Houston Methodist. Leading Medicine

Neck FAQ

Question:

I was an engineering student before I went into med school. Now I'm seeing all kinds of applications for the CAD programs I used with my engineering projects. It would be so easy to use this when planning orthopedic surgery for example. This has probably crossed someone else's mind. What kind of studies are being done in this area?

Answer:

You are quite right that Computer Aided Design (referred to as CAD models) is widely used in many areas of study from theatre lighting to engineering bridges. In the field of orthopedics, it has been applied to the study of new surgical procedures like the cervical artificial disc replacement (CADR). The use of cervical artificial disc replacements (CADR) is still in the first decade (10 years) of study. Before conducting studies on humans, computer simulation can be used to assess the biomechanical effects on movement. This concept is referred to as kinematics. In a recent study from Korea, mathematicians joined mechanical engineers and orthopedic surgeons to compare different types of cervical disc implants using a computer-aided design model. They used the CT scans of a young, healthy 21-year-old man to build the spinal model. With a computer-aided model, everything is done in three-dimensions. The effect of force and load with motion is calculated by the computer rather than on a live subject. Two different types of artificial disc implants were compared. Both were made of cobalt-crome with a polypropylene (plastic) core (inner piece). The artificial device mimicked the natural anatomy of a disc with its outer layer (annulus fibrosus) and the inner core (nucleus propulsus). Placement was at the C56 level where the majority of disc implants are currently placed. All material and mechanical properties of the implanted device were programmed into the computer-aided design model. Likewise, force, load, friction, tension, and angles were included in the model. In this way, the model could be put through thousands of spinal movements normally available in the human body. The results could be studied without subjecting a live human to that kind of experimentation. Range-of-motion and load placed on the facet (spinal) joints were measured. The effects of load on spinal flexion-extension were evaluated. Data was also collected on the effects of side-bending load, rotational (twisting) load, force on the spinal (facet) joints, and stress on the spinal ligaments. Tension on the polyethylene core was also measured. As this study showed, the use of computer-aided design (CAD) provided a biomechanical comparison between two different types of artificial disc implants. Long-term human studies will be needed to assess final outcomes but this is a good place to start. It's noninvasive and allows for many different choices of force and load application without causing injury to anyone. CAD is a natural fit for something like this. Sang-Hun Lee, MD, et al. Comparison of Cervical Spine Biomechanics After Fixed- and Mobile-Core Artificial Disc Replacement: A Finite Element Analysis. In Spine. April 20, 2011. Vol. 36. No. 9. Pp. 700-708.

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