score was 3 of 7 (standard deviation [SD], 1.4; ICC, 0.86), with agreement for each item ranging from 0.54 (moderate) to 0.83 (almost perfect). Clinical questions were judged as sensible in 125 (95%), searches were exhaustive in 102 (77%), and risk of bias assessments were undertaken in 91 (69%). Seven (5%) meta-analyses addressed possible explanations for heterogeneity using a priori subgroup hypotheses and 24 (18%) presented results that were immediately clinically applicable. Investigators undertook duplicate assessments of eligibility, risk of bias, and data extraction in 46 (35%) and rated overall confidence in the evidence in 24 (18%). Later publication year, increasing Journal Impact Factor, increasing number of databases, inclusion of Randomized Controlled Trials, and inclusion of non-English studies were significantly associated with higher credibility scores (p<.05). The mean score for reporting was 18 of 27 (SD, 4.4; ICC, 0.94).

CONCLUSIONS

The credibility of many current spine surgery meta-analyses is limited. Researchers can improve future meta-analyses by performing exhaustive literature searches, addressing possible explanations of heterogeneity, presenting results in a clinically useful manner, reproducibly selecting and assessing primary studies, addressing confidence in the pooled effect estimates, and adhering to guidelines for complete reporting.

Cervical spine kinematics after anterior cervical discectomy with or without implantation of a mobile cervical disc prosthesis; an RCT

Background

When surgically treating cervical degenerative disc disease, the most commonly performed procedure is anterior cervical discectomy. This procedure is performed with, or without fusion promoting methods. For both options the rate of fusion is high and there is much debate whether fusion of the treated segment is a contributing factor to accelerated degeneration of adjacent motion segments. In an effort to prevent degeneration of adjacent segments (ASDeg) due to loss of mobility at the operated level, cervical disc arthroplasty (CDA) was introduced. To evaluate the effectiveness of CDA in preventing ASDeg long term studies are necessary. However, prevention of ASDeg is based on the premise that mobile disc prostheses preserve cervical spine motion in a physiological way. In this article the authors describe a short term protocol for a study that aims to investigate whether CDA reaches the intended goal: restoration or preservation of physiological cervical spine motion. To this end, a technique is used to establish the sequence of contributions of cervical motion segments to flexion/extension of the spine.

Methods

24 subjects between 18 and 55 years old, with radicular symptoms due to a herniated disc between C5 and C7, refractory to conservative therapy are randomized to simple discectomy, or CDA. These groups are preceded by a pilot group of three subjects receiving CDA. Fluoroscopic flexion-extension recordings are acquired preoperatively, and at three and 12 months postoperative. At these same time points, patient reported outcomes are collected, and a neurological examination is performed by and independent physician.

Discussion

Studies investigating arthroplasty determine mobility by measuring segmental range of motion (sROM), which gives no information other than presence, and quantity, of mobility. SROM suffer from high variability. The authors therefore chose to use a method previously used in healthy controls, to describe the dynamic process of cervical spine motion in more detail. Determining cervical spine motion patterns has been reported to be more consistent than sROM. If a physiological motion pattern is absent after surgery in the CDA group, prevention of future ASDeg is less likely. Radiological outcomes will be correlated to clinical outcomes.

Trial Registration

NCT00868335

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0479-4) contains supplementary material, which is available to authorized users.

The Mobi-C cervical disc for one-level and two-level cervical disc replacement: a review of the literature

BACKGROUND

Cervical disc arthroplasty (CDA) is a novel motion-preserving procedure that is an alternative to fusion. The Mobi-C disc prosthesis, one of many Food and Drug Administration (FDA)-approved devices for CDA, is the only FDA-approved prosthesis for two-level CDA. Hence, it may allow for improved outcomes compared with multilevel fusion procedures.

PURPOSE

To critically assess the available literature on CDA with the Mobi-C prosthesis, with a focus on two-level CDA.

METHODS

All clinical articles involving the Mobi-C disc prosthesis for CDA through September 1, 2014 were identified on Medline. Any paper that presented Mobi-C CDA clinical results was included. Study design, sample size, length of follow-up, use of statistical analysis, quality of life outcome scores, conflict of interest, and complications were recorded.

RESULTS

Fifteen studies were included that investigated Mobi-C CDA, only one of which was a level Ib randomized control trial. All studies included showed non-inferiority of one-level Mobi-C CDA to one-level anterior cervical discectomy and fusion (ACDF). Only one study analyzed outcomes of one-level versus two-level Mobi-C CDA, and only one study analyzed two-level Mobi-C CDA versus two-level ACDF. In comparison with other cervical disc prostheses, the Mobi-C prosthesis is associated with higher rates of heterotopic ossification (HO). Studies with conflicts of interest reported lower rates of HO. Adjacent segment degeneration or disease, along with other complications, were not assessed in most studies.

CONCLUSION

One-level Mobi-C CDA is non-inferior, but not superior, to one-level ACDF for patients with cervical degenerative disc disease. The Mobi-C CDA procedure is associated with high rates of HO. Two-level Mobi-C CDA may be superior to two-level ACDF. However, insufficient evidence exists, thereby mandating a need for unbiased, well-designed prospective studies with well-defined outcomes in the future.