Avascular Necrosis of the Talus

In these images, are the very typical appearance of the bone associated with AVN of the talus. These are not an XR but an MRI, which is the most useful imaging test to diagnose AVN. Note the presence of the white or black irregular shadows in the middle of the talus, which is the dead bone.

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 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.

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.

This patient was treated for AVN of the talus with a triple arthrodesis, seen on the left XR, and then followed four months later with a total ankle replacement seen in the right hand two pictures. The ability to perform a total ankle replacement depends to some extent on the quality of the talus bone, and the severity of the AVN.                 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.

The problem with AVN of the talus, is that blood supply does not simply return, and there are very few ways to improve the circulation to the talus. Below is a list of some alternative ways we are able to treat this condition.

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, there is often sufficient bone underneath the talus then to support the ankle prosthesis.
   
   
3. Drilling of the talus. 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.