 Researchers previously conducted a study at the Royal Devon and Exeter Hospital which compared the effects of two techniques; the use of diamorphine in a spinal injection, and the injection of pain killer around a nerve supplying the leg femoral nerve block, FNB. Whilst the research showed that FNB gave better pain relief, there are still concerns that it causes weakness which may interfere with movement. A newer technique has evolved over recent years in which pain killer is injected directly around the knee during the operation. This is known as local infiltration analgesia LIA and the potential advantages are that it is simple, safe and does not cause leg weakness. 