To evaluate the association between metformin use and incident osteoarthritis (OA) in people with diabetes and the impact of dosing.

Nested case-control study within a cohort of >1.4 million individuals from Sweden.

Participants were aged 35–80 years in 2005, without diabetes or OA. We identified persons with incident diabetes between 2006 and 2016 and excluded those with OA before the diabetes diagnosis and those with an incident OA diagnosis within 3 years of the diabetes diagnosis. Cases were defined as individuals with incident OA before 2020 and were matched with up to four controls without OA in the same period, by sex, diabetes duration, birth year (±1 year) and date of diabetes diagnosis (±180 days) using incidence density sampling. Metformin use before the index date (OA diagnosis) was the main exposure. Secondary exposures were quartiles of total metformin use (defined daily doses (DDD)) and duration-adjusted use (DDD/day), reflecting average daily use. We estimated risk ratios with 95% CIs using conditional logistic regressions, adjusted for age at diabetes diagnosis, education, immigration status and comorbidities.

Incident OA diagnosis in primary or specialist care (International Classification of Diseases codes M15–M19).

We identified 4007 cases and 14 111 controls. Any metformin use was not associated with OA risk (risk ratio (RR) 1.02, 95% CI 0.93 to 1.12). Results for higher total use (0.98 (95% CI 0.86 to 1.11)) and duration-adjusted use (0.92 (95% CI 0.79 to 1.07)) showed no or inconclusive associations.

In individuals with incident diabetes and no prior OA, metformin was not linked to a lower risk of developing OA.

Type 2 diabetes mellitus (T2DM) and osteoarthritis (OA) are globally prevalent chronic diseases that affect millions of individuals in ageing populations. Hip and knee replacements are well established and effective treatments in patients suffering from end-stage OA. Understanding how T2DM influences the outcomes of these surgeries is important for optimising patient care and improving surgical results. This study aimed to explore the association of T2DM with reoperation (regardless of the reason), adverse events (AEs) and mortality after primary hip and knee replacement surgery.

Observational study based on prospectively collected registry data analysed retrospectively.

Data from several Swedish national quality registers and health data registers were used to create a study database. 109 938 and 80 897 primary hip and knee replacements due to OA, performed between 2008 and 2019 (hip) and 2009 and 2018 (knee), were included in the study.

The risk of complications, such as reoperation, AEs and mortality, was investigated by estimating HRs using Cox regression, and OR using logistic regression, unadjusted and adjusted for confounding factors, such as patient characteristics, socioeconomic status and comorbidities, and mediators, such as surgical factors.

Adjusted multivariable Cox-regression analysis showed no T2DM-associated risk of reoperation after hip or knee replacement, adjusted HR 1.10 (95% CI 0.99 to 1.23) and 1.09 (95% CI 0.96 to 1.24), respectively, while T2DM was associated with increased risk of death after hip and knee replacement, adjusted HR 1.40 (95% CI 1.34 to 1.47) and 1.38 (95% CI 1.31 to 1.45). Adjusted logistic regression analysis showed T2DM-associated increase of reoperation within 90 days (OR 1.23 (95% CI 1.05 to 1.43)) and increased mortality within 90 days (OR 1.42 (95% CI 1.01 to 1.95)) following hip replacement; however, this was not the case after knee replacement, OR 1.08 (95% CI 0.85 to 1.36) for reoperation and OR 1.29 (95% CI 0.84 to 1.94) for mortality. Several factors closely linked with T2DM, such as body-mass index and comorbidities, were identified as important when assessing risk of reoperation and mortality. Regarding AEs within 30 and 90 days, very slight but not statistically significant T2DM-associated increases were seen after either hip replacement, OR 1.01 (95% CI 0.91 to 1.11) and 1.07 (95% CI 0.98 to 1.16) or after knee replacement, OR 1.05 (95% CI 0.93 to 1.17) and 1.08 (95% CI 0.98 to 1.19).

The observed risk of reoperation suggests that T2DM alone was not a strong justification to advise against hip or knee replacement in individuals with T2DM deemed eligible for joint replacement. The T2DM-associated increased mortality after hip and knee replacement is challenging to interpret, as T2DM itself without undergoing hip or knee replacement surgery is associated with increased mortality.