Cervical Disc Replacement (Cervical Disc Arthroplasty)

1. Introduction and Rationale

2. Anatomy Relevant to the Procedure

• Anterior cervical triangle - bordered by sternocleidomastoid laterally, trachea and esophagus medially
• Carotid sheath - retracted laterally; contains carotid artery, internal jugular vein, vagus nerve
• Recurrent laryngeal nerve - at risk with retraction; runs in the tracheoesophageal groove (left side more reliable, preferred side for approach by some surgeons)
• Sympathetic chain - lies on the longus colli; vigorous lateral retraction causes Horner's syndrome
• Disc space - C5-6 and C6-7 are most commonly affected. The uncinate processes define the lateral extent of disc removal; they must be preserved for foraminal decompression and as a guide for implant sizing
• Vertebral artery - lies in the transverse foramen of C6 and above; at risk if uncinate process is breached

3. Indications (Box 45.8, Campbell's)

• Symptomatic cervical disc disease at one or two levels between C3 and T1
• Confirmed on MRI/CT/myelography showing herniated nucleus pulposus, spondylosis, or loss of disc height
• Failed ≥6 weeks of conservative therapy
• Age 20-70 years
• No contraindications present

4. Contraindications

5. Pre-operative Workup

• X-rays (AP, lateral, flexion-extension): Assess instability, disc height, lordosis, existing osteophytes, motion at the target level (must show ≥2 degrees to qualify)
• MRI: Confirms level, quantifies cord/root compression, assesses disc hydration, evaluates facet joints
• CT scan: Evaluates extent of spondylosis, bony anatomy, foraminal stenosis, OPLL
• DEXA scan: Rules out osteoporosis (T-score ≥ -1.0 required)
• Neurological assessment: NDI (Neck Disability Index), VAS pain score, mJOA for myelopathy

6. Devices Available

• Constrained (ball-in-socket): ProDisc-C, Prestige - fixed center of rotation
• Semi-constrained / mobile core: Bryan, Mobi-C - allow translation + rotation
• Unconstrained: Allow 6 degrees of freedom; approximate normal disc kinematics

• Metal-on-metal (cobalt-chrome alloy): Prestige
• Metal-on-polyethylene: ProDisc-C, Mobi-C, Secure-C
• Polymer core (polyurethane + titanium endplates): Bryan

7. Surgical Technique

Approach

• Standard anterior Smith-Robinson approach, usually right-sided
• Patient supine, neck slightly extended (Gardner-Wells traction or head halter optional)
• Longitudinal incision along the medial border of sternocleidomastoid

Steps

1. Exposure: Blunt dissection through the platysma; carotid sheath retracted laterally, trachea/esophagus medially; longus colli elevated laterally to expose the disc
2. Level confirmation: C-arm fluoroscopy with spinal needle
3. Disc removal: Complete anterior discectomy; ALL sectioned carefully (unlike ACDF, some motion must be preserved)
4. End-plate preparation: Distraction maintained with Caspar pins; cartilaginous endplates removed down to cortical bone using curettes and rasps - cortical bone must be preserved (unlike fusion, no bone grafting)
5. Decompression: Posterior osteophytes removed with high-speed burr/Kerrison rongeurs; bilateral foraminal decompression performed
6. Sizing and trialing: Template used; prosthesis must span as much endplate area as possible to distribute load evenly
7. Implantation: Device inserted and impacted/screwed into place; position confirmed with fluoroscopy in both planes
8. Ideal position (Fig. 45.18):
   • Height similar to adjacent normal discs
   • Maximum endplate coverage
   • Centrally positioned in both sagittal and coronal planes

Intraoperative pitfalls

• Undersized implant → stress concentration per unit area → subsidence; inadequate endplate coverage → heterotopic ossification and osteophytes → loss of motion
• Malpositioning (coronal plane) → unilateral foraminal narrowing → radiculopathy
• Overstuffing (oversized implant) → facet joint distraction → axial neck pain, referred scapular pain, reduced segmental motion

8. Advantages Over ACDF

9. Results and Evidence

• NDI scores and VAS neck/arm pain equivalent or better with CDA
• Reoperation at the index level lower with CDA
• Secondary surgery at adjacent levels significantly lower with CDA
• Motion preservation better maintained with arthroplasty vs arthrodesis
• NORCAT trial (Norwegian Cervical Arthroplasty Trial): CDA = ACDF at 2 years for single-level disease

10. Complications

• The most common late complication
• Graded 0-4 (McAfee classification):
  • Grade 0: No HO
  • Grade 1: HO outside disc space
  • Grade 2: HO within disc space without bridging
  • Grade 3: HO bridging with preserved motion
  • Grade 4: Complete fusion (ankylosis)
• Grade 3-4 HO eliminates the motion-preserving benefit of CDA
• Risk factors: inadequate endplate coverage, undersized implant, retained posterior osteophytes

11. Post-operative Management

• Soft collar for comfort only (not mandatory)
• Early mobilization and physiotherapy
• No rigid immobilization (unlike ACDF)
• Activity restrictions: avoid contact sports for 6 weeks
• Follow-up radiographs at 6 weeks, 3 months, 6 months, 1 year - assess motion, HO formation, implant position
• NDI and VAS scoring at each visit

12. Special Considerations

• Two-level CDA (C4-5 and C5-6, or C5-6 and C6-7): FDA-approved for Mobi-C; evidence shows superiority over two-level ACDF in reoperation rates
• CDA vs posterior foraminotomy: CDA preferred when anterior pathology predominates; posterior foraminotomy for soft lateral disc herniation is an equally effective, less invasive option
• Facet condition: CT mandatory pre-operatively; significant facet degeneration is an absolute contraindication as CDA treats only the disc joint (one of three joints in the motion segment)
• Bone quality: DEXA scan mandatory; osteoporosis predisposes to endplate subsidence and HO

13. Summary