History of Osteoarthritis

Mr. Black, 34 years old, was admitted to the hospital with a fractured right lower leg. Mr Black has a history of Osteoarthritis. He has a cast in place to immobilise his leg. The doctor has ordered hourly neurovascular observations. 

Mr Black was having anticoagulation therapy before he went to theatre, and it is still charted to be administered twice daily. What should you consider before administering his evening injection?