Materials Used in Orthopaedic Implants

Physical Characteristics—Strength and Flexibility

Strength

Certainly, an orthopaedic implant should be designed to be as strong as possible. Even in everyday activities, you will place high levels of mechanical stress on your bones and joints. An implant must be able to withstand these stresses day to day without breaking or permanently changing its shape. It should also be designed to withstand the accumulated effect of repeating these stresses.

Flexibility

While strength characteristics of implants are important, they must also be somewhat flexible to avoid shielding of bones from stress (what doctors call “stress shielding”). To understand stress shielding, you have to understand that the human body may tend to reduce or eliminate its own parts when they are not used. Your muscles, for example, can be built up by lifting weights. But when you stop lifting weights, you will eventually begin to lose the extra muscle that you have built up.

Similarly, your bones can remain strong only if they are regularly placed under a reasonable stress. And if they are never stressed, your body will actually begin to lose bone tissue, causing the remaining bone to become weak.

When stress is applied to an orthopaedic implant that is very stiff, the implant absorbs most of the stress. But when stress is applied to a more flexible implant, some of the stress passes through the implant so it can be shared with the surrounding bone. That’s good because your bones need to be stressed. That’s why flexibility is important.