Author: Charbel Saade
Institute: Royal Prince Alfred Hospital Sydney Australia

Patient Presentation

Anatomy

The wrist is the most commonly injured region of the upper extremity. Fractures of the distal radius and ulna account for three fourths of wrist injuries. The carpal bones themselves are injured much less frequently but account for up to 10% of injuries to the structures of the hand.

The importance of the neurovascular structures are the deep branches of the ulnar nerve and the ulnar artery run deep to the flexor carpi ulnaris tendon through the Guyon canal. They pass near the hamate and capitate and can be involved with injuries to these structures. The ulnar nerve innervates the intrinsic muscles of the hand, including the hypothenar muscles, interossei, ulnar lumbricals, and adductor pollicis.

The median nerve lies between the flexor carpi radialis and the palmaris longus tendon in the carpal tunnel. The median nerve innervates the thenar compartment and provides sensation to the radial portion of the hand. Any displacement of the normal anatomic alignment of the wrist can injure this nerve.

The blood supply to the hand is via the radial and ulnar arteries, which form the dorsal palmar arch. The scaphoid bone receives its blood supply from the distal part of this arch, which is prone to injury. Therefoer correct and accurate imaging of the wrist is required in order to eliminate the possibility of avascular necrosis of the scaphiod.

Image Courtesy of netterimages.com

Colles fracture is the most common extension fracture pattern. The term is classically used to describe a fracture through the distal metaphysis approximately 4 cm proximal to the articular surface of the radius. However, now the term tends to be used loosely to describe any fracture of the distal radius, with or without involvement of the ulna, that has dorsal displacement of the fracture fragments.

Smith's fracture is typically caused by a fall onto a supinated forearm or hand with generation of a hyperflexion force. On striking the ground, the hand locks in supination while the body's momentum forces the hand into hyperpronation. A direct blow to the dorsum of the wrist with the hand in flexion and forearm pronated can also produce a similar fracture pattern. Another mechanism is punching with the wrist in a slightly flexed position.

Scanning Technique

Images

Comments:

When evaluating a fracture of the distal radius or ulna, carefully check the normal anatomic alignments. The radiocarpal joint viewed on the lateral film normally has 11° of palmar angulation with a range of 1-23°. Ulnar angulation on the AP film is normally 15-30°. The radial length, which is the distance between the ulnar aspect of the distal radius and the tip of the radial styloid, normally measures 11-12 mm.

Look for an associated ulnar styloid fracture and involvement of the radiocarpal joint or DRUJ. If the radius appears to be angulated and/or displaced significantly, maintain a high degree of suspicion for a concomitant fracture of the ulna.

Scaphoid fractures often are not seen on routine radiographs. Scaphoid views taken with the wrist deviated toward the ulna and slightly supinated may help to demonstrate a fracture. The approximately 10-15% of fractures that are occult may be apparent on plain films after 10-14 days as bony reabsorption occurs at the fracture site. While not appropriate for ED workups, CT scans and bone scans as early as 3 days after injury may aid in the diagnosis.

Injuries to the hamate and trapezium can be visualized best with a carpal tunnel view. Like scaphoid injuries, injuries to the lunate and capitate may not be well visualized on plain films, and CT scan may be required.

Diagnosis

There is an obvious oblique fracture of the radial styliod with the fracture extending into and within the radial articulating surface. There is moderate scaphiod fat pad inflammation and and increased swelling within the radial ulnar articulation. There is also remarkable inflammation pf the pollicies ligaments of the wrist. There is no obious scaphiod fractures. The Radial Styliod fracture is preserved and aligned. This study is unable to determine whether this fracture is a smith's or colles fracture since there is minimal displacement. However the fragments seen around the fracture is consistent with a Smith's Fracture since the fragment is above the fractured area, thus, the mechanism of injury was a downward landing with the wrist in supinated nature.