Dispelling The Misconceptions About Subtalar Arthroereisis
Subtalar arthroereisis has a long evolutionary history since its first conception in the 1940s. Since then, researchers have created and abandoned many different methods, materials and devices. The promise of the next great device to stabilize the subtalar joint complex without osteotomy or arthrodesis usually diminished with long-term usage.
The need to stabilize the talus on the calcaneus without arthrodesis has been a quest for many foot and ankle innovators. However, the scientific literature on this subject has led to many misconceptions as to the true power of the subtalar arthroereisis. Accordingly, let us provide some clarification on this controversial subject.
One of the first misconceptions is that arthroereisis is a “joint blocking” procedure. A joint blocking procedure would imply a limitation of the normal range of motion of that joint. The purpose of an arthroereisis procedure is to limit the excessive motion of the joint in order to restore that joint complex back to normal.
Many have called the devices inserted into the sinus tarsi “subtalar joint implant(s).” This leads one to believe that the device actually inserts into a joint. The reality is that these devices are completely extra-articular. The subtalar joint complex consists of two or three joints: posterior, middle and anterior joints. Sometimes the middle and anterior joints join together to form one continuous joint. In between the posterior portion of the complex and anterior portion is the area of the sinus tarsi, which has no cartilage, no interaction between two or more bones and, finally, is not a joint.
This is important as a “joint implant” has a negative connotation. It usually means that the joint is arthritic and not properly functioning. Therefore, in order to insert this device, one must resect the joint and the implant will replace the function of at least one-half of the joint. Furthermore, most joint implants do not last long and usually need to be replaced after so many years. The term joint implant also indicates not only a more aggressive surgery but also a long recovery usually involving physical therapy.
A better term is sinus tarsi implant or stent. Presently, we can define a stent as any medical device that supports tissue in order to help prevent the abnormal closure or obliteration of that tissue. For example, when one inserts a stent into the sinus of the tarsal bones, it prevents the abnormal closure of that space.
When Should Patients Undergo Subtalar Arthroereisis?
Myth: Surgeons should only perform the subtalar arthroereisis procedure in children. Researchers first developed this procedure with children in mind, primarily because they thought the materials were not durable enough for adults. Furthermore, the thought was that as a child grew, arthroereisis would help to prevent the secondary symptoms of the excessive hindfoot motion. Another reason why children underwent this procedure more than adults had to do with the activity levels of adults.
The initial materials were bone grafts and then medical grade plastics were in use. The problem with bone grafts was they eventually became absorbed or simply lost correction with time. The high-grade medical plastics and silicone devices usually fragmented after the repeated forces from the talus grinding on the calcaneus. Furthermore, once the materials broke down, this led to a possible foreign body reaction. Overall, these materials were less than ideal as a long-term solution.
Maxwell and Brancheau were the first to design a titanium version of a sinus tarsi device modeled after the Valenti design. Initially, this device was mainly in use for pediatric patients and due to the improved material, geriatric patients received the device. The use of titanium created a new level of excitement into the possibility of stabilizing the talus on the calcaneus in adult patients. This opened the door to expand the age range. Even though there was still a gap between the pediatric and geriatric patients’ usage, more patients were able to have this option.
As time progressed, foot surgeons continued to push the envelope to include more active adults with further success. Adults need this procedure as much as any other age group. The problem with instability of the subtalar joint complex is that even though the pathologic condition is present, it may take decades before there are symptoms in the hindfoot.
Myth: Surgeons should not perform subtalar arthroereisis in pediatric patients. In contrast, many foot physicians believe one should only perform this procedure in patients once they have achieved skeletal maturity. The thinking is that the device could lead to stunted osseous growth, leading to more damage as the child grows.
This is simply not true. The sooner the subtalar joint complex stabilizes, the sooner the excessive forces on the musculoskeletal tissues are eliminated. This prevents the cumulative trauma disorders inflicted on these tissues with every step taken.
Clarifying The Long-Term Effects Of Arthroereisis
Myth: Subtalar arthroereisis stents will lead to arthritis within the sinus tarsi later in life. The sinus tarsi is devoid of cartilage and is instead filled with ligamentous tissue, the function of which is to limit the amount of excessive motion of the talus on the calcaneus. Since arthritis is the chronic inflammation within a joint and the sinus tarsi is not a joint, a sinus tarsi stent cannot lead to arthritis within the sinus tarsi.
A subtalar arthroereisis procedure is not joint destructive since it is completely extra-articular. After a thorough search of peer-reviewed literature on subtalar arthroereisis, I could not find one article on the development of “arthritis” within the sinus tarsi after the use of a sinus tarsi implant.
Myth: After the child grows to skeletal maturity, one can remove the sinus tarsi device and maintain osseous correction. This has never been proven as a stand-alone procedure. Many times after removal of the devices, the foot maintains correction. However, some overlook the fact that these patient also underwent other adjunctive osseous and/or soft tissue procedures. Any time I have removed the sinus tarsi device, over time the talus once again ended up slipping out of alignment. One needs to leave these devices in place so they can perform their function.
Myth: As children age, they will need a larger device since the bones will have grown larger. There are no pediatric or adult-sized sinus tarsi devices. According to GraMedica, the manufacturer of the HyProCure sinus tarsi stent, the most common size of the HyProCure sinus tarsi device in the adult foot is size 7. This is followed by size 6.
These two sizes account for more than 70 percent of sinus tarsi stents used all over the world.1 Therefore, if a child receives a size 6 or 7, he or she already has the most common adult sized stent.
We know that by the age of 3, the surrounding osseous chambers of the sinus tarsi have developed yet the growth plates of the talus and calcaneus are still open. This means that the overall dimensions of the sinus tarsi will stay the same yet the bones themselves will continue to grow. Most likely, once the surgeon places the stent into the pediatric foot, the stent size should not change.
Distinguishing Among Sinus Tarsi Stent Designs
Myth: All sinus tarsi stents are the same. There have been many different designs throughout the past decades and for good reason. The sinus tarsi is angulated in an oblique fashion. There are two sections to the sinus tarsi: the outer, more open area referred to as the sinus portion of the sinus tarsi and the deeper, narrower portion called the canalis.
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.
For argument’s sake, even if these structures were damaged, this artery is not the main source of blood to the talus. There is a complex network of blood vessels supplying blood to the talus. The upper surface of the sinus tarsi is not perfectly round and it has an apex to it. The good news is that the artery and nerve are located at the highest level of the peak. There is a space between that peak and where the talus would come into contact with the sinus tarsi device. These devices do not traumatize the artery and nerve to the sinus tarsi.
How Arthroereisis Affects The Achilles Tendon
Myth: Any time one inserts a sinus tarsi stent, the Achilles tendon needs to undergo a lengthening procedure. Many foot physicians believe it is the tight Achilles tendon that forces the displacement of the talus, leading to the obliteration of the sinus tarsi. I have found this not to be true. Furthermore, it is only on a rare occasion that I find it necessary to perform a lengthening procedure. Usually, it is only in an extreme case of flatfoot when the condition is so severe that one needs to perform other osseous procedures.
If the Achilles tendon is the primary etiology, then the talus should stabilize itself after a lengthening procedure of the tendon. This does not occur. One can make a reverse argument that instability of the talus could cause the Achilles to contract and tighten.
The gastroc-soleal complex serves as a powerhouse to aid in the propulsion of the foot. It is a strong supinator of the foot. In patients with hyperpronation, these muscles have to work extra hard to overcome the excessive pronation and perform their regular duty. During the gait cycle, the Achilles immediately senses this excessive strain via mechanoreceptors within the tendon and muscle belly, and action occurs to counteract this pathologic strain on the tissues.
Once one has restored the subtalar joint complex to a better alignment, this eliminates the excessive pronatory forces to the tendon, therefore eliminating the excessive strain on the Achilles. Due to the decreased strain, the mechanoreceptors are able to relax, leading to an “internal” lengthening of the gastroc-soleal complex.
I have had many patients with chronic Achilles tendinitis in whom I have performed a subtalar arthroereisis procedure without an Achilles tendon lengthening. Within a short period of time, there was resolution of Achilles tendinitis. If a subtalar arthroereisis procedure would place an additional strain on the Achilles tendon, it would make the tendinitis get worse, not better.
Furthermore, in regard to patients in whom I have performed the subtalar arthroereisis without an Achilles tendon lengthening, I have not had one patient ever complain of Achilles tendon pain or the development of Achilles tendinitis.
Subtalar Arthroereisis And Flatfoot: What You Should Know
Myth: Subtalar arthroereisis is for flat feet only. This is where some surgeons get into trouble with subtalar stabilization with a sinus tarsi stent. There are many definitions for flatfoot. Some think it implies only a foot that is rigid and completely flat with no arch while others define flatfoot as any foot with a lower than normal arch.
The true indication of a subtalar arthroereisis procedure is instability of the talus on the calcaneus leading to partial or full obliteration of the sinus tarsi. This pathologic condition can occur in patients from ages 3 to 93. Many patients have a very high calcaneal inclination angle, which indicates a high arched foot, yet they exhibit the instability of the subtalar joint complex and suffer from the symptoms of this very common condition.
The ideal patient for subtalar arthroereisis exhibits the deformity but cannot achieve stabilization with custom-molded orthoses. This patient also does not have a deformity that is severe enough for more aggressive surgery. In some situations, the surgeon pushes the envelope and tries an arthroereisis in semi-flexible or rigid flatfoot conditions. Most likely, the procedure will fail in these patients. Arthroereisis as a standalone procedure works the best in mild to moderate cases. Severe cases of flexible flatfoot are better served with a combination of arthroereisis and rearfoot reconstructive procedures.
Many people of all ages who suffer with flexible talar instability can benefit from this minimally invasive, life changing procedure. Do not let the misconceptions or myths deter you from providing this modality to your patients suffering from the ill effects of hyperpronation. When one weighs the possible complications of subtalar arthroereisis versus the complications
of lifelong damage from hyperpronation, I would venture that the choice is obvious.
Dr. Graham is a Fellow of the American College of Foot and Ankle Surgeons and a Fellow of the American Society of Podiatric Surgeons. He practices at the Center for Foot and Ankle Disorders in Shelby Township, Mich. He is the inventor of the HyProCure sinus tarsi device.
For further reading, see “Keys To Preventing Complications With Subtalar Joint Implants” in the January 2010 issue of Podiatry Today or “Techniques And Experiences In Foot And Ankle Surgery,” a supplement to the August 2006 issue.
1. Available at http://www.hyprocuredoctors.com/knowledge/