# Cervical Disc Arthroplasty > Cervical disc arthroplasty for NEET-SS Neurosurgery: motion preservation versus ACDF, device selection, contraindications and heterotopic ossification. - Canonical URL: https://prepelephant.com/topics/neet-ss/neurosurgery/cervical-disc-arthroplasty - Exam / course: NEET-SS · Subject: Neurosurgery - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Cervical Disc Arthroplasty", PrepElephant, https://prepelephant.com/topics/neet-ss/neurosurgery/cervical-disc-arthroplasty ## 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.