Knee

Closure with barbed sutures?

There is plenty of evidence from primary studies through to randomised controlled trials and meta-analyses that suture closure reduces the infection rate following orthopaedic surgery. Anecdotally, patients prefer the look of a hand-sewn closure to the rather ugly scars left by clips. Surgeons, however, quite like the convenience and consistency provided by clips, and as such they have continued to be popular. Barbed sutures offer the neat scar and subcutaneous position of a suture, but as they do not rely on knots these sutures also provide the convenience of clips. They are increasingly being used in total joint arthroplasty, but in contrast to traditional sutures and clips, few studies have been conducted on their use, and in particular their infection rates. Surgeons in New York, New York (USA) have been using barbed sutures for closure in their unicompartmental knee arthroplasties (UKA) and report the outcomes of 839 unicompartmental knees closed with either the Quill barbed suture (Surgical Specialties Corporation; Wyomissing, Pennsylvania), or traditional closure consisting of a mixture of 2/0 monocryl and clips.¹ The study cohort consisted of 333 Quill closures and 506 conventional closures. Outcome measures included wound infections. Slightly surprisingly, all eight wound infections occurred in the Quill cohort. Given the low event rate and small numbers, it is possible to ignore these findings. Nonetheless, this is the best evidence there is at present, and it indicates significantly higher superficial infection rates with the Quill suture. Not unreasonably, the authors recommend against the use of barbed sutures in the subcuticular closure of UKAs.

Minimally invasive knee arthroplasty at five years

Surgeons and patients alike love the thought of minimally invasive or keyhole surgery, and with less soft-tissue disruption, reduced scarring and soft-tissue pain, from a surgical perspective the results seem likely to be preferable. We have never been huge fans here at 360, as the results of arthroplasty are to a certain extent determined by the accuracy of implantation, meticulous attention to surgical technique and the delicate task of getting the thing in straight, all of which are more difficult with a ‘mini’ approach. This, combined with the general lack of good-quality evidence to support the use of minimally invasive hip or knee arthroplasty, has caused us to stay away. However, we were delighted to see the five-year results of a study from Rotterdam (The Netherlands), designed to evaluate the benefit (or otherwise) of minimally invasive midvastus and conventional total knee arthroplasty (TKA).² The authors report their randomised controlled trial of 100 TKAs (97 patients) randomised to either midvastus or conventional surgery. The primary outcome measure was the clinical patient-reported outcome measure (PROM), with the knee injury and osteoarthritis outcome score (KOOS), Oxford knee score (OKS), Knee Society score (KSS) and short form (SF-12) reported. In addition, the usual gamut of secondary outcome measures including and skin incision length were reported. This long-term five-year study essentially demonstrated no clinical outcome differences between the two groups based on multiple assessment scores. Overall, alignment was similar, although the posterior slope was greater with the mini-midvastus approach. Finally, there were more complications in larger males using the mini-midvastus approach, thus encouraging surgeons to use the conventional TKA approach in all patients. It seems that this study yields some good answers about the longer-term outcomes of midvastus total knees. The clinical outcomes appear comparable; however, there is a marginally higher complication rate and the implants are not as accurately placed, with the benefit being on average a 2 cm shorter incision.

KOOS-JR for knee arthroplasty

In the second of a pair of papers reporting the development of joint-specific scores for reporting total knee and hip arthroplasty outcomes, the study team from New York, New York (USA) have followed a very similar approach with the knee injury and osteoarthritis outcome score (KOOS) as they did with the hip disability and osteoarthritis (HOOS) outcome score.³ While each of the myriad existing scores has its own exponents and its own benefits, the advantage of the new score is that not only is it properly constructed and validated, but the authors have also managed to reduce the sense of the KOOS score into just seven questions. The KOOS-JR was found to have high internal consistency and may become the standard of outcome testing for total knee arthroplasty in the future.

Metal allergy and arthroplasty

In the fast-moving, connected society in which we live, patients are being given more and more (often slightly unusual) information – all available 24/7 and at their fingertips. We wonder if the rise in patients concerned about the possibility of metal allergy affecting the outcomes of total knee arthroplasties may be due to an increasingly connected, neurotic few; after all, these have been in use for decades and there never used to be a problem. The alternative explanation of course is that there is in fact a problem. Orthopaedic surgeons are finding that having conversations with patients about a possible allergy to certain metals potentially precludes the patient from a standard ‘off the shelf’ joint arthroplasty. Some have reported up to 48% of the population having some form of metal allergy, most commonly nickel. The team in Exeter (UK) have produced an incredibly useful review of where the latest scientific evidence is at present.⁴ The authors highlight that there is some confusion about the issues around metal-on-metal (MoM) bearings and an allergy to certain metals that form part of a joint arthroplasty. Some joint registries (such as the Australian Orthopaedic Association National Joint Replacement Registry) have reported metal hypersensitivity to be the fifth most common cause for revision, contributing to 5.9% of revisions. However, since these registry data were published in 2012, the wording has been changed to ‘metal-related pathology’. With the new classification, the number of revisions associated with metal-related pathology has dropped to 0.5%, as reported in 2014. Even classifying what is meant by ‘sensitivity to metal’ is somewhat controversial. To date, there do not appear to be any studies to suggest that a hypersensitivity to metals is responsible for aseptic loosening. One very interesting observation was from a comparison between the joint registry data in Denmark and the Danish patch registry data. There was no association between metal allergy and total hip arthroplasty (THA) in patients linked by the two registries. However, these data could not be extrapolated to total knee arthroplasty (TKA) as only 0.5% of the THA population of over 70 000 had a positive patch test, which is well below what would be expected in the general population. This brings into question the accuracy of the patch registry data, and therefore whether any meaningful conclusions can be drawn from it. Despite the confusing amount of evidence in the literature, there is considerable support to use standard implants in patients who have a proven metal hypersensitivity. However, this hasn’t stopped implant companies developing ‘hypoallergenic’ components. In TKA, some will elect to use a hypoallergenic femoral component with an all-polyethylene tibial component. While the authors accept that hypersensitivity to metal exists, the real problem, they suggest, is metal wear debris similar to polyethylene debris causing an immunological response, resulting in aseptic loosening. Therefore, they conclude that at present there is not sufficient evidence to support the use of unproven hypoallergenic components. They suggest that it is in the patient’s best interest to continue using standard implants with a proven track record. Nonetheless, we still face being questioned by patients about the materials used in their implants, and if the outcome following their joint arthroplasty is below their expectations they will believe that this is due to a pre-existing hypersensitivity.

What’s wrong with ‘all-poly’?

There are some significant (theoretical at least) advantages to the all-polyethylene tibia. The elimination of the interface on the ‘backside’ of the polyethylene theoretically reduces the incidence of backside wear. Perhaps more crucially, since there is no modulus mismatch, there is no possibility of subsurface stress concentrations and macroscopic failure. Detractors argue that the all-polyethylene design doesn’t allow for flexibility when implanting or the exchange of polyethylene, and that the tibial component may subside or crack. In their review of over 31 900 primary total knee arthroplasties (TKAs) performed over a 43-year period, these authors from Rochester, Minnesota (USA) set out to establish what exactly the outcomes were of their own mixed series of patients with all-polyethylene and metal-backed tibial components.⁵ Outcomes were assessed in terms of revision-free survival and, perhaps surprisingly, the all-tibial components were the out-and-out winners. The all-polyethylene design demonstrated an improved five-, ten-, 20- and 30-year survivorship compared with the metal-backed designs. In addition, the all-polyethylene design was superior in terms of secondary outcomes including reduced rates of post-operative infection, fracture, and tibial component loosening regardless of age or BMI. This paper will, we are sure, pour fuel on the fire of the ongoing debate: modular or not, metal-backed or not. It is worth bearing in mind that this is a series with significant long-term follow-up, lending credibility to the results, but by definition this also means that the implants reported do not feature the latest tribology or design features. As it stands currently based on this result, the future looks rather bright for an all-polyethylene tibia.