A number of issues which impact on the ability to recruit patients to the study

Open-labelled, randomised controlled trial. Patients will be assessed pre-operatively, at 24 and 48 hours for the primary outcome and secondary outcomes (except for Oxford Knee Score which will be assessed pre-operatively and at 6 months post-operatively by the ortho-paedic team).

Primary Objective: To demonstrate whether adductor canal nerve infusions result in superior patient mobilisation within the first 48 hours following total knee replacement compared to femoral nerve catheter infusions.

Secondary Objective: To identify whether adductor canal nerve infusions result in superior analgesia within the first 48 hours following total knee replacement compared to femoral nerve catheter infusions.

We are comparing a continuous adductor canal block with a low concentration continuous femoral nerve block. We currently use a low dose femoral nerve catheter based technique as part of our standard treatment strategy for total knee arthroplasty. The use of a catheter provides prolonged analgesia compared to a single shot block, and also allows a lower concentration of local anaesthetic to be employed, thus potentially reducing the incidence of motor blockade. The concentration of local anaesthetic employed in our routine practice (0.0625% L- Bupivacaine) is lower than that routinely used in many other centres, and most clinical studies have compared higher concentrations of local anaesthetic - this might be expected to produce more motor blockade. The concentration we use is higher than the minimum effective concentration for a femoral catheter infusion for knee arthroplasty.

Inclusion Criteria:

• Subject has a diagnosis of rheumatoid or osteoarthritis and listed for a primary total knee replacement.
• Participant is willing and able to give informed consent for participation in the study.
• Male or Female, aged between 18 and 85 years.
• American Society of Anesthesiologists (ASA) score I-III
• Able (in the clinical staff's opinion) and willing to comply with all study requirements.
• Willing to allow his or her General Practitioner and consultant, if appropriate, to be noti-fied of participation in the study.

Exclusion Criteria:

• Patient refusal
• Chronic pain (defined as consumption of >480mg codeine/24hrs or ANY regular strong opiate consumption by the oral/transdermal route)
• Patients aged <18 or >85
• ASA score >III
• Body mass index (BMI) >35
• Lacking mental capacity to give consent to enter trial/undergo surgery
• Contraindications to catheter placement (coagulopathy , systemic sepsis or infection at placement site, pre-existing neuropathy) or any other component to the study treatment pathway.
• Participant who is terminally ill
• Allergy/intolerance to study medications
• Any other significant disease or disorder which, in the opinion of the Investigator, may either put the participants at risk because of participation in the study, or may influence the result of the study, or the participant's ability to participate in the study.