The PA view is obtained with the hand opened, pronated, and placed flat against the cassette. The fingers are spread apart so that the lateral soft-tissue margins do not overlap. Care should be taken to assure that the interphalangeal, metacarpophalangeal, and carpometacarpal joints are projected open. The entire hand should be included from the distal phalanges through the distal forearm (Fig. 4.4).

In the lateral view, the hand is positioned with the ulnar side down, radius and ulna superimposed. For foreign body localization, the hand is placed in extension, with all bones superimposed (Fig. 4.5).

In the fan (flexion) lateral view, the fingers are flexed and spaced like a fan. This allows visualization of the interphalangeal and metacarpophalangeal joints. In a well-positioned fan lateral view, the second through fifth metacarpals should be superimposed (Fig. 4.6).

The oblique view is obtained by obliquing the hand externally 45° to the tabletop. An accurately positioned oblique view will demonstrate the heads of the second and third metacarpals without superimposition and slight superimposition of the fourth and fifth metacarpal heads. In addition, the phalangeal joints should be open without overlap of the proximal and distal articulations (Fig. 4.7).

The AP view (Robert’s view) of the thumb is obtained with the hand internally rotated so that the thumbnail rests against the cassette. There should be no rotation of the phalanges and metacarpals. In this position the interphalangeal, metacarpophalangeal, and carpometacarpal joints should be opened (Fig. 4.8).

The true lateral view (Bett’s view) requires the hand to be flexed and slightly rotated externally to achieve a true lateral. All views of the thumb should demonstrate the carpometacarpal joint through the distal phalanx (Fig. 4.9).

The oblique view is obtained with the thumb in its natural position with the hand in the PA position and flattened against the cassette (Fig. 4.10).

For the PA view described by Kapandji, the hand is positioned with a routine lateral view. The wrist is pronated 15° and extended 15°. The thumb is in the axis of the radius, and the surface of the nail is parallel to the cassette. The X-ray beam is ­centered on the trapeziometacarpal joint using a 30° cranial inclination. On the X-ray, the sesamoids project symmetrically on the head of the first metacarpal. The scaphoïdo-trapezial joint line is well visible (Fig. 4.11a).

For the lateral view described by Kapandji, the hand is positioned as with a routine PA view of the hand. The wrist is ulnar deviated till the thumb lies in the axis of the radius. Then the hand is pronated, till the surface of the nail is perpendicular to the cassette. The vertical X-ray beam is centered on the trapeziometacarpal joint. On the X-ray, the first metacarpal and the phalanges of the thumb are in strict lateral view, and the two sesamoids are superimposed (Fig. 4.11b).

Radiography alone in many instances allows accurate classification of fractures and dislocations. Radiographs can assess the degree of displacement, angulation, shortening, and rotation of fractures. They also allow classification of the fracture type (transverse, oblique, spiral, comminuted, impacted, or avulsion) and if there is extension to the articular surface (Fig. 4.12).

Close inspection of an apparent extra-articular fracture is required to ensure that no portion of the fracture line involves the joint surface. The majority of thumb metacarpal fractures occur at the base, and the classification system includes whether the fracture is intra-articular versus extra-articular (Fig. 4.13). Discerning whether the articular surface is involved in the fracture is critical as this dictates management. CT scanning is helpful at times, particularly with regard to potential impaction injury and to define the carpometacarpal (CMC) joint and fracture fragment position in intra-articular injuries. Usually the information obtained from radiographs can be enough to determine if surgical treatment is warranted or not.

Dislocations of the fingers can be accurately classified by the direction of displacement with dorsal proximal interphalangeal (PIP) joint dislocation being the most common (Fig. 4.14). Despite the inherent stability of the thumb joints, the vulnerable anatomic position of the first phalanges often subjects the joints to mechanical strain that lead to subluxation or dislocation of the metacarpophalangeal (MCP) and interphalangeal (IP) joints. The interposition of the sesamoid within the joint is pathognomonic of a complex dislocation (Fig. 4.15).

The most common closed tendon injury of the finger is disruption of the extensor tendon of the DIP or mallet finger [6]. In this setting, standard three-view radiographs are important to evaluate for the possible presence of volar subluxation of the distal phalanx as well as a significant intra-articular fracture (greater than 30 % of joint surface). These two observations are important to describe because both are indications for surgery; they are best assessed on a true lateral view (Fig. 4.16). This type of injury usually results from a direct blow to the tip of the finger causing forced flexion of the distal phalanx and extensor tendon injury. The tendon may be partially torn, completely torn, or associated with a distal phalanx avulsion fracture.

In the setting of flexor digitorum profundus tendon injury (jersey finger), which is disruption of the flexor digitorum profundus tendon from its distal attachment, standard three-view radiographs should be obtained to rule out avulsion fractures and intra-articular injuries. This injury occurs when a flexed DIP joint is suddenly and forcefully hyperextended, leading to rupture of the flexor digitorum profundus ­tendon. This is most commonly seen in contact sports, such as American football and rugby, when an athlete’s finger catches on another player’s jersey [7]. The ring finger is involved in 75 % of jersey finger cases [8] (Fig. 4.17).

Central slip extensor tendon injuries occur when the PIP joint is forcibly flexed while actively extended or with volar dislocation of the PIP joint. Standard three-view radiographs should be obtained to rule out an avulsion fracture. If the fracture involves more than 30 % of the joint, then orthopedic referral is indicated. In most cases of central slip injuries, the plain radiographs are negative. If there is a delay in treatment, the intact lateral bands of the extensor tendon can slip inferiorly, resulting in a boutonniere deformity [6] (flexion of the PIP joint with hyperextension of the DIP and MCP joints) (Fig. 4.18).

A gamekeeper’s thumb (skier’s thumb) occurs when there is forced abduction and hyperextension of the thumb resulting in injury to ulnar collateral ligament of the first metacarpophalangeal joint. In a suspected gamekeeper’s thumb, radiographs should be obtained to exclude fracture, prior to performing a stress test (Fig. 4.19). If there is a bony fragment with greater than 2 mm displacement or involving greater than 10–20 % of the articular surface, orthopedic referral is indicated [9]. Unless there is an associated bony avulsion, the injury will be radiographically occult. In these cases, a stress examination with manual abduction may show subluxation compared to the contralateral uninjured thumb [10]. However, there is a theoretical risk of converting a nondisplaced ulnar collateral ligament tear into a displaced one as a result of a stress examination [11, 12]. Among skiers, the frequency of thumb injuries is second only to knee injuries [13].

Plain radiographs will also identify the presence of radiopaque foreign bodies. Metallic objects (except aluminum) and all glass foreign bodies are opaque on radiographs (Fig. 4.20). Most plastic and wooden foreign bodies are not opaque on radiographs [14]. It is important that all patients be thoroughly screened for foreign bodies before undergoing an MRI (Fig. 4.21).

Plain radiographs provide important information when conservative management of fractures or dislocations is indicated. In some clinical scenarios, the operative ­treatment of fractures is not indicated or possible, and conservative procedures remain the treatment of choice. Plain radiographs are used to check the correction of fracture displacement and for early callus development (Fig. 4.22). They also assess for proper alignment following closed reduction.

Intraoperative fluoroscopy and postoperative X-rays provide valuable information to the surgeon both during operative stabilization of fractures-dislocations and in the postoperative setting. Surgeons rely on imaging to check the placement of hardware and bony alignment.

In addition to the clinical examination, radiographs are important to assess for ­nonunion or malunion.

Malunion is a frequently encountered complication in hand fractures [15]. Malunion fractures are those that heal with a deformity of angulation, rotation, or overriding of the fragments. This is caused by failure to reduce the fragments into proper alignment or failure to hold them in position until union.

Nonunion occurs when the healing process is incomplete and stops around 6–9 months with no possibility of complete healing; however, it is extremely unusual to achieve nonunion in the metacarpals and phalanges. There are two types of ­nonunion: atrophic and hypertrophic. The overwhelming majority of nonunions in the hand are of the atrophic type. Radiographically, there is sclerosis of the fracture surface and closure of the medullary canal in the hypertrophic type. There is ­osteoporosis and tapering of fracture ends in the atrophic type.

Infection may be a complication seen following finger trauma. The diagnosis of osteomyelitis is based primarily on clinical findings, with data from the initial ­history, physical examination, and laboratory tests serving as benchmarks against which treatment response is measured [16]. Plain radiography is the primary initial diagnostic study.

Radiographic evidence of bone destruction by osteomyelitis may not appear until approximately 2 weeks after the onset of infection. The radiographs may reveal osteolysis, periosteal reaction, and sequestra (segments of necrotic bone separated from living bone by granulation tissue) [17].

Posttraumatic osteoarthritis occurs when the joint surface wears away following an injury to the joint cartilage. Most commonly, this occurs when the fracture involves the cartilage surface of the joint. If the fracture extends into the joint surface, the cartilage can become uneven and prone to osteoarthritis. Plain radiography is an excellent modality to assess for joint space loss and osteophyte formation (Fig. 4.23).

In addition to helping evaluate the clinical concern, radiographs may reveal unexpected findings. These findings may include arthritides, congenital malformations or tumor (Fig. 4.24).