People aged 16 or over.

Scheduled for elective, posterior lumbar-instrumented spinal surgery +/- decompression (including patients undergoing this surgery following a previous lumbar discectomy or decompression).

Able to give informed consent, with interpreters provided where necessary.

Patients with drug sensitivity or allergy to any of the trial agents, i.e. intrathecal opioid or local anaesthetic.

 Patients undergoing fusion at  more than 3 vertebral levels.

Patients with an infection or tumour at the block site or surgical site.

Patients meeting criteria for American Society of Anaesthesiologists Physical Status Classification Grade 4-5.

Patients undergoing surgery during emergency admission (this would preclude a detailed risk-benefit conversation with a consultant anaesthetist, which our PPI group told us was vital pre-consent).

 Patients scheduled for single-level microdiscectomy and decompression only.

Patients undergoing anterior surgery.

Patients who have previously had posterior lumbar instrumentation.

Current pregnancy: a pregnancy test, in the female patients of childbearing age is routine immediately prior to surgery.