Essential Insights On Treating End-Stage Ankle Arthritis
The current systems (second-generation implants) are more advanced with extensive modifications. These total ankle implants include semi-constrained, cement-less designs, mobile and fixed-bearing designs.6,10,11 Studies with the newer generation implants show that survivorship of total ankle arthroplasty implants ranges from 70 percent to 98 percent at three to six years and from 80 percent to 95 percent at eight to 12 years when researchers define survivorship as the retention of metal components.12 A recent study by Mann and coworkers indicated the survival rate of the STAR implant was 96 percent at five years and 90 percent at 10 years.13 As more long-term studies are published, improving survivorship is making ankle replacement an increasingly popular option versus the longer established ankle arthrodesis.
Are We Seeing A Shift With Ankle Arthroplasty Being Favored More Than Ankle Arthrodesis?
The improved timing of gait and theorized protection of adjacent joints are also persuasive arguments for replacing rather than fusing the ankle joint.14 Researchers have shown that total ankle arthroplasty, regardless of the specific implant used, improves functional outcomes.15 In fact, functional outcomes tend to favor arthroplasty over arthrodesis. Saltzman and colleagues have reported the initial results of a prospective controlled trial comparing total ankle replacement with ankle arthrodesis, demonstrating the superiority of total ankle replacement in postoperative pain relief and functional outcome.16 Several studies have shown statistically equivalent changes in pain scores between arthroplasty and arthrodesis.
Specifically, a systematic review of the literature by Haddad and coworkers showed comparable AOFAS scores of 78.2 and 75.6 for arthroplasty and arthrodesis respectively.5 However, arthroplasty is technically difficult and more experienced surgeons generally perform it.
One important factor in the outcome is the position of the talar component. A study by Barg and coworkers indicated that an anterior-posterior offset ratio of 0 on a lateral ankle radiograph not only corresponded to reduced pain but also improved functional outcome as measured by the AOFAS score in a two- to eight-year follow up.17 Brodsky and colleagues showed that patients exhibited improved walking velocity, cadence and stride length after undergoing a total ankle arthroplasty.18 These patients had improved ankle power, increased ankle range of motion and improved hip and knee range of motion, leading to overall improvement in ankle function and gait.
In comparing the gait of healthy patients, those who had prior total ankle arthroplasty and those with prior ankle arthrodesis, Piriou and coworkers found that while neither the arthroplasty nor the arthrodesis patients returned to “normal” gait, the arthroplasty group showed a greater reduction in limp, greater movement at the ankle, a symmetrical timing of gait and a restored ground reaction force pattern.14
Revision rates are also comparable. The total ankle arthroplasty revision rate is around 7 percent with the primary reason for revision being loosening or subsidence. The revision rate following ankle arthrodesis is about 9 percent with non-union being the major factor. Of note, 1 percent of patients who previously underwent ankle arthroplasty required a below-the-knee amputation in comparison to 5 percent who had undergone arthrodesis.7