Cervical Disc Arthroplasty (Total Disc Replacement)

Indication. Symptomatic single- or two-level cervical radiculopathy or myelopathy from a soft-disc herniation (or spondylotic compression in a well-selected patient) that has failed at least six weeks of non-operative care — physiotherapy, NSAIDs and selective nerve-root blocks — where the motion segment is still worth preserving. Patient preference for motion preservation after an informed discussion of the adjacent-segment disease risk is itself a valid indication once the anatomical criteria are met. The ideal candidate is a young, active patient (typically less than 60 years) with a soft-disc herniation, preserved segmental motion (greater than 5 degrees on flexion-extension films), minimal facet arthrosis, no instability (translation less than 2 mm) and no significant segmental kyphosis, who understands that the goal is motion preservation rather than a guaranteed cure. Relative indications include two-level disease in which a fusion would create a long lever arm stressing adjacent segments, and a professional or recreational need to keep cervical rotation and flexion-extension. Contraindications.

Consent specifically for recurrent laryngeal nerve injury (1-3 percent hoarseness, higher on the right at C6-7), dysphagia (5-15 percent transient, less than 1 percent permanent), oesophageal perforation (less than 0.5 percent), vertebral artery injury (less than 0.5 percent), implant migration or subsidence (2-5 percent), heterotopic ossification (10-50 percent), persistent or new neurologic deficit (1-2 percent), and the possibility of conversion to fusion if intra-operative findings preclude arthroplasty. Setup. Supine on a radiolucent table, head in slight extension on a donut or Mayfield headrest, shoulders taped caudally so the lower cervical spine is visible on fluoroscopy, and a scapular roll to maintain lordosis. General endotracheal anaesthesia with MEP and SSEP neuromonitoring for myelopathy cases. Have a high-speed burr, Caspar distractor, radiolucent retractors, implant-specific trials and inserters, and biplanar C-arm fluoroscopy ready throughout.

The goal is a complete discectomy and neural decompression through the Smith-Robinson anterior approach, then seating of a mobile disc prosthesis exactly in the midline so the segment keeps moving. The exposure — the avascular plane between the carotid sheath laterally and the visceral column medially — is the heart of the operation and is laid out as the first steps below (and in depth on the Smith-Robinson approach to the anterior cervical spine page).

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How devices are classified. By constraint — unconstrained (no fixed centre of rotation, e.g. a mobile core), semi-constrained, and constrained (a fixed ball-and-socket centre of rotation) — and by bearing surface: metal-on-polyethylene, metal-on-metal, or ceramic.

What they are trying to reproduce. Physiological segmental kinematics, including a mobile, posteriorly located instantaneous centre of rotation and the coupled flexion-extension and lateral bending of a normal segment — rather than behaving like a single fixed hinge. The goal is to restore the centre of rotation, not merely fill the space.

Why technique decides whether motion is actually preserved. The device must be correctly sized to the endplates (over- or undersizing risks subsidence or poor fit), placed in the midline and parallel to the endplates, with disc-space height and lordosis restored and the endplates preserved, not over-resected. Malposition, undersizing or endplate violation lead to subsidence, migration, accelerated wear and osteolysis, abnormal facet loading and more heterotopic ossification — each of which defeats the whole point of the operation.

Good bone quality is needed both for fixation and to resist subsidence, which is part of why osteoporosis is a contraindication.

Post-operative protocol | Phase | Timing | Mobilisation and activity | Imaging and review | |-------|--------|---------------------------|--------------------| | Immediate | Day 0-2 | Mobilise out of bed on day of surgery or day 1; soft collar for comfort only (most discard by day 3); paracetamol, NSAIDs, short opioid course | AP and lateral radiographs before discharge; monitor for swelling, dysphagia, hoarseness, new deficit | | Early | 2-6 weeks | Light activities and desk work by 2-4 weeks; no heavy lifting or contact sports for 6-12 weeks; gentle cervical range of motion from 2 weeks | Wound check and radiographs at 2 weeks | | Late | 6 weeks on | Full activities including sport by 3 months if asymptomatic | Dynamic radiographs at 6 weeks, 3, 6 and 12 months, then annually | Most patients return to desk work by 2-4 weeks and to full activities including sport by about 3 months. Dynamic radiographs monitor motion preservation and watch for early heterotopic ossification. Special situations

Complications

Why preserve motion. Cervical disc arthroplasty was developed to reduce the adjacent-segment degeneration that occurs in roughly 25-30 percent of patients at 10 years after ACDF. By preserving physiologic motion, the theoretical load transfer to adjacent discs and facets is reduced. Landmark trials. Multiple FDA Investigational Device Exemption trials (Prestige, ProDisc-C, Secure-C, PCM, Mobi-C) demonstrated non-inferiority to ACDF at 2 and 7 years, with superior preservation of range of motion and lower re-operation rates for adjacent-segment disease in some series. Heterotopic ossification. The most common device-specific complication. Incidence ranges from 10-50 percent at 5 years depending on implant design and patient factors. Grade III-IV HO eliminates the motion-preserving benefit and converts the arthroplasty into a de facto fusion. Adjacent-segment disease. Meta-analyses suggest a modest reduction in symptomatic adjacent-segment disease requiring surgery (approximately a 50 percent relative risk reduction at 7-10 years), but the absolute benefit remains small and long-term data beyond 10 years are still maturing.