Prediction of Ligament Length and Carpal Diastasis During Wrist Flexion–Extension and After Simulated Scapholunate Instability

Abstract

Purpose To determine the role of the carpal ligaments during wrist flexion/extension and to understand if maintaining integrity of only the dorsal scapholunate ligament is adequate for maintaining stability of the scapholunate joint. Methods This study combined motion analysis and manual digitization of ligament attachment regions to generate predictions of carpal ligament length and implied strain during wrist motion and length changes after simulated ligamentous injury. Results Thirteen ligaments and 22 ligament segments (sub portions) were modeled. Ligament length change with respect to wrist angle was measured. Eleven segments had minimum stretch or elongation from neutral wrist position over the entire wrist range of motion for any ligament cut condition. The remaining eleven segments had more than 10% stretch in some portion of flexion/extension. In general, ligaments had increased stretch during wrist flexion and after cutting the entire scapholunate ligament (SLL) and the dorsal intercarpal ligaments off the scaphoid. Conclusion Disruption of the membranous and palmar portions of the SLL and the dorsal intercarpal ligament off the scaphoid did not result in the development of an increased 3-dimensional scapholunate gap as measured by differences in ligament length calculations between the scaphoid and lunate. This may be indicative of a pre-dynamic instability condition (prior to clinical signs and x-ray findings) that is stabilized by the dorsal SLL preventing the increase in 3-dimensional scapholunate gap. This may also support surgical treatment recommendations, which suggest repair of the dorsal component only of the SLL will be effective. Disruption of the dorsal intercarpal ligament off the scaphoid or lunate did not result in further significant changes. Therefore the dorsal SLL has an important role in preventing scapholunate ligament instability. Clinical Relevance These results provide insight into the abnormal kinematics as various ligaments are compromised.

Scapholunate Interosseous Ligament Anatomy and Biomechanics

“…Nikolopoulos et al 63 reported a volar load to failure value of 86 N, which was roughly equal to that of the dorsal SLIL (83 N) at an elongation rate of 5 mm/min. The linear stiffness for the volar SLIL (32.8 N/mm) was greater than that of the dorsal SLIL (27.7 N/mm), which refutes the sectioning studies of Patterson et al 54 Logan et al 51 reported a volar load to failure of 125 N, which was actually twice that of the dorsal SLIL segment (62 N), but this was conducted at an elongation rate of 100 mm/min. Lee et al 64 used magnetic resonance imaging to measure the in vivo strain on the SLIL subregions when the wrist was axially loaded in extension to simulate a fall on an outstretched hand.…”

Length changes of scapholunate interosseous ligament at different wrist positions: an in vivo 3-dimension image study

“…We defined the three regions of the SLIL according to their known bone insertions and marked the origin and insertion of these ligaments on the surfaces of the bone reconstructions [1,2,13,19,21] (Fig. 1).…”

Perilunate carpal dislocation. Clinical evaluation of patients operated with reduction and percutaneous fixation without capsular-ligament repair

“…Therefore, it is difficult to predict the movement of carpal bones after ligament lesions with imaging studies and clinical tests alone. 2 …”

“…It is believed that carpal instability is more common than previously thought and that degenerative disease is the end result of undiagnosed instability. 2 …”

“…Previous studies have investigated the dynamic and static aspects of scapholunate instability (defined as a radiographic increase in space between the scaphoid and the lunate) and the consequences for the wrist. 2 …”