Anatomy clinical correlates: Wrist and hand

In everyday life, we rely on our hands for a variety of reasons, from vigorously typing out notes while watching an Osmosis video to playing musical instruments or participating in sports.

Unfortunately, since we use them so much, the hands are quite prone to injury.

Alright, let's start by looking at distal forearm fractures.

There’s two kinds: Colles fracture, which are a direct result of falling on an extended wrist, and Smith fracture, which results from falling on a flexed wrist, or a direct blow to the posterior forearm.

With Colles fractures, the displaced radial fragment moves posteriorly, or dorsally, and the ulnar styloid process can also become fractured.

Clinically, when the distal radial segment moves dorsally this is called a “dinner fork deformity” because when viewed laterally, the hand and wrist are slightly curved anteriorly making it look like a fork.

With Smith fractures, on the other hand, the displaced distal radial fragment moves anteriorly, or ventrally, which clinically translates as a “garden spade” deformity.

Next, let’s look at carpal bone fractures, of which the most common are scaphoid fractures.

Scaphoid fractures occur as a result of falling on the lateral side of an outstretched hand in abduction.

Clinically, this results in pain and tenderness on the lateral side of the wrist and hand, in a location called the anatomical snuffbox, which is where you can palpate the scaphoid bone between the tendons of extensor pollicis longus on the medial side and extensor pollicis brevis and abductor pollicis longus on the lateral side.

The big problem with these fractures is that because the blood vessels supply the distal part of the scaphoid first then come back and supply the proximal part, a fracture in the middle of this bone disrupts the blood supply.

This can cause avascular necrosis and non union of the proximal fragment of the scaphoid, which is basically when the bone dies off because of lack of blood, and degenerative wrist joint disease.

Initial X-rays often miss scaphoid fractures at first, so when there is tenderness on palpation of the anatomical snuffbox in a patient who fell on an outstretched hand, it’s important to still treat it as a fracture to avoid this complication.

When still suspecting a scaphoid fracture after an initial negative x-ray, a CT or MRI scan can be done, or a follow up x ray can be done in 7-14 days.

Management for a non-displaced scaphoid fracture is immobilization with a cast or thumb spica splint, where displaced fractures may need to be treated surgically.

Furthermore, serial x-rays should be done during recovery to monitor for osteonecrosis of the proximal segment.

Another carpal bone, called the lunate, can also be subject to injury.

The lunate is found in the proximal row of carpal bones medial to the scaphoid, and is susceptible to volar, or anterior dislocation into the carpal tunnel during a fall on an outstretched hand, though less likely to be injured than the scaphoid bone.

Lunate bone dislocation can result in compression of the median nerve within the carpal tunnel, resulting in median nerve compression signs and symptoms.

This includes pain and paraesthesia in the radial 3 and a half digits, weakness of the first and second lumbrical, thenar atrophy, and weakness of thumb abduction and opposition of the affected hand.

On a lateral x-ray of the hand, volar lunate dislocation can be recognized by the ‘spilled teacup’ sign.

Another common pathology of the hand that you probably have heard of is carpal tunnel syndrome.

Carpal tunnel syndrome occurs when the median nerve is compressed within the carpal tunnel, which is a space created by the transverse carpal ligament forming the roof of the carpal tunnel, and the carpal bones forming the floor.

The median nerve, along with 9 flexor tendons enter the hand through the carpal tunnel, and increased pressure in this space can compress the median nerve, resulting in median nerve compression signs and symptoms.

Risk factors for carpal tunnel are pregnancy, edema, obesity, rheumatoid arthritis, hypothyroidism, diabetes, acromegaly, and may be associated with repetitive use of the hands and wrist.

There are two popular clinical tests used to test for carpal tunnel syndrome.

The first is Phalen maneuver, where both wrists are flexed to 90 degrees, and the dorsal surfaces of the hands are pressed together.

A positive test is when the symptoms of carpal tunnel are reproduced in prolonged position of up to 60 seconds.

The second is the Tinel sign, which is performed by repeatedly percussing firmly over the carpal tunnel, and if carpal tunnel symptoms appear, that’s a positive test.

To confirm the diagnosis of carpal tunnel syndrome, a nerve conduction study frequently combined with electromyography is used to assess the degree of nerve damage and muscle denervation.

The management of carpal tunnel syndrome is typically non surgical.

Initially, a wrist splint can be used to immobilize the wrist in a neutral position to prevent excess flexion or extension that can worsen symptoms.

If this does not work, steroid injections can be used to reduce inflammation.

Significant impairment may require surgical decompression of the median nerve with a longitudinal incision through the transverse carpal ligament to decrease pressure.

However, it is important to avoid the recurrent branch of the median nerve, which is susceptible to injury during this operation, or any superficial laceration of the palm in general.

Injury to the recurrent branch of the median nerve would lead to dysfunction of the three thenar muscles which it supplies, but no sensory deficits, resulting in thumb movement dysfunction and loss of the thumb’s overall usefulness.