Current Insights On Internal Fixation Of Subtalar Fusions
Sharing findings from the literature and pearls from their own experience, these authors examine pertinent considerations and keys to facilitating optimal placement of internal screw fixation in subtalar joint arthrodesis procedures.
The subtalar joint (STJ) arthrodesis is a well-documented procedure in elective reconstructive hindfoot surgery, for pain relief in cases of subtalar joint arthrosis and occasionally in the treatment of highly comminuted traumatic fractures. In addition, the subtalar joint fusion may be beneficial in the treatment of talocalcaneal coalitions, adult acquired flatfoot, posterior tibial tendon dysfunction, Charcot neuroarthropathy, and hindfoot varus or valgus deformity.1-10
There are many technical pearls to performing this arthrodesis successfully. One of these pearls involves the fixation construct. Surgeons most commonly utilize large diameter screws for internal fixation of this arthrodesis. Still, there is variety to the number and size of screws one selects as well as the orientation in which the surgeon places these screws.
One can access the subtalar joint from either the traditional lateral approach over the sinus tarsi or from a medial approach between the posterior tibial and flexor digitorum longus tendons. For the lateral approach, make an incision two fingerbreadths inferior to the distal fibula, extending distally to just proximal to the fourth metatarsal base. During the dissection through the subcutaneous tissue, keep aware of the local sural nerve, which is inferior to the incision.
Retract the peroneal tendons inferiorly. Leave the extensor digitorum muscle belly in its fascial layer and reflect it dorsally. Evacuate the sinus tarsi, allowing access in the middle facet of the subtalar joint. Using a sharp osteotomy, gently release the interosseous ligament and work posterior to the posterior facet. The use of a lamina spreader allows direct visualization of the posterior facet. Remove the cartilage with a series of osteotomes and curettes. Then fenestrate the subchondral bone with a 2.5 mm drill bit and pulverize the subchondral bone with a ¼-inch curved osteotome.
The medial approach utilizes the interval between the posterior tibial tendon and flexor digitorum longus tendon. One can readily view the inferior aspect of the talar head and follow the plantar joint line posterior to the middle facet of the subtalar joint. Careful identification of the inferior extensions of the deltoid ligament is important for later repair if release is necessary for exposure. Joint preparation and takedown are identical to the lateral approach.
Appropriate positioning of the hindfoot is crucial to this procedure. A neutral or mild valgus of the hindfoot is the ideal position. When it comes to deformity correction, one frequently needs to lateralize the talus back up on top of the calcaneus in a scissors fashion to correct medial collapse of the hindfoot.
Key Considerations With Performing The ‘Top-Down’ And ‘Bottom-Up’ Approaches
In regard to the anterior to posterior subtalar joint screw placement (aka the “top-down approach”), this technique is generally easier if the patient is supine and there is one surgeon who does not need lifting help for the leg. Holding the hindfoot in the non-dominant hand will allow gentle and accurate correction while placing the screw dorsal to plantar. The anatomical landmarks are just lateral to the tibialis anterior tendon and directed at an oblique angle toward the lateral wall of the calcaneus.