Artificial Disc Replacement: Candidacy, Criteria, and Who Is Not a Candidate

Who is a candidate for artificial disc replacement?

Artificial disc replacement (ADR) is a surgical procedure considered for select individuals suffering from chronic, debilitating spinal pain caused by degenerative disc disease or disc herniation, particularly when conservative treatments have failed, and specific anatomical and health criteria are met.

Understanding Artificial Disc Replacement (ADR)

Artificial disc replacement (ADR), also known as total disc arthroplasty, is a surgical procedure designed to replace a damaged or degenerated intervertebral disc with a prosthetic implant. Unlike spinal fusion, which aims to permanently join two or more vertebrae, ADR seeks to preserve motion and flexibility in the affected spinal segment. This approach is rooted in biomechanical principles, aiming to restore the natural kinematics of the spine and potentially reduce the risk of adjacent segment disease, a common long-term complication associated with spinal fusion.

Primary Indication: Degenerative Disc Disease (DDD)

The most common reason for considering artificial disc replacement is symptomatic degenerative disc disease (DDD). DDD is a condition where the intervertebral discs, which act as shock absorbers between the vertebrae, break down over time due to age, injury, or genetic predisposition. This degeneration can lead to chronic pain, instability, and nerve compression.

Key characteristics of DDD suitable for ADR:

• Single-level or two-level disease: ADR is typically performed on one or, less commonly, two adjacent spinal levels. Multi-level degeneration usually contraindicates ADR.
• Cervical or Lumbar Spine: ADR is most frequently performed in the cervical (neck) and lumbar (lower back) regions, as these areas experience significant motion and are prone to disc degeneration. Thoracic (mid-back) ADR is far less common.

Core Candidacy Criteria for ADR

The decision to proceed with artificial disc replacement is complex, requiring a thorough evaluation by a spine specialist. Candidates must meet a stringent set of criteria to ensure the highest likelihood of a successful outcome and minimize risks.

Failure of Conservative Treatment

• Exhaustion of non-surgical options: Patients must have undergone a significant period (typically at least 6 months) of non-operative treatments without substantial relief. This includes physical therapy, medication (NSAIDs, muscle relaxants), epidural steroid injections, chiropractic care, and activity modification.

Specific Symptomatology

• Radiculopathy: Pain, numbness, tingling, or weakness radiating into an arm or leg, caused by nerve root compression.
• Myelopathy (cervical spine): Symptoms related to spinal cord compression, such as gait disturbance, loss of fine motor skills, or weakness in the extremities.
• Axial Pain: While ADR can address axial (midline) back or neck pain, it is often more effective for radicular symptoms. The source of axial pain must be clearly attributable to the degenerated disc.

Imaging Findings

• Confirmed disc degeneration: MRI, CT scans, or X-rays must clearly demonstrate disc degeneration at the symptomatic level(s).
• No significant instability: While the affected segment may show some motion, gross instability or spondylolisthesis (forward slippage of one vertebra over another) beyond a certain degree often contraindicates ADR, favoring fusion.
• Absence of significant facet joint arthritis: This is a critical criterion. ADR aims to preserve motion. If the facet joints (small joints at the back of the spine that enable movement) are significantly arthritic, preserving motion may exacerbate their pain, making fusion a more appropriate option.

Anatomical Suitability

• Healthy adjacent discs: The discs above and below the affected level should be relatively healthy to withstand the altered biomechanical stresses post-surgery.
• Adequate bone quality: Sufficient bone density is crucial for the implant to integrate securely. Patients with osteoporosis are generally not candidates.
• No significant spinal deformity: Severe scoliosis, kyphosis, or other spinal deformities typically rule out ADR.

General Health and Lifestyle Factors

• Good overall health: Patients should be in good general health, free from active infections or uncontrolled systemic diseases (e.g., diabetes, autoimmune disorders).
• Non-smoker: Smoking significantly impairs healing and increases the risk of complications. Patients are often required to quit smoking well in advance of surgery.
• Realistic expectations: Patients must understand the potential benefits, risks, and recovery process associated with the surgery.
• Body Mass Index (BMI): While not an absolute contraindication, extremely high BMI can increase surgical risks and may influence candidacy.

Contraindications: Who is NOT a Candidate?

Several conditions and factors would generally disqualify an individual from artificial disc replacement:

• Multi-level spinal degeneration: Typically more than two levels requiring intervention.
• Significant facet joint arthritis or degeneration at the affected level.
• Spinal instability or spondylolisthesis that is severe or progressive.
• Osteoporosis or osteopenia: Compromised bone density.
• Active infection (e.g., discitis, osteomyelitis).
• Spinal tumor or history of spinal malignancy.
• Prior spinal surgery at the same level (e.g., previous fusion, laminectomy that destabilized the segment).
• Inflammatory arthritis (e.g., rheumatoid arthritis, ankylosing spondylitis).
• Morbid obesity.
• Pregnancy.
• Psychological factors: Uncontrolled pain behaviors, severe depression, or unrealistic expectations.

The Multidisciplinary Decision Process

The determination of candidacy for artificial disc replacement is a collaborative effort involving a neurosurgeon or orthopedic spine surgeon, often alongside neurologists, pain management specialists, and physical therapists. This multidisciplinary approach ensures all aspects of the patient's condition, including their pain, neurological status, imaging findings, and overall health, are thoroughly evaluated against the strict criteria for this advanced surgical procedure. Patients considering ADR should engage in open dialogue with their medical team to understand if this option aligns with their specific condition and goals.