Indications for Total Lumbar Disk Replacement

Indications for Total Lumbar
Disk Replacement

Rudolf Bertagnoli

Artificial Disk Prosthesis

Indications

Contraindications

Case Studies

Group I: “Ideal” Indications

Group II: “Good” Indications

Group III: “Expanded” Indications

Conclusion

Chronic back pain and musculoskeletal diseases are among the most common reasons for consultations worldwide. Back pain is a result of alterations in the natural mechanics of the lumbar spine associated with degeneration of the intervertebral disk. Even though disk degeneration is a normal aging process of the lumbar spine¹ younger people are also affected. This results from a change in lifestyle, the tendency to sedentary work, and other unhealthy factors that promote degenerative disk disease (DDD).² This fact leads to an increasing number of people worldwide who suffer from back pain and therefore to a greater necessity for better treatment options on the spinal market.

Primarily many of patients’ back ailments can be treated with conservative therapy. But the number of cases that have failed conservative treatment is growing,³ and consequently the need for surgical intervention rises.

Potential pain sources in the lumbar spine are the disks, the facet joints, and the spine muscles. Conservative therapy is the first step to relieve pain. There are different surgical options for patients who have failed conservative treatment and still suffer from back pain. Due to the fact that fusion and nucleotomies are not optimal solutions for every patient, total disk replacement (TDR) has become more important in recent years. Fusion surgery achieves no restoration of the natural disk function and also eliminates the motion of the affected segment. This may lead to “fusion diseases,” such as facet hypertrophy, spinal stenosis, or adjacent level disk degeneration.² Nucleus replacement technologies (nucleus arthroplasty) are still under investigation and at this time there is no standard definition as to which degree of annulus degeneration and disk height loss will achieve a successful implantation.⁴ Nucleotomies are not indicated for patients with multilevel degenerative disk disease.⁴

The ideal goals of any low back pain surgery should be decompression of neurogenic structures, pain relief, preserving the range of motion, and achieving segmental motion. All of these requirements can be reached in a TDR surgery where the whole damaged disk is replaced by an artificial disk.

Artificial Disk Prosthesis

Artificial disk prostheses replace the disk completely and, opposite to nucleus replacement devices, they are biomechanically independent of the disk tissue.5 An ideal artificial disk should restore the disk height and segmental motion, generate kinetics at the spinal triple joint complex, and absorb shocks.⁶ The goal is to mimic the loading and motion characteristics of the natural intervertebral disk whereby degeneration of the adjacent levels will be not accelerated. Due to the fact that more and more younger people are affected by DDD a TDR prosthesis should work properly for many decades.⁷

In search of better possibilities to treat degenerative disk disease, the development of total disk replacement has increased over the last several years. Various prostheses are under clinical trial or have already entered the market. The lumbar devices with the longest experience are the SB Charité (DePuy Spine, Raynham, MA) and the ProDisc-L (Synthes, Inc., West Chester, PA).

The SB Charité was the first total disk device that entered clinical trials (in 1984). The most unconstrained of all prostheses consists of two cobalt-chromium-molybdenum (CoCrMo) alloy end plates that surround a biconvex polyethylene core. The latest version has a hydroxyapatite coating.

The ProDisc-L, designed in the late 1980s, is a semicon-strained prosthesis consisting of a monoconvex polyethylene core and two CoCrMo end plates coated with a titanium plasmapore surface.

Two other devices that have been in clinical trials over the last few years are the Maverick Artificial Disc (Medtronic Sofamor Danek, Memphis, TN), and more recently the FlexiCore prosthesis (Stryker Spine, Kalamazoo, MI).

According to the design and the function total lumbar disk prostheses can be classified into three groups: unconstrained prostheses (e.g., Charité), semiconstrained devices (e.g., ProDisc-L, Maverick), and constrained prostheses (e.g., FlexiCore). At this point there are basic types to classify the kinematics of the prosthesis:

1. Clinical classification (unconstrained, semiconstrained, constrained) defines the behavior compared with the physiological motion pattern; for example, the unconstrained Charité most closely imitates the natural motion pattern by having a changing center of rotation (COR) during flexion-extension and lateral bending motion. ProDisc-L or Maverick has a fixed COR and forces the segment to run in a predefined motion pattern.

2. Biomechanical classification defines the mechanical stop of the prosthesis. Constrained devices have a mechanical stop within the normal physiological range of motion, semiconstrained devices have the mechanical stop outside the range of normal physiological motion. In contrast, unconstrained devices are without mechanical stop. Depending on these kinematics, the condition of the facets plays a more (unconstrained devices) or less (semi-constrained and constrained devices) important role.