Extensor Compartments and Extensor Zones of the Hand

Extensor Compartments

There are a whole lot of wrist/finger extensors trying to fit in the wrist and anatomically these are divided into 6 compartments.

  1. First compartmentit’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
  2. Second compartment
    • ECRB (extensor carpi radialis brevis): attaches to 3rd MC
    • ECRL (extensor carpis radialis longus): attaches to 2nd MC
  3. Third compartment
    • EPL (extensor pollicis longus): passes around Lister’s tubercle of radius and inserts on distal phalanx of thumb (extends thumb IPJ)
  4. 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)
  5. Fifth compartment
    • EDM (extensor digiti minimi): attaches to extensor expansion of little finger
  6. Sixth compartment
    • ECU (extensor carpi ulnaris): attaches to base of 5th MC

Extensor Zones

  • 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

Juncturae Tendinum

  • 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 (1st metacarpal) Fractures

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.

Type IV

  • 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 (and how to number and name them)

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

  1. Incisors – 8 in total
  2. Cuspids aka Canines – 4 in total
  3. Bicuspids aka Premolars – 8 in total
  4. 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)

Flexor Tenosynovitis (Kanavel’s Signs)

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)

  1. Tenderness along the whole tendon sheath (late sign)
  2. Finger held in flexion
  3. Fusiform swelling (sausage finger)
  4. 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.

Femoral Triangle

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.

Anatomy of the ear

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.

Lip Anatomy

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.

Lung surface anatomy and chest tubes vs needle decompression

Surface anatomy of the lungs

  • Lungs extend from about 2 cm above the clavicle down to the 6th rib in the midclavicular line and 8th rib in the midaxillary line
  • The oblique fissure goes from the 6th rib midclavicular line to T3 in the back
  • The horizontal fissure (only on the right) starts at the 4th rib at the sternum and then meets the oblique fissure at the 5th rib in the midaxillary line.
  • The pleura generally is 2 ribs below

Chest Tube

Insert a chest tube in the 4th or 5th intercostal space in the anterior axillary line. When making the incision, make it one rib below the intercostal space you want to insert the tube into. Also, remember to go above the rib, as the neurovascular bundles travel along the underside of the ribs.

These can be done to relieve a pneumothorax, drain a malignant pleural effusion, drain a empyema, or drain a hemopneumothorax. They can also be placed post-operatively following a thoracotomy, esophagectomy or cardiac surgery.

Needle Decompression

These are used in a pinch when a patient is suspected to have a tension pneumothorax and needs immediate decompression. A 14 or 16 gauge needle is inserted above the 2nd or 3rd rib in the midclavicular line.

A tension pneumothorax is recognized by:

  • Dyspnea
  • Hypotension
  • Decreased breath sounds on the affected side
  • Distended neck veins
  • Trachea deviating away from affected side

 

Salter-Harris Growth Plate Fracture Classification

The Salter-Harris fracture classification has to be just about the most sensible classification systems in medicine, as least as far as the mnemonic goes. It is a system used to grade growth plate fractures and conveniently uses Salter’s name as the way to remember.

  1. SEPARATED (the bone and the growth plate have come apart) – but it actually looks normal on x-ray (you can only tell on physical exam)
  2. Fracture ABOVE the growth plate
  3. Fracture LOWER (below) the growth plate – fracture extends to the articular surface
  4. Fracture THROUGH the growth plate
  5. Fracture ERASING/compressing/squashing the growth plate – this is the worst kind because with disruption of the growth plate comes disruption of growth. Some odd things can cause these ones like frostbite, electric shock and irradiation. They’re hard to see on x-rays but show up on MRIs.

Find that lesion! (deep tendon reflexes of the arm)

The arm has too many muscles. It also has too many nerves.

The problem is that someone comes in with weakness or numbness and you need to think, “Where in the brain/spine/nerve root/bits of brachial plexus/terminal branch is the actual problem?!”

One of the ways to help suss this out is by testing the deep tendon reflexes.

  • Only biceps reflex absent – might be problem with musculocutaneous nerve or C5
  • Both brachioradialis and triceps absent – problem with the radial nerve
  • Only triceps absent – potential problem with C7

Of course you should correlate the reflex findings with the sensory findings and motor strength (remember the good old ASIA exam for testing specific nerve roots) to help determine if it is a terminal branch issue or something higher up.

And don’t forget to grade those reflexes!

Grade Description
0 Absent
1+ Diminished
2+ Normal
3+ Brisk
4+ Very brisk +/- Clonus

Generally upper motor neuron (UMN) lesions result in hyperreflexia while lower motor neuron (LMN) lesions result in hyporeflexia.

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