Partially Threaded Cannulated Compression Headless Screws
Juan B. Gerstner Garcés, Leslie Grujic, Christina A. Kabbash, Stefan Rammelt, Andrew K. Sands, Michael P. Swords, Ewe J. Yeap
Approved by the AO Technical Commission in 2019 for foot and ankle indications, Cannulated Compression Headless Screws are available in a variety of designs and in diameters ranging from 2.0 mm to 7.5 mm. Depending on the concept how compression between two fragments is achieved and how well the insertion of the screw can be performed depending on the individual situation, the screws provide a certain amount of compression between those two fragments. Even so the screw insertion seems to be relatively easy, it is challenging to reliably provide the intended compression between the two fragments when the K-Wire guiding the screw insertion is the only element keeping the reduction during insertion.
The Cannulated Headless Screw (Fully Threaded) System was subsequently developed as a line extension to the Cannulated Compression Headless Screw system, focusing on hand and wrist procedures, and was approved in 2025.
Innovative design features
The new Partially Threaded Cannulated Compression Headless Screws have a compound cutting edge on the tip for easier insertion designed to reduce insertion force for cutting the thread into the bone. The thread on the shaft of the screw comes in two different lengths. A differential thread pitch between the tail and head of the screw generates compression. The wider distal threads advance into the far fragment faster while the proximal threads gradually enable the two fragments to compress. The optimal compression is provided when the screw is fully seated at or below the bone surface.
Cutting efficiency testing
The cutting efficiency of the new screws was tested to measure the axial load needed for the screw to cut and tap into simulated bone. The tests have shown that the axial load needed to insert the new Partially Threaded Cannulated Compression Headless Screws into a foam block simulant is lower than that of other similar devices. This is an important advantage regarding the insertion of the screw in two ways. In the cortex of the first fragment the improved cutting efficiency allows easier insertion and advancement of the screw. When the screw reaches the second fragment the improved cutting efficiency reduces the distraction of the far fragment, retaining initial reduction.
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