When the subtalar dislocation happens, the talonavicular
joint also becomes dislocated. There are two types of subtalar dislocations:
medial subtalar dislocation and lateral subtalar dislocation. Medial
dislocations are 4 times as common as lateral dislocations. Some of these
dislocations can be open and urgent reduction is important to decrease skin
necrosis and interruption of the circulation of the foot. After either closed
or open reduction, the subtalar joint is usually stable. Lateral subtalar
dislocation means that the foot goes lateral. As the foot goes lateral, the
structure in the medial side becomes trapped. The posterior tibial tendon
blocks successful closed reduction of the lateral subtalar dislocation. Lateral
subtalar dislocation is a bad type. It is worse than the medial subtalar
dislocation and is not as common. The foot goes lateral and as the foot goes
lateral, the medial structures get pulled from also trying to go lateral. As
you try to reduce the foot to its normal position, then there can be some
entrapment, usually the posterior tibial tendon. This tendon will be interposed,
and you will be unable to do closed reduction. This lateral subtalar
dislocation will have a high incidence of fractures of the surrounding tarsal
bones, and the subtalar joint could be unstable after reducing the dislocation.
Lateral subtalar dislocations are more open than the medial subtalar
dislocations. Open subtalar dislocations have a high incidence of infection. If
the patient sustained an open injury to the foot with complete extrusion of the
talus, the treatment should be to give the patient antibiotics and debride the
wound, clean the talus using betadine solution or normal saline with
antibiotics, and after the wound is debrided, implant the talus back into its
bed. You may want tot use external fixator after that. The medial subtalar
dislocation is different. Rarely the dislocation is irreducible (it usually
reduces easily). Irreducible dislocation can be due to: impaction fracture of
the head of the talus, interposition of the extensor digitorum brevis tendon
(popular in exams), or interposition of the peroneal tendons. In medial
subtalar dislocation, the foot appears supinated. In lateral dislocation, the
foot appears pronated. The majority of both dislocations can be managed by
closed reduction and immobilization, which the closed reduction should be done
as soon as possible to decrease the risk of skin complications. Closed
reduction is probably difficult in about 5-10% of medial dislocations and
15-20% of lateral dislocations. The dislocation can be reduced easily, and you
will get an x-ray to evaluate and see if the dislocation is reduced or not, but
you will probably also see it clinically. If you do not have a fracture or any
fragments in the post-reduction x-rays, then the success rate with a splint or
immobilization cast is very good. The medial dislocation has a better prognosis
than the lateral dislocation. In the medial subtalar dislocation, the late
instability is rare, and the duration of immobilization should be short (about
3-4 weeks). If you have a lateral subtalar dislocation, you may want to
evaluate the foot by CT scan after closed reduction and splinting the patient.
The reason that you get a CT scan, is to see if you have any bony fragments
that need to be removed or fixed, and that can also be done for the medial
subtalar dislocation if you think it is necessary. These bony fragments can
cause the subtalar joint to be unstable. The lateral subtalar dislocations are
a high energy injury. They are frequently associated with small osteochondral
fractures. Larger fragments should be fixed, and a small fragment that is
entrapped in the joint should be excised. If you think the joint is unstable
after reduction, check for the presence of a large intra-articular fracture and
try to reduce it and fix it. You want to start early range of motion, so
immobilize the patient for a short period to avoid stiffness but try to avoid
the recurrence of the dislocation or the instability. The subtalar dislocations
can cause stiffness of the subtalar joint and degenerative arthritis. If you
can’t do closed reduction then you need to do open reduction, and you need to
know that the extensor digitorum brevis is usually the entrapped in medial
subtalar dislocation, and the tibialis posterior is the one that is usually
entrapped in the lateral subtalar dislocation.
