Cervical disc replacement is a surgical procedure for the treatment of discogenic cervical spondylosis that preserves the alignment and motion of cervical segments and reduces degeneration of adjacent segments. Anterior discectomy and fusion (ACDF) is the main classical procedure for the treatment of cervical spondylosis and nerve root and myelopathy due to acute disc herniation. The use of anterior cervical plates has improved the success rate of single- and two-segment cervical non-implant fusions, and the combination of plates with intervertebral autologous or allogeneic bone grafting preserves the curvature and disc height of the cervical segments.
Current clinical studies have focused on disc degeneration in adjacent segments after cervical spine surgery, and cadaveric specimens have been studied to show increased normal cervical mobility and internal disc pressure near the fused segment. The evidence from these studies has laid the theoretical foundation for the study of cervical disc replacement (CDR) prosthesis, but before the clinical application of CDR can be However, before CDR can be used clinically, it needs to be clarified whether cervical disc replacement and ACDF can achieve similar results and prevent cervical degeneration in the segment adjacent to the surgery. In this article, we analyze the development, application, and prognosis of CDR and compare it with ACDF, taking into account the latest research evidence.
Indications and contraindications for CDR
The indications for CDR currently accepted by orthopedic surgeons include: postoperative reconstruction of cervical medullary nerve compression caused by disc herniation; surgical treatment of nerve compression caused by ossification of the C3-T1 intervertebral foramen; absolute contraindications to its use are cervical deformity, unilateral neck pain, immobility of the motion segment, instability, degeneration of the synovial joint, infection, etc. Relative contraindications include rheumatoid arthritis, renal failure, osteoporosis, tumors, and preoperative glucocorticoid use, etc. Auerbach et al. retrospectively analyzed 167 patients undergoing elective cervical spine surgery and found that approximately 43% of patients met the indications for CDR, and the percentage increased to 47% if adjacent spine degeneration was taken into account.
CDR History
Since the introduction of the first generation of disc prostheses, there have been tremendous advances in their design and process. Early models of non-restricted 2-part gold-to-gold ball and socket prostheses required screw riveting to the vertebral body and were abandoned due to postoperative difficulties in swallowing and screw loosening. After many years of development, the more classic cervical disc prosthesis is now the fifth generation (Figure 1, Medtronic), which is composed of titanium-ceramic and other materials, and the surface of the prosthesis is covered with a perforated titanium plasma membrane to facilitate bone growth into the prosthesis. Each type of disc prosthesis has a specific design and therefore each has a different placement technique, and there are many studies on various prostheses, but they are usually compared to ACDF. Other types of prostheses include BryanCDR (Medtronic, Inc., Figure 2), ProDisc-C type prosthesis (syntheses, Figure 3), PCM prosthesis (Nuvasive, Figure 4), CerviCore prosthesis (stryker, Figure 5), etc. Regardless of the type of prosthesis design, it must have features such as intersegmental motion, maintenance of disc height and physiological curvature of the spine, and these prostheses should have long term stability, slow wear rate to reduce possible inflammatory reactions and osteolysis, no change in adjacent segmental spinal motion mechanics, and price and reduced complications compared to ACDF.
Figure 1: Medtronic, Prestige LP prosthesis, non-restricted ball-and-socket titanium-ceramic surface structure prosthesis.
Figure 2: Medtronic, Bryan Prosthesis, unrestricted titanium prosthesis with polyethylene perforated film covering the surface of the prosthesis.
Figure 3: synthes, ProDisc-C type prosthesis, metal to UHMWPE joint, which can be riveted to the vertebral endplate by means of a keel.
Figure 4: Nuvasive, PCM prosthesis, consisting of two metal prostheses with a flat plate shape and a present wavy surface covered by a polyethylene perforated membrane.
Figure 5: Stryker, CerviCore prosthesis, a semi-restricted prosthesis with a saddle-like design, metal-to-metal interface, and a keel to rivet the prosthesis to the vertebral body.
CDR biomechanical and kinematic features
The promotion of CDR in clinical practice is based on the assumption that the kinematic characteristics of the spine change after cervical fusion, thereby accelerating the degeneration of symptomatic discs in the adjacent segments and requiring re-surgical intervention. Diangelo et al. showed increased compensatory motion of the adjacent segment after cervical fusion, but no such mechanical changes were found in patients with CDR. proximal segment degeneration, and one of these patients required surgical treatment.
It has been more frequently shown that disc pressures in the proximal segment are higher than normal in patients undergoing vertebral fusion, whereas in patients with CDR there is no elevated disc pressure. In addition, a study by Chang et al. found increased pressures on the synovial joints during postoperative spinal extension in patients with CDR. Both in vitro and in vivo studies have demonstrated that CDR is effective in preserving the sagittal position of the vertebral body in the replaced segment and the range of motion such as cervical rotation and lateral bending. In contrast to CDR and ACDF, CDR patients have reduced intervertebral motion in the proximal segment, whereas the opposite is true for ACDF. It has been shown that patients with CDR have reduced intervertebral motion in the proximal segment at 1 month and 3 months postoperatively, whereas 2 years postoperatively, intervertebral motion in the proximal segment returns to preoperative levels. At 2 years postoperatively, cervical curve curvature was better maintained in post-CDR patients than in ACDF.
Clinical and imaging prognosis
Data from recent clinical studies show that ACDF patients who undergo autologous or allogeneic bone grafting improve intervertebral fusion rates and improve clinical functional prognostic outcomes, even in patients who smoke. The fusion rate progressively decreases as the number of ACDF segments increases. In a randomized controlled study, both ACDF and CDR patients were found to have significantly better cervical spine neurological function than preoperatively, with CDR showing a more significant improvement in overall function and a lower probability of needing revision.
Kim et al. conducted a 19-month postoperative follow-up study of 51 CDR and 54 ACDF patients and found that ACDF patients were 3.5 times more likely than CDR patients to exhibit adjacent segmental degeneration (e.g., osteophyte formation, narrowing of the disc space, and calcification of the anterior longitudinal ligament) on imaging, and that postoperative motion of the intervertebral space was significantly greater at the cephalic and caudal ends of fusion in both segments of ACDF patients than in CDR patients. amplitude was significantly greater than in patients with CDR. A comparative study of 223 CDR patients and 198 ACDF patients showed no significant difference in the rate of upper extremity and cervical symptom relief between ACDF and CDR postoperative patients during the 2-year postoperative follow-up, but the CDR group had better outcomes than the ACDF group in terms of overall neurological improvement rate and time to return to work. There are also other studies in the literature that indicate that CDR is better than ACDF in terms of overall functional improvement rates, which are not listed here.
In a randomized controlled study approved by the FDA, 103 patients with CDR and 106 patients with ACDF were followed up for up to two years, and the CDR group showed better neurological recovery at 6 months after surgery, and the CDR group showed better cervical function index at 3 months after surgery. However, the differences in neurological recovery, cervical function index, VAS pain score, return to work, and patient satisfaction at 2 years after surgery were not significant. The success rate of prosthesis placement (no revision, no displacement, no reoperation or additional fixation, etc.) was better in the CDR group than in the ACDF group. Analysis of the clinically important time period revealed better outcomes in the CDR group than in the fusion group. Although there was no statistically significant difference in function between the two groups at 2 years postoperatively, the CDR group recovered nerve function faster than the fusion group in the postoperative period.
Multi-segmental lesions can be treated with multi-segmental CDR. Goffin et al. reported that a controlled study of 89 patients with single-segment CDR and 9 patients with multi-segmental CDR treated for 4 and 6 years found good continuation of SF-36, cervical function index, and improvement in cervical and upper extremity pain from 4 to 6 years postoperatively. They reported approximately a 6.1% revision rate and a 4.1% proximal segment surgery rate.
CDR in reoperative patients and hybrid internal fixation techniques
CDR may benefit patients who develop symptomatic proximal segment degeneration as a result of failed cervical fusion or posterior decompression.Sekhon et al. reported the results of a study of nine patients who developed proximal segment degeneration after cervical fusion and six patients who failed posterior laminectomy decompression with CDR and found significant improvements in VAS scores, ODI scores Philips et al. reported the results of a 2-year follow-up study of 25 patients treated with CDR for adjacent segmental degeneration after fusion and compared them with 126 patients treated with CDR for the first time, and found that there was a significant improvement in the postoperative cervical function index and VAS scores in both groups. The postoperative adverse events and reoperation rates were 1.6% and 7.7%, respectively.
Patients with symptomatic multisegmental cervical spondylosis are not an appropriate population for CDR replacement at every segment, but combined use of ACDF and CDR can avoid the adverse consequences of long-segment cervical fusion. a study by Barbagallo et al. of 24 multisegmental cervical patients treated with combined CDR and ACDF reported that at 23 months of postoperative follow-up, 21 patients with SF-36, cervical function index, etc., were improved, no prosthesis-related complications were found at the end of follow-up, and the incidence of non-symptomatic heterotopic ossification was 8.3%.
Shin et al. conducted a controlled study in groups of 40 patients with C3-C7 multisegmental cervical spondylosis, with one group of patients (20) undergoing two-segment ACDF and one group undergoing single-segment ACDF combined with single-segment CDR. The combined treatment group had better recovery of cervical spine functional indices at 1 and 2 years postoperatively and better recovery of VAS scores at 1 and 12 months postoperatively, but both had comparable results in terms of improvement in upper extremity pain. The recovery of cervical spine motor function at the C2-C7 segment was faster in the combined group, and no complications such as heterotopic ossification or prosthesis failure occurred in either group after surgery.
Complications
Fountas et al. retrospectively analyzed 1015 patients with single-, double-, and triple-segment ACDF and plate fixation and found that operative mortality due to esophageal perforation occurred in 0.1%, dysphagia in 9.5%, recurrent laryngeal nerve palsy in 3.1%, hematoma requiring surgical removal in 2.4%, dural tear in 0.5%, esophageal perforation in 0.3%, internal fixation failure in 0.1%, Horner’s syndrome 0.1%, and incisional infection 0.1%.
From the prospective, randomized, controlled study of CDR by the FDA IDE, it was found that most complications were common postoperative complications, such as gastrointestinal or urinary events, and there was no significant correlation with the CDR internal fixation device, but patients in the CDR group had a higher incidence of adverse events (dysphagia in 10% of patients and incisional infection in 2.8% of patients) and a lower incidence of perioperative neurological events. The CDR and ACDF groups had similar incidence rates, but the CDR group had a lower reoperation rate. In contrast, Riley et al. reported a 28% incidence of dysphagia 2 years after ACDF compared with 21% in the CDR group, and McAfee et al. reported a lower incidence of dysphagia in the CDR group compared with the ACDF group. esophageal pressure was higher than in C3-C4 segment ACDF and C5-C6 segment CDR, the investigators concluded that the need to pull the esophagus and expose the screw holes when placing screws in the plate on the opposite side of the surgery during ACDF + plate fixation may have had an effect on the high esophageal pressure.
Goffin et al. evaluated 102 patients with CDR for complications; postoperative complications included: one case of prosthetic displacement; one case of anterior vertebral hematoma requiring hematoma debridement; 10 cases of neurological impairment; one case of vocal cord paralysis; and one case of removal of the prosthetic device 6 years postoperatively due to recurrent bony bulge and spinal cord compression. four patients still had persistent neurological symptoms in the original operated segment postoperatively, and four patients had new neurological symptoms in the remaining segments. A follow-up study of 229 patients with CDR found a total of 4 dural tears and 5 cases requiring reoperation.
A survey of 54 patients (65 prostheses) with CDR who did not have NSIADs to prevent heterotopic ossification found that the incidence of asymptomatic grade III or IV heterotopic ossification at 4 years postoperatively was 63%, although most patients were satisfied with the outcome of the procedure. In a 2-year follow-up study of 72 patients, the incidence of heterotopic ossification was found to be 9.4%, and the rate of imaging-visible degeneration of the adjacent segment was 12.5%. Reduced motion of the intervertebral motion segment due to heterotopic ossification was found in 11-44% of patients with CDR. Some investigators have suggested that heterotopic ossification represents a major pathologic mechanism of adjacent segment degeneration, but its impact on clinical functional prognosis is limited.
Sekhon et al. reported 15 reoperative patients undergoing CDR replacement and about 6.7% had postoperative complications such as persistent dysphagia, reoperation, subluxation or new onset of neurological symptoms. The use of hybrid fixation devices can reduce the incidence of asymptomatic heterotopic ossification with fewer device-related complications.
The current academic focus has shifted from spinal and neurological exposure to CDR prosthesis wear. Animal studies have confirmed that dural exposure to metal particles such as cobalt and titanium in rabbits results in increased macrophages in the bird effusion, and changes in dural fibrosis, inflammatory changes, and macrophage granules are found in the histology of the dura. Local exposure to stainless steel, titanium, and UHMWPE can lead to upregulation of IL-6 expression levels in the spinal cord and dural tissue. Late onset foreign body allergic reactions after CDR placement have been reported in the literature.
Efficacy analysis
Market analysis reports that around 2010, CDR procedures accounted for approximately 47.9% of spinal fusion procedures, with an annual medical spend of approximately $2.18 billion, and had a profound impact on the treatment of spinal disorders in the United States. CDR prostheses cost approximately $4,000 and ACDF costs $2,500 in the United States, but the high rate of reoperation and adjacent segment degeneration after ACDF may add to the potential cost of ACDF to some extent.
In summary
The CDR procedure provides definitive symptom relief and preserves the range of motion of the cervical spine segments, reduces disc pressures in adjacent vertebral segments, and the replacement prosthesis remains in good working order 2-4 years after surgery. the CDR prosthesis alone or in combination with ACDF has shown good results in treating patients with multisegmental cervical spondylosis. The rate of prosthesis-related complications is low and comparable to that of ACDF. Although the cost of the prosthesis is slightly higher than that of the fusion, the benefits gained later in the procedure can offset the upfront cost to some extent. All clinically available studies have reported high follow-up times, with 2 and 4 years being the most common, and more large samples with long follow-up times are needed in later years.