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

Combined effect of artificial cervical disc replacement and facet tropism on the index-level facet joints: a finite element study

BACKGROUND

Artificial Cervical Disc Replacement (ACDR) is an effective treatment for cervical degenerative disc diseases. However, clinical information regarding the facet joint alterations after ACDR was limited. Facet tropism is common in the sub-axial cervical spine. Our previous research indicated that facet tropism could lead to increased pressure on the cervical facet joints. This study aimed to assess the impact of facet tropism on the facet contact force and facet capsule stress after ACDR.

METHODS

A C2-T1 cervical finite element model was constructed from computed tomography (CT) scans of a 28-year-old male volunteer. Symmetrical, moderate asymmetrical (7 degrees tropism), and severe asymmetrical (14 degrees tropism) models were created at the C5/C6 level by altering the facet orientation at the C5-C6 level. The C5/C6 ACDR was simulated in the intact, moderate asymmetrical and severe asymmetrical models. A 75-N follower load with 1.0-Nm moments was applied to the top of C2 vertebra in the models to simulate flexion, extension, lateral bending, and axial rotation with the T1 vertebra fixed. The range of motions (ROMs) under all moments, facet contact forces (FCFs) and facet capsule strains were tested.

RESULTS

In the asymmetrical model, the right FCFs considerably increased under flexion, extension, right bending, left rotation, especially under right bending the right sided FCF of the severe asymmetrical model was about 5.44 times of the neutral position, and 3.14 times of the symmetrical model. and concentrated on the cephalad part of the facets. The facet capsule stresses on both sides remarkably increased under extension, lateral bending and right rotation. In the moderate and severe asymmetrical models, the capsule strain was greater on both sides of each position than in the symmetric model.

CONCLUSIONS

The face tropism increased facet contact force and facet capsule strain after ACDR, especially under extension, lateral bending, and rotation, and also could result in abnormal stress distribution on the facet joint surface and facet joint capsule. The results suggest that face tropism might be a risk factor for post-operative facet joint degeneration progression after ACDR. Facet tropism may be noteworthy when ACDR is considered as a surgical option.

Long-term outcomes of anterior cervical dynamic implants: motion-sparing or a delayed fusion?

BACKGROUND CONTEXT

Use of an anterior cervical dynamic implant (ACDI) is generally considered a nonfusion technique for treating cervical degenerative disorders. However, there is limited research focused on evaluating the long-term clinical and radiographic outcomes of ACDI.

PURPOSE

To analyze the long-term clinical and radiographic outcomes of ACDI in the treatment of degenerative cervical disorders.

STUDY DESIGN

A retrospective cohort study.

PATIENTS SAMPLE

Patients with degenerative cervical disorders who underwent anterior cervical discectomy and dynamic cervical implant (DCI) implantation between May 2012 and August 2020 at our institution were included in this study.

OUTCOME MEASURES

Clinical outcomes were assessed using the modified Japanese Orthopedic Association (mJOA), visual analog scale (VAS) scores and patient reported satisfaction rate. Imaging assessment parameters included intervertebral height (IH), intervertebral disc height (IDH), C2-7 range of motion (ROM), segmental ROM, the degree of DCI subsidence and anterior migration, heterotopic ossification (HO) as well as adjacent segment degeneration (ASD).

METHODS

JOA and VAS scores were obtained through questionnaire. The patient reported satisfaction was rated as very satisfied, satisfied, less satisfied and dissatisfied at the final follow-up. The position of the implants, IDH and IH were evaluated on lateral radiographs. ROM at C2-7, ROM at operated level were measured on dynamic radiographs. Cervical 3 -dimensional computer tomography (CT) and magnetic resonance image (MRI) images were used to assess the presence of HO and ASD. The clinical and radiologic variables between the preoperative period and different follow-up time point were statistically analyzed by unpaired t-tests or chi-square tests. Statistical significance was defined as p<.05.

RESULTS

A total of 92 patients (51 males and 41 females) were included in this study. Among them, there were 36 cases of cervical spondylotic myelopathy, 26 cases of cervical radiculopathy, and 30 cases of myeloradiculopathy. The mean age was 55.1±12.6 years. The number of operated levels was single level in 57 patients, 2 levels in 31 patients, and 3 levels in 4 patients. The average follow-up period was 81.3 months (range: 35-135 months). The mean JOA scores showed a gradual increase at 1 month, 1 year, and the final follow-up (12.0±0.7,13.5±0.8, and14.4±1.1 respectively) compared to the preoperative score (9.1±0.9, p<.01). VAS scores significantly decreased at 1 month, 1 year, and the final follow-up (4.1±0.7, 2.3±0.9, and 2.0±0.8 respectively) compared to the preoperative score (7.2±l .2, p<.01). At the final follow-up, the patient reported satisfaction was rated as very satisfied, satisfied, less satisfied and dissatisfied (79%, 10%, 10%, 1% respectively). Revision surgery was not required for any of the patients during the follow-up period, either due to instrumentation failure or adjacent segmental diseases. In the radiographic assessment, there was a notable increase in IH and IDH after surgery compared to preoperative values (33.0±4.0 mm vs. 30.7±3.0 mm, p<.01 and 6.7±2.4 mm vs. 4.6±0.9 mm, p<.01 respectively), which gradually decreased at 1 year and the final follow-up (IH: 32.1±2.5 vs. 30.9±3.5 p=.024; IDH: 5.3±1.5 mm vs. 4.3±0.6 mm, p=.043 respectively). At the 1-month postoperative follow-up, the segmental ROM exhibited a decrease compared with preoperative values (6.2±1.8° vs. 7.5±2.0° p=.044), followed by an increase at the 1-year follow-up (6.2±1.8° vs. 6.4±1.5° p=.078), but ultimately decreased at the final follow-up (6.4±1.5° vs. 2.9±0.6°, p<.01). HO was observed in approximately 81.5% of cases (75/92), while a great proportion (41.3%) of patients experienced varying degrees of prosthesis subsidence and anterior migration during the follow-up.

CONCLUSION

At the long-term follow-up, a high incidence of HO, along with varying degrees of subsidence and migration of the prosthesis, were observed in most patients. As the motion preservation capability of the ACDI gradually diminishes, delayed intervertebral autofusion becomes a more likely outcome compared to motion sparing.

An in Vivo, Three-Dimensional (3D), Functional Centers of Rotation of the Healthy Cervical Spine

OBJECTIVE

This study examined cervical center of rotation (COR) positions in 7 postures using validated cone beam computed tomography (CBCT) combined with 3D-3D registration in healthy volunteers.

METHODS

CBCT scans were performed on 20 healthy volunteers in 7 functional positions, constructing a three-dimensional (3D) model. Images were registered to the neutral position using 3D-3D registration, allowing analysis of kinematic differences and rotational axes. COR measurements were obtained for each segment (C2/3 to C6/7) in each posture.

RESULTS

The CORs of C2/3 to C6/7 were predominantly posterior (-5.3 ± 3.8 ∼ -0.6 ± 1.2 mm) and superior (16.5 ± 6.0 ∼ 23.6 ± 3.2 mm) to the intervertebral disc's geometric center (GC) in flexion and extension. However, the C4/5 segment's COR was anterior to the GC (2.0 ± 9.8 mm) during flexion and close to it in the right-left direction. During left-right twisting, the CORs of C2/3-C6/7 were posterior (-21.8 ± 10.5 ∼-0.9 ± 0.8 mm) and superior (3.1 ± 7.5 ∼23.2 ± 3.6 mm) to the GCs in anterior-posterior and superior-inferior directions, without consistent right-left directionality. During left-right bending, each segment's COR was predominantly posterior (-25.2 ± 13.1 ∼-6.5 ± 9.9 mm) and superior (0.3 ± 12.5 ∼12.1 ± 5.1 mm) to the GC in anterior-posterior and superior-inferior directions, except for the C2/3 segment, located inferiorly (-5.9 ± 4.1 mm) in left bending. The right-left COR position varied across segments.

CONCLUSIONS

Our findings reveal segment-specific and posture-dependent COR variations. Notably, the CORs of C3/4, C4/5, and C5/6 consistently align near the intervertebral disc's GC at different postures, supporting their suitability for total disc replacement surgery within the C3/4 to C5/6 segments.

Comparable long-term outcomes in patients undergoing total disc replacement or anterior cervical discectomy and noninstrumented fusion

BACKGROUND CONTEXT

Anterior cervical discectomy and fusion (ACDF) is the leading surgical treatment for cervical radiculopathy. However, ACDF surgery has been suggested for to accelerate the degeneration of the adjacent cervical discs, which causes so-called adjacent segment disease (ASD). Over the past 2 decades, total disc replacement (TDR)/cervical disc arthroplasty (CDA) has become an increasingly common method for treating degenerative cervical diseases. The rationale is that a synthetic disc prosthesis may preserve motion at the operated level, which is expected to lead to reduced stress on the other cervical levels and thus decrease the risk of developing ASD. However, since the method was first introduced in the early 2000s, the long-term outcome after it is still not completely understood.

PURPOSE

Our goal was to compare the long-term outcomes of TDR and ACDF procedures.

STUDY DESIGN

Retrospective case-control study.

PATIENT SAMPLE

All patients who underwent TDR due to degenerative cervical disease at Helsinki University Hospital between 2006 and 2012 (38 patients) and matched control patients who underwent ACDF during this period (76 patients) for degenerative disc disease.

OUTCOME MEASURES

The primary outcome measure was the rate of reoperations and further cervical surgeries. Secondary outcome measures included neck symptoms (Neck Disability Index, or NDI), health-related quality of life (EQ-5D-3L), satisfaction with the surgery, radiological outcomes, and employment status.

METHODS

The medical records of all patients who underwent TDR due to degenerative cervical disease at Helsinki University Hospital between 2006 and 2012 and those of the matched control patients were analyzed retrospectively. Questionnaires were sent to all available patients at the end of the follow-up (median 14 years) to evaluate their employment status, levels of satisfaction with the surgery, current neck symptoms, and health-related quality of life. Radiological outcomes were evaluated from the cervical plain radiographs, which were taken either at the end of the follow-up as a part of the present study or earlier on for other clinical reasons, but at least 2 years after index surgery.

RESULTS

The total rate of reoperations and further cervical surgeries during the follow-up of a median of 14 years was 7/38 (18%) in the TDR group and 6/76 (8%) in the ACDF group (p=.096, ns.). Total disc replacement patients were reoperated earlier, and the 5-year reoperation rate was significantly higher in the TDR group (11% vs 1.3%, p=.026). None of the TDR patients underwent further cervical surgery more than 6 years after index surgery, whereas 5/6 (83%) of the reoperated ACDF patients were reoperated after that time. There were no significant differences in the NDIs between the patient groups. The employment rate and health-related quality of life were slightly higher in the TDR group, but the differences were statistically nonsignificant. TDR was significantly better at maintaining the angular range of motion at the operated level, and the fusion rate was significantly lower among this group.

CONCLUSIONS

There were no significant differences in the long-term outcomes of ACDF and TDR when measured by reoperation rates, employment status, NDI, EuroQoL, and satisfaction with surgery. Reoperation rate and, on the other hand, employment rate and health-related quality of life, were higher in the TDR group, but the differences were statistically nonsignificant. However, TDR patients were reoperated earlier, and the 5-year reoperation rate was significantly higher in the TDR group. Randomized long-term studies in which these methods are compared are needed to further clarify the differences between them.

Disc prosthesis versus fusion with cage in single level cervical degenerative spine disease - A retrospective case-control patient reported outcome study

AIM

To compare the clinical outcome of single level cervical degenerative spine disease treated surgically with motion preserving anterior cervical disc arthroplasty versus anterior cervical discectomy and fusion (ACDF).

METHODS

Patients treated with cervical disc arthroplasty at Aalborg University Hospital and ACDF at Aarhus University Hospital were matched 1:2. Primary outcome measures were Neck Disability Index (NDI), EQ-5D-3 L and Numeric rating scale (NRS) for arm- and neck pain. Data was collected by telephone interviews regarding present and retrospective data.

RESULTS

50 patients treated with cervical disc arthroplasty were matched to 100 ACDF patients covering November 2011 to December 2018. Mean improvements for NRS neck pain three-months postoperative, and NDI were significantly better in the cervical disc arthroplasty group, with intergroup differences of 1.56 (p = 0.02) and 5.01 (p = 0.01) respectively. A subgroup analysis of the half of the cohort with the longest follow-up (mean 7.6 years) showed, in favour of cervical disc arthroplasty, mean improvements of NDI: 8.80 (p = 0.00), EQ5D: - 0.19 (p = 0.04), NRS neck three months follow-up: 3.70 (p = 0.00) and long follow-up: 2.54 (p = 0.01) and NRS arm three months follow-up: 2.02 (p = 0.01). Radiologic examination indicated preserved mobility in 80% of the implanted protheses at 24-month post-surgical follow-up.

CONCLUSION

Surgical treatment of one level degenerative cervical spine disease with cervical disc arthroplasty or anterior cervical discectomy and fusion has a similar good clinical outcome after a mean follow-up of 5.6 years. However, cervical disc arthroplasty displayed long-term superiority in the half of the cohort with the longest follow-up time averaging 7.6 years.

Impact of bone-implant gap size on the interfacial osseointegration: an in vivo study

BACKGROUND

The bone-implant gap resulted from morphological mismatch between cervical bony endplates and implant footprint may have adverse impact on bone-implant interfacial osseointegration of cervical disc arthroplasty (CDA). The purpose of the study was to evaluate the impact of bone-implant gap size on the interfacial osseointegration in a rabbit animal model.

METHODS

A series of round-plate implants with different teeth depth (0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm) was specifically designed. A total of 48 New Zealand white rabbits were randomly categorized into four groups by the implants they received (0.5 mm: group A, 1.0 mm: group B, 1.5 mm: group C, 2.0 mm: group D). At 4^th and 12^th week after surgery, animals were sacrificed. Micro-CT, acid fuchsin and methylene blue staining and hematoxylin and eosin (HE) staining were conducted.

RESULTS

At 4^th week and 12^th week after surgery, both micro-CT and HE staining showed more new bone formation and larger bone coverage in group A and group B than that in group C and group D. At 12^th week, the bone biometric parameters were significantly superior in group C when compared with group D (p < 0.05). At 12^th week, hard tissue slicing demonstrated larger portion of direct contact of new bone to the HA coating in group A and group B.

CONCLUSIONS

Bone-implant gap size larger than 1.0 mm negatively affected bone-implant osseointegration between compact bone and HA coated implant surface.

Clinical and radiological outcome 1-year after cervical total disc replacement using the Signus ROTAIO - Prosthesis

INTRODUCTION

The instantaneous center of rotation (iCOR) of a motion segment has been shown to correlate with its total range of motion (ROM). Importantly, a correlation of the correct placement of cervical total disc replacement (cTDR) to preserve a physiological iCOR has been previously identified. However, changes of these parameters and the corresponding clinical relevance have hardly been analyzed. This study assesses the radiological and clinical correlation of iCOR and ROM following cTDR.

MATERIALS/METHODS

A retrospective multi-center observational study was conducted and radiological as well as clinical parameters were evaluated preoperatively and 1 year after cTDR with an unconstrained device. Radiographic parameters including flexion/extension X-rays (flex/ex), ROM, iCOR and the implant position in anterior-posterior direction (IP ap), as well as corresponding clinical parameters [(Neck Disability Index (NDI) and the visual analogue scale (VAS)] were assessed.

RESULTS

57 index segments of 53 patients treated with cTDR were analyzed. Pre- and post-operative ROM showed no significant changes (8.0° vs. 10.9°; p > 0.05). Significant correlations between iCOR and IP (Pearson's R: 0.6; p < 0.01) as well as between ROM and IP ap (Pearson's R: - 0.3; p = 0.04) were identified. NDI and VAS improved significantly (p < 0.01). A significant correlation between NDI and IP ap after 12 months (Pearson's R: - 0.39; p < 0.01) was found.

CONCLUSION

Implantation of the tested prosthesis maintains the ROM and results in a physiological iCOR. The exact position of the device correlates with the clinical outcome and emphasize the importance of implant design and precise implant positioning.

Sagittal intervertebral rotational motion: a deep learning-based measurement on flexion–neutral–extension cervical lateral radiographs

Background

The analysis of sagittal intervertebral rotational motion (SIRM) can provide important information for the evaluation of cervical diseases. Deep learning has been widely used in spinal parameter measurements, however, there are few investigations on spinal motion analysis. The purpose of this study is to develop a deep learning-based model for fully automated measurement of SIRM based on flexion–neutral–extension cervical lateral radiographs and to evaluate its applicability for the flexion–extension (F/E), flexion–neutral (F/N), and neutral–extension (N/E) motion analysis.

Methods

A total of 2796 flexion, neutral, and extension cervical lateral radiographs from 932 patients were analyzed. Radiographs from 100 patients were randomly selected as the test set, and those from the remaining 832 patients were used for training and validation. Landmarks were annotated for measuring SIRM at five segments from C2/3 to C6/7 on F/E, F/N, and N/E motion. High-Resolution Net (HRNet) was used as the main structure to train the landmark detection network. Landmark performance was assessed according to the percentage of correct key points (PCK) and mean of the percentage of correct key points (MPCK). Measurement performance was evaluated by intra-class correlation coefficient (ICC), Pearson correlation coefficient, mean absolute error (MAE), root mean square error (RMSE), and Bland-Altman plots.

Results

At a 2-mm distance threshold, the PCK for the model ranged from 94 to 100%. Compared with the reference standards, the model showed high accuracy for SIRM measurements for all segments on F/E and F/N motion. On N/E motion, the model provided reliable measurements from C3/4 to C6/7, but not C2/3. Compared with the radiologists’ measurements, the model showed similar performance to the radiologists.

Conclusions

The developed model can automatically measure SIRM on flexion–neutral–extension cervical lateral radiographs and showed comparable performance with radiologists. It may provide rapid, accurate, and comprehensive information for cervical motion analysis.

Subjective and Objective Quality-of-Life Assessment of Outcome Measures in Cervical Spine Surgery for Degenerative Changes

Cervical spine diskectomy is a commonly used procedure in degenerative disease of cervical spine surgery. However, it is difficult to assess the quality of life after this widely applied and variously modified procedure. This literature review presents cervical diskectomy results, according to various scales and measures in multidirectional surgical strategies. Using relevant databases, we tried to find the best treatment options for degenerative disk disease and the best method of quality-of-life assessment, searching for modalities that may influence the outcome.

The Changes in Cervical Biomechanics After CTDR and Its Association With Heterotopic Ossification: A Systematic Review and Meta-analysis

STUDY DESIGN

A systematic review and meta-analysis.

OBJECTIVES

Cervical total disc replacement (CTDR) can preserve range of motion (ROM) of the operated spinal segment in cadaver studies. Evidence is less clear in clinical trials. The present study aims to investigate the differences in cervical biomechanics before and after CTDR and its association with heterotopic ossification (HO) development.

METHOD

Articles that reported the rate of HO and ≥1 difference in cervical biomechanics were included in quantitative analyses. We pooled the mean difference (MD) of cervical biomechanics before and after CTDR. Subgroup analyses and metaregression analyses were conducted to identify potential contributors to heterogeneity.

RESULTS

Of the 599 studies screened, 35 studies were included in the final analysis. In comparison with preoperative values, ROM of the spinal segment inferior (MD: 0.38; 95% CI: 0.02 to 0.74) and superior (MD: 0.43; 95% CI: 0.12 to 0.75) to the surgical spinal segment, functional spinal unit (FSU) angle (MD: 2.23; 95% CI: 1.11 to 3.35), and C2/C7 Cobb angle (MD: 3.49; 95% CI: 1.73 to 5.25) significantly increased after CTDR. In contrast, FSU and cervical ROM at baseline were no different from follow-up. On multivariable meta-regression analyses, HO and ROM-limiting HO were not associated with changes in cervical biomechanics. Single-level CTDR and duration of follow-up were associated with changes in cervical biomechanics.

CONCLUSION

Our study reported the pooled mean of biomechanics at baseline and final follow-up and their differences. The changes in biomechanics were not associated with the rates of HO and ROM-limiting HO.

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.

Spontaneous Fusion After Cervical Disc Arthroplasty: A Case Report and Literature Review

Objective

To report a rare case of spontaneous fusion (SF) following cervical disc arthroplasty (CDA), to review the related literature, and to propose a new measure to prevent it.

Methods

The course of a patient with SF is described here. The potential causes, risk factors, and preventive measure of SF after CDA published in previous studies have also been reviewed and discussed.

Results

A 63-year-old man presented with a 6-month history of progressive neck pain and developed left C-7 radiculopathy 4 years ago. Magnetic resonance imaging revealed disc herniation at the C6–C7 levels resulting in compression of the left C-7 nerve root. The patient underwent CDA at the C6–C7 levels, during which a PRESTIGE cervical disc device was implanted. He failed to follow-up regularly as recommended postoperatively because he was completely free from the pain in his neck and left upper limb. Four years later, he was readmitted with a 2-month history of occasional neck stiffness. Plain radiographs indicated complete radiographic fusion of the C6–C7 levels with trabecular bone bridging surrounding the cervical disc prosthesis, and dynamic imaging showed no motion. He was seen at regular follow-up visits for up to 60 months without special treatment, as his symptoms of neck stiffness were minor and his symptom has not worsened since then.

Conclusion

SF after CDA is a rare condition that can be attributed to patient- or prosthesis-related causes, and its risk factors are diverse. SF after CDA did not affect the patient’s clinical outcome, and no special treatment was required for it. Practitioners should be aware of this rare complication and advise patients of the risks before performing CDA.

Correlation of neural foraminal motion after surgical treatment of cervical radiculopathy with long-term patient reported outcomes

Background

Post-surgical changes in adjacent segment motion are considered a factor in further development of degeneration and cervical radiculopathy. The objective was to examine the extent of correlations between physiological motion of cervical foramina and long-term patient reported outcomes (PRO).

Methods

Biplane X-ray imaging and CT-based markerless tracking were used to measure 3D static and dynamic dimensions during neck axial rotation and extension from 18 patients treated for C5-6 radiculopathy with fusion or arthroplasty. Minimum foraminal height (FH.Min) and width (FW.Min), and their range (FH.Range and FW.Range) achieved during a motion task were calculated for adjacent levels (C4-5 and C6-7) at 2.0±0.6 years post-surgery. The modified Japanese Orthopedic Association score (mJOAS), the Neck Disability Index (NDI) including the visual analogue scale (VAS) for neck and arm pain, and the EuroQol EQ-5D score were recorded at 6.5±1.1 years post-surgery. The relationships between 6.5-year outcomes and 2-year foraminal motion were examined using regression.

Results

Worsening patient-reported outcomes were generally associated with lower values of FW.Min (P<0.05 to P<0.008), the associations being stronger for neck extension (r² up to 0.43). Dynamic foraminal measurements from the C6-7 level more significantly and consistently correlated with mJOAS, EQ-5D and NDI Arm Pain VAS (r²=0.27 to 0.43; P<0.03 to P<0.008), whereas those from the C4-5 level correlated with NDI Neck Pain VAS (r²=0.33; P<0.02).

Conclusions

Dynamic 3D foraminal dimensions at 2-year post-surgery, notably FW.Min measured in neck extension at adjacent levels, were associated with PRO at 6.5 years post-surgery. These relationships provide insight into the motion related factors in development of pain and loss of function, and may help develop markers or objective outcome measures.

Cervical Total Disc Replacement and Heterotopic Ossification: A Review of Literature Outcomes and Biomechanics

Anterior cervical discectomy and fusion (ACDF) immobilizes surgical segments and can lead to the development of adjacent segment degeneration and adjacent segment disease. Thus, cervical total disc replacement (CTDR) has been developed with the aim to preserve the biomechanics of spine. However, heterotopic ossification (HO), a complication following CTDR, can reduce the segmental range of motion (ROM) and defects the motion-preservation benefit of CTDR. The pathological process of HO in CTDR remains unknown. HO has been suggested to be a self-defense mechanism in response to the non-physiological biomechanics of the cervical spine following CTDR. The current literature review is concerned with the association between the biomechanical factors and HO formation and the clinical significance of HO in CTDR. Endplate coverage, disc height, segmental angle, and center of rotation may be associated with the development of HO. The longer the follow-up, the higher the rate of ROM-limiting HO. Regardless of the loss of motion-preservation benefit of CTDR in patients with HO, CTDR confers patients with a motion-preservation period before the development of ROM-limiting HO. This may delay the development of adjacent segment degeneration compared with ACDF. Future clinical studies should explore the association between HO and changes in biomechanical factors of the cervical spine.

Incidence of Fusion Across Total Disc Replacement With Heterotopic Ossification: Are Ball and Socket Disk Replacements Fusing With and Without Radiographic Evidence

STUDY DESIGN

This is a level III retrospective study.

OBJECTIVE

The authors aim to review the outcomes and complications of ball and socket total disk replacements (TDRs).

SUMMARY OF BACKGROUND DATA

TDR is a motion-preserving technique that closely reproduces physiologic kinematics of the cervical spine. However, heterotopic ossification and spontaneous fusion after implantation of the total cervical disk have been reported in several studies to decrease the range of motion postulated by in vitro and in vivo biomechanical studies.

METHODS

The medical records of 117 consecutive patients undergoing cervical TDR over a 5-year period with Mobi-C, Prodisc-C, Prestige LP, and Secure-C implants were followed. Outcomes assessed included Visual Analogue Scale neck and arm and Neck Disability Index scores. The radiographic assessment looked at heterotopic ossification leading to fusion and complication rates.

RESULTS

Of the 117 patients that underwent TDR, 56% were male with the group's mean age being 46.2±10.3 years and body mass index of 18.9±13.6 kg/m. The longest follow-up was 5 years with Prodisc-C group, with overall fusion noted in 16% of patients. One patient was also noted to have fusion which was not seen radiographically but noted intraoperatively for adjacent segment disease. There has been no demonstrable radiographic fusion seen in the Prestige LP group, however, the follow-up has only been 12-24 months for this group.

CONCLUSION

In this study, we have demonstrated radiographic fusion anterior to the ball and socket TDR as well as the uncovertebral joint. We postulate that with the use of a mobile core disk there is an increased potential for fusion leading to a nonfunctional disk replacement.

Heterotopic ossification and radiographic adjacent-segment disease after cervical disc arthroplasty

OBJECTIVE

Cervical disc arthroplasty (CDA) is an accepted motion-sparing technique associated with favorable patient outcomes. However, heterotopic ossification (HO) and adjacent-segment degeneration are poorly understood adverse events that can be observed after CDA. The purpose of this study was to retrospectively examine 1) the effect of the residual exposed endplate (REE) on HO, and 2) identify risk factors predicting radiographic adjacent-segment disease (rASD) in a consecutive cohort of CDA patients.

METHODS

A retrospective cohort study was performed on consecutive adult patients (≥ 18 years) who underwent 1- or 2-level CDA at the University of Calgary between 2002 and 2015 with > 1-year follow-up. REE was calculated by subtracting the anteroposterior (AP) diameter of the arthroplasty device from the native AP endplate diameter measured on lateral radiographs. HO was graded using the McAfee classification (low grade, 0-2; high grade, 3 and 4). Change in AP endplate diameter over time was measured at the index and adjacent levels to indicate progressive rASD.

RESULTS

Forty-five patients (58 levels) underwent CDA during the study period. The mean age was 46 years (SD 10 years). Twenty-six patients (58%) were male. The median follow-up was 29 months (IQR 42 months). Thirty-three patients (73%) underwent 1-level CDA. High-grade HO developed at 19 levels (33%). The mean REE was 2.4 mm in the high-grade HO group and 1.6 mm in the low-grade HO group (p = 0.02). On multivariable analysis, patients with REE > 2 mm had a 4.5-times-higher odds of developing high-grade HO (p = 0.02) than patients with REE ≤ 2 mm. No significant relationship was observed between the type of artificial disc and the development of high-grade HO (p = 0.1). RASD was more likely to develop in the lower cervical spine (p = 0.001) and increased with time (p < 0.001). The presence of an artificial disc was highly protective against degenerative changes at the index level of operation (p < 0.001) but did not influence degeneration in the adjacent segments.

CONCLUSIONS

In patients undergoing CDA, high-grade HO was predicted by REE. Therefore, maximizing the implant-endplate interface may help to reduce high-grade HO and preserve motion. RASD increases in an obligatory manner following CDA and is highly linked to specific levels (e.g., C6-7) rather than the presence or absence of an adjacent arthroplasty device. The presence of an artificial disc is, however, protective against further degenerative change at the index level of operation.

Clinical and Radiological Outcome of a New Total Cervical Disc Replacement Design

STUDY DESIGN

A nonrandomized, prospective, and single-center clinical trial of the ProDisc Vivo prosthesis.

OBJECTIVE

The aim of this study was to investigate the clinical and radiological results of a refined total cervical disc replacement (cTDR), the ProDisc Vivo, with two years of follow-up (FU). The incidence of implant-related complications was recorded as a secondary outcome variable.

SUMMARY OF BACKGROUND DATA

Previous generations of the ProDisc artificial cervical disc replacement generate high primary stability due to keel-based designs with opening of the anterior cortex during the implantation and subsequent high rates of heterotopic ossifications.

METHODS

Clinical outcome scores included the Neck Disability Index (NDI), Visual Analogue Scale (VAS), arm and neck pain self-assessment questionnaires. The radiological outcome included the range of motion (ROM) and the occurrence of heterotopic ossifications. The incidence of implant-related complications with new implant design was recorded as a secondary outcome variable.

RESULTS

A total of 55 patients received a single-level treatment with the ProDisc Vivo cTDR between C3/4 and C6/7, with a follow-up rate of 78%. The clinical outcome scores improved in all parameters significantly (P = 0.0001) (NDI: 68.3 → 17.4; VAS arm: 6.3 → 1.4; VAS neck: 4.9 → 1.6). The ROM of the index-segment did not show a significant change (P = 0.26) (7.9° → 9.2°). Heterotopic ossifications at the index segment was found as grade 0 in 58%, grade 1 in 22%, grade 2 in 10%, grade 3 (with functional impairment of the prosthesis) in 7%, and grade 4 in 3% of the cases. We observed three implant-related complications (5.5%), with two implant dislocations anteriorly and one low-grade infect.

CONCLUSION

cTDR with ProDisc Vivo demonstrated a significant and sustained improvement of all clinical outcome parameters. A less invasive implantation mechanism with lower primary stability of the cTDR might be a reason for a higher dislocation rate than the keel-based previous generation ProDisc C.

LEVEL OF EVIDENCE

4.

Is the behavior of disc replacement adjacent to fusion affected by the location of the fused level in hybrid surgery?

BACKGROUND CONTEXT

Hybrid surgery (HS), consisting of cervical disc arthroplasty (CDA) at the mobile level, along with anterior cervical discectomy and fusion at the spondylotic level, could be a promising treatment for patients with multilevel cervical degenerative disc disease (DDD). An advantage of this technique is that it uses an optimal procedure according to the status of each level. However, information is lacking regarding the influence of the relative location of the replacement and the fusion segment in vivo.

PURPOSE

We conducted the present study to investigate whether the location of the fusion affected the behavior of the disc replacement and adjacent segments in HS in vivo.

STUDY DESIGN

This is an observational study.

PATIENT SAMPLE

The numbers of patients in the arthroplasty-fusion (AF) and fusion-arthroplasty (FA) groups were 51 and 24, respectively.

OUTCOME MEASURES

The Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), and Visual Analog Scale (VAS) scores were evaluated. Global and segmental lordosis, the range of motion (ROM) of C2-C7, and the operated and adjacent segments were measured. Fusion rate and radiological changes at adjacent levels were observed.

METHODS

Between January 2010 and July 2016, 75 patients with cervical DDD at two contiguous levels undergoing a two-level HS were retrospectively reviewed. The patients were divided into AF and FA groups according to the locations of the disc replacement. Clinical outcomes were evaluated according to the JOA, NDI, and VAS scores. Radiological parameters, including global and segmental lordosis, the ROM of C2-C7, the operated and adjacent segments, and complications, were also evaluated.

RESULTS

Although the JOA, NDI, and VAS scores were improved in both the AF and the FA groups, no significant differences were found between the two groups at any follow-up point. Both groups maintained cervical lordosis, but no difference was found between the groups. Segmental lordosis at the fusion segment was significantly improved postoperatively (p<.001), whereas it was maintained at the arthroplasty segment. The ROM of C2-C7 was significantly decreased in both groups postoperatively (AF p=.001, FA p=.014), but no difference was found between the groups. The FA group exhibited a non-significant improvement in ROM at the arthroplasty segment. The ROM adjacent to the arthroplasty segment was increased, although not significantly, whereas the ROM adjacent to the fusion segment was significantly improved after surgery in both groups (p<.001). Fusion was achieved in all patients. No significant difference in complications was found between the groups.

CONCLUSIONS

In HS, cephalic or caudal fusion segments to the arthroplasty segment did not affect the clinical outcomes and the behavior of CDA. However, the ROM of adjacent segments was affected by the location of the fusion segment; segments adjacent to fusion segments had greater ROMs than segments adjacent to arthroplasty segments.

Long-Term Outcomes After Microscopic Anterior Cervical Foraminotomy with a Minimum 10-Year Follow-Up

BACKGROUND

Microscopic anterior cervical foraminotomy (MACF) is a surgical technique for unilateral cervical radiculopathy that preserves segmental motion and avoids adjacent segmental degeneration, but little is known of its long-term outcomes.

METHODS

A retrospective minimum 10-year follow-up study was conducted on patients treated by 1 surgeon. Clinical outcomes were assessed using a visual analog scale of neck and arm pain, Neck Disability Index, and Odom criteria. Surgical outcomes were assessed using additional procedure rates. Radiologic outcomes were estimated by measuring disc heights, segmental angles, and range of motion at the surgical level and adjacent segments, and so on.

RESULTS

Of the 94 patients who underwent MACF between January 2000 and December 2004 by 1 surgeon, 69 were enrolled in this study. Median follow-up period was 11.9 years (range, 10.0-14.5 years). Visual analog scales for neck or arm pain and Neck Disability Index improved significantly during follow-up period (P < 0.001). Also, according to the Odom criteria, an excellent or good outcome was achieved in 62 patients (89.9%) at final follow-up. An additional procedure was performed in 10 patients (14.5%) for symptom recurrence during the follow-up period. The only risk factor found to be related to the need for an additional procedure was a small preoperative range of motion at the surgical level (P = 0.018). Although mean disc height at the surgical level decreased significantly (from 6.23 ± 1.10 to 5.17 ± 1.12 mm; P = 0.004), adjacent discs were not significantly affected.

CONCLUSIONS

Although some radiologic results have shortcomings, the results of this study suggest that MACF has favorable long-term outcomes.

Heterotopic Ossification After Cervical Total Disc Replacement at 7 Years-Prevalence, Progression, Clinical Implications, and Risk Factors

Background

Heterotopic ossification (HO) is a known risk following cervical total disc replacement (CTDR) surgery, but the cause and effect of HO are not well understood. Reported HO rates vary, and few studies are specifically designed to report HO. The effects on outcomes, and the risk factors for the development of HO have been hypothesized and reported in small-population, retrospective analyses, using univariate statistics.

Methods

Posthoc, multiple-phase analysis of radiographic, clinical, and demographic data for CTDR as it relates to HO was performed. HO was radiographically graded for 164 one-level and 225 two-level CTDR patients using the McAfee and Mehren system. Analysis was performed to correlate HO grades to clinical outcomes and to evaluate potential risk factors for the development of HO using demographics and baseline clinical measures.

Results

At 7 years, 1-level clinically relevant HO grades were 17.6% grade 3 and 11.1% grade 4. Two-level clinically relevant HO grades, evaluated using the highest patient grade, were 26.6% grade 3 and 10.8% grade 4. Interaction between HO and time revealed significance for neck disability index (NDI; P = .04) and Visual Analog Scale (VAS) neck pain (P = .02). When analyzed at each time point NDI was significant at 48-84 months and VAS neck at 60 months. For predictors 2 analyses were run; odds ratios indicated follow-up visit, male sex, and preoperative VAS neck pain are related to HO development, whereas hazard ratios indicated male sex, obesity, endplate coverage, levels treated, and preoperative VAS neck pain.

Conclusions

This is the largest study to report HO rates, and related outcomes and risk factors. To develop an accurate predictive model, further large-scale analyses need to be performed. Based on the results reported here, clinically relevant HO should be more accurately described as motion-restricting HO until a definitive link to outcomes has been established.

Clinical and radiographic outcome of dynamic cervical implant (DCI) arthroplasty for degenerative cervical disc disease: a minimal five-year follow-up

Background

To evaluate the mid- to long-term clinical and radiographic outcomes of anterior cervical discectomy and dynamic cervical implant (DCI) arthroplasty for degenerative cervical disc disease.

Methods

From April 2010 to October 2010, 38 patients with single- or double-level cervical disc herniation underwent anterior cervical discectomy and DCI arthroplasty. The clinical results and radiographic outcomes of these 38 patients (42 levels) were retrospectively evaluated. The clinical results included the visual analogue scale, Japanese Orthopaedic Association score, Neck Disability Index score, 36-item short form health survey questionnaire, and incidences of complications and neurological deterioration. Radiographic results including cervical alignment, intervertebral height, cervical range of motion (ROM), ROM of the functional spinal unit, adjacent intervertebral ROM, migration, subsidence, and heterotopic ossification (HO) were assessed on plain radiography, three-dimensional computed tomography, and magnetic resonance imaging.

Results

The mean follow-up period was 72.3 months (range 68–78 months). During follow-up, all patients showed significant improvements in the visual analogue scale score, Japanese Orthopaedic Association score, Neck Disability Index score, 36-item short form health survey physical component summary score and mental component summary score. The ROM of the functional spinal unit was partly reduced. The DCI migrated forward in 10 of 42 (23.8%) cases, and HO was detected in 24 of the 42 (57.1%) DCI segments. Subsidence was observed in 14 of 42 (33.3%) DCI segments. Two patients experienced symptom recurrence, and were treated conservatively.

Conclusions

The clinical efficacy of DCI arthroplasty was maintained during mid- to long-term follow-up. HO formation is a common phenomenon, leading to a substantial decrease in ROM at the index level and recurrence of neurological symptoms. The incidence of implant subsidence and migration is relatively high, leaving a potential risk of symptoms at the index level and adjacent segment degeneration. We consider that the first choice for patients with degenerative cervical disc disease should still be total disc replacement or anterior cervical discectomy and fusion, rather than DCI arthroplasty.

Clinical experience and two-year follow-up with a one-piece viscoelastic cervical total disc replacement

BACKGROUND

The purpose of this study is to present clinical outcome data from a 2-year post-market study of a viscoelastic one-piece cervical total disc replacement (TDR) in Europe.

METHODS

Thirty-nine patients were implanted at five surgical sites in an European post-market clinical study. Clinical outcomes included improvement of neck disability index (NDI) and visual analog scale scores for neck and arm pain from baseline to 2-year follow-up, neurological examinations, patients view on the success of surgery, complications, and subsequent surgical interventions.

RESULTS

Thirty patients had the Freedom^® Cervical Disc (FCD) implanted at a single level, and nine patients were implanted at two adjacent levels. The population had a similar distribution of male [20] and female [19] subjects, with a mean age of 45 years. All self-administered outcome measures showed significant clinically important improvements from baseline to the 2-year follow-up. Mean preoperative NDI score improved from 48% to 20%, 13%, 8%, 6% and 4% at 6 weeks, 3, 6, 12, and 24 months, respectively. Average preoperative visual analog scale (VAS) scores of the neck, right and left arm pain intensity and frequency showed significant improvement. All neurological outcome measurements showed immediate improvement from preoperative values and continued improvement throughout 2 years follow-up. From pre-op to 24 months, neurological deficits declined in the population from 21% to 6% for reflex function, 62% to 17% for sensory function, and 38% to 3% for motor function. No patients experienced a deterioration in any measured outcomes compared with the preoperative situation. Patient satisfaction increased over 2 years post-op, with 83% of patients responding that they would "definitely" choose to have the same treatment for their neck/arm condition and another 11% responding that they would "probably" choose to have the same treatment.

CONCLUSIONS

The FCD performs as expected in patients with single-level and two-level degenerative disc disease.

Anterior cervical discectomy and fusion surgery versus total disc replacement: A comparative study with minimum of 10-year follow-up

Based on long-term follow-ups, this study was designed to investigate the incidence and risk factors for postoperative adjacent segment degeneration (ASD) after anterior cervical discectomy and fusion (ACDF) or total disc replacement (TDR) in treating cervical degenerative diseases. Between January 2000 and December 2005, 108 cases undergoing ACDF and 78 undergoing TDR, were enrolled into this study. All medical records were retrospectively collected. Every patient was followed up at least 10 years. Outcome assessment included visual analogue scale (VAS) score, Neck Disability Index (NDI) score, Japanese Orthopaedic Association (JOA) score, and radiographic parameters. Consequently, thirty-eight (35.2%) of 108 cases suffered from ASD in ACDF group, and 26 (33.3%) of 78 cases in TDR group. There was no statistical difference between the two groups regarding ASD incidence, VAS/NDI/JOA score, recovery rate. Logistic regression analysis showed that age (OR = 2.86, 95% CI, 1.58-4.14) and preoperative segmental lordosis (OR = 1.90, 95% CI, 1.05-3.20) were risk factors associated with increased odds of ASD regardless of surgical procedures. On the other hand, preoperative overall lordosis (OR = 0.54, 95% CI, 0.26-0.82) was most likely protective. In conclusion, advanced age and preoperative segmental lordosis were identified as risk factors for postoperative ASD, while preoperative overall lordosis proves to be a protective factor.

Adjacent Segment Degeneration Following Anterior Cervical Discectomy and Fusion Versus the Bryan Cervical Disc Arthroplasty

Background

Anterior cervical discectomy and fusion (ACDF) is an established treatment for degenerative disease of the cervical disc, but adjacent segment degeneration or instability may develop long term. The aim of this study was to investigate the risk factors for adjacent segment degeneration following ACDF compared with the use of the Bryan artificial disc for cervical disc arthroplasty (CDA).

Material/Methods

A prospective comparative study included 93 patients who underwent ACDF or CDA with the Bryan artificial cervical disc between 2002 and 2004, and who had more than eight years of follow-up. There were 29 cases in the CDA group and 39 cases in ACDF group, with a follow-up rate of 73.12%. Clinical results and imaging data were assessed before and after surgery.

Results

There was no significant difference between the two groups in radiographic parameters at each follow-up time point. There were 19 cases of adjacent segment degeneration (48.72%) in the ACDF group, and 13 cases of adjacent segment degeneration (44.83%) in the CDA group, with no statistically significant difference (P>0.05). Univariate analysis showed that advanced age (OR 1.271, 95% CI 1.005–1.607), low preoperative overall lordosis (OR 0.858, 95% CI 0.786–0.936) and low preoperative segmental lordosis (OR 1.185, 95% CI 1.086–1.193) were significantly correlated with adjacent segment degeneration.

Conclusions

Equally good clinical outcomes were achieved with both the ACDF and the Bryan CDA. Increasing patient age was associated with adjacent segment degeneration in both patient groups.

Bone loss of vertebral bodies at the operative segment after cervical arthroplasty: a potential complication?

OBJECTIVE Bony overgrowth and spontaneous fusion are complications of cervical arthroplasty. In contrast, bone loss or bone remodeling of vertebral bodies at the operation segment after cervical arthroplasty has also been observed. The purpose of this study is to investigate a potential complication-bone loss of the anterior portion of the vertebral bodies at the surgically treated segment after cervical total disc replacement (TDR)-and discuss the clinical significance. METHODS All enrolled patients underwent follow-up for more than 24 months after cervical arthroplasty using the Baguera C disc. Clinical evaluations included recording demographic data and measuring the visual analog scale and Neck Disability Index scores. Radiographic evaluations included measurements of the functional spinal unit's range of motion and changes such as bone loss and bone remodeling. The grading of the bone loss of the operative segment was classified as follows: Grade 1, disappearance of the anterior osteophyte or small minor bone loss; Grade 2, bone loss of the anterior portion of the vertebral bodies at the operation segment without exposure of the artificial disc; or Grade 3, significant bone loss with exposure of the anterior portion of the artificial disc. RESULTS Forty-eight patients were enrolled in this study. Among them, bone loss developed in 29 patients (Grade 1 in 15 patients, Grade 2 in 6 patients, and Grade 3 in 8 patients). Grade 3 bone loss was significantly associated with postoperative neck pain (p < 0.05). Bone loss was related to the motion preservation effect of the operative segment after cervical arthroplasty in contrast to heterotopic ossification. CONCLUSIONS Bone loss may be a potential complication of cervical TDR and affect early postoperative neck pain. However, it did not affect mid- to long-term clinical outcomes or prosthetic failure at the last follow-up. Also, this phenomenon may result in the motion preservation effect in the operative segment after cervical TDR.