14.2 Hand, Wrist & Forearm

Anatomy of the Hand and Wrist

The hand and wrist are the most commonly imaged parts of the upper extremity, and the ARRT expects precise projection selection. Each hand contains 14 phalanges (three per finger, two in the thumb), 5 metacarpals, and 8 carpal bones. The carpals form two rows. From lateral (thumb side) to medial, the proximal row is scaphoid, lunate, triquetrum, and pisiform; the distal row is trapezium, trapezoid, capitate, and hamate. A useful mnemonic is So Long To Pinky, Here Comes The Thumb. The scaphoid (navicular) is the most frequently fractured carpal and a classic exam scenario after a fall on an outstretched hand.

Hand Projections

The PA hand places the palm down with the fingers extended and slightly separated; the CR is perpendicular to the third metacarpophalangeal (MCP) joint. A slight flexion of the digits is avoided for the routine PA, but for a PA wrist slight flexion of the fingers places the carpals in closer contact with the IR and reduces the scaphoid's normal foreshortening.

The PA oblique hand rotates the hand 45 degrees externally (laterally) and supports the fingers on a step-wedge (45-degree) sponge so the phalanges stay parallel to the IR; without the sponge the fingers foreshorten and the interphalangeal joints close. The CR again enters the third MCP joint. The lateral hand (extension for foreign bodies/metacarpal alignment, or fan lateral for the phalanges) places the thumb side up.

The Scaphoid and Ulnar Deviation

Because the scaphoid lies obliquely and foreshortens on a routine PA wrist, dedicated scaphoid imaging uses ulnar deviation (ulnar flexion). Turning the wrist toward the ulnar (little-finger) side swings the scaphoid into a position more parallel to the IR, elongating it and opening it from adjacent carpals. The Stecher method adds ulnar deviation with either a CR angled 15-20 degrees proximally (toward the elbow) or the wrist elevated about 20 degrees on a sponge with a perpendicular CR. A scaphoid series may take multiple angled PA projections to detect a subtle fracture that is invisible immediately after injury.

The Carpal Canal (Gaynor-Hart Method)

To demonstrate the carpal canal (carpal tunnel) and the palmar carpal bones - the pisiform, the hamulus (hook) of the hamate, the trapezium, and the scaphoid - use the Gaynor-Hart tangential (inferosuperior) projection. The wrist is hyperextended (dorsiflexed) by having the patient pull the fingers back, and the CR is angled about 25-30 degrees to the long axis of the hand, directed to a point about 1 inch distal to the base of the third metacarpal. This projection is ordered for suspected carpal tunnel narrowing or a hamulus fracture.

Forearm

The forearm requires both the wrist and elbow joints on the image. The AP forearm is taken with the hand supinated (palm up); supination keeps the radius and ulna parallel and un-crossed. If the hand is pronated, the radius crosses over the ulna and the study is diagnostically useless - a frequently tested error. The lateral forearm is taken with the elbow flexed 90 degrees and the hand in a true lateral (thumb up) position, which superimposes the radius and ulna at the distal end and stacks the humeral epicondyles at the elbow. Always angle or align to avoid excluding a joint; a shaft-only forearm image misses common both-bone and Monteggia/Galeazzi injuries.

The Thumb (First Digit)

The thumb is unique because its natural resting position is already oblique, so the routine projections differ from the other digits. The AP thumb is the true frontal view: the hand is internally rotated until the posterior surface of the thumb rests on the IR (a mild discomfort for the patient), which avoids the magnification and self-superimposition that a PA thumb would create. The PA oblique and lateral thumb complete the series, and the CR is centered to the first metacarpophalangeal joint. The first carpometacarpal (CMC) joint at the base of the thumb - a common site of osteoarthritis and the Bennett fracture - is included on these images.

Evaluation Criteria and Scenario

A well-positioned upper-extremity image shows open joint spaces, no rotation (bilateral concavity of the shaft cortices is symmetric), and the correct anatomy in profile. On a PA wrist the ulnar styloid should appear in profile on the medial side. Scenario: a patient falls on an outstretched hand, has anatomic snuffbox tenderness, but the initial PA, oblique, and lateral wrist look normal. Because an acute scaphoid fracture is often radiographically occult, the correct response is a dedicated ulnar-deviation scaphoid series (including a Stecher-method projection), and if still negative the patient is treated and re-imaged in 7-10 days when bone resorption makes the fracture line visible. This clinical reasoning - matching mechanism of injury to the right projection - is exactly what the Procedures category tests. As a final quick-reference, the standard centering points are: hand to the third MCP joint, wrist to the midcarpal area, forearm to the mid-shaft with both joints included, and the thumb to the first MCP joint - and every image needs an anatomic side marker exposed within the collimated field.