Ankle replacement
Encyclopedia
Ankle replacement, or ankle arthroplasty, is a surgical procedure to replace the damaged articular surfaces of the human ankle joint with prosthetic components. This procedure is becoming the treatment of choice for patients, replacing the conventional use of arthrodesis
, i.e. fusion of the bones. The restoration of range of motion is the key feature in favor of ankle replacement with respect to arthrodesis. However, clinical evidence of the superiority of the former is still to be demonstrated.
and the excellent results attained by arthroplasty
at other human joints have encouraged numerous prosthesis
designs also for the ankle
. In the following decade, the disappointing results of long-term follow-up clinical studies of the pioneering designs has left ankle arthrodesis as the surgical treatment of choice for these patients. More modern designs have produced better results, contributing to a renewed interest in total ankle arthroplasty
over the past decade.
Nearly all designs from pioneers featured two-components; these designs have been categorized as incongruent and congruent, according to the shape of the two articular surfaces. After the early unsatisfactory results of the two-component designs, most of the more recent designs feature three-components, with a polyethylene
meniscal bearing interposed between the two metal bone-anchored components. This meniscal bearing should allow full congruence at the articular surfaces in all joint positions in order to minimize wear and deformation of the components. Poor understanding of the functions of the structures guiding ankle motion in the natural joint (ligaments and articular surfaces), and poor restoration of these functions in the replaced joint may be responsible for the complications and revisions.
joint replacement
s are:
As with other joint replacement
s, the traditional dilemma between mobility and congruency must be addressed. Unconstrained or semiconstrained designs allow the necessary mobility but require incongruent contact, thereby giving rise to large contact stresses and potentially high wear rates. Conversely, congruent designs produce large contact areas with low contact stresses but transmit undesirable constraint forces that can overload the fixation system at the bone-component interface.
The general contraindications are:
Other potential contraindications such as capsuloligamentous instability and hindfoot or forefoot deformities affecting correct posture, are not considered relevant if resolved before or during this surgery.
Clinical ankle scores, such as the American Orthopaedcic Foot and Ankle Society (AOFAS) is an outcome rating system for ankle replacements. It is composed of the parameters pain (max 40 points), function (max 50 points) and alignment (max 10 points). Further outcome instruments include radiographic assessment of component stability and migration, and the assessment of its functionality in daily life using gait analysis
or videofluoroscopy
; the latter is a tool for three-dimensional measuring of the position and orientation of implanted prosthetic components at the replaced joints.
Arthrodesis
Arthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical...
, i.e. fusion of the bones. The restoration of range of motion is the key feature in favor of ankle replacement with respect to arthrodesis. However, clinical evidence of the superiority of the former is still to be demonstrated.
History
Since the early 1970s, the disadvantages of ankle arthrodesisArthrodesis
Arthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical...
and the excellent results attained by arthroplasty
Arthroplasty
Arthroplasty is an operative procedure of orthopedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced with something better or by remodeling or realigning the joint by osteotomy or some other procedure.-Background:Previously, a popular form of arthroplasty was...
at other human joints have encouraged numerous prosthesis
Prosthesis
In medicine, a prosthesis, prosthetic, or prosthetic limb is an artificial device extension that replaces a missing body part. It is part of the field of biomechatronics, the science of using mechanical devices with human muscle, skeleton, and nervous systems to assist or enhance motor control...
designs also for the ankle
Ankle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
. In the following decade, the disappointing results of long-term follow-up clinical studies of the pioneering designs has left ankle arthrodesis as the surgical treatment of choice for these patients. More modern designs have produced better results, contributing to a renewed interest in total ankle arthroplasty
Arthroplasty
Arthroplasty is an operative procedure of orthopedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced with something better or by remodeling or realigning the joint by osteotomy or some other procedure.-Background:Previously, a popular form of arthroplasty was...
over the past decade.
Nearly all designs from pioneers featured two-components; these designs have been categorized as incongruent and congruent, according to the shape of the two articular surfaces. After the early unsatisfactory results of the two-component designs, most of the more recent designs feature three-components, with a polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
meniscal bearing interposed between the two metal bone-anchored components. This meniscal bearing should allow full congruence at the articular surfaces in all joint positions in order to minimize wear and deformation of the components. Poor understanding of the functions of the structures guiding ankle motion in the natural joint (ligaments and articular surfaces), and poor restoration of these functions in the replaced joint may be responsible for the complications and revisions.
Prosthetic design
The main objectives of the prosthetic design for ankleAnkle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
joint replacement
Joint replacement
Replacement arthroplasty [from Greek arthron, joint, limb, articulate, + -plassein, to form, mould, forge, feign, make an image of], or joint replacement surgery, is a procedure of orthopedic surgery in which the arthritic or dysfunctional joint surface is replaced with an orthopaedic prosthesis...
s 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.
As with other joint replacement
Joint replacement
Replacement arthroplasty [from Greek arthron, joint, limb, articulate, + -plassein, to form, mould, forge, feign, make an image of], or joint replacement surgery, is a procedure of orthopedic surgery in which the arthritic or dysfunctional joint surface is replaced with an orthopaedic prosthesis...
s, the traditional dilemma between mobility and congruency must be addressed. Unconstrained or semiconstrained designs allow the necessary mobility but require incongruent contact, thereby giving rise to large contact stresses and potentially high wear rates. Conversely, congruent designs produce large contact areas with low contact stresses but transmit undesirable constraint forces that can overload the fixation system at the bone-component interface.
Indications
The indications for the operation in general are as follow:- patients with primary or posttraumatic osteoarthritisOsteoarthritisOsteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
with relatively low functional demand; - patients with severe ankleAnkleThe ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
rheumatoid arthritisRheumatoid arthritisRheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...
but not severe osteoporosisOsteoporosisOsteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
of the ankle; - patients suitable for arthrodesisArthrodesisArthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical...
but rejecting it.
The general contraindications are:
- varus or valgus deformity greater than 15 degrees, severe bony erosion, severe talus subluxation;
- substantial osteoporosisOsteoporosisOsteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
or osteonecrosis particularly affecting the talus; - previous or current infections of the footFootThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws...
; - vascular diseaseVascular diseaseVascular disease is a form of cardiovascular disease primarily affecting the blood vessels.Some conditions, such as angina and myocardial ischemia, can be considered both vascular diseases and heart diseases .Cigarette smoking is the major risk factor....
or severe neurologic disorders; - previous arthrodesisArthrodesisArthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical...
of the ipsilateral hip or kneeKneeThe knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
or severe deformities of these joints.
Other potential contraindications such as capsuloligamentous instability and hindfoot or forefoot deformities affecting correct posture, are not considered relevant if resolved before or during this surgery.
Outcome
The outcome of an ankle replacement includes factors like ankle function, pain, revision and implant survival. Outcome studies on modern designs show a five-year implant survival rate between 67% and 94%. and ten-year survival rates around 75%.Clinical ankle scores, such as the American Orthopaedcic Foot and Ankle Society (AOFAS) is an outcome rating system for ankle replacements. It is composed of the parameters pain (max 40 points), function (max 50 points) and alignment (max 10 points). Further outcome instruments include radiographic assessment of component stability and migration, and the assessment of its functionality in daily life using gait analysis
Gait analysis
Gait analysis is the systematic study of animal locomotion, more specific as a study of human motion, using the eye and the brain of observers, augmented by instrumentation for measuring body movements, body mechanics, and the activity of the muscles. Gait analysis is used to assess, plan, and...
or videofluoroscopy
Fluoroscopy
Fluoroscopy is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and fluorescent screen between which a patient is placed...
; the latter is a tool for three-dimensional measuring of the position and orientation of implanted prosthetic components at the replaced joints.