The goal of this study is to prevent blood clots from forming during surgery and a few days after total knee replacement surgery. This study will help us identify whether using a blood thinner in the operating room will stop blood clots from forming during the operation.

Venous thromboembolism is a major cause of morbidity and mortality after lower limb orthopaedic surgery in the adult patient. If, as suggested, DVT formation begins intra-operatively then targeting this period to prevent clot formation could substantially reduce DVT rates in the TKA population. The present study aims to determine whether this intra-operative regional heparinization technique is effective in preventing the intra-operative formation of DVT following TKA, as evidenced by venography in the early post-operative period.

Inclusion Criteria:

1. Undergoing unilateral primary total knee arthroplasty
2. Males and non-pregnant females ages 18-90 (pre-menopausal females will undergo a serum pregnancy test at screening)
3. Full weight bearing status (of non-operated leg) following surgery
4. Patient able to understand and willing to sign informed consent

Exclusion Criteria:

• 1) Known hypersensitivity to contrast media 2) Patients taking Metformin 3) Serum creatinine above 180Fmol/L 4) Platelets < 100 x 10 9/L, INR/PTT > 1.5 x normal 5) History of heparin induced thrombocytopenia 6) Allergy to heparin or fish 7) Prior use of protamine sulfate (i.e., protamine-containing insulin) 8) Vasectomized or infertile males 9) History of bleeding disorder 10) Bilateral total knee arthroplasty 11) History of stroke or myocardial infarction in previous 6 months 12) Traumatic spinal anaesthesia (two or more attempts and/or bloody) 13) History of previous DVT/PE 14) Active peptic ulcer disease (e.g., GI bleed, rectal bleed) 15) Currently on chronic anticoagulant therapy 16) Contra-indication to heparin 17) Patient is taking part in any other investigational study 18) Previous contralateral TKR or hip replacement