A gauge is used to see applicable screw length, and therefore the thread cut is then created with acceptable tap or self-tapping screws are used or screws are placed in metaphyseal bone.
Interfragmentary lag screws offer compression across 2 bone surfaces with the lag technique. A lag bolt could be a type of static compression and is applicable to intra-articular fractures to keep up reduction and diaphyseal fractures for stability and alignment. Ideally, lag bolt fixation produces most interfragmentary compression once the screw is placed perpendicular to the fracture line.
Most lag fixation techniques need extra stabilization to neutralize the axial bending and movement forces applied to the bone throughout purposeful trauma implants surgical treatment. This can be provided by a neutralization or buttress plate or external fixation.
If lag screws are to be used unaccompanied by neutralization plate fixation, particularly in long spiral fractures (>2 times the diameter of the concerned bone), the best inclination of the screw is halfway between the perpendiculars to the fracture plane and to the long axis of the bone. Inserting the screw perpendicular to the long axis of the bone may also be thought of, as a result of longitudinal or shear compression that might cause the screw or screws to tighten.
Interfragmentary screw fixation alone could also be acceptable for avulsion injuries during which shear forces generate metaphyseal and epiphyseal intra-articular fractures, provided the bone quality is better.
A fully threaded screw will function a lag bolt with the close to cortex over drilled to the dimensions of the screw’s major (thread) diameter (4.5 mm). Once the close to the cortex is drilled, that provides a gliding hole, a drill sleeve with the outer diameter of the bit (4.5 mm) is inserted into a hole and therefore the normal drill bit (3.2-millimeter shaft diameter) is employed to drill the cortex.
As the screw threads hold the distal cortex, compressive power is generated through the axis of the screw to the screw head, inflicting the fracture fragments to be compressed. The same mechanical result is generated by a part of the threaded screw, with all threads entirely inside the other bony fragment.
Cannulated screws are currently provided by most orthopedic equipment manufacturers in sizes from mini fragment to 7.5 mm, sometimes with a cancellous thread, however, the cortical patterns also are obtainable, as they’re usually utilized in periarticular/metaphyseal bone. The guidewire is typically placed underneath fluoroscopic management and permits for initial conditional fixation.
Cannulated screws are amenable to a transdermic technique, like used with a hip pin, or could also be used with restricted open reduction techniques and might facilitate minimize soft tissue dissection and periosteal removal. Most styles are currently self-drilling and self-tapping, however, some might need predrilling over the guidewire in areas with dense bone.
The guide wires are sometimes terminally the threaded, although nonthreaded wires also are offered. In drilling over the guidewire, it’s counseled to not drill over the threaded portion, as a result of the wire could also be unknowingly removed at the side of removal of the drilling bit. This might end in a problem relocating the drill hole through soft tissue or loss of probationary fixation.
The fallback power of cannulated 7-mm a cancellous screw was tested against that of 7-mm non cannulated screws and 3.5-mm cannulated and non cannulated screws in 2 studies; no major distinction was calculated. However, the studies were specific to those screw styles, and different styles and sizes cannot essentially be assumed to possess similar fixation properties. It ought to stay in mind that cannulated screws are usually ten times as pricey as similar sized non cannulated screws; so, non cannulated screws ought to be used once technically possible.
Self-tapping screws have the advantage of extracting a step-in screw insertion, thereby decreasing operative time. The fluted style of the screw cuts a pointy path within the predrilled hole, eliminating the necessity for tapping. Baumgart et al showed that insertion force and fallback strength were comparable for broached and self-tapping screws. Provided that the cutting tip didn’t protrude through the second cortex did they notice a reduction of fallback strength of roughly 10%.
Schatzker et al incontestible that self-tapping screws inserted at 80% of thread-stripping force then removed and reinserted twelve times lost no important holding power. Once a self-tapping screw is inserted as a lag screw, care should be taken to avoid missing the other cortex; the screw is usually at an angle to the diaphyseal shaft, or it should prove exhausting to advance the screw whereas conjointly sound, particularly with the onerous cortical bone. It’s affordable to contemplate tapping the other cortex 1st to assist with the alignment and advancement of the lag screw.
Locked screws are incorporated in additional recent plate styles and should be inserted as unicortical or bicortical screws, reckoning on the kind of plate and fracture. These screws, with reduced pitch, create negligible axial force if any, one provides biomechanical fixation by locking the screw head into the plate with a tapered thread, perpendicular to the plate.