• hospital mortality [ Time Frame: 1months after operation ] [ Designated as safety issue: Yes ]
• sensory function in lateral cutaneous nerve [ Time Frame: 0mins, 10mins 20mins post insertion of local anaesthetic ] [ Designated as safety issue: No ]
• sensory function of femoral nerve [ Time Frame: 0mins, 10mins, 20mins after insertion of local anesthetic ] [ Designated as safety issue: No ]
• sensory function of obturator nerve [ Time Frame: 0mins, 10mins, 20mins after insertion of local anesthetic ] [ Designated as safety issue: No ]
• motor function of obturator nerve [ Time Frame: 0mins, 10mins and 20minutes after insrtion of local anesthetic ] [ Designated as safety issue: No ]
• motor function of femoral nerve [ Time Frame: 0mins,10mins and 20mins post insertion of local anesthetic ] [ Designated as safety issue: No ]
• acute mental test scores [ Time Frame: 6hours and 24 hours post operatively ] [ Designated as safety issue: No ]
• total morphine dose administered [ Time Frame: 6hours and 24 hours post operstively ] [ Designated as safety issue: No ]
• day first mobilise post operatively [ Time Frame: post operatively 0-10 days ] [ Designated as safety issue: No ]
• patient satisfaction scores [ Time Frame: 6 hours and 24hours post operatively ] [ Designated as safety issue: No ]

Studies have suggested a link with effective pain relief and reduced illness and death in very unwell patients. This study will determine the most effective method of injecting local anaesthetic around the nerves which supply the hip joint. Local anaesthetic will be injected around the hips nerve supply using either ultrasound, loss of resistance or electrical nerve stimulator to guide the positioning of the needle on patients due for elective total hip replacement. The patient will then be observed for 30 minutes and the patient ability to move or feel the upper leg will recorded. A standard anaesthetic and a hip replacement operation will then be performed. Standard pain relief protocols will be used the operation and after the operation. After the operation we will record the amount of morphine used and how happy the patients have been with their treatment at 6 hours after the operation and at 24 hours after the operation. The first day the patient is able to walk on their new hip replacement will also be recorded.

• Procedure: determination of method with highest efficacy (ultrasound or nerve stimulator)
• Procedure: nerve stimulator
• Procedure: loss of resistance

• Placebo Comparator: Anterior psoas compartment nerve block inserted using loss of resistance
• Active Comparator: Anterior psoas compartment nerve block inserted using nerve stimulator
• Active Comparator: Anterior psoas compartment nerve block inserted using ultrasound

Inclusion Criteria:

• Elective primary total hip arthroplasty under general anaesthesia
• ASA<=4
• Able to give informed consent
• Able to cooperate with sensory and motor testing of lower limb function

Exclusion Criteria:

• Abnormal clotting screen (coagulopathy) or thrombocytopenia (<100,000)
• Acute mental test score of <=7 at any time pre or post operatively
• Allergy to local anaesthetic
• Signs, symptoms or laboratory evidence of local infection or systemic sepsis
• No pre-existing neurological deficit (sensory or motor) affecting lower limb
• Patients with lower limb amputations