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.

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.

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.

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.

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.

Biomechanical evaluation of cervical disc replacement with a novel prosthesis based on the physiological curvature of endplate.

BACKGROUND: Most of the current available cervical disc prostheses present a flat surface instead of an arcuate surface which is most similar to the morphology of cervical endplate. Therefore, we designed a novel prosthesis (Pretic-I, Trauson) based on the physiological curvature of the cervical endplate. Biomechanical evaluation of cervical disc replacement (CDR) with this novel prosthesis was performed and compared with the Prestige LP prosthesis. METHODS: Three motion segments of 18 cadaveric cervical specimens (C2-C7) were evaluated with a 75 N follower load. Overall, the biomechanics of three models, intact specimen, CDR with the novel prosthesis and CDR with the Prestige LP prosthesis, were studied to gain insight into the effective function of the novel prosthesis. The range of motion (ROM) of all three segments and intradiscal pressure (IDP) on adjacent levels were measured and analysed. RESULTS: Compared to the intact condition, the ROM of all three segments showed no significant difference in the replacement group. Moreover, there was also no significant difference in the ROM between the two prostheses. Besides, the IDP on the cranial adjacent level showed no obvious difference between the two prostheses; nevertheless, the IDP on the caudal adjacent level of the novel prosthesis was significantly less than the Prestige LP prosthesis. CONCLUSIONS: In summary, the novel disc prosthesis was effective to maintain the ROM at the target segment and adjacent segments. Besides, CDR with the novel prosthesis could reduce the IDP on the caudal adjacent level to a certain extent, compared with the Prestige LP prosthesis.

Review of long-term outcomes of disc arthroplasty for symptomatic single level cervical degenerative disc disease.

INTRODUCTION: Cervical disc arthroplasty (CDA) was developed as an alternative for anterior cervical discectomy and fusion (ACDF) for nerve root decompression. The rationale behind CDA was to help prevent adjacent segment degeneration which potentially may lead to additional surgery. Multiple randomized controlled trials have evaluated a myriad of disc arthroplasty devices over the past 10 years and provided data regarding clinical benefits and safety. Their long-term data, reporting results at 5-10 years, presents the opportunity to comment on the overall efficacy, safety and reported complications of these devices. This report reviews results of the Prestige, proDisc-C, Mobi-C Disc and various other arthroplasty devices and provides an overall report of the longest term available data and comparisons between devices. AREAS COVERED: This review summarizes previously published articles in a literature search using keywords: 'cervical disc arthroplasty', 'cervical total disc replacement', 'anterior cervical decompression and fusion', 'anterior cervical arthrodesis', 'symptomatic degenerative disc disease' and commercial names of devices. EXPERT COMMENTARY: CDA, with the devices reviewed, resulted in favorable outcomes in comparison to ACDF for the treatment of symptomatic cervical degenerative disc disease (DDD) taking in to account the long-term functional recovery, adverse events, development of adjacent segment degeneration and subsequent surgical interventions.

Use of an Ultrasonic Bone Curet for the Extraction of a Cervical Artificial Disc: A Novel Application: A Case Report.

CASE: Eighteen months after implantation of a C6-C7 cervical artificial disc (ProDisc-C; DePuy Synthes), a 44-year-old woman presented with right-sided C7 radiculopathy. Imaging revealed posterior subsidence of the prosthesis, with C7 foraminal stenosis. An ultrasonic curet was used to safely and effectively extract the prosthesis without neurologic complication; safe access for the insertion of an intervertebral cage was facilitated. CONCLUSION: The ultrasonic curet was a safe and effective adjunct for revision artificial cervical disc replacement surgery; this technique may help to reduce potential injury to neural structures in a procedure with a traditionally high complication rate.

Spinal motion preservation surgery: indications and applications.

Fusion is one of the most commonly performed spinal procedures, indicated for a wide range of spinal problems. Elimination of motion though results in accelerated degeneration of the adjacent level, known as adjacent level disease. Motion preservation surgical methods were developed in order to overcome this complication. These methods include total disc replacement, laminoplasty, interspinous implants and dynamic posterior stabilization systems. The initial enthusiasm about these methods was followed by certain concerns about their clinical usefulness and their results. The main indications for total disc replacement are degenerative disc disease, but the numerous contraindications for this method make it difficult to find the right candidate. Application of interspinous implants has shown good results in patients with spinal stenosis, but a more precise definition is needed regarding the severity of spinal stenosis up to which these implants can be used. Laminoplasty has several advantages and less complications compared to fusion and laminectomy in patients with cervical myelopathy/radiculopathy. Dynamic posterior stabilization could replace conventional fusion in certain cases, but also in this case the results are successful only in mild to moderate cases.

Clinical results of cervical disc replacement with the Baguera C prosthesis after two years follow-up.

We studied pain, neurological, and functional outcomes of one and two-levels cervical arthroplasties using a semi-constrained prosthesis for symptomatic cervical degenerative discopathies. Retrospective analysis of 95 patients in a multicentric registry over 2 years FU. Implant-related complications, subsequent surgery and neurological deterioration were not observed. After two years, improvement of > 20% of the NDI was observed in 81.8%, of > 20% of the neck pain in 75.5% and of 20% in arm pain in 77.6%. A > 15% QOL improvement (SF 36 questionnaire) was recorded in 76.5% (physical) and in 77,6% (mental). Greater benefits of cervical arthroplasty were observed in patients under 50 without previous surgeries and with preoperative NDI > 30%, confirming a safe and effective technique.

Clinical and radiological outcome at 10 years of follow-up after total cervical disc replacement.

PURPOSE: Previous studies have demonstrated that total cervical disc replacement (cTDR) represents a viable treatment alternative to the 'gold standard' anterior cervical discectomy and fusion for the treatment of well-defined cervical pathologies at short- and mid-term follow-up (FU). However, the implementation and acceptance of a non-fusion philosophy is closely associated with its avoidance of adjacent segment degeneration. Proof of the functional sustainability and clinical improvement of symptoms at long-term FU is still pending. The aim of this ongoing prospective study was to investigate the clinical and radiological results of cTDR at long-term FU. METHODS: 50 patients were treated surgically within a non-randomised prospective study framework with cTDR (ProDisc C™, Synthes, Paoli, PA, USA). Patients were examined preoperatively followed by routine clinical and radiological examinations at 1, 5 and 10 years after surgery, respectively. In addition to the clinical scores, conventional X-ray images of the cervical spine were taken in anteroposterior and lateral view as well as flexion/extension images. Clinical outcome scores included parameters such as the Neck Disability Index (NDI), Visual Analogue Scale (VAS), arm and neck pain self-assessment questionnaires as well as subjective patient satisfaction rates. The radiological outcome variables included the range of motion (ROM) of the implanted prosthesis between maximum flexion and extension images, the occurrence of heterotopic ossifications and radiographic signs of adjacent segment degenerative changes. The reoperation rate following cTDR was recorded as a secondary outcome variable. RESULTS: A significant and maintained clinical improvement of all clinical outcome scores was observed after a mean FU of 10.2 years (VASarm 6.3-2.1; VASneck 6.4-1.9; NDI 21-6; p < 0.05). An increase in the incidence and the extent of heterotopic ossifications was noted during the post-operative course with a significant influence on the function of the prosthesis, which, however, did not reveal any detrimental effect on the patients' clinical symptomatology. Prosthesis mobility declined from 9.0° preoperatively and 9.1° at 1 year FU to 7.7° and 7.6° at the five- and ten-year FU examinations, respectively. Radiological signs of adjacent segment degeneration were detected in 13/38 (35.7%), however, in only 3/38 (7.9%) patients this radiological changes were associated with clinical symptoms requiring conservative treatment. Intraoperative technical failure in two cases required interbody fusion with a cage (2/50). One patient (1/48, 2.1%) treated this motion device had revision surgery at the index level. CONCLUSION: Cervical total disc replacement with ProDisc C demonstrated a significant and maintained improvement of all clinical outcome parameters at a follow-up of ≥10 years. The present long-term data reveal that with an exceptionally low implant-related reoperation rate and low symptomatic adjacent segment degeneration rate, cTDR may be regarded as a safe and viable treatment option.

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

In cervical artificial disc replacement (C-ADR), sometimes we encountered with such cases that implants of adjacent height both fit the target disc space properly. No study was available discussing the choice of implant height and the clinical outcomes under such circumstance. The purpose of this study was to evaluate the impact of different implant heights on the clinical outcomes and radiographic results when the implants of adjacent height both fit the disc space properly. This retrospective study included 34 patients underwent single-level C-ADR at the C5-C6 level at our institution. In these 34 patients, implant with either 5 mm height or 6 mm height fit the surgical level properly without overstretching the disc space or the facet joint space. Clinical outcomes were evaluated using the Japanese Orthopedic Association score, visual analog scale (VAS), and Neck Disability Index. Radiographic assessments were conducted on static and dynamic radiographs for the determination of the disc space height, intersegmental range of motion (ROM), and the ROM of the functional spinal unit (FSU) at the surgical level. The baseline information of the patients, such as age, gender, weight, follow-up time, and diagnosis, was similar between the 2 groups (P > .05). Postoperative mean VAS in group B was significantly lower than that in group A (2.1 ±â€Š0.7 vs. 2.7 ±â€Š1.0, P < .05). The mean VAS decrease in group B was significantly larger than that in group A (5.3 ±â€Š0.8 vs. 4.6 ±â€Š1.1, P < .05). Significant difference was found in the postoperative disc height of the surgical segment between the 2 groups (6.4 ±â€Š0.4 mm vs. 7.5 ±â€Š0.5 mm, P < .05). No significant differences were noted in the intersegmental ROM and ROM of the FSU between the 2 groups both before the surgery and at the last follow-up (P > .05). No hypermobility or instability was observed in these patients. Our results suggested that when implants of adjacent height both fit the disc space properly, using the larger implant could result in better pain relief without the risk of segmental hypermobility in patients underwent single-level C-ADR at the C5-C6 level.

Why Lumbar Artificial Disk Replacements (LADRs) Fail.

STUDY DESIGN: A retrospective review of prospectively collected data. OBJECTIVE: To determine why artificial disk replacements (ADRs) fail by examining results of 91 patients in FDA studies performed at a single investigational device exemption (IDE) site with minimum 2-year follow-up. SUMMARY OF BACKGROUND DATA: Patients following lumbar ADR generally achieve their 24-month follow-up results at 3 months postoperatively. MATERIALS AND METHODS: Every patient undergoing ADR at 1 IDE site by 2 surgeons was evaluated for clinical success. Failure was defined as <50% improvement in ODI and VAS or any additional surgery at index or adjacent spine motion segment. Three ADRs were evaluated: Maverick, 25 patients; Charité, 31 patients; and Kineflex, 35 patients. All procedures were 1-level operations performed at L4-L5 or L5-S1. Demographics and inclusion/exclusion criteria were similar and will be discussed. RESULTS: Overall clinical failure occurred in 26% (24 of 91 patients) at 2-year follow-up. Clinical failure occurred in: 28% (Maverick) (7 of 25 patients), 39% (Charité) (12 of 31 patients), and 14% (Kineflex) (5 of 35 patients). Causes of failure included facet pathology, 50% of failure patients (12 of 24). Implant complications occurred in 5% of total patients and 21% of failure patients (5 of 24). Only 5 patients went from a success to failure after 3 months. Only 1 patient went from a failure to success after a facet rhizotomy 1 year after ADR. CONCLUSIONS: Seventy-four percent of patients after ADR met strict clinical success after 2-year follow-up. The clinical success versus failure rate did not change from their 3-month follow-up in 85 of the 91 patients (93%). Overall clinical success may be improved most by patient selection and implant type.

A 6-DOF parallel bone-grinding robot for cervical disc replacement surgery.

Artificial cervical disc replacement surgery has become an effective and main treatment method for cervical disease, which has become a more common and serious problem for people with sedentary work. To improve cervical disc replacement surgery significantly, a 6-DOF parallel bone-grinding robot is developed for cervical bone-grinding by image navigation and surgical plan. The bone-grinding robot including mechanical design and low level control is designed. The bone-grinding robot navigation is realized by optical positioning with spatial registration coordinate system defined. And a parametric robot bone-grinding plan and high level control have been developed for plane grinding for cervical top endplate and tail endplate grinding by a cylindrical grinding drill and spherical grinding for two articular surfaces of bones by a ball grinding drill. Finally, the surgical flow for a robot-assisted cervical disc replacement surgery procedure is present. The final experiments results verified the key technologies and performance of the robot-assisted surgery system concept excellently, which points out a promising clinical application with higher operability. Finally, study innovations, study limitations, and future works of this present study are discussed, and conclusions of this paper are also summarized further. This bone-grinding robot is still in the initial stage, and there are many problems to be solved from a clinical point of view. Moreover, the technique is promising and can give a good support for surgeons in future clinical work.

Long-term clinical and radiographic outcomes of the Prestige LP artificial cervical disc replacement at 2 levels: results from a prospective randomized controlled clinical trial.

OBJECTIVE The aim of this study was to assess long-term clinical safety and effectiveness in patients undergoing anterior cervical surgery using the Prestige LP artificial disc replacement (ADR) prosthesis to treat degenerative cervical spine disease at 2 adjacent levels compared with anterior cervical discectomy and fusion (ACDF). METHODS A prospective, randomized, controlled, multicenter FDA-approved clinical trial was conducted at 30 US centers, comparing the low-profile titanium ceramic composite-based Prestige LP ADR (n = 209) at 2 levels with ACDF (n = 188). Clinical and radiographic evaluations were completed preoperatively, intraoperatively, and at regular postoperative intervals to 84 months. The primary end point was overall success, a composite variable that included key safety and efficacy considerations. RESULTS At 84 months, the Prestige LP ADR demonstrated statistical superiority over fusion for overall success (observed rate 78.6% vs 62.7%; posterior probability of superiority [PPS] = 99.8%), Neck Disability Index success (87.0% vs 75.6%; PPS = 99.3%), and neurological success (91.6% vs 82.1%; PPS = 99.0%). All other study effectiveness measures were at least noninferior for ADR compared with ACDF. There was no statistically significant difference in the overall rate of implant-related or implant/surgical procedure-related adverse events up to 84 months (26.6% and 27.7%, respectively). However, the Prestige LP group had fewer serious (Grade 3 or 4) implant- or implant/surgical procedure-related adverse events (3.2% vs 7.2%, log hazard ratio [LHR] and 95% Bayesian credible interval [95% BCI] -1.19 [-2.29 to -0.15]). Patients in the Prestige LP group also underwent statistically significantly fewer second surgical procedures at the index levels (4.2%) than the fusion group (14.7%) (LHR -1.29 [95% BCI -2.12 to -0.46]). Angular range of motion at superior- and inferior-treated levels on average was maintained in the Prestige LP ADR group to 84 months. CONCLUSIONS The low-profile artificial cervical disc in this study, Prestige LP, implanted at 2 adjacent levels, maintains improved clinical outcomes and segmental motion 84 months after surgery and is a safe and effective alternative to fusion. Clinical trial registration no.: NCT00637156 (clinicaltrials.gov).

Cervical arthroplasty: what does the labeling say?

OBJECTIVE The aim of this paper was to comprehensively review each of the Food and Drug Administration (FDA)-approved labels of 7 total cervical disc replacements, assess the exact methodology in which the trial was conducted, and provide a broad comparison of these devices to allow each surgeon to determine which disc best suits his or her specific treatment goals based on the specific labels and not the studies published. METHODS The FDA-approved labels for each of the 7 artificial discs were obtained from the official FDA website. These labels were meticulously compared with regard to the statistical analysis performed, the safety and efficacy data, and the randomized controlled trial that each artificial disc was involved in to obtain the FDA approval for the product or device. Both single-level and 2-level approvals were examined, and primary and secondary end points were assessed. RESULTS In the single-level group, 4 of the 7 artificial discs-Prestige LP, Prestige ST, Bryan, and Secure-C-showed superiority in overall success. Prestige ST showed superiority in 3 of 4 outcome measures (neurological success, revision surgery, and overall success), while the other aforementioned discs showed superiority in 2 or fewer measures (Prestige LP, neurological and overall success; Bryan, Neck Disability Index [NDI] and overall success; Secure-C, revision surgery and overall success; Pro-Disc C, revision surgery). The PCM and Mobi-C discs demonstrated noninferiority across all outcome measures. In the 2-level group, Prestige LP and Mobi-C demonstrated superiority in 3 outcome measures (NDI, secondary surgery, and overall success) but not neurological success. CONCLUSIONS This paper provides a comprehensive analysis of 7 currently approved and distributed artificial discs in the United States. It compares specific outcome measures of these devices against those following the standard of care, which is anterior cervical discectomy and fusion. This information will provide surgeons the opportunity to easily answer patients' questions and remain knowledgeable when discussing devices with manufacturers.

Biomechanical evaluation of a novel integrated artificial axis: A finite element study.

Various modified instruments are used for the anterior reconstruction of the tumor lesion affecting the second cervical vertebra, but there have been no reports regarding individual integrated artificial axis (IAA) prosthesis fabricated by selective laser melting. In the present work, a new type of IAA prosthesis has been designed with a 3-dimensional (3D) finite element model of normal occiput-the fourth cervical vertebra being established to assess its biomechanics. For easy comparison, another 3D finite element model is also established for the T-shaped Harms cage and an additional posterior fixation was performed on each model. The models are tested under a preliminary loading of 40 N to simulate cervical physical action including flexion, extension, lateral bending, and rotation. Under various loads from 4 different directions, the maximum stress and displacement of the IAA are less than those of the modified T-shaped Harms cage. Except for flexion, the maximum stress of the third cervical vertebra endplate of the IAA is smaller than that of the modified T-shaped Harms cage. The new prosthesis with axis is a good choice for upper cervical operation, which not only can greatly increase the operation stability of the upper cervical segment but also could significantly reduce the risk of fixation failure due to Harms cage subsidence.