Forces on a Cannulated Screw Screwing into a Bone

What are the different external forces experienced by a cannulated screw when screwed into a bone?

1. Driving force

2. Gravity

3. Normal force from the bone

4. Friction

5. Potentially forces due to carried weight or muscle contractions

Answer:

These forces, such as the driving force, gravity, normal force from the bone, friction, and potentially forces due to carried weight or muscle contractions, can be represented on a free-body diagram.

When a cannulated screw is screwed into a bone, it is subjected to various external forces that influence its behavior and stability. Let's break down each force:

1. Driving Force:

The driving force is the force applied to rotate the screw into the bone. It is crucial for proper insertion and fixation.

2. Gravity:

The weight of the screw itself exerts a downward gravitational force. This force must be considered when evaluating the overall load on the screw.

3. Normal Force from the Bone:

As the screw penetrates the bone, the bone exerts an upward normal force on the screw. This force opposes the insertion of the screw and affects its stability.

4. Friction:

Frictional forces come into play between the threads of the screw and the inner surface of the drilled hole in the bone. Proper lubrication and thread design are important to minimize friction.

5. Other Potential Forces:

Depending on the specific case, there may be additional forces acting on the screw. These could include forces due to muscle contractions, the weight the bone carries, or other external factors.

It's important to consider all these forces when analyzing the behavior of a cannulated screw in a bone to ensure proper function and longevity of the device.