Lag screw principles | 合法醫療器材資訊網

Alagscrewisusedtocompressfracturefragments.Itisthreadedintotheoppositecortex,andslidesthroughaholeinthenearcortex.

Insertion of a fully-threaded lag screw requires drilling a glide hole in the near cortex, on the same axis as the thread hole in the far cortex.

Glide hole: The cortex under the screw head is drilled to the size of thread diameter so that the thread gets no purchase. Thread hole: A drill hole which is the same diameter as the core of the screw is drilled, and a tap is used to cut the spiral groove that receives the thread of the screw. The result is a thread hole.

One can drill both cortices with the thread hole sized drill and then overdrill the near cortex. Alternatively, the gliding hole is drilled first, and a drill sleeve is placed within it to direct the drill bit for the thread hole in the far cortex.