In a subclan aery block at outer border of 1st rib, all of the following aeries help in maintining the circulation to upper limb except?
**Core Concept**
The subclavian artery is a major artery that supplies blood to the upper limb, and its blockage at the outer border of the 1st rib can compromise limb circulation. In such a scenario, collateral circulation from other arteries helps maintain blood flow to the upper limb. This question tests the understanding of the collateral circulation pathways that arise from the subclavian artery.
**Why the Correct Answer is Right**
The subclavian artery blockage at the outer border of the 1st rib leads to the formation of a network of collateral vessels that arise from the vertebral arteries, internal thoracic artery, and thyrocervical trunk. These collateral vessels help maintain blood flow to the upper limb by providing an alternative route for blood to reach the subclavian artery. Specifically, the vertebral arteries contribute to the formation of the costocervical trunk, which in turn gives rise to the deep cervical artery that anastomoses with the subclavian artery.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the suprascapular artery is a branch of the thyrocervical trunk, which is one of the arteries that contribute to the collateral circulation in case of a subclavian artery blockage.
* **Option B:** This option is incorrect because the thyrocervical trunk itself is one of the arteries that contribute to the collateral circulation in case of a subclavian artery blockage.
* **Option D:** This option is incorrect because the costocervical trunk, which is a branch of the subclavian artery, gives rise to the deep cervical artery that anastomoses with the subclavian artery, thus helping to maintain blood flow to the upper limb.
**Clinical Pearl / High-Yield Fact**
In case of a subclavian artery blockage, the vertebral arteries and internal thoracic artery play a crucial role in maintaining blood flow to the upper limb through their collateral vessels. This is a classic example of the body's ability to compensate for a blockage in one major artery by recruiting collateral circulation from other arteries.
**Correct Answer: D.**