Knee

Re-admission following total knee arthroplasty: are complications to blame?

In these days of bundled payments and financial penalties for re-admissions, with some healthcare systems imposing enforced financial implications on hospitals and surgeons where patients are re-admitted within a fixed time period, the surgeon now faces dual burdens. On the one hand, there is significant pressure to reduce hospital admissions and length of stay, and, on the other, there are penalties if the patients are re-admitted (higher re-admission rates seem almost inevitable with day-case or 24-hour stay arthroplasty). Surgeons in the Hospital for Special Surgery in New York, New York (USA) are taking a look at the somewhat contentious issue of re-admission after surgery for total knee arthroplasty (TKA).¹ Aiming to clarify what the causes and risk factors are after surgery, they used the Statewide Planning and Research Cooperative System (SPARCS) database from the New York State Department of Health to identify 377 705 patients, all of whom had undergone TKA between 1997 and 2014 in New York State. In total, there were 22 076 re-admissions within 30 days: an overall incidence of 5.8%. The authors extracted the ID-9 codes for re-admission and attributed them as due to complications as a result of the primary procedure (ICD-9 attributable and a wider definition agreed by expert opinion) or unrelated. The authors then undertook a multivariable analysis to examine the incidence, causation and predisposing factors for re-admission following surgery for a TKA. There were differing rates of re-admission between units included in the study, with a median rate of 3.9%. Using the two criteria defined in the study, 11% were ICD-9 attributable to the knee arthroplasty, and 31% were potentially attributable on the expanded expert list. The authors identified older age (> 85 years, odds ratio (OR) = 1.32), male gender (OR = 1.41), Medicaid coverage (OR = 1.40), and various comorbidities as increasing risk factors for knee-related re-admissions. However, although smaller units had a higher re-admission rate, this was not specific to knee-related complications and appeared to be important in units operating on < 90 patients per year. The key take home point of this study is that re-admission for any cause after TKA is much higher than for total knee-specific causes. With this being the case, orthopaedic surgeons and their units should not be punished for every hospital re-admission after surgery. Hospital administrators and healthcare funders should recognise and make the distinction between separate re-admissions that should not be bundled with the index procedure payment, if the complications are different and not related to the index surgery.

Total knee constraint and surgical technique: any effect on survival?

Constraint and ligament substitution is an interesting area in total knee arthroplasty (TKA), and there are certainly a number of differing philosophies as to what is best. At one end of the spectrum, there are some surgeons who will undertake rotating hinge knee arthroplasties, even as a primary procedure. On the other, there are those who will do their utmost to retain the ligaments, and preferentially insert posterior cruciate ligament (PCL)-retaining implants – even into valgus knees, which potentially require more constraint. These authors from Adelaide (Australia) reason that there are potentially two types of surgeons: those who always undertake posterior-stabilised implants; and those who use cruciate-retaining knees where possible (sometimes known as kinematic and minimally stabilised, respectively).² The authors sought to take advantage of these preferences to test the assertion that kinematic knee arthroplasty survival is poorer due to case selection, as those with a preference for minimal stability will undertake kinematic knees in more complex cases. The authors constructed a form of intention-to-treat analysis using the apparent surgical preferences from the Australian Joint Registry. They then went on to compare outcomes between posterior-stabilised and cruciate-retaining TKAs. The study showed interesting results in a large patient population. However, it is important to recognise the drawbacks in this method, in that by comparing surgeons who used one prosthesis exclusively, the study is really a comparison of surgical philosophy and technique as opposed to a comparison of implants. The primary outcome of this study was the hazard ratio (HR) for revision, which was calculated using cumulative percentage revision. The data set follows patients for up to 13 years, where the cumulative percentage revision was 5.0% (95% CI 4.0% to 6.0%) versus 6.0% (95% CI 4.2% to 8.5%) for surgeons who preferred minimally stabilised versus posterior-stabilised, respectively. Therefore, there were no overall significant differences in the cumulative percentage revision rates between the groups. Slightly confusingly, however, the hazard ratios were significantly different for all causes (HR 1.45, 95% CI 1.30 to 1.63), for loosening or lysis (HR 1.93, 95% CI 1.58 to 2.37), and for infection (HR 1.51, 95% CI 1.25 to 1.82). Further studies using prospective randomised cohorts are clearly needed here to determine whether these differences are true in all patient populations. Estimation of risks in large cohort studies with variable follow-up and loss to follow-up is always rather difficult, and we are somewhat perturbed by the apparent conflict in overall cumulative revision risk and calculated hazard ratios for revision. Clearly, one would expect causes such as infection not to vary between the two techniques, with a reported HR of 1.45 (which is not, of course, a 45% increased risk of revision, despite the report here).³ Despite the flaws in the study design, analysis, and reporting, here at 360 we do think that this study is worthy of mention – it does focus on a topical and poorly studied question: what should the inherent position for knee stabilisation be?