Ankle Joint Replacement
Total Ankle Replacement Explained by Dr. Tim O'Carrigan
Just like Total Hip Replacement and Total Knee Replacement ,Total Ankle Replacement is performed to treat pain and stiffness in the ankle arising from advanced arthritis.
The most common form of arthritis affecting the ankle is osteoarthritis. Osteoarthritis is a disease of cartilage leading to loss of cartilage that eventually leads to bone grinding on bone. Similar to the loss of rubber on your car tyre that can lead to exposure of the underlying casing. This obviously is painful and can lead to swelling, stiffness and if the underlying wear is uneven then it can lead to deformity.
Ankle osteoarthritis is usually caused by trauma. This can be an old fracture or cartilage damage that has occurred from an ankle sprain. Cartilage damage can lead to progressive arthritis over time.
Instability can also lead to arthritis of the ankle - A chronically unstable ankle can lead to accumulated damage to a joint and arthritis with deformity.
Chronic malalignment either above or below the ankle joint can lead to osteoarthritis because of uneven forces that act across the joint leading to uneven cartilage wear. This can include a malunited tibial fracture or severe uncorrected flat foot deformity.
Ankle arthritis can also be caused by inflammatory arthritis such as Rheumatoid Arthritis. This is much less common than osteoarthritis.
The two main surgical treatment options are:
- Ankle fusion
- Total Ankle Replacement
Ankle fusion is where surgery is done to get the tibia and talus bones to join together by preparing the joint surfaces and internally fixing with screws or plates. This obviously eliminates all movement at the ankle joint and therefore relieves pain.
The advantages of an ankle fusion are:
- It relieves pain
- It is robust- once the bones are fused they won’t break down or wear out.
- It can be used to treat all cases of ankle arthritis including cases with severe deformity.
- You can still walk well with a good ankle fusion.
The disadvantages of an ankle fusion are:
- Loss of movement. A fusion by definition eliminates movement. Joints are designed to move so if a joint no longer moves then it increases pressure on surrounding joints to provide movement. This joint/joints is the Subtalar joint and the Talonavicular and Calcaneocuboid joints
- Tendency to arthritis developing in other joints over time- this relates to disadvantage 1- the subtalar joint has a high incidence of developing osteoarthritis in the long term(10-15 years) with an ankle fusion. The only treatment for subtalar osteoarthritis is fusion. That means that the stiffness of the ankle and foot can increase over time.
The advantages of an ankle replacement are:
- It relieves pain just like the ankle fusion
- It preserves movement. Joints are designed to move and it is much better to relieve pain and preserve movement.Ankle replacements do not usually restore normal movement like the patient had when they were young but even preserving small amounts of movement assist with walking more normally and reducing pressure on surrounding joints because of stiffness(see disadvantages of ankle fusion)
- More normal gait- gait studies have shown that a good ankle replacement is better at restoring normal gait than a good ankle fusion but the difference is somewhat subtle.
The disadvantages of an ankle replacement are:
- Ankle replacements are not suitable for all cases of ankle arthritis. A fusion is better if there is:
a. a history of infection
b. severe stiffness
c. marked deformity above or below the ankle- deformity arising from the ankle joint itself can usually be corrected with the ankle replacement but this is not always the case
d. inadequate soft tissue envelope- severe scarring/adherent skin graft/soft tissue stiffness can make a total ankle replacement too risky
- Ankle replacements don’t last forever. As time progresses we are getting more confident with the potential longevity of ankle replacements but historically the revision rate for ankle replacements is higher than total knee or hip replacements. There are many factors that influence this the discussion of which is beyond the scope of this article. The age of a patient has to be considered along with the potential requirement for a revision in the future when one is considering a total ankle replacement.
How do we do an Ankle Replacement?
An ankle replacement is done under a general anaesthetic. My Anaesthetist does an ankle block using an ultrasound machine to increase the accuracy. This provides excellent pain relief for the first 24hours after the surgery. A tourniquet is applied to the leg and the leg is prepped and draped in a standard manner.
A surgical approach to the ankle from the front is performed and this exposes the ankle joint. Using the X-ray machine in theatre a jig is applied that allows accurate cuts to be made on the bottom of the tibia and other instruments allow preparation of the talus.
A metal plate with a roughened surface on the tibial bone side and a smooth surface on the joint side is inserted. This provides initial stability but long term stability is achieved by the bone growing onto the metal component. A similar metal cap is applied to the top of the talus and then a plastic insert ( same special plastic used in knee and hip replacements) is inserted between the metal components.
Alignment, soft tissue balancing and stability are all checked and then the wound is closed in layers and a plaster backslab(not a full cast) is then applied.
Achilles Tendon Lengthening- The achilles tendon can be very tight as part of the arthritic process and sometimes it is necessary to perform an achilles tendon lengthening at the time of insertion of the total ankle replacement. If this is required then we need to keep the patient in a cast for six weeks to allow early healing of the tendon.
Lateral Ligament Reconstruction- Instability can be a cause of arthritis developing in an ankle and this may need to be addressed when a total ankle replacement is inserted. Therefore a lateral ligament reconstruction is sometimes performed as part of an ankle replacement. this does not increase the recovery time.
Subtalar Joint Fusion- Subtalar joint arthritis can be present with ankle arthritis and can be a reason for incomplete pain relief following a total ankle replacement. If it is felt that there is symptomatic STJ arthritis then we sometimes perform a subtalar joint fusion at the same time as the total ankle replacement.
Correcting the alignment outside of the ankle joint is extremely important to a successful total ankle replacement and it is common to require a Heel Shift procedure in addition to the ankle replacement.
This where we perform a cut in the heel bone(calcaneus) to correct either a varus deformity where the heel curls in or a valgus deformity where it angles out.
This is often done through a keyhole procedure and fixed with a screw.
Tarsal Tunnel Release
The main nerve to the foot called the Tibial Nerve passes through a fibrous tunnel on the inside of the ankle (similar to the carpal tunnel in the wrist).
It is sometimes necessary to do a prophylactic release of this tunnel (Tarsal Tunnel Release) when we are performing a heel shift.
With the heel shift the tunnel can narrow down putting pressure on the nerve and this can cause pain and/or numbness on the sole of the foot which we can avoid by performing a tarsal tunnel release before the heel osteotomy.
There are a number of other procedures that are sometimes necessary to correct associated deformity that has contributed to the development of the ankle arthritis and are necessary to achieve a well aligned and well balanced ankle joint replacement.
These can include bony and soft tissue procedures to correct a Flat Foot Deformity or a Cavus Deformity(High Arch)- These deformities are opposites but when severe they can contribute to the development of ankle arthritis.
Two Stage Ankle Replacement
Occasionally a patients deformity is so severe that we need to stage the ankle replacement.
That is where we do an initial procedure to correct all of the deformity but don’t do the ankle replacement and we allow this to heal.
Once it is healed then we do a second stage procedure to perform the ankle replacement. This second stage is usually straightforward because all of the deformity has been corrected.
The second stage is usually done at about three months when we are confident all of the bone and soft tissue procedures performed at that first stage have healed.
The patient’s leg is elevated and circulation observations are performed by the nursing staff overnight. A PCA(patient controlled analgesia) is provided but patients often have little or no pain because of the block. This is good because narcotic analgesics such as morphine are excellent pain relievers but some patients are very sensitive to them causing nausea and they can increase drowsiness.
Patients are usually in hospital 2-3 days. The length of time depends on how mobile the patient is and being cleared by physio. Patients are non weight bearing for six weeks. This is to allow the bone to get some early growth onto the components. To be non weight bearing they can use crutches but there are alternatives. Many patients find crutches difficult because of balance and the strain on the upper limbs. There are scooters available called the “knee walker oz” which many patients find very useful to mobilise in a safe and convenient manner. The physio can make an assessment with the patient about what is the best method to use.
The patient is also discharged home on clexane injections. This is a blood thinner which reduces the risk of DVT. These injections are maintained while the patient is non weight bearing and in a brace. That means 6 weeks. The patient and their partner/family are instructed on how to do the injections by the nursing staff prior to discharge.
The patient is then reviewed 10 days to two weeks post op so the backslab can be removed and the stitches removed. The patient is then placed in a moonboot which can be removed for showering and range of motion exercises. The exception to this is when an achilles tendon lengthening is performed as part of the total ankle replacement. In this case the patient is in a cast for 6 weeks.
We also get a doppler ultrasound to check whether there is a DVT present or not. if it is negative then the clexane is continued but if it is positive then the patient needs to go on to Warfarin or an equivalent. this is co ordinated by the patients local doctor or an outpatient service at the local hospital.
At the six week mark an xray is taken and the patient can start weight bearing as tolerated in the moonboot. The moonboot is continued for another six weeks so you are not walking without a brace for a total of 3 months after a total ankle replacement.
Some physiotherapy may be required but most of the “physio” is walking. that action strengthens the requisite muscles over time.
The patient is then followed up at the six month and 12 month postop points and then 2 and 5 years postoperatively. More frequent reviews will be performed if clinically necessary to ensure that the patient is progressing well and to monitor for any problems.
Like any surgery Total Ankle Replacement has a risk of complications. Each patient is thoroughly assessed preoperatively to identify any particular potential problems their circumstances may create and strategies are utilised to address these issues and mitigate any risks. This is part of the LRSNSW difference.
Complications can relate to the anaesthetic and these are discussed in the article on informed consent- click here
With respect to Total Ankle Replacement there is a risk of:
- Infection- infection can complicate any surgery but in joint replacement of the hip knee or ankle it is a particularly devastating complication. Removal of the prosthesis is usually required in order to eradicate the infection and the salvage would normally require an ankle fusion. Therefore we are extremely careful in theatre to minimise any risk of infection. Careful soft tissue management is also a very important component to maximise the chance of rapid would healing. Fortunately infection of an ankle replacement is very rare.
- Nerve or Blood Vessel injury- Foot and ankle surgery is similar to hand surgery in that there are multiple superficial and deep nerves supplying the foot. The foot is very sensitive which is why foot pain can be very severe and debilitating. We are aware of all the nerves and blood vessels and take great care to try to avoid injury. In total ankle replacement the main nerve at risk is the deep peroneal nerve which passes lateral to our main incision and has to be retracted to allow access to the joint. This stretching can lead to some numbness on the top of the foot typically between the big toe and the second toe. This can reduce or resolve fully over time.
- Wound Healing Problems- Careful protection of the soft tissues during surgery and meticulous suturing of the wound reduces the risk of wound healing problems. Wound problems are unusual and usually superficial but in its worst form can lead to deep infection.
- Fracture- It is possible to have a fracture complicate insertion of a total ankle replacement. This is usually the medial malleolus and can be internally fixed still allowing a successful outcome.
- Stiffness- Arthritis of the ankle is usually associated with a loss of range of motion. The preoperative range of motion will influence how flexible the ankle will be postoperatively. When inserting the ankle replacement we try to strike a balance between flexibility and stability. An ankle that is too “loose” may have a very good range of motion but there is a higher chance of instability. Any range of motion is greater than would be achieved if there was an ankle fusion and even relatively small amounts of movement can assist a more normal walking pattern but it is important to understand that a total ankle replacement will rarely achieve a completely normal range of motion.
- Incomplete pain relief- There are quite a few joints around the ankle which can have arthritis just like the ankle joint and therefore a total ankle replacement whilst relieving the pain from the arthritic ankle it will not relieve pain which may be arising from other joints and therefore the pain relief may not be complete. It can be difficult to determine clinically what contribution various joints are contributing to the overall pain profile. That is why we sometimes combine a total ankle replacement with fusion of another joint such as the subtalar joint.
- Osteolysis- Cysts can develop in bone around joint replacements and if they get big enough they can cause loosening of a component to develop. This can lead to pain. This is called Aseptic Loosening and is the most common cause of joint replacements to fail in the long term. Around the ankle, cysts can lead to fracture if they weaken the bone sufficiently. If recognised in time these cysts can be opened up and cleaned out and bone grafted. This can prevent loosening of the ankle joint replacement and avoid revision. There is less bone stock around an ankle replacement and therefore cysts need to be treated a little more aggressively than they do with knee or hip replacements.
- Dislocation- The total ankle replacement has a mobile special plastic disc that sits between the tibial and talar components. It is possible for this disc to dislocate. This is extremely rare but would be a cause of revision.
- Complex Regional Pain Syndrome- The understanding of pain and how it is caused and experienced by the body as well as its biology is one of the frontiers of modern medicine. Our ability to understand pain will improve the development of medications that will relieve pain more effectively. Complex Regional Pain Syndrome is a spectrum of pain syndromes where someone experiences excessive pain in response to an operation or an injury. Sometimes this can be triggered by a nerve injury where it is called Causalgia. It can occur spontaneously in response to quite innocuous injuries. It is characterised by an oversensitivity and excessive pain with swelling, stiffness and circulation changes. CRPS can complicate any surgery.
If a nerve is divided it can lead to permanent numbness but if it gets caught up in scar tissue this can lead to a painful condition called a neuroma.
If recognised early then it can be treated with appropriate medications and physiotherapy is a very important part of the treatment. Early review by a pain medicine specialist can help reduce the severity of the syndrome and reduce the risk of permanent problems.
Total Ankle Replacement can be an excellent solution to the pain and stiffness from ankle arthritis. With careful patient selection, meticulous insertion and follow up we can make a tremendous difference to the quality of life of our patients.