An ulnar nerve block uses local anaesthetic to block the nerve at the wrist, allowing procedures on the ulnar side of the hand and in the 5th finger (grey area on diagram).
Distribution of the Ulnar Nerve in the hand
Suitable for use in injuries requiring procedures on the 5th finger and/or ulnar side of hand (i.e. over the 5th metacarpal) with treatment of duration less than 30- 45 minutes such as:
Finger or hand lacerations requiring suturing
Manipulation of phalangeal fractures or interphalangeal joint dislocations
Manipulation of 5th metacarpal fractures
Patient able to cooperate with injections and for the procedure intended
Formal consent not required but procedure should be clearly documented
pain as the injection is made
nerve block might not work
bruising and bleeding at the site of injection
Dressing pack with antiseptic (Chlorhexidine or similar)
5ml syringe filled with lignocaine 1% or 2% (with or without adrenaline)
Note: maximum dose of lignocaine is 3 mg/kg
Warm lignocaine to body temperature (i.e. in your hand) to reduce discomfort
25G needle (orange) for the injection
Consider EMLA application over injection site
Consider Nitrous Oxide for sedation whilst injections are occurring
Positioning and technique
Patient positioned with palm held upwards and slightly flexed with wrist appropriately draped and prepared with aseptic technique
Identify the flexor carpi ulnaris tendon (the ulnar nerve runs immediately underneath this tendon)
An injection is made 1-2 cm proximal to the proximal wrist crease with the needle horizontal (i.e. coming from the ulnar side and aiming towards the radius), aiming to infiltrate lignocaine a few millimetres beneath the carpi ulnaris tendon
The needle is aspirated to ensure that it is not in a vessel
If parasthesia is felt, then do not inject as this indicates that the needle lies within the nerve and will damage it
2-3 ml of lignocaine is injected slowly and should inject easily if in the right place
Allow up to 10 minutes for the block to become effective. If the area still has some sensation, a repeat injection can improve the effect (after another 5-10 minutes).
It may be necessary to inject 2-3 mls of lignocaine subcutaneously around the ulnar styloid to block the dorsal sensory branch of the nerve which may not have been blocked with the initial injection (branches off just above wrist, so hopefully blocked with first injection).
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