Racial Disparities in Utilization and Outcomes of Cervical Disc Arthroplasty

STUDY DESIGN

Retrospective study.

OBJECTIVE

We examined racial disparities in (1) cervical disc arthroplasty (CDA) versus anterior cervical discectomy and fusion (ACDF) utilization and (2) CDA in-hospital outcomes.

SUMMARY OF BACKGROUND DATA

ACDF and CDA are established treatments for cervical disc disease. While CDA may offer certain advantages over ACDF, its utilization patterns have not been comprehensively explored.

METHODS

This study of 2012 to 2019 discharges from the National Inpatient Sample included White, Black, and Hispanic patients aged 18 years and older who underwent elective ACDF or CDA. Patient demographics, comorbidities, cervical spine diagnoses, and hospital characteristics were extracted. Survey-weighted logistic regression modeled the adjusted association between race and CDA (vs. ACDF) utilization; an interaction between race and year examined temporal changes in disparities. For CDA outcomes, multivariable logistic regression was used for binary outcomes (nonhome discharge, combined complications, and dysphagia) and linear regression for length of stay.

RESULTS

The cohort included 712,355 weighted procedures (97.6% ACDF; 84.2% White, 9.7% Black, 6.1% Hispanic). CDA utilization increased from 1.0% of the procedures in 2012 to 3.8% in 2019. Black and Hispanic patients had significantly lower odds than White patients of receiving CDA versus ACDF (OR=0.77, 95% CI: 0.66-0.89, P=0.001; OR=0.80, 95% CI: 0.69-0.93, P=0.003) respectively. There was no statistically significant interaction between race and discharge year (P=0.50). For in-hospital CDA-specific outcomes, Black (vs. White) patients were more likely to experience dysphagia (OR=2.70, 95% CI: 1.53-4.78, P=0.001) and combined complications (OR=3.10, 95% CI: 1.91-5.05, P <0.001). There were no significant differences in any CDA outcome for Hispanic versus White patients.

CONCLUSIONS

This study revealed decreased utilization of CDA versus ACDF in minority patients, a pattern that persisted over time despite overall increasing CDA utilization. In addition, a higher burden of dysphagia and combined complications following CDA in Black patients warrants further examination.

LEVEL OF EVIDENCE

III.

Biomechanical analysis of single and multi-level artificial disc replacement (ADR) in cervical spine using multi-scale loadings: A finite element study

Artificial disc replacement (ADR) is a clinical procedure used to diagnose cervical degenerative disc disease, preserving range of motion (ROM) at the fixation level and preventing adjacent segment degeneration (ASD). This study analyzed the biomechanics of ADR by examining range of motion (ROM), stress levels in bone and implants, and strain in the bone-implant interface using multi-scale loadings. The study focused on single- and double-level patients across various loading scales during physiological motions within the cervical spine. Results showed increased ROM in single-level and double-level fixations during physiological loadings, while ROM decreased at the adjacent level of fixation with the intact cervical spine model. The Prodisc-Implant metal endplate experienced a maximum von Mises stress of 432 MPa during axial rotation, confirming the long durability and biomechanical performance of the bone-implant interface.

Should patient eligibility criteria for cervical disc arthroplasty (CDA) be expanded? A retrospective cohort analysis of relatively contraindicated patients undergoing CDA

BACKGROUND CONTEXT

Cervical disc arthroplasty (CDA) is a safe and effective alternative to anterior cervical discectomy and fusion (ACDF) in the treatment of various degenerative pathologies with advantages of motion preservation and lower rates of adjacent segment degeneration (ASD). Absolute contraindications for CDA have been well outlined in order to prevent adverse outcomes in patients. However, in cases of patients with relative contraindications (kyphotic deformity, prior cervical surgery, etc.), there remains controversy. There is minimal literature evaluating long-term outcomes in this patient population.

PURPOSE

To compare long-term clinical and functional outcomes of CDA in typical patients versus those with relative contraindications.

DESIGN

Retrospective cohort review.

PATIENT SAMPLE

Eighty-nine patients were included in the study: 55 (no contraindications) in Group 1 and 34 (relatively contraindicated) in Group 2 and 26 (preoperative segmental kyphosis) in Group 3.

OUTCOME MEASURES

(1) Patient demographics; (2) perioperative data; (3) rates of complications and revisions; (5) visual analogue scale (VAS), and neck disability index (NDI) scores.

METHODS

Patients were placed in the relatively contraindicated cohort if they possessed at least one of the following: (1) segmental kyphosis of 5° to 10°, (2) significant loss of disc height (between 50% and 75% of initial measurements or 1.5-3mm), (3) bridging osteophytes, and (4) prior cervical spine surgery based on preoperative cervical radiographs. The other cohort included patients without any relative contraindication who underwent CDA over the same time frame. Additionally, a subgroup analysis was used to compare those without any contraindications to those with only preoperative segmental kyphosis. Patients were included in this study if they met the following criteria: over 18 years of age, minimum follow-up of 24 months, and availability of complete medical records. Patient demographics, levels operated on, and perioperative outcomes were assessed between the two groups. Revision and complication rates were recorded. Functional outcomes scores were compared using VAS and NDI scores at 6-months, 12-months and final follow-up.

RESULTS

Mean follow-up was 40.8 months in Group 1 and 38.3 months in Group 2 (p=.569). Complication rates were 21.8% in Group 1 and 26.4% in Group 2 (p=.615). Complication rates in a comparison between Groups 1 and 3 were statistically insignificant (p=.383). The most common complication was transient approach-related postoperative dysphagia (Group 1: 20% vs Group 2: 23.5%, p=.693). No significant differences were observed in the rates of transient dysphonia (Group 1: 0.0% vs Group 2: 2.9%, p=.201), adjacent segment degeneration (ASD) (Group 1: 1.8% vs Group 2: 0.0%, p=.429), infection (Group 1: 1.8% vs Group 2: 2.9%, p=.712), heterotopic ossification (Group 1: 49.1% vs Group 2: 50.0%, p=.934) or spontaneous fusion (Group 1: 1.8% vs Group 2: 2.9%, p=.728). No revision surgeries were observed in either cohort. All three groups demonstrated significant improvements in their VAS and NDI scores compared with preoperative measurements (p<.001), but no significant differences were found in the degree of improvement between groups at any point in time.

CONCLUSIONS

Our study found no significant differences in clinical and functional outcomes between patients undergoing 1- and 2-level CDA with relative contraindications versus typical patients. These findings suggest that patient eligibility criteria for CDA may warrant expansion. However, future prospective studies over a longer period of follow-up are necessary to corroborate our results.

Is Cervical Disk Arthroplasty a Suitable Alternative to Treat Degenerative Cervical Myelopathy?

STUDY DESIGN

Systemic review.

OBJECTIVE

To understand the role of cervical disk arthroplasty in the treatment of cervical myelopathy.

SUMMARY OF BACKGROUND DATA

The surgical management of degenerative cervical myelopathy (DCM) most frequently involves decompression and fusion, but stiffness introduced by the fusion and adjacent segment degeneration remain problems that can result in significant morbidity. Cervical disk arthroplasty (CDA) is a newer procedure that has been demonstrated to be safe and effective for the management of cervical spine degenerative disk disease, but it has not been traditionally considered as a treatment option for DCM and the use for this indication has not been extensively studied.

MATERIALS AND METHODS

A systematic review was undertaken using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines using a search strategy to query all relevant articles on the use of cervical disk arthroplasty in the setting of cervical myelopathy over a 20-year period (2004-2023). This review examines the literature to assess our current understanding of the appropriateness, safety, and value of CDA in the treatment of DCM.

RESULTS

A total of 844 patients received CDA across the 14 studies that met inclusion criteria, with an average of 60.3±40.4 patients per study (range: 11-152 subjects). Featured studies included 5 (35.7%) prospective studies, of which 2 were randomized. All studies had primary outcome measures of disability and/or pain scores, with the Japanese Orthopedic Association myelopathy score and neck disability index as the most commonly assessed. Four (26.7%) studies compared arthroplasty with arthrodesis. Safety of CDA for DCM was found in all studies with improvement in clinical outcome measurements.

CONCLUSION

Cervical disk arthroplasty appears to be a safe and effective surgical option in the management of degenerative cervical myelopathy. Further study is needed to assess if arthroplasty provides clinical improvement in DCM of comparable magnitude and durability as traditional fusion strategies.

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.

Cervical Total Disc Replacement: Indications and Technique

Cervical total disc replacement devices have been marketed in the United States (US) since 2007, with abundant level 1 evidence published on the treatment. Adherence to the strict inclusion/exclusion criteria and the surgical technique training of the US clinical trials remains the consistent and conservative approach to patient selection and implantation technique. However, patient selection and surgical technique remain debated among US surgeons as the published data and available cervical total disc replacements continue to grow.

Outcomes After Cervical Disc Arthroplasty Versus Stand-Alone Anterior Cervical Discectomy and Fusion: A Meta-Analysis

STUDY DESIGN

Systemic review and meta-analysis.

OBJECTIVES

To review and compare surgical outcomes for patients undergoing stand-alone anterior cervical discectomy and fusion (ACDF) versus cervical disc arthroplasty (CDA) for the treatment of cervical spine disease.

METHODS

A systematic search was performed on PubMed, Medline, and the Cochrane Library. Comparative trials measuring outcomes of patients undergoing CDA and stand-alone ACDF for degenerative spine disease in the last 10 years were selected for inclusion. After data extraction and quality assessment, statistical analysis was performed with R software metafor package. The random-effects model was used if there was heterogeneity between studies; otherwise, the fixed-effects model was used.

RESULTS

In total, 12 studies including 859 patients were selected for inclusion in the meta-analysis. Patients undergoing stand-alone ACDF had a statistically significant increase in postoperative segmental angles (mean difference 0.85° [95% confidence interval = 0.35° to 1.35°], P = .0008). Patients undergoing CDA had a decreased rate of developing adjacent segmental degeneration (risk ratio = 0.56 [95% confidence interval = -0.06 to 1.18], P = .0745). Neck Disability Index, Japanese Orthopedic Association score, Visual Analogue Scale of the arm and neck, as well as postoperative cervical angles were similar between the 2 treatments.

CONCLUSIONS

When compared with CDA, stand-alone ACDF offers similar clinical outcomes for patients and leads to increased postoperative segmental angles. We encourage further blinded randomized trials to compare rates of adjacent segmental degeneration and other postoperative outcomes between these 2 treatments options.

Patient Selection in Cervical Disc Arthroplasty

BACKGROUND

Patient selection for cervical disc arthroplasty (CDA) in the United States remains a topic of debate among surgeons. Many surgeons base US patient selection for CDA implantation on the Food and Drug Administration (FDA) indications/contraindications. While off-label use does occur, the frequency and extent of off-label use in the US remains largely unknown. Outside the United States, patient selection is notably less stringent; however such data also remain largely unpublished or presented/published with a low level of evidence. Here, we will review the current approved US on-label patient selection criteria for CDA and discuss the rationale and supporting evidence to expand these criteria in the United States.

METHODS

A PubMed literature search was completed using the keywords "cervical disc arthroplasty" and "cervical disc replacement." The articles were evaluated by the authors for patient selection criteria.

CONCLUSIONS

The current published data do not conclusively prove that the patients excluded from CDA by strict adherence to FDA indications would benefit from CDA surgery over anterior cervical discectomy and fusion. As surgeons, it is a difficult decision regarding when to expand indications to include off-label use of CDA. In our practice, generally CDA patient selection agrees with the FDA indications and contraindications, as there is a lack of level 1 evidence to confirm effectiveness of CDA outside of the current FDA indications. We will likely need more well-constructed studies to include prospective and controlled trials that specifically evaluate the "off-label" applications before US surgeons are convinced to expand indications and insurance companies agree to reimburse.

Optimization of Three-Level Cervical Hybrid Surgery to Prevent Adjacent Segment Disease: A Finite Element Study

Hybrid surgery (HS) allows surgeons to tailor fusion and arthroplasty in the treatment of multiple-level cervical disc degeneration. However, the decision making of selecting either ACDF or ADR for each level in three-level HS remains controversial and has not been fully investigated. This study was aimed to optimize three-level cervical hybrid constructs by systematically investigating their biomechanical properties and their effect on adjacent levels. A finite element model of cervical spine (C2–C7) was developed, and eight C3–C6 surgical models including six HS were constructed. The range of motion (ROM) in flexion, extension, lateral bending, and axial rotation under 2.0 Nm moments with 30 N follower load were simulated. The von Mises stress, strain energy at the adjacent intervertebral disc (IVD) and force at the adjacent facet were calculated. The ROM of the hybrid constructs and adjacent levels was close to that of the intact spine. HS with arthroplasty performed at C5-6 had better performance in terms of ROM reduction at the inferior adjacent level (C6-7). Moreover, C-D-D and 3ADR had best performance in reducing the von Mises stress and strain energy at C6-7. All HS reduced the facet burden at both C2-3 and C6-7 levels. However, the major drawback of HS revealed here is that the effect of C6-7 protection is at the cost of increased C2-3 IVD burden. In conclusion, we recommend C-D-D and 3ADR for patient with C3–C6 disc degeneration without predisposing C2-3 condition. C-C-D could be a good alternative with a lower medical cost. This analysis guides the decision making in three-level cervical HS before future cadaver studies or human clinical trials.

In which cases do surgeons specializing in total disc replacement perform fusion in patients with cervical spine symptoms?

PURPOSE

The purpose was to investigate reasons and their frequency for why total disc replacement (TDR) specialty surgeons performed anterior cervical discectomy and fusion (ACDF) rather than TDR.

METHODS

A consecutive series of 464 patients undergoing cervical spine surgery during a 5-year period by three TDR specialty surgeons was reviewed. For each ACDF, the reason for not performing TDR was recorded.

RESULTS

TDR was performed in 76.7% of patients (n = 356) and ACDF in 23.3% (n = 108). The most common reason for ACDF versus TDR was anatomical (conditions that may not be adequately addressed with TDR and/or may interfere with device function), which occurred in 64 of 464 patients (13.79%). The second most common reason was insurance (denial/lack of coverage n = 17, 3.23%), and deformity/kyphosis not addressable with TDR was noted in 13 (2.80%). Pseudoarthrosis repair led to ACDF in three patients (0.65%), two did not receive TDR due to osteoporosis (0.43%), and in two others (0.43%) ACDF was undertaken due to high risk of heterotopic ossification. There was one case (0.22%) each of: nickel allergy, trauma with posterior element fracture, TDR removal, multiple prior cervical spine surgeries, concern about artifact on future imaging studies, benign osteoblastic bone, and limitation to adequate surgical approach for TDR. ACDF patients' mean age was significantly greater than TDR patients' (55.3 vs. 46.7 years; p < 0.01). TDR group had significantly more single-level procedures than ACDF (60.8% vs. 43.5%; p < 0.05).

CONCLUSION

The most common reason for ACDF versus TDR was anatomy that may compromise segmental stability and/or TDR functionality. Older age and greater number of operated levels may be related to anatomical factors, primarily significant osteophytes and severely degenerated facets. These factors, as well as deformity/kyphosis, are more common in older patients and require multi-level treatment. This study found that many patients are good cervical TDR candidates; however, even among TDR specialists, ACDF may be preferred where it is prudent to not take undue risks. These slides can be retrieved under Electronic Supplementary Material.

Analysis of the Factors That Could Predict Segmental Range of Motion After Cervical Artificial Disk Replacement: A 7-Year Follow-up Study

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

To identify the potential preoperative factors and surgical technique factors that are associated with long-term range of motion (ROM) after surgery. Further, this article aimed to guide selection of patients with cervical artificial disk replacement and a fine surgical technique.

SUMMARY OF BACKGROUND DATA

Segmental ROM is the most important parameter concerning cervical kinematics after a cervical artificial disk replacement. There are few researches regarding the influencing factors on postoperative ROM, and consistent results have not yet been reported.

METHODS

The cohort comprised a total of 68 disks implanted into 57 patients who were retrospectively analyzed. The mean follow-up period was 84.1 months. Segmental ROM and other useful parameters were measured using lateral neutral, extension, and flexion radiographs, which were obtained preoperatively, 3 months after surgery, and at last follow-up. Preoperative CT and clinical assessment were also used. To find out associated factors, the patients were divided into 2 groups according to the segmental ROM at last follow-up.

RESULTS

After surgery, the clinical outcomes were satisfactory. The segmental ROM at last follow-up (7.8±4.3 degrees) was preserved without significant change from preoperative ROM (8.8±3.8 degrees). The patients who had a better segmental ROM after surgery were found to have a higher preoperative segmental ROM, a younger age, a better disk insertion angle, and disk insertion depth. These 4 factors were identified as independent risk factors (P=0.027, 0.017, 0.036, and 0.046, respectively) for long-term ROM.

CONCLUSIONS

The postoperative long-term, segmental ROM was well preserved and found to be affected by the preoperative segmental ROM, patient's age, disk insertion angle, and disk insertion depth.

Cervical disc replacement surgery: indications, technique, and technical pearls

PURPOSE OF REVIEW

Cervical disc replacement (CDR) is a surgical option for appropriately indicated patients, and high success rates have been reported in the literature. Complications and failures are often associated with patient indications or technical variables, and the goal of this review is to assist surgeons in understanding these factors.

RECENT FINDINGS

Several investigations have been published in the last 5 years supporting the use of CDR in specific patient populations. CDR has been shown to be comparable or favorable to anterior cervical discectomy and fusion in several meta-analyses and mid-term follow-up studies. CDR was developed as a technique to preserve motion following a decompression procedure while minimizing several of the complications associated with fusion and posterior cervical spine procedures. Though success with cervical fusion and posterior foraminotomy has been well documented in the literature, high rates of mid- and long-term complications have been clearly established. CDR has also been associated with several complications and challenges with regard to surgical technique, though improvements in implant design have lead to an increase in utilization. Several devices currently exist and vary in terms of material, design, and outcomes. This review paper discusses indications, surgical technique, and technical pearls and reviews the CDR devices currently available.