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Bryan Cervical Disc Features

The Bryan Arthroplasty Procedure

Preoperative Planning

Operative Setup

Site Preparation

Neural Element Decompression

Device Placement

Clinical Experience

Methods

Outcome Assessment

Results

Summary

The treatment of degenerative cervical disk disorders is one of the most satisfying aspects of a neurosurgeon’s or an orthopedic spine surgeon’s practice. In general, those patients with pathology requiring surgical treatment present with classic findings, complaints, and imaging studies that make the diagnosis of myelopathy and radiculopathy due to disk disease straightforward. The surgical options commonly employed have been extensively studied and their efficacy and safety are well documented. Most importantly, patient outcomes are uniformly satisfying with acceptable morbidity and a mortality rate well below 1%.^1,2 In light of the endorsement of the current surgical treatment of degenerative cervical disk disorders, one could reasonably wonder why an entirely new approach such as cervical disk arthroplasty need be considered.

The impetus to pursue arthroplasty in the cervical spine is not due to outright failure of current surgical options. Rather, it arises from a desire to avoid the shortcomings and inherent morbidities that accompany those approaches.

In the treatment of radiculopathy and myelopathy, ventral removal of compressive disk space lesions is easily achieved with an anterior microdiskectomy. However, subsequent fusion eliminates the motion segment, changing spinal biomechanics in the process. Adjacent segment hypermobility and progressive adjacent segment degeneration have been documented in several reports. Hilibrand et al looked at adjacent segment disease following cervical arthrodesis.^3,4 They noted symptomatic disease defined as new onset radiculopathy or myelopathy appropriate for surgical treatment occurring annually in nearly 3% of their patients.³ Radiographic evidence of adjacent segment degeneration can be much higher. Goffin et al found more than 90% of patients treated with fusion had evidence of adjacent segment degenerative disk disease 5 years after surgery.⁵ Whether or not adjacent segment degenerative disk disease is accelerated by fusion or simply an expression of multilevel degenerative disease has not been conclusively answered in the medical literature. Perhaps tilting the scales in favor of fusion as a significant contributing factor is further consideration of Goffin et al’s paper.⁵ They compared rates of subsequent adjacent segment disease in patients fused for degenerative disk disease to those undergoing fusion for trauma and found no significant difference. Thus fusion appears to be an independent variable in regard to the breakdown of the adjacent segment because the trauma patients were not undergoing an operation for a degenerative condition.

Sagittal plane balance is frequently altered with anterior cervical procedures. Subsidence of the interbody fusion graft and kyphosis of the fused segment are known iatrogenic deformities associated with the fusion procedure.^6,7 This loss of lordosis may hasten adjacent segment degeneration because changes to both local and distant intervertebral alignment will alter biomechanics of the spine.

Even when fusion does not accompany anterior cervical diskectomy, loss or impairment of mobility of the treated segment is predictable. In one study, ~90% of patients treated with anterior microdiskectomy without arthrodesis went on to spontaneous fusion, with most experiencing kyphotic change.⁸ Anterolateral foraminotomy has been advocated by a few authors as a method of preserving the disk while providing decompression.^9,10 The procedure removes the ipsilateral uncovertebral joint or portions of it to expose and remove the offending pathology. Excellent results have been reported by one surgeon retrospectively reviewing his own results.⁹ However, the procedure has not enjoyed uniform success. Another report showed that reoperation was required in 30% of the patients treated with that procedure. In addition, the same authors found only 52% of their patients experienced good or excellent outcomes.¹¹

A posterior approach such as laminoforaminotomy may be considered as an option for neural element decompression that does not compromise the motion segment. Although this approach can provide satisfying results for foraminal disk herniations, many surgeons are uncomfortable applying this technique to large or medially positioned lesions, especially if osteophytic change is recognized.

Other morbidity associated with anterior cervical fusion depends on the choices the surgeon makes in regard to technique. Iliac crest graft harvest is associated with chronic hip pain in nearly 30% of patients.12 Plate fixation, currently in vogue, has been shown to contribute to dysphagia, especially when thick or rough-surfaced plates are used.¹³ Finally, pseudarthrosis is a well-known complication of anterior cervical fusion. Depending on graft material, number of levels fused, and smoking history, a pseudarthrosis rate as high as 50% has been reported.¹⁴ The treatment of pseudarthrosis often necessitates a second operation. Another drawback of fusion is the months of activity restriction that most surgeons impose postoperatively on their patients. This has little to do with the recovery from radiculopathy or myelopathy. Rather, this convalescent period is imposed to achieve a solid fusion.

Avoiding fusion may be motivation enough to entertain a surgical alternative without even considering the issue of motion preservation. Absent degenerative deformity or instability, fusion is performed primarily to mitigate the iatrogenic damage created during decompression for treatment of radiculopathy and myelopathy.

Bryan Cervical Disc Features

Cervical disk arthroplasty devices are classified according to their makeup. Composed of polymer (polyurethane core) and metal (titanium end plates), the Bryan Cervical Disc prosthesis (Medtronic Sofamor Danek, Memphis, TN) is categorized as a metal-on-poly device (Fig. 7–1). Currently, all other metal-on-poly cervical arthroplasty devices have ultra high molecular weight polyethylene (UHMWPE) cores. UHMWPE has a higher modulus of elasticity than polyurethane, making it less compressible.¹⁵ The compressibility of the Bryan core allows it to accommodate sudden axial loads, similar to a shock absorber on an automobile. The dome-shaped, polished titanium end plates are merged with a polyurethane sheath. The sheath prevents fibrous tissue ingrowth and contains particulate debris generated by the moving surfaces. Located inside this shell is the donut-shaped polyurethane nucleus. At the top and bottom of the device are filling ports that allow sterile saline instillation prior to insertion. The saline functions as a lubricant. The device is axially symmetric and also symmetric in a caudad to cephalad direction.

Because the joint lacks synovium, concerns for a focal reaction to wear debris are not as acute. Although particle toxicity or an immune response to debris is a potential concern, the materials in the Bryan device have a long history of orthopedic and cardiac surgery usage without undue concern about toxicity.16 Debris created from the articulation between the nucleus and the metallic end plates is theoretically contained by the sheath, preventing a biological reaction.

Detailed wear analysis within a motion simulator showed that after 10 million cycles the Bryan device lost 0.75% of its mass. Animal studies found debris in the tissues in one of two chimpanzees and four of nine goats. All goats were implanted with the spine in a flexed orientation, creating a worst-case environment for sheath abrasion against posterior bone unique to the goat model. Particle generation and release were achieved, allowing the development team to evaluate particle morphology and biological response. Particles averaging 3.9 m were noted in the loose connective tissue of the epidural space without an inflammatory response. This is in contrast to control group animals with cervical plates that had more debris and inflammatory responses identified.16

Related posts:

Prosthetic Disk Nucleus Partial Disk Replacement: Pathobiological and Biomechanical Rationale for Design and Function Complications of Lumbar Disk Arthroplasty Spinal Kinetics Cervical Disc Biomechanical Testing Protocol for Evaluating Disk Arthroplasty DIAM (Device for Intervertebral Assisted Motion) Spinal Stabilization System Nonfusion Stabilization of the Degenerated Lumbar Spine with Cosmic

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