Ankle Problems > Avascular Necrosis of Talus

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.

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%.

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 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.

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.

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.

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.

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.

 

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