Fig. 7

Elliptical configuration of the radioscaphoid joint. a Upper image is a 3D volume rendered image of a normal CT of the wrist which depicts the distal ulna and radius viewed en face, showing the elliptical nature of the radial fossa’s scaphoid articulation site (black outline). Lower image depicts a sagittal CT reformat view of the radioscaphoid joint. Due to the elliptical nature of the radioscaphoid articulation, changes in position of the scaphoid in relation to the carpus due to rotary subluxation of the scaphoid, will result in incongruence with excessive loading and contact at the dorsal and volar aspects of the radioscaphoid joint (white asterisks). b The normal radioscaphoid joint resembles two parallel nested spoons as depicted by the upper image. With flexion and extension (arrows) full articular contact occurs between the surfaces with congruence and even distribution of the load throughout the joint. Lower image depicts what occurs with rotary subluxation of the scaphoid. When the axis of the spoons changes and they are now perpendicular to each other, the contact surfaces are disrupted and the load is shifted to the dorsal and volar aspect of the articulation leading to destruction and degeneration (black asterisks)