S20.4 - Other and unspecified superficial injuries of back wall of thorax
S20.42 - Blister (nonthermal) of back wall of thorax
S20.421 - Blister (nonthermal) of right back wall of thorax
S20.422 - Blister (nonthermal) of left back wall of thorax
S20.429 - Blister (nonthermal) of unspecified back wall of thorax