Biomedical Engineering Reference
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advocate arthroplasty instead of arthrodesis, even though long-term follow-up results haven't been
satisfactorily reported.
In 1966, Fernstrom implanted stainless steel balls into the intervertebral space after discectomy
of cervical and lumber vertebrae (Fernstrom 1966). This is considered to be the first generation of
spinal arthroplasty. The clinical result of Fernstrom's innovation was not quite satisfactory, primarily
because of settlement. The stainless steel balls fell into the endplate and failed to maintain the inter-
vertebral height of patients within months after implantation. Today, great advances have been made
in the biomechanical and kinematic characterization of disc prostheses. Roughly 20 kinds of spinal
arthroplasty devices are currently in use worldwide, with each product displaying its own unique
properties. ProDisc, Bryan, and PCM (Porous Coated Motion) are the most popular of these devices.
The ProDisc prosthesis (Figure 17.2) uses a cobalt chromium (CoCrMo) alloy for its upper and lower
plates and an ultra-high-molecular-weight polyethylene (UHMWPE) core. It is a semiconstrained
prosthesis. The keels on the surface anchor it into the vertebral endplates with a fixed center of rotation.
The Bryan prosthesis (Figure 17.3) is composed of two titanium-alloy shells and a polyurethane
core. It is an unconstrained device that theoretically allows range of motion in all planes. A flexible
membrane with inner lubricating liquid surrounds the artificial core.
FIgure 17.2
ProDisc prosthesis.
FIgure 17.3
Bryan prosthesis.
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