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.

Lumbar Total Disk Replacement Device Removals and Revisions Performed During a 20-Year Experience with 2141 Patients.

STUDY DESIGN: This was a retrospective study with prospective patient contact attempted to collect current data. OBJECTIVE: The purpose was to investigate the incidence and reasons for lumbar total disk replacement (TDR) removal or revision. SUMMARY OF BACKGROUND DATA: A concern regarding lumbar TDR was safety, particularly the need for device removal or revision. This may be particularly important considering removal/revision requires repeat anterior exposure with an increased risk of vascular injury. METHODS: Data were collected for a series of 2141 lumbar TDR patients, beginning with the first case experience in 2000. The mean follow-up was 78.6 months. For each case of device removal/revision, the reason, duration from index surgery, and procedure performed were recorded. RESULTS: Of 2141 patients, 27 (1.26%) underwent TDR removal or revision. Device removal was performed in 24 patients (1.12%), while three patients underwent revision (0.14%). Of the 24 removals, 12 were due to migration and/or loosening, three developed problems post-trauma, two developed lymphocytic reaction to device materials, two had ongoing pain, and there was one case of each: TDR was too large, vertebral body fracture (osteoporosis), lytic lesion, device subsidence and facet arthrosis, and infection seeded from a chest infection 146 months post-TDR. The three revisions were for Core repositioning (technique error), device repositioning after displacement, and core replacement due to wear/failure. With respect to timing, 37.0% of removals/revisions occurred within one-month postimplantation. Of note, 40.7% of removals/revisions occurred in the first 25 TDR cases performed by individual surgeons. There was one significant vascular complication occurring in a patient whose TDR was removed due to trauma. This was also the only patient among 258 with ≥15-year follow-up who underwent removal/revision. CONCLUSION: In this large consecutive series, 1.26% of TDRs were removed/revised. The low rate over a 20 year period supports the safety of these devices.

Prosthesis design and likelihood of achieving physiological range of motion after cervical disc arthroplasty: analysis of range of motion data from 1,173 patients from 7 IDE clinical trials.

BACKGROUND CONTEXT: The functional goals of cervical disc arthroplasty (CDA) are to restore enough range of motion (ROM) to reduce the risk of accelerated adjacent segment degeneration but limit excessive motion to maintain a biomechanically stable index segment. This motion-range is termed the "Physiological mobility range." Clinical studies report postoperative ROM averaged over all study subjects but they do not report what proportion of reconstructed segments yield ROM in the Physiological mobility range following CDA surgery. PURPOSE: To calculate the proportion of reconstructed segments that yield flexion-extension ROM (FE-ROM) in the Physiological mobility range (defined as 5°-16°) by analyzing the 24-month postoperative data reported by clinical trials of various cervical disc prostheses. STUDY DESIGN/SETTING: Analysis of 24-month postoperative FE-ROM data from clinical trials. PATIENT SAMPLE: Data from 1,173 patients from single-level disc replacement clinical trials of 7 cervical disc prostheses. OUTCOME MEASURES: 24-month postoperative index-level FE-ROM. METHODS: The FE-ROM histograms reported in Food and Drug Administration-Investigational Device Exemption (FDA-IDE) submissions and available for this analysis were used to calculate the frequencies of implanted levels with postoperative FE-ROM in the following motion-ranges: Hypomobile (0°-4°), Physiological (5°-16°), and Hypermobile (≥17°). The ROM histograms also allowed calculation of the average ROM of implanted segments in each of the 3 motion-ranges. RESULTS: Only 762 of 1,173 patients (implanted levels) yielded 24-month postCDA FE-ROM in the physiological mobility range (5°-16°). The proportions ranged from 60% to 79% across the 7 disc-prostheses, with an average of 65.0%±6.2%. Three-hundred and two (302) of 1,173 implanted levels yielded ROM in the 0°-4° range. The proportions ranged from 15% to 38% with an average of 25.7%±8.9%. One-hundred and nine (109) of 1,173 implanted levels yielded ROM of ≥17° with a range of 2%-21% and an average proportion of 9.3%±7.9%. The prosthesis with built-in stiffness due to its nucleus-annulus design yielded the highest proportion (103/131, 79%) of implanted segments in the physiological mobility range, compared to the cohort average of 65% (p<.01). Sixty-five of the 350 (18.6%) discs implanted with the 2 mobile-core designs in this cohort yielded ROM≥17° as compared to the cohort average of 9.3% (109/1,173) (p<.05). At 2-year postCDA, the "hypomobile" segments moved on average 2.4±1.2°, those in the "physiological-mobility" group moved 9.4±3.2°, and the hypermobile segments moved 19.6±2.6°. CONCLUSIONS: Prosthesis design significantly influenced the likelihood of achieving FE-ROM in the physiological mobility range, while avoiding hypomobility or hypermobility (p<.01). Postoperative ROM averaged over all study subjects provides incomplete information about the prosthesis performance - it does not tell us how many implanted segments achieve physiological mobility and how many end up with hypomobility or hypermobility. We conclude that the proportion of index levels achieving postCDA motions in the physiological mobility range (5°-16°) is a more useful outcome measure for future clinical trials.

Comparison of Clinical and Imaging Outcomes of Cervical Disc Replacement in Patients with Different Hounsfield Units.

OBJECTIVE: To compare clinical and imaging outcomes after cervical disc replacement (CDR) in patients with different Hounsfield units (HU). METHODS: We performed a retrospective study of patients with cervical degenerative disc disease treated by 1-level and 2-level Prestige-LP arthroplasty. The patients were divided into group A (HU <320), group B (HU 320-347), and group C (HU >347) according to the results of cervical vertebral HU measurement in the literature, and the clinical and radiographic results were compared among the 3 groups. RESULTS: A total of 127 patients were reviewed, comprising 13 patients in group A, 31 patients in group B, and 83 patients in group C. The clinical parameters were significantly improved postoperatively in the 3 groups (P < 0.05). However, no significant differences were found among the 3 groups at the final follow-up (P > 0.05). The mean postoperative intervertebral space height (ISH) was 4.76 ± 0.45 mm, 5.23 ± 0.81 mm, and 6.26 ± 1.12 mm in the 3 groups, respectively. The postoperative ISH in group C was significantly higher than those in the other groups at the final follow-up (P < 0.001). One patient in group A and 1 patient in group B had implant subsidence, and degeneration at the inferiorly adjacent level was radiographically identified in 30.77% patients in group A, 16.13% patients in group B, and 9.64% patients in group C. However, there were only significant differences between group A and group C in subsidence (P = 0.011) and occurrence of adjacent level degeneration (P = 0.032). CONCLUSIONS: The HU value has a large variation range among the patients with T-score ≥ -2.5. We found significantly increased rates of implant subsidence, loss of ISH, and adjacent segment degeneration in patients with lower HU value undergoing CDR. However, these radiographic complications did not predispose patients with lower HU value to worse clinical outcomes. Routine application of HU combined with dual-energy X-ray absorptiometry measurement to evaluate bone quality may help to screen the optimal candidates for CDR and reduce the implant-related complications.

Association of cervical sagittal alignment with adjacent segment degeneration and heterotopic ossification following cervical disc replacement with Prestige-LP disc.

PURPOSE: Cervical sagittal balance plays important roles in transmitting the load of the head and maintaining global spinal balance. This study aimed to identify the association of cervical sagittal alignment with adjacent segment degeneration (ASD) and heterotopic ossification (HO) after Prestige-LP cervical disc replacement (CDR). METHODS: We enrolled 132 patients who underwent one-level Prestige-LP CDR with 2-10 years of follow-up. Cervical sagittal alignment parameters, including the degree of C2-C7 lordosis (CL), functional spinal unit angle (FSUA), sagittal vertical axis (SVA),, and T1 slope (T1s), were measured. ASD and HO were evaluated at the last follow-up. Unpaired t tests and logistic regression analysis were used to identify the associations of cervical sagittal alignment with ASD and HO. RESULTS: We found that patients who developed ASD showed significantly lower FSUA (2.1° vs. -1.4°, p < 0.001) and T1s values (28.4° vs. 25.5°, p = 0.029) after surgery. Similarly, the postoperative CL was significantly better in patients without ASD or HO (18.0° vs. 14.4°, p = 0.043). The decrease in the T1s at the last follow-up was significantly larger in the patients with ASD (-11.0° vs. -3.2°, p = 0.003), HO (-6.7° vs. -2.7°, p = 0.050), and ASD or HO (-7.0° vs. -0.8°, p < 0.001) than in those without ASD or HO. Multivariate logistic regression analysis showed that both the FSUA and T1s are associated with ASD and that the degree of CL is associated with postoperative complications. CONCLUSION: The results imply that maintaining cervical sagittal alignment after Prestige-LP CDR is important.

Dynamic foraminal dimensions during neck motion 6.5 years after fusion and artificial disc replacement.

OBJECTIVE: To compare changes in foraminal motion at two time points post-surgery between artificial disc replacement (ADR) and anterior cervical discectomy and fusion (ACDF). METHODS: Eight ACDF and 6 ADR patients (all single-level C5-6) were tested at 2 years (T1) and 6.5 years (T2) post-surgery. The minimum foraminal height (FH.Min) and width (FW.Min) achieved during neck axial rotation and extension, and the range of these dimensions during motion (FH.Rn and FW.Rn, respectively) were measured using a biplane dynamic x-ray system, CT imaging and model-based tracking while patients performed neck axial rotation and extension tasks. Two-way mixed ANOVA was employed for analysis. RESULTS: In neck extension, significant interactions were found between year post-surgery and type of surgery for FW.Rn at C5-6 (p<0.006) and C6-7 (p<0.005), and for FH.Rn at C6-7 (p<0.01). Post-hoc analysis indicated decreases over time in FW.Rn for ACDF (p<0.01) and increases in FH.Rn for ADR (p<0.03) at the C6-7 adjacent level. At index level, FW.Rn was comparable between ACDF and ADR at T1, but was smaller for ACDF than for ADR at T2 (p<0.002). In axial rotation, differences were found between T1 and T2 but did not depend on type of surgery (p>0.7). CONCLUSIONS: Changes were observed in the range of foraminal geometry at adjacent levels from 2 years to 6.5 years post-surgery that were different between ACDF and ADR for neck extension. These changes are contrary to the notion that motion at adjacent levels continue to increase following ACDF as compared to ADR over the long term.

Five-year Results of a Randomized Controlled Trial for Lumbar Artificial Discs in Single-level Degenerative Disc Disease.

STUDY DESIGN: A prospective, multicenter, randomized, controlled, investigational device exemption (IDE) noninferiority trial. OBJECTIVE: The aim of this study was to compare the 5-year safety and effectiveness of the activL Artificial Disc with Control Total Disc Replacement (TDR) systems (ProDisc-L or Charité) in the treatment of patients with symptomatic single-level lumbar degenerative disc disease (DDD). SUMMARY OF BACKGROUND DATA: The activL Artificial Disc received Food and Drug Administration approval in 2015 based on 2-year follow-up data. METHODS: Eligible patients presented with symptomatic, single-level, lumbar DDD who failed ≥6 months of nonsurgical management. At entry, 324 patients were randomly allocated (2 : 1) to treatment with activL (n = 218) or Control (n = 106, including n = 65 ProDisc-L and n = 41 Charité) TDR. At 5-year follow up, a total of 261 patients (176 activL patients and 85 Control patients) were available for analysis. RESULTS: The primary composite endpoint at 5 years for activL patients was noninferior to Control TDR. Relative to baseline, reductions in back pain severity and improvements in Oswestry Disability Index (ODI) were maintained for both the activL and Control TDR groups through 5 years. The activL group showed significantly better range of motion for flexion-extension rotation, flexion-extension translation, and disc angle, compared with Control TDR. Freedom from a serious adverse event through 5 years was 64% in activL patients, 47% in Control patients (log-rank P = 0.0068). Freedom from index-level and adjacent-level reoperation was high for TDR patients, ranging between 94% and 99%, respectively. CONCLUSION: Long-term evidence supports lumbar total disc replacement as safe. The next-generation activL Artificial Disc is more effective at preserving range of motion than first-generation lumbar TDRs (ProDisc-L and Charité) and offers a higher safety profile. Other primary and secondary outcomes are similar between disc designs. LEVEL OF EVIDENCE: 2.

Crystallinity dependency of the time-dependent mechanical response of polyethylene: application in total disc replacement.

Degeneration of the intervertebral disc (IVD) is a leading source of chronic low back pain or neck pain, and represents the main cause of long-term disability worldwide. In the aim to relieve pain, total disc replacement (TDR) is a valuable surgical treatment option, but the expected benefit strongly depends on the prosthesis itself. The present contribution is focused on the synthetic mimic of the native IVD in the aim to optimally restore its functional anatomy and biomechanics, and especially its time-dependency. Semi-crystalline polyethylene (PE) materials covering a wide spectrum of the crystallinity are used to propose new designs of TDR. The influence of the crystallinity on various features of the time-dependent mechanical response of the PE materials is reported over a large strain range by means of dynamic mechanical thermo-analysis and video-controlled tensile mechanical tests. The connection of the stiffness and the yield strength with the microstructure is reported in the aim to propose a model predicting the crystallinity dependency of the response variation with the frequency. New designs of TDR are proposed and implemented into an accurate computational model of a cervical spine segment in order to simulate the biomechanical response under physiological conditions. Predicted in-silico motions are found in excellent agreement with experimental data extracted from published in-vitro studies under compression and different neck movements, namely, rotation, flexion/extension and lateral bending. The simulation results are also criticized by analyzing the local stresses and the predicted biomechanical responses provided by the different prosthetic solutions in terms of time-dependency manifested by the hysteretic behavior under a cyclic movement and the frequency effect.

The Mobi-C® cervical disc and other devices for two-level disc replacement: overview of its safety and efficacy.

INTRODUCTION: Cervical disc arthroplasty (CDA) has become an acceptable alternative for anterior cervical discectomy and fusion (ACDF) for a significant patient population with cervical radiculopathy and/or myelopathy secondary to degenerative changes in the cervical spine. There are sufficient mid- and long-term data supporting performance and safety of one-level CDA. With the success of single-level cervical CDA, considerable interest exists about CDA use for multilevel cervical degenerative disc disease (DDD). This review analyzes the safety and efficacy of two-level CDA for treatment of symptomatic cervical DDD with focus on the Mobi-C® Cervical Disc. AREAS COVERED: This review summarizes previously published articles in a literature search using keywords: 'two-level-anterior cervical arthrodesis; two-level anterior cervical decompression and fusion (ACDF); two-level cervical disc arthroplasty (CDA); two-level cervical total disc replacement; two-level symptomatic degenerative disc disease (DDD); Mobi-C® disc'. EXPERT OPINION: Two-level CDA with the Mobi-C® device demonstrated equivalent, and in certain aspects, favorable outcomes compared to ACDF for treatment of symptomatic cervical 2-level degenerative disc disease (DDD) indicating a satisfactory safety and efficacy profile.

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.

Total Disk Replacement Adjacent to a Multilevel Fusion in the Cervical Spine: A Biomechanical Motion Analysis.

OBJECTIVE: Cervical total disk replacement (TDR) has emerged as a motion-preserving alternative to anterior cervical diskectomy fusion (ACDF). Biomechanical studies have demonstrated that the TDR preserves motion at the diseased segment and minimizes motion and stress at adjacent segments compared with fusion. There has been growing interest in performing a TDR adjacent to a cervical fusion. The purpose of this study was to investigate the kinematics of a TDR after sequentially fusing adjacent segments. METHODS: Seven fresh-frozen human cadaveric cervical spine specimens from C1-T1 were used (average age, 56.2 ± 7.3 years). The effect on cervical flexion-extension motion, by instrumenting a TDR above or below a 1-, 2-, or 3-level fusion, was measured. The protocol consisted of taking fluoroscopic images of each cervical specimen obtained at maximal angular displacement in flexion and extension during force application. Cobb angles were measured on digital radiographs to determine flexion-extension range of motion (ROM). RESULTS: Segmental ROM of the C6-7 TDR in the unfused spine was 11.3° ± 1.9°. After performing a 3-level fusion at C3-6, the motion of the C6-7 TDR increased to 12.9° ± 1.3° (P = 0.33). ROM of the C2-3 TDR in the unfused spine was 5.0° ± 1.1°. After performing a 3-level fusion of C3-6, the C2-3 TDR segmental motion was 6.1° ± 1.3° (P = 0.09). CONCLUSIONS: Biomechanically performing a cervical TDR adjacent to a long-segment fusion did not subject the implant to significantly greater motion than when the TDR was instrumented alone.

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.

Superiority of 2-Level Total Disk Replacement Using a Cervical Disk Prosthesis Versus Anterior Cervical Diskectomy and Fusion.

The purpose of this study was to evaluate the superiority of total disk replacement (TDR) using a cervical disk prosthesis vs anterior cervical diskectomy and fusion (ACDF). Ninety-six patients with a diagnosis of degenerative disk disease with radiculopathy or myeloradiculopathy at 2 contiguous levels from C-3 to C-7 were randomly allocated to the TDR group (n=48) or the ACDF group (n=48). Outcome measures were recorded preoperatively and 1 week and 3, 6, 12, 24, and 81 months postoperatively. A total of 80 patients completed the follow-up, including 38 in the TDR group and 42 in the ACDF group. Japanese Orthopaedic Association, visual analog scale, and Neck Disability Index scores showed statistically significant improvement from baseline in both groups. Moreover, compared with the TDR group, the ACDF group had statistically greater visual analog scale scores from 12 months and Neck Disability Index scores from 3 months. Compared with the ACDF group, the TDR group had statistically greater range of motion at both the superior and the inferior treated levels at 3, 6, 12, 24, and 81 months postoperatively. Compared with the TDR group, the ACDF group had statistically greater range of motion at the superior adjacent levels at 6, 12, 24, and 81 months and at the inferior adjacent levels at 24 and 81 months postoperatively. The occurrence of adjacent-segment degeneration at both the superior and the inferior adjacent levels was greater in the ACDF group than in the TDR group. Total disk replacement was safe and effective and a statistically superior alternative to ACDF for degenerative disk disease at 2 contiguous levels. It could reduce the occurrence of adjacent-segment degeneration at the superior and the inferior adjacent segments by reducing the range of motion. [Orthopedics. 2018; 41(6):344-350.].

Annular closure device for disc herniation: meta-analysis of clinical outcome and complications.

BACKGROUND: Lumbar intervertebral disc herniation is a common cause of lower back and leg pain, with surgical intervention (e.g. discectomy to remove the herniated disc) recommended after an appropriate period of conservative management, however the existing or increased breach of the annulus fibrosus persists with the potential of reherniation. Several prosthesis and techniques to reduce re-herniation have been proposed including implantation of an annular closure device (ACD) - Barricaid™ and an annular tissue repair system (AR) - Anulex-Xclose™. The aim of this meta-analysis is to assist surgeons determine a potential approach to reduce incidences of recurrent lumbar disc herniation and assess the current devices regarding their outcomes and complications. METHODS: Four electronic full-text databases were systematically searched through September 2017. Data including outcomes of annular closure device/annular repair were extracted. All results were pooled utilising meta-analysis with weighted mean difference and odds ratio as summary statistics. RESULTS: Four studies met inclusion criteria. Three studies reported the use of Barricaid (ACD) while one study reported the use of Anulex (AR). A total of 24 symptomatic reherniation were reported among 811 discectomies with ACD/AR as compared to 51 out of 645 in the control group (OR: 0.34; 95% CI: 0.20,0.56; I2 = 0%; P < 0.0001). Durotomies were lower among the ACD/AR patients with only 3 reported cases compared to 7 in the control group (OR: 0.54; 95% CI: 0.13, 2.23; I2 = 11%; P = 0.39). Similar outcomes for post-operative Oswestry Disability Index and visual analogue scale were obtained when both groups were compared. CONCLUSION: Early results showed the use of Barricaid and Anulex devices are beneficial for short term outcomes demonstrating reduction in symptomatic disc reherniation with low post-operative complication rates. Long-term studies are required to further investigate the efficacy of such devices.

Strain behavior of malaligned cervical spine implanted with metal-on-polyethylene, metal-on-metal, and elastomeric artificial disc prostheses - A finite element analysis.

BACKGROUND: Postoperative alterations in cervical spine curvature (i.e. loss of lordotic angle) are frequently observed following total disc replacement surgery. However, it remains unclear whether such changes in lordotic angle are due to preoperative spinal deformities and/or prostheses design limitations. The objective of the study is to investigate strain and segmental biomechanics of the malaligned cervical spine following total disc replacement. METHODS: Three disc prostheses were chosen, namely a metal-on-polyethylene, a metal-on-metal, and an elastomeric prosthesis, which feature different geometrical and material design characteristics. All discs were modelled and implanted into multi-segmental cervical spine finite element model (C3-C7) with normal, straight and kyphotic alignments. Comparative analyses were performed by using a hybrid protocol. FINDINGS: The results indicated that as the spine loses lordotic alignment, the prosthesis with elastomeric core tends to produce significantly larger flexion range of motion (difference up to 6.1°) than metal-on-polyethylene and metal-on-metal prostheses. In contrast, when the treated spine had normal lordotic alignment, the range of motion behaviors of different prostheses are rather similar (difference within 1.9°). Large localized strains up to 84.8% were found with the elastomeric prosthesis, causing a collapsed anterior disc space under flexion loads. INTERPRETATION: Changes in cervical spinal alignments could significantly affect the surgical-level range of motion behaviors following disc arthroplasty; the in situ performance was largely dependent on the designs of the artificial disc devices in particular to the material properties.

Clinical and radiographic outcomes of cervical disc arthroplasty with Prestige-LP Disc: a minimum 6-year follow-up study.

BACKGROUND: Cervical disc arthroplasty (CDA) has been considered as an alternative to cervical arthrodesis in the treatment of cervical degenerative disc diseases (CDDD). The aim of this study was to assess the long-term clinical and radiographic outcomes of CDA with Prestige-LP Disc. METHODS: A total of 61 patients who underwent single- or two-level CDA with Prestige-LP Disc were retrospectively investigated at a minimum of 6-year follow-up. Clinical assessments included visual analogue scale (VAS) for neck and arm pain, Neck Disability Index (NDI), and Japanese Orthopedic Association (JOA) score. Radiological evaluations included range of motion (ROM) of the index and adjacent levels, segmental angle, cervical sagittal alignment, heterotopic ossification (HO) and adjacent segment degeneration (ASD). RESULTS: Significant and maintained improvement in VAS for neck and arm, NDI and JOA were observed after a mean follow-up of 82.3 months (p < 0.001). The preoperative ROM of the index level was 9.7°, which was maintained at 2-and 4-year follow-up (9.3°, p = 0.597; 9.0°, p = 0.297), but was decreased to 8.0° at final follow-up (p = 0.019). Mobility was maintained in 80.5% (62/77) of the implanted prostheses at final follow-up. ROM of the superior and inferior adjacent segments, cervical sagittal alignment and cervical angel were all maintained. The incidence of HO was 42.9% at final follow-up, but it did not influence the clinical outcome. Radiographic ASD were detected in 29.5% of the patients. However, the incidence of symptomatic ASD was only 6.6%. CONCLUSION: Cervical disc arthroplasty with Prestige-LP Disc demonstrated a maintained and satisfactory clinical outcome at a minimal of 6-year follow-up, with majority of the prostheses remained mobile. Cervical disc arthroplasty with Prestige-LP Dis can be considered as an effective surgical method in treating CDDD.

Implantation of a bone-anchored annular closure device in conjunction with tubular minimally invasive discectomy for lumbar disc herniation: a retrospective study.

BACKGROUND: Minimally invasive techniques for lumbar discectomy have been recommended as superior to open techniques due to lower blood loss, lower rates of infection and shorter recovery. There are, however, concerns that this approach does not sufficiently remove the herniated nuclear material, thus leaving the patient susceptible to reherniation requiring reoperation. The purpose of this study was to examine the safety and viability of an annular closure device in limiting reherniation and reoperation in a cohort of patients undergoing minimally invasive lumbar discectomy with the assistance of an annular closure device. METHODS: We retrospectively analysed the results from patients treated by a single surgeon between March 2011 and December 2017. All patients had been diagnosed with a large (≥ 5 mm) defect and were treated via minimally invasive surgical techniques. Outcomes included demographic data, the procedural duration and the rates of symptomatic reherniation and reoperation. RESULTS: 60 patients were included in the study. The mean age was 42 years (range: 19-66); mean BMI was 24.1 (range: 16.7-36.3). Mean surgical duration was 29 min (range: 16-50). Reoperation was required in 5% (3/60) of patients, although only 3% (2/60) experienced symptomatic reherniation at the index level. No other complications were reported. CONCLUSIONS: In our study, the use of an annular closure device during minimally invasive lumbar discectomy in a population of patients with large herniations was associated with low rates of reherniation and reoperation at the index level. While more research is required, the results of this study demonstrate the safety and viability of the annular closure device as an adjunct to minimally invasive discectomy.

Comparative Study Between M6-C and Mobi-C Cervical Artificial Disc Replacement: Biomechanical Outcomes and Comparison with Normative Data.

OBJECTIVE: Cervical spondylosis affects a huge proportion of the middle-aged population. Degenerative changes can occur in multiple regions of the cervical spine typically affecting the joints, intervertebral discs and endplates. These changes lead to compression of adjacent nervous structures, which results in radiculopathic and myelopathic pain. Various treatment modalities are currently available with non-surgical approaches the initial go to if there is no symptomatic cord compression. Anterior cervical discectomy and fusion, or arthroplasty are the two common surgical approaches if non-surgical treatments fail to relieve symptoms of the patients or there are signs of central cord compression. However, studies have shown that there is an increased risk of adjacent segment disease related to fusion. Cervical disc arthroplasty aims to restore normal range of motion (ROM) in patients with pain and disability due to degenerative disc disease resistant to conservative care. Two common disc prostheses used include M6-C and Mobi-C. Both prostheses comprise a mobile polymer segment sandwiched between two metal endplates with mechanisms resembling an actual intervertebral disc. This study aims to compare the kinematics associated with these prostheses, against the normal range of motion in the non-degenerative population. METHOD: Patients who underwent M6-C or Mobi-C disc replacements by the senior author from 2012 to 2015 were identified at a single tertiary institution. Routine 3-month postoperative lateral radiographs were analyzed for flexion and extension ROM angles at the involved vertebral level by two independent authors. Data was compared to previous published studies investigating cervical spine ROM of asymptomatic patients. RESULTS: There was no statistical significance in the difference of overall flexion range between M6-C and Mobi-C prostheses. However, overall range of extension of Mobi-C was greater compared to M6-C (P = 0.028). At C5-6 , the range of flexion for both implants were similar but lesser compared to asymptomatic patients (P < 0.001). Range of extension was greater in the Mobi-C group (14.2° ± 5.1°) compared to the M6-C (7.3° ± 4.6°) (P = 0.0009). At C6-7 , there were no statistical differences in both range of flexion and extension between the two prostheses and asymptomatic patients (P > 0.05). CONCLUSION: The early results regarding restoration of ROM following cervical arthroplasty using either M6-C or Mobi-C prosthesis are encouraging. Long-term follow-up studies are necessary to observe the change in ROM over time with physiological loading and wear patterns.