Anatomy of the Ankle
The ankle joint is more complex than you might initially think. It is not a simple “ball and socket” type of joint like you have in your hip or shoulder. It is a type of hinge joint, and it is made up of three joints. One of the joints is called the talocrural joint; the ankle joint proper. The second joint is called the subtalar joint; also known as the talocalcaneal joint. The third is called the inferior or distal tibiofibular joint. These names sound complicated, but they are just descriptions of the areas or bones that come together to form the joint. The ankle joint proper, talocrural joint, is the area where the lower leg meets a bone in the foot called the talus. This is the area we are referring to when we are talking, in general, about the ankle. This joint is also where most of the weight bearing occurs in the ankle. However, the talus bone in the foot also sits upon another bone, the calcaneus. The calcaneus is your heel bone. This is the bone that transmits a lot of the weight bearing to the ground. The talus bone above it does not touch the ground in normal functioning feet and ankles. The distal tibiofibular joint is a joint that forms between the two bones of the lower leg; the tibia (shin bone) and fibula. It is these three joints that allow for the full range of motion in the ankle; up and down, side to side, and all around. In the places where different bones come together (joints), there is the need to reduce friction during movement of the bones. The ends of bones within joints are covered in a very smooth type of cartilage called articular cartilage. Articular cartilage is excellent at reducing friction during movement. However, over time, or due to injury, illness, or infection, the articular cartilage can become damaged or wear away. When this happens inflammation is usually the result, and with inflammation comes pain, discomfort, and eventually dysfunction.
Injuries and Problems of the Ankle Joint
One of the more common causes of pain and dysfunction in the ankle joint is arthritis. Research has shown that about 1-7% of patients have osteoarthritis in this joint. The pain is caused when the bones in the ankle joint lose the protective and friction reducing covering of cartilage, and the joint becomes “bone on bone.” This can be from wear and tear, like in osteoarthritis, but also can be from traumatic injury, rheumatoid arthritis (RA), or infection. End-stage ankle arthritis is the most common cause leading to total ankle replacement. Some research has shown that up to 78% of cases of painful end-stage ankle osteoarthritis were due to post-traumatic ankle osteoarthritis.
Types of Surgical Interventions for the Ankle
There are two general types of surgical options for treating ankle pain and dysfunction. They are arthrodesis or ankle fusion surgery, and total ankle arthroplasty or total ankle replacement (TAR) surgery. The best candidates for ankle replacement surgery generally have a lower body mass index (BMI), adequate bone health for implantation, limited or correctable ankle deformities, a stable foot, and are middle aged or elderly.
In arthrodesis surgery there is a fusion of the bones of the ankle, specifically the tibia, fibula, and the talus. This procedure provides very good pain relief, but you lose the range of motion in the joint, because the bones are completely connected together into one piece. This is the traditional ankle surgery technique for treating end-stage osteoarthritis in the ankle.
Total Ankle Replacement (TAR)/Arthroplasty
In total ankle arthroplasty, medical implant components are used to replace the damaged bone, cartilage, and joint surfaces in the ankle joint. The earliest forms of this surgery used two components, one of metal and one of a type of plastic. These early (1st generation) implants gave poor results and had high failure rates, and were abandoned. Over the last 30-plus years there have been a few phases (2nd, 3rd, and 4th generation) of improvements in ankle joint replacement implant technology. One of the most common types of implants is made up of three components; however there are newer two component designs still being developed and used with excellent results. There are a variety of implant types for total ankle replacement, but the modern types typically come in 3 forms:
- Components with tibial stem
- Components with bars
- Components that are flat
Your surgeon will discuss with you the best options for your particular needs.
In the total ankle replacement surgery, the surgeon will typically enter in through the front of the ankle joint. The damaged portion of the lower leg bone (tibia) will be removed and be replaced with a metal and plastic implant. The damaged portion in the foot bone (talus) will be removed and replaced with a metal implant. If there is a need to correct any deformity or joint angle problems, the surgeon will make adjustments to address these issues. After the damaged bone is removed, the surgeon will use trial components in the joint to get an accurate measure of the size of the final implants required to have the best range of motion and stability possible.
After the final implants are selected and inserted into the appropriate areas, the surgeon will do a final check of the stability and range of motion of the ankle joint. Note that some types of implants use bone cement, others do not. Your physician will discuss the particular details of your implant type with you prior to your surgery. After implantation of the components, the surgeon will close the incision with sutures or staples and the wound will be dressed and bandaged. You will be transferred to the post-op recovery room after the surgery is complete.
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