Screw insertion into locking plates

1. Principles

Locking plates allow for the insertion of two different types of screws

  • Locking head screws
  • Nonlocking screws

Generally, locking screws are preferred as there is less chance of the screw loosening.

Further advantages of locking screws vs nonlocking screws can be found here.

Depending on the producer, locking head screws may need to be placed at a right angle to the plate and centered to allow the locking head to engage.

Different locking plate shapes and sizes are available.

When inserting a nonlocking screw in a locking plate, up to 30° angulation is possible. The need for angled screw insertion can depend on fracture anatomy and the requirements for screw fixation.

Generally, locking head screws and conventional screws are self-tapping. On rare occasions, tapping may be desirable when the surgeon encounters unusually dense or sclerotic cortical bone, such as in the atrophic edentulous mandible.

Tapping is accomplished using the bone-tap instrument discussed here.

Locking head vs locking plate screw

2. Insertion of monocortical locking and nonlocking head screws into a locking miniplate

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

Drill the hole with the appropriate-sized drill bit.

Monocortically inserted screws are generally drilled to a depth of 5–6 mm. Stop drilling once one feels the loss of resistance from the outer cortex.

Use copious irrigation to prevent over-heating the bone.

Screws are inserted using a screwdriver.

Locking head screws lock into the threaded holes of the locking plate as they are inserted.

Use of threaded drill buide

3. Insertion of bicortical 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 in the center of the plate hole and perfectly perpendicular to the plate; so that the screw head can lock evenly.

Threaded drill guides of different lengths are available. The drill guides can be used to manipulate the plate on the mandible and protect the surrounding soft tissues during drilling.

Drill a bicortical hole with the appropriate sized drill bit. Once the inner cortex hole has been completed, care should be taken to avoid over-drilling and damaging the soft tissue and other structures beyond the inner cortex.

Use copious irrigation to prevent over-heating the bone.

Drilling of the hole

Screw length determination

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

Screw length determination

Screw insertion

Insert the screw using a screwdriver. The screw will stop turning when the locking head is fully engaged into the threaded plate.

Screw insertion

4. Insertion of nonlocking screws in locking screw plate

Drilling of hole

If angulation of the screw is required, the threaded drill guide cannot be used. A non-threaded drill guide can provide correct angulation and protect the surrounding soft tissues during the drilling sequence.

If the screws are to be used bicortically, care should be taken to avoid over-drilling and damaging the soft tissue and other structures beyond the inner cortex.

Use copious irrigation to prevent over-heating the bone.

Insertion of nonlocking screws in locking screw plate

Screw length determination

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

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

Screw insertion

Insert the screw using a screwdriver and not a power tool. It is possible to over-tighten the screw and risk displacing the fracture.

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

91 X060 Screw insertion into locking plates
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