Ankle replacement

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 requiring arthroplasty, 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 has only been demonstrated for particular isolated implant designs. 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 requiring arthroplasty, 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 has only been demonstrated for particular isolated implant designs. Since the early 1970s, the disadvantages of ankle arthrodesis 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. The main objectives of the prosthetic design for ankle joint replacements are: As with other joint replacements, 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.