In vivo non-contact regions of proximal scaphoid in six extreme wrist positions

Abstract

Introduction: Fractures of the scaphoid are the most common carpal injuries, account for 80-90% of all carpal fractures. 5-15% nonunion of scaphoid fractures were reported even with adequate primary treatment, which probably progresses to osteoarthritic changes several decades later. Researches regarding to scaphoid physiological characteristic in vitro and in vivo and kinds of trials in clinical practice are being kept on going, which contribute much to our clinical practice. With the advancing wrist arthroscopy, 3D-print patient-specific drill guide, and intraoperative fluoroscopic guidance, dorsal approach (mini-invasive and percutaneous technique) is being popular, through which we can implant the screw in good coincidence with biomechanics and with less disturbing tenuous blood supply of the scaphoid. Investigating the noncontact area of the dorsal proximal scaphoid in different wrist positions can facilitate preoperatively estimating insert point of the screw.

Materials and methods: Eight volunteers were recruited to accept CT scans in six extreme wrist positions. The images of DICOM mode were imput into the Mimics analytical system, the segmented scaphoid, lunate and radius were exported in mode of ASCII STL and were opened in the software of Geomagic studio. We created four planes based on anatomic markers on the surface of the radius and scaphoid to confine the proximal scaphoid to form the so-called non-contact regions. We measured and compared the areas in six targeted positions.

Results: Amidst six extreme wrist positions, area of the non-contact region in extreme dorsal extension (59.81 ± 26.46 mm²) was significantly the smallest, and it in extreme palmar flexion significantly was largest (170.51 ± 30.44 mm²). The non-contact regions increased in order of dorsal extension, supination, ulnar deviation, radial deviation, pronation and palmar flexion. As for two-group comparison, the non-contact region showed significantly larger (p < 0.05) in palmar flexion than the others except for in pronation individually, and in radial deviation (p < 0.05) than in dorsal extension.

Conclusions: Sufficient space was available for the screw started from the dorsal approach despite the wrist positions.

Keywords: In vivo; Non-contact regions; Scaphoid; Wrist position.

Fig. 1

Four planes (e) were created to confine proximal part of the scaphoid into the non-contact region (f). Plane one (a) was perpendicular to the articular aspect of the distal radius and included two points, the tip of radial styloid and the dorsal tip of the radial sigmoid notch. Plane two (b) was based three points, the tip of radial styloid and the dorsal tip and the volar tip of the radial sigmoid notch. Plane three (c) was decided with three points along the proximal ridge of the scaphoid. Plane four (d) was paralleled with the scapholunate interosseous conjuncture through the inflection points of the scaphoid (from the proximal part to the scapholunate interosseous conjuncture)

Fig. 2

In the CT images, longitudinal axes of the third metacarpus and of the distal radius in the coronal plane and in the sagittal plane forming the angles of the radio-ulnar deviation (a) and the flexion-extension (b), respectively, and lines connecting two tips of the radial sigmoid notch and of the ulnar ECU (extensor carpi ulnaris tendon) notch in the horizontal plane forming the angles of rotation (c)