Volar Lunate Facet Fractures of the Distal Radius: Fracture Mapping Using 3D CT Scans.

 Fractures of the distal radius involving the lunate facet at the volar articular surface are unstable injuries and are usually managed operatively. Management of these fractures is challenging as our understanding of the exact fracture characteristics and associated injuries to the carpus is poor.  This study aims to define the anatomy and associated injuries of lunate facet fractures using three-dimensional computed tomography (CT) scans and fracture mapping techniques.  A consecutive series of CT wrists was analyzed to identify intra-articular fractures involving the lunate facet at the volar distal radius. Fractures were mapped onto standardized templates of the distal radius using previously described fracture mapping techniques. We also identified instabilities of the carpus including volar carpal translation, ulnar translocation, scapholunate diastasis, and distal radioulnar joint (DRUJ) instability.  We present 23 lunate facet fractures of the distal radius. The lunate facet fragment displaces in a volar and proximal direction and the lunate always articulates with the displaced fragment. The smaller fragments displace a greater amount, in a volar direction, with pronation. The fracture tends to occur between the origin of the short and long radiolunate ligaments.  Lunate facet fractures are frequently comprised of osteoligamentous units of the distal radius involving the short and long radiolunate ligaments and the radioscaphocapitate ligament. Assessment and management of volar carpal subluxation, scapholunate instability, ulnar translocation, and DRUJ instability should be considered.  Our mapping of these fractures contributes to our understanding of the anatomy and associated instabilities and will aid in surgical planning and decision making.