Isolated injury of the dorsal scapholunate ligament caused by intracarpal pronation

Abstract

The mechanism of scapholunate injuries was originally described by Mayfield et al. (1980) as a combination of wrist extension, ulnar deviation and intracarpal supination. This injury pattern causes dorsal migration of the proximal pole of the scaphoid. As loading continues, the scapholunate joint is separated and the palmar portion of the scapholunate ligament is injured. The injury then progresses in a dorsal direction due to supination, with subsequent tearing of the dorsal part of the scapholunate ligament. This is considered as the first stage in perilunate instability. The European Wrist Arthroscopy Society adopted a Stage IIIB, an isolated dorsal widening due to a partial dorsal scapholunate injury created in a cadaveric setup and evaluated arthroscopically (Messina et al., 2013). In our practice, we have encountered a number of cases where only the dorsal part of the scapholunate ligament was injured, which seems incompatible with the generally accepted mechanism of injury described by Mayfield et al. (1980). Our hypothesis is that these injuries are caused by an isolated hyperpronation of the carpus in relation to the distal radius. We reviewed the medical records and imaging of 102 consecutive scapholunate repairs and reconstructions that were performed between January 2010 and September 2020. We specifically looked at the mechanism of injury. In 22 cases the mechanism of injury was unknown. Nineteen patients (24%) described a rotational injury of the wrist. Sixty-two per cent reported a classical fall on the outstretched hand or hyperextension, 10% a hyperflexion with impact and 4% a traction injury. A typical cause of a rotational injury was the sudden blockage of a drill machine, which causes pronation of the carpus with the hand fixed and the forearm usually in a neutral position. Medical imaging showed a partial injury of the dorsal scapholunate interosseous ligament in 15 out of the 19 rotational cases (Figure 1). This specific injury type was confirmed during surgical reconstruction (Figure 2). We made a biomechanical study to verify this concept. Two cadaveric specimens were subjected to an intracarpal pronation force with the forearm fixed in a neutral position. In this setting, we were able to reproduce an isolated dorsal scapholunate rupture without injury of the palmar portion of the scapholunate ligament (Online supplementary Video OS1). This supports the hypothesis of hyperpronation as a cause of scapholunate injuries and is in line with the findings of Esplugas et al. (2016), who investigated the effect of muscular stabilization in scapholunate injuries. Their research suggests that activation of Journal of Hand Surgery (European Volume) 2021, Vol. 46(8) 891–900 journals.sagepub.com/home/jhs