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.

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.

Rotator Cuff: Subscapularis

The rotator cuff is composed of four muscles

  1. Supraspinatus – abduction
  2. Infraspinatus – external rotation
  3. Teres minor – external rotation
  4. Subscapularis – internal rotation

Rotator cuff injuries are incredibly common and it is helpful to figure out which of the four muscles is the major source of the problem (there is of course the possibility that multiple ones are injured/irritated).

For the subscapular (innervated by the suprascapular nerve C5,6) you can test internal rotation of the arm. The patient places the dorsum of their hand on their lower back. The examiner then pushes on the hand while the patient tries to lift the hand from the lower back. Pain or weakness is a positive test.

Rotator Cuff: Infraspinatus & Teres Minor

The rotator cuff is composed of four muscles

  1. Supraspinatus – abduction
  2. Infraspinatus – external rotation
  3. Teres minor – external rotation
  4. Subscapularis – internal rotation

Rotator cuff injuries are incredibly common and it is helpful to figure out which of the four muscles is the major source of the problem (there is of course the possibility that multiple ones are injured/irritated).

For the infraspinatus (innervated by the suprascapular nerve C5,6)  and the teres minor (innervated by the axillary nerve, C 5,6) you can test external rotation of the arm. The patient holds the arm next the body (adducted) with the elbow flexed to 90 degrees. The examiner then attempts to internally rotate the arm while the patient resists. Pain or weakness is a positive test.

Rotator Cuff: Supraspinatus (empty can test)

The rotator cuff is composed of four muscles

  1. Supraspinatus – abduction
  2. Infraspinatus – external rotation
  3. Teres minor – external rotation
  4. Subscapularis – internal rotation

Rotator cuff injuries are incredibly common and it is helpful to figure out which of the four muscles is the major source of the problem (there is of course the possibility that multiple ones are injured/irritated).

For the supraspinatus (innervated by the suprascapular nerve C5,6) you can do the “empty can test“. The patient holds out the affected arm (abducts) with elbow extended and wrist pronated. Like they were, in fact, pouring out a can of soda (or “pop” as we call it here). The examiner then pushes down on the extended arm and the patient tries to resist. Pain or weakness is a positive test.

Bones and joints of the hand and wrist

Of course the majority of the bones in the hand we pretty straight forward. You have your metacarpals, appropriately named first through fifth and the same goes with the phalanges. The important thing to remember is that the thumb is phalanges-challenged and only has two instead of three. The reason this can mess people up is that in the thumb only has one interphalangeal (IP) joint whereas the fingers have a proximal interphalangeal (PIP) joint and a distal interphalangeal (DIP) joint.

It’s usually the CMC joint of the thumb (AKA the TMC joint because it’s an articulation between the trapezium and 1st metacarpal) that gives women grief in later life as its prone to arthritis.

Then there are the carpal bones (8 in total)

  • S – scaphoid
  • L – lunate
  • Tq – triquetrum
  • P – pisiform
  • Tm – trapezium
  • Td – trapezoid
  • C – capitate
  • H – hamate

There are plenty of mnemonics to remember them, the one I learned was Some Lovers Try Positions That They Can’t Handle (which goes from thumb across one row and then from the thumb across the more distal row)

The radioulnar joint is one of the articulation points for supination and pronation and the radiocarpal joint is the articulation for extension and flexion.