Die doel van intramedullêre naels met twee lagskroewe was om beenaankoop en rotasiebeheer binne die femorale kop te verhoog, voorkoming van afsny en uiteindelike fiksasie mislukking. In vergelyking met 'n intramedullêre spyker met 'n enkellagskroef, 'n tweelagskroefontwerp bied vergelykbare styfheid en stabiliteit en het 'n merkbaar hoër mislukkingssterkte.
Z-effect and Reverse Z-effect
Nietemin, this implant design has resulted in the identification of a new failure pattern known as the Z-effect phenomenon (see picture below), which shows up as the head/neck fragment collapsing, causing the superior lag screw to protrude and the inferior lag screw to migrate lateral to the nail.
The opposite effect, migration of the superior lag screw laterally and the inferior lag screw medially, is described by the reversed Z-effect.
The reason behind the Z-effect
The following theories were put out to explain how the Z-effect developed:
1. Lateral buttress deficit.
2. Unstable medial cortex.
3.The femoral head’s continuous friction and axial loading in varus
4.The osteoporotic head
Ways to avoid Z-effects
Putting the inferior lag screw above the calcar of the femoral neck may be the best way to position the lag screws in the head to prevent Z-effects. This will improve bone anchoring and prevent screwcut-out.Using a dual lag screw intramedullary nail may be something surgeons want to avoid in cases of intertrochanteric hip fractures with significant medial cortical comminution.If a longer inferior screw was employed, the loads were more evenly distributed between the implant and the two cephalic screws in the bone.
Noot:Die kopiereg behoort aan die oorspronklike skrywer en die tydskrif,Plasings is slegs vir leer en kommunikasie.