Discuss the scapular anastomosis. Include discussion of blood flow in the normal case and in the case of ligation of the axillary artery.

The subclavian a gives off the thryrocervical trunk which subsequently gives off the transverse cercical and suprascapular aa. Distally, the subclavian a passes the 1st rib and afterwards it is referred to as the axillary a. The trans. cervical and suprascap. aa run parallel in front of the brachial plexus, cross the lower part of the neck and turn post. The trans. cervical heads towards the levatator scapulae and rhomboids. The suprascap a heads for the scapular notch, crosses over the sup transverse scapular lig (the suprascap n goes under) and then goes on to vascularize the supra/infraspinous fossae. At its 3rd part, the axillary a gives off the subscapular a which gives off the circumflex scapular a. The circum. scap a turns post through the triangular space and passes upwards in the infraspinous process. Branches of the transverse cervical and suprascapular aa connect with branches of the circumflex scapular a creating an anastamosis around the scapula. If the 3rd part of the subclavian a is blocked (as could happen when is passes the 1st rib) or the 1st/2nd part of the axillary a is ligated, blood will flow will be reversed in the circumflex scapular and subscapular aa, now flowing towards/into the axillary a. Blood is able to continue flowing through axillary a, supplying branches distally and the more proximal branches that had been blocked. Blood flowing superiorly/medially in the axillary a can also be though of as flowing in the reverse direction. Because intercostal aa are in contact with the dorsal scapular a, blood coming from the desc aorta is also able to participate in the anastamosis. (Grants shows the dorsal a connecting with the subscapular a inferior to the scapula, which would contribute to the anastamosis, but I did not read about this contribution in HH). Such contact ensures that a block in the aorta can be circumvented as follows - blood flows from the arch of aorta to the subclavian vessels, through the scapular anastamosis, into the intercostal aa via the dorsal scapular a and finally back into the aorta. It is important to note that the enlarged perforating vessels may erode bone or cause notching of the ribs over time. (After re-reading the question, maybe more should be included about the direction of normal blood flow? I would def include a pic w/ arrows on the test-like in Grants.) -- DavidStiffler - 27 Sep 2006 - 20:04

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