C.-Y. CHANG,* Y.-C. SHIH, H.-J. WANG and M.-S. HSIEH§*Hemophilia Center, Department of Pediatrics, Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei MedicalUniversityHospital; DepartmentofOrthopaedicsandTraumatology,GraduateInstituteofClinicalMedicine,CollegeofMedicine,TaipeiMedicalUniversity,Taipei Medical University Hospital; Department of Diagnostic Radiology, Taipei Medical University Hospital; and § Orthopedics Research Center andSchool of Medicine, Department of Orthopaedics and Traumatology, Taipei Medical University, Taipei Medical University Hospital, Taipei, TaiwanPopliteal cysts, also known as Baker cysts, are often seen in patientswho seek treatment for knee pain, with a reported incidence of5% 58% of patients [1]. They are caused by distension of thebursae around the popliteal fossa, and the most common site is thegastrocnemio-semimembranosus bursa. They are divided into pri-mary and secondary cysts. The former are often attributed totrauma or inflammation. The latter are often secondary to intraar-ticular disease which results in bursa distension by synovial fluidfrom the knee through communication between the joint capsuleand bursa [2]. Popliteal cysts are not rare, but are extremely rare inhaemophiliacs, despite haemophilic arthropathies often being found.Rodriguez et al. reported a boy with severe haemophilia A withhaemorrhage into a popliteal cyst, which was a primary cyst [3]. Wereport one case we believe to be the first report of an adult withsevere haemophilia A with a ruptured secondary popliteal cyst,presenting as unusual refractory recurrent haemorrhage of the lowerleg.This 37-year-old man weighing 70 kg who has severe haemo-philia A and arthropathy of bilateral knees visited our hospital inOctober 2007. According to his statement, he had received on-demand replacement therapy of recombinant factor VIII (rFVIII) foryears. His gene defect is an intron 22 inversion. His right medialproximal tibia was hit in an accident in October 2005. After that,he suffered from refractory intermittent right lower leg haemorrhagewith pain and received repeated rFVIII replacement therapy at onehospital. In April 2006, he sought out a second opinion at anotherhospital, and received repeated treatments with 1500 U rFVIII andneedle aspiration of haematoma. Because haemophilic cyst found inthe right lower leg, he received the endoscopy for debridement andremoval of the cyst (maybe due to wanting wound as small aspossible) in early December 2006, with inhibitors of 0 Bethesda unit(BU). As a result of recurrence, the 2nd and 3rd endoscopies wereperformed in late December, 2006 and January, 2007, with rFVIIIused as a continuous drip during and after surgery. Because ofrecurrence and inhibitors of 4.3 BU in January, 2007, prophylacticFeiba at 50 U kg