Hemi-diaphragmatic palsy is a common undesirable effect of interscalene block, with an
incidence of up to 100%. Mechanism of palsy is thought to be related to spread of local
anaesthetic anterior to the anterior scalene muscle. We hypothesize that by injecting saline
in this anatomical location prior to performing an interscalene block the incidence of
phrenic palsy will be reduced.