Research

In-theatre diagnostic tests for periprosthetic infection

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There has been a lot of industry-driven pressure towards the use of expensive assays, and one in particular, anti-defensin alpha-1, to establish the presence or absence of infection intra-operatively during joint revision surgery. Despite the tantalising nature of a bedside instant diagnostic test, uptake has been far from 100% — in part due to the limited (and mostly commercially sponsored) research on its use and partly due to the competing test leukocyte esterase, which is essentially just a standard ‘cheap-as-chips’ urine dipstick. Recognising the current dichotomy in practice, a review team in Bristol (UK) have undertaken a well conceived systematic review and meta-analysis to enlighten us all as to what exactly the evidence is for each approach.¹ The study team’s stated aim in the abstract of their paper was to “synthesize the evidence on the accuracy of the alpha-defensin immunoassay and leukocyte esterase colorimetric strip test for the diagnosis of PJI compared with the Musculoskeletal Infection Society diagnostic criteria”. Their extremely extensive literature review yielded just 11 studies evaluating the accuracy of one or more of these two diagnostic tests. The study team undertook a data-pooling approach to evaluate the sensitivity, specificity and receiver-operator characteristic (ROC) curve for both diagnostic tools. In short, there was no statistically discernible difference between the two, both showing superb sensitivity and specificity with a ROC area under the curve of 0.99 for the alpha-defensin assay and 0.97 for the leukocyte esterase dipsticks. Both were equally impressive from a diagnostic accuracy perspective, however, given the massive cost difference, the feeling around the editorial desks at 360 HQ is that – for the moment at least – the leukocyte esterase tests win out drastically on cost savings alone. This meta-analysis suggests that using a simple urine dipstick is equally as accurate and is a fraction of the cost.

Orthopaedic replicas

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I would strongly recommend all orthopaedic surgeons with an interest in arthroplasty to read this annotation from London (UK), published in a recent issue of The Bone & Joint Journal.² Excellent outcomes with long-term follow-up continue to be reported in the literature for lower limb arthroplasty. Not only can patients expect a successful outcome in terms of pain relief and function, but the results are also durable in the long term. It is also widely reported that with an ageing population, the demand for lower limb arthroplasty is expected to rise. Increasingly, the cost of performing a total hip or knee arthroplasty has come under close scrutiny with efforts to reduce patients’ length of stay in hospital and increase theatre productivity. An additional focus has been on the cost of the implants we use, particularly with a number of the well-established implants coming off patent. Are these implants, however, really ‘good enough’? The two most publicised disasters in orthopaedic arthroplasty implants is the Capital Hip System (3M; St Paul, Minnesota) — a copy of the Charnley — and the articular surface replacement (ASR), a copy of the Birmingham hip. Neither of these lightly modified implants appeared terribly different even to the educated consumer, however, both were significant disasters. The authors of this important article highlight the difficulty in identifying the true costs of manufacturing an implant due to the lack of transparency. Estimates have suggested that the actual manufacturing of the implant represents approximately 30% of the final cost, while the sales and marketing represent 40%. Similar to the drug industry, as patents expire, generic ‘copies’ of well established implants are starting to appear on the market. However, there is very little regulation of how these copies are manufactured, nor how they are monitored once they are on the market. We would thoroughly commend this annotation to 360 readers.