Introduction
One of the main focuses of the recent advances in Spine surgery has been on motion preservation of a degenerative functional spinal unit.
Anterior discectomy and fusion is still the gold standard procedure for symptomatic cervical disc disease. However, long-term results following fusion showed evidence of adjacent segment disease, especially in young and active population1. This has led to the development of cervical disc replacement with the aim of reducing adjacent spondylitic change.
Cummins attempted to address the shortcoming of cervical arthrodesis 15 years ago2. His pioneering efforts in the development of a metal-on-metal cervical artificial disc laid the foundation on which the Prestige (Medtronic Sofamor Danek, Inc., Memphis, TN) was designed.
Indications and goals of total cervical disc replacement
The indications for cervical total disc replacement are principally the same as for ACDF (anterior cervical decompression and fusion) with a few exceptions. A symptomatic disc, which lead to arm and/or neck pain and/or radiculopathy with sensory-motor deficits. These symptoms may be caused by a herniated disc and/or osteophytes compressing adjacent exiting nerves roots or the spinal cord. The goals are to restore the intervertebral disc height and neuroforaminal height to prevent recurrence of neurologic compression.
There is general consensus, that the ability of an artificial disc to correct deformities and to restore physiological lordosis is limited.
A total disc replacement is contraindicated in all types of anterolisthesis and in patients who have had a laminectomy.
The use of arthroplasty in the myelopathic patient, as opposed to fusion surgery, is a controversial area. While a reasonable option for patients with normal sagittal balance, minimal degenerative disease, and one- or two-level disc disease causing root compression, there are many situations where fusion is a better choice than arthroplasty in most situations.
Some of the Currently Available Cervical Disc Prostheses
Prestige (Medtronic Sofamor Danek, Memphis, USA)
The second generation of the Cummins/Bristol cervical disc was Prestige I cervical prosthesis (also named Frenchay artificial joint), developed in 1998. It is a two-piece prosthesis constructed of stainless steel and employs a ball-in-groove articulation (Medtronic Sofamor Danek;). This semi-constrained arrangement allows a greater degree of translation to occur with rotation. It is a modified version of the original Cummins prosthesis which was based on a ball-and-socket design.
The Prestige II was designed in 1999 and main difference to its predecessor being a more anatomic end-plate design; porous coated to improve bony ingrowth3. In a prospective, randomised clinical trial, Porchet et al4 compared the Prestige II Cervical Disc with ACDF for the treatment of single-level disease and their radiographic results showed that Prestige II disc maintains motion at the treated level without adjacent-segment compromise.
The Prestige ST became available in 2002 and the major change from Prestige II was a 2-mm reduction in the height of each anterior flange. Mummaneni PV et al5 in a randomised controlled trial compared ACDF in patients treated for symptomatic single-level cervical degenerative disc disease with PRESTIGE ST Cervical Disc System. The PRESTIGE ST Cervical Disc System maintained physiological segmental motion at 24 months after implantation and was associated with improved neurological success, improved clinical outcomes, and a reduced rate of secondary surgeries compared with ACDF.
The Prestige LP is manufactured from a unique titanium ceramic composite material that is highly durable and image-friendly on computed tomographic and magnetic resonance imaging scans. The ball-and-trough articulation is identical to that of the Prestige ST. Initial fixation is achieved via four rails, two on each component, which engage the vertebral bodies. The plasma-spray titanium coating encourages subsequent bony integration.
The Food and Drug Administration (FDA) cleared the Prestige ST Cervical Disc System in July 2007.
ProDisc-C (Synthes Spine, Paoli, PA, USA)
The ProDisc-C cervical disc replacement (Synthes) is constructed of two cobalt-chromium-molybdenum endplates with a metal-on-polyethylene bearing surface and a fixed polyethylene core. The surfaces of the prosthesis towards the bones bear a plasma-spray titanium layer for secondary fixation by bone ingrowth. A central keel that inserts in a slot with in the cranial and caudal vertebral bodies.
Bryan Disc (Medtronic Sofamor Danek, Memphis, USA)
The Bryan cervical disc consists of a polycarbonate, polyurethane core situated between two convex porous coated titanium shells and encapsulated around the periphery by a polymer sheath. This design allows for a range of motion in flexion/extension, lateral bending, rotation and translation as well as coupled motions similar to the normal cervical spine functional unit.
In 2002 Goffin et al. reported one year follow-up on the results of 60 patients treated with the Bryan® intervertebral cervical disk prosthesis. Ninety per cent of patients reported functional success with no segmental autofusions, and only one device extrusion required a re-operation. Subsequently, there have been numerous reports of successful use of the Bryan cervical disk.
Sasso et al in a recent paper7 compared motion parameters for single-level anterior cervical discectomy /fusion and Bryan disc replacement at the index level and adjacent segments. This study reveals that there is no difference in flexion/extension Range of motion at the level above and below either a fusion or Bryan arthroplasty. There is, however, an increase in anterior/posterior translation at the cephalad adjacent level in patients with arthrodesis while the Bryan arthroplasty retains normal translation for the same amount of flexion/extension at the adjacent level and hence concluded that latter may delay adjacent level degeneration by preserving preoperative kinematics at adjacent levels.
CerviCore (Stryker Spine, Allendale, NJ)
The CerviCore disc replacement device (SpineCore) is metal on metal design with a saddle-shaped bearing surface to provide a centre of rotation below the bottom base plate for flexion and extension, and simultaneously maintaining a centre of rotation in the bone above for lateral bending.
The Porous Coated Motion (PCM) prosthesis (Cervitech, Inc., Rockaway, NJ)
The PCM disc is named for its “porous coated motion” design and includes a uniarticular design with one center of rotation maintained below the intervertebral space. It is made of standard metallic cobalt chrome alloy which hold in place a central ultra high molecular weight polyethylene spacer. Primary stability is achieved by a press-fit implantation. This device relies on a gliding motion limited by the facet joints rather than angular rotation found in ball-and-socket devices. The criticism of this device relates to this movement, which has been perceived to stress the facet joints more than other designs.
The National Institute for Clinical Excellence guidance (2005) concluded: “Current evidence on the safety and efficacy of prosthetic intervertebral disc replacement appears adequate to support the use of this procedure. However, they commented on the fact that there are few data available concerning the use of two level (Bi-level) prostheses. and little long term data available particularly in relation to potential reduction in adjacent level degeneration as compared to fusion.
Complications
Few early complications have been reported from cervical arthroplasty. Nondevice related complications include those related to the decompression such as postoperative haematoma, dysphagia, dysphonia, spinal fluid leak or persistent symptoms from inadequate decompression. Some series report problems with misplacement or hardware failure and instances of paravertebral ossification.
As with any artificial joint replacement, wear characteristics are of significant concern. Biologically active debris shed from polyethylene, metal, and bone cement components of knee and hip joint replacements has been shown to lead to an immune inflammatory response resulting in bone resorption and implant failure. Link et al. in 2004 reported that the axial load in the cervical spine is only one ninth of the load seen in the lumbar spine and significantly lower than the axial loads seen across the knee or hip joint2. Due to the lower loads seen, this may lead to the generation of less particulate debris with cervical arthroplasty.
Summary
The emergence of cervical arthroplasty has changed the face of cervical spinal surgery. There is great optimism that cervical arthroplasty will improve the already good to excellent results achieved with anterior cervical decompression and fusion for symptomatic cervical disc disease.
Further longitudinal follow up studies are needed to assess the long-term clinical results of cervical disc replacement surgery .Its potential advantages in terms of long-term symptom relief, disease progression at the level of surgery and adjacent levels, and requirement of revision surgery is yet to be determined.
So far, Arthroplasty has predominantly been used for radiculopathy and myelopathy, secondary to acute disc herniations or degenerative spondylotic change. As experience broadens, new and expanded indications may be identified like, disc replacement for neck pain, deformity correction or revision of earlier fusion.
References
- A.S. Hilibrand, G.D. Carlson, M.A. Palumbo, P.K. Jones and H.H. Bohlman, Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis, J Bone Joint Surg (Am) 81 (1999), pp. 519-528
- B.H. Cummins, J.T. Robertson and S.S. Gill, Surgical experience with an implanted artificial cervical joint, J Neurosurg 88 (1998), pp. 943-948
- Traynelis VC. The Prestige cervical disc replacement. Spine J 2004;4:310S-4S
- Porchet F, Metcalf NH. Clinical outcomes with the Prestige II cervical disc: preliminary results from a prospective randomized clinical trial. Neurosurg Focus (United States) 2004; 17:6.
- Mummaneni PV, Burkus JK, Haid RW, Traynelis VC, Zdeblick TA. Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine. 2007 Mar;6(3):198-209.
- Sasso RC, Best NM. Cervical kinematics after fusion and bryan disc arthroplasty. J Spinal Disord Tech. 2008 Feb;21(1):19-22
