Lunotriquetral (LT) instability results from a disruption of the dorsal and palmar LT interosseous complex. A spectrum of pathology is possible, proportional to the magnitude and acuity of ligamentous disruption. Degenerative membrane perforation may be asymptomatic. Partial tears of the LT membrane may produce dynamic instability, and complete ligament dissociation may produce a static VISI pattern.
Lunotriquetral instability most commonly follows a specific injury. Hyperextension at the wrist is a common mechanism. Weakness and a decreased range of motion are usually present. Pain is precipitated with radial-ulnar deviation, and sometimes a "clunk" is audible. The individual may perceive instability or a giving-way sensation. Ulnar paresthesias are occasionally present.
Three provocative maneuvers for LT instability have been described: the compression, ballottement, and shear tests. Compression of the triquetrum in the ulnar snuffbox using a radially directed force may elicit pain, suggesting LT or triquetrohamate pathology. Ballottement of the LT ligament is performed by grasping the pisotriquetral unit
between the thumb and index finger of one hand and the lunate between the thumb and index of the other. An anteroposterior translation motion is performed between these bones. Pain and dorsal palmar laxity greater than that on the opposite side signify a positive test. The shear test is performed with the elbow supported on the hand table and the forearm in neutral rotation. The examiner's contralateral thumb is placed dorsally over the lunate as the ipsilateral thumb loads the pisotriquetral joint from the palmar side (Fig. 64—2). The test is positive when pain, crepitance, or abnormal LT mobility is elicited. Comparison with the contralateral wrist is important for all provocative tests.
A variety of imaging studies can support a diagnosis of LT instability. Standard anteroposterior radiographs may be normal in partial tears. Findings in complete dissociation include disruption of Gilula's arcs, proximal triquetral translation, and LT overlap. Unlike scapholunate dissociation, a widening of the interosseous interval is not visualized. Positive ulnar variance should be noted. When present, it may be the cause of an attritional LT tear and require treatment.
Arthroscopy has both a diagnostic and therapeutic role. Direct inspection and palpation of the LT ligament, TFCC, capsular structures, and articular surfaces allows accurate diagnosis of LT pathology. Midcarpal arthroscopy is important for the assessment of LT stability.
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