Tag Archives: MSK

Scaphoid Shift Test

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Scaphoid-Shift

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)

  1. Use the same hand as the patient’s affected hand (suspicious of a right scaphoid problem? Use your right hand to test)
  2. Place your hand on the patient’s so that your thumb is over the volar surface of the scaphoid tubercle (the distal pole). Don’t apply any pressure (remember this area is probably at least a little sore and you want to remain friends for now)
  3. Gently move the wrist through ulnar/radial deviation (you can be fancy and consider this your Watson Test) and flexion/extension to relax the patient
  4. With the patient’s wrist in neutral extension and neutral (or slight radial deviation), forcefully and quickly push the scaphoid tubercle in the dorsal direction
    1. At this point, the patient is likely no longer your friend
  5. Note the degree of shift, any crepitus or clunk, and pain evoked.
  6. Remember to compare this to the opposite wrist

Describing where things are on the hand

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hand-descriptions

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?)

Which finger (digit?!) is which?

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.

  1. Thumb = D1
  2. Index = D2
  3. Long = D3
  4. Ring = D4
  5. Small = D5

Which side of the hand?

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.

  • Thumb side = RADIAL
  • Small finger side = ULNAR

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)

Treatment of scaphoid fractures

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scaphoid-flow-chart

BUY THIS AS A STUDY CARD

Scaphoid fractures are very common but due to its weird blood supply, the scaphoid is prone to not healing well (review the anatomy of the scaphoid in this doodle). This is why fractures of the scaphoid and even SUSPECTED fractures of the scaphoid are treated very conservatively.

Even if you’re suspicious of a fracture but don’t see one on x-ray, that’s enough to subject someone to a cast for 2 weeks and then bring them back to re-x-ray.

This doodle goes through the basic algorithm for treating scaphoid fractures centred around a timeline to show how long the treatment course can be. There are of course nuances to the management, so take a person’s work and hobbies and handedness into consideration. Also, don’t be afraid to consult your friendly hand/wrist specialist.

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).

Innervation of the lower leg

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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:

  1. Superficial peroneal nerve
  2. Deep peroneal nerve
  3. Sural nerve
  4. Saphenous nerve
  5. Calcaneal branch of the tibial nerve
  6. Medial branch of plantar nerve
  7. 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.

Extensor Compartments and Extensor Zones of the Hand

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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 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
  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

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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.

Flexor Tenosynovitis (Kanavel’s Signs)

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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.

Rotator Cuff: Subscapularis

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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

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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.