Authors of section

Authors

Paulo Barbosa, Felix Bonnaire, Kodi Kojima

Executive Editors

Steve Krikler, Chris Colton

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Lag screws (transverse fracture)

1. Lag screw principles

As the screw is tightened, the thread advances in the main tibial fragment and this pulls the head of the screw, and therefore the malleolar fragment, towards the main body of the tibia.

The smooth shaft of the screw prevents any significant hold between itself and the surrounding bone.

The length of the screw shaft must be chosen so that the threaded part of the screw lies fully within the opposite bone fragment, but does not penetrate beyond the denser epiphyseal cancellous bone.

To prevent the screw head from sinking into the thin malleolar cortex, the use of a washer is recommended.

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2. Patient preparation and approach

The patient may be placed in the following positions:

For this procedure a medial approach is normally used.

lag screws oblique or vertical fractures

3. Reduction

Cleaning the fracture site

It is important to visualize and inspect the joint, searching for any bone and cartilage fragments that may have been detached from the medial malleolus or from the talus.

Anatomical reduction

Reduce the fracture anatomically with the use of small pointed reduction forceps, taking care with the soft tissues.

To monitor the perfect articular reduction, a limited antero-medial arthrotomy will permit visual inspection of the joint surface.

Do not strip the periosteum more than necessary.

lag screws transverse fracture

Preliminary fixation

Insert a 1.6 mm K-wire as perpendicularly as possible to the fracture plane.

As decided in preoperative planning, this K-wire should occupy the planned position of the posterior lag screw.

Check the reduction visually (especially anteriorly) and under image intensification.

lag screws transverse fracture

4. Fixation

Drilling

Make a stab incision through the deltoid ligament. With the protection of the drill sleeve, drill a 2.5 mm hole as perpendicularly as possible to the fracture plane, and parallel and anterior to the K-wire. Do not drill to the lateral cortex.

Care must be taken to avoid penetration of the ankle joint.

Keeping the drill in place, check its position and the reduction under image intensification.

lag screws transverse fracture

Tapping

Measure the drill depth and tap the malleolar fragment only with the 4.0 mm cancellous bone tap, using the protection sleeve. The length of the screw chosen is based on the principle that all thread must lie proximal to the fracture plane. Be careful not to choose a screw that is too long, as its thread will come to lie in the fattier cancellous bone of the metaphysis, rather than in the denser bone of the former epiphysis.

lag screws transverse fracture

Insertion of the anterior screw

The chosen 4.0 mm cancellous bone screw should come to rest with its threads completely beyond the fracture line.

The use of a washer is recommended, especially in osteoporotic bone.

Insert the screw without excessive tightening.

lag screws transverse fracture

Replace the K-wire with a lag screw

Remove the K-wire. Make a stab incision through the deltoid ligament and enlarge the K-wire track with a 2.5 mm drill and protection sleeve.

After measuring the length and tapping the malleolar fragment, insert the second chosen 4.0 mm cancellous bone screw.

The fracture will be suitably fixed with the two cancellous bone screws and the joint surface reconstructed.

lag screws transverse fracture

5. Postoperative treatment of infra- and trans-syndesmotic malleolar fractures

A bulky compression dressing and a lower leg backslab, or a splint, are applied, and the limb is kept elevated for the first 24 hours or so, in order to avoid swelling and to decrease pain.

In anatomically reconstructed, stable malleolar fractures, early active exercises and light partial weight bearing are encouraged after day one. In osteoporotic bone, weight bearing should be postponed.

X-ray evaluation is made after 1 week and then monthly until full healing has occurred. Progressive weight bearing is recommended as tolerated.