Executive Editor: Joseph Schatzker

Authors: Richard Buckley, Andrew Sands

Talus - Posterior process

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Glossary

1 Diagnosis top

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Mechanism of the injury

This fracture is often confused with an ankle sprain. The mechanism of this injury is an axial load. Diagnosis is often very difficult.


Posterior process fracture enlarge

Imaging

A plain x-ray may be diagnostic, but coronal CT scans are often necessary for a complete definition of the injury.
The presence of an os trigonum which is a developmental failure of the fusion of the posterior tubercle of the talus with its body may be very confusing in making a diagnosis. The aspect of the os trigonum facing the rest of the talus is corticated whereas a fresh fracture is not. If there is any doubt, a bone scan or an MRI would be definitive.

The x-ray shows a posterior process fracture. Case by courtesy of Dr. Steven Steinlauf, Florida, USA.

2 Surgical indications top

Fractures of the posterior process of the talus enlarge

Fractures of the posterior process of the talus may involve the subtalar joint, if they are large.
Because this is an intraarticular fracture, if displaced, anatomic reduction and stable fixation has to be restored to prevent the development of posttraumatic arthritis. If the fracture is comminuted and reduction and fixation is not possible, then one should consider resection. Similarly, if a symptomatic nonunion develops, the fragment should be resected. If this piece is large, screw fixation may be necessary.
If the fracture is completely undisplaced, then immobilization and non-weightbearing is indicated.

3 Approach top

Posterolateral approach enlarge

The posterolateral or posteromedial approaches allow visualization of this fragment.


Posteromedial approach enlarge

Anatomy enlarge

Anatomy

The posteromedial approach is extremely useful and follows the plane between flexor hallucis longus and the Achilles tendon. The neurovascular structures lie posteromedially behind the medial malleolus and must be protected.


Skin incision enlarge

Skin incision

Using the Achilles as the lateral boundary, and the neurovascular structures posteromedially, a skin incision is made centered over the subtalar joint using image intensification.


Superficial dissection enlarge

Superficial dissection

The structures that run behind the medial malleolus are very important here. The most posterior structure, flexor hallucis longus, is identified so the surgeon can go posterior and lateral to it and medial to the Achilles tendon.


Deep dissection enlarge

Deep dissection

The tendon sheath of the flexor hallucis longus must be opened. This allows the retraction of the tendon together with the neurovascular bundle and gains exposure of the fracture.
Lateral to the tendon sheath of the FHL is the posterior tubercle of the talus.
The surgeon must be careful not to be too proximal and mistake the distal tibia for the talus. Fixation and debridement can now be completed.

4 Reduction and preliminary fixation top

Reduction enlarge

Reduction

Because this fragment is frequently very small, a K-wire may be used as a joystick to help with the reduction which is carried out with the help of an image intensifier.


Preliminary fixation enlarge

Preliminary fixation

The fragment will often not accept more than a single screw. Therefore it is best to use a threaded K-wire guide of a corresponding cannulated screw for provisional fixation. This threaded K-wire is then introduced into the middle of the fragment, once reduced, and advanced into the body of the talus. A cannulated lag screw can then be used for fixation.


Preliminary fixation with eccentric K-wire enlarge

Preliminary fixation with eccentric K-wire

A second K-wire should be placed eccentrically, if possible, to provide rotational control of this small fragment of cortical bone. It will be removed when fixation is complete.
If possible, two screws would be optimal, but often not possible.

5 Screw fixation top

Rule of thirds enlarge

Pearl: rule of thirds

This fracture is often quite small, or multifragmented.
If the piece is one large fragment, then screw fixation is preferred. If the piece is very small then resection may be a better option. K-wires alone may be used but present difficulty (migration) if used alone.

A nice rule to remember is the rule of thirds. If the size of the screw head is more than one third of the size of the fragment, then this small piece may comminute into many pieces. If the size of the screw head is less than a third of the fragment, then successful fixation may be achieved.


Drilling enlarge

Drilling

With the central K-wire in place, drill the gliding hole with the corresponding drill bit, drilling only the fragment. Then drill the thread hole in the body of the talus.


Screw insertion enlarge

Screw insertion

Measure the depth for screw length.
A cannulated partially threaded screw will be used for fixation. Thus depending on the size of the fragment, one would use either the 2.4 mm, or the 3.5 mm screw and the corresponding drill bits.
Careful technique will ensure that the small posterior process does not fragment.
K-wires usually are removed so they do not migrate.


Second screw for rotational stability enlarge

Second screw for rotational stability

In order to secure rotational stability, it is necessary to insert a second screw, or if not possible, then a K-wire. Screws are preferable to a K-wire. Therefore try to insert a smaller screw to achieve rotational stability.

Use image intensification to make certain that reduction is anatomic and that the fixation has been appropriately inserted to maintain stability and articular congruity.

v2.0 2017-01-20