Purpose: This study continued our previous investigations of the ligaments stabilizing the scaphoid and lunate in which we examined the scapholunate interosseous ligament, the radioscaphocapitate, and the scaphotrapezial ligament. In this current study, we examined the effects of sectioning the dorsal radiocarpal ligament, dorsal intercarpal ligament, scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments. In the current study, the scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments were sectioned in a different order than performed previously.Methods: Three sets of 8 cadaver wrists were tested in a wrist joint motion simulator. In each set of wrists, only 3 of the 5 ligaments were cut in specific sequences. Each wrist was moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the 3 ligaments were sectioned in various sequences and after the wrist was moved through 1,000 cycles of motion.Results: Dividing the dorsal intercarpal or scaphotrapezial ligaments did not alter the motion of the scaphoid or lunate. Dividing the dorsal radiocarpal ligament alone caused a slight statistical increase in lunate radial deviation. Dividing the scapholunate interosseous ligament after first dividing the dorsal intercarpal, dorsal radiocarpal, or scaphotrapezial ligaments caused large increases in scaphoid flexion and lunate extension. Conclusions:Based on these findings, we concluded that the scapholunate interosseous ligament is the primary stabilizer and that the other ligaments are secondary stabilizers of the scapholunate articulation. Dividing the dorsal radiocarpal, dorsal intercarpal, or scaphotrapezial ligaments after cutting the scapholunate interosseous ligament produces further changes in scapholunate instability or results in changes in the kinematics for a larger portion of the wrist motion cycle. KeywordsScapholunate instability; wrist; biomechanics Treatment of soft tissue injuries of the wrist is clinically frustrating. The diagnosis of which specific ligaments are injured is difficult. The most common instability problem occurs at the scapholunate (SL) joint. Many surgical procedures have been advocated, but the long-term outcomes of these procedures are undetermined. One of the primary difficulties in understanding this problem is that the specific function of the carpal ligaments is not known. It is important to define the function and relative importance of these structures to develop better surgical treatments for the injured SL joint. This biomechanical study is one of a series of experiments that evaluates the importance of ligaments that attach to the scaphoid or lunate. 1,2 According to previous anatomical studies 3-9 there are 7 ligaments that crossover or attach to the scaphoid or lunate. These are the scapholunate interosseous ligament (SLIL), the radioscaphocapitate ligament (RSC), the long radiolunate liga...

This study evaluated the effects of sectioning the scapholunate interosseous ligament, radioscaphocapitate ligament, and scaphotrapezial ligament on the kinematics of the scaphoid and lunate. Eight cadaver upper extremities were placed in a wrist joint simulator and moved in continuous cycles of flexion-extension and radial-ulnar deviation. Positional data of the scaphoid and lunate were obtained in the intact state, after the scapholunate ligament was cut; after the scapholunate and scaphotrapezial ligaments were cut; after the scapholunate, scaphotrapezial, and radioscaphocapitate ligaments were cut; and after all 3 ligaments were cut and the specimen was placed through an additional 1,000 cycles of flexion-extension. Cutting the scapholunate ligament caused changes in scaphoid and lunate motion during flexion-extension, but not radial-ulnar deviation. Additional sectioning of the scaphotrapezial ligament followed by the radioscaphocapitate ligament caused further kinematic changes in these carpal bones. One thousand cycles of motion after all 3 ligaments were sectioned caused additional kinematic changes in the scaphoid and lunate. The scapholunate ligament appears to be the primary stabilizer between the scaphoid and lunate. The radioscaphocapitate and scaphotrapezial ligaments are secondary restraints. Repetitive cyclic motion after ligament sectioning appears to have additional deleterious effects on carpal kinematics.

Based on these findings it was concluded that the SLIL is the primary stabilizer and the RSC and ST are secondary stabilizers of the scapholunate articulation. Repetitive motion after ligament injury probably results in further carpal instability.

No abstract

This study suggests that the bony anatomy of the radius and scaphoid have a role in stabilizing the carpus after ligament injury. The effect of ligament sectioning on producing carpal instability may be moderated by the bone geometry of the radiocarpal joint. This may explain why some people may have a tear of the scapholunate interosseous ligament but not present with clinical symptoms.

No abstract

No abstract

Purpose: To determine the in vitro motion of the scaphoid and lunate during wrist circumduction and wrist dart-throw motions and to see how these motions change after the ligamentous stabilizers of the scaphoid and lunate are sectioned in a manner simulating scapholunate instability.Methods: Twenty-one fresh-frozen cadaver forearms were moved through a dart-throw motion and a circumduction motion using a wrist joint simulator. Scaphoid and lunate motion were measured with the wrist ligaments intact and after sectioning of the scapholunate interosseous ligament, the scaphotrapezium ligament, and the radioscaphocapitate ligament. Results:In the intact wrist the scaphoid and lunate moved more during circumduction than during the dart-throw motion. With ligamentous sectioning the scaphoid flexed more and the lunate extended more during both the circumduction and dart-throw motions. During the circumduction motion both before and after sectioning the global motion of the scaphoid was greater than that of the lunate. After sectioning the scaphoid motion increased and the lunate motion decreased. Conclusions:The scaphoid and lunate motions were observed to change remarkably after ligamentous sectioning. The observed changes in carpal motion correlate with the clinical observation that after ligamentous injury arthritic changes occur in the radioscaphoid joint and not in the radiolunate joint. Analysis of the injured wrist in positions that combine flexion-extension and radialulnar deviation may allow noninvasive diagnosis of specific wrist ligament injuries. KeywordsCarpal motion; wrist circumduction motion; wrist dart-throw motion; kinematics; scapholunate interosseous ligament; scaphoid; lunate Many activities involving the wrist are motions that require a combination of wrist flexionextension and radial-ulnar deviation. These motions frequently include a dart-throw type of motion. 1 Although the in vivo and in vitro motions of the wrist carpal bones during planar wrist flexion-extension and planar wrist radial-ulnar deviation have been studied, 2 − 13 a dart-throw motion only now is being studied in an organized biomechanical fashion. 14 − 16 For this study we chose to study a dart-throw motion with a limited (20° total) radial-ulnar deviation motion, which may not be indicative of the motion used in throwing a ball or other activities with extreme ranges of motion. In some activities such as stirring a bowl, wrist circumduction is the primary motion. The purpose of this study was to determine the in vitro motion of the scaphoid and lunate during these functional arcs of wrist motion. A second purpose was to see how these motions change after the ligamentous stabilizers of the scaphoid and lunate are sectioned in a manner simulating scapholunate instability. MethodsA wrist-joint motion simulator 17 was used to move 21 fresh-frozen cadaver wrists through cyclic dart-throw and cyclic circumduction motions. The average age of the specimens was 67 years (range, 31−87 y) and there were 11 male and 10 female speci...