When performing total knee replacement surgery, the surgeon has a choice as to which type of surgical technique to use. The standard technique at the Royal Infirmary in Edinburgh is the so-called 'medial parapatellar' exposure. And alternative and more recently introduced technique is the 'Mid-vastus approach' in which the surgeon will cut through less of the muscle at the front of the leg. In this study we compare the two surgical techniques in a so-called randomized trial. This means that we put people randomly into two groups, one group will receive surgery with the 'Mid-vastus approach' and the other group the surgery with the 'Medial parapatellar approach'. It is hypothesized that people who receive the Mid-vastus approach recover quicker and have a better short-term functional outcome than people who receive the 'Medial parapatellar approach'.

This study is a prospective randomized controlled double blind trial in which both immediate post-operative recovery and functional outcome at 6 weeks, 3 and 6 months after total knee replacement surgery will be assessed for two different types of surgical approach; Medial Parapatellar and Mid-vastus.

Functional outcome will be assessed by recording the kinematics of the lower limb joints in addition to muscle activity (electromyography) during walking, stair ascending and descending and getting up from a chair through computerized 3D motion analysis. Outcome measures will be recorded immediate post surgery and at medium follow-up and will cover all areas of the World Health Organisation, International Components of Functioning, Disability and Health (ICF) components 'Body Structures and Functions/Impairments' ,'Activities and Participation' and 'Personal factors'. It is hypothesized that by minimizing the damage to the quadriceps, patients operated using the Mid-vastus approach will have better muscle function and will therefore have more normal knee range of motion, knee joint loading and muscle activity patterns compared to those with the Medial Parapatellar approach.

Inclusion Criteria:

• Total knee arthroplasty
• Osteoarthritis
• Surgery at Royal Infirmary Edinburgh by participating surgeons

Exclusion Criteria:

• A Body Mass Index of more than 40
• Fixed valgus deformity of more than 15 degrees
• Inflammatory polyarthritis
• disorders of the feet, ankles or hips or spine causing abnormal gait or significant pain
• dementia
• severe visual impairment
• neurological conditions affecting movement
• inability to give informed consent