Artificial Disc Replacement

What is degenerative disc disease (DDD)?

Degenerative disc disease is not a single diagnosis—it is a spectrum of age- and load-related changes affecting the disc and surrounding structures, which in some patients becomes a source of pain and neurological symptoms.

The intervertebral disc functions as a shock absorber between the vertebrae. Its center (nucleus pulposus) is rich in water and proteoglycans, while the outer ring (annulus fibrosus) is composed of strong collagen fibers that provide structural containment.

With age, microtrauma, genetic predisposition, and other factors, the disc may:

• dehydrate,
• lose height,
• develop annular fissures/tears,
• be accompanied by osteophytes, endplate changes (Modic changes), facet degeneration, and thickening of the ligamentum flavum.

Collectively, these changes are referred to as degenerative disc disease and may contribute to axial pain, nerve compression, or spinal canal stenosis.

How does it develop—what happens inside the disc?

Degeneration is, to a degree, a normal component of aging. In some individuals, however, the process is accelerated and becomes clinically meaningful.

At a molecular and biomechanical level:

• The nucleus loses water and proteoglycans → reduced disc elasticity and height.
• The annular fibers weaken and develop fissures, increasing susceptibility to disc bulge or herniation.
• Altered load transfer promotes facet joint overload/hypertrophy and thickening of the ligamentum flavum, often contributing to stenosis.
• The body may respond with osteophyte formation along the endplates—small bony projections that can narrow neural passageways.

On MRI, a degenerated disc typically demonstrates low T2 signal, reduced height, and may show associated Modic changes in adjacent endplates.

What symptoms can it cause?

The same imaging findings may be entirely asymptomatic in one patient and highly painful in another—this is why clinical correlation is essential.

Potential clinical manifestations depend on the location and severity of degeneration:

• Axial pain:
  • chronic neck or low-back pain,
  • worsening with prolonged sitting/standing, bending, or loading.
• Radiculopathy:
  • radiating pain into the arm or leg (including sciatica),
  • numbness, tingling, or weakness in a specific muscle group.
• Myelopathy (primarily cervical):
  • gait imbalance, loss of fine hand dexterity,
  • weakness, spasticity, hyperreflexia.
• Neurogenic claudication (lumbar stenosis):
  • leg pain/numbness after walking,
  • relief with forward flexion (e.g., leaning over a shopping cart).

Important: pain severity does not always correlate with MRI “appearance.” Mild imaging changes may be highly symptomatic—and vice versa.

How is it diagnosed and how do we identify the “pain generator”?

The goal is not only to document degeneration, but to determine which level and which structure is responsible for the patient’s symptoms.

Evaluation typically includes:

• Detailed history and neurological examination.
• MRI of the cervical or lumbar spine to assess degeneration, herniation, stenosis, and neural compression.
• Flexion–extension X-rays to evaluate instability and alignment (particularly important when considering arthroplasty).
• In selected cases: provocative discography (discogram) or diagnostic facet blocks to refine localization of the pain source.

Surgical decisions should never rely on imaging alone. They require concordance between symptoms, examination, and imaging findings.

What is spinal fusion and when is it indicated?

Spinal fusion is the traditional surgical treatment for degenerative disc disease that fails comprehensive conservative care—particularly when instability, deformity, or significant mechanical pain is present.

In the cervical spine, the most common procedure is Anterior Cervical Discectomy and Fusion (ACDF): the degenerated disc is removed, neural elements are decompressed, and the disc space is reconstructed (often with a cage/graft and plate) to promote a solid bony fusion.

In the lumbar spine, multiple fusion techniques are used (e.g., PLIF, TLIF, ALIF), following the same principle. Fusion can:

• stabilize a painful motion segment,
• eliminate pathological micromotion that generates pain,
• achieve excellent, durable outcomes in appropriately selected patients.

What are the drawbacks of fusion (adjacent segment degeneration)?

The key trade-off with fusion is that motion is eliminated at the treated level, and biomechanical load may be redistributed to adjacent segments.

Potential consequences include:

• Increased mechanical stress at adjacent levels → potential acceleration of degenerative change.
• Development of new symptomatic degeneration or disc herniation at the level above or below (“adjacent segment disease”).
• Long-term series suggest that within 10 years after ACDF, up to ~25% of patients may develop clinically relevant adjacent segment disease that can require additional treatment.

Not every fusion leads to future surgery. However, adjacent segment disease is an important consideration—especially in younger, more active patients.

What is disc arthroplasty (artificial disc replacement)?

Disc arthroplasty involves placement of a mobile artificial disc after anterior discectomy, instead of performing a fusion.

Key goals of arthroplasty include:

• Removal of the painful/degenerative disc and decompression of nerves and/or spinal cord.
• Restoration of disc height and foraminal dimensions.
• Preservation of physiological—or near-physiological—motion at the treated level.
• Reduction of biomechanical overload on adjacent segments.

Modern implants are typically metallic or metal–polymer constructs (e.g., metal-on-polyethylene), with surfaces designed to promote bony integration at the endplates. There are approved systems for both cervical and lumbar use in carefully selected indications.

Who is (and is not) a candidate for artificial disc replacement in the neck & low back?

Disc arthroplasty is not appropriate for every patient. It requires rigorous selection of the patient, the level, and the underlying pathology.

Cervical disc arthroplasty

Typical indications:

• Single-level degenerative disc disease causing radiculopathy and/or mild-to-moderate myelopathy.
• Failure of an adequate trial of conservative management (typically 4–6 weeks) including medication, physiotherapy, and/or injections.
• Preserved motion at the index level and no significant spondylolisthesis.

Contraindications (examples):

• Advanced spondylosis with substantial height loss (e.g., >50%).
• Dynamic instability on flexion–extension radiographs.
• Kyphotic deformity or severe facet arthropathy.
• Prior extensive posterior decompression (e.g., laminectomy) at the same level.
• Osteoporosis, metabolic bone disease, recent infection, or major trauma.

Lumbar disc arthroplasty

Typical indication:

• Refractory discogenic low-back pain at a single level despite 6–12 months of structured, comprehensive conservative treatment.

Contraindications (examples):

• Instability, spondylolisthesis, significant facet arthropathy.
• Severe stenosis or multilevel disease.
• Marked disc collapse, osteoporosis, or metabolic bone disease.
• Complex history of intra-abdominal surgery, inflammatory bowel disease, or pelvic inflammatory disease—requiring individualized planning and, when appropriate, collaboration with a general/vascular surgeon.

How is the procedure performed (cervical & lumbar arthroplasty)?

The approach is similar to fusion, but the objective is motion preservation at the treated level.

Cervical disc arthroplasty

• Performed through an anterior cervical approach on a radiolucent table.
• A discectomy is completed with meticulous decompression of the nerve roots and/or spinal cord.
• The bony endplates are preserved to reduce the risk of implant subsidence.
• The artificial disc is implanted under fluoroscopic guidance.
• Postoperatively, anti-inflammatory medication may be used to reduce the risk of heterotopic ossification.

Lumbar disc arthroplasty

• Performed via an anterior retroperitoneal approach, typically with vascular-surgery collaboration.
• The disc space is exposed and major vessels are mobilized with dedicated retractors.
• An extensive discectomy is performed while preserving the bony endplates.
• Trials are used to size the implant, followed by definitive placement.
• Most patients begin gradual mobilization the next day.

How effective is it—what does the evidence show?

Prospective, randomized data are encouraging—particularly for cervical arthroplasty—while long-term follow-up remains essential.

Overall, current evidence suggests:

• In the cervical spine, disc arthroplasty demonstrates equivalent or superior outcomes compared with ACDF for pain, function, and return to work, with lower reoperation rates at the index and/or adjacent levels in mid-term follow-up.
• In the lumbar spine, total disc replacement can provide comparable or modestly improved outcomes in carefully selected patients compared with fusion, particularly for pain and functional measures.
• Motion preservation has been demonstrated in the mid-term. The most robust long-term data (e.g., 15–20 years across implant generations) continue to evolve.

What are the potential complications and what is recovery like?

Like all spine procedures, disc arthroplasty carries specific risks, while also sharing many general considerations with fusion surgery.

Potential complications of disc arthroplasty

• Implant migration or subsidence, particularly if the endplates are violated or the implant is undersized.
• Rarely, significant implant displacement with risk to adjacent neural, vascular, or visceral structures.
• Heterotopic ossification—bone formation around the implant that can reduce motion and, in advanced cases, effectively “auto-fuse” the segment.
• Persistent or recurrent symptoms, with possible need for revision surgery or conversion to fusion.
• Approach-related risks (e.g., voice/swallowing issues in cervical approaches; vascular/visceral complications in lumbar anterior approaches), similar to ACDF/ALIF.

Recovery and return to activity

• Hospital stay is commonly 1–2 days, depending on the procedure and individual factors.
• Early mobilization is encouraged—gentle walking from the first postoperative day, with avoidance of heavy lifting and abrupt loading for several weeks.
• Return to sedentary work is often possible within a few weeks; heavier manual work typically requires more time and individualized guidance.