History

Materials, Biomechanics, and Wear

The main metal alloys used in devices are titanium, cobalt chromium, and stainless steel [14]. There are also a number of bearing interfaces: metal-on-metal, metal-on-polymer (polyurethane), ceramic-on-ceramic and ceramic-on-polymer. The material selection and device design should be optimized so as to preserve motion, reduce friction, and improve durability. Maintenance of the normal kinematics of the spine is one of the primary goals in disc arthroplasty. The cervical spine is inherently dynamic, with flexion, extension, and lateral bending in addition to anterior and posterior translation. One example of how cervical disc arthroplasty attempts to mirror the natural motion of the cervical spine is demonstrated in Fig. 3.1. Rousseau et al. [15] examined the intervertebral kinematics after use of a ball and socket device (either the Prestige LP or Prodisc-C) and concluded this design did not fully preserve natural range of motion or center of motion between flexion and extension. This may be attributed to the absence of translation when using a constrained prosthesis [16]. Additionally, a comparison of constrained devices featuring a fixed core (Prodisc-C) and mobile core (Mobi-C) evaluated stress on the polyethylene core, pressure on the facet joint, and biomechanical impact; the fixed core device exhibited less pressure on the facet joint, more pressure on the core, and a more severe biomechanical impact if the device is not centered, while the opposite was seen in devices with a mobile core [17]. A major cause of failure of cervical disc replacement is wear debris, which can trigger an inflammatory reaction leading to osteomyelitis, pain, and loosening of the device [18]. Veruva et al. [19] conducted a systematic review to determine any adverse effects from the materials used in the different devices. It was reported that metal-on-polymer replacements could lead to polymer wear debris, thus stimulating an innate response. Metal-on-metal devices could generate metallic wear debris causing activation of the adaptive immune system and subsequent tissue reactions.

Preoperative Evaluation and Imaging

Preoperative imaging for cervical disc arthroplasty involves plain radiographs and more advanced imaging techniques. Anteroposterior, odontoid, neutral lateral, and flexion-extension lateral radiographic views should be obtained. The flexion-extension lateral views can be used to assess the preoperative mobility of the cervical spine. MRI or CT scans offer a more comprehensive evaluation of the index surgical level, particularly regarding the presence of conditions such as spondylosis, neurologic compression, and pre-existing facet arthropathy. Myelography can be incorporated to gain additional information. These imaging studies could also reveal contraindications for this procedure.

Technique

The anterior cervical spine is approached as discussed in Chap. 1. A nasogastric tube can be placed for easier identification and protection of the esophagus. The neutral to slightly lordotic position is preferred, which can be created with the use of a small towel bump under the neck rather than between the shoulders or under the thoracic spine, which can cause a hyperlordotic position. A donut pillow is placed under the head to prevent it from rolling. Taping of the shoulders can additionally stabilize the operative field and may be utilized in order to obtain light traction. A right or left Smith-Robinson approach is used to expose the levels of interest and adequate decompression is completed. Of note, in comparison to an anterior cervical discectomy and fusion, a more rigorous decompression is often necessary with cervical disc replacement. The posterior longitudinal ligament should always be removed to maximize the biomechanics of the device. A wide foraminotomy should also be performed as the level will continue to remove and any foraminal stenosis can lead to recurrent radicular symptoms. Meticulous hemostasis should be maintained in an effort to keep a clear operative field and minimize the risk of heterotopic ossification.

Prior to endplate preparation, exact sagittal position of the vertebrae should be confirmed with lateral fluoroscopic imaging. Anteroposterior views should place spinous processes at the target level centered between pedicles to ensure coronal plane alignment. Next, sizing of the device should be assessed. The largest diameter disc possible for the prepared space should be utilized. This can be accomplished with preoperative templates, radiographs, and CT. Intraoperatively, trials along with fluoroscopy confirm or allow for adjustment of the final device implanted. Endplate preparation is generally implant-specific. Milling of the endplate is required for the Bryan system and creating a bony trough is required for the Prodisc-C’s endplate keel. Regardless of manufacturer-specific endplate preparation, subchondral bone should be preserved as much as possible to prevent subsidence. After the endplate is prepared, centering and neurologic decompression should again be checked.

The artificial disc device is then implanted, with the appropriate depth based on implant design. Fluoroscopic imaging ensures appropriate coronal and sagittal plane positioning. The prosthesis should cover the endplates on both fluoroscopic views [30]. Lastly, implants are fixed with any implant-specific instrumentation and final imaging is performed. Wound closure should proceed with meticulous hemostasis to prevent postoperative wound complications and heterotopic ossification.

Prestige

Burkus et al. [34] reported the 7-year postoperative clinical outcomes of ACDF compared to those for patients receiving TDA with the Prestige Cervical Disc. Neurological status was improved or maintained in 88.2% TDA patients and 79.7% ACDF patients. Rates of additional surgical procedures was also reduced in patients undergoing TDA versus ACDF at 4.6% and 11.9%, respectively. NDI scores, success, work status, rate of adverse events, and adjacent segment motion were similar between both groups.

Peng et al. [35] completed a prospective study looking at clinical and radiographic outcomes for patients that underwent ACDF and TDA with the Prestige LP Cervical Disc. Follow-up time was an average of 2.9 years with a minimum of 2 years. Significant improvement in metrics for neck and limb pain, neurogenic symptoms, myelopathy, and quality of life was observed for all patients, although no statistically significant difference was noted between patients in the ACDF and TDA groups. Physiologic motion was maintained at the surgical level for TDA and no significant difference in motion was exhibited at the adjacent segments. This finding contrasted ACDF which resulted in increased motion at adjacent levels; these changes in motion patterns have been implicated in adjacent level degeneration.

PCM Disc Prosthesis

Phillips et al. [36] conducted a study to assess the 5-year postoperative outcomes of ACDF versus TDA with the PCM disc. Scores for NDI, neck and arm pain, patient satisfaction, rates of dysphagia, and a general health summary for patients receiving TDA were significantly superior to those with ACDF. Radiological findings mirrored these results, as degeneration at the superior disc level was seen in 33.1% of the TDA patients compared to 50.9% ACDF patients. People in the TDA group also had fewer secondary surgeries and maintained range of motion at the 5-year follow-up with an average flexion-extension value of 5.2°.

ProDisc-C

Zigler et al. [37] compared the 5-year postoperative clinical outcomes of ACDF and a cervical total disc replacement using ProDisc-C . Neurological status, patient satisfaction, and number of adverse events were not significantly different between these two groups. However, patients who underwent TDA reported less neck pain intensity and frequency and had lower rates of secondary surgery (2.9% for TDA patients and 11.3% for ACDF patients). Range of motion was also maintained in the ProDisc-C patients at the 5-year follow-up.

Adjacent segment motion was evaluated by Kelly et al. [38] following ACDF versus TDA using the ProDisc-C prosthesis . Flexion-extension films were obtained of the 199 patients to assess range of motion 2 years following surgery. Both cranial and caudal adjacent segments demonstrated a statistically significant increase in motion for the ACDF patients, although there was no difference observed between the ACDF and TDA groups.

Mobi-C

Radcliff et al. [39] recently reported on the long-term outcomes of a multicenter randomized clinical trial with 7-year follow-up comparing ACDF to TDA. Interestingly, this analysis demonstrated clinical superiority of two-level TDA over two-level ACDF and non-inferiority of single-level TDA versus single-level ACDF. The overall success rates of two-level TDA and two-level ACDF patients were 60.8% and 34.2%, respectively. Success rates of single-level TDA and single-level ACDF were similar between cohorts. Both the single- and two-level TDA and ACDF groups showed significant improvement in NDI scores, pain scores, and SF-12 MCS/PCS scores. In the single-level cohort, there was an increased percentage of TDA patients who reported themselves as “very satisfied” (90.9% vs. 77.8%). There was a lower rate of adjacent level secondary surgery in the single-level TDA patients (3.7%) versus the ACDF patients (13.6%). In the two-level TDA group, the NDI success rate was significantly greater (79% vs. 58%), as was the rate of patients who were “very satisfied” with treatment (85.9% vs. 73.9%). The rate of subsequent surgery at the index level was significantly lower in the two-level TDA group compared to the ACDF group (4.4% vs. 16.2%). The rate of adjacent level secondary surgery was significantly lower in the two-level TDA (4.4%) patients compared to the ACDF (11.3%) patients.

An assessment of the occurrence of heterotopic ossification (HO) in patients presenting with extremity radiculopathy receiving TDA using the Mobi-C was completed by Park et al. [40]. Mean follow-up time was 40 months for the 75 patients. NDI scores and neck and arm pain levels all improved significantly between preoperative and postoperative evaluation. HO occurred in 67 levels at 12 months, and then at 80 levels by 24 months following the procedure , out of a total of 85 surgical levels. A univariate and multivariate logistic regression indicated that anterior HO was significantly associated with surgical technique, although the study was limited by follow-up time and number of patients enrolled.

Bryan Cervical Disc

Quan et al. [41] analyzed the clinical and radiological outcomes of a Bryan cervical disc arthroplasty at 8 years postoperative. None of the 21 patients required revision surgery and 19 reported an ability to perform daily activities without limitations. Motion was maintained to an average range of 10.6 +/− 4.5 degrees in 78% of the cases. Evidence of HO was seen in nearly half of the patients, many presenting with grades 3 and 4 HO. Four patients developed adjacent segment degeneration, although this only occurred in patients who exhibited signs of degenerative disc changes prior to their operation.

In a similar study, Dejaegher et al. [42] provided a 10-year follow-up to TDA with the Bryan prosthesis. Neurological success was achieved in 89% of the 72 patients, and over 80% of the prostheses had mobility of at least 2 degrees. Adverse events, specifically cases of radiculopathy and myelopathy, were reported by 24% of the patients, of which 8% required additional surgery to address new or recurrent symptoms . In an FDA IDE trial, Sasso et al. [43] conducted a prospective, randomized controlled trial of the Bryan cervical disc arthroplasty compared to ACDF and followed patients for 10 years. At this time point, arthroplasty demonstrated a significantly improved NDI (8 vs. 16) and a lower reoperation rate (9% vs. 32%).

Secure-C

Vaccaro et al. [29] compared the 2-year patient outcomes of using TDA with the Secure-C to ACDF. A total of 380 patients were included in this study. Mean surgery time was significantly shorter with ACDF. NDI reduction and improvement in neck and arm pain were seen at a higher rate in TDA patients; patient satisfaction and neurologic status were also better for this group. Radiological assessments indicated that 84.6% of TDA patients were range of motion successes at 24 months, with mean flexion-extension of 9.7°. It was also observed that 89.1% of patients who received ACDF had successful fusion at 24 months.

Pearls and Pitfalls

• 
  

  Cervical TDA is a viable FDA-approved tool in the armamentarium of the spine surgeon, but indications and contraindications should be seriously considered after obtaining patient history and preoperative diagnostics.

  
  
• 
  

  Patients with single-level and two-level cervical disease should be assessed for infection, osteoporosis, allergies, severe spondylosis or instability, facet arthropathy, and axial neck pain prior to considering TDA since these are all contraindications to the procedure.

  
  
• 
  

  Although there are no gold-standard diagnostics to assess facet arthropathy, consider CT, MRI, and facet blocks to aid in diagnosis.

  
  
• 
  

  Generally speaking, patients with less than 3 mm of disc space or greater than 15° of kyphotic deformity are poor candidates for cervical TDA.

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