- See:
Screw Menu
- Discussion:
- involves placement of one or more screws across a frx or osteotomy site to achieve interfragmentary compression;
- note that the direction along which the compression acts (inclination of lag screw) must coincide well w/ perpendicular axis of the fracture surface;
- as Johner et al (1983) have shown, frx sliding will occur if the compression is applied at an angle greater than 20 deg in relation to axis
perpendicular to the fracture surface;
- it has been written that if more than one lag screw can be positioned across a frx site, then plate fixation of the frx is not necessary;
- fortunately, only one or two disaters w/ this statedgy are required for the orthopaedist to realize that this is not true;
-
self tapping screws:
- if self tapping screws are inadvertently angled, they will cut a new path and destroy already cut thread, which is a disadvantage;
- self tapping screws should therefore not be used as lag screws;
- Technique:
- lag screw is best positioned at
right angles to the fractures plane;
- reduction:
- in order to find best location and inclination, forceps compressing fracture temporarily substitutes for function of the lag screw;
- lag screw replaces the forceps;
- gliding hole:
- the gliding hole (near cortex) is overdrilled w/ the appropriately sized bit;
- the appropriate sized dril bit corresponds to the outer diameter of the screw;
- take care not to drill past the far cortex;
- thread hole:
- insert the "golf tee" or a drill sleeve into the overdrilled cortex;
- for gliding hole to function properly, the screw must be positioned in axis of the drill hole;
- appropriate sized drill bit is inserted to drill the far cortex;
- 1.5 mm sized screw requires 1.1 mm drill bit
- 2.0 mm sized screw requires 1.5 mm drill bit
- 2.7 mm sized screw requires 2.0 mm drill bit
- 3.5 mm sized screw requires 2.5 mm drill bit
- 4.5 mm sized screw requires 3.2 mm drill bit
- measure screw length:
- screw length must be long enough to allow screw tip to protrude 2 mm beyond far cortex;
- bone tap
- insert appropriately sized bone tap to cut across far cortex;
- counter-sink:
- apply the countersink to make the screw head to improve seating on the anterior fibula and to make the head less prominent;
- the countersink will cause the screw to sink deeper, causing it to be more proud;
