Cervical Disc Arthroplasty (CDA)

Cervical Disc Prosthesis

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Cervical disc arthroplasty (CDA) is a motion-preserving surgical option for treatment of symptomatic cervical degenerative disc disease causing radiculopathy or myelopathy. The procedure involves removal of the pathological disc and replacement with an artificial prosthesis that maintains segmental motion.

Historical Development

The concept emerged from successful total hip and knee arthroplasty. The first cervical disc replacement was performed in 1966 by Fernström using a stainless steel ball bearing. Modern designs began with the Bryan disc (approved 2009), followed by ProDisc-C, Prestige LP, and Mobi-C.

Epidemiology and Usage

CDA represents approximately 5-10% of anterior cervical procedures in Australia. Usage is increasing but remains limited by strict indications and device cost. Most common level is C5-6 followed by C6-7.

Relevant Cervical Anatomy

Understanding the motion segment is essential for CDA:

Motion Segment Components:

• Intervertebral disc (nucleus and annulus)
• Facet joints (zygapophyseal joints)
• Uncovertebral joints (joints of Luschka)
• Ligaments (ALL, PLL, ligamentum flavum)

Normal Cervical Motion:

• Total cervical ROM: 45-55° flexion, 55-70° extension
• C5-6 and C6-7 contribute most motion (15-20° each)
• Coupled rotation/lateral bending

Biomechanics of CDA

Load Sharing:

• Healthy disc: 80% axial load through disc, 20% through facets
• After CDA: Similar load distribution if properly positioned
• Facet overload occurs with posterior device placement

Center of Rotation (COR):

• Normal COR is within the disc space, slightly posterior
• CDA devices attempt to replicate normal COR
• Anterior COR placement causes excessive facet loading

Adjacent Segment Biomechanics

Fusion Effects:

• Increased stress at adjacent levels
• Hypermobility compensation
• Accelerated degeneration over time

CDA Theoretical Benefits:

• Maintains near-normal motion
• Reduces stress concentration
• May slow ASD progression

By Bearing Surface

By Constraint

Unconstrained:

• Bryan, Prestige
• Full freedom of motion
• Relies on soft tissues for stability

Semi-constrained:

• ProDisc-C, Mobi-C, PCM
• Ball-and-socket with controlled motion
• Some intrinsic stability

By Fixation

Keel Fixation: ProDisc-C - immediate stability, more bone removal Press-fit/Porous: Bryan, Prestige - bone ingrowth, less bone removal Screw Augmented: Some designs allow supplemental fixation

Patient Selection - The Most Critical Step

Physical Examination

Standard cervical spine examination with focus on:

• Neurological deficit (motor, sensory, reflexes)
• Spurling test for radiculopathy
• Myelopathy signs (Hoffmann, hyperreflexia, gait)
• Range of motion assessment
• Axial neck pain evaluation

Contraindications

Absolute:

• Active infection
• Osteoporosis (T-score below -2.5)
• Metabolic bone disease
• Metal allergy (device-specific)
• Prior surgery at operative level
• Significant instability (translation more than 3mm)
• Ankylosing spondylitis
• OPLL

Relative:

• Facet arthropathy
• Moderate kyphosis
• More than 2 levels involved
• Age over 60
• Significant osteophyte formation
• Workers compensation claims

Essential Imaging

Additional Studies

DEXA Scan: Assess bone mineral density - T-score below -2.5 is contraindication

EMG/NCS: Confirm radiculopathy, exclude peripheral neuropathy

Diagnostic Injections:

• Selective nerve root blocks for radiculopathy
• Facet injections if uncertain pain source
• Discography (controversial, rarely used)

Intraoperative Complications

Postoperative Complications

Early:

• Hematoma (rare but serious)
• Infection (less than 1%)
• Neurological worsening (rare)
• Dysphagia (common, usually transient)

Late/Device-Specific:

Heterotopic Ossification (HO)

McAfee Classification:

• Grade 0: No HO
• Grade I: HO present, not affecting motion
• Grade II: HO affecting motion but not completely bridging
• Grade III: Complete bridging (spontaneous fusion)
• Grade IV: Complete fusion with no motion

HO is radiographically common but clinically significant HO is relatively rare. Most patients maintain satisfactory motion despite some HO formation.

Immediate Postoperative Period

Day of Surgery:

• Mobilize out of bed same day
• Clear liquid diet, advance as tolerated
• Monitor for hematoma (airway compromise)
• Neurological checks every 2 hours
• Ice for swelling, voice rest

Day 1-2:

• Discharge home if stable (outpatient or overnight stay typical)
• No collar required in most cases
• Swallowing exercises for dysphagia
• Wound care instructions

Early Recovery (Weeks 1-6)

Activity Guidelines:

• ROM exercises begin immediately (unlike fusion)
• Light activities as tolerated
• Walking encouraged
• Avoid heavy lifting (more than 5 kg) for 2 weeks
• No driving until off narcotics and comfortable looking over shoulder

Wound Care:

• Keep incision clean and dry
• Steri-strips fall off naturally (7-14 days)
• Sutures/staples removed at 10-14 days
• No submerging wound for 2 weeks

Return to Activities

Follow-up Schedule

Standard Protocol:

• 2 weeks: Wound check, early progress
• 6 weeks: Clinical and radiographic assessment
• 3 months: ROM assessment, return to full activity clearance
• 6 months: Routine follow-up
• 12 months: Final outcome assessment
• Annually thereafter: As needed or per protocol

Radiographic Follow-up:

• Flexion-extension views to confirm motion preservation
• Assess device position and HO development
• Compare to baseline

Clinical Outcomes

IDE Trial Results (5-7 year follow-up):

Multiple prospective randomized trials have demonstrated:

• CDA is non-inferior to ACDF for neurological success
• Similar improvements in NDI, VAS arm, VAS neck
• Possibly lower reoperation rates with CDA
• Patient satisfaction equivalent

Range of Motion Preservation

Average ROM at Operated Level:

• Preoperative: 8-12°
• Postoperative: 7-10° (most motion preserved)
• Adjacent levels: No significant hypermobility

Adjacent Segment Disease

Radiographic ASD at 5-10 years:

• ACDF: 35-40%
• CDA: 20-25%

Symptomatic ASD (requiring surgery):

• ACDF: 2.9% per year
• CDA: 1-2% per year (possibly lower)

Long-Term Device Survivorship

At 10 years:

• Overall device survival: greater than 90%
• Revision to fusion: 5-10%
• Spontaneous fusion (HO): 5-15%

Two-Level CDA

Only Mobi-C FDA-approved for 2 levels

Considerations:

• Patient selection even more critical
• Both levels must meet criteria
• Outcomes generally equivalent to single-level
• Cost implications

Failed CDA - Revision Options

Indications for Revision:

• Persistent pain with confirmed source
• Device failure (subsidence, migration)
• Progressive neurological deficit
• Severe HO limiting motion

Revision Options:

• Revision CDA (rare, technically demanding)
• Conversion to ACDF (most common)
• Posterior decompression/fusion

CDA Following Prior Fusion

Generally Contraindicated:

• Adjacent level CDA after ACDF controversial
• Some surgeons perform "hybrid" constructs
• Limited data on outcomes
• Risk of hypermobility at CDA level

Workers Compensation

Considerations:

• Higher failure rates reported
• May be relative contraindication
• Patient selection paramount
• Some surgeons avoid CDA in workers comp

Cost-Effectiveness

• Higher upfront device cost than ACDF
• Potential savings from reduced reoperations
• Cost-effectiveness studies show mixed results
• Value may emerge with longer follow-up

CDA Decision Pathway

Step 1: Confirm Indication

• Cervical radiculopathy or myelopathy
• Failed 6+ weeks conservative treatment
• Imaging correlates with symptoms

Step 2: Assess CDA Candidacy

• Age (ideal under 45, consider up to 60)
• Single or 2-level disease
• No facet arthropathy on CT
• No instability on dynamic radiographs
• No OPLL
• Adequate bone density (T-score above -2.5)

Step 3: Identify Contraindications

• Absolute: OPLL, instability, osteoporosis, infection
• Relative: Age over 60, facet disease, 3+ levels, kyphosis

Step 4: Shared Decision Making

• Present CDA vs ACDF options
• Discuss theoretical benefits and limitations
• Consider patient preferences and expectations

Step 5: Proceed with Appropriate Procedure

• CDA if all criteria met
• ACDF if any contraindication or patient preference

Current Practice in Australia

Cervical disc arthroplasty is performed in Australia with access to FDA-approved devices including Prestige LP, ProDisc-C, and Mobi-C. The procedure is typically performed in private hospitals with experienced spine surgeons.

Patient selection follows international guidelines with emphasis on appropriate indications. Most surgeons reserve CDA for younger patients with single-level disease and no contraindications.

Medicolegal Considerations

Informed consent should address that CDA is an alternative to well-established ACDF, that long-term data beyond 10 years is still emerging, device-specific risks and characteristics, and the possibility of conversion to fusion if CDA fails.

Documentation of patient selection criteria and absence of contraindications is essential for medicolegal protection.

Key Takeaways

1. Patient Selection is Paramount: CDA requires strict adherence to indications and contraindications - facet arthropathy, instability, OPLL, and osteoporosis preclude CDA

2. Equivalent Clinical Outcomes: Multiple IDE trials demonstrate CDA is non-inferior to ACDF for neurological success and patient-reported outcomes at 5-10 years

3. Motion Preservation: CDA maintains 8-10° of motion at the operated level, potentially reducing stress on adjacent segments

4. ASD Reduction: Radiographic ASD is reduced with CDA compared to ACDF, though clinical significance of this finding remains debated

5. Complications Differ: While approach-related complications are identical to ACDF, CDA has unique issues including HO, subsidence, and device-specific failures

6. Know the Contraindications: Exam questions commonly test identification of contraindications - remember DISC (Deformity, Instability, Spondylosis, Calcium loss)

7. Technique Differs: Unlike ACDF, endplate preservation is critical for CDA - violation may require conversion to fusion