Tag Archives: blood supply

Scaphoid bone anatomy and fractures

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scaphoid_fracturesThe scaphoid bone is one of the eight carpal bones of the wrist (you can check out this doodle for a refresher).

The scaphoid is the most commonly fractured carpal bone, accounting for almost 70% of fractures. It tends to be young males who break their scaphoid this is both an anatomical thing: younger kids get ligament injuries and older folks break their distal radius and a lifestyle thing: falling on outstretched hands (skateboarding, snowboarding) or throwing a punch both place a lot of force across the scaphoid leading to fractures.

The bad thing about scaphoid fractures is that the blood supply (from a branch of the radial artery) comes from distal to proximal. Since most fractures happen at the waist of the scaphoid the likelihood of having poor blood supply to the fracture site is quite high. It doesn’t help matters that around 80% of the scaphoid is articular surface (joint surface), so if it doesn’t heel well, it can lead to problems with arthritis of the wrist later on.

 

Presentation

Scaphoid fractures present with a pretty classic story and the person is usually swollen and bruised and will have tenderness in their “snuffbox.” So even if the x-ray doesn’t show a fracture, it’s best to treat with a cast for comfort and safety and then recheck them in 2 week’s time (this will be discussed in a separate post).

Lip Anatomy

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Lip lacerations are kind of a big deal when it comes to facial injuries. It’s because whether we admit it or not, they’re a very important part of the overall cosmetic appearance of the face.

The tricky thing is the vermillion border, which is a fancy term for where the red of the lips meets the rest of the face. The lip is then further divided into the dry vermillion (the part that you put lip stick on, because it’s the part that you can see with the mouth closed) and the wet vermillion (the part that you don’t put lipstick on unless you want it on your teeth).

So when you’re repairing lips, you need to make sure that everything lines up juuuust right. The other important considerations are that unlike fingers, you can’t just pump the lips full of local anesthetic because it will distort the anatomy, this means that a nerve block is preferred. The upper lip receives innervation from the infraorbital nerve (a branch of CNV2) and the lower lip receives innervation from the inferior alveolar nerve (more specifically the mental nerve, which originate from CNV3).

Blood supply comes from the superior and inferior labial arteries (guess which one goes to which lip), which are branches off the facial artery.

DANGER ZONE!!! (the cavernous sinus)

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The danger zone on the face is a little triangle from the corners of the mouth up to the bridge of the nose. The reason it has such an epic name is because due to its venous drainage (from the facial veins and pterygoid plexus) there’s the possibility of infection traveling from that area into the cavernous sinus.

The cavernous sinuses (there’s one on each side) is an area posterior to the maxillary sinuses and lateral to the pituitary. It receives blood from the superior and inferior ophthalmic veins, superficial cortical veins and the basilar plexus. The blood then drains into the petrosal sinuses (you guessed it, there’s a superior and inferior one of those too) and then those drain into the internal jugular vein.

The thing about the cavernous sinuses a whole lot of important stuff passes through it.

  • CN III (occulomotor)
  • CN IV (trochlear)
  • CN V1 (ophthalmic branch of trigeminal)
  • CN V2 (maxillary branch of trigeminal)
  • CN VI (abducens)
  • Internal carotid (and the sympathetic fibres on the carotid)

This means that if you are so unfortunate as to have infection tract back into it, there can be some nasty consequences like meningitis and cavernous sinus thrombosis which will generally present as problems involving those nerves.

The abducens and carotid are more medial and thought to be more bathed in the warm loving venous drainage meaning these are generally the first to show signs of a problem a-brewin’.

Blood supply of the GI tract

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blood_supply_GI

Turns out there’s a lot of stuff in the abdomen. One could even say there’s almost as much as in the hand. Maybe.

There are three main trunks/arteries off the descending aorta that supply the blood to the guts.

  1. Celiac trunk – foregut (stomach to where the bile duct enters the duodenum)
    1. Common hepatic
      • Hepatic proper
        • Left hepatic
        • Right hepatic
      • Right gastric
      • Gastroduodenal
    2. Left gastric
    3. Splenic
  2. Superior mesenteric artery – midgut (from where the bile duct enters the duodenum to 2/3 across the transverse colon)
    1. Right colic
    2. Middle colic
    3. Ileocolic
    4. Ileal and jejunal branches
  3. Inferior mesenteric artery – hindgut (from 2/3 across the transverse colon to the rectum)
    1. Left colic
    2. Sigmoid
    3. Superior rectal

Stomach

The stomach is needy and gets a pretty excellent blood supply, which makes remembering is a little tricky

  • Lesser curve: right and left gastric arteries
  • Greater curve: right gastroepipiloic/gastro-omental (off the gastroduodenal artery) and left gastroepipiloic/gastro-omental (off the splenic artery)
  • Fundus: short gastrics (off the splenic artery)

Coronary artery supply and corresponding MIs

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I think in my head I always thought that the coronary artery circulation was much more complicated than it really is. The simple way to boil it down is that the right coronary artery (RCA) does the right ventricle and the back of the heart. While the left coronary artery (LCA) does most of the anterior and some of the back depending on the circumflex artery and individual variation.

SA Node: usually supplied by the RCA (in 60% of people) but can also be supplied by the LCA
AV Node: supplied by the RCA

Dominance of circulation

Right-dominant (80%): Posterior interventricular (PIV) & at least 1 posterolateral branch arise from the RCA
Left-dominant (15%): PIV & at least 1 posterolateral branch arise from left circumflex artery
Balanced (5%): dual supply of posteroinferior LV from RCA and circumflex

So what this means is that if you see a inferior MI pattern on an ECG, there is likely a posterior infarct as well. Not to mention that you should be worried about both your AV and SA node.

Arteries and veins of the upper limb

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This image has two parts, one where the vessels are unlabelled so you can try to fill in the blanks and one where they are so you can check your answers.

This is probably the most popular little image I have created to date and is one of the reasons that I decided to start a website dedicated just to scientific doodles.