The ankle joint is the primary articulation responsible for efficient transmission of compressive, shear, and rotatory forces from the ground to the remainder of the lower extremity. Its primary motion, though it is not a simple hinge occurs in the sagittal plane. While averaging 40 – 60°, only 30° is required for steady-state walking (10° dorsiflexion and 20° plantarflexion). Rotation of the talus within the ankle mortise also occurs and averages 10° (external rotation with dorsiflexion). The presence of rotation makes the ankle joint a biplanar articulation.
The ankle transmits two to three times the forces experienced by the hip or the knee but has only one-third the surface area to dissipate the load. Despite this, it is one of the most arthritis-resistant articulations in the body. Increased joint congruency (partly due to a thinner cartilage), a predominantly rolling motion and more favorable biomechanical and biochemical articular cartilage properties confer a resilience that sees symptomatic arthritis of the ankle 9 times less common in presentation than that of the knee. Despite this some 50,000 new cases present each year in the US.
Unlike hip and knee pathologies, degenerative ankle disease is primarily related either to a single historical traumatic event or altered ankle mechanics. Malleolar, tibial plafond, talus or osteochondral fractures compromise articular congruity and result in accelerated wear. On average, 14% of ankle fractures progress to post-traumatic arthritis, the incidence correlating with fracture severity. Altered mechanics most commonly seen in the setting of chronic ankle instability and often associated with a subtle cavus/varus foot increases local contact stresses with similar results. Other less common aetiologies include inflammatory and Charcot arthropathies as well as haemochromatosis.
Ankle arthritis typically presents with pain, stiffness and swelling. The ankle’s mechanical contribution to the second rocker of the gait cycle and the necessary dorsiflexion required explain difficulties in crouching, descending stairs and walking up an inclined surface. Gait aberrations include early heel rise and antalgism (shorted stance phase). Diagnosis is based upon clinical history, physical examination and radiographic investigation. Weightbearing X-rays (AP, Mortice, and lateral) generally suffice, while CT further localises pathology and contributes important information about neighbouring tarsal joint integrity.
Nonoperative management of ankle arthritis mirrors that of any weightbearing joint in terms of activity modification, weight loss, oral analgesics and anti-inflammatory therapy. Oral chondroitin and glucosamine supplementation can provide symptomatic relief in patients who have early arthritis. Intra-articular injections of corticosteroid are often used to decrease inflammation and pain. Most clinical studies refer to the knee, where the beneficial effects are often limited to a period of eight weeks, with no difference between the effects of steroid and placebo over a longer time-period. Though widely used, their efficacy in the arthritic ankle has not been studied. The assumption is that long-term benefits are limited.
Viscosupplementation (hyaluronic acid injections) for knee arthritis has been approved by the FDA as a medical device, not as a drug and many products are in use in the United States since 1997. They have proven efficacious in the management of osteoarthritis of the knee and preliminary studies demonstrate a benefit in the ankle joint.
Ankle braces, strapping, encapsulative foot wear, and rocker based designs attempt to limit the painful stimulus of ankle motion either by restricting motion or substituting for motion, in particular ankle dorsiflexion (the 2nd rocker in stance phase of gait), all with variable success. Brace material and design determine the degree of support provided. The widely utilized Arizona brace imparts the stiffness of fitted leather while moulded thermoplastic AFOs (ankle foot orthosis) confer more rigidity. Appropriately sized, fitted and padded, they can alleviate symptoms although their long-term use must be weighed against individual patient requirements and expectations. Heel wedging can redistribute loads to intact cartilage in a varus or valgus ankle.
Rocker based footwear has become popular of late, with the manufacture of more esthetically pleasing designs. An appropriately placed rocker sole can obviate the painful dorsiflexion component necessary (10˚) in the normal gait cycle and provide symptomatic improvement.
Having exhausted nonoperative measures, patients can be counseled on the merits and shortcomings of a range of surgical interventions for isolated talocrural arthritis.
Operatively, open or arthroscopic debridement is indicated, and invariably is successful where mechanical symptoms predominate and where the articular surface is largely intact. Anterior impingement symptoms respond well to chielectomy, and as for early knee pathology arthroscopic shaving of unstable cartilage lesions can give temporary though less consistent results. Microfracture, subchondral drilling, mosaicplasty and autologous chondrocyte implantation are generally reserved for focal cartilage defects and have little role in advanced disease.
The principle of redistributing the joint reaction forces, so as to offload the diseased area is well established in the management of unicompartmental knee arthritis, through high tibial and supracondylar osteotomies. Similarly an off-loading osteotomy, above (supramalleolar), below (calcaneal) or through (intraarticular) the ankle joint endeavors to preserve and selectively load intact articular cartilage. In select patients, particularly a young individual this can preserve joint function and delay the need for fusion or replacement.
Where there is extensive articular compromise surgical options are largely limited to either fusion or replacement.
Arthrodesis or fusion traditionally has been perceived as the gold standard in treating talocrural arthritis (see image). A well positioned arthrodesis (plantigrade, slight valgus with external rotation, and posterior translation) is still the first line in the young active individual, offering good pain relief and function, despite aberrations in gait (decreased cadence and stride length). The oxygen consumption during steady-state walking is increased by 3%, and gait efficiency is 90%. Open or arthroscopic approaches exist with a variety of fixation techniques based upon surgeon preference. Immobilisation for a period of up to 12 weeks is recommended to secure solid union.
Looking critically at the literature, the reported first-time fusion rate approximates 90%. Of these, 90% report substantial pain relief, which in effect is an 81% success rate. Of those satisfied with their results, functional limitations must be expected; difficulty walking on uneven ground, stair ascent or descent and aching with prolonged standing or working. In the long term accelerated distal joint degeneration is inevitable, if followed long enough (100% at 22 years) and rates have been reported of the magnitude of 50% hindfoot arthritis at 8 years. Extending the fusion mass to incorporate the subtalar joint further stiffens the hindfoot and compromises function.
These fusion statistics have been the driving force in motion preserving ankle replacement development (see image). Total ankle replacement (TAR) has evolved considerably since the disappointing initial surgeries of the 1970s and 80s. Contributing factors in terms of implant design (nonanatomic and mal-constrained), surgical technique (excessive bone resection) biofixation (cement) and poor patient selection (young and advanced deformity) have largely been addressed with current 5 and 10 year survival, reported at highs of 98 and 90% respectively. All modern ankle replacement designs comprise 3 components.
1. A metallic baseplate that is fixed to the tibia
2. A domed metallic component that resurfaces the talus
3. A bearing surface of ultra high molecular weight polyethylene (poly)
Total Ankle Replacement
Two piece or fixed bearing systems have a locking mechanism between the poly and the base plate, 3 piece or mobile bearing designs allow the bearing surface to articulate with the baseplate and the talar component. Both designs are semiconstrained. Proponents of mobile bearing designs claim a reduction in shear and torsional forces at the bone implant interface. Opponents believe that the addition of a further bearing surface increases polywear. No level-one evidence exists to recommend one design over the other.
TAR is performed in the vast majority of cases through an anterior approach with the aid of alignment jigs. Balancing of the foot is essential and may entail supplementary bony or soft tissue procedures to optomise function and longevity. Rehabilitation involves immobilization for 6 weeks followed by graduated weightbearing thereafter.
To date no randomized prospective head to head trial exists comparing arthrodesis and ankle replacement. The two most significant contributions to the literature in this regard within the past two years include a systematic review of the literature addressing the intermediate and long-term outcomes of interest in total ankle arthroplasty and ankle arthrodesis (level 4 evidence) and a prospective controlled comparative surgical trial (level 2). Both confirmed the comparative results of each procedure. The latter, which prompted FDA approval of mobile bearing implants also highlighted better function with equivalent pain relief with TAR at 24 months follow-up.
Therefore, prospective studies are needed to compare the two procedures in similar patient groups.
The capacity to return to recreational activity after arthroplasty or arthrodesis has been debated. No conclusive studies exist which directly compare return to participation in sport in these groups. Arthroplasty proponents have documented a significant increase in sports activity after TAR with better overall functional results in the sports active individual than inactive ones. No such studies exist in the arthrodesis group although consensus supports a resumption of all but high impact sport activities.
Traditionally due to the historical failures of ankle replacement, the ideal patient selection criteria for TAR are the older, low BMI, sedentary, with minimal deformity individual. Good short to intermediate term results can be expected in this group. As the boundaries are extended the expected results are less predictable.
TAR failure typically occurs through talar component failure or poly wear. Revision results are less convincing and conversion to a fusion at this stage while very possible is technically challenging, certainly where there is extensive bone loss.
In summary, despite the fact that the ankle is an arthritis-resistant joint, it responds poorly over time to traumatic injury and malalignment. Activity and lifestyle modification and symptomatic treatment with analgesics and encapsulative or rocker type footwear are first line interventions.
Some disease is amenable to arthroscopic debridement/chielectomy or joint preserving realignmnent procedures.
Treatment of end-stage disease is limited to either ankle fusion or replacement. Advances in replacement over the past decades mean that in select patients pain relieving, motion-preserving surgery is a viable option where ankle fusion was the traditional gold standard.