Lunotriquetral injuries: Arthroscopic management

Relevant anatomy and biomechanics

The lunotriquetral interosseous ligament (LTIL) is C -shaped, similar to the scapholunate interosseous ligament (SLIL), and consists of true ligamentous dorsal and palmar subregions and an intervening fibrocartilaginous membranous portion. The palmar region is the thickest and strongest when tested to failure, and it is biomechanically the most important region in the transmission of load and strain from the triquetrum to the lunate, which is the opposite of the SLIL. These findings support the concept that the lunate is suspended between the scaphoid and the triquetrum. In an uninjured wrist, the scaphoid imparts a flexion moment to the proximal carpal row, while the triquetrum imparts an extension moment. These opposing moments are balanced by the ligamentous attachment to the lunate. With a loss of integrity of the LTIL, the triquetrum tends to extend while the scaphoid and lunate attempt to flex, exerting a flexion moment through the SLIL and an extension moment through the LTIL. The dorsal LTIL is more important as a rotational constraint, whereas the palmar LTIL is the strongest and transmits the extension moment of the triquetrum as it engages the hamate. The membranous proximal portion is of little biomechanical significance. Secondary constraints include the triquetrohamate ligament and the triquetrocapitate (TC) ligament; the ulnolunate ligament (ULL) and the ulnotriquetral (UT) ligament; and the dorsal radiocarpal ligament (DRCL) and the dorsal intercarpal (DIC) ligament.

A number of authors have proposed a possible mechanism of injury for LTIL tears. Mayfield et al. performed a biomechanical cadaver study and found that an LTIL tear occurred with a radial-sided force with the wrist in extension and ulnar deviation. The thenar eminence contacts the ground first and forces the carpus into supination. They believed that LTIL tears occurred as a part of the spectrum of perilunate dislocation (stage III). Stanley and Trail believed that an isolated LTIL tear occurred as a part of a reverse Mayfield injury. Stage I includes a triangular fibrocartilage complex (TFCC) detachment. In stage 2 the injury passes between the triquetrum and the lunate from the dorsal side to the palmar side. Garcia-Elias proposed another possible mechanism of injury: During a fall, when the hypothenar eminence hits the ground, the pisiform drives the triquetrum dorsally. The lunate doesn’t move because it is constrained by the radius dorsally and the long radiolunate ligament (LRL) palmarly. The resultant shear stress disrupts the LTIL.

An isolated partial LTIL tear increases the motion between the lunate and triquetrum but is not sufficient to cause a static carpal collapse. Ritt et al. reported no significant changes in carpal kinematics with isolated disruption of the proximal or dorsal subregions of the LTIL, but sectioning the proximal and palmar components of the ligament resulted in flexion of both the lunate and triquetrum, producing a volar intercalated segment instability (VISI) pattern. The triquetrum supinated away from the lunate after sectioning of the entire LTIL. Greater VISI occurred after sectioning the DRC and DIC ligaments. Horii et al. demonstrated similar findings in that it was necessary to section the DRC and DIC ligaments to produce a static VISI deformity after a complete sectioning of the LTIL. Loss of the dorsal ligament restraint allowed the lunate to flex more easily, in part by shifting the point of capitate contact palmar to the lunate axis of rotation. Additional causes of VISI include perilunate and reverse perilunate injury patterns, fractures of the distal radius or carpal bones, degenerative wear from ulnar abutment, prolonged repetitive stress, and inflammatory arthritis or synovitis. Not all LTIL tears are traumatic. In an anatomical study of 100 cadaver wrists, Viegas et al. found a 27.6% incidence in specimens greater than 60 years old and no tears in specimens younger than 45 years old. This underscores the importance of the preoperative clinical examination to identify the pain generator and to differentiate asymptomatic ligament perforations from pathological tears.

Diagnosis

Patients with an LTIL disruption may exhibit signs and symptoms that correspond to the degree of instability. A typical patient with an LTIL injury usually presents with a history of acute trauma or repetitive stress. A history of a fall onto the hypothenar eminence of a dorsiflexed wrist may point to an LTIL injury. Ulnar-sided wrist pain is usually intermittent and is worsened with wrist rotation and ulnar deviation. A painful click may occur with radioulnar deviation and the patient may have a feeling of instability. The physical examination often demonstrates tenderness over the dorsum of the lunotriquetral (LT) joint. There may be pain when lateral pressure is applied to the triquetrum in the ulnar snuffbox, which lies between the flexor carpi ulnaris (FCR) and extensor carpi ulnaris (ECU), just distal to the ulnar styloid. This foveal tenderness is also frequently present with associated TFCC tears. Provocative tests that stress the LT joint may reveal pain or crepitus. The triquetral ballottement test 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 and then applying an anteroposterior stress. Laxity and pain are indicative of an LTIL tear. The shear test is similar and is performed by supporting the dorsum of the lunate with one hand while translating the pisotriquetral joint dorsally, creating a shear force at the LT joint. A diagnostic midcarpal injection of local anesthetic may improve the pain.

Standard radiographs are typically normal but an ulnar-positive variance and ulnar impingement with a lunate cyst may be seen with chronic cases ( Fig. 7.1 ). Disruption of the LTIL results in proximal translation of the triquetrum and/or LT overlap and possibly a disruption of Gilula lines, but an increased gap between the lunate and triquetrum is rarely seen. The mean triquetrolunate angle is +14 degrees, but Reagan et al. found this angle to average −16 degrees with LT dissociation. Provocative radiographic views, including radial deviation or ulnar deviation, and clenched-fist anteroposterior views, are often helpful. A VISI deformity indicates longstanding instability ( Fig. 7.2 A–C). An arthrogram or MR arthrogram may reveal an LTIL perforation but it may also occur in a patient with an asymptomatic ulnar-positive wrist. Arthroscopy is necessary to assess the degree of dynamic instability. Viegas et al. proposed a staging system for traumatic tears: Stage I: a partial or complete tear but no VISI. Stage II: a complete tear and a dynamic VISI. Stage III: a complete LTIL tear with disruption of the DRC and DIC ligaments, resulting in a static VISI. The Geissler classification has largely supplanted this staging scheme because it quantifies the degree of instability and not the size of the tear.

Treatment

Acute or chronic injuries without dissociation or a VISI instability pattern can be initially treated with immobilization and NSAIDs for up to 6 weeks. A midcarpal cortisone injection may decrease any synovitis. The presence of associated injuries to the ulnar side of the wrist joint, especially those of degenerative cartilage, alters the treatment. Treatment options include direct ligament repair, ligament reconstruction with autogenous tendon graft, ^, LT joint arthrodesis, midcarpal arthrodesis ( Fig. 7.3 A–D), and an ulnar shortening osteotomy (USO). A capsulodesis using the extensor retinaculum or the DRCL have also been described in a small number of patients.