The Herbert screw (invented by Timothy Herbert) is a variable pitch

cannula A cannula (; Latin meaning 'little reed'; plural or ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces ...

ted screw typically made from

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

for its biocompatible properties as the screw is normally intended to remain in the patient indefinitely. It became generally available in 1978. It is one of the earliest designs of headless compression screws which are used to achieve interfragmentary compression through its differential pitch between the threads at each end of the screw(distance between adjacent threads of screw). It is used in scaphoid, capitellum, radial head and in osteochondral fractures. Other uses include osteochondritis dissecans & small joint arthrodesis.

References

Orthopedic screws {{orthopedics-stub