Total knee arthroplasty or replacement (TKA) is a surgery performed for osteoarthritis of the knee which is increasingly performed as the population ages. It is a painful surgery and one of the methods to reduce post-operative pain is performing a regional anaesthesia technique. The current practice is to perform a femoral nerve block (FNB) which blocks the nerves supplying the knee joint and the thigh muscles (quadriceps). This provides effective analgesia. However, it also results in weakness of the quadriceps and may result in falls post-operatively.

Adductor canal block (ACB) is a new, alternative regional anaesthesia technique which is hypothesised to provide as effective analgesia, with less quadriceps weakness compared to FNB, hence potentially reducing the risk of falls post-operatively.

Investigators aim to study if the analgesia provided by ACB is as good as FNB while preserving quadriceps strength.

Inclusion Criteria:

• ages 45-85
• American Society of Anaesthesiologists physical status 1-3
• BMI 18-35 kg/m2

Exclusion Criteria:

• inability to give consent, communicate, cooperate
• Patients with regular consumption of strong opioids (morphine, oxycodone) or steroids
• Patients with allergy to local anaesthetics or any drugs included in the study
• Patients with lower limb surgery in the preceding year
• Patients with pre-existing neurological deficits
• Patients who are unsuitable for general anaesthetics (eg difficult airway)