Lunotriquetral Ligament Injuries, Midcarpal Instability, and Volar Intercalated Segment Instability



Lunotriquetral Ligament Injuries, Midcarpal Instability, and Volar Intercalated Segment Instability


William F. Pientka II

Jonathan D. Boyle

Timothy R. Niacaris

David M. Lichtman



LUNOTRIQUETRAL LIGAMENT INJURIES



  • Functional anatomy



    • Intrinsic wrist ligaments are thickenings of the wrist capsule, which show organized, stress-oriented alignment of collagen fibers.1


    • Lunotriquetral (LT) ligament is composed of three distinct portions: dorsal, membranous, and volar components.



      • Volar aspect of LT ligament is the thickest and biomechanically strongest component.2,3,4


      • Dorsal LT ligament functions as main restraint to rotational deformity.3,5


      • Membranous portion is fibrocartilage and functions mainly to permit smooth gliding at the radiocarpal and midcarpal joint surfaces by creating a continuous smooth articulation between the lunate and the triquetrum.


    • Dorsal radiotriquetral (DRT) ligament reinforces LT stability via dorsal anatomic connections to LT ligament.


  • Kinematics



    • The lunate and triquetrum are integral parts of the proximal row (PR). Physiologic PR motion is controlled by intercarpal joint reaction forces.


    • With radial deviation, the scaphoid is forced into flexion and the lunate and triquetrum passively follow due to strong scapholunate (SL) and LT ligamentous attachments.



      • This leads to a physiologic VISI (volar intercalated segmental instability; volar-facing lunate).


    • With ulnar deviation, the triquetrum is forced into extension due to its unique helicoid articulation with the hamate.



      • The lunate passively follows leading to a physiologic DISI (dorsal intercalated segment instability; dorsal-facing lunate).



  • Pathology and pathomechanics



    • Pathology involves a tear in the membranous, volar, or dorsal components (can be all three).


    • LT instability requires a tear of the membranous portion PLUS a tear in either the dorsal or palmar components.1


    • In LT instability, the lunate is abnormally flexed (VISI deformity) as a result of the unresisted flexion moment generated by the scaphoid.6,7,8



      • Lichtman’s “ring concept of carpal kinematics” hypothesizes that physiologic wrist “loading” creates a flexion moment at the scaphotrapeziotrapezoid (STT) joint and an extension moment at the triquetrohamate (TH) joint, keeping an intact wrist balanced and motionless.9



        • With disruption of the LT ligament, compression through the STT joint leads to scaphoid and lunate flexion while the head of the capitate forces the triquetrum ulnarly and into an extended position.


        • This uncoupling of torque forces at the LT joint leads to a static VISI deformity (Figure 21.1).7


    • Complete LT ligament tear may not be sufficient in isolation to cause a VISI deformity, but may show divergence of the LT joint with extreme wrist flexion and radial deviation.10


  • Etiology



    • Result of a backward fall onto an outstretched hand with the wrist extended and ulnarly deviated



      • Force directed through the hypothenar region drives the pisiform into the triquetrum, forcing it dorsally.


      • LT ligament is injured as the lunate remains in place due to constraint by the long radiolunate ligament and the radiocarpal joint.6


      • The force on the ulnar wrist leads to intercarpal pronation, which overloads the LT ligament without disrupting the SL ligament.10,11,12



    • Occasionally occurs as a “forme fruste” of perilunate injury or dislocation.8



      • Stage III of progressive perilunate instability is LT ligamentous disruption (Figure 21.2).13


      • Chronic LT instability can occur after repair of the SL dissociation with failure to recognize LT injury in perilunate dislocations.


    • Another proposed mechanism of injury is a fall onto a pronated, radial deviated, and flexed wrist.14


    • Ulnar positive variance is often associated with acute and attritional (chronic) LT ligament pathology due to increased stress on the triquetrum (and triangular fibrocartilage complex [TFCC] complex) in ulnar deviation.15,16


    • Isolated LT injuries may also occur with a dorsally applied force with the wrist flexed.7



      • This injury pattern causes the interosseous portion of the LT ligament to fail, leaving the volar radiolunotriquetral ligament intact.7



  • Classification (Table 21-1)



    • The Geissler classification of SL ligament injuries may also be applied to LT ligament injuries.17


  • Clinical presentation



    • Ulnar wrist pain, weakness, wrist click, loss of range of motion, instability, ulnar sensory deficits, dinner fork deformity


    • Point tenderness at the LT interval


    • Painful click with ulnar deviation and pronation


    • Not specific, as this may also be present in midcarpal instability (MCI)


  • LT ballottement test11



    • Lunate is grasped between the thumb and index finger of one hand, and the triquetrum is grasped with the other hand and an attempt is made to translate the triquetrum on the stabilized lunate.


    • Test is positive when translation recreates the patient’s symptoms.


  • Shear test18,19



    • With the elbow flexed and the forearm in neutral, the examiner’s thumb is used to apply a dorsal force to the triquetrum while their other thumb applies a volar force to the lunate.


    • Laxity of the LT joint compared to the contralateral side, or a recreation of the patient’s symptoms is considered positive.


  • Radiographic presentation

May 7, 2019 | Posted by in ORTHOPEDIC | Comments Off on Lunotriquetral Ligament Injuries, Midcarpal Instability, and Volar Intercalated Segment Instability
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