Load sharing in parallel vs orthogonal screws

• maveric
In summary, the conversation discusses the use of screws in fixing fractures in orthopaedic surgery. The configurations of screws used, such as parallel or orthogonal, are based on the fracture pattern or manufacturer's implant designs. The speaker's question is about the load distribution between two interlocking screws and whether it can be defined based on their configuration. The expert suggests that the primary purpose of fasteners in a joint is to create clamping force, which is responsible for the joint's strength. A basic picture or diagram would be helpful for further discussion.
maveric
Hi I would be grateful for some help or pointers for the following question.
I am an orthopaedic surgeon and often when we fix fractures we use screws to hold the bone in place.

We use different configurations of screws (ie one or two parallel or orthogonal, two screws at right angles to each other) based on either the fracture pattern or sometimes we are driven to use this configuration based on the manufacturers implant designs such as in intramedullary nails, which are rods we pass into the bone to fix fractures. In intramedullary nails we pass the screws through the bone and nail in a manner that if effectively 'locks' the nail hence they are called locking screws. (http://orthopedics.about.com/cs/brokenbones/g/imrod.htm)

My question is if I am using two interlocking screws to fix a fracture how will the load be distributed between the screws if I use two parallel screws vs orthogonal screws ( screws at right angle to each other). What i am really after is can the load distribution on screws be defined based on its configuration in an engineering or mathematical sense.

I hope i make sense and any help would be appreciated.

Many thanks

It's a bit tough to understand the geometry of what you deal with so perhaps we can start with some basics about fasteners...

A fastener for a joint has one major purpose. That is to create clamping force. The fasteners are usually NOT the members that carry the load in a joint. The frictional forces created by the clamping is responsible for the strength of the joint. Granted there are always exceptions and this is definitely not an absolute. However, the clamping force created in the joint is paramount to the joint's strength and the required sizing of the fasteners.

If there is any way you can provide a basic picture or diagram to discuss, that would be a huge help.

1. What is load sharing in parallel vs orthogonal screws?

Load sharing in parallel vs orthogonal screws refers to the distribution of weight or force between two or more screws that are used to secure an object or structure. In parallel screws, the weight or force is distributed evenly among all screws, while in orthogonal screws, the weight or force is distributed more towards the screw closest to the load.

2. How does load sharing differ in parallel vs orthogonal screws?

In parallel screws, the weight or force is distributed evenly among all screws, which means that each screw is carrying an equal amount of the load. In orthogonal screws, the weight or force is distributed more towards the screw closest to the load, which means that this screw will bear more of the load compared to the other screws.

3. What are the advantages of using parallel screws for load sharing?

The advantage of using parallel screws for load sharing is that it distributes the weight or force evenly among all screws, which reduces the stress on each individual screw. This results in a more stable and balanced load distribution, which can increase the overall strength and durability of the structure.

4. When should orthogonal screws be used for load sharing?

Orthogonal screws should be used for load sharing when the load is not evenly distributed or when there is a need for a specific screw to bear more of the load. For example, in a structure where there is a heavy load on one side, orthogonal screws can be used to distribute the weight more towards that side for better support.

5. Are there any limitations to using parallel or orthogonal screws for load sharing?

One limitation of using parallel screws for load sharing is that if one screw fails, the load will not be evenly distributed among the remaining screws, which could result in an unbalanced load distribution and potentially lead to further failures. As for orthogonal screws, they may not be suitable for all types of structures and may require more precise calculations for proper load distribution.

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