Diabetes and ankle replacement

Diabetes and foot problems are closely linked, to the point that in many healthcare systems combined care of the foot sequelae of diabetes with multidisciplinary medicine, vascular surgery, orthopaedic surgery and podiatric ward rounds has become the standard of care. While there is a broad range of data to support various treatment options for diabetic feet, the implications of diabetes for those contemplating ankle arthroplasty are not well described.

Surgeons in Seoul (South Korea), always keen to share their clinical data, have written up the results of 43 diabetic and 130 non-diabetic ankle replacements as a case-controlled series. They attempted to establish what the clinical and surgical outcomes of ankle replacement are and if they differ between the two cohorts.⁴

Clinical outcomes were measured with the Ankle Osteoarthritis Scale (AOS) and the American Orthopaedic Foot and Ankle Society (AOFAS) scores and these were both significantly better in the non-diabetic cohort. This was mirrored in surgical outcomes, with around double the failure rate at five years (21% vs 11.6%) in the diabetic cohort. Unsurprisingly, the problems were more acute in the uncontrolled diabetic group with high rates of delayed wound healing and higher rates of early osteolysis. In an implant with only relative indications and concerns about the longer-term outcomes and associated complications, this comparative case series does suggest to us here at 360, for the time being at least, that extreme care should be taken offering these implants to diabetic patients.

Fixed-bearing ankle replacement

The outcomes of ankle replacements have been steadily improving, unlike the hip replacement, as eloquently argued in this month’s feature article. The optimum prosthesis design, bearing surface and fixation method are yet to be defined. The earliest successful ankle arthroplasties relied on a mobile-bearing prosthesis to accommodate for imbalance in the soft-tissues and potential malalignment, however, the drawbacks of two bearing surfaces may in part explain the relatively high rates of osteolysis and loss of fixation. An alternative method is the fixed-bearing prosthesis. Using intramedullary jigging and a modular tibial component, the INBONE prosthesis aims to optimise alignment, fixation and generation of wear debris.

Surgeons in Durham (USA) have some experience with the implant and report their consecutive three-year series of 194 primary ankle replacements at the short-term follow-up point of three years.⁵ While these types of case series will never set the world alight, it is refreshing to find a large case series with thoroughly reported outcome scores including functional (AOFAS, VAS, Timed Up and Go), quality of life (SF-36), radiographic and surgical outcomes.

In this closely monitored series, the patients reported improved clinical and quality of life scores at a mean follow-up of 3.7 years. As would be expected, all outcome measures improved over the pre-operative scores. Perhaps most importantly the surgical team were able to achieve correction for both coronal tibiotalar angle and sagittal plane correction which was maintained at final follow-up. The overall revision rate during the period of the study was 6%, with a 5% rate of subsidence likely to be unstable and lead to failure. The overall survival rate of the implant of 89% for the period of the study is in line with other ‘benchmark’ series and suggests that the INBONE style concept provides comparable results to other technologies (such as mobile bearing ankles) at just over three years.