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
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.
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.
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.
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
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
Occasionally occurs as a “forme fruste” of perilunate injury or dislocation.8
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
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.
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.
Standard posteroanterior and lateral are the first-line images to be obtained.
May be normal or may show disruption of Gilula’s lines20 with LT overlap or proximal triquetral migration (Figure 21.3)21,22
Static LT injuries may not be evident on standard wrist radiographs; however, radial/ulnar deviation view may reveal an LT disruption.
VISI deformity on standard lateral wrist radiographs indicates static instability and is considered a possible sign of “LT dissociation.”21
Normal radiographic LT angle is 14° dorsal tilt, but in LT dissociation this angle has been shown to be a negative (volar) angle.10
SL angle less than 30° along with an LT angle greater than 15° indicates LT dissociation.6