Total Ankle Arthroplasty

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What is an Ankle Arthroplasty?

Ankle arthroplasty is when the ankle joint (Talocrural Joint) is replace with prosthetic components comprised of polyethylene and metal and is preferred to ankle arthrodesis (fusion) as range of movement and function an not compromised. Main objectives of the arthroplasty are to

1. Replicate ROM of the talocrural joint
2. Function well under weight bearing
3. Be wear resistent 
4. Maintain alignment and stability 

History of Total Ankle Arthroplasty 

Ankle replacement surgery has been available for over two decades however it is a far less common procedure than hip or knee arthroplasty owing to the less frequent incidence of osteoarthritis ankle pathology. The majority of ankle osteoarthritis is secondary to trauma.

Until relatively recently, ankle joint arthrodesis (fusion) was the gold standard of treatment, but this was not without its complications, e.g. non-union,Osteoarthritis in the other mid/hind foot joints and stiffness and loss of proprioception

     Total ankle replacement was developed in the 1970's but initially was plagued with high long term failure rates. The older prosthesis loosened or malfunctioned and frequently needed to be removed.  In the late 70's Dr. Frank G. Alvine an orthopedic surgeon from Sioux Falls, SD developed the Agility Ankle which was the first FDA approved total ankle implant in use in the United States. Since its introduction the Agility Ankle System has gone through several modifications. Currently the Agility Ankle System is the most widely used ankle prosthesis. With more than 20 years of experience it has the longest followup of any fixed bearing device.

On May 29, 2009 the medical news today announced the FDA approved the first mobile bearing device called the Scandinavian Total Ankle Replacement System (STAR). As a condition of FDA approval the company (Small Bone Innovations Inc.) must evaluate the safety and effectiveness of the device during the next eight years.

     In a systematic review of the literature published in the Journal of Bone and Joint Surgery in 2007, the intermediate outcome of total ankle arthroplasty appears to be similiar to that of ankle arthrodesis however data was sparse.  In a study comparing reoperation rates following ankle arthrodesis and total ankle arthroplasty SooHoo, Zingmond and Ko confirmed that ankle replacement is associated with a higher risk of complications as compared with ankle fusion, but also has potential advantages in terms of a decreased risk of the patient requiring subtalar joint fusion.  In a seven to sixteen year follow up on the Agility Total Ankle Arthroplasty, Knecht, Estin, Callagham et al concluded that the relatively low rates of radiographic hindfoot arthritis and revision procedures at an average of nine years after the arthroplasty are encouraging.

     Although interest in total ankle replacements is increasing, midterm clinical results to date are few and often have not been validated by independent pratitioners. In addition no level I or II studies have been published.

Clinically Relevant Anatomy

For detailed anatomy see here

Talocrural Joint

The ankle joint is a synovial hinge joint comprised of hyaline covered articular surfaces of the talus, the tibia as well as the fibula, allowing up to 20 degrees dorsiflexion and 50 degress plantarflexion. The distal ends of the tibia and fibula are held together firmly by ligaments of the medial (Deltoid) and lateral ligament complexes of the ankle which can be damaged and contribute to ankle arthritis (Ankle Sprain). The ligaments hold the tibia and fibula into a deep bracket-like shape in which the talus sits.

The Talus

• TheROOF of the joint is the distal inferior surface of the tibia
• The MEDIAL SIDE of the joint is formed of the medial malleolus of the tibia
• The LATERAL SIDE of the joint is formed of the lateral malleolus of the fibula

The articular part of the talus looks like a cylinder and fits snugly into the bracket provided by the syndemosis of the tibia and fibula, when looking down upon the talus the articular surface is wider anteriorly than posteriorly. Subsequently this increases the congruent, stable nature of this joint when it is in dorsiflexion. As this is a synovial joint, a membrane is present as well as a fibrous membrane providing the same functions as any other synovial jointSynovial Membrane[11]. 

The Arthroplasty

Indication for Procedure

There is no well-defined indication for a Total Ankle Arthroplasty. Surgery is considered only when conservative treatment has been attempted with no improvement. The operation is mainly being executed in patients who suffer from different types of arthrides. This cause advanced arthritic changes of disabling pain and loss of ankle motion. The ankle is most frequently affected by post-traumatic arthritis. Total ankle joint replacement is also indicated following unsuccessful ankle arthrodesis  the ‘ideal’ patient for ankle joint replacement is an elderly person with the low physical demands who has good bone stock, normal vascular status, no immune-suppression, and excellent hind foot-ankle alignment. Generally here are common indications for arthroplasty:

1. Primary or post-traumatic osteoarthritis
2. Severe rheumatoid arthritis
3. Rejected arthrodesis

Common contraindications are:

1. Severe talus subluxation, severe valgus or varus deformity
2. Substantial osteoporosis
3. Neurological disorders or recurrent infection

Pre-operative Procedure and Definitive Diagnosis

Weight bearing A-P and lateral mortise views of bilateral ankles is required to make effective preparation and anticipation of that will be required in the surgery. The rearfoot alignment (Cobey/Saltzman) view is essential to evaluate the ankle joint and identify any calcaneal-totibial deformities. This is performed by getting the patient to stand, elevated with a cassette positioned at 15 degres anteriorly inclined with the x-ray bemed perpendicular to the film. This position is altered if deformities are present, after this has been taken anterior distal tibial angle (ADTA) is measured. The ADTA is formed by the mechanical axis of the tibia and the joint orientation line of the ankle in the sagittal plane and measures 80° ± 3° in the normal lower extremity. In the coronal plane, the lateral distal tibial angle (LDTA), the tibial-talar angle and the calcaneal tibial alignment should be measured. The LDTA is formed by the distal tibial articular surface and the anatomical axis of the tibia and measures 89° ± 3°.29, if this is decreased this represents a varus deformity. The tibial-talar angle (Figure 3C) is defined by the tibial and talar articular surfaces in the ankle joint. When the tibialtalar angle is >10° the joint is defined as incongruent (unstable).

"If an abnormal ADTA or LDTA is present (sagittal or coronal deformity), the center of rotation of angulation (CORA) is measured. The CORA is the intersection of the mid-diaphyseal line and the line starting from the middle of the joint and perpendicular to the abnormal ADTA or LDTA (Figure 4). The CORA can be located at the joint line level (usually due to anatomical joint line malalignment or to ankle degeneration) or proximally (usually due to tibial deformities/fractures)". So as you can see there are many consideration to be taken, and multiple angles to be analysed and this is important and any  instability and malalignment of the new prosthesis can be excessively worn or may even fail.

Surgical Procedure

To perfrom the procedure the patient is positioned supine with the hip slightly elevated and a tourniquet on the proxinal thight to restrict blood flow during the procedure. Next a 10 cm incision is made over the centre of the joint line to expose the relevent anatomical structures. Once the structures have been exposed the crucial nerves and tendons are identified as to protect and ensure their integrity to minimise operative complications, these include; peroneal nerves, tibialis anterior and extensor hallucis longus. This is also to achieve correct talocrural alignment and soft tissue balance to ensure the prosthesis can achieve plantar grade in standing. It is also important to debride and correct any osteophytes or any other structures that can contribute to malalignment. Depending on the natural angle of the talocrural joint (varus or valgus) more bone medially or laterally may have ot be removed, this also may occur if the joint is deep or shallow as it may need to be reduced or elevated.

Once the joints have been corrected and bones properly aligned the new components are trialed making sure rull ROM and stability is achieved. If dorsiflexion is limited and not due to malalignment then achilles tendon lengthening is required, the same goes for if there is instability in inversion or eversion the ligaments are reconstructed. Persistent malalignment can occure and may need separate procedures to correct such as subtalar fusion depending on severity and correctability. 

Physical Therapy Management

As it will be explained in the pre-operation and post-operation phase the multi-disciplinary team involved with the patient have a big role in making the arrangements before and after the surgery, this may involve physiotherapists, occupational therapists, discharge nurses, staff nurses, healthcare assistants as well as doctors. Both pre and post operative phases are integral to the progress of the patient and the pre-op should not be overlooked as important as it can be easy to focus on post-op.

Pre-Operative Phase

Before the surgery one of the main job for the team is to educate the patient about what will happen before, during and after the surgery as this will give the patient the opportunity to prepare, mentally rehearse, ensure smooth transition through short-term to long-term goals but also help control and reduce post-operative pain

ROM, muscle strength, gait and deviations will all be recorded as to compared before and after arthroplasty and ensure the patient is as optimal strength prior to operation if possible. For safety and ease of transition is can be important that the patient learns how to walk with crutches so they can perform ADL’s as soon as possible post arthroplasty but also understand that they will be non-weight bearing after the arthroplasty.

As will all procedures under general anesthetic there are common pulmonary postoperative complications (PPC's) which need to be controlled and risk reduced and this can be explained at this stage as well. 

Post-Operative Phase

It is important to ensure the risk of PPC's are reduced and respiratory physiotherapy may be used at this early stage, cough, deep breathing exercises and early mobility are essential here to reduce atelectasis and reinstate the muscoscilliary elevator as soon as possible. 

Atelecatsis occurs in 90% of anesthetized patients which leads to a 16-20% reduction in functional residual capacity which is why the alveoli tend collapse resulting in increased work of breathing, hypoxia, reduced compliance, V/Q mismatch and risk of pneumonia. There is a 9% chance of developing pneumonia and this is where physiotherapy intervention is crucial at reducing the rate of all of these complications.

IT IS IMPORTANT TO KNOW YOUR OWN HOSPITALS/SURGEONS GUIDELINES FOLLOWING ARTHROPLASTY OR ANY OPERATION AND THE FOLLOWING SHOULD ONLY BE USED TO EDUCATE AND CONSIDER SOME BASIC/COMMON PROTOCOLS

THIS SHOULD NOT BE USED IN REPLACEMENT OF THE SURGEONS PROTOCOL

THIS IS A PROTOCOL BY THE ROYAL NATIONAL ORTHOPAEDIC HOSPITAL NHS TRUST, utilising the best available evidence

Initial Rehab 0-4 Weeks

Restrictions:

• Non-weight bearing 2/52 with a back slab
• Below knee POP at 2/52 and begin full weight bearing in this POP
• POP removed at 4/52 and aircast boot is considered
• Elevation
• If sedentary employment, return to work at 4/52 as long as elevated and protected

Goals:

• Safe and independent mobility with walking aid
• Independent with exercise programme
• Know monitoring and protection

Treatment:

• POP
• Pain-relief
• POLICE
• Basic circulatory exercises
• Mobility

Progress when:

Out of POP, fully weight bearing, no complications and then refer to physiotherapy out patients

Recovery Rehab 4 weeks - 3 months

Restrictions:

• No strengthening against resistance until 3 months if any tendon transfers 
• No stretching tendons if transferred

Goals:

• Independent from aircast boot
• Achieve full ROM 

Treatment:

• Pain relief, swelling management
• Advice, education, postural advice, monitoring complications, pacing
• Gait re-education
• Exercises --> PROM,AAROM, AROM, light strengthening, core stability, balance/proprioception, stretching
• Hydrotherapy
• Orthotics
• Manual therapy --> SSTM's, mobilisations

Progress when:

Full ROM, independently mobile, neutral foot position in standing

Intermediate Rehab 12 weeks - 6 months

Restrictions: 

• None

Goals:

• Independent with no aids
• Normal footwear
• Grade 5 strength
• Grade 4 strength in tendons transferred

Treatment:

• Pain relief, swelling management
• Advice, education, postural advice, monitoring complications, pacing
• Gait re-education
• Exercises --> PROM,AAROM, AROM, light strengthening, core stability, balance/proprioception, stretching
• Hydrotherapy
• Orthotics
• Manual therapy --> SSTM's, mobilisations

Progress when:

Normal footwear, independent with no aids, pain controlled, strength 5/5 (4/5 if tendon transferred)

Final Rehab 6 months - 1 year

Goals:

• Return to gentle no-impact/low impact sports
• Grade 5 strength in transferred tendons

Treatment:

• Maximise function
• End stage exercises, balance and proprioception and sport specific
• Manual therapy

Additional Information

After the surgery it is important that the patient keeps moving and performing his daily activities. However there is still discussion between physicians about when the patient should start again with exercising. There are some that allow exercise immediately after surgery. But some say it is considered best to wait until there is a satisfactory bony in growth as shown radio graphically. However it’s the job of the physician to try to improve:  the patient’s ROM of the ankle, maintain the ROM in the hip and knee, increase the muscle strength with exercise for the Gluteus Maximus, Quadriceps femoris muscles and the muscles that are responsible for dorsal flexion and the plantar flexion of the ankle. Postoperative mobilization begins early, with rapid progression to resumption of normal activities. The goal is to obtain 10° of dorsal flexion and 30° of plantar flexion. For patients who have almost no motion in their ankle is any motion an improvement. 

In early postoperative period it is important that the incision heals and the implant becomes solidly fixed to the bony bed to do this they will use a below knee non-weight bearing immobilization. This is maintained until there is satisfactory bony in growth. ^. Another goal is to increase the ROM of the ankle and maintain the hip and the knee ROM.

After a few months the patient needs to make an appointment with the doctor. Here they will take X-ray scans to see if there are no complications like: joint debridement for osseous impingement; the next most common procedures were extra-articular procedures for axial misalignments and component replacements. 

Recent Related Research (from Pubmed)

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