The traditional landmarks to locate the injection site and orientation of the spinal needle for spinal anesthesia are based on palpation of surface bony landmarks. However the actual injection target into the CSF is located at an unknown depth inside the patients 3 dimensional spinal anatomy which can itself vary in its orientation relative to these surface markers.Also bony surface markers may not be palpable in some patients or the patient may have altered spinal alignment. Thus an already blind procedure can become even more misguided involving multiple trial and error needle insertions. On the other hand ultrasound allows visualisation of deep target structures which are impalpable, it allows assessment of spinal alignment and thus directs the orientation of the seeking needle more accurately. Performing US in real-time during needle insertion gives continuous feedback about the correct needle approach path which should reduce the number of blind needle passes.

Inclusion Criteria:

• Consenting patients of at least 18 years of age undergoing spinal anesthesia for elective lower limb surgery

Exclusion Criteria (are as for Spinal anesthesia generally)

• Patient refusal
• Sepsis or local infection at the site of injection
• Hypovolemia
• Coagulopathy (INR ≥1.5, Platelets < 75X 109 /L, anticoagulant therapy)
• Indeterminate neurologic disease
• Increased intracranial pressure
• Local anesthetic allergy
• Infection distinct from the site of injection
• Unknown duration of surgery

Patients presenting for elective lower limb orthopaedic surgery to a specialist orthopaedic hospital.