The ankle joint is made up of three bones: the lower end of the tibia (shinbone), the fibula (the small bone of the lower leg), and the talus, the bone that fits into the socket formed by the tibia and fibula. The talus sits on top of the calcaneus (the heel bone). The talus moves mainly in one direction. It works like a hinge to allow your foot to move up and down.
Ligaments on both sides of the ankle joint help hold the bones together. Many tendons cross the ankle to move the ankle and the toes. (Ligaments connect bone to bone, while tendons connect muscle to bone.) The large Achilles tendon at the back of the ankle is the most powerful tendon in the foot. It connects the calf muscles to the heel bone and gives the foot the power for walking, running, and jumping.
Inside the joint, the bones are covered with a slick material called articular cartilage. Articular cartilage is the material that allows the bones to move smoothly against one another in the joints of the body. The cartilage lining is about one-quarter of an inch thick in most joints that carry body weight, such as the ankle, hip, or knee. It is soft enough to allow for shock absorption but tough enough to last a lifetime, as long as it is not injured.
Surgery to replace the ankle joint with an artificial joint (called ankle arthroplasty) is becoming more common. Recent advances in the design of the artificial ankle and changes in the way the operation is performed have made artificial ankle replacement a growing alternative to ankle fusion for the treatment of ankle arthritis. The restoration of range of motion is the key feature in favor of ankle replacement with respect to arthrodesis. There is another very important aspect to ankle replacement in that it avoids the stresses that occur following ankle fusion or arthrodesis. When an ankle joint is fused, there is of course no up and down movement in the ankle. There does however remain for some patients a limited amount of up and down movement which occur in the adjacent joints.
Indications : The ideal patient, is someone who is over the age of 50, is not too heavy, and is not extremely active
Patients with primary or posttraumatic osteoarthritis with relatively low functional demand.
Patients with severe ankle rheumatoid arthritis but not severe osteoporosis of the ankle.
Patients suitable for arthrodesis but rejecting it.
Contraindications are :
Varus or valgus deformity greater than 15 degrees, severe bony erosion, severe talus subluxation.
Substantial osteoporosis or osteonecrosis particularly affecting the talus.
Previous or current infections of the foot.
Vascular disease or severe neurologic disorders.
Previous arthrodesis of the ipsilateral hip or knee or severe deformities of these joints.
Capsuloligamentous instability and hindfoot or forefoot deformities affecting correct posture.
Objectives of the prosthetic design for ankle joint replacements are:
To replicate original joint function, by restoring an appropriate kinematics at the replaced joint
To permit a good fixation of the components, which would involve an appropriate load transfer to the bone and minimum risk of loosening
To guarantee longevity of the implant, which is mainly related to wear resistance
Feasibility of implantation, because of the small dimensions of the joint
Risks for any anesthesia are: Allergic reactions to medicines, Breathing problems Risks for ankle replacement surgery are:
Allergic reaction to the artificial joint
Ankle weakness, stiffness, Pain or instability
Blood vessel damage
Bone break during surgery ,Malleolar fracture
Dislocation of the artificial joint
Loosening of the artificial joint over time
Deep infection of the joint, Wound infection
Delayed wound healing or breakdown
DVT or pulmonary embolism
Failure of implant ,Further surgery needed ,Fusion needed following replacement surgery