People can be whiners sometimes. Their hand will be in a cast for some break and you’ll take it off and they will say, “my hand is stiiiiifffff”
It’s not just them, the mechanics of their hand is working against them and if the cast wasn’t positioned properly, it can make matters much worse as far as stiffness is concerned. This is why when a hand or wrist is being casted or splinted, care is taken to put it in the position that will minimize stiffness.
The “safe position” is also known as the intrinsic plus position as it favours the weaker motions of MCP flexion and IP extension that are difficult to recover.
Wrist: The weight of your hand, gravity and resting muscle tension all work together to pull the wrist into flexion. When the wrist is flexed, there is more tension on the extrinsic extensor muscles and they pull the MCP joints into extension. The extrinsic flexors are stronger than the extensors and pull the IP joints into flexion. Taking the tension off the extensors limits their pull across the MCP joints.
The position of flexed wrist, extended MCP joints and flexed IP joints is known as intrinsic minus.
Metacarpal Phalangeal (MCP) Joint: These joints are a little funny due to the collateral ligaments on either side. These ligaments pass slightly above the axis of rotation of the joint, this means that when the joint is flexed, they’re at their longest and when the joint is extended, they’re at their shortest. This is due to the famed “CAM EFFECT.” Though often quoted, you have to wonder, what is a cam*? This website explains it well.
* This does not apply to all those people who remember basic mechanical principles or were trained in something more hands-on than neuroscience
Interphalangeal (IP) Joints: The ligaments around the IP joints are at maximum stretch when they are fully extended (aka 0 degrees)
A prolapsed (slipped) disc is when the squishy innards of the disc (nucleus pulposus) bulge out past the stiffer wall of the disc (annulus fibrosis). The problem is that sometimes when this happens, the bulge can impinge the spinal cord or the spinal nerve root. This could result in an anterior cord syndrome (remember this doodle) or it could just knock out the nerve root, resulting in a specific radiculopathy (check out this doodle for where to check for numbness and weakness).
The tricky thing to remember is that though, for example, the L3 root exits at L3, if the L3,4 disc herniates, it doesn’t hit the L3 root but the L4.
Slipped L3,4 disc = L4 nerve injury
The disc hits the nerve after it has branched off the spinal cord, but before it has exited the vertebral canal.
For the most part, bleeding in the brain (intracranial hemorrhage) is a pretty bad thing. Though like most things in medicine, there are varying degrees of badness, all with different mechanisms that help us sort of why we really wouldn’t want something to happen.
Intracranial hemorrhages are categorized into 5 subtypes, and are given obvious sounding names depending on where the bleed is in the brain and in relation to the layers of the meninges.
- Epidural (above the dura, right under the skull)
- Subdural (below the dura, above the arachnoid)
- Subarachnoid (below the arachnoid, above the brain)
- Intraventricular (in the ventricles)
- Intraparenchymal (in the meat* of brain)
* The brain is not meaty, “parenchyma” means the functional part of the organ
The poor pia mater did not get any hemorrhage named after it, but if you want you can think of intraparenchymal as “subpial” just so it doesn’t feel left out.
Telling them apart
The most confusing thing, and thing that likes to get asked the most on exams, is the difference between epidural and subdural hematomas.
|Above the dura
||Below the dura
||Below the arachnoid
|Respects suture lines
||Doesn’t respect suture lines
||No respect for anything
|High force trauma
||Low force trauma
||Aneurysm rupture or high force trauma
|Arterial blood (commonly the middle meningeal artery)
||Venous (from venous plexus)
||Arterial from the circle of Willis
|Lentiform (lens-shaped) or biconcave on CT
||Cresent (banana-shaped) on CT
||Lining surface, going into fissures and sulci and sella (death-star)
||May be insidious (worsening headache over days)
||Acute presentation (thunderclap headache)
The reason intraventricular and intraparenchymal aren’t included in the table as they each have a bunch of causes, but for both of them trauma is a potential cause as well as hypertension and stroke. It’s good to remember that premature infants are at a much higher risk of intraventricular hemorrhages.
Blood on CTs
- New blood: bright white
- 1-2 weeks: isodense
- Old blood (2-3 weeks): dark grey
The lower leg (and especially the foot) have a pretty fancy pattern of skin innervation by the terminal branches. For example, the skin of the foot is innervated by 7 separate nerves:
- Superficial peroneal nerve
- Deep peroneal nerve
- Sural nerve
- Saphenous nerve
- Calcaneal branch of the tibial nerve
- Medial branch of plantar nerve
- Lateral branch of plantar nerve
Also good to keep in mind that the anterior compartment is innervated by the deep peroneal nerve, the lateral compartment by the superficial peroneal nerve and the posterior compartment by the tibial nerve.
There are a whole lot of wrist/finger extensors trying to fit in the wrist and anatomically these are divided into 6 compartments.
- First compartment – it’s this that is affected in de Quervain tenosynovitis
- APL (abductor pollicis longus): attaches to 1st MC
- EPB (extensor pollicis brevis): attaches to base of proximal phalanx
- Second compartment
- ECRB (extensor carpi radialis brevis): attaches to 3rd MC
- ECRL (extensor carpis radialis longus): attaches to 2nd MC
- Third compartment
- EPL (extensor pollicis longus): passes around Lister’s tubercle of radius and inserts on distal phalanx of thumb (extends thumb IPJ)
- Fourth compartment – the posterior interosseus nerve lies on the floor of this compartment
- EDC (extensor digitorum communis): no direct attachment to phalanx, attaches to the extensor expansions
- EIP (extensor indicis proprius): lies ulnar to 1st EDC tendon)
- Fifth compartment
- EDM (extensor digiti minimi): attaches to extensor expansion of little finger
- Sixth compartment
- ECU (extensor carpi ulnaris): attaches to base of 5th MC
- Zone I: over the DIP (this is where mallet finger injuries occur)
- Zone II: middle phalanx
- Zone III: over the PIP
- Zone IV: proximal phalanx
- Zone V: over the MCP
- Zone VI: dorsum of hand/metacarpals
- Zone VII: over the extensor retinaculum/carpals
- Zone VIII: proximal wrist
- This is the connections of fascia between the EDC tendons and why you can’t stick your ring finger up alone, as it prevents independent movement.
- It can also lead to confusion about whether an extensor tendon has been cut as the juncture tendinum transmits MCP joint extension even if a tendon is cut (as long as it’s cut distal to the JT)
- But it’s also helpful as it prevents the cut tendon from retracting up into the forearm
Thumb fractures, and by this I mean 1st metacarpal fractures, have a couple of distinct patterns that are different from the other metacarpals.
Type I: Bennett Fracture
- This fracture is intra-articular on the ulnar side of the first metacarpal, basically making a little triangle
- It’s that little ulnar fragment that stays attached to the trapezium by the virtue of the volar ligament
- The distal aspect of the metacarpal gets supinated and dislocated radially no thanks to the adductor pollicis
- The fragment gets pulled proximally by the abductor pollicis brevis and abductor pollicis longus
Type II: Rolando Fracture
- You can think of this fracture as a really busted up Bennett’s (comminuted). It is also intra-articular and usually makes a Y or T shape
- These kind generally heal poorly but thankfully are fairly rare
Type III: Other extra-articular fractures
- This is basically any other 1st metacarpal fracture (all the extra-articular ones)
- They are the most common, but don’t have fancy names, just lame ones like “transverse“, “oblique“, etc.
- These really only exist in paediatrics and involve the proximal physis (growth plate)
Treatment: it’s best to treat Bennett and Rolando Fractures with thumb spica splints and then refer them to your friendly neighbourhood plastic surgeon or orthopaedic surgeon as they might need pinning or an open reduction.
Teeth are pesky things, there are a bunch of them and they all seem to have a bunch of different names. Technically speaking, a full set of adult teeth is 32. However many people end up getting their wisdom teeth taken out, bringing them down to only 28 teeth in total.
There are 4 “types” of teeth
- Incisors – 8 in total
- Cuspids aka Canines – 4 in total
- Bicuspids aka Premolars – 8 in total
- Molars – 12 in total (counting the wisdom teeth)
Of course, to say “the 2nd incisor on the top right” is just far too many words to say and write down, so different coding systems were developed to make things snappier. The most commonly used system in North America and the one that’s used by the World Health Organization is the FDI World Dental Federation notation.
The FDI system numbers the 4 quadrants of the mouth, starting at the top-right and going clockwise:
- 1 = top right
- 2 = top left
- 3 = bottom left
- 4 = bottom right
Each tooth is then numbered starting at the middle and working back:
- 1 = first incisor
- 2 = second incisor
- 3 = cuspid/canine
- 4 = first bicuspid/premolar
- 5 = second bicuspid/premolar
- 6 = first molar
- 7 = second molar
- 8 = third molar (wisdom tooth)
Suppurative (infectious) flexor tenosynovitis is a medical emergency because the tendon sheath is a closed space and too much swelling can lead to compartment syndrome and necrosis.
* You can’t really get these complications in extensor tendons as it is an open space (no tendon sheath)
There are 4 cardinal signs of flexor tenosynovitis (Kanavel’s Signs)
- Tenderness along the whole tendon sheath (late sign)
- Finger held in flexion
- Fusiform swelling (sausage finger)
- Pain with passive extension *this is the earliest finding
It is usually caused by some sort of inoculation, but this can be something very small and the patient may not be aware that he/she had ever been injured (can also be caused by local or hematogenous spread). It’s not unreasonable to get an x-ray to rule out other things and if there’s a fever or they seem very unwell, you can do blood cultures. You also probably want to start the patient on some broad spectrum antibiotics such as vancomycin + ciprofloxacin (or ceftriaxone).
Treatment is tendon sheath drainage and debridement as well as antibiotics.
The femoral triangle is a convenient triangle where the femoral nerve, artery and vein pass from the abdomen to the leg. The best part about this is that they’re all quite superficial, making it a great place to stick things in (place catheters, nerve blocks, etc).
Because the femoral triangle is often getting poked at for various reasons, it’s important to know what’s where because you don’t want to be hitting the nerve when you meant for the artery (or vice versa).
The triangle is made up by the sartorius, adductor longus and inguinal ligament and if you just remember NAVVAN.
Who knew that the ear could have so many parts to it? This is getting into some detailed anatomy, but you will be able to impress your staff person with your incredible knowledge.
As a side note, you may also be able to impress your local piercer, as most of the more unusual ear piercings are simply named after the bit of ear the hole is going through.