Carpus: Perilunate and Greater Arc Injuries

INTRODUCTION

Perilunate dislocations (PLDs) and interosseous ligament tears are among the most common forms of carpal injuries. They are primarily an injury of the younger population and have many possible causes. Seen in the emergency department, patients most often present in the acute setting with PLDs as part of a poly-trauma; therefore, these injuries must not be missed during the primary or secondary survey. In lower-energy injuries, patients often present to the clinic and are often improperly diagnosed with a low-grade wrist sprain. Studies have shown that even with adequate radiographic images, the diagnosis is missed up to 25% of the time.

∗ To my family and friends and those who have trained me, and those I have trained: From all of whom I have learned.

The consequences of a missed diagnosis of PLD may be severe. The natural history of the injury, if left untreated, results in disabling wrist arthritis. Irreversible neurologic damage may also result when there is an untreated associated median nerve injury. Delayed treatment is possible; however, it is not recommended. PLDs should be treated as soon as they are recognized.

ANATOMY

The anatomy of the wrist is complex and out of the scope of this review of PLDs. Therefore, only the structures involving PLDs are discussed. The osseous anatomy of the wrist includes the radius, ulna, carpus, and metacarpus. The proximal carpal row and the radial and ulnar styloids are important structures as related to PLD. These bones are involved in two joints—the radiocarpal and the midcarpal. The ligamentous anatomy is important as well, since PLDs are primarily ligamentous injuries. Vascular and muscular structures are rarely involved in PLDs, and only one neurologic structure (the median nerve) is routinely involved.

The distal radius provides the proximal articular surface for the radiocarpal joint. It is a biconcave structure that articulates with the scaphoid and the lunate, each with its own fossa. The scaphoid and lunate fossae are separated by an interfacet prominence primarily composed of cartilage. The ulnocarpal joint is cushioned, and the distal radioulnar joint is stabilized by the triangular fibrocartilage complex (TFCC), which is not discussed here.

The scaphoid acts as a bridge between the proximal and distal carpal rows and plays an integral role in PLDs. It articulates with the trapezium and the trapezoid at its distal pole and articulates proximally with the lunate and capitate. Two important anatomic variants of the midcarpal joint relate to whether the lunate has one or two facets. In the type II lunate, two facets articulate with the capitate and the proximal pole of the hamate. Conversely, in the type I lunate, the lunate has one facet that articulates only with the capitate. Radiographically, the radiocarpal and midcarpal articulations may be assessed with Gilula’s lines. These radiographic lines are smooth and unbroken in a normal wrist. Any abnormal interruptions of these lines indicate carpal pathology ( Fig. 44-1 ).

The ligamentous anatomy of the wrist is subclassified into extrinsic and intrinsic ligaments.

Extrinsic Ligaments

On the radial side, the volar extrinsic ligaments originate on the radius and are the main stabilizers of the radiocarpal joint. These include the radioscaphocapitate (RSC), the long radiolunate (LRL), the short radiolunate (SRL), and the radioscapholunate (RSL, ligament of Testut).

The radioscaphocapitate extends from the radial styloid across the waist of the scaphoid to the palmar aspect of the capitate and is a major contributor to radiocarpal stability. The radioscapholunate does not contribute to carpal stability and acts primarily as a neurovascular conduit for the anterior interosseous artery and nerve. Between the radioscaphocapitate and the long radiolunate at the level of the radiocarpal joint is the space of Poirier, which is a well-described area of capsular weakness. The ulnar extrinsic ligaments pass from the ulna to the lunate and triquetrum volarly, the ulnolunate (UL) and ulnotriquetral (UT), respectively. The long radiolunate is the strongest extrinsic ligament; both the short radiolunate and the long radiolunate act as the primary stabilizers for the lunate and prevent lunate translocation.

The dorsal ligaments provide stability of the scaphoid to the radius. These include the dorsal wrist capsule, which is strengthened by the dorsal radiocarpal ligament (DRC) and the dorsal intercarpal ligament (DIC). These ligaments span the radiocarpal and midcarpal joints and act as a buttress to the scaphoid. During flexion and extension of the wrist, these two ligaments change orientation so that the scaphoid may move freely in its arc.

Intrinsic Ligaments

Intrinsic ligaments attach two carpal bones. The most important intrinsic ligaments are the scapholunate and lunotriquetral interosseous ligaments. The scapholunate interosseous ligament (SLIL) is strongest dorsally, and the lunotriquetral interosseous ligament (LTIL) is stronger palmarly. The intact SLIL resists the tendency of the scaphoid to independently fall into flexion while the trapezium (which is dorsal) pushes the scaphoid into flexion as the wrist is radially deviated. As the scaphoid flexes, the entire carpal row flexes with it during radial deviation. Similarly, the triquetrum, via its helicoid articulation with the hamate, tends to extend when the wrist is ulnarly deviated. The LTIL therefore pulls the lunate and scaphoid into extension when the wrist is ulnarly deviated in an intact proximal row.

MECHANISM OF INJURY

Perilunate injuries are caused by wrist hyperextension and supination and are predominantly the result of a high-energy impact. The two causes of perilunate injuries are falls from a height and motor vehicle accidents. The wrist is extended beyond the limits of the ligamentous constraints of the volar ligaments causing tensile forces palmarly and dorsal compressive forces. The resulting force may cause tears in the volar ligaments, leading to a PLD.

EVALUATION AND DIAGNOSIS

A comprehensive history and physical examination must be performed in addition to obtaining the proper radiographic images. A history of a high-energy impact or repetitive wrist sprains may prompt the need to obtain further radiographs. Patients typically present with pain, swelling, and decreased range of motion. Neurovascularly, patients may present with an acute median neuropathy (carpal tunnel syndrome). This has been reported in approximately 25% with a range of 16% to 46% in various studies.

Standard wrist radiographs including posteroanterior, lateral, and oblique views should be obtained. In addition, if the history and physical examination suggest, ipsilateral forearm and elbow radiographs should also be obtained as part of a trauma survey. If a ligament injury is suspected based on history and physical examination but cannot be corroborated on standard radiographs, a stress view—a posteroanterior view while clenching the fist with the wrist in ulnar deviation—also should be obtained. Comparing the injury film with normal films, one should always draw Gilula’s lines. Any interruption of these lines is indicative of carpal pathology. In addition, an increase in space of more than 2 mm between two bones that is not matched on the contralateral injured side is diagnostic of a ligament disruption. Radiographs of the injured side must also be evaluated for any concomitant fractures of other structures in the hand and wrist.

CLASSIFICATIONS

Dorsal intercalated segment instability (DISI) and volar intercalated segment instability (VISI) are two common forms of carpal instability. DISI is a palmar translation or dorsiflexion of the lunate due to loss of support from the SLIL. The diagnosis of DISI is made on a lateral radiograph of the wrist. The measurement of the angle between the long axis of the scaphoid and the transverse axis of the lunate (normally 47 degrees) is more than 60 degrees with a DISI deformity ( Fig. 44-2 A ). VISI is volar flexion of the lunate due to loss of support from the LTIL. The diagnosis of VISI is made on a lateral radiograph. The scapholunate angle measures 30 degrees or less ( Fig. 44-2 B). Investigators have shown that tears of the interosseous ligaments alone are insufficient to lead to these forms of carpal instability. Rather, the dorsal extrinsic ligaments attenuate with increased stress owing to the loss of stability contributed by the interosseous ligaments, and this loss is essential for the development of the traditional DISI and VISI deformities.

Carpal instability injuries are progressively classified into four groups: carpal instability dissociative (CID), carpal instability nondissociative (CIND), carpal instability complex (CIC), and carpal instability adaptive (CIA). Instability injuries may be further classified into greater arc and lesser arc injuries. Greater arc injuries involve a fracture of the radius, ulna, and/or carpus. Fractures of the scaphoid, radial styloid, ulnar styloid, capitate, and triquetrum are most common.

CID instabilities are within the proximal row and include lunotriquetral dissociations and scapholunate dissociations. Scaphoid fractures may also lead to CID (greater arc). Scapholunate dissociations may be dynamic or static based on the number of ligaments involved. These are described in more detail in the text that follows. Regarding acute, traumatic LTIL injuries, the lunotriquetral tear typically shows instability but no VISI on radiographs. Diagnosis of VISI associated with CID requires both a lunotriquetral and a dorsal radiocarpal ligament tear. On radiographs, there is a disruption of Gilula’s lines. Chronic injuries often include degeneration of the proximal lunotriquetral with concomitant injuries to the triangular fibrocartilage complex, the ulnar extrinsic ligaments, and/or the extensor carpi ulnaris subsheath.

CIND instabilities are between the proximal and distal carpal rows or the proximal row and the distal radius. Ulnar translocation is a common form of CIND between the radius and proximal carpal row. Ulnar translocation is classified into types I and II. Type I injuries are caused by rheumatoid arthritis, radioscaphocapitate injuries, or laxity of ligaments. Radiographs show the entire carpus ulnarly translocated with increased space between the radial styloid and scaphoid ( Fig. 44-3 A ). The lunate also no longer sits within its fossa. Type II injuries differ in that the scaphoid is located within its fossa. Radiographs indicate that the scaphoid is normal in appearance; however, the scapholunate interval is widened, and only the lunate and triquetrum are ulnarly translocated ( Fig. 44-3 B).

Midcarpal CIND instabilities may be associated with trauma and may also be atraumatic because of laxity of the ulnar arcuate ligament. The entire row is volarly flexed in a VISI-type deformity. Unsupported lateral radiographs show the deformity with the hand falling into supination. The physical examination is important, since many of the radiographic findings are normal. The scapholunate and lunotriquetral intervals as well as Gilula’s lines are normal owing to the intact interosseous ligaments. Arthrograms are often normal.

The diagnosis of CIND is typically made during physical examination with the midcarpal clunk test.That is, a clunk is felt as the wrist is passively radially to ulnarly deviated while applying an axial load across the metacarpal heads. This midcarpal clunk is often the only physical finding.

CIC injuries are instabilities between both the distal radius and the proximal row and the proximal and distal carpal rows. These include both perilunate and reverse perilunate injuries. The Mayfield classification, discussed next, describes a progressive perilunate injury spectrum.

Mayfield described a classification system based on a reproducible sequence of injuries after placing a force on an extended wrist for CIC-type injuries. He described these injuries as lesser arc injuries ( Fig. 44-4 A ). Mayfield noted that force applied to the thenar eminence progressed around (or through) the scaphoid, which resulted in flexion of the scaphoid. The force then progressed through the scaphocapitate and capitolunate joints (or capitate) and finally through the lunotriquetral ligament (or triquetrum). This led to four distinct stages (I–IV) of injury ( Fig. 44-4 B).

In stage I, or scapholunate dissociation, the scapholunate ligament (lesser arc) or the scaphoid (greater arc) is disrupted. This dissociation may be dynamic or static. In static dissociation, a wrist radiograph reveals the Terry Thomas sign, a statically widened scapholunate interval (more than 3 mm), and/or the signet ring sign, which is the scaphoid superimposed on itself as a result of flexion of the distal pole of the scaphoid. Static dissociations are often associated with DISI deformities, visualized on lateral radiographs as a scapholunate angle greater than 60 degrees. These deformities require a disruption of both the SLIL and the dorsal radiocarpal ligament. These findings together are classified as rotatory subluxation of the scaphoid ( Fig. 44-5 ). To visualize dynamic instabilities, stress view radiographs are necessary to show a widened scapholunate interval and a flexed scaphoid.