Pain control after hip replacement surgery is important to ensure patient comfort, allow
mobilisation, and aid recovery. The investigators propose a simple and pragmatic study
comparing two different anaesthetic techniques in the provision of pain relief after hip
surgery. Patients will be randomised to receive either spinal anaesthesia containing morphine
or spinal anaesthesia without morphine and an ultrasound guided fascia iliaca nerve block.
Although morphine is an effective pain killer, its side effects include itch, urinary
retention, nausea and potentially fatal breathing problems. If the nerve block can be shown
to provide comparable pain relief to spinal morphine, then morphine could be removed from the
spinal injection. This could reduce side effects and improve patient safety. The
investigators wish to investigate whether ultrasound guided fascia iliaca plane block
provides analgesia which is comparable to that of intrathecal opioid for primary hip
arthroplasty in the first 24 hours after hip replacement surgery