4th to 8th ribs are involved. 3rd and 9th may be involved.
However 1st and 2nd are spared as these intercostal arteries are not direct branches of thoracic aorta and hence do not form a part of the collateral pathway. They are branches of the costocervical trunk and hence they are spared.
H/o hypertension since 1 year.
Feeble pulses in lower limbs.