Biomechanical Properties of a Lag Screw

A Lag Screw is a type of bolt used to fasten objects together. They are available in a variety of lengths, widths, and packaging options. They are also available in a number of different materials including steel zinc, stainless, and more. There are even options that do not require predrilling to save time and money on the job site. These heavy-duty fasteners can last for years with proper care and use.

Compared to the conventional blade and hex-head screws, lag screws provide a more uniform bone purchase, due to the fact that they have a helical tip that can penetrate through multiple threads in the same area. However, the helical tip of the lag screw may increase the risk of lateral entanglements and the ability to pierce through bone tissue. This can result in a less reliable fixation of the fractured bone.

The purpose of this study was to compare the biomechanical properties of conventional-blade and hex-head lag screws with a novel blade screw in a severe osteoporotic bone model. To simulate the femoral trochanteric bone, polyurethane foam blocks were used. These are an excellent bone substitute material, as they have a very high consistency with only +- 10% density variation. Three torsional and one push-in test were performed to analyze the force and energy needed for each component to achieve 30 deg of rotation and to exert 4-mm displacement.

Both the hex-head and conventional-blade screws were able to reach a maximum torque of 45 N, while the novel blade screw reached a maximum of 70 N. The hex-head and conventional-blade nails were also able to generate a push-in force of 20 N, while the novel blade screw generated a push-in force of 27 N.

However, a major limitation of this study is the use of a bone model instead of real bone. This could lead to a higher variance in the experimental results, which would make it difficult to compare the two types of screws. In addition, the simulated bone may not be as dense as actual human bone.

Lag screw provides rigid fixation for the management of proximal femoral trochanteric fractures. The ability of this method to achieve good angulation and proper reduction allows for an easy application in the symphysis region, while it is more challenging to access the body and condyles because of anatomic limitations. Additionally, the reverse cutting edge on the screw thread may cause problems with removal when attempted in a regular counterclockwise direction. This can result in a break of the screw shaft. This is an undesirable outcome in a fractured bone. Hence, the need for a proper understanding of the mechanics of this device is important. In order to minimize the risk of complications associated with this type of fixation, further studies are warranted. This may include a comparison of the clinical outcomes of these two types of screws with real-bone specimens. This would help to identify the best treatment for femoral trochanteric fractures. 5/16 to mm

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