Subtalar fusion
Technique
The patient is positioned supine on the
operating table with a bump under the
ipsilateral hip so as to internal rotate
the leg. This allows good visualization of the lateral aspect of the foot.
The incision is marked on the foot by
identifying the appropriate anatomy. The
incision runs from the tip of the
lateral malleolus to the base of the
fourth metatarsal.
C arm can be used to identify the relevant and atomic structures make sure the foot is at the edge of the table as this will assist with inserting the hardware and help with better visualization of the
surgical field.
The skin incision is then made over the marking it's not necessary to use the
full extent of the marketing for an
isolated subtalar fusion. If the calcaneo-cuboid joint needs to be fused the
incision can be extended to the base of
the fourth metatarsal.
Careful dissection is made through the soft tissue protecting all relevant neurovascular structures. It is important to maintain hemostasis while bisecting using diathermy. Extensor digitorum brevis muscles is identified and carefully dissected. In the younger patient this muscle is quite well-developed. In elderly patient this muscle is often atrophied. It's easy just to split the muscle belly in half to gain access to the subtalar joint. If we have a well-developed muscle belly we
carefully dissect it out so as to identify the edges and the origin of the extensor digitorum brevis muscle. The muscle is then released from this origin and sub-periosteally dissected of the calcaneus the muscle is released all the way to the calcaneo-cuboid joint. The muscle belly
is then reflected distally and switch it
to the distal skin so as to take it out of the surgical field and improve visualization of the subtalar joint. The peroneal tendons are identified in the proximal aspect of the incision. It's very important to do this carefully as it's very easy to cut these tendons once the preroneal tendons have been identified. A sharp human retractors inserted medial to the peroneal tendons as well as the CFL ligament, going around the posterior aspect of the subtalar joint.
The capsule of the posterior facet is then
incised exposing the subtalar joint.
The use of self-retaining retractor is helpful maintaining the exposure of
the surgical field. The subtalar joint is identified. It's quite a tight space to
work in using a sharp osteotome, the lateral half of the posterior facet is denuded of its cartilage. Then we remove debris from the subtalar joint. By removing the lateral half, we have now made space to insert a smooth lamina spreader. The lamina spreader is first placed in the joint and opened up.
Now we can start better visualizing the full
extent of the posterior facet. It is important to meticulously remove all debris from inside the joint. With good visualization of the posterior facet the osteotome is now used to denude the remaining cartilage and remove any sclerotic bone from the joint surfaces. It is important to get down to a healthy bleeding subchondral bone.
You should take your time for preparing the joint surfaces as this is a critical part of achieving a successful fusion. When working in the posteromedial aspect of the joint, be cautious as the flexor tendons run in this area. With the sharp osteotome, it's very easy to damage the tendon's. The flexor tenons will become visible in the depths, you can be confident that you've seen the full extent of the joint
The joint is washed out with copious amounts of normal saline to remove all the small debris now that we finish the preparation of the posterior half of the joint.
A lamina spreader inserted posteriorly. The anterior half of the joint is now prepared in the same manner with osteotome. To visualize the middle and anterior facet the sinus tarsi area has to be depleted. The soft tissue is carefully removed using sharp dissection.
Once the middle and anterior facets
become visible, they can be prepared in a
similar fashion using sharp osteotome
and curette.
Now we debride the entire joint cartilage and sclerotic bone down to healthy bleeding subchondral bone.
The joint is washed out once again with copious amounts of normal saline for the last time. Then sharp 3.5 millimeter drill bit is then used to perforate the prepared
joint surfaces. The reason for doing this
is to form channels which allow marrow
elements to access the fusion site this
aids in achieving a successful bony
fusion. Make sure to drill both the
calcaneal and talar sides of the joint
surface. The reason for using a drill bit
rather than a k wire is that it would bring healthy cancellous bone into the fusion site. Swap the lamina spreader anterior again so the posterior half of the joint can now be drilled. In cases with very sclerotic subchondral bone a thin osteotome can be used. This is done to improve the success of the fusion. We are now ready to insert the hardware fixation. The screws are inserted to the posterior aspect of the heel. it's very important to make sure that these aren't inserted over the weight-bearing surface.
We can put our hand placed on the
plantar aspect of the foot and the
incision made proximal to it, so as to
avoid the hardware being on the
weight-bearing surface. The lamina spreader should be left inside. This is done, so that we can visualize the placement of our K wires. The first wire is placed in the lateral half of calcaneus aiming into the mid substance of the posterior facet. A second wire is placed in the medial half of the calcaneus slightly
more anterior that serves to engage the neck of the talid.
Once your K wires are placed.The lamina spreader can be removed. The subtalar joint is then reduced. Take your time in reducing the joint and make sure
that it's in the anatomical position of the
proximately 5 to 10 degrees of vulgus.
Once the reduction is done, your assistant can drive the K wires up into the talus.
Check by confirming that the heel is approximately five to ten degrees of valgus relative to the lower leg. Correct placement of the K wires is checked under fluoroscopy both on the AP and lateral views. Once the reduction is done and
placement of K wires is done. The screw lengths can be measured it's approximately 5 millimeters less than the
measured length so it is not to penetrate the ankle joint. Minimize Hardware prominence which could cause discomfort for the patient.
Confirm correct position and length of the screws inserted. it's also good to check that good compression has been achieved
across the fusion site.
The extensor digitorum brevis muscle is
now reattached to its origin using
interrupted vicryl sutures. The wound is then carefully closed in layers using vicryl sutures.
It is important not to forget the wound at the back of the heel which we close with sutures. The leg is then immobilized in
well padded plaster cast with the ankle in the neutral position. It is advisable to elevate the leg so as to minimize post-operative swelling.