The Liberty Lock System

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The Liberty Lock System

Karl C. Maritato

In 2012, a new form of polyaxial screw placement in locking plates was introduced with liberty lock plates. The benefit of polyaxial plate design is the ability to angle the screws in the screw hole of the plate, where traditional locking plates require 0° of angulation (true perpendicularity to the plate). Without polyaxial design, angulation of the screws in the screw holes results in inadequate screw locking and difficult insertion and removal. In addition, being confined to 0° of angulation in the plate limits use in certain clinical situations, such as near fracture sites, joints, and growth plates. Lastly, because locking plates are frequently used with an IM pin, it can be easier to avoid the pin if one is able to angulate the screw.

The liberty lock polyaxial mode of action is different than other reported poly‐axial systems [1, 2], as the screws do not cut the threads into the screw holes. The locking holes and screws are manufactured to work together to provide for a polyaxial locking mechanism. The screw holes are manufactured with “interrupts” in the thread, allowing the bone screw four entry points into the threaded hole of the plate. The bone screw has two entry points in the locking thread on the screwhead. By combining these two features, the screw can be angled up to 15° in any direction, while virtually eliminating any potential cross threading of the locking screws.

The plates and screws are made of 316LVM stainless steel, which is austenitic. Austenitic stainless steel is more resistant to corrosion and is very formable, making it a good choice for locking plates. The screwheads utilize the hexalobe (aka stardrive) drive mechanism. This drive allows for increased torque, which has been shown to allow for a stronger locking mechanism in locking plates [1].

The pushout strength of the 3.5 mm screws has been investigated in the laboratory at various angles up to 15° within the 3.5 mm plate. With 2.5 Nm of insertion torque, the push‐out force (N) was noted to be as follows: 0°, 3320 N; 5°, 3087 N; 10°, 2778 N; 15°, 2500 N.

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Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on The Liberty Lock System

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