Perilunate Fracture Dislocations 

Perilunate dislocations (see image below) and perilunate fracture dislocations are the most devastating closed injuries of the wrist.^{[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]} They often are missed on initial evaluation, leading to devastating complications. These injuries occur as the final stage of a spectrum of injuries progressing around the wrist in a radial-to-ulnar direction.

In the setting of a high-energy wrist injury, radiographs must be scrutinized carefully for perilunate dislocation or one of its variants. Prompt open reduction with ligamentous repair or reconstruction is necessary to achieve favorable results. Posttraumatic arthrosis may result following these injuries irrespective of treatment, requiring a late salvage operation.

Prior to the advent of radiography, fractures of the distal radius, carpal instability, and carpal dislocations were at best difficult to distinguish. In 1855, Malgaine was the first to publish a description of perilunate fracture dislocations. Later, Cousins, Destot, and de Quervain reported on this injury. Tavernier reported the first true series in 1906. Destot contributed greatly to the general understanding of wrist instability in the work Injuries of the Wrist: A Radiographic Study (1918).^[12]

Subsequently, enthusiasm for the study of wrist instability was lost until 1968, when Fisk presented the Royal College of Surgeons Hunterian Lecture on the concept of the intercalated segment, referring to the kinematics of the proximal carpal row. In 1972, Linscheid and colleagues further modified the intercalated segment concept by introducing the terms volar intercalated segment instability (VISI) and dorsal intercalated segment instability (DISI).^[13] In 1980, Mayfield and coauthors illustrated the mechanism of perilunar wrist instability as a series of 4 stages resulting in perilunate dislocations or lunate dislocations.^[14]

The perilunate dislocation and the perilunate fracture dislocation are injuries that involve traumatic rupture of the radioscaphocapitate (RSC) ligament, the scapholunate interosseous ligament, and the lunotriquetral interosseous ligament. Fractures of the radial styloid, the scaphoid, the trapezium, the capitate, and the triquetrum also may be associated with the dorsal or the volar perilunate dislocation. The result of perilunate dislocation and of perilunate fracture dislocation is an extremely unstable wrist, potentially producing devastating complications.^[15]

Frequency

Little is known about the true incidence of perilunate dislocations and perilunate fracture dislocations. Because the subtlety of wrist injuries often is not appreciated fully, many believe that perilunate injuries in general are underdiagnosed. Perilunate dislocation, lunate dislocation, and perilunate fracture dislocation variants have been estimated to comprise less than 10% of all wrist injuries. In a study reviewing perilunate dislocations, 61% were of the transscaphoid perilunate type.

Perilunate dislocations and perilunate fracture dislocations typically occur in young adults who are exposed to high-energy trauma, such as a fall from a height. In these injuries, the fall generally results in the wrist being axially loaded by the body, trapping the hand in the hyperextended and ulnarly deviated position. The angle of hyperextension determines the extent of injury. If sufficient loads are applied, the ulnarly deviated wrist, hyperextended beyond 100 º, produces a perilunate dislocation or one of the fracture dislocation variants.

Pure ligamentous perilunar injuries of the wrist are classified as lesser arc injuries, while the transosseous variants are regarded as greater arc injuries. The mechanism of perilunate dislocations has been described as a 4-stage process, as follows:

• First stage - The RSC ligament and the scapholunate interosseous ligament rupture.
• Second stage - Dislocation of the capitolunate joint occurs as the injury progresses through the space of Poirier.
• Third stage - The lunotriquetral interosseous ligament ruptures.
• Fourth stage - The lunate becomes dislocated.

This mechanism has been reproduced in a cadaver model by applying pronation and ulnar deviation on a hyperextended cadaver wrist.

Most patients present acutely following a fall from a height onto a dorsiflexed wrist. Patients with perilunate dislocations and perilunate fracture dislocations may demonstrate obvious clinical deformities, such as marked swelling, or they can present rather innocuously complaining of a sprained wrist. In the dorsal perilunate dislocation or one of its transosseous variants, the carpus is dislocated dorsally, and the radius is prominent volarly; in the pure lunate dislocation, the lunate alone is prominent volarly. These injuries are diagnosed late in up to 25% of cases.

Because of the high-energy nature of perilunate fracture dislocations, a careful, thorough trauma survey with assessment for associated injuries of the head, thorax, and extremities is imperative. Damage to the median nerve is the most common associated injury in lunate and perilunate dislocations of the wrist. In certain situations, volar skin lacerations could represent an open dislocation or fracture dislocation.

Additionally, the volar skin can become ischemic because of pressure from the volar radius (resulting from dorsal dislocation of the hand). With long-standing perilunate dislocations, patients may present with arterial compromise or established compartment syndromes.

To achieve optimal treatment results, all perilunate dislocations and all perilunate fracture dislocations must undergo accurate open reduction and internal fixation as soon after the injury as possible.^[16] Like other dislocations, the perilunate dislocation is an emergency and should be reduced as soon as possible. This may be performed in the emergency room, with delay of the definitive procedure, as any fracture associated with perilunate dislocations typically requires stabilization with small compression screws or percutaneous pins. It is sometimes necessary to delay the definitive procedure because of the patient's overall condition, excessive swelling of the wrist and hand, or the need for appropriate surgical assistance.

If, once the perilunate dislocation is reduced, the definitive procedure is delayed, the patient should be observed carefully for skin or neurologic compromise. Once reduced, the extremity is elevated and iced until the definitive procedure is performed. If closed reduction cannot be obtained in the emergency department, the patient must be taken promptly to the operating room for open reduction. Median nerve palsy is the most common complication following delay in the reduction of perilunate dislocation and perilunate fracture dislocation.

The carpus is composed of 2 rows of bones: the proximal carpal row (scaphoid, lunate, and triquetrum) and the distal carpal row (trapezium, trapezoid, capitate, and hamate).^[17] The wrist joint is composed of 2 types of ligaments, intrinsic and extrinsic. The intrinsic ligaments are short, stout ligaments that stabilize adjacent carpal bones, while the extrinsic ligaments span the proximal carpal row and the distal carpal row.

Within the proximal carpal row, the scapholunate interosseous ligament binds the scaphoid to the lunate.^[18] The scapholunate interosseous ligament has 3 portions: proximal, distal, and volar. The dorsal portion of this ligament supplies the majority of stabilizing strength to the scapholunate articulation. The lunotriquetral interosseous ligament secures the articulation of the lunate and the triquetrum. Although stout, the interosseous ligaments of the proximal carpal row allow relative motion between the scaphoid and lunate and between the lunate and the triquetrum.

The distal carpal row is also stabilized by intrinsic ligaments, such as the capitohamate ligament, which is composed of dorsal, deep, palmar, and longitudinal components. The scaphotrapeziotrapezoidal (STT) joints are stabilized by a ligamentous complex that is intrinsic and extrinsic in nature. These ligaments include the scaphotrapezial ligament, a scaphocapitate capsular ligament, and the dorsal and palmar STT capsular ligaments. The extrinsic carpal ligaments provide the structural integrity for the articulations of the proximal and distal carpal rows. The RSC ligament originates from the radial styloid, crosses the waist of the scaphoid, and inserts on the volar waist region of the capitate.

Immediately ulnar to the RSC ligament is the radiolunotriquetral ligament, which originates from the radial styloid, sends an attachment to the volar aspect of the lunate, and then terminates on the triquetrum. The short radiolunate originates from the most ulnar aspect of the distal radial articular surface and inserts on the proximal volar aspect of the lunate. From the base of the ulnar styloid, 2 ligaments — the ulnocapitate and the ulnotriquetral — originate. A portion of the ulnotriquetral ligament continues across the midcarpal joint to insert on the waist of the capitate and join the RSC ligament, forming an inverted V. This ligament is known as the ulnocapitate ligament, and the inverted-V confluence is known as the arcuate ligament. Just proximal to the base of the V is a soft spot, the space of Poirier.

Found between the short radiolunate ligament and the radiolunotriquetral ligament is the radioscapholunate ligament, which is also known as the ligament of Testut. The ligament designation of this structure is a misnomer, because histologic studies have shown that it is a vascular structure devoid of any true collagen fibers and that it lacks structural integrity.

Within the dorsal capsule of the wrist are 2 ligaments of particular importance, the dorsal intercarpal and dorsal radiocarpal ligaments. The dorsal intercarpal ligament courses transversely from the waist of the scaphoid across the carpus, inserting onto the dorsal aspect of the triquetrum. The dorsal radiocarpal ligament spans a distance from its origin on the radial styloid to its place of insertion on the dorsal aspect of the triquetrum. Together, these 2 ligaments form a V, with the base of the V on the triquetrum. Between the limbs of the V is the less substantial dorsal wrist capsule.

Only a life-threatening condition should delay the prompt reduction of a perilunate dislocation or a perilunate fracture dislocation. Even in this dire circumstance, however, a closed reduction can generally be performed without compromising the treatment of the life-threatening condition that takes priority. Once the fracture is reduced, definitive treatment can be delayed until the patient's condition has been stabilized or optimized.