Implant Design and the Anchoring Mechanism Influence the Incidence of Heterotopic Ossification in Cervical Total Disc Replacement at 2-year Follow-up

Device profile of the Mobi-C artificial cervical disc: an overview of its safety and efficacy

INTRODUCTION

The Mobi-C Cervical Disc Replacement is a motion preserving alternative to anterior cervical discectomy and fusion in properly indicated patients. In 2013, Mobi-C became the first cervical disc in the United States approved to treat more than one level of the cervical spine. The FDA determined Mobi-C to be statistically superior to fusion at two levels, based on the primary endpoint of a prospective, concurrently controlled and randomized multicenter clinical trial.

AREAS COVERED

The history of Mobi-C and cervical disc arthroplasty is discussed. The unique biomechanics and structure of Mobi-C, the clinical results, the long term follow-up, the disc's biomechanics, and cost-effectiveness research are described. The competitive landscape is overviewed.

EXPERT OPINION

The evidence in this article supports the use of the Mobi-C cervical disc prosthesis as a viable alternative to fusion surgery in selected patients. Mobi-C has a relatively long track record compared to most other cervical disc prostheses. Thus far, Mobi-C is a very good option for preserving cervical motion based on long term follow-up, for achieving favorable clinical outcomes, and for maintaining patient safety. The Mobi-C cervical disc prosthesis is generally viewed positively, supported by clinical experience and research findings.

Could the different surgical goals of fusion and non-fusion also be achieved in combination within the same patient? Clinical and radiological outcome of hybrid cervical spine surgery

PURPOSE

Hybrid cervical spine surgery (HS) is a novel surgical strategy wherein an artificial disc replacement is done with a cervical fusion nearby with a stand-alone titanium cage to combine the advantages in both procedures. The aim of this study was to evaluate interactions of these devices within the same patient, and to analyze, if the different goal of each implant is accomplished.

METHODS

Thirty-six patients were treated surgically within a non-randomized retrospective study framework with HS. Patients were examined preoperatively followed by clinical and radiological examination at least one year postoperative. Clinical outcome was detected with NDI, VAS arm/neck, pain self-assessment questionnaires and subjective patient satisfaction. Radiological assessments included RoM, segmental lordosis, cervical lordosis of C2-C7, subsidence, ap-migration and heterotopic ossifications (HO) at the cTDR levels.

RESULTS

Statistically significant improvement of all clinical scores was observed (NDI 37.5 to 5.76; VASarm 6.41 to 0.69; VASneck 6.78 to 1.48). Adequate RoM was achieved at cTDR levels. RoM in the ACDF levels was reduced statistically significant (p < 0.001), and solid fusion (> 2°) was achieved in all evaluated fusion level. Global lordosis (C2-C7) increased statistically significant (2.4° to 8.1°). Subsidence and HO at the cTDR levels did not occur.

CONCLUSIONS

HS results in preservation of the segmental motion in the cTDR and fast and solid fusion in the cage cohort simultaneously. Patient safety was proven. In carefully selected cases, HS is a safe and viable treatment option by choosing the right "philosophy" level per level.

Experimental measurements of micromotions of the cementless intervertebral disc prostheses in the cadaver bone

BACKGROUND

Sufficient primary stability is mandatory for successful bony prosthetic incorporation. Therefore, defined micromotion values of 150 μm should not be exceeded as higher values might compromise the ingrowth of bone trabeculae to the implant surface. The aim of this study was to evaluate the primary stability of different cementless disc prosthesis in a cadaver model.

METHODS

Four different implants with different anchoring and bearing concept were tested with a target level of L4/5. 26 specimens were randomly allocated to 1 of the 4 different implants with 6 speciments in each group. Two groups were formed depending on the anchoring (spikes vs. fin) and bearing concept (non-/semi- vs. constrained). Each implant was tested regarding primary stability in a hydraulic simulator allowing simultaneous polyaxial segment movements and axial loading. The measurements were recorded on the lower plate of the prosthesis.

FINDINGS

The majority of the implants showed micromotion values below 200 μm in all planes. Only one prosthesis presented borderline longitudinal amplitudes that were significant higher than the other planes. Furthermore, significant differences were observed in the sagittal plane when comparing spike and keel anchoring. Spike anchoring implants showed superior tresults to keel anchoring implants (40 μm vs. 55 μm; p = .039), while the non-/semi-constrained bearing concept was more advantageous compared to constrained group (40 μm vs. 63 μm; p = .001).

INTERPRETATION

Spike anchoring and non-constrained implants might provide better primary stability.

Effects of endplate coverage and intervertebral height change on heterotopic ossification following cervical disc replacement

Background

Heterotopic ossification (HO) is a common complication after cervical disc replacement (CDR). Biomechanical factors including endplate coverage and intervertebral disc height change may be related to HO formation. However, there is a dearth of quantitative analysis for endplate coverage, intervertebral height change and their combined effects on HO.

Methods

Patients who underwent single-level or two-level CDR with Prestige-LP were retrospectively reviewed. Clinical outcomes were evaluated through Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI) score, and visual analogue scale (VAS) score. Radiological data, including the prosthesis-endplate depth ratio, intervertebral height change, posterior heterotopic ossification (PHO) and angular parameters, were collected. Logistic regression analysis was used to identify the potential risk factors. Receiver operating characteristic curves were plotted and the cut-off values of each potential factors were calculated.

Results

A total of 138 patients with 174 surgical segments were evaluated. Both the prosthesis-endplate depth ratio (P < 0.001) and post-operative disc height change (P < 0.001) were predictive factors for PHO formation. The area under the curve (AUC) of the prosthesis-endplate depth ratio, disc height change and their combined effects represented by the combined parameter (CP) were 0.728, 0.712 and 0.793, respectively. The risk of PHO significantly increased when the prosthesis-endplate depth ratio < 93.77% (P < 0.001, OR = 6.909, 95% CI 3.521–13.557), the intervertebral height change ≥ 1.8 mm (P < 0.001, OR = 5.303, 95% CI 2.592–10.849), or the CP representing the combined effect < 84.88 (P < 0.001, OR = 10.879, 95% CI 5.142–23.019).

Conclusions

Inadequate endplate coverage and excessive change of intervertebral height are both potential risk factors for the PHO after CDR. Endplate coverage less than 93.8% or intervertebral height change more than 1.8 mm would increase the risk of PHO. The combination of these two factors may exacerbate the non-uniform distribution of stress in the bone-implant interface and promote HO development.

Cervical Total Disc Replacement: Expanded Indications

Cervical total disc replacement (cTDR) is now a firm alternative to anterior cervical discectomy and fusion (ACDF) for degenerative disc disease (DDD). Robust level 1 data from Federal Drug Administration-approved clinical trials demonstrated that cTDR is in any case equally safe and effective compared with ACDF for 1- or 2-level DDD. Furthermore, from early postoperative to long-term follow-up of 10 to 15 years, cTDR rates superiorly in many primary clinical outcomes. According to the published literature, at least nine different cTDR devices share this consistent pattern. On the other hand, the surgical treatment of more than 2-level disc disease is haunted by an elusive paradox. It is easily understandable that 3- and 4-level ACDF, with the well-known associated limitations, is not the superlative intervention for a spine segment anatomically designed to provide motion, as cervical spine is. Furthermore, multilevel ACDF exacerbates many of the clinical and biomechanical complications related with single-level fusion. However, as cTDR is not immaculate of constraints and failures, its clinical safety and efficacy and cost-effectiveness in multilevel anterior compressive pathology need to be established. This article analyses the current available evidence supporting the expanded indication of cTDR to 3- and 4-level disc disease, either stand-alone or adjacent to fusion, from a less stringent European perspective.

Effect of Disc Height and Degree of Distraction on Heterotopic Ossification After Cervical Disc Replacement

BACKGROUND

Heterotopic ossification (HO) is a potential and severe complication of cervical disc replacement (CDR). However, the underlying mechanism of CDR and its association with preoperative disc height loss (DHL) and postoperative degree of distraction remain unclear. We hypothesized that DHL and postoperative degree of distraction could predict HO after CDR.

METHODS

Data were obtained from 127 patients who underwent single-level CDR with a minimum follow-up of 2 years. DHL and adjusted degree of distraction (ADD) were obtained from lateral radiographs, and HO was evaluated at the last follow-up appointment. Receiver operating characteristic curves were calculated to verify the diagnostic value of DHL and ADD in predicting HO.

RESULTS

Both DHL and ADD were significantly larger in the HO group than in the non-HO group (P < 0.05). DHL ≥24.97% increased the risk of HO by 5 times (P = 0.003, 95% confidence interval 1.62-15.49), and ADD ≥36.67% increased the risk of HO by 3.87 times (P < 0.001, 95% confidence interval 1.81-8.27). A combined DHL and ADD (combined parameter) cutoff of 60.36 had a sensitivity of 87.18%, specificity of 67.35%, and area under the curve of 0.77 for predicting HO.

CONCLUSIONS

DHL and ADD are associated with the development of HO after CDR. The cutoff value of DHL may narrow the criteria for CDR with the aim of reducing HO formation. The combined parameter may help surgeons to select the most suitable implant height to reduce the prevalence of HO.

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.

Multilevel cervical arthroplasty-clinical and radiological outcomes

BACKGROUND

Cervical disc arthroplasty (CDA) is a valid option for single-level cervical disc disease (CDD) as an alternative to fusion. However, the use in 3- and 4-level disc disease is under scrutiny with scarce data published so far. Our aim was to study clinical and radiological outcomes of arthroplasty in patients with multilevel CDD.

METHODS

Retrospective analysis of clinical records, pre- and post-operative neutral/dynamic X-rays of patients who underwent CDA in multilevel CDD (2-4 levels). We evaluated sagittal balance parameters (C2-7 and index angle, SVA), global and segmental range of motion (ROM)), neck and arm VAS, Odom's criteria, re-operation rate, adjacent segment disease (ASD), willingness to undertake the same procedure again. Rate of heterotopic ossification (HO) was studied for follow-up >2 years. A subgroup analysis was performed regarding 2-level versus 3- or 4-level arthroplasty.

RESULTS

Thirty-two patients were included, 6 males and 26 females, mean age of 46 years (range, 30-63). Seventy-seven cervical disc levels were treated with the same artificial disc. Twenty-one patients were operated on 2 levels, nine in 3 levels, and 2 patients in 4 levels. Post-operatively, there was a decrease in SVA (-2.2±8.36 mm, P=0.098) and an increase in global (3.7±9.6º, P=0.042) and index (1.3±6.1º, P=0.071) ROM. Mean nVAS and aVAS decreased (7.5±1.1 to 2.5±1.5; 6.3±1.9 to 2.2±1.7, P<0.05). Two-level versus 3-4 level patient subgroups showed a lower SVA (-1.3±8.1 mm P=0.47; -3.4±6.3 mm P=0.107), a slight increase in global (1.6±9.4º P=0.44; 7.2±11.7º P=0.07) and index (1.1±4.7º P=0.12; 1.3±8.1º P=0.35) ROM. HO was present in 9.9% (7/71) of disc levels operated, none of them with grade 3 or 4.

CONCLUSIONS

Multilevel CDA provides good clinical and radiological outcomes, preserving global and segmental cervical mobility, while having a beneficial effect on sagittal balance. These results hold for 2 to 4 levels, making this technique a valuable option in selected patients with cervical multilevel CDD.