Warfarin use and risk of knee and hip replacements

Ballal P, Peloquin C, Boer CG, Neogi T · Annals of the Rheumatic Diseases

The comparison that removes confounding by indication, because both groups needed anticoagulating: warfarin users had 1.59 times the risk of knee or hip replacement compared with DOAC users (95% CI 1.31-1.92), and longer warfarin use carried higher risk.

Population

Adults with atrial fibrillation newly prescribed warfarin or a direct oral anticoagulant in a UK primary-care records database; 857 joint-replacement cases and 3,428 matched controls

Intervention

Warfarin (a vitamin K antagonist)

Comparator

Direct oral anticoagulants, which do not touch vitamin K

Limitations

Nested case-control within a records database, so joint replacement stands in for end-stage osteoarthritis and radiographs were not read; channelling between warfarin and DOAC prescribing may still differ by frailty and renal function. Matching cases and controls by general practice, which absorbs local differences in prescribing and in referral to surgery, pulls the estimate down to 1.36 (1.11-1.66).