2. Chronic venous leg ulcer (as defined by the current AWMF guidelines: therapy resistant ulcer that shows no improvement within 3 months despite of optimal phlebological therapies or is not healed within 12 months) for at least 6 weeks but shorter than 3 years diagnosed by doppler ultrasonography (DUS), ankle brachial index (ABI, 0.9-1.3), physical examination and dermatological review;