Biomedical Engineering Reference
In-Depth Information
8
Joint Replacement Implants
Duncan E. T. Shepherd
8.1
Introduction
Human synovial joints, such as the ankle, fingers, hip, and knee, enable articulation
between two bone ends. The bone ends in a joint are covered with articular cartilage
that enables the low friction movement of the joints. The joints are outstanding
as they can last and be trouble-free for a lifetime. However, the joints of some
people can be affected by disease, such as osteoarthritis or rheumatoid arthritis,
that causes destruction of the articular cartilage joint surface. In the advanced
stages of the disease, this can result in great pain, disability, and a poor quality
of life for the person. Joint replacement implants have been one of the great
successes in healthcare where the diseased synovial joint is replaced with an
artificial joint manufactured from synthetic materials [1]. This chapter deals with
joint replacement implants, detailing the materials used in their manufacture and
the various designs of implants that exist for the ankle, fingers, hip, knee, and
wrist. It is also important to have an understanding of how engineers go about
designing joint replacement implants, and later in the chapter the main stages of
the design process for joint replacement implants are discussed.
8.2
Biomaterials for Joint Replacement Implants
Materials that are used in the manufacture of joint replacement implants include
metals, polymers, ceramics, and elastomers. All these materials must be biocom-
patible for use in the human body meaning that the materials should not cause an
adverse reaction to the body (e.g., nontoxic, noncarcinogenic) and the body should
not cause the material to degrade (e.g., corrosion, reduced strength) [2].
Metals are typically used for the stems of implants since they have the necessary
strength to prevent fracture, a high enough Young'smodulus to prevent appreciable
deflection, and good fatigue strength to be able to survive the cyclic loading nature
of joint replacement implants in the human body. Stainless steel, cobalt chrome
