Motion-preserving cervical total disc replacement via Smith-Robinson anterior approach | advanced
Surgical Imaging
The trap: Assuming a right-sided approach is always safer or that nerve injury risk is symmetric.
The fix: The recurrent laryngeal nerve loops under the subclavian on the right and under the aortic arch on the left. At C6-7 the right nerve is more vulnerable because its course is more oblique and superficial. Most surgeons therefore select a left-sided Smith-Robinson approach for C6-7 arthroplasty. Document the side chosen and the rationale in the operative note.
Location: The sympathetic chain lies on the longus colli muscle approximately 10-15 mm lateral to the midline; aggressive lateral retraction or electrocautery can cause permanent Horner syndrome.
Risk: Unilateral ptosis, miosis and anhidrosis. Prevention requires staying strictly within the medial half of the longus colli when releasing the prevertebral fascia and avoiding monopolar cautery near the lateral border.
Location: The oesophagus lies immediately medial to the carotid sheath and is retracted with a blunt blade or self-retaining retractor with smooth blades.
Risk: Perforation presents with post-operative neck swelling, crepitus, fever and dysphagia. Prevention includes gentle blunt dissection, frequent relaxation of retractors, and placement of a nasogastric tube in high-risk revisions to allow palpation of the oesophageal wall.
Location: The vertebral artery enters the transverse foramen at C6 and ascends within the uncinate process region; the distance from midline to artery at C5-6 is approximately 15-18 mm.
Risk: Aggressive lateral decompression or uncinate resection can lacerate the artery, causing massive bleeding or posterior circulation stroke. Always confirm the position of the uncovertebral joints on pre-operative CT and limit lateral resection to the medial half of the uncinate.
Why different: Excessive removal of subchondral bone or use of an oversized implant leads to early subsidence and loss of segmental lordosis.
Implications: Ideal preparation removes only cartilage while preserving dense endplate bone. Intra-operative fluoroscopy must confirm that the implant footprint covers at least 80 percent of the endplate and that distraction is limited to 2 mm above resting disc height.
Recognition: Bridging bone anterior or posterior to the implant on lateral radiographs at 6-24 months indicates Grade III-IV heterotopic ossification and loss of the motion-preserving benefit.
Prevention: Meticulous haemostasis, avoidance of bone dust in the field, and consideration of short-course NSAID prophylaxis in high-risk patients (male sex, multilevel disease). Once formed, revision to fusion is the only reliable salvage.
S.M.I.T.HAPPROACH — Smith-Robinson Anterior Cervical Exposure
I.M.P.L.A.N.TIMPLANT — Critical Technical Points for Cervical TDR
C.O.M.P.L.E.XCOMPLICATION — Recognition and Prevention of TDR Failures
Surgical Indications
Absolute Indications
- Single- or two-level cervical radiculopathy or myelopathy from soft-disc herniation with preserved segmental motion
- Failure of at least 6 weeks of non-operative management including physiotherapy, NSAIDs and selective nerve root blocks
- Patient preference for motion preservation after informed discussion of adjacent-segment disease risk
Relative Indications
- Young active patient (less than 60 years) with minimal facet arthrosis and no significant kyphosis or instability
- Two-level disease where fusion would create a long lever arm and increase stress on adjacent segments
- Professional or recreational need for preserved cervical rotation and flexion-extension
Contraindications
Absolute:
- Ankylosis or spontaneous fusion at the index level
- Severe spondylosis with greater than 50 percent disc height loss or large posterior osteophytes
- Osteoporosis (T-score less than -2.5) or metabolic bone disease
- Active infection, tumour or inflammatory arthropathy
- Greater than 2 mm translation on dynamic radiographs (instability)
- Significant cervical kyphosis (greater than 10 degrees segmental)
Relative:
- Previous anterior cervical surgery at the same level
- Severe facet arthropathy or arthropathy requiring posterior decompression
- Multilevel disease (three or more levels) — higher risk of heterotopic ossification and motion loss
- Smoking or systemic steroids that impair bone ingrowth
Evidence Base
Motion Preservation versus Fusion
Cervical disc arthroplasty was developed to reduce the incidence of adjacent-segment degeneration that occurs in 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 Randomised Controlled Trials
Multiple FDA IDE 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 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.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 48-year-old man with single-level C5-6 soft-disc herniation causing radiculopathy has failed 8 weeks of conservative treatment. Dynamic radiographs show 8 degrees of motion at C5-6, no instability, and CT confirms minimal facet arthrosis. He is keen to avoid fusion. Outline your indications assessment and operative plan for cervical disc arthroplasty.”
“You are planning a C6-7 cervical disc arthroplasty. The patient is a 52-year-old woman with C7 radiculopathy. Describe the specific anatomic considerations at C6-7 and how they influence your approach and implant placement.”
“A 45-year-old man undergoes uneventful single-level C5-6 arthroplasty. On the first post-operative day he develops progressive neck swelling, dysphagia and stridor. What is your differential diagnosis and immediate management?”