Obesity and revision surgery, mortality, and patient-reported outcomes after primary knee replacement surgery in the National Joint Registry: A UK cohort study.

BACKGROUND: One in 10 people in the United Kingdom will need a total knee replacement (TKR) during their lifetime. Access to this life-changing operation has recently been restricted based on body mass index (BMI) due to belief that high BMI may lead to poorer outcomes. We investigated the associations between BMI and revision surgery, mortality, and pain/function using what we believe to be the world's largest joint replacement registry. METHODS AND FINDINGS: We analysed 493,710 TKRs in the National Joint Registry (NJR) for England, Wales, Northern Ireland, and the Isle of Man from 2005 to 2016 to investigate 90-day mortality and 10-year cumulative revision. Hospital Episodes Statistics (HES) and Patient Reported Outcome Measures (PROMs) databases were linked to the NJR to investigate change in Oxford Knee Score (OKS) 6 months postoperatively. After adjustment for age, sex, American Society of Anaesthesiologists (ASA) grade, indication for operation, year of primary TKR, and fixation type, patients with high BMI were more likely to undergo revision surgery within 10 years compared to those with "normal" BMI (obese class II hazard ratio (HR) 1.21, 95% CI: 1.10, 1.32 (p < 0.001) and obese class III HR 1.13, 95% CI: 1.02, 1.26 (p = 0.026)). All BMI classes had revision estimates within the recognised 10-year benchmark of 5%. Overweight and obese class I patients had lower mortality than patients with "normal" BMI (HR 0.76, 95% CI: 0.65, 0.90 (p = 0.001) and HR 0.69, 95% CI: 0.58, 0.82 (p < 0.001)). All BMI categories saw absolute increases in OKS after 6 months (range 18-20 points). The relative improvement in OKS was lower in overweight and obese patients than those with "normal" BMI, but the difference was below the minimal detectable change (MDC; 4 points). The main limitations were missing BMI particularly in the early years of data collection and a potential selection bias effect of surgeons selecting the fitter patients with raised BMI for surgery. CONCLUSIONS: Given revision estimates in all BMI groups below the recognised threshold, no evidence of increased mortality, and difference in change in OKS below the MDC, this large national registry shows no evidence of poorer outcomes in patients with high BMI. This study does not support rationing of TKR based on increased BMI.

Factors associated with implant survival following total hip replacement surgery: A registry study of data from the National Joint Registry of England, Wales, Northern Ireland and the Isle of Man.

BACKGROUND: Nearly 100,000 people underwent total hip replacement (THR) in the United Kingdom in 2018, and most can expect it to last at least 25 years. However, some THRs fail and require revision surgery, which results in worse outcomes for the patient and is costly to the health service. Variation in the survival of THR implants has been observed between units and reducing this unwarranted variation is one focus of the "Getting it Right First Time" (GIRFT) program in the UK. We aimed to investigate whether the statistically improved implant survival of THRs in a high-performing unit is associated with the implants used or other factors at that unit, such as surgical skill. METHODS AND FINDINGS: We analyzed a national, mandatory, prospective, cohort study (National Joint Registry for England, Wales, Northern Ireland and the Isle of Man [NJR]) of all THRs performed in England and Wales. We included the 664,761 patients with records in the NJR who have received a stemmed primary THR between 1 April 2003 and 31 December 2017 in one of 461 hospitals, with osteoarthritis as the only indication. The exposure was the unit (hospital) in which the THR was implanted. We compared survival of THRs implanted in the "exemplar" unit with THRs implanted anywhere else in the registry. The outcome was revision surgery of any part of the THR construct for any reason. Net failure was calculated using Kaplan-Meier estimates, and adjusted analyses employed flexible parametric survival analysis. The mean age of patients contributing to our analyses was 69.9 years (SD 10.1), and 61.1% were female. Crude analyses including all THRs demonstrated better implant survival at the exemplar unit with an all-cause construct failure of 1.7% (95% CI 1.3-2.3) compared with 2.9% (95% CI 2.8-3.0) in the rest of the country after 13.9 years (log-rank test P < 0.001). The same was seen in analyses adjusted for age, sex, and American Society of Anesthesiology (ASA) score (difference in restricted mean survival time 0.12 years [95% CI 0.07-0.16; P < 0.001]). Adjusted analyses restricted to the same implants as the exemplar unit show no demonstrable difference in restricted mean survival time between groups after 13.9 years (P = 0.34). A limitation is that this study is observational and conclusions regarding causality cannot be inferred. Our outcome is revision surgery, and although important, we recognize it is not the only marker of success of a THR. CONCLUSIONS: Our results suggest that the "better than expected" implant survival results of this exemplar center are associated with implant choice. The survival results may be replicated by adopting key treatment decisions, such as implant selection. These decisions are easier to replicate than technical skills or system factors.

The association between cement type and the subsequent risk of revision surgery in primary total hip replacement.

Background and purpose - To further improve the success of joint replacement surgery, attention needs to be paid to variations associated with improved or worsened outcomes. We investigated the association between the type of bone cement used and the risk of revision surgery after primary total hip replacement. Methods - We conducted a prospective study of data from the National Joint Registry for England and Wales between April 1, 2003 and December 31, 2013. 199,205 primary total hip replacements performed for osteoarthritis where bone cement was used were included. A multilevel over-dispersed piecewise Poisson model was used to estimate differences in the rate of revision by bone cement type adjusted for implant type, head size, age, sex, ASA grade, and surgical approach. Results - The rate of revision was higher in DePuy CMW3 medium viscosity with gentamicin (IRR 2.0, 95% CI 1.5-2.7) and DePuy SmartSet high viscosity plain (IRR 2.7, 95% CI 1.1-5.5), and lower in DePuy CMW1 high viscosity plain (IRR 0.44, 95% CI 0.19-0.89) bone cements compared with Heraeus Palacos high viscosity with gentamicin. Revision rates were similar between plain and antibiotic-loaded bone cement. Interpretation - The majority of bone cements performed similarly well, excluding DePuy SmartSet high viscosity and CMW3 high viscosity with gentamicin, which both had higher revision rates. We found no clear differences by viscosity or antibiotic content.