Dispelling The Misconceptions About Subtalar Arthroereisis
The fact of the matter is that the majority of sinus tarsi devices are only inserted into the sinus portion of the sinus tarsi. The recommended placement of these devices is such that the medial/deeper end of the device should line up with the “50 yard line” or the bisection of the talus. The deeper/medial half of the “50 yard line” leads to the entrance of the canalis portion of the sinus tarsi. These devices are classified as type I and are directed from lateral to medial. The lateral tissues anchor the type I design within the sinus tarsi. The majority of motion of the talus on the calcaneus occurs in the lateral half of the sinus tarsi. That combined with the fact that there is a great amount of torque on the device with every step taken could explain the eventual loosening of the device long-term and the need for removal.
A type II device is medially anchored deeper into the canalis portion of the sinus tarsi. The HyProCure sinus tarsi stent is currently the only medially anchored sinus tarsi stent. This device is oriented obliquely to follow the path of the sinus tarsi, maintaining its desired open position. Therefore, all sinus tarsi devices are not the same.
What About Perceived Complications With Subtalar Arthroereisis?
Myth: During the subtalar arthroereisis procedure, the surgeon partially transects the talocalcaneal interosseous ligament within the sinus tarsi and this can lead to increased instability to the subtalar joint complex. In order to perform the procedure properly, one does need to transect the ligamentous tissues within both the canalis and sinus portions of the sinus tarsi.
This serves two purposes. First, it creates a tissue envelope or opening for the insertion of the device. Second, the tissues will reattach to each other. This serves to incorporate tissue growth onto and around the stent device. Essentially, the tissues grab hold of the stent to help lock it into place. These tissues were not performing their intended function to prevent the excessive talar motion. Even if the sinus tarsi device had to be removed, this would cause bleeding of the involved tissues, which would then lead to reformation and healing of the tissue.
Many surgeons perform a “sinus tarsi decompression” procedure for patients who suffer with chronic pain within the sinus tarsi. This procedure involves the radical excision and removal of all of the contents within the sinus tarsi. A subtalar arthroereisis procedure leaves these tissues intact at their attachment points into the talus and calcaneus. Removing these tissues could lead to failure of the sinus tarsi device since there is nothing to adhere to it. It is not recommended to remove the contents of the sinus tarsi during a subtalar arthroereisis procedure.
The manufacturers of a few of the type I sinus tarsi devices suggest that the surgeon leaves these deeper tissues intact and one should not violate them. However, in the next steps of the procedure, the surgeon must insert various “dilators” to open the sinus tarsi and to trial size. One would insert these dilators deep within the sinus tarsi and they act to separate these tissues. The real reason is to prevent too deep of a placement of the type I device as there have been situations when the sinus tarsi stent pushed completely through the sinus tarsi and ended up on the other side of the foot. The theory is that if the deeper tissues are intact, this would help to reduce this complication.
Myth: Creating the tissue envelope for the sinus tarsi device will damage the artery and nerve within the sinus tarsi, leading to avascular necrosis of the talus. The surgeon will use specialized curved scissors when transecting the tissues within the central portion of the sinus and canalis portions of the sinus tarsi. The cutting edge of the scissor blade is located in the central part of the scissor and not on the outer section of blade. The artery and nerve to the sinus tarsi are located right under the neck of the talus and the dull portion of the scissor cannot cut these structures.