Cervical Artificial Disc Replacement Research Articles

Clinical and Radiological Results of the DISCOVERTM Cervical Disc Replacement with Minimum Two-Year Follow-Up

Clinical and Radiological Results of the DISCOVERTM Cervical Disc Replacement with Minimum Two-Year Follow-Up Cervical artificial disc replacement (ADR) has the potential of preventing adjacent segment degeneration. Although data pertaining to different cervical ADR exist, little is known about the functional outcome of DISCOVER ADR.

Cervical artificial disc replacement with ProDisc-C: Clinical and radiographic outcomes with long-term follow-up

Cervical artificial disc replacement (ADR) is indicated for the treatment of severe radiculopathy permitting neural decompression and maintenance of motion. We evaluated the clinical and radiographic outcomes in cervical ADR patients using the ProDisc-C device (DePuy Synthes, West Chester, PA, USA) with a 5–9year follow-up. Data were collected through a prospective registry, with retrospective analysis performed on 24 consecutive patients treated with cervical ADR by a single surgeon. All patients underwent single- or two-level ADR with the ProDisc-C device. Outcome measures included neck and arm pain (visual analogue scale), disability (neck disability index [NDI]), complications and secondary surgery rates. Flexion-extension cervical radiographs were performed to assess range of motion (ROM) of the device and adjacent segment disease (ASD). Average follow-up was 7.7years. Neck and arm pain improved 60% and 79%, respectively, and NDI had an improvement of 58%. There were no episodes of device migration or subsidence. Mean ROM of the device was 6.4°. Heterotopic ossification was present in seven patients (37%). Radiographic ASD below the device developed in four patients (21%) (one single-level and three two-level ADR). No patient required secondary surgery (repeat operations at the index level or adjacent levels). Fourteen out of 19 patients (74%) were able to return to employment, with a median return to work time of 1.3months. The ProDisc-C device for cervical ADR is a safe option for patients providing excellent clinical outcomes, satisfactory return to work rates and maintenance of segmental motion despite radiographic evidence of heterotopic ossification and ASD on long-term follow-up.

Comparison of Dysphagia Between Cervical Artificial Disc Replacement and Fusion

Prospective randomized controlled trial. To determine and explain any differences in self-reported dysphagia between patients treated with artificial disc replacement and anterior cervical decompression and fusion (ACDF). Dysphagia after anterior cervical spine surgery has in previous studies been evaluated regarding different influencing factors. Surgical technique, number of treated levels, and type of implant has been shown to be of possible importance. One hundred thirty-six patients from a randomized controlled trial between artificial disc replacement and ACDF in 1 or 2 surgical levels were evaluated regarding dysphagia. Evaluation was done with the dysphagia short questionnaire preoperatively, at 4 weeks, 3 months, and 1 and 2 years postoperatively. Reconstruction in the artificial disc replacement group was performed with the Discover artificial disc. Bone graft and anterior plating was used in the ACDF group. Type of implant was blinded to the patients and the surgeon until time of implantation. Demographics and dysphagia short questionnaire levels were similar in both groups preoperative. At 4 weeks of follow-up postoperatively, dysphagia was significantly higher in both groups than baseline levels, P < 0.01. No significant differences were seen between the groups until follow-up at 2 years, which showed significantly higher dysphagia short questionnaire levels in the ACDF group, P = 0.04. The difference was statistically significant in both patients treated with 1- and 2-level surgery, P = 0.029 and P = 0.032, respectively. A logistic regression model showed a stronger association to type of implant than to number of surgical levels. Duration of surgery was highly associated to number of surgical levels but did not differ significantly between types of implant. Long-term postoperative dysphagia could be explained by bulk of implant or decreased motion in the cervical spine. However, it is doubtful if differences between the groups in this study can be interpreted as a clinically important difference. 2.

Comparison of cervical kinematics between patients with cervical artificial disc replacement and anterior cervical discectomy and fusion for cervical disc herniation

Comparison of cervical kinematics between patients with cervical artificial disc replacement and anterior cervical discectomy and fusion for cervical disc herniation

Comparison of cervical kinematics between patients with cervical artificial disc replacement and anterior cervical discectomy and fusion for cervical disc herniation

Background contextAlthough anterior cervical discectomy and fusion (ACDF) is an effective treatment option for patients with cervical disc herniation, it limits cervical range of motion, which sometimes causes discomfort and leads to biomechanical stress at neighboring segments. In contrast, cervical artificial disc replacement (ADR) is supposed to preserve normal cervical range of motion than ACDF. A biomechanical measurement is necessary to identify the advantages and clinical implications of ADR. However, literature is scarce about this topic and in those available studies, authors used the static radiological method, which cannot identify three-dimensional motion and coupled movement during motion of one axis. PurposeThe purpose of this study was to compare the clinical parameters and cervical motion by three-dimensional motion analysis between ACDF and ADR and to investigate the ability of ADR to maintain cervical kinematics. Study designThis was a prospective case control study. Patient samplePatients who underwent ADR or ACDF for the treatment of single-level cervical disc herniation. Outcome measuresVisual analog scale (VAS), Korean version of Neck Disability Index (NDI, %), and three-dimensional motion analysis were used. MethodsThe patients were evaluated by VAS and the Korean version of the NDI (%) to assess pain degree and functional status. Cervical motions were assessed by three-dimensional motion analysis in terms of sagittal, coronal, and horizontal planes. Markers of 2.5 cm in diameter were attached at frontal polar (Fpz), center (Cz), and occipital (Oz) of 10–20 system of electroencephalography, C7 spinous process, and both acromions. These evaluations were performed preoperatively and 1 month and 6 months after surgery. ResultsThe ACDF and ADR groups revealed no significant difference in VAS, NDI (%), and cervical range of motion preoperatively. After surgery, both groups showed no significant difference in VAS and NDI (%). In motion analysis, significantly more range of motion was retained in flexion and extension in the ADR group than the ACDF group at 1 month and 6 months. There was no significant difference in lateral tilt and rotation angle. In terms of coupled motion, ADR group exhibited significantly more preserved sagittal plane motion during right and left rotation and also showed significantly more preserved right lateral bending angle during right rotation than ACDF group at 1 month and 6 months. There was no significant difference in other coupled motions. ConclusionThree-dimensional motion analysis could provide useful information in an objective and quantitative way about cervical motion after surgery. In addition, it allowed us to measure not only main motion but also coupled motion in three planes. ADR demonstrated better retained cervical motion mainly in sagittal plane (flexion and extension) and better preserved coupled sagittal and coronal motion during transverse plane motion than ACDF. ADR had the advantage in that it had the ability to preserve more cervical motions after surgery than ACDF.

Cervical kinematics and radiological changes after Discover artificial disc replacement versus fusion

Background contextThe cervical disc arthroplasty has emerged as a promising alternative to the anterior cervical discectomy and fusion (ACDF) in patients with radiculopathy or myelopathy with disc degeneration disease. The advantages of this technique have been reported to preserve the cervical mobility and possibly reduce the adjacent segment degeneration. However, no studies have compared the clinical outcomes and radiological results in patients treated with Discover artificial disc replacement to those observed in matched group of patients that have undergone ACDF. PurposeWe conducted this clinical study to compare the cervical kinematics and radiographic adjacent-level changes after Discover artificial disc replacement with ACDF. Study designAnalysis and evaluation of data acquired in a comparative clinical study. Patient sampleThe number of patients in the Discover and ACDF group were 149 and 196, respectively. Outcome measuresThe Neck Disability Index (NDI) and visual analog scale (VAS) pain score were evaluated. The range of movement (ROM) by the shell angle, the functional segment unit and global angles were measured, and the postoperative radiological changes at adjacents levels were observed. MethodsA total of 149 patients with symptomatic single or two-level cervical degenerative diseases received the Discover cervical artificial disc replacement from November 2008 to February 2010. During the same period, there were a total of 196 patients undergoing one or two-level ACDF. The average follow-up periods of the Discover disc group and ACDF group were 22.1 months and 22.5 months, respectively. Before surgery, patients were evaluated using static and dynamic cervical spine radiographs in addition to computerized tomography and magnetic resonance imaging. Static and dynamic cervical spine radiographs were obtained after surgery and then at 3- and 6-month follow-up. Then, the subsequent follow-up examinations were performed at every 6-month interval. The clinical results in terms of NDI and VAS scores, the parameters of cervical kinematics, postoperative radiological changes at adjacent levels, and complications in the two groups were statistically analyzed and compared. No funding was received for this study, and the authors report no potential conflict of interest–associated biases in the text. ResultsAlthough the clinical improvements in terms of NDI and VAS scores were achieved in both the Discover and ACDF group, no significant difference was found between the two groups for both single- (VAS p=.13, NDI p=.49) and double-level surgeries (VAS p=.28, NDI p=.21). Significant differences of cervcial kinematics occurred between the Discover and the ACDF group for both the single- and double-level surgeries at the operative segments (p<.001). Except the upper adjacent levels for the single-level Discover and ACDF groups (p=.33), significant increases in adjacent segment motion were observed in the ACDF group compared with the minimal ROM changes in adjacent segment motion noted in the Discover group, and the differences between the two groups for both single and double-level procedures were statistically significant (p<.05). There were significant differences in the postoperative radiological changes at adjacent levels between the Discover and ACDF groups for the single-level surgery (p<.001, χ2=18.18) and the double-level surgery (p=.007, χ2=7.2). No significant difference of complications was found between the Discover and ACDF groups in both single (p=.25, χ2=1.32) and double-level cases (p=.4, χ2=0.69). ConclusionsThe adjacent segment ROM and the incidence of radiographic adjacent-level changes in patients undergoing ACDF were higher than those undergoing Discover artificial disc replacement. The cervical mobility was relatively well maintained in the Discover group compared with the ACDF group, and the Discover cervical disc arthroplasty can be an effective alternative to the fusion technique.

ProDisc-C cervical disc two-segment replacement from severe cervical spondylosis

Objective To investigate the clinical effect of ProDisc-C cervical disc replacement for two-segment severe cervical spondylosis.Methods Seventeen cases of two-segment severe cervical spondylosis aged from 36-59 years old were treated with artificial cervical disc replacement.The patients were followed up for 24 to 55 months after operation.The visual analogue scale (VAS),Japanese Orthopedic Association (JOA) scores,cervical curvature overall and the range of motion of the replacement segment were evaluated pre-and 3,12 and 24 months post-operation.Results The VAS scores at 3,12 and 24 months post-operation were 3.8 ± 1.9,1.9 ± 0.8 and 1.1 ± 0.4 respectively,which were significantly reduced as compared with pre-operation (6.3 ± 2.7,P ＜ 0.05).The JOA scores at 3,12 and 24 months postoperation were 13.4 ± 1.5,15.2 ± 1.1 and 15.9 ± 1.4 respectively,which were significantly increased as compared with pre-operation (8.7 ± 2.1,P ＜ 0.05).There was no statistically significant difference in the cervical curvature overall before and 24 months after operation (P ＞ 0.05).There was significant difference in the range of motion of the replacement segmentl before and 24 months after operation (P ＜ 0.05).Conclusion The clinical effect of ProDisc-C cervical disc replacement for two-segment severe cervical spondylosis is satisfactory and it can maintain good cervical activity after operation. Key words: Artificial cervical disc replacement; Cervical spondylosis

Utilization Trends of Cervical Artificial Disc Replacement after FDA Approval Compared to Anterior Cervical Fusion: Adoption of New Technology

Utilization Trends of Cervical Artificial Disc Replacement after FDA Approval Compared to Anterior Cervical Fusion: Adoption of New Technology

Utilization trends of cervical artificial disc replacement during the FDA investigational device exemption clinical trials compared to anterior cervical fusion

While anterior cervical discectomy and fusion (ACDF) is the gold standard surgical treatment for cervical disc disease, concerns regarding adjacent segment degeneration lead to the development of cervical disc arthroplasty (CDA). This study compares the utilization trends of CDA versus ACDF during the period of the Food and Drug Administration Investigational Device Exemption clinical trials from 2004 to 2007. The Healthcare Cost and Utilization Project Nationwide Inpatient Sample database was used to identify CDA and ACDF procedures performed in the USA between 2004 and 2007. The prevalence of CDA and ACDF procedures was estimated and stratified by age, sex, diagnosis, census region, payor class, and hospital characteristics. The average length of hospital stay, total charges, and costs were also estimated. The number of CDA surgeries significantly increased annually from 2004 to 2007 and mostly took place at urban non-teaching hospitals. There were no regional differences between CDA and ACDF utilization. There was no difference between sex or admission type between CDA and ACDF patients. ACDF patients were older and had more diabetes, hypertension, and chronic obstructive pulmonary disease. CDA patients were more likely to be discharged home and had shorter hospital stays but had a higher rate of deep venous thrombosis than ACDF patients. Significantly more CDA patients had private insurance while more ACDF patients had Medicare. The average cost was higher for ACDF than CDA. While ACDF dominated surgical intervention for cervical disc disease during the trial period, CDA utilization increased at a significantly greater rate suggesting rapid early adoption.

The incidence of heterotopic ossification in cervical artificial disc replacement in Chinese mainland population: A meta-analysis

Objective To investigate the incidence of heterotopic ossification in cervical artificial disc replacement in Chinese mainland population by meta-analysis.Methods The related literatures published between 1997 and June 2012 were collected from both English databases,including Pubmed,Ovid,Cochrane library and Embase,and Chinese databases including Chinese Biomedical Literature Database,China National Knowledge Infrastructure,VIP database and Wanfang database.Literatures were selected in strict accordance with the inclusion and exclusion criteria.Studies providing data of prevalence of heterotopic ossification after cervical artificial disc replacement in Chinese mainland population were included.The information of literatures was extracted by excerpts questionnaire,and recorded by two independent researchers.I2 was calculated to test heterogeneity among studies.A random effects model was used if I2 ≥25％.Subgroup analysis was done according to the number of levels of disc replacement,brands of implants and duration of follow-up.Sensitivity analysis was done according to the sample size.The Meta-Analyst software was used for statistical analysis.Results A total of forty studies (1822 cases) were included in this study.The pooled incidence of heterotopic ossification was 7.3％ (95％CI:4.7％ to 11.0％).For single and mixed level disc replacement,the incidence was 11.6％ and 5.8％,respectively.For single and mixed level disc replacement using Bryan disc,the incidence was 13.8％ and 5.4％,respectively,and the total incidence was 7.2％.No matter the single or mixed level disc replacement,the incidence of heterotopic ossification increased with follow-up.Conclusion The incidence of heterotopic ossification in cervical artificial disc replacement is high in Chinese mainland population,while it is lower than in foreigners.However,it is necessary to monitor its long-term incidence due to its increase with follow-up. Key words: Cervical vertebrae; Prostheses and implants; Ossification, heterotopic; Meta-analysis

The Effect of Range of Motion After Single-level Discover Cervical Artificial Disk Replacement

A biomechanical study of cervical artificial disk replacement (CADR). This study aimed to investigate the range of motion (ROM) of the treated segment, the ROM of the adjacent segments, the global ROM in the sagittal plane, and the total neck ROM in the 3 cardinal planes after single-level Discover CADR. CADR could theoretically preserve the motion function of the treated segment without affecting the adjacent segments significantly. Although previous studies have reported excellent clinical outcomes and ROM of the treated segment after CADR, few studies have focused on the ROM of the adjacent segments, the global ROM, and the total neck motion. C5/6 Discover CADR was performed in 58 patients (37 male and 21 female) between September 2008 and September 2010. Anteroposterior, lateral, and flexion-extension lateral radiographies were performed before operation and at the 1-year follow-up. Clinical parameters, including the Japanese orthopedic association score, the neck disability index, and the visual analogue scale, were evaluated. The ROM of the treated segment (C5/6) and the adjacent segments (C4/5 and C6/7) and the global ROM (C2/7) were measured by radiography. To evaluate the total neck ROM, the cervical ROM device was advocated. Preoperative and postoperative data were compared using the paired t test. The Japanese orthopedic association score was 14.3 at the 1-year follow-up as compared with the preoperative score of 8.7. Other scoring systems had improved postoperatively, including the neck disability index from 85.1 to 68.6 and the visual analogue scale from 7.8 to 3.3. Compared with the preoperative ROM, the postoperative ROM increased by 3.0 degrees (27.0%) in C5/6, 1.3 degrees (13.7%) in C4/5, and 1.8 degrees (17.6%) in C6/7. The postoperative global ROM also increased by 6.7 degrees (15.2%) compared with preoperative global data. Compared with the preoperative total neck motion, the postoperative total neck motion increased by 8.3 degrees (9.3%) in the sagittal plane and 6.1 degrees (7.7%) in the coronal plane. There was an insignificant increase of 0.8 degrees (0.6%) in the horizontal plane. This study demonstrated that the single-level Discover CADR increased the ROM of the treated segment and the adjacent segments. There was also an increase in the global ROM and the total neck motion in the sagittal and the coronal planes, although there was no significant difference in the horizontal plane before and after operation.

Cervical artificial disc replacement

Cervical disc replacement has recently become available in the United States and is gaining notoriety. It is widely publicized throughout the media and medical journals. Despite this, few clinicians are familiar with the actual indications for cervical disc arthroplasty. The role of disc replacement is somewhat of an enigma when treating cervical pathology. This article is intended to describe the procedure of cervical artificial disc replacement and address its appropriate use. The indications have been reviewed along with discussion regarding which patients may benefit from this surgical procedure.

The predisposing factors for the heterotopic ossification after cervical artificial disc replacement

Background contextHeterotopic ossification (HO) is defined as a formation of bone outside the skeletal system. The reported HO occurrence rate in cervical artificial disc replacement (ADR) is unexpectedly high and is known to vary. However, the predisposing factors for HO in cervical ADR have not yet been elucidated. PurposeInvestigation of the predisposing factors of HO in cervical arthroplasty and the relationship between degeneration of the cervical spine and HO occurrence. Study designRetrospective study to discover predisposing factors of HO in cervical arthroplasty. Patient sampleA total of 170 patients who underwent cervical ADR were enrolled including full follow-up clinical and radiologic data. Outcome measuresRadiologic outcomes were assessed by identification of HOs according to McAfee's classifications. MethodsThis study enrolled a total of 170 patients who underwent cervical ADR. Pre-existing degenerative change included anterior or posterior osteophytes, ossification of the anterior longitudinal ligament, posterior longitudinal ligament, or ligamentum nuchae. The relationships between basic patient data, pre-existing degenerative change, and HO were investigated using linear logistic regression analysis. ResultsAmong all 170 patients, HO was found in 69 patients (40.6%). Among the postulated predisposing factors, only male gender and artificial disc device type were shown to be statistically significant. Unexpectedly, preoperative degenerative changes in the cervical spine exerted no significant influence on the occurrence of HOs. The odds ratio of male gender compared with female gender was 2.117. With regard to device type, the odds ratios of Mobi-C (LDR medical, Troyes, France) and ProDisc-C (Synthes, Inc., West Chester, PA, USA) were 5.262 and 7.449, respectively, compared with the Bryan disc. ConclusionsDefinite differences in occurrence rate according to the gender of patients and the prosthesis type were identified in this study. Moreover, factors indefinably expected to influence HO in the past were not shown to be risk factors thereof, the results of which may be meaningful to future studies.

Comparison of the mid-term follow-up results between Bryan cervical artificial disc replacement and anterior cervical decompression and fusion for cervical degenerative disc disease

Objective To evaluate the mid-term tollow-up results of cervical artificial disc replacement (CADR) for cervical degenerative disc disease,and to explore whether it can reduce the occurrence of adjacent segment degeneration (ASD).Methods A prospective comparative study of 93 patients who underwent CADR or anterior cervical decompression and fusion (ACDF) for cervical degenerative disc disease were conducted.All patients were followed up for more than 6 years.The Japanese Orthopaedic Association (JOA) score,neck disability index (NDI),Odom's scale,X-rays and magnetic resonance imaging (MRI) were used to evaluate the clinical and radiologic results.Results Twenty eight patients who underwent CADR and 35 patients who underwent ACDF had complete follow-up data.At final follow-up,the JOA score and NDI improved significantly in both groups.Between the two groups,there was no significant difference in terms of JOA score,NDI and Odom's scale.The sagittal alignment was well maintained in both groups.The total cervical spine range of motion (ROM) had no significant change for the CADR group,whereas,it significantly decreased for the ACDF group.The ROM at the replacement level of CADR patients decreased from 9.5° ± 3.7° before operation to 7.0° ± 3.0° 3 months after operation,and it was maintained to 6.6° ± 4.1° at final follow-up without significant decrease.Lateral radiographs and T2-weighted MRI showed the incidence of ASD in CADR group was significantly lower than that in ACDF group.Conclusion The six-year follow-up results of CADR are basically satisfactory.Compared with ACDF,it could better preserve physiological motion and biomechanics of cervical spine,and reduce the incidence of ASD. Key words: Cervical vertebrae; Intervertebral disk; Prosthesis implantation; Spinal fusion; Follow-up studies

Reversal of Anterior Cervical Discectomy and Fusion With Cervical Artificial Disc Replacement

Case report and review of the literature. To present a conversion of an anterior cervical discectomy and fusion (ACDF) with a cervical artificial disc replacement in a 39-year-old woman and to review the relevant literature. Return of functional spinal unit motion 9 years after attempted fusion is extremely rare. The patient underwent an attempted anterior cervical discectomy and fusion 9 years earlier for bilateral hand numbness and leg weakness. Most of her neurological deficits had resolved after the index operation, but returned 2 months before the second operation and were unresponsive to nonoperative treatment. Computed tomography (CT) myelography showed recurrence of cervical disc herniation at the cephalad adjacent segment, which compressed the spinal cord. There was still some osteophyte at the C5/6 level that was also causing compression to the spinal cord. A solid fusion was suspected at this level. Surgery was performed to take down the grafted region and replace both levels with artificial disks. The range of motion (ROM) of the revised level at the 6-month follow-up was well preserved, there was no sign of instability at either operated level. The 6-month follow-up CT scan shows that, there was no obvious compression in the spinal canal. The remobilized facet joints of C5/6 segment have not demonstrated further degeneration. The patient's neck symptom and neurological function were significantly recovered. This case demonstrates application of a cervical artificial disc replacement to restore motion at a level that was previously grafted and fused. In select cases, cervical artificial disc replacement may represent a reasonable alternative to a repeated attempt at fusion. It is imperative that preoperatively lack of fusion of the facet joints be demonstrated on reconstructed CT scanning.

An incomplete paraplegia following the dislocation of an artificial cervical total disc replacement

Replacement of the cervical intervertebral disc by artificial implants, known as cervical total disc replacement (CTDR), is becoming a generally applied method instead of using the gold standard of the anterior cervical discectomy and fusion. Hypothetically, the preserved mobility results in the protection of the neighboring segments. There is growing evidence that results in patients who underwent CTDR were not inferior when compared to results in patients who underwent anterior cervical discectomy and fusion. The authors report a case of a healthy 53-year-old man who suffered an incomplete paraplegia below C-6 following the dislocation of an artificial CTDR device into the spinal canal with consequent compression of the spinal cord.

Symptomatic adjacent segment disease after cervical total disc replacement: re-examining the clinical and radiological evidence with established criteria

Although several publications in the last decade have proved equality in safety and efficacy of the total disc replacement (TDR) to the anterior fusion procedure in cervical spine, the claim that TDR may reduce the incidence of adjacent segment disease (ASD) has not been corroborated by clinical evidence. We attempt to predict the true incidence of symptomatic ASD after TDR surgery in the cervical spine at one or two levels at a median follow-up period of 4 years. A total of 763 patients were screened to participate in four different Food and Drug Administration device exemption trials for artificial cervical disc replacement at three collaborating institutions. Two hundred seventy-one patients qualified and enrolled in the trials. One hundred seventy-three randomized to receive artificial disc replacement surgery, and 167 have completed a 4-year or longer follow-up. Patients experiencing cervical radiculopathy symptoms in the follow-up period were worked-up with clinical examinations, magnetic resonance imaging of the cervical spine, and other diagnostic studies. Once a clinical correlation was established with the imaging evidence of adjacent segment degeneration, a careful record was maintained to document the subsequent medical and/or surgical treatment received by these patients. Statistical analysis was performed to determine the true incidence of and factors affecting the ASD after cervical disc replacement in these patients. Twenty-six patients (15.2%) were identified to satisfy our criteria for ASD at the median follow-up of 51 months, with the annual incidence of 3.1% as calculated by life tables. The actuarial 5-year freedom from ASD rate was 71.6%±0.6%, and the mean period for freedom from ASD was 70.4±2.1 months. The incidence of symptomatic ASD after cervical TDR is 3.1% annually regardless of the patient's age, sex, smoking habits, and design of the TDR device. The presence of osteopenia and lumbar degenerative disease significantly increase the risk of developing ASD after anterior cervical surgery.

Biomechanical Analysis of Cervical Finite Element Model

The finite element method is often used in the field of biomechanical analysis. It can study the mechanical response of the internal organization without any experiments on the human body. The paper studies the biomechanics of the cervical spine by the method of finite element analysis. Firstly, the finite element model of the cervical spine including cervical vertebrae and soft tissue is constructed. Secondly, biomechanical analysis of cervical finite element model which is validated to be reasonable and reliable is completed. The results of the control group, the anterior cervical decompression and fusion surgery group, and the artificial cervical disc replacement surgery group are obtained to study the motion degree and ligament force of cervical spine. Thirdly, the summary of the biomechanical analysis of cervical finite element model is concluded.

In vivo analysis of cervical kinematics after implantation of a minimally constrained cervical artificial disc replacement.

To better understand cervical kinematics following cervical disc replacement (CDR), the in vivo behavior of a minimally constrained CDR was assessed. Radiographic analysis of 19 patients undergoing a 1-level CDR from C4-5 to C6-7 (DISCOVER, Depuy-Spine, USA) was performed. Neutral-lateral and flexion-extension radiographs obtained at preop, postop and late follow-up were analyzed for segmental angle and global angle (GA C2-7). Flexion-extension range of motion was analyzed using validated quantitative motion analysis software (QMA®, Medical Metrics, USA). The FSU motion parameters measured at the index and adjacent levels were angular range of motion (ROM), translation and center of rotation (COR). Translation and COR were normalized to the AP dimension of the inferior endplate of the caudal vertebra. All motion parameters, including COR, were compared with normative reference data. The average patient age was 43.5 ± 7.3 years. The mean follow-up was 15.3 ± 7.2 months. C2-7 ROM was 35.9° ± 15.7° at preop and 45.4° ± 13.6° at follow-up (∆p < .01). Based on the QMA at follow-up, angular ROM at the CDR level measured 9.8° ± 5.9° and translation was 10.1 ± 7.8 %. Individuals with higher ROM at the CDR level had increased translation at that level (p < .001, r = 0.97), increased translation and ROM at the supra-adjacent level (p < .001, r = .8; p = .005, r = .6). There was a strong interrelation between angular ROM and translation at the supra-adjacent level (p < .001, r = .9) and caudal-adjacent level (p < .001, r = .9). The location of the COR at the CDR- and supra-adjacent levels was significantly different for the COR-X (p < .001). Notably, the COR-Y at the CDR level was significantly correlated with the extent of CDR-level translation (p = .02, r = .6). Shell angle, which may be influenced by implant size and positioning had no impact on angular ROM but was correlated with COR-X (p = .05, r = -.6) and COR-Y (p = .04, r = -.5). The COR is an important parameter for assessing the ability of non-constrained CDRs to replicate the normal kinematics of a FSU. CDR size and location, both of which can impact shell angle, may influence the amount of translation by affecting the location of the COR. Future research is needed to show how much translation is beneficial concerning clinical outcomes and facet loading.

Metanalysis of Heterotopic Ossification (HO) Following Cervical Artificial Disc Replacement (CADR)

Metanalysis of Heterotopic Ossification (HO) Following Cervical Artificial Disc Replacement (CADR)