Lag Screw – A New Washer Design That Reduces Cut-Out Rates in Trabecular Bone

Lag Screw are heavy, threaded fasteners used to hold two pieces of wood together. They have coarse threads designed to grip into wooden textures and feature a hex or square head that requires a wrench or ratchet to drive. These screws are often used in construction to connect wood beams together.

They are available in different lengths depending on the project, but all lag screws have a common feature: an external hex head. Hex lag screws are typically manufactured from a corrosion resistant material such as silicon bronze. They can also be manufactured from stainless steel for corrosive and marine environments.

The hex lag screw can be modified with an RC blade that widens the surface and increases its volume, effectively blocking migration through an increase in friction force. A biomechanical study showed that this modification significantly decreased rotation instability of the proximal fragment and varus collapse of the femoral head in intertrochanteric fractures.

Compared to plates, the lag screw technique provides a more rigid internal fixation of the craniofacial skeleton and is appropriate for a variety of traumatic and reconstructive situations. However, the lag screw placement may be associated with a cut-out rate that can affect bony reunion in some patients.

The purpose of this article is to discuss a new washer design that reduces the tendency for lag screw cutting-out in trabecular bone. The traditional washers, which are mandatory in most lag screw systems, transfer the tensile load from the screw head to the thin cortical plate and require countersinking. This excessively loads the small support area of the lag screw head and weakens its contact with the bone, which increases the risk of cut-out. Lag Screw

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