Avascular Necrosis Resources had the pleasure of interviewing Dr. James K. DeOrio, Associate Professor and orthopedic surgeon at Duke University and the former Director of the Foot and Ankle Fellowship at the Mayo Clinic Jacksonville. Dr. DeOrio is considered one of the foremost experts in the field of orthopedic surgery of the foot and ankle. Dr. DeOrio's interview responses appear as quotations throughout this article.

According to Dr. DeOrio, Avascular Necrosis (or Osteonecrosis) of the talus is usually the result of one of two conditions:

• Trauma (75%)
  
  “Trauma [...] causes a disruption in the blood supply to the talus bone either through (a) a dislocation of the ankle, open or closed, which tears the blood vessel to the talus bone causing the main body of the talus or a part of it to die or (b) a fracture (break) of the talus bone in which the blood vessel to the bone is separated with the bony fragments.”

• Steroid Use (25%)
  
  “Steroid use [...] impairs the flow of oxygen to the talus bone causing it to die.”

Motor vehicle accidents and falls are the most common causes of trauma to the talus that lead to Avascular Necrosis.[1]  Sports such as snowboarding and martial arts are reported to be increasingly frequent causes of talus trauma as well.[2]

The primary factor correlating talus trauma and the eventual development of AVN is the specific type of injury to the talus and how much the injury impacts the blood supply to the bone. Fractures that do not shift or displace the talus much tend to have less of an impact to the blood vessels within the bone and thus are less likely to result in AVN. With fractures, Dr. DeOrio's goal is to “fix the fracture and hope there is enough blood supply to the bone to allow it to heal.” Alternatively, “treatment for the dislocation is to relocate the bones in proper position, repair the soft tissues and hope the blood supply to the bone may have been stretched but not torn apart.” Unfortunately, however, complete talus dislocation usually results in the development of AVN most of the time.[3]

In the early onset stages of Avascular Necrosis of the talus, patients may begin experiencing symptoms very similar to arthritis where basic movement of the ankle alone can cause tightness and discomfort. In fact, early stage AVN of the talus is often misdiagnosed as osteoarthritis. As the AVN effects on the talus progress, the lack of blood supply causes deformation, roughening, and eventual collapse of the bone.  With the bone no longer able to provide adequate support, the cartilage then crumbles and gives way, resulting in a bone-on-bone condition.  Dr. DeOrio's analogy is that it's “sort of like a thick coat of paint on a balloon -- if the balloon breaks, the paint more or less crumbles because of lack of support.” Collapse and the process of collapse can become completely debilitating and make walking even short distances excruciatingly painful and sometimes impossible.

The unique structure of the talus as well as its vascular connections make treating Avascular Necrosis of the talus quite challenging. The major blood supply to the talus comes by way of an artery (posterior tibial artery) that is precariously attached to the outside far end of the bone.

Posterior tibial artery attachment to the talus

GNU FDL Image

If this fragile arterial connection is torn or detached, blood cannot reach the talus -- in which case there is little hope the areas impacted by Avascular Necrosis can naturally heal. In regards to non-surgical treatment options for AVN of the talus, according to Dr. DeOrio, “Except for bracing and limited activity to avoid discomfort, there are no great non-surgical treatments.” After exhausting all reasonable non-surgical treatment options, doctors normally turn to one of the following surgical procedures:

Surgical Treatment Options

Fusion of the ankle

Ankle fusion surgery is a procedure where the worn-out or damaged joint surfaces are removed or prepared and then the ankle is fused together using metal implants.

Dr. DeOrio offers insight into the ankle fusion procedure: “For the fusion, the dead bone has to be removed and if the defect is not large then the patient can have a primary ankle fusion with fixation of the talus to the tibia. If there is involvement of the joint below the ankle, called the subtalar joint, then both the ankle and the subtalar joint need to be fused. Rarely, only the subtalar joint needs to be fused. An ankle or a subtalar fusion is a good option. However, combined they leave the hindfoot very stiff. Furthermore, if there is a large piece of dead bone in the ankle, it can be replaced with frozen bone from cadavers and a rod inserted going up from the heel into the tibia (shin bone).”

The resulting joint is permanently stiff, but usually results in a pain-free joint, at least for a while. A healed ankle fusion is quite durable and allows patients to walk with a near normal stride and motion. However, surgeons have found that a fused ankle imposes a number of additional stresses on other joints of the foot which over time can result in painful arthritis or damage to these other joints. In fact, many ankle fusions require later surgery to correct the resulting new problems.[4]

Ankle fusion surgery has been the most commonly suggested treatment option for severe degenerative ankle conditions, such as advanced stage Avascular Necrosis of the talus, because until recently there have not been many widely accepted or successful ankle replacement products. However, with an understanding of ankle fusion limitations, many doctors foresee total ankle replacement becoming more commonplace in the near future.  In fact, Dr. DeOrio explained, “many orthopedic surgeons, understanding that the patient may later be a candidate for ankle replacement, have begun doing fusions with preservation of the bone and ligaments. This can be done arthroscopically (through small puncture holes) or openly through the same (front of the ankle) incision an ankle replacement would be done years from now. The key is to leave the small bone of the ankle, the fibula, in place and not remove it as some techniques for ankle fusion have required in the past.” This type of ankle fusion procedure can provide immediate relief to patients deemed unsuitable for ankle replacement, such as younger patients or patients with still-active degenerative bone conditions, while still allowing for a permanent long-term fix down the road.  

Total ankle replacement

Just ten years ago, total ankle replacements were not considered very viable treatment options, let alone suitable for complicated patient cases such as Avascular Necrosis of the talus. Now, however, general opinion about ankle replacement is changing thanks to improvements in current products and increasingly positive clinical trial and study results. In addition, there are new ankle replacement products with significant advancements that have arrived on the market which should, hopefully, make ankle replacement as trusted and common of a procedure as knee or hip replacement in the future.

Early ankle replacement devices suffered from a number of shortcomings and consequently earned less than positive reputations. Clinical studies and professional reports have shown some early generation ankles sometimes loosen, sink, or migrate over time. In some cases, these early ankle replacements would wear out in as little as two to five years.[5]  Second generation ankles replacement devices, such as the DePuy Agility and the S.T.A.R. (Scandinavian Total Ankle Replacement), have since emerged and improved upon early issues and “demonstrated reasonable functional outcomes.”[6][7]  In fact, Dr. DeOrio states that the S.T.A.R. ankle replacement has “been put in worldwide more than any other ankle.”

Newer ankle replacement products, such as those just hitting the market in recent years, have drastically raised the bar yet again by introducing radically new features aimed at squelching doubts raised by early ankle shortcomings once and for all. This new generation of ankle replacement devices improves upon three major areas: ankle anchoring, accurate placement and installation, and enhancing the longevity and serviceability of the implant.

To help illustrate some of the improvements found in new ankle replacement devices, let's compare the long used DePuy Agility LP (4th Generation) ankle and the newly released Wright Medical Technology INBONE Total Ankle.  The DePuy Agility LP is the 4th generation revision of a traditional design used for over 20 years.[8]  The Agility system consists of a block of ongrowth metal inserted into the ankle.  It has a plastic portion affixed to it which contacts another metal piece that is fitted into the talus. The fibular bone needs to be locked to the tibia and this is usually done with a plate and two screws.  In contrast, the INBONE Total Ankle product is a radically new design characterized by stems inserted deeply into the tibia and talus so that the bone grows onto the metal.  Mounting the ankle replacement device right through the center of the tibia and talus is reported to provide better balance while spreading pressure forces through the entire bone and mount area. In short, centralized tibia and talus mounting helps to spread out the load over a larger area and reduces focused pressure points while also reducing off-axis twisting type forces on the ankle. Compare the images below and note the two screws and plate in the image on the left and then note the single long stems in the image on the right.
 

Dr. DeOrio, who has personally completed over 180 total ankle replacement surgeries using the INBONE product, is able to offer the following first-hand expertise as to why the INBONE is such a leap in ankle replacement technology:

“Because the bone needs to grow into the metal roughened titanium spray, the metal needs to be stable on the bone for that to happen. If the metal is constantly shifting on the bone, ingrowth or ongrowth will not occur. The designers of the INBONE ankle have designed a modular stem that goes up in the tibia. This is advantageous for increased stability of the component in the tibia because sometimes the patients can have avascular bone on the top side of the ankle joint, the tibia. The INBONE ankle also only cuts off the top of the talus bone whereas other ankle designs call for resection of the sides. This give the talus bone additional stability which is especially important if part of the talus bone is not alive. The standard stem for the talar component then sits down into the talus. Additionally, the design engineers have created a much longer stem, the talocalcaneal stem. This stem goes through the subtalar joint into the calcaneus. For the same reasons cited above for the tibial stem the more stable the prosthesis is at time of insertion, the greater the chance the bone will grow onto the metal and lock the prosthesis in place. And because this long stem is inserted in more bone, it is more stable than shorter fixation methods.” (Editor's note: Being a new product, this new modular talocalcaneal stem is still pending FDA approval.) “Currently, efforts are being made to allow surgeons to use the stem in special cases until it becomes approved for other cases.”

One may visually compare the two products side-by-side (as in the images above), and the differences in engineering are apparent. Beyond enhanced stability, another major advantage to the new style of engineering found in the INBONE Total Ankle is that it provides the maximum bearing surface area. More bearing surface area translates to lower stresses on the ankle implant components. The point of this design change is to spread out the load and forces over the largest area possible in order to reduce individual points of wear and hopefully help these new devices to last longer.

Engineering advancements aside, an ankle replacement device is only as good as the quality of its installation. An improperly aligned or poorly mounted device will lead to slippage, premature wear, implant failure, or possible harm to a patient. Thus, another critical technological leap that puts the new INBONE Total Ankle in an entirely higher class is its custom-created surgical installation kit. The custom installation instrumentation contains built-in stabilization, alignment, and surgical cutting guides, making the surgical installation process much more exact.

The installation of other ankle replacement products is a more manual process, placing a much higher demand on the skill of the surgeon to ensure proper drilling, cutting, and installation.  Hence, the repeatable accuracy of the INBONE Total Ankle's installation instrumentation is considered by many doctors to be the benchmark for all future products.  Indeed, Dr. DeOrio informs us that DePuy has a new device called the Mobility Total Ankle now under FDA trials which, according to unreleased  information, “is a three-component, cementless, unconstrained, mobile-bearing prosthesis with a dedicated instrumentation system. The prosthesis incorporates some unique design modifications which allow minimal bone resection and the instrumentation allows repeatable and accurate surgical outcomes.” This early information about the latest offering from DePuy is likely confirmation that many implant devices of the future will utilize a custom-engineered installation kit to ensure safer and more accurate installation.

Even with all the advancements and improvements in ankle replacement devices, Dr. DeOrio reports that some insurance companies still treat total ankle replacement as “investigational and experimental.” Clearly the bad reputation earned by some of the earlier devices has left a lasting impression with some insurers. Hopefully, news of the successful installations and statistics reflecting positive results will soon turn the tide of acceptance such that the replacement of ankles will be considered as common as that of knees or hips. In the meantime, patients who are deemed potential candidates for ankle replacement should be prepared to work with doctors and insurance companies in case justification for the procedure is required.

In summary, patients with Avascular Necrosis of the talus may now have new surgical options to consider. The INBONE Total Ankle device is one of the first of a new breed of ankle replacement products leveraging significant advancements in medical and mechanical engineering. Furthermore, other companies like DePuy are already engaged in clinical trials of very promising devices as well. If you are a patient with Avascular Necrosis of the talus and are considering a surgical correction, there are definitely very exciting new devices now on the market making ankle replacement a much more viable treatment option for AVN then ever before.

Core decompression of the talus

Core decompression of the talus is a process where a surgeon uses a special hollow drill bit to remove cores (plugs) of bone from a necrotic site. Some studies, such as the 1996 study of 11 patients with AVN of the talus done by doctors at Johns Hopkins, yielded very promising results where patients reported significant improvement seven years after undergoing a core decompression surgery.[9]  Furthermore, in 2003, Dr. David Hungerford, Sr., former chief orthopedic surgeon at Johns Hopkins, clarifies the viability and application of core decompression of the talus by writing:

“While I don't consider it [core decompression of the talus] 'experimental', AVN of the talus is so rare that there is very little experience with it. As with core decompression of other joints, there is not a lot of evidence of revascularization, but it does stimulate new blood supply and new bone formation and this seems to 'stabilize' the bone. The evidence is not as strong for the talus as it is for the hip simply because there are so few cases. It is quite effective for pain relief.”[10] 

In short, Dr. Hungerford confirms that core decompression of the talus is undeniably successful for pain relief, although it is unlikely to aid in healing and revascularization.
 

Muscle flap transplant

A muscle flap transplant is a very new procedure in which a small muscle on the outside of the foot is moved into the talus. The idea behind this procedure is that the blood supply to the muscle will help improve and sustain the blood supply to the talus. Short-term results by the researching hospital seem promising.[11]
 

Bone graft

Some Avascular Necrosis cases with specific matching conditions may be candidates for a “free vascularized bone graft,” a procedure where tiny blood vessels attached to a piece of bone are transplanted into the talus. The major limitation to free vascularized bone grafting of the talus is that there must be an adequate blood supply for both the graft and the surgical site.

 
Dr. James K. DeOrio
Dr. James K. DeOrio is Associate Professor at Duke University and orthopedic surgeon at Duke University Hospital.  Formerly, Dr. DeOrio served as Director of the Foot and Ankle Fellowship at the Mayo Clinic Jacksonville.  Today, Dr. DeOrio is considered one of the foremost experts in the field of orthopedic surgery of the foot and ankle as he has done more INBONE ankle replacements than anyone in the world (180) and currently does more ankle replacements in the U.S. than any other surgeon.  Please see his complete profile for practice and contact information.

References
[1] American Academy of Orthopedic Surgeons ,”Fracture of the Talus”. Retrieved on 2008-03-05.
[2] Dr. Stepfan Eriksson, “The Ankle”, Fight Times.  Retrieved on 2008-03-12.
[3] The Institute for Foot and Ankle Reconstruction at Mercy Medical Center, “Avascular Necrosis of the Talus”. Retrieved on 2008-03-05.
[4] “Ankle Fusion Surgery: An Option for the Treatment of Degenerative Arthritis”, www.allaboutarthritis.com. Retrieved on 2008-03-05
[5] Gladius Lewis , PhD, “Biomechanics of and Research Challenges in Uncemented Total Ankle Replacement”, Clinical Orthopaedics and Related Research (Number 424, pp. 89-97).
[6] Mark E. Easley, MD, Christopher J. Vertullo, MBBS, FRACS, W. Christopher Urban, MD and James A. Nunley, MD. “Total Ankle Arthroplasty”, J Am Acad Orthop Surg, Vol 10, No 3, May/June 2002, 157-167.
[7] PLR Wood, H Prem, and C Sutton. “Total Ankle Replacement: Medium-term results in 200 Scandinavian Total Ankle Replacements”, Journal of Bone and Joint Surgery,  May 2008.  Retrieved 2008-03-19.
[8] “The Agility™ LP Total Ankle Replacement: An Alternative to Fusion”, http://www.myanklereplacement.com. Retrieved on 2008-03-23.
[9] Michael A. Mont, Lew C Schon, Marc W. Hungerford, and David S. Hungerford. “Avascular Necrosis of the Talus Treated by Core Decompression”, The Journal of Bone and Joint Surgery, May 1996, 827-830.
[10] “Core Decompression for AVN talus”, http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=00B6HG.
[11] The Institute for Foot and Ankle Reconstruction at Mercy Medical Center, “Avascular Necrosis of the Talus”. Retrieved on 2008-03-05.
[12] Maurice Laude, “Anatomy of the talus and the surrounding bony and articular structures”, Laboratory of Anatomy and Organogenesis, Amiens Medical School. Retrieved on 2008-03-10.
[13] “The INBONE Total Ankle”, Wright Medical Technology, http://www.inbone.com.

Conflict of Interest Disclosures
Dr. James K. DeOrio is a consultant for Wright Medical Technology, the manufacturer of the INBONE Total Ankle device.

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