In a Subclan aery block at the outer border of 1st rib, all of the following aeries help in maintaining the circulation to upper limb except?
**Core Concept**
The subclavian artery is a vital blood vessel that supplies blood to the upper limb. A block at the outer border of the 1st rib can compromise blood flow to the arm. To maintain circulation, collateral pathways are essential. The subclavian artery's anastomoses with the axillary, vertebral, and internal thoracic arteries form a network of vessels that help bypass a blockage.
**Why the Correct Answer is Right**
When the subclavian artery is blocked at the outer border of the 1st rib, collateral circulation is established through the:
- **Axillary artery**: anastomoses with the subscapular artery and the thoraco-acromial artery to form the pectoral branch.
- **Vertebral artery**: anastomoses with the costocervical trunk to form the deep cervical artery.
- **Internal thoracic artery**: anastomoses with the superior epigastric artery and the musculophrenic artery.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not directly involved in maintaining circulation to the upper limb in case of a subclavian artery block at the outer border of the 1st rib.
**Option B:** This option is incorrect because it is not directly involved in maintaining circulation to the upper limb in case of a subclavian artery block at the outer border of the 1st rib.
**Option D:** This option is incorrect because it is not directly involved in maintaining circulation to the upper limb in case of a subclavian artery block at the outer border of the 1st rib.
**Clinical Pearl / High-Yield Fact**
The subclavian artery's block at the outer border of the 1st rib can be tested using the Adson's test, which involves checking for a pulse in the radial artery while rotating the arm and applying pressure on the scalene muscles.
**Correct Answer: A.**