Update on cervical disc arthroplasty: where are we and where are we going?

A Dynamic Interbody Cage Improves Bone Formation in Anterior Cervical Surgery: A Porcine Biomechanical Study

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) with a rigid interbody spacer is commonly used in the treatment of cervical degenerative disc disease. Although ACDF relieves clinical symptoms, it is associated with several complications such as pseudoarthrosis and adjacent segment degeneration. The concept of dynamic fusion has been proposed to enhance fusion and reduce implant subsidence rate and post-fusion stiffness; this pilot preclinical animal study was conducted to begin to compare rigid and dynamic fusion in ACDF.

QUESTIONS/PURPOSES

Using a pig model, we asked, is there (1) decreased subsidence, (2) reduced axial stiffness in compression, and (3) improved likelihood of bone growth with a dynamic interbody cage compared with a rigid interbody cage in ACDF?

METHODS

ACDF was performed at two levels, C3/4 and C5/6, in 10 pigs weighing 48 to 55 kg at the age of 14 to 18 months (the pigs were skeletally mature). One level was implanted with a conventional rigid interbody cage, and the other level was implanted with a dynamic interbody cage. The conventional rigid interbody cage was implanted in the upper level in the first five pigs and in the lower level in the next five pigs. Both types of interbody cages were implanted with artificial hydroxyapatite and tricalcium phosphate bone grafts. To assess subsidence, we took radiographs at 0, 7, and 14 weeks postoperatively. Subsidence less than 10% of the disc height was considered as no radiologic abnormality. The animals were euthanized at 14 weeks, and each operated-on motion segment was harvested. Five specimens from each group were biomechanically tested under axial compression loading to determine stiffness. The other five specimens from each group were used for microCT evaluation of bone ingrowth and ongrowth and histologic investigation of bone formation. Sample size was determined based on 80% power and an α of 0.05 to detect a between-group difference of successful bone formation of 15%.

RESULTS

With the numbers available, there was no difference in subsidence between the two groups. Seven of 10 operated-on levels with rigid cages had subsidence on a follow-up radiograph at 14 weeks, and subsidence occurred in two of 10 operated-on levels with dynamic cages (Fisher exact test; p = 0.07). The stiffness of the unimplanted rigid interbody cages was higher than the unimplanted dynamic interbody cages. After harvesting, the median (range) stiffness of the motion segments fused with dynamic interbody cages (531 N/mm [372 to 802]) was less than that of motion segments fused with rigid interbody cages (1042 N/mm [905 to 1249]; p = 0.002). Via microCT, we observed bone trabecular formation in both groups. The median (range) proportions of specimens showing bone ongrowth (88% [85% to 92%]) and bone volume fraction (87% [72% to 100%]) were higher in the dynamic interbody cage group than bone ongrowth (79% [71% to 81%]; p < 0.001) and bone volume fraction (66% [51% to 78%]; p < 0.001) in the rigid interbody cage group. The percentage of the cage with bone ingrowth was higher in the dynamic interbody cage group (74% [64% to 90%]) than in the rigid interbody cage group (56% [32% to 63%]; p < 0.001), and the residual bone graft percentage was lower (6% [5% to 8%] versus 13% [10% to 20%]; p < 0.001). In the dynamic interbody cage group, more bone formation was qualitatively observed inside the cages than in the rigid interbody cage group, with a smaller area of fibrotic tissue under histologic investigation.

CONCLUSION

The dynamic interbody cage provided satisfactory stabilization and percentage of bone ongrowth in this in vivo model of ACDF in pigs, with lower stiffness after bone ongrowth and no difference in subsidence.

CLINICAL RELEVANCE

The dynamic interbody cage appears to be worthy of further investigation. An animal study with larger numbers, with longer observation time, with multilevel surgery, and perhaps in the lumbar spine should be considered.

Biomechanics of Cervical Disc Arthroplasty Devices

Prosthesis design has an influence on the quantity and quality of postoperative motion after cervical disc arthroplasty. Prostheses with built-in resistance to angular and translational motion may have an advantage in restoring physiologic motion. The ability of a prosthesis to work with remaining bony and soft tissues to restore motion and load-sharing is a function of the kinematic degrees of freedom DOF, axis of rotation for a given motion, and device stiffness. How these characteristics allow the prosthesis to work with the patient's anatomy will determine whether the prosthesis is successful at restoring motion and mitigating adjacent-level stresses.

Biomechanics of Cervical Disc Arthroplasty-A Review of Concepts and Current Technology

Activities of daily living require the subaxial cervical spine (C2-C7) to have substantial mobility. Cervical degenerative changes can cause abnormal motions and altered load distribution, leading to pain and limiting the ability of individuals to perform activities of daily living. Anterior cervical discectomy and fusion (ACDF) has been widely used to treat symptomatic cervical spondylosis. Clinical studies have shown cervical disc arthroplasty (CDA) to be a viable alternative to ACDF for the treatment of radiculopathy and myelopathy. The benefits of CDA are based on the premise that preservation of physiologic motions and load-sharing at the treated level would lead to longevity of the index-level facet joints and mitigate the risk of adjacent segment degeneration.This review article classifies cervical disc prostheses according to their kinematic degrees of freedom and device constraints. Discussion on how these design features may affect cervical motion after implantation will provide the reader with valuable information on how disc prostheses may function clinically.The ability of a disc prosthesis to work in concert with remaining bony and soft tissue structures to restore physiologic motion and load-sharing is a function of the following design features and surgical factors: Kinematic degrees of freedom-Prostheses that allow translation independent of rotation allow, in theory, the spinal anatomy to dictate segmental motion after CDA potentially restoring physiologic motion and load-sharing. A 6-degrees-of-freedom disc prosthesis may be best equipped to achieve the intended function of CDA.Built-in stiffness-A disc prosthesis with built-in resistance to angular and translational motion may have an advantage in restoring stability to a hypermobile segment without eliminating motion.Surgical factors related to prosthesis implantation may influence cervical segments after CDA. These factors include the amount of disc space distraction caused by the prosthesis, prosthesis placement in the sagittal and coronal planes, and integrity of the soft tissue envelope.

Scientific Contributions of the Mexican Association of Spine Surgeons (Asociación Mexicana de Cirujanos de Columna-AMCICO) to the Global Medical Literature: A 21-Year Systematic Review

BACKGROUND

Contributions from Latin America to the global literature are scarce; until 2011, spine surgeons had published 320 articles in indexed journals.

METHODS

This systematic review evaluates the scientific production of the Mexican Association of Spine Surgeons (Asociación Mexicana de Cirujanos de Columna-AMCICO) from its inception in 1998 to 2018 with the PRISMA statement using PubMed and Google Scholar search engines. The inclusion criteria were spine-related articles in indexed journals providing any (or no) level of evidence with ≥1 AMCICO member as an author. Journal metrics, article metrics, and author variables were analyzed using SPSS version 25.

RESULTS

Of the 444 surgeons historically belonging to AMCICO, only 126 members contributed a total of 441 articles between 1998 and 2018. An average of 21.00 annual publications with an annual scientific output per capita of 0.05 was found. The most frequent evidence level was III (211 articles, 48%), the highest level was I (12 articles, 3%). The main study objective was clinical research, with 308 articles (70%), and the main study foci was trauma, with 103 articles (23%). An average impact factor of 0.16 and 0.92 was obtained for publications in Spanish and English, respectively.

CONCLUSIONS

Scientific publications by AMCICO members are scarce, with a per capita annual index of 0.05 from a total of 441 articles in indexed journals. Second, the impact factor of these journals is low, with a mean value of 0.53. Further strategies should be implemented to increase the number and track the record of Mexican contributions to the scientific literature.

Clinical Relevance of Cervical Kinematic Quality Parameters in Planar Movement

Comprehending cervical spinal motion underlies the understanding of the mechanisms of cervical disorders. We aimed to better define the clinical relevance of cervical spine kinematics, focusing on quality parameters describing cervical spine planar motion. The most common study focuses were kinematic quality parameters after cervical arthroplasty and in normal subjects, patients with cervical degeneration, and patients with cervical deformities. Kinematic quality parameters are important for cervical degeneration prevention, being detected sooner than differences on imaging examinations and being significantly related to the degree of cervical degeneration. Kinematic quality parameters are effective for evaluating the changes of cervical motion pattern after cervical fusion and non‐fusion, assessing operative and adjacent segments in the early stages, and predicting adjacent segment degeneration. However, owing to current research limitations, and controversy about the changes of kinematic quality parameters after different surgical procedures, current assessments are limited to cervical spine flexion and extension. Different osteotomy methods of cervical deformity have different effects on cervical motion patterns and quality parameters. Choosing the most effective surgical method remains a challenge and kinematic quality parameters in cervical deformity are important future research topics. This review highlights the instantaneous center of rotation, the center of rotation, and the instantaneous axis of rotation as being important kinematic quality parameters of cervical spinal motion. These can be used to detect abnormal cervical mobility, to diagnose cervical degeneration, to design disc protheses, and to evaluate surgical effects earlier than other methods. Owing to limitations of research methods there is variation in the way parameters are defined by various researchers. No uniform standard exists for defining degenerative motion quality parameters in normal asymptomatic, degenerative, and postoperative patients. Therefore, further study is required. New study techniques and defining kinematic quality parameters in normal subjects will clarify the definitions of these parameters, enhancing their future clinical usefulness.

Does Resection of the Posterior Longitudinal Ligament Affect the Stability of Cervical Disc Arthroplasty?

Background

The need for posterior longitudinal ligament (PLL) resection during cervical total disc arthroplasty (TDA) has been debated. The purpose of this laboratory study was to investigate the effect of PLL resection on cervical kinematics after TDA.

Methods

Eight cadaveric cervical spine specimens were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) to moments of ±1.5 Nm. After testing the intact condition, anterior C5-C6 cervical discectomy was performed followed by PLL resection and implantation of a compressible, 6-degrees-of-freedom disc prosthesis (M6-C, Spinal Kinetics Inc, Sunnyvale, California). Next, a second prosthesis was implanted at C6-C7 with PLL intact. Finally, the C6-C7 PLL was resected while the disc prosthesis remained in place. Segmental range of motion (ROM) and stiffness in the high flexibility zone around the neutral posture were analyzed using repeated measures ANOVA.

Results

At C5-C6, following TDA and PLL resection, FE, LB, and AR ROMs decreased significantly. Anterior and posterior disc height, segmental lordosis, and flexion stiffness increased significantly. At C6-C7, TDA with the PLL intact resulted in a significant increase in anterior disc height and segmental lordosis with no change in posterior disc height. FE, LB, and AR ROMs all decreased significantly, while flexion stiffness increased significantly compared to intact. PLL resection at C6-C7 did not result in a notable change compared to TDA with PLL intact. At the same level, flexion stiffness decreased following PLL resection compared to TDA with a value closer to intact. Two-level TDA (C5-C7) with PLL resection did not result in a loss of segmental stability.

Conclusion

PLL resection did not significantly affect motion segment kinematics following cervical TDA using a prosthesis with inherent stiffness. Motion segment stiffness loss after PLL resection can be compensated for by a TDA design that can provide resistance to angular motion.

Comparison of the adverse events of anterior cervical disc replacement versus anterior cervical discectomy and fusion: A protocol for a systematic review and meta-analysis of prospective randomized controlled trials

BACKGROUND

In the current surgical therapeutic regimen for symptomatic cervical degenerative disc disease, both anterior cervical discectomy and fusion (ACDF) and anterior cervical disc replacement (ACDR) are still widely accepted. However, many complications exist in both surgeries. Therefore, this study aims to compare the adverse events between ACDR and ACDF, and provide vital evidence-based guidance for spine surgeons and designers to evaluation of prognosis and improvement of dynamic devices.

METHODS

A systematic review and meta-analysis that will be performed according to the PRISMA. The electric database of PubMed, Medline, Embase, Google Scholar, and Cochrane library will be systematic search. A standard data form will be used to extract the data of included studies. We will assess the studies according to the Cochrane Handbook for Systematic Reviews of Interventions, and perform analysis in RevMan 5.3 software. Fixed effects models will be used for homogeneity data, while random-effects will be used for heterogeneity data. The overall effect sizes will be determined as weighted mean difference (WMD) for continuous outcomes and relative risk (RR) for dichotomous outcomes.

RESULT

The results of this study will be disseminated via international or national conferences, or submit to peer-reviewed journal in spinal field.

CONCLUSION

The conclusion of this study will provide key evidence-based guidance for spine surgeons and designers to the evaluation of prognosis and improvement of dynamic devices.

Are Controversial Issues in Cervical Total Disc Replacement Resolved or Unresolved?: A Review of Literature and Recent Updates

Since the launch of cervical total disc replacement (CTDR) in the early 2000s, many clinical studies have reported better outcomes of CTDR compared to those of anterior cervical discectomy and fusion. However, CTDR is still a new and innovative procedure with limited indications for clinical application in spinal surgery, particularly, for young patients presenting with soft disc herniation with radiculopathy and/or myelopathy. In addition, some controversial issues related to the assessment of clinical outcomes of CTDR remain unresolved. These issues, including surgical outcomes, adjacent segment degeneration (ASD), heterotopic ossification (HO), wear debris and tissue reaction, and multilevel total disc replacement (TDR) and hybrid surgeries are a common concern of spine surgeons and need to be resolved. Among them, the effect of CTDR on patient outcomes and ASD is theoretically and clinically important; however, this issue remains disputable. Additionally, HO, wear debris, multilevel TDR, and hybrid surgery tend to favor CTDR in terms of their effects on outcomes, but the potential of these factors for jeopardizing patients' safety postoperatively and/or to exert harmful effects on surgical outcomes in longer-term follow-up cannot be ignored. Consequently, it is too early to determine the therapeutic efficacy and cost-effectiveness of CTDR and will require considerable time and studies to provide appropriate answers regarding the same. For these reasons, CTDR requires longer-term follow-up data.

Solid radiographic fusion with a nonconstrained device 5 years after cervical arthroplasty

Cervical disc arthroplasty (CDA) has been gaining popularity as a surgical alternative to anterior cervical discectomy and fusion. Spontaneous fusion following a CDA is uncommon. A few anecdotal reports of heterotrophic ossification around the implant sites have been noted for the BRYAN, ProDisc-C, Mobi-C, PRESTIGE, and PCM devices. All CDA fusions reported to date have been in devices that are semiconstrained.

The authors reported the case of a 56-year-old man who presented with left C-7 radiculopathy and neck pain for 10 weeks after an assault injury. There was evidence of disc herniation at the C6–7 level. He was otherwise healthy with functional scores on the visual analog scale (VAS, 4.2); neck disability index (NDI, 16); and the 36-item short form health survey (SF-36; physical component summary [PSC] score 43 and mental component summary [MCS] score 47). The patient underwent total disc replacement in which the DISCOVER Artificial Cervical Disc (DePuy Spine, Inc.) was used. The patient was seen at regular follow-up visits up to 60 months. At his 60-month follow-up visit, he had complete radiographic fusion at the C6–7 level with bridging trabecular bone and no motion at the index site on dynamic imaging. He was pain free, with a VAS score of 0, NDI score of 0, and SF-36 PCS and MCS scores of 61 and 55, respectively.

Conclusions

This is the first case report that identifies the phenomenon of fusion around a nonconstrained cervical prosthesis. Despite this unwanted radiographic outcome, the patient's clinical outcome was excellent.

Clinical and radiographic evaluation of cervical disk replacement: a retrospective study

Studies have shown the effectiveness of cervical disk replacement. However, clinical outcomes, particularly by radiographic assessment during the 36-month follow-up visit, have not been reported for cervical disk replacement with Mobi-C (LDR, Austin, Texas) disk prostheses. A retrospective study was conducted at 10 centers across China and included 65 patients who underwent single-level Mobi-C disk prosthesis replacement from October 2009 to July 2010. Clinical and radiographic data were collected before replacement, 7 days postoperatively, and 1, 3, 6, 12, 24, and 36 months postoperatively. Clinical and neurologic outcomes were assessed by the Japanese Orthopaedic Association (JOA) score, visual analog scale (VAS), Neck Disability Index (NDI), and Odom's criteria. Static and dynamic radiographs were measured to determine intervertebral height and range of motion (ROM) of the cervical spine, the functional spinal unit, the treated segment, and adjacent segments. JOA, VAS, and NDI scores showed statistically significant improvement 36 months after replacement (P<.05). The ROM of the cervical spine, functional spinal unit, treated segment, and adjacent segments did not show a significant difference before and after replacement (P>.05). The intervertebral height of the treated segment increased significantly, and the intervertebral height of adjacent segments showed no statistical significance between time points and at follow-up. Clinical outcomes indicated that Mobi-C artificial cervical disk replacement is reliable. Radiographic data showed that it plays a role in reconstruction or maintenance of intervertebral height and ROM of the cervical spine, functional spinal unit, treated segment, and adjacent segments after Mobi-C cervical disk replacement.

Cervical disc arthroplasty: a critical review and appraisal of the latest available evidence

Anterior cervical discectomy and fusion (ACDF) has been a very successful procedure in the management of cervical radiculopathy and myelopathy. Concerns with adjacent segment disease and the desire to preserve physiological motion have led to technological and clinical efforts for cervical disc arthroplasty. The suggested move to cervical disc replacement has led to this latter procedure being one of the most scrutinised surgical treatments in the twenty-first century. Short- and medium-term prospective randomised clinical trials and systematic reviews show cervical disc replacement to be at least as good as ACDF as regards the clinical outcomes in the management of degenerative cervical spondylosis. This is logical since the neural decompression procedure is essentially the same. However, the rationale for arthroplasty over arthrodesis has been built on two main proposed roles: the preservation of segmental motion and the prevention of adjacent segment disease. Whilst results thus far show that this first role seems to be achieved, its clinical significance is as yet unproven; the second is so far not proven. In addition, the long-term fate of the implants is also unknown. Long-term safety and efficacy, therefore, still await further clinical studies.

Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial: clinical article

OBJECT

Cervical total disc replacement (TDR) is intended to treat neurological symptoms and neck pain associated with degeneration of intervertebral discs in the cervical spine. Anterior cervical discectomy and fusion (ACDF) has been the standard treatment for these indications since the procedure was first developed in the 1950s. While TDR has been shown to be a safe and effective alternative to ACDF for treatment of patients with degenerative disc disease (DDD) at a single level of the cervical spine, few studies have focused on the safety and efficacy of TDR for treatment of 2 levels of the cervical spine. The primary objective of this study was to rigorously compare the Mobi-C cervical artificial disc to ACDF for treatment of cervical DDD at 2 contiguous levels of the cervical spine.

METHODS

This study was a prospective, randomized, US FDA investigational device exemption pivotal trial of the Mobi-C cervical artificial disc conducted at 24 centers in the US. The primary clinical outcome was a composite measure of study success at 24 months. The comparative control treatment was ACDF using allograft bone and an anterior plate. A total of 330 patients were enrolled, randomized, and received study surgery. All patients were diagnosed with intractable symptomatic cervical DDD at 2 contiguous levels of the cervical spine between C-3 and C-7. Patients were randomized in a 2:1 ratio (TDR patients to ACDF patients).

RESULTS

A total of 225 patients received the Mobi-C TDR device and 105 patients received ACDF. At 24 months only 3.0% of patients were lost to follow-up. On average, patients in both groups showed significant improvements in Neck Disability Index (NDI) score, visual analog scale (VAS) neck pain score, and VAS arm pain score from preoperative baseline to each time point. However, the TDR patients experienced significantly greater improvement than ACDF patients in NDI score at all time points and significantly greater improvement in VAS neck pain score at 6 weeks, and at 3, 6, and 12 months postoperatively. On average, patients in the TDR group also maintained preoperative segmental range of motion at both treated segments immediately postoperatively and throughout the study period of 24 months. The reoperation rate was significantly higher in the ACDF group at 11.4% compared with 3.1% for the TDR group. Furthermore, at 24 months TDR demonstrated statistical superiority over ACDF based on overall study success rates.

CONCLUSIONS

The results of this study represent the first available Level I clinical evidence in support of cervical arthroplasty at 2 contiguous levels of the cervical spine using the Mobi-C cervical artificial disc. These results continue to support the use of cervical arthroplasty in general, but specifically demonstrate the advantages of 2-level arthroplasty over 2-level ACDF. Clinical trial registration no.: NCT00389597 (ClinicalTrials.gov).

Cervical arthroplasty: the beginning, the middle, the end?

Cervical arthroplasty has developed as an alternative to spinal fusion for the treatment of cervical radiculopathy and myelopathy. The popularity of artificial discs has grown as the evidence of complications following arthrodesis has increased, making the theoretical advantages (motion preservation, altering the natural history of disease, prevention of adjacent segment disease) of disc replacement more attractive. However, as more discs are implanted and the length of follow-up increases, reported complications such as heterotopic ossification, device migration and spontaneous fusion of arthroplasty devices are growing. As a result, surgeons and patients face a challenge when deciding between motion-preserving or fusion surgery. Currently, there is inadequate evidence to promote extensive use of artificial discs for cervical spondylosis, despite promising short-term and intermediate clinical outcomes. However, there is also insufficient evidence to cease using them completely. The use of arthroplasty over fusion in the long term can only be justified if the incidence of adjacent segment disease decreases as a result. Despite the level of investment and research into arthroplasty outcomes, long-term follow-up has yet to be completed and has not convincingly demonstrated the effect of artificial discs on adjacent segment disease. Further long-term randomised trials are necessary to determine whether cervical arthroplasty is able to reduce the incidence of adjacent segment disease and, in doing so, replace arthrodesis as the gold standard treatment for cervical spondylosis.

Comparison between single- and multi-level patients: clinical and radiological outcomes 2 years after cervical disc replacement

In cervical multi-level degenerative pathology, considering the morbidity of the extensive fusion techniques, some authors advocate for the multilevel disc replacement. This study compared the safety and efficacy of disc replacement with an unconstrained prosthesis in multi- versus single-level patients. A total of 231 patients with cervical degenerative disc disease (DDD) who were treated with cervical disc replacement and completed their 24 months follow-up were analyzed prospectively: 175 were treated at one level, 56 at 2 levels or more. Comparison between both groups was based on usual clinical and radiological outcomes [Neck Disability Index (NDI), Visual Analog Scale (VAS), Range of Motion, satisfaction]. Safety assessments, including complication and subsequent surgeries, were also documented and compared. Mean NDI and VAS scores for neck and arm pain were improved in both groups similarly. Improvement of mobility at treated segments was also similar. Nevertheless, in the multi-level group, analgesic use was significantly higher and occurrence of Heterotopic Ossification significantly lower than in the single-level group. Subject satisfaction was nearly equal, as 94.2% of single-level group patients would undergo the surgery again versus 94.5% in the multi-level group. The overall success rate did not differ significantly. Multi-level DDD is a challenging indication in the cervical spine. This study showed no major significant clinical difference between the two groups. We need further studies to know more about the impact of multi-level arthroplasty, especially on the adjacent segments, but these results demonstrate initial safety and effectiveness in this patient sample.

Primary and coupled motions after cervical total disc replacement using a compressible six-degree-of-freedom prosthesis

This study tested the hypotheses that (1) cervical total disc replacement with a compressible, six-degree-of-freedom prosthesis would allow restoration of physiologic range and quality of motion, and (2) the kinematic response would not be adversely affected by variability in prosthesis position in the sagittal plane. Twelve human cadaveric cervical spines were tested. Prostheses were implanted at C5-C6. Range of motion (ROM) was measured in flexion-extension, lateral bending, and axial rotation under ± 1.5 Nm moments. Motion coupling between axial rotation and lateral bending was calculated. Stiffness in the high flexibility zone was evaluated in all three testing modes, while the center of rotation (COR) was calculated using digital video fluoroscopic images in flexion-extension. Implantation in the middle position increased ROM in flexion-extension from 13.5 ± 2.3 to 15.7 ± 3.0° (p < 0.05), decreased axial rotation from 9.9 ± 1.7 to 8.3 ± 1.6° (p < 0.05), and decreased lateral bending from 8.0 ± 2.1 to 4.5 ± 1.1° (p < 0.05). Coupled lateral bending decreased from 0.62 ± 0.16 to 0.39 ± 0.15° for each degree of axial rotation (p < 0.05). Flexion-extension stiffness of the reconstructed segment with the prosthesis in the middle position did not deviate significantly from intact controls, whereas the lateral bending and axial rotation stiffness values were significantly larger than intact. Implanting the prosthesis in the posterior position as compared to the middle position did not significantly affect the ROM, motion coupling, or stiffness of the reconstructed segment; however, the COR location better approximated intact controls with the prosthesis midline located within ± 1 mm of the disc-space midline. Overall, the kinematic response after reconstruction with the compressible, six-degree-of-freedom prosthesis within ± 1 mm of the disc-space midline approximated the intact response in flexion-extension. Clinical studies are needed to understand and interpret the effects of limited restoration of lateral bending and axial rotation motions and motion coupling on clinical outcome.

Analysis of factors that may influence range of motion after cervical disc arthroplasty

BACKGROUND CONTEXT

Cervical artificial disc replacement is increasingly becoming popular among spine surgeons. Cervical disc arthroplasty aims to afford spinal stability and then balance this with flexibility. One of the fundamental benefits from performing cervical arthroplasty instead of fusion is preservation of motion in both the functional spinal unit (FSU) and the overall cervical spine. Eventually, preservation of segmental motion is believed to prevent the development of adjacent segment degeneration. But to justify its use, disc replacement prosthesis must demonstrate actual motion in vivo and preserve range of motion (ROM) after surgery as long as it allows. Without preservation of motion, disc prosthesis becomes just a functional arthrodesis equivalent.

PURPOSE

The purpose of this study was to analyze the possible factors affecting cervical spine ROM after single-level cervical disc arthroplasty.

STUDY DESIGN/SETTING

This is a retrospective radiological study of patients with symptomatic single-level cervical disc disorder who received the cervical disc prosthesis (Bryan Cervical Disc Prosthesis; Medtronic Sofamor Danek, Memphis, TN, USA).

PATIENT SAMPLE

Procedure was performed in 39 patients.

OUTCOME MEASURES

The outcome measures were statistical correlation of possible factors and ROM.

METHODS

We investigated possible factors that could affect cervical ROM after surgical intervention using cervical disc replacement. For this, we focused on two main components, namely, patient factors and technical factors. First, we examined patient factors, such as age, sex, preoperative FSU ROM, and preoperative overall cervical spine (whole cervical spine) ROM. Second, we then investigated technical factors, such as the amount of bone resection, disc insertion angle, and disc insertion depth. Then, our study searched if there was any statistical correlation between these factors and the postoperative cervical ROM.

RESULTS

Significant correlation was found between the postoperative overall cervical spine ROM and preoperative overall cervical spine ROM (p<.0001, R(2)=0.9062). Postoperative FSU ROM is closely correlated to both the preoperative FSU ROM (p<.0001) and the disc insertion angle (p=.0097). However, no significant correlation was noted between age, sex, disc insertion angle, and disc insertion depth.

CONCLUSION

Significant correlation was found between the postoperative overall cervical spine ROM and preoperative overall cervical spine ROM. Postoperative FSU ROM is closely correlated to both the preoperative FSU ROM and the disc insertion angle. Careful preoperative evaluation of the patient's radiographs and meticulous surgical technique during the surgical procedure could aid in achieving the goals and benefits of cervical disc arthroplasty.