Hippocrates, the Greek “father of Western Medicine,” once described walking as “man’s best medicine.” We often take our ability to walk for granted; for example, observe how many people will drive their car a short distance to the neighborhood market to pick up some groceries when they could walk instead. They could choose to perform the same chore at a fraction of the cost while simultaneously earning the physical and mental dividends of a walk.
Close your eyes for a moment and try to imagine not being able to walk. Imagine that you are one of millions of people who were affected with a severely debilitated hip joint caused by arthritis. In this unpleasant scenario, simple tasks that you now take for granted—getting out of bed, climbing stairs, walking to the market—would become painful; you might become dependent on a cane, crutches or pain relief medication. In severe cases, most of your independence in the form of your mobility (your ability to walk), would be gone: certainly, this would be a frightening scenario for any of us.
Fortunately, for sufferers of severe hip debilitation, talented and skilled orthopedic surgeons can replace the hip with a prosthesis. Currently, a total of more than 600,000 hip replacements are carried out worldwide each year. Roughly 180,000 are performed in the U.S. In most cases, these surgeries are successful and allow the patient to regain mobility, independence, and quality of life.
Hip Prosthesis Design
Each hip prosthesis is made up of two parts: the acetabular component, a socket or cup which partly replaces the acetabulum and the femoral component, or stem, which replaces the femoral head and part of the femoral neck. The outer aspect of the metal shell is designed so that living bone will adhere to an irregular, porous, mesh or beaded surface. The inner liner acts as the bearing surface which may be made of different materials such as ceramic, metal or plastic.
The biomedical engineers who design the prosthesis use many tools as part of their craft, and one of the tools they use is simulation software. Simulation software is used to test potential hip prosthesis designs, thereby reducing the number of physical prototypes (and hence, the cost and time) that is required in order to get a product to the manufacturing stage and eventually into the operating room, where the prosthetic can be implanted into the patient.
What Gets Simulated and Why?
Think for a moment about the activity of walking: each patient has a different weight, they have different body proportions, and they have a different set of walking habits. Therefore, a wide range of stresses including their directions, their motions, and their number per day must be simulated, as well as longevity assumptions (no one wants to repeat a hip replacement operation). Furthermore, because walking is such a repetitive activity, the effects of friction must be taken into account. Only certain materials are biocompatible with tissues and bones and have reliable chemical stability and safety, so any simulation must allow for accurate material assumptions.
Simulation software is usually expensive, and therefore frequently out-of-reach for many biomedical engineers and startup companies. However, with the new modeling paradigm, which delivers simulation as a service, the cost is dramatically reduced. This enables creative biomedical engineers and cash-strapped startup companies to dream up and cost-effectively test new prosthetic devices. Because cloud-based simulation software reduces the cost and time of creating new prosthetic devices, these devices become available to more suffering patients—and they become available sooner.
With the more affordable software, engineering simulation will hopefully play an increasingly enabling and vital role in the design of prosthesis and hence restore the quality of life for many of us.
Take a look at this stress analysis of a hip prosthesis carried out with SimScale and use it as a template for your own analysis.
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