The experience of pain is common among hospital inpatients. Orthopaedic surgery often results in significant pain, which may last for some time. About one in eight people will experience long-term or chronic pain after surgery, which can impact on quality of life and mood. Some risk factors are known for chronic post surgical pain (CPSP) and these include patient factors, surgical factors and anaesthetic factors. We know that mood problems (anxiety and depression) increase the risk of CPSP. What is not known is how short term changes in mood are related to the experience of pain after surgery and how this impacts on CPSP. This study is designed to investigate the relationship between both short and long-term mood problems and short and long-term pain and quality of life after orthopaedic surgery. The study will provide valuable information to allow us to design a psychological intervention, which might reduce the risk of short-term post surgical pain and CPSP.