Objective To demonstrate the anatomical and biomechanical basis of scaphoid ring sign in advanced Kienbock’s disease. Methods The study consisted of two sections. The ligaments stabilizing the proximal pole of the scaphoid were observed in 5 specimens. Under 12 kg dead weight load through the tendons of the flexion carpal radial, the flexion carpal ulnar, the extension carpal radial, and the extension carpal ulnar for 5 minutes, the stresses of the scaphoid fossa and lunate fossa were measured in the case of neutral, flexion, extension, radial deviation and ulnar deviation of the wrist joint under normal and rupture conditions respectively by FUJI prescale film and FPD-305E,306E.Results Based on anatomical study, the ligaments stabilizing the proximal pole of the scaphoid consisted of the radioscaphocapitate ligament, long radiolunate ligament and scapholunate interosseous ligament; and the latter two ligaments restricted dorsal subluxation of the proximalpole of the scaphoid. When compared rupture condition with normal condition, thescaphoid fassa stress of radial subregion was not significantly different (0.90±0.43 vs 0.85±0.15), and the ones of palmar, ulnar and dorsal subregions decreased (0.59±0.20, 0.52±0.05 and 0.58±0.23 vs 0.77±0.13, 0.75±0.08 and0.68±0.09) in the case of extension; the scaphoid fassa stresses of all subregions increased or had no difference in the case of neural, flexion, radial deviation and ulnar deviation. The lunate fossa stresses of all subregions increased in thecase of neural, and the ones of all subregions decreased or had no difference inthe case of flexion, extension, radial deviation and ulnar deviation.Conclusion Rotary scaphoid subluxation should be treated operatively at Ⅲ B stage of Kienbock’s disease to avoid traumatic arthritis of theradioscaphoid joint.
Objective To assess the possibility of placing the posterior pedicle screw on atlas. Methods Twenty human cadaver specimens were used to insert pedicle screws in atlas, through the posterior arch or the pedicle of C1 into the lateral mass. The screw entry point was on the posterior surface of C1 posterior arch and at the intersection of the vertical line through the center of C2 inferior articular process and the horizontal line at least 3 mm below the superior rim of the C1 lamina. The screw of 3.5 mm in diameter was placed in a direction of 10° medial angle and 5° upwardangle. After placement of C1 pedicle screw, the distance from C1 screw entry point to the mediallateral midpoint of C1 pedicle, the maximum length of screw trajectory and the actual screw trajectory angles were measured. The direction of screw penetrating through the cortical of C1 pedicle or lateral mass and the injuries to the vertebral artery and spinal cord were observed.Results Forty pedicle screws were placed on atlas, the mean distance from C1 screw entry point to the medial-lateral midpoint of C1 pedicle was (2.20±0.42)mm, the maximum length of screw trajectory averaged (30.51±1.59)mm, and the actual screw trajectory angle measured (9.7±0.67)° in a medial direction and (4.6±0.59) ° in a upward direction. Only 1 screw penetrated the upper cortical bone of the atlas pedicle because the upward angle was too large, and 8 screws were inserted so deep that the inferior cortical bone of the C1 lateral mass was penetrated. But no injuries to the vertebral artery and spinal cord wereobserved. Conclusion C1 posterior pedicle screw fixation is quite accessible and safe, but the su