[Ulnar instability of the carpus]

Ulnar instabilities of the carpus are rare findings depending on a dissociation of the lunotriquetral (LT-) junction. They are frequently not recognized or confused with ulnocarpal complaints of other origin due to missing typical clinical or radiological indications. The central structures are the os triquetrum and its connections to the os lunatum, the distal carpal row, radius and ulna. The most important causes are injuries, but degeneration, ulnar impaction syndrome or the ulna plus variant can also be involved. The symptoms are ulnar-sided pain, sensations of instability and weakness as well as "clunking" sensations in the ulnar wrist. Clinical examination may reveal tenderness in the LT-interval, between the ECU- and FCU-tendons, and displacement of the triquetrum on palpation. The LT-interval is rarely extended in conventional X-rays. A VISI position of the os lunatum is found in instabilities of higher degree. A distinct diagnosis is only achieved by arthroscopy. Conservative treatment consists of 4-8 weeks of arm immobilization. Diagnostic arthroscopy can be combined with débridement and/or closed reduction of the LT-interval with consecutive percutaneous k-wire fixation. If a repair of the LT-ligament is not possible, reconstructive methods are indicated. They include extrinsic tenodesis with part of the extensor carpi ulnaris tendon, ligamentoplasty or osteoligamentous autografts. The role of lunotriquetral arthrodesis is considered to be controversial, due to a high rate of non-fusions. Simple correction of the LT-dissociation does not resolve the static instability of the proximal row (VISI-position of the lunatum). In these cases, salvage procedures such as limited arthrodesis of the wrist, proximal row carpectomy or complete arthrodesis are indicated.