Acquired hemophilia A (AHA) is a rare autoimmune bleeding disorder caused by autoantibodies against factor VIII and may present with life-threatening hemorrhage. Postoperative presentation is uncommon and may lead to delayed diagnosis, as bleeding is often initially attributed to surgical causes.

We report a 64-year-old man with post-traumatic knee arthritis and retained hardware who underwent navigation-assisted total knee replacement. The procedure was uneventful with an estimated blood loss of 300 mL. On postoperative day two, he developed acute knee swelling with persistent bleeding through a negative-pressure wound dressing. Urgent re-exploration and hematoma evacuation were performed; however, diffuse bleeding persisted despite adequate surgical hemostasis, requiring activation of a massive transfusion protocol.

Laboratory investigations demonstrated isolated prolongation of activated partial thromboplastin time (aPTT) at 65.3 seconds. Further coagulation studies revealed markedly reduced factor VIII activity with circulating factor VIII inhibitors, confirming AHA. Hemostasis was achieved following treatment with FEIBA and NovoSeven under hematology guidance. The patient subsequently recovered well and was discharged with outpatient follow-up.

This case highlights acquired hemophilia A as a rare but important differential diagnosis in persistent postoperative bleeding following total knee replacement. Early recognition, prompt coagulation workup, and multidisciplinary management are essential to improve outcomes.

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