By Guy Matgé
The aim of most new implants for cervical disc replacement is to maintain or to restore function. In the past years there have been a large number of reports on advantages and disadvantages of cervical disc arthroplasty with prostheses. The new Dynamic Cervical Implant aims at combining the advantages of the safe gold standard fusion technique with motion preservation philosophy.
Since 2002, the basic ideas when developing this prosthesis, were preservation of motion and adjacent-level protection. The Omega shape was designed to fit to the lateral anatomical view of the disc and the adjacent endplates. The aim was a one piece anatomical-shaped, self-fixing dynamic spacer made of titanium, easy to implant like a cage. The Dynamic Cervical Implant stabilises the cervical spine while providing controlled motion in flexion-extension, the main motion in subaxial C-Spine.
Shock absorption, a main advantage compared to most existing prostheses prevents adjacent accelerated degeneration. Further design changes from a squared (first generation implants in 2004) to a more rectangular shape (second generation, 2008) and sharper teeth improved primary stability of the implant. The surgical technique refined over years, taking more care with optimal sizing and positioning of Dynamic Cervical Implant (maximal endplate coverage, centre of rotation in the posterior one-third) following adapted decompression of the neuronal structures.
Although anterior cervical fusion works well at one level, long-term studies have shown symptomatic adjacent level disease needing re-operations in 7–15% at 20 years follow-up. This is much more than natural degeneration and related to suppression of the functional unit (rigidity). A motion preservation and control procedure is clearly indicated to delay fusion as long as possible.
Indications for Dynamic Cervical Implant concern all mobile cervical segments from C3 to C7 in disc herniation, degenerative discopathy, central or lateral stenosis. Adjacent level protection above or below an already fused level is an excellent indication in my experience.
Severe degeneration, mostly of immobile segments, remains an indication for fusion. Severe mechanical instability, absence of motion at the index level, osteoporosis, fractures, infections and tumours are clear contra-indications for the implant. Pre-operative dynamic views as well as MRI are systematically performed to clear these pitfalls.
Forty four patients underwent dynamic cervical stabilisation using the second generation Dynamic Cervical Implant device between 2008 and 2010 at a single institution for the treatment of one-level (n=36), two-level (n=6) and three-level (n=2) cervical disc disease. Follow-up ranged from 6–24 months. Clinical outcomes consisted of Neck Disability Index (NDI) and Visual Analog Scale scores at baseline and at latest follow-up. Flexion-extension radiography was evaluated for the presence of device-level motion (>3°), device failures, device subsidence, and heterotopic ossification. There was maintenance of index-level motion in 40/44 of patients. Neck disability index and Visual Analog Scale neck and arm pain scores were significantly reduced at each postoperative timepoint compared with baseline.
Ninety three per cent of patients were very satisfied and 7% somewhat satisfied, while 100% would elect to have the surgery again at one year follow-up. There were two asymptomatic anterior device migrations that required revision due to device undersizing respectively too anterior positioning, three cases of minor (non-bridging) heterotopic ossification, one case of asymptomatic endplate subsidence, and no cases of accelerated adjacent segment disease requiring intervention.
Dynamic Cervical Implant has several more indications than conventional disc prostheses because of controlled rotation: therefore degenerative arthropathy, a cervical pain generator, remains an indication for this implant which is different from most other total disc replacements. A soft disc herniation in young patients could justify the cost of a disc prosthesis at 2.5 times the price of Dynamic Cervical Implant.
Guy Matgé is a neurosurgeon at the National Neurosurgical Department Centre Hospitalier de Luxembourg, Luxembourg. He is the inventor of the Dynamic Cervical Implant.