Cervical Disc Arthroplasty
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Direct answer
Motion preservation distinguishes cervical disc arthroplasty from anterior cervical discectomy and fusion: through the same Smith-Robinson anterior exposure, the degenerated disc is removed, the neural elements decompressed, and a mobile prosthesis — Mobi-C, Prestige LP, ProDisc-C or Bryan among them — seated in the space, retaining segmental flexion-extension and rotation. The indication is one- or two-level symptomatic cervical radiculopathy or myelopathy from soft disc herniation or spondylosis in a spine that still moves normally; Mobi-C holds the distinction of regulatory approval for two contiguous levels. Randomised comparisons against ACDF demonstrate non-inferiority for neurological outcome with lower rates of secondary surgery at adjacent levels, which is the rationale. The contraindication list is the exam: established facet arthropathy, osteoporosis, instability (over 3.5 mm translation or more than 11 degrees of angulation on flexion-extension films), marked kyphosis, infection and ankylosing disorders — motion preservation in a segment that should not move simply relocates the failure.
What you must remember
- Indication box: one or two contiguous levels, radiculopathy or myelopathy from disc disease, preserved motion, absent instability and healthy facets; the operation is a decompression that happens to preserve motion, not a substitute for fusion in an unstable spine.
- Instability numbers (White and Panjabi): translation over 3.5 mm or angulation beyond 11 degrees on dynamic films contraindicates arthroplasty and points to fusion.
- Device literacy: Mobi-C (mobile core; approved for two levels), Prestige LP, ProDisc-C, Bryan — know one two-level-approved name for the exam.
- The failure mode to name: heterotopic ossification around the prosthesis, graded I-IV, with grades III-IV effectively ankylosing the segment and negating the purpose; oversized or undersized implants and off-centre placement raise the risk.
- Evidence position: non-inferior to ACDF for neurological recovery, with fewer adjacent-level reoperations in the major device trials — but adjacent segment degeneration is partly constitutional, so arthroplasty reduces rather than abolishes it.
- Indian economics: the prosthesis is an out-of-pocket expense several times the cost of a cage or allograft ACDF, so patient selection in Indian practice is dominated by affordability as much as anatomy.
Selecting the arthroplasty patient
A 38-year-old businessman has eight months of left C6 radiculopathy — biceps and brachioradialis weakness, diminished biceps reflex, numb thumb and index finger — failing conservative care. MRI shows a left paracentral soft disc extrusion at C5-6. The checklist runs: dynamic films show no listhesis or abnormal angulation; the facet joints on axial imaging are pristine; bone density is normal; the segment is lordotic within a lordotic spine; the patient is 38, not 68. Every box ticks, so a C5-6 arthroplasty is planned, preserving that segment's contribution to flexion-extension and rotation, and his neighbouring levels gain a statistical, not absolute, protection.
Now vary the case: a 62-year-old with kyphotic spondylotic myelopathy at two levels, facetal hypertrophy and a spondylolisthesis of 4 mm. Arthroplasty here violates three contraindications at once; ACDF with a cage and plate is the honest answer. The art of the topic is that the operation is easy — the selection is the examination. And the third scenario, the 45-year-old with a soft single-level disc but severe osteoporosis on screening: motion preservation in osteopenic bone invites subsidence and migration, so fusion again.
Where candidates slip
Two slips recur. The first is overselling the concept — stating that arthroplasty prevents adjacent segment disease, when the trials support reduced adjacent-level reoperation, and degeneration at neighbouring segments continues at a slower, partly genetically driven rate. The second is forgetting that the decompression is identical to ACDF: candidates describe the prosthesis eloquently and the neural decompression not at all, yet a beautifully seated prosthesis over an inadequate foraminotomy fails for the same reason an ACDF fails — residual compression. The viva favourite is the heterotopic ossification question: know that higher grades convert the motion segment into a fusion, and that meticulous endplate preparation, correct sizing and avoiding excessive drilling are the practical countermeasures.
Frequently asked questions
What is the principal rationale for cervical disc arthroplasty over ACDF?
Preservation of segmental motion with reduced rates of adjacent-level secondary surgery demonstrated in the major randomised device trials.
Which radiological parameters define cervical instability that contraindicates arthroplasty?
Translation exceeding 3.5 mm or angulation over 11 degrees on flexion-extension radiographs, per the White and Panjabi criteria.
What is heterotopic ossification in this context?
Bone formation around the prosthesis graded I-IV; grades III and IV bridge or ankylose the segment, defeating motion preservation.
Which device is approved for two contiguous levels?
Mobi-C, among the commonly cited devices, holds two-level approval in the pivotal trials.
Why is osteoporosis a contraindication?
Poor endplate bone stock risks prosthesis subsidence and migration, so fusion with appropriate grafting is preferred.