This is not an exhaustive overview of the muscles of the arm and forearm, but it demonstrates some of the tricky relationships that often catch people up. Some of the key points of compression are also noted and the muscles are coloured per their innervation. One thing not mentioned in the doodle that is important to notice is the way that the aponeurosis of the biceps veers medially (ulnarly) this is why it is also a supinator and not just an elbow flexor.
The branches of the three main terminal branches of the brachial plexus can be difficult to remember. Even worse is trying to remember where all of those pesky compression points are and why it is that you get some symptoms with some and not others.
This diagram attempts to clarify the branches of the radial, median, and ulnar nerves and where they can get squished along the way. There are of course, slight anatomic variations, but this is a good starting point. I’ve even included where the famed Martin-Gruber anastomosis and the Riche-Cannieu anastomosis are, since they can make an otherwise (totally not) straightforward examination of a median or ulnar nerve palsy more muddied since both carry motor fibers between the two nerves.
Most interestingly is John Struthers, whose namesake structures compress the median nerve as a ligament and the ulnar nerve as an arcade.
I’ve drawn the brachial plexus before showing more of its anatomical relationships (which is actually why the trunks and cords are named as they are). As I’m gearing up studying, I created this more schematic diagram of the plexus, including the distal targets (mostly the muscles but some sensory too).
Hopefully this will help you figure out “where is the lesion?” when you are faced with a brachial plexus question on your exams (and in life) as well.
I’ve also included a printable version for your printing and pasting-up-to-the-wall-to-passively-absorb pleasure.
Long thoracic: serratus anterior
Dorsal scapular: rhomboids, levator scapulae
Suprascapular: supraspinatus, infraspinatus, sensory to the AC & GH joints
Nerve to subclavius: subclavius
Lateral pectoral: pec major (clavicular head), sensation to pec
Superior subscapular: subscapularis (upper part)
Thoracodorsal (aka middle subscapular): lat dorsi
Inferior subscapular: subscapularis (lower part), teres major
Medial pectoral: pec minor, pec major (sternocostal head)
Medial cutaneous n. of arm: sensory to medial surface of arm (tiny area)
Medial cutaneous n. of forearm (antebrachial cutaneous): sensory to skin over biceps and medial forearm
The most common use for vancomycin is in invasive Gram positive infections
This is where vancomycin can get tricky, because you are aiming for a target trough (between dose) serum concentrations.
Starting dose should be 15-20 mg/kg (based on actual not ideal body weight) every 12 hours. This usually works out to 1-2 g IV Q12H. If the kidneys are not working well, reduce the dose.
There are many different variations of RRT, but the main principles behind it can be quite simple.
In hemodialysis, diffusion is responsible for removing unwanted solutes and water. The setup involves a semipermeable membrane that can allow water and some water-soluble molecules to pass. Blood will flow on one side of the membrane, under pressure, while the dialysate (contains glucose and some electrolytes) generally flows on the other side in the opposite direction. This creates a suitable concentration gradient for unwanted molecules to pass into the dialysate, while excess water is forced across the membrane based on the amount of pressure is applied by the dialysis circuit.
Tumescent solution is also called “Klein’s Solution” after the physician who characterized the recipe and the use of it.
It’s called “tumescent” because it makes things tumescent, which is a fancy word for swollen. Tumescent is a dilute solution of lidocaine, epinephrine, and sodium bicarbonate that is injected in the subcutaneous tissue (fat). The epinephrine is the most important ingredient as it causes vasoconstriction, this means that the blood loss that could be a big problem for large procedures like burn surgery and liposuction becomes much less of a big deal.
The other interesting thing is that since fat is relatively avascular compared to other tissues, the “safe amount” of tumescent is much higher than what is normally stated for injections of lidocaine or epinephrine.
For example, it was reported by Klein that the toxic dose of lidocaine for tumescent solution is 35 mg/kg of body weight.
There are a few different recipes for tumescent anesthesia, the one presented in the doodle is the one first outlined by Klein, some use more or less lidocaine or epinephrine.
The carpal bone ossify aka turn into bone aka magically become visible on an x-ray in a predictable order.
The easiest way to remember is that it starts at the capitate (smack dab in the middle) and then goes in a ulnarly-directed spiral. I was going to say “clockwise” or “counter-clockwise” but that would depend on which side of which hand you were looking at. So capitate, followed by hamate and then down to triquetrum and so on. Except for the pisiform, being a sesamoid bone it gets left behind and only develops years later.
I included the distal radius and distal ulna in there for good measure.
I know I could have been fancier with changing the length of the metacarpals or their growth plates, but it was more fun to make the animated gif.
The scaphoid shift test aka midcarpal shift test is a variation of the Watson Test for scaphoid instability. A positive test can be caused by scapholunate ligament laxity or injury.
The Watson test evaluates scaphoid instability as the wrist is moved from radial to ulnar deviation (it’s not an “active” test)
To do the scaphoid shift test (as described by Lane in 1993)
For being such a small anatomic location, people find it very difficult to describe where on the hand or digits things are actually happening when there is an injury.
I think part of it stems back to medical school when we are taught that the digits all have numbers, the thumb is D1, index D2 and so forth. The problem comes when people say “the 3rd finger” and all of the sudden one has no idea whether they are talking about the long finger (D3) or the ring finger (D4 but then, the thumb doesn’t count as a finger, does it?)
This is why it’s always best to call digits by their names, this even goes for metacarpals. It is totally OK, and generally less confusing to call a bone the index finger metacarpal.
The same goes for which side of the hand the problem is on. There is no lateral or medial side to the hand. One could argue that it’s how someone is in anatomical position, so obviously the small finger side is medial, unfortunately very few people walk around in anatomic position and it’s their thumbs that point to the body.
So best to describe side by two things that stay put regardless of how someone has their hands in space: the radius and the ulna.
Finally for the top and bottom (or is it back and front) of the hands: use the terms DORSAL (where the nails are) and VOLAR (or palmar)
The clotting cascade was one of the first doodles posted on Sketchy Medicine, I’ve now updated it to include some of the Novel Oral Anticoagulants (NOACs): Dabigatran, Rivaroxaban and Apixiban.
(Adapted from Jackson II & Becker, 2014)
(From Siegal, 2015)