 The patients will be recruited from one hospital in Gouda over a 6 months inclusion period. All patients over 18 years, scheduled for a meniscectomy, diagnostic arthroscopy or removal of corpora libera will be eligible for inclusion. Patients will be excluded when they suffer from any kind of coagulation disorder, use of hormonal anticonception, in case of pregnancy or puerperium, when they have a history of venous thrombosis, had major surgery or cast-immobilisation of the lower extremity in the past two months, have a neoplasm or inflammatory disease, have a BMI30, or when they use anticoagulant therapy. Patients will generally receive spinal anaesthesia. Patients who are nevertheless exposed to any other type of anaesthesia will be excluded as well, to keep the effect of anaesthesia equal for all participants. 