Avascular Necrosis of the Talus

Definition

Avascular necrosis (AVN) is a process that is due to the temporary or permanent loss of the blood supply to an area of bone. As a result, the bone tissue dies and the bone collapses. If AVN involves the bones of a joint (e.g.: the talus) it often leads to destruction of cartilage, resulting in arthritis and pain. In the case of the talus, 3 joints can be affected; the ankle joint, the talonavicular joint (a joint in the middle of the foot), and the subtalar joint (the joint below the ankle). The ankle joint allows up and down movement of the foot, while the subtalar and talonavicular joints allow in and out movement of the foot. The normal function of the subtalar joint is to allow walking on uneven surfaces, inclined surfaces, ladders, etc. without falling.

Causes of AVN

AVN can be caused by 2 large categories – trauma and nontraumatic. In the case of trauma, a fracture (breaking) of the bone disrupts the blood supply to the bone leading to AVN. There are many causes of nontraumatic AVN. These include idiopathic (no cause is ever found), steroids (eg. anabolic and high dose corticosteroids (prednisone) given for such diseases as rheumatoid arthritis, lupus, and cancer), excess alcohol consumption, sickle cell anemia, radiation treatments, and chemotherapy.

Anatomy

Above is a diagram of a foot. The talus is pictured, along with the joints it creates.

Avascular Necrosis

These images demonstrate the typical appearance of talar AVN. These are not X-rays, but an MRI, which is the most useful imaging test to diagnose AVN. Note the presence of the white (left) or black (right) irregular shadows in the middle of the talus, which is the dead bone.

Avascular necrosis of the talus can be quite devastating, and lead to total loss of the ankle joint with arthritis, deformity and pain. The development of AVN is determined to a large extent by the type of the talus fracture. There are those fractures which are not very severe (they do not shift or displace much), and in these fractures, the incidence of AVN is lower. However, when the talus dislocates out of the ankle socket, the incidence of AVN is very high, almost 100%.

This is a typical fracture of the talus. The fracture line is irregular, but there is not very much displacement of the two pieces of the fractured bone. This is called a minimally displaced fracture, and although AVN could develop, it is less likely.                 These are also examples of a fracture of the talus with very little displacement. The development of AVN is unlikely in these fractures.                   On the left, is an XR of a talus with fracture where the main part of the talus in the back (called the body of the talus) is dislocated. The same applies to the picture on the right, which is a CAT scan where the fracture is very displaced. In both these fractures, the development of AVN is more likely.                 In this fracture the entire body of the talus has dislocated out of the back of the ankle, and AVN develops in 100% of these fractures.

The development of AVN is related to the type of the fracture, and not the manner in which it is treated. This is because of the blood supply to the talus, which is torn with certain fracture types, and not with others, and regardless of how the talus is put back together, the blood supply cannot change. Interestingly however, the presence of AVN does not change the rate of healing of the fracture. We call the healing of the fracture “union”. If the fracture does not heal at all, this is a “non-union”, and if the fracture heals in a poor position, this is called a “mal-union”. Even in fractures where AVN does develop, the fractured bone invariably goes on to union. There seems to be just enough blood supply left coming across the fracture to heal it, but not enough to maintain the blood supply for a totally viable talus. This is important when planning treatment following treatment of the fracture.

The fracture on the left has been treated with screws. Although the fracture has healed and the talus is in very good position, AVN has developed. Note the overall color of the talus bone in the front (which is normal, compared to the white color of the bone in the back, which is diagnostic of AVN.)

The care of the limb after any fracture in the foot and ankle is based upon the premise that a limited amount of standing, walking and bearing weight on the foot is permissible. This makes sense, since pressure on the fracture with walking before the fracture has healed will lead to a shift in the bones resulting in a non-union, or a malunion. This has particular relevance with the fracture of the talus where one is concerned about the development of AVN, since the surgeon is understandably concerned about the consequences of bone healing if AVN occurs. If AVN does occur, the talus can break up into small pieces, fragment and collapse. This is not however predictable. The majority of fractures which develop AVN do not go on to collapse, and the AVN is limited to small segments of the talus.

Orthopedic surgeons were understandably concerned about the development of AVN, and as such limited the patient from walking on the leg at all, worrying about the possibility that AVN would progress and lead to collapse of the bone. In fact, this has never been demonstrated to be necessary, and once the fracture has healed, bearing of weight on the leg is actually permissible. There is no evidence to suggest that the patient has to remain off the foot using crutches for an indefinite period of time to prevent the talus from collapsing further. The foot may need to be protected, using a boot or a brace, and certain activities with impact on the leg may need to be restricted, but walking should be acceptable. Once collapse of the talus occurs, then problems begin, including arthritis and deformity. These are very difficult to correct surgically, but with newer reconstructive treatments available have been very successful.

Treatment Options

1. Fusion

The classical way to treat talar AVN is with an ankle fusion.

This is talar AVN due to chemotherapy for cancer. You can see on the left, that the talus is white and collapsed. This patient was treated with an ankle fusion. This was done by opening the joint, removing all the cartilage, and placing screws across the ankle to hold it.

This is an example of a very severe form of AVN of the talus. Most of the talus is white, the shape of the talus has changed, since it has collapsed, and there is very little cartilage space left in either the ankle or the subtalar joints, indicating severe arthritis. The arthritis and the AVN was treated as is shown in the pictures below by removing the screws which were inserted to fix the original talus fracture, and then by inserting screws into the back of the joints of the foot to fuse the joints together. This operation is called a triple arthrodesis.

A triple arthrodesis has been performed here. This operation only corrects some aspects of the problem, the arthritis of the hindfoot and the deformity. It does not correct the arthritis of the ankle, which still remains.

2.  Total Ankle Replacement

Traditionally, when arthritis of the ankle joint occurs after AVN and talus fracture, a fusion of the ankle has been recommended. This fusion is a complicated operation, and the results of the fusion are not always predictable and ankle motion is lost. For this reason, alternative treatments are desirable. In particular, instead of the fusion of both the ankle and the subtalar joint which is illustrated below, following a fusion of the subtalar joint, an ankle joint replacement can be performed. This is an exciting alternative, and we are gaining more experience with this surgery over time.

Severe AVN in this patient was associated with collapse of the talus, and arthritis of both the ankle and the subtalar joints. Traditional treatment has been to fuse both the ankle and the subtalar joints. The problem with fusion, is that there is limited blood supply into the talus, and the success of the fusion is not always that good.                   The patient above was treated with a subtalar fusion with a specialized bone graft inserted into the subtalar joint, in order to lift up and elevate the height of the back of the foot. 5 months later, once the first surgery was done successfully, a total ankle replacement was performed. Look at the right hand picture, and you will see that the screws from the fusion and the fracture have been removed and the ankle replacement inserted.                 This is the range of up and down motion (called dorsiflexion and plantarflexion) of the ankle following the total ankle replacement after a fracture of the talus associated with AVN.

Now, with newer total ankle replacement implants, we can make custom implants when necessary.

	This a picture on the left with talar AVN and ankle and subtalar arthritis. A custom total ankle replacement with a long-stem was used to simultaneously replace the ankle and fuse the subtalar joint. This is advantageous because it fixes the subtalar pain with the fusion and it also provides a larger base for the talus implant since a majority of the talus is missing or dead.

3. Core Decompression

Another surgical option is core decompression. The principal behind this technique is to drill a hole in the talus, which may lead to decompression of the bone and resultant healing of the talus because it increases the blood supply to the talus. This has also been successfully used for AVN of other joints/bones. It can only be used at the early stages of AVN. 

	This a picture from the operating room of a patient having a core decompression. A large bore is placed into the talus.

4. Muscle Flap

Another option is a vascularized muscular transfer. The principal behind this technique is to swing a muscle to this area which brings a blood supply with it.

	This is a patient being prepared for the vascularized graft.

5.  Vascular Bone Graft

Another option is a vascularized bone transfer. The principal behind this technique is to place a bone with its blood supply to the talus.

6.  Shock Wave

Yet another option for talar AVN is the use of shock wave (extracorporeal shock wave therapy – ESWT). It is a high-intensity acoustic application (also used to break up kidney stones). No surgery is required, but you do have to be put to sleep in the operating room. The application of shock wave therapy in certain musculoskeletal disorders has been around for approximately 15 years, and the success rate in non-union of long bone fracture, calcifying tendonitis of the shoulder, tennis elbow and plantar fasciitis ranged from 65% to 91%. The complications are low. Recently, shock wave therapy was extended to treat other conditions including avascular necrosis of femoral head, patellar tendonitis (jumper's knee), osteochondritis dessicans and non-calcifying tendonitis of the shoulder. Shock wave therapy is a novel therapeutic modality without the need of surgery and it’s risks. It is convenient and cost-effective. The exact mechanism of shock wave therapy remains unknown. Shock wave induces blood vessel formation which can treat the underlying cause of talar AVN.

7.  Total Talus Replacement

Lastly, a complete total talus replacement can be used.

This is a patient with talar AVN. Notice the talar collapse and resulting arthritis.

This is a X-ray taken in the operating room of the above patient, after removal of his talus.                   This is picture from the operating room, holding the talar implant. It is made out of metal and has the same shape as the normal talus.                     This is the X-ray with the total talus implant placed in the patient.

This technique is extremely new, and we do not have long-term results yet. 

Summary of the Treatment of AVN of the Talus

1. Fusion of the ankle: This has been a treatment recommended but of course glues together the ankle and limits the up and down range of motion permanently. The fusion is not easy to accomplish, and the success rate of this type of surgery can be unpredictable.

2. Total ankle replacement: Total ankle replacement is now an accepted treatment for ankle arthritis, but cannot always be performed if AVN is present. The ankle replacement must have a good bone to sit on, and if the AVN is extensive, it cannot be performed. However, as illustrated here, if a fusion of the subtalar joint is performed first (sometimes using a custom implant), there is often sufficient bone underneath the talus then to support the ankle prosthesis.

3. Drilling of the talus (decompression): There is a lot of evidence that by creating a hole with either a drill or a device that looks like a kitchen tool used to core an apple, that we can increase the blood supply to the talus. The drilling creates little holes and channels that allow tiny little blood vessels to grow and improve the blood supply to the talus.

4. Muscle flap: All muscle has a blood supply to it in order to stay alive. We have developed an operation which moves a small muscle on the side of the outside of the foot into the talus. This is a new procedure, and with the short term follow up of these patients, the results seem to be good.

5. Free vascularized bone graft: It is possible to take a tiny blood vessel attached to a piece of bone and using the microscope, to transplant this into the talus.

6. Shock wave (ESWT): This is a nonsurgical method that increases the blood supply to the talus.

7. Total talus replacement: This is a novel technique of replacing the talus with a metal implant.