INTRODUCTION

The anatomy of the wrist is closely tied to carpal instability, which is broadly defined as the lack of adequate ligamentous and skeletal support to maintain a wrist stable to external forces of pinch and grasp. When anatomic failure occurs within the wrist, instability either at rest (static) or with use (dynamic) follows as a consequence of bone fracture, ligament tear, or a combination of both.

An important support system of the wrist includes the interosseous ligaments, which connect the individual carpal bones: the scapholunate (SL) and lunotriquetral (LT) ligaments. They are recognized as the important stabilizing structures of the proximal carpal row. Carpal instability is increased when the extrinsic ligaments are also involved.

Isolated injury of the LT interosseous ligament complex and associated structures is less common and is poorly understood compared with the other proximal row ligament injury, scapholunate dissociation. Much more has been published on the etiology and treatment of carpal instability on the radial side of the wrist. However, symptomatic disruption of the LT supporting ligaments from either a traumatic or a degenerative cause is not unusual. The spectrum of injuries ranges from isolated partial tears to frank dislocation, and from dynamic to static carpal instability.

LT disruption as a specific carpal injury was described by Reagan and associates in 1984. The general awareness of this problem is often poor, which explains why many LT injuries still are currently missed or confused with other ulnar-sided wrist problems. The differential diagnosis of ulnar-sided discomfort includes triquetrohamate instability, pisotriquetral injury or arthrosis, extensor carpi ulnaris (ECU) instability or tendinitis, periarticular calcification, lesions of the triangular fibrocartilaginous complex (TFCC), distal radioulnar joint subluxation, arthritis, chondromalacia of the distal ulna, ulnocarpal impaction syndrome, and ulnar neurovascular syndromes. Hamate hook or body fracture causes ulnar-sided wrist problems as well.

The diagnosis of LT instability depends on an accurate history, careful and precise clinical examination, appropriate stress tests, and radiographic imaging. LT dissociation, the most severe form of LT tears, can be seen on lateral radiographs as a static volar intercalated segmental instability (VISI) pattern.

Treatment may be conservative or surgical, depending on the clinical symptoms, and may include ligament repair or reconstruction, various forms of intercarpal fusion, proximal row carpectomy, or complete wrist arthrodesis.

ANATOMY AND KINEMATICS

Strong intrinsic interosseous membranes tightly connect the three bones of the proximal carpal row to each other. The LT ligament consists of dorsal and palmar ligamentous portions and a proximal fibrocartilaginous membrane. The palmar fibers are the strongest and lend maximum stability to the joint. Dorsally, the scaphotriquetral (dorsal intercarpal) and radiotriquetral ligaments are important secondary stabilizers of the articulation and can influence the carpal kinematics significantly.

Because the three bones of the proximal carpal row have no tendinous insertions and therefore no dynamic constraints, normal kinematics and joint stability are dependent on the joint surface configuration as well as on intrinsic and extrinsic (radiocarpal) ligaments. The proximal row thus acts as an intercalated segment between the radius and distal row. The relative motion of this segment is determined by the articular surface of the distal radius and the triangular fibrocartilage and by the force applied through the distal row.

In ulnar deviation, the proximal row extends, and the distal row flexes. The dorsal scaphotriquetral (intercarpal) ligament tightens, increasing midcarpal contact and pulling the triquetrum into its low extended position relative to the hamate. The scaphoid is extended and supinated in this position, which also pulls the lunate into extension.

In radial deviation, the reverse occurs with proximal row flexion and distal row extension. The dorsal radiotriquetral ligament (i.e., the dorsal radiocarpal ligament) becomes taut, increasing compression across the LT joint and restraining the lunate from palmar flexion and dorsal translation. When the dorsal radiotriquetral ligament and the LT ligament are torn, a VISI deformity results with a palmar-flexed lunate.

An interesting fact is that wrist laxity increases the vulnerability of the wrist to injury. Garcia-Elias and associates demonstrated that there is a tendency for wrists with a shorter ulna to have greater triquetral displacement than wrists with a positive ulnar variance. Whether this results from the action of the prominent ulna preventing the triquetrum from migrating proximally or from the presence of stiffer LT ligaments is not known. Indirectly, this finding supports the concept of ulna-negative wrists being more prone to wrist instability. Indeed, while ulna-positive wrists may develop an ulnocarpal impaction syndrome, in ulna-negative wrists the triquetrum is less constrained proximally, thus exposing the intercarpal ligaments to a higher risk of rupture when the wrist is forcefully twisted.

PATHOMECHANICS

The “primary” wrist instability is referred to as a carpal instability dissociated (CID) pattern, in which the interosseous scapholunate and LT ligaments are injured either alone or in combination with the palmar radiocarpal and ulnocarpal ligaments. When the interosseous ligaments are intact but attenuated, a secondary carpal instability called a carpal instability nondissociative (CIND) pattern may occur.

When both LT and dorsal radiotriquetral ligaments were experimentally sectioned in cadaver studies, the flexion moment of the scaphoid became unconstrained, inducing a conjoined rotation of the scaphoid and lunate into flexion, with subsequent anterior subluxation of the capitate. This resulted in a static VISI pattern of instability. In less advanced ligament sectioning, when only the palmar and dorsal LT ligaments were sectioned, increased mobility of the LT joint was detected (dynamic instability), but without a complete destabilization of the carpus.

In a cadaver study by Horii and associates, the dorsal and palmar LT ligaments and interosseous membrane were sectioned, leaving the extrinsic ligaments initially intact. The authors were able to document alterations in the orientation, position, and mobility of the screw-displacement axes of the individual carpal bones after sectioning the LT ligament complex. This resulted in an average 5 degrees of position change of the proximal carpal bones relative to the radius, but no static collapse during physiologic loading. This degree of instability may allow sufficient abnormal movement to produce synovitis, ligamentous tension, cartilage wear, and, as a result, the clinical symptoms of pain noted in LT ligament tears. In these instances of isolated interosseous ligament injury, a dynamic form of LT instability can be present, often manifested by a painful “clunk” as the wrist is moved from radial to ulnar deviation.

After division of the intrinsic LT ligaments, further sectioning of the extrinsic dorsal radiotriquetral and scaphotriquetral ligaments allows the lunate to follow the scaphoid into a static VISI position.

Thus, although an LT ligament tear may lead to wrist pain, it is insufficient to produce static instability by itself. Similarly, attenuation or laxity of the peritriquetral ligaments may also explain the VISI deformity that occurs in patients with inflammatory disease and congenital ligamentous laxity.

MECHANISM OF INJURY

A force applied to the palmar radial aspects of the carpus with the wrist dorsiflexed and ulnarly deviated induces intercarpal supination, causing an injury that progresses in a radial to ulnar direction. Mayfield and colleagues demonstrated that this mechanism may result in a variety of carpal fractures: it may follow a purely ligamentous path about the lunate and space of Poirier, or it may culminate in a combination of bone and soft tissue injuries. Injury to the LT support structures occurs as the third stage in the Mayfield classification only after a scapholunate injury or scaphoid fracture (stage I) and after lunocapitate dissociation (stage II). The combination of all three injuries usually results in a dorsal intercalated segmental instability (DISI) pattern.

A solitary LT ligament sprain is found more commonly after an isolated ulnar-sided wrist injury, which could occur by a fall onto an outstretched hand that is held in extension and radial deviation. The force on the hypothenar eminence induces intercarpal pronation, which tightens the ulnar-palmar ligamentous structures and drives the capitate into the LT joint.

Isolated LT tears may also occur with forced wrist flexion. A dorsally applied force then permits the LT interosseous fibers to fail, sparing the palmar radiolunotriquetral ligament.

Patients without a history of trauma or inflammatory arthritis may have degenerative LT ligament lesions. An ulna-positive variant facilitates LT membrane degeneration via a wear mechanism or by altering intercarpal kinematics.

CLINICAL FINDINGS

LT dissociation may present as a spectrum of clinical conditions, ranging from asymptomatic partial tears to painful complete dissociation with static collapse, causing a forklike deformity and prominence of the distal ulna. A history of a specific injury is usually present.

Symptoms are usually intermittent and are especially prominent with deviation or rotation of the wrist. Other frequently reported symptoms include diminished motion, weakness of grip, a sensation of instability or giving way, and ulnar nerve paresthesias. A painful wrist crepitus is usually present with radial-ulnar deviation.

The wrist examination should encompass the entire ulnar side. Inspection may demonstrate the fork-shaped deformity of a static VISI collapse pattern in which the carpus appears palmarly subluxed at the distal radioulnar carpal joint. A palpable wrist catch or crepitation may be significant. Ulnar deviation with pronation and axial compression elicits dynamic instability with a painful clunk when a midcarpal or LT instability injury is present. Palpation always demonstrates point tenderness at the LT joint. Three provocative tests are helpful for accurate localization of the pathologic site: the ulnar compression test, the LT ballottement test, and the dorsal-palmar shear test.

Pain elicited with the compression test may be of LT origin, but it may also arise from the triquetral hamate joint. In this test, the triquetrum is pushed from an ulnar to radial direction against the lunate, stressing the LT ligament.

Ballottement of the triquetrum is performed by grasping the pisotriquetral unit between the thumb and index finger of one hand and the lunate between the thumb and index finger of the other hand to stress up and down the LT interval. The purpose of the test is to rock or “ballotte” the lunate against the triquetrum to demonstrate pain related to instability, cartilage loss, or local synovitis.

The shear test, described by Kleinmann, is performed with the forearm in neutral rotation and the elbow on the examination table. The examiner´s contralateral thumb is placed over the dorsum of the lunate. With the lunate supported, the ipsilateral thumb directly loads the pisotriquetral joint from a palmar to dorsal direction, creating a shear force at the LT joint. The goal of the test is to place a dorsal shear force by lifting the pisiform and triquetrum dorsally on the fixed lunate.

All these test results are considered positive if increased LT mobility, pain, or crepitation is elicited.

Ulnocarpal impaction syndrome is not infrequently present in LT injury secondary to a positive ulna variance, and it may be the primary source of discomfort.

CLASSIFICATION

Viegas and associates described the following clinical classification of LT ligament tear:

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  Grade 1: Partial or incomplete LT ligament tear without VISI deformity

  
  
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  Grade 2: Complete LT ligament tear with lesion of the palmar ligaments and dynamic VISI deformity

  
  
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  Grade 3: Complete LT ligament tear with lesion of the palmar and dorsal ligaments and static VISI deformity

IMAGING

A wide variety of imaging studies can be useful in the diagnosis of ulnar wrist abnormalities, such as cineradiography, arthrography, magnetic resonance imaging (MRI), and arthroscopy.

Although standard wrist views (posteroanterior and lateral radiographs) appear normal with partial tears, complete dissociations may result in certain changes. Most characteristic of this injury is disruption of the normal convex arc of the proximal row (Gilula´s lines). This is visualized as a stepoff between the lunate and the triquetrum and a flattened arch to the proximal row on a posteroanterior x-ray. Unlike scapholunate dissociation, an increased space is not seen between the lunate and the triquetrum. Occasionally, the triquetrum may overlap the lunate or the lunate may translate ulnar to its normal position. If a static collapse pattern is present, the carpal height ratio will be abnormal. A neutral rotation posteroanterior view should be obtained to assess ulnar variance.

Lateral radiographs may also be normal in the absence of carpal collapse, but often they demonstrate a VISI pattern as a result of a complete LT dissociation. The longitudinal axis of the triquetrum, defined as a line passing through the distal triquetral angle and bisecting the proximal articular surface, forms an angle with the lunate of 14 degrees (range +31 to −3 degrees) normally. Patients with LT dissociation exhibit a negative angle (mean value −16 degrees). VISI deformity causes an alteration of the scapholunate and capitolunate angles in which the scapholunate angle is 40 degrees or less. The lunate and capitate, which normally are collinear, collapse in a zigzag fashion, resulting in an angle greater than 10 degrees and often much larger. The lunate center of rotation lies dorsal to the midaxial line of the capitate and may exhibit slight dorsal subluxation.

Motion studies are helpful occasionally. These include anteroposterior views in maximal radial and ulnar deviation plus a clenched-fist view, and sagittal views in flexion, extension, and deviation.

Cineradiography is also helpful and should be performed at the time of wrist arthrography. This permits fluoroscopic examination of the dye column as well as performance of stress maneuvers that may document the cause of a wrist clunk.

In arthrography, false-negative and false-positive results may occur.

Preexisting rheumatoid arthritis increases the likelihood of intercompartmental communication. Both radiocarpal and midcarpal injection techniques are used. Midcarpal injection may add to accuracy because less detail of the proximal row is obscured.

Technetium 99m bone scans show increased uptake in the lunate or triquetral bones (or both) in instances of LT ligament tears.

Other useful diagnostic tools are MRI and wrist arthroscopy. However, the sensitivity and specificity of MRI compared with arthroscopy are unsatisfactory for detecting pathology in the interosseous ligaments, particularly the LT ligaments.

ARTHROSCOPY

Arthroscopic examination of the wrist can provide excellent views of the palmar radiocarpal und ulnocarpal ligaments and facilitates an inspection of the interosseous ligaments that is superior to that which can be achieved with open arthrotomy. Visualization of these ligaments arthroscopically can also demonstrate small differences in ligament tension, direction of action, and their substance or integrity between carpal bones.

The interval between the lunate and triquetrum may be difficult to identify arthroscopically because joint articular cartilage blends across the ligament between these two bones. Palpation with an arthroscopic probe allows one to determine with a high degree of accuracy whether there is a loss of continuity of the scapholunate and LT interosseous ligaments. Small degenerative interosseous ligament tears can be clearly distinguished from larger traumatic when the arthroscopic visualization is combined with palpation with a hook probe and passive manipulation of the scaphoid on the lunate or lunate on the triquetrum.

TREATMENT

Factors governing the choice of treatment method for LT sprains include the extent of the tear and the resultant instability, the elapsed time between injury and treatment, and the presence of associated injury or degenerative changes.

Initial management of all acute and most chronic tears (sprains without static carpal collapse) should be conservative, with an above-elbow cast or splint immobilization with a pad beneath the pisiform and over the dorsum of the distal radius to maintain optimal alignment.

In acute and chronic dissociations and chronic tears unresponsive to conservative management, operative correction may be indicated by the symptoms. The goal of surgical intervention is the realignment of the lunocapitate axis, the reestablishment of the rotational integrity of the proximal carpal row, and the reduction of abnormal intercarpal motion.

Various procedures have been used to achieve these goals. These include open or closed reduction with percutaneous Kirschner-wire fixation, ligament repair, ligament reconstruction, extensor carpi ulnaris tenodesis procedure, LT arthrodesis, midcarpal arthrodesis, proximal row carpectomy, and total wrist fusion. In addition, ulnar shortening has been used alone or in combination with these procedures to treat degenerative tears associated with ulnar carpal abutment.

Acute LT dissociation may occasionally be treated by closed or open reduction and internal fixation alone. The experience of Knoll and associates shows that Kirschner wires alone have been unsatisfactory in maintaining LT alignment, resulting in the development of a VISI deformity.

Biomechanical studies have shown that the LT ligament is a key element in VISI.

For most patients without arthritic change or significant residual perilunar instability, restoration of LT stability by ligament repair, reconstruction, or LT arthrodesis is most appropriate.