Screw insertion into locking plates

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 Principles
 Placement of locking head screws into a locking plate
 Placement of conventional screws
Principles

Locking plates allow for insertion of two different types of screws

  • Locking head screws
  • Conventional screws

Generally, locking screws are preferred as there is less chance of the screw loosening.
2.4 mm locking head screws must be placed at right angle to the plate and centered to allow a locking head to engage.
2.0 mm locking head screws are usually placed at a right angle to the plate but minor angulations are possible.

Occasionally the surgeon must place a screw in an angled fashion. This can be done using a conventional “nonlocking” screw. Up to 30° angulation is possible using conventional screws with a locking plate. This can be done based on the patient anatomy and requirements of screw fixation.

Generally, locking head and conventional screws are self-tapping. On rare occasions, when the surgeon encounters unusually dense cortical bone, especially when using 3.0 mm screws, tapping of the hole may be indicated.


Placement of locking head screws into a locking plate

Drilling of the hole
When using a locking head screw, use the threaded drill guide to keep the drill hole in the center of the plate and perfectly perpendicular so the screw head can lock evenly.

There is a long and a short threaded drill guide available for use. The drill guides can be used to manipulate the plate on the mandible and to protect the surrounding soft tissues during the drilling sequence.

Drill a hole with the appropriate sized drill bit. Monocortically inserted screws are generally drilled to a depth of 4–6 mm. Once the near cortex has been drilled, the surgeon feels a loss of resistance that indicates to stop drilling. One of the few indications of monocorticality when using a reconstruction plate 2.4 is the fixation of a vascularized bone flap.

This system is designed to be used with screws fixed bicortically. They require drilling through both cortices. Once the second cortex hole has been completed, care should be taken not to overdrill and damage soft tissue and other structures beyond the second cortex.

Use copious irrigation to cool the bone.


Pearl: using long drill guide as joy-stick
Use the long threaded drill guide as a joy-stick to manipulate and stabilize the plate during the drilling sequence.
The long threaded drill guide provides additional protection of the surrounding soft tissues during the drilling sequence.


Screw length determination
Use a depth gauge to determine the appropriate screw length for bicortical screw insertion.


Screw insertion
Insert the screw manually. The screw will stop turning when the locking head is fully engaged into the threaded plate.

Generally, using just digital pressure ensures an adequate tightness of the screw.


Placement of conventional screws

Drilling of hole
If angulation of the screw is required, the threaded drill guide cannot be used. A conventional nonthreaded drill guide can be used to provide correct angulation and protect the surrounding soft tissues during the drilling sequence.

Note: a conventional screw is placed in an angled fashion with a nonthreaded drill guide to avoid a tooth root.

Drill a hole with the appropriate sized drill bit. Monocortically fixed screws are generally drilled to a depth of 4–6 mm. Once the near cortex has been drilled, the surgeon will feels a loss of resistance that indicates to stop drilling.

Screws fixed bicortically require drilling through both cortices. Once the second cortex hole has been completed, care should be taken not to overdrill and damage soft tissue and other structures beyond the second cortex.

Use copious irrigation to cool the bone.


Screw length determination
Use a depth gauge to determine the appropriate screw length for screws inserted bicortically.


Screw insertion
Insert the conventional screw manually. It is possible to overtighten the screw and risk displacing the fracture.

Generally, using just digital pressure ensures the adequate tightness of the screw.