Revision TKA – Why does it occur and how to solve specific problems - Editorial

Over the last decades Total Knee-Arthroplasty (TKA) has become one of the most frequently performed surgeries. Although great majority of our patients are satisfied after surgery, the absolute number of TKA-Revisions (TKA-R) has increased simultaneously. One factor for the rising number of revisions is the fact that our patients with primary TKA has become younger. Many registries and studies could show that age is an important factor for revision.^1,2 The younger the patient the more likely they fail. To reduce the number of failures and to optimise TKA-R outcome it is important to understand the reasons for failure. Many articles have dealt with that question already.^3,4 In this issue, Mathis and Hirschman looked on that topic from a more international standpoint. They focus on answering the question whether in all parts of the world the reasons are similar or if there is a variation to analyse the causes for such differences. In an additional manuscript, Mathis et al. have included their own experience of aspetic revisions in a specialised Hospital in Switzerland. Interestingly, in their setup a completely different ratio of the failure mechanisms is described, showing that local specialties also play an important role.

Due to the fact, that the reasons for TKA failure are multiple, a meticulous and standardised analysis should be implemented in order to detect them as good as possible. Many papers on this topic exist,⁵ however, most of them just describe their own algorithm. In this volume, Röhner et al. analysed the existing literature on pre-Op work-up and summarized what tests are evidence based and therefore are important to perform and which are not. Based on this evidence they present a diagnostic algorithm that can be used as a basis for aspetic failures.

When it comes to TKA revision, instability and bone defects are two major aseptic issues to deal with. Instability is a general term, which covers a huge variety of subtypes and reasons. Morgan-Jones and Graichen are presenting an algorithm to differentiate between the different types of and reasons for instability. In addition, even more importantly they present a solution for each type, based on the classification. Therefore this classification might probably help to treat instability more standardised and by that hopefully more successful. For a successful treatment of instability the support of the implant is another important part. In their article, Marya and Singh are describing the different types of constraint and the indication in which situation which constraint is required. Both articles together sum up nicely the relevant issues on treatment of instability in TKA revision.

Treatment of bone defects in R-TKA has changed enormously over the past decade. Different options were added to the traditional cemented and cementless stem fixation. In this issue, specialists present on their favourite fixation device and describe the strength and weakness of each of it. While James et al., one of the high-volume metaphyseal sleeve users present their long-term outcome; Kirschbaum et al. describe their mid-term results on cones. Additionally, Tan gives an overview on the role of cement in RTKA. He highlights the advantages and limitations of cementless, hybrid and fully cementless stem fixations. This adds important information on the aspects of implant fixation. We hope that based on all these results it becomes easier to compare the strength of each construct. Finally, the editors believe that it is maybe not a one or the other decision, but a defined indication for all of them in the huge variety of bone defects, of course with some overlap in indications, based on personal preference and experience.

Sleeves and Cones became very successful over the past years, and multiple publications confirm good-excellent midterm results for both of them.^6,7 Although their names are often used as synonyms, they are completely different constructs. While cones are defect fillers and independent from the implants, sleeves are parts of the implant. Often an advantage is combined with a disadvantage simultaneously. Due to the fact, that sleeves are part of the implant, positioning in bowed bones and recreating the joint line in huge metaphyseal femoral defects are sometimes difficult. Cones on the other hand, deal with the problem of multiple fixation interfaces and that their use is mainly limited to cemented implants. The great thing that unites both is their success. Based on this success some authors described already their experience to use sleeves without stems.^8,9 In an analysis of the existing in vitro and in vivo literature Graichen et al. summarizes the options and limitations of such a stemless construct.

However, occasionally well-fixed implants need to be revised due to other reasons than loosening. Both, sleeves as well as cones are a special challenge for implant removal. To give some tips and tricks we have integrated an article by Lekkreusuwan et al., in which he describes options and techniques for implant removal while the sleeve is left in situ. Besides the technical challenge, the article focus on the indication for such a procedure.

Another disadvantage of both fixation devices is cost. As both solutions are expensive, their usage in many countries of the world is very limited. To cover the specific situation of implant fixation in Asia Gopinathan et al. present in their article other, not so expensive options that are widely used in particular in this part of the world. Based on their description these techniques can reversely be used in specific cases in Europe too.

Reason number one for early failures is Periprosthetic Joint Infection (PJI).^10,11 Due to its relevance, we have integrated three manuscripts in this issue dealing with it. As in aspetic revisions, it is as important in septic revisions to analyse the knee and all around systematically. The identification of the infection is a multidisciplinary task demonstrating the importance for building up an Infection Team. Suren et al. present on their diagnostic algorithm in PJI and even more importantly, they summarise the existing evidence on the different diagnostic tools. The senior author of this author group is part of the German PJI group of the German Society of Arthroplasty (AE) and the algorithm presented is showing the consensus of this group.

Beside sufficient diagnostics, a surgical technique for the treatment of PJI is important. Multiple publications dealt with the ongoing discussion one-stage versus two-stage revision.^12,13 In the recent years, the question has changed a bit and focus now more on the factors that might allow successful single stage and those that need to be respected for 2 stage revisions.¹⁴ Lazic et al. summarise all those aspects in the second manuscript of this group. However, before a surgeon or an institution starts asking themselves those questions too, it needs to be stated, that only with a lot of experience and standardisation the success rate can be increased in the future. Boelch et al. deal with the very problematic subgroup of patients with persistent infection after implant removal and spacer implantation. Based on their data they recommend avoiding spacer exchange whenever possible. Overall, a sufficient workload of this extremely challenging entity of RTKA is recommended and building up regional infection centres something to follow-up on.

Last but not least, 2 more very challenging topics of RTKA are added in this issue. The topic of periprosthetic fracture and the one of Extensor mechanism failure. While periprosthetic fractures become more and more relevant due to an increasing number of implants in place and the fact of an aging world, extensor mechanism problems remains at constant lower numbers. This limited experience is also shown in the literature, as no real classification exist and the recommendations are more based on personal experience than evidence. In this volume, Strauch summarizes the existing literature and developed their classification. Based on this classification he presents treatment options. As he worked in different health care systems in Europe, his experience is not so much based on local training and specific system situations. Mayr et al. finally summarise the existing classifications on periprosthetic fractures nicely and gives tips on treatment options for this huge variety of fractures.

We hope that the reader will get an actual update on the relevant TKA-R topics. As all authors are working in high-volume revision centres at different parts of the world, this issue should add many tips for daily practice. In summary, we believe that only by bringing together the different aspects we will be able to improve outcome of RTKA in the future.