Carpal Bone Injuries Clinical Presentation

Distal radius, scaphoid, and lunate fractures are usually the result of a fall onto an outstretched hand, but they may also be caused by direct trauma (eg, during impact with a football helmet). ^{[5, 6]}

Extension fractures of the distal end of the radius

These fractures result from a fall onto a pronated, dorsiflexed hand. Upon striking a hard surface, the hand becomes fixed while the momentum of the body produces 2 forces: (1) a twisting force, which causes excessive supination of the forearm, and (2) a compression force, which acts vertically through the carpus to the radius.

The lunate acts as the apex of a wedge against the articular surface of the radius and causes different injuries, depending on the age of the patient. In very young children, a greenstick fracture of the distal radius occurs, with or without an associated fracture of the distal ulna. In adolescents, separation of the lower epiphysis with dorsal displacement or crushing of the radial epiphysis occurs. In adults, a fracture occurs within 1 in (2.5 cm) of the carpus. The distal fragment is usually proximally and distally displaced. In all age groups, the fracture may be complicated by injury to the median nerve, injury to the sensory branch of the radial nerve, fracture of the scaphoid, and/or dislocation of the lunate.

Although rare, a true Colles fracture is a transverse fracture of the radius, 1.57 in (4 cm) proximal to the wrist joint with backward, upward, and outward displacement of the distal fragment. In current practice, the term Colles fracture is loosely applied to any complete fracture of the distal end of the radius with an associated dorsal displacement of the hand on the forearm.

Colles fractures frequently result in radial-shortening deformities, reflex sympathetic dystrophy, and/or osteoarthritis. Although most Colles fractures can be treated with closed reduction, the majority of Smith fractures require orthopedic surgery (eg, Kirschner wires [K-wires] for anatomic reduction). ^[7]

Extension fractures of the distal end of the radius (reverse Colles fracture/Smith fracture)

A true Smith fracture is a fracture of the entire thickness of the distal radius, 0.5-1 in (1.3-2.5 cm) above the wrist. The lower end of the radius is proximally and volarly displaced. Smith fractures have come to be known as any fracture of the distal radius with an associated anterior (volar) displacement. ^[8]  See the images below.

One mechanism of injury is a direct blow to the dorsum of the hand with the hand in the flexed position. More frequently, a Smith fracture is caused by an indirect mechanism, such as when a person falls backward onto an outstretched hand in supination. Upon striking the ground, the hand locks in supination while the body's momentum forces the hand into hyperpronation, resulting in a typical hyperpronation injury.

Median nerve compression in the carpal tunnel is a common complication of a Smith fracture. Loss of this nerve function is manifested by the loss of thumb opposition and decreased sensation to the thumb, index finger, long finger, and radial half of the ring finger. If left untreated, this injury results in reflex sympathetic dystrophy. The majority of Smith fractures require orthopedic surgery (eg, K-wires for anatomic reduction).

Pseudocarpal injuries

The definition of pseudocarpal injuries is limited to injuries that involve the distal end of the radius and ulna (just proximal to the carpus), with clinical signs that mimic carpal bone injuries. Examples include articular disk injuries of the wrist, dislocations of the inferior radioulnar joint, and traumatic dislocation of the distal end of the ulna.

These injuries are rare and require consultation with an orthopedist for definitive management. Recognizing these injuries in the emergency department or on the field is important to avoid misdiagnosis or delay in appropriate management.

Wrist articular injuries

Injury to the articular disk of the wrist occurs from multiple mechanisms. Articular injuries coexist with the other more common injuries, although isolated injuries to the articular disk can occur. The most common pathologic defect is a tearing of the disk from its attachment at the margin of the ulnar notch of the radius. The primary function of the triangular disk of the wrist is to prevent lateral displacement of the ulna.

The most common mechanism of injury is dorsiflexion and pronation of the hand. Less frequently, extreme hyperextension and supination may cause injury. Volar and dorsal dislocation of the radial head may coexist.

Traumatic dislocation of the distal end of the ulna

Dislocation or subluxation of the distal end of the ulna is most often associated with radial fractures. However, acute traumatic dislocation or subluxation of the ulnar head without fracture can occur and is often not immediately recognized.

The ulnar head may be displaced anteriorly or posteriorly, depending on the mechanism of injury. Extreme extension and pronation of the hand produces a dorsal dislocation of the ulnar head. Extreme extension and supination of the hand produces a volar dislocation of the ulnar head.

A Galeazzi fracture is a specific type of radial fracture that is associated with a displaced distal radioulnar subluxation.

Ulnar styloid fractures frequently result in nonunion fractures, which require eventual, definitive surgical repair.

Traumatic dislocation of the distal end of the radius

A Monteggia fracture represents a displaced proximal ulnar fracture with radial dislocation. In most cases, the radial head is displaced anteriorly; radial nerve injuries are common with this type of injury.

Carpal bone dislocation

Carpal bone injuries are common in individuals of all age groups, but they are particularly common in adolescents. A solid knowledge of anatomy is essential for the clinician to comprehend the factors involved in these types of injuries and the rationale for therapy.

The scaphoid is usually fractured secondary to hyperextension of the wrist, often from falls onto the outstretched hand. The scaphoid is wedged between the radius and the surrounding carpal bones, particularly the capitate. Scaphoid fractures are usually associated with other injuries of the wrist, including dislocation of the radiocarpal joint, dislocation between the 2 rows of carpal bones, fracture-dislocation of the distal end of the radius, fracture at the base of the thumb metacarpal, and dislocation of the lunate.

Radiocarpal fracture-dislocation may result in entrapment of the ulnar nerve and artery.

Lunate and perilunate dislocation

These rare injuries may have a poor outcome if they are not recognized in a timely fashion. An exact diagnosis is often difficult to make based on radiographic findings. The 4 specific projections that help when taking comparison x-ray films are the anteroposterior (AP), lateral, 45° of pronation, and 45° of supination views.

Knowledge of the exact injury mechanism can help predict the resulting dislocation. Carpal bone dislocation is usually the result of extreme flexion or extension injuries of the wrist. The type of dislocation or fracture-dislocation produced by these mechanisms depends on the direction and intensity of the acting force or the position of the hand in relation to the forearm at the moment of impact.

The integrity of the lunate-capitate relationship is the most crucial factor in all dislocations of the wrist. The resulting lesions are directly related to the disruption or preservation of this articulation.

Extension injuries

When the hand is forced into extension (eg, during fall onto an outstretched hand), dorsal perilunate dislocation or volar lunate dislocation occurs. Commonly, a scaphoid fracture or scaphoid fracture-dislocation complicates the dorsal perilunate dislocation.

Flexion injuries

Dorsal dislocation of the lunate can occur when the hand and carpus are hyperflexed, such as with a fall onto the back of the hand. The upward force that is generated when the hand contacts the ground and the downward force that acts through the radius forces the capitate to rotate anteriorly, driving the lunate backward into a dorsal position.

Volar perilunate dislocation occurs when the hand and carpus are not hyperflexed. With this injury, the carpus is driven anteriorly toward the lunate. The lunate remains in its normal position, with the radius and the rest of the carpus dislocating anteriorly to the lunate. Volar perilunate dislocation is often associated with scaphoid fractures.

The aforementioned carpus injuries require consultation with a specialist and are usually treated with open reduction and internal fixation.

Lunate fractures

Lunate fractures most often result from a dorsiflexion injury or the impact of the heel of the hand with a hard surface. Patients usually present with weakness of the wrist and pain, which is aggravated with compression along the third digital ray.

Capitate fractures

Capitate fractures occur in approximately 15% of all carpal bone fractures. The size and position of the capitate make it susceptible to injury because it is the largest carpal bone and articulates with 7 bones. The blood supply is from the dorsal segment and is often disrupted, resulting in avascular necrosis, which is intimately related to the axial motion of the third metacarpal.

Capitate fractures usually result from direct blows or falls onto hard surfaces. These injuries most often occur with the hand in dorsiflexion and are often associated with other injuries.

The sports medicine clinician must always differentiate between a wrist fracture and a wrist dislocation.

Wrist dislocation

Pain is usually localized to the dorsum of the wrist over the radioulnar joint. Pronation or supination against resistance causes pain, and occasionally, a click may be heard when the wrist is rotated. X-ray examination findings are usually grossly negative.

With a dorsal dislocation, the patient usually has a history of acute wrist injury. Marked prominence of the ulnar head is present on the dorsum of the wrist with the hand locked in pronation. Attempts to supinate the wrist cause severe pain.

With a volar dislocation, the patient usually has a history of an acute injury to the wrist with loss of the normal prominence of the ulnar head on the dorsum of the wrist. Prominence of the ulnar head on the volar aspect of the wrist occurs with the hand locked in supination. The transverse diameter of the wrist is narrowed; attempts to pronate the hand cause severe pain.

Wrist fracture

Although ecchymosis is not always present, edema and point tenderness around the wrist should alert the clinician to the likelihood of a fracture (thereby preventing the misdiagnosis of a sprain or dislocation). Perform a thorough range-of-motion examination with pronation and supination to access pain and limitation of motion. ^{[9, 10]}

With a distal-radius fracture, the patient has point tenderness along the distal radius. Look for acute carpal tunnel syndrome. A median nerve examination is particularly important in patients who have dorsally displaced distal radius fractures, because this injury is associated with acute carpal tunnel syndrome.

With a scaphoid fracture, the patient has point tenderness in the anatomic snuffbox (located between the extensor pollicis longus and extensor pollicis brevis tendons). A study by Mallee et al concluded that anatomical snuff box tenderness was the most sensitive clinical test for scaphoid fractures. ^[11]

With a lunate fracture, the patient has point tenderness over the lunate fossa (located distal to the radius at the base of the long-finger metacarpal).

Nerve injury

Upon patient presentation and after treatment, the sports medicine practitioner must document the neurovascular status of the patient's affected extremity. Carefully note the ulnar and median nerve function. The ulnar nerve is often injured with closed fractures of the pisiform, triquetrum, hamate, and fourth and fifth metacarpals.

The motor branch of the ulnar nerve is the chief motor nerve of the hand. The sensory branch is rarely affected.

Blunt trauma to the hypothenar eminence may result in contusion to the ulnar nerve, with resulting neuropraxia.

Median nerve injury, including traumatic carpal tunnel syndrome, is manifested by sensory disturbances in the thumb, index, and long fingers and is associated with Colles fractures, perilunate dislocations, and carpal bone injuries.

If a large hematoma is present, it may be aspirated or surgically removed after consultation with the appropriate specialist.

Compression along the volar ligament results in pain and paresthesias along the median nerve. The thenar eminence exhibits muscle atrophy only late in this disorder.

Acute reduction of the displaced fracture is indicated if an acute injury is secondary to a displaced fracture and there is compression of the ulnar or median nerve.

Wrist articular injuries

Management of these injuries must exactly mirror the mechanism of injury. For example, with pronation injuries, treatment involves supinating the hand with the elbow flexed at 90°. With a supination injury, pronation corrects the defect.