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Syndesmotic screw fixation, review article



X ray ankle AP and lateral views showing perfect position of syndesmotic screws and X ray after syndesmotic screws extraction.

Syndesmotic injury
Definition 
It is a lesion of the ligaments that connect the distal fibula and the tibia. These ligaments are surrounded on both sides by the anterior and posterior tibial tubercles. There may be an associated injury of the deltoid ligament.

Anatomy 
Stability of the tibiofibular syndesmosis is
provided by osseous congruity and soft tissue restraints. The ligamentous
restraints referred to as the syndesmosis complex. Four ligamentous structures have been defined. The anterior inferior tibiofibular ligament anatomically spans the syndesmosis anteriorly. The posterior inferior tibiofibular ligament spans the syndesmosis posteriorly. An avulsion of
the tubercle on the posterior surface of the distal tibia is an indication of an osseo-ligamentous injury. The third component of the syndesmosis complex is the interosseous ligament. Inferior or posterior transverse ligament has been variably detected.

The deep deltoid ligament has a role in limiting external rotation and providing syndesmotic stability.

The tibiofibular syndesmosis is a synovial joint, movement at the syndesmosis is minimal because of osseous and ligamentous anatomy.

Incidence 
Thirty percent of rotational ankle fractures and ten percent of ankle sprains. However, theses numbers may be increased if we consider that some cases are missed. 

Sixty percent of reoperations attributed to syndesmotic malreduction. 

Mechanism of injury 
In Lauge-Hansen pronation external rotation injuries. In a high fibular fracture ,that occurs in twisting injuries of the ankle, there is a disruption of the syndesmosis. Syndesmotic injury may also occur in some transsyndesmotic fractures.

Fractures of the proximal fibula may be associated with syndesmotic injury and instability of the syndesmotic complex. Restoration of both length and rotation of the fibula are of great importance. Associated fractures are fixed thereafter.

Isolated or associated injury 
Injury to the tibiofibular syndesmosis occurs both as isolated injury and as a component of twisting ankle fractures.

Clinically 
clinical findings will include ankle pain, tenderness directly over the anterior syndesmosis.
 Positive squeeze: pain at ankle with squeezing the tibia and fibula at mid calf.
 External rotation tests:
 probably most reliable test, neutral ankle with knee flexed 90o, hold tibia in neutral and  externally rotate foot.

X ray findings
1.  Clear space:- between the medial border of the fibula and the lateral border of the posterior tibia.

-it is  measured one cm above the plafond.

-it should be approximately five mm or less on both the AP and mortise views in normal ankle.

2.  Overlap between the fibula and the anterior tibial tubercle

- it is greater than six mm on the AP view

-it is greater than one mm on the mortise view 

3.  Stress films for syndesmotic instability

- In which there is application of an external rotation and abduction force

- usually performed under anesthesia 

Assessment of the syndesmotic reduction  
Assessing syndesmotic reduction intra-
operatively. It can be divided in direct and indirect methods. Direct reduction methods include open and arthroscopic approaches, while indirect methods include fluoroscopy and intraoperative 3d imaging. 
1- direct visualization:
this allows for direct reduction.
2- Arthroscopy:
Ankle arthroscopy is used for diagnosis of ankle syndesmotic injuries by directly
visualizing the Anterior inferior tibiofibular ligament fibers or diastasis at the tibiofibular syndesmosis.
3- Fluoroscopy
-AP or mortise views of the ankle. talar dome lateral view of the ankle is done and the distance from the posterior or anterior border of the fibula to the posterior malleolus or anterior tibial cortex, respectively, were measured
and compared with the contralateral ankle with reduction adjusted.
- a bone hook is used to pull the fibula laterally to examine the syndesmotic complex. 
- pushing and pulling the fibula with the fingers, or a bone hook to test for antero-posterior translation of the fibula.
4- Intraoperative 3-Dimensional Imaging
CT is the gold standard for assessing the adequacy of syndesmosis reduction. 

Approach to achieve anatomic syndesmotic reduction 

1-Anatomic Fracture Fixation
Open reduction internal fixation of the malleolar fracture. We can use a small bone hook to pull the lateral malleolus distally until we get a perfect congruence of the distal tibiofibular joint.

Preliminary fixation with a K-wire

Fix the reduction with a K-wire, we insert it  from the lateral side, distal to the planned distal screw and one to two cm above the joint line. The ankle joint during this should be in neutral.

Confirm reduction under image intensification in both planes and compare it with the uninjured ankle.


2-Implants used for Syndesmotic Fixation
-Syndesmotic stability was achieved using tricortical or quadricortical trans-syndesmotic screws. We use a 2.5 mm drill bit through the fibula and the lateral cortex of the tibia. It should be just proximal to the inferior tibiofibular joint, 30 degrees from posterior to anterior and parallel to the tibial plafond with the ankle joint in the neutral position. The screw may be placed through a hole in the plate.
We must tap in both fibula and tibia. Tap the thread and insert a 3.5 mm or 4.5 mm cortex screw. The foot position should be in neutral. Check position and reduction of the screw. Insert the second positioning screw parallel to and 1.5–2 cm proximal to the first screw.

Once satisfactory reduction and hold with screws has been confirmed, the K-wire is removed.

Recently, transsyndesmotic fixation is not an absolute necessity if the components of the syndesmosis complex are

able to be repaired.

-Suture button devices are less rigid.

Pitfalls
-Failure to achieve anatomic fixation of associated fractures. Which may be seen
fluoroscopically as fibular shortening or malrotation, will not allow anatomic syndesmotic reduction.
-Failure to fix and reduce a posterior malleolar fracture, particular large.
-Improperly apply trans-syndesmotic clamp, screw, or suture-button fixation. 
-Failure to assess syndesmotic reduction.

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