Intraosseous infusion, illustration. This process is used to inject directly into the marrow of a bone. The injecting device is at upper right, being operated at an angle of up to 30 degrees from the vertical. The bone being injected into here is the tibia, one of the lower leg bones. The femur (thigh bone) is at left, along with the patella (knee-cap) in the knee joint. This method of injection is used to deliver drugs when intravenous access in a patient is not available or difficult.