Warfarin Use Linked to Knee and Hip Replacement in OA Patients

Patients who take the vitamin K antagonist warfarin to prevent thromboembolic events are significantly more likely to require knee or hip replacement surgery — a surrogate endpoint for end-stage osteoarthritis — than are patients who take direct oral anticoagulants (DOACs), results of a UK-based study showed.

In a nested case-control study, warfarin use was associated with a 1.5-fold risk for knee and hip replacement, compared with use of DOACs.

The findings provide additional evidence for the role of vitamin K and vitamin K–dependent proteins for limiting osteoarthritis progression, said lead author Priyanka Ballal, MD, a rheumatology fellow at Boston University.

"Given the prevalence and impact of osteoarthritis, our data, along with the existing literature, support the need for a well-powered, randomized, controlled trial for evaluating vitamin K supplementation in osteoarthritis. Our study also raises the consideration of using DOACs over warfarin when indicated in people with or at risk of osteoarthritis," she said in a plenary session at the virtual annual meeting of the American College of Rheumatology.

Warfarin targets vitamin K for its role in coagulation, but vitamin K is also an essential co-factor for vitamin K-dependent proteins in bone and cartilage, Ballal said,

Inadequate vitamin K levels are associated with abnormal joint tissue mineralization, and with increased incidence and prevalence of osteoarthritis. In a randomized, controlled trial, vitamin K supplementation was associated with trends toward less osteoarthritis progression among patients with vitamin K deficiency, she said.

To see whether warfarin therapy has biologic effects similar to that seen in patients with vitamin K deficiency, Ballal and colleagues conducted a nested, case-control study using data from The Health Improvement Network (THIN), an electronic medical record database of patients enrolled with general practitioners in the United Kingdom.

The sample included adults aged 40-80 years with atrial fibrillation who had received one or more prescriptions for warfarin or a DOAC beginning in 2009, a year after DOACs were first marketed in the United Kingdom, and within 1 year of the index date (date of joint replacement surgery). The researchers excluded patients with knee or hip replacements before 2014, severe comorbidities that would limit joint replacement, or who had used either warfarin or a DOAC prior to study entry. Each case was matched by age, gender, and index date with up to four control patients (those who did not have surgery).

A total of 913 cases and 3652 controls were included. The groups had similar characteristics (sex, age, cancer, renal disease, chronic lung disease, hypertension, and incidence of venous thromboembolism [VTE]), except for somewhat higher rates of diabetes and heart failure among controls, and a higher rate of obesity among cases.

The investigators first looked at warfarin use among all knee and/or hip replacement cases and controls and calculated an odds ratio of 1.57 (95% CI, 1.30 - 1.89) for knee and hip replacement with warfarin after adjustment for body mass index, factors influencing choice of anticoagulant, comorbidities, other medications, general practitioner visits, and hospitalizations.

The association between warfarin and joint replacement held up in an analysis restricted to knee replacement only, with an adjusted OR of 1.48 (95% CI, 1.16 - 1.89).

There was also a clear association between duration of warfarin use and risk of knee and hip replacement.

"This abstract suggests the role of adequate vitamin K may be important in decreasing progression of osteoarthritis, which would then favor patients with OA who are on warfarin to consider changing to a DOAC; however, further studies are needed to confirm this finding and consider its impact on VTE and wound healing postop," said Minna Kohler, MD, director of the rheumatology musculoskeletal ultrasound program at Massachusetts General Hospital in Boston. Kohler, who was not involved in the study, replied to an email request for comment.

The study was supported by grants from the National Institutes of Health. Ballal and Kohler reported having no conflicts of interest to disclose.

American College of Rheumatology (ACR) 2020 Annual Meeting: Abstract 0934. Presented November 7, 2020.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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