Screw Displacement Axis Research Articles

An in-vivo study of normal wrist kinematics.

The motion of the hand relative to a reference frame embedded in the radius is described using the screw displacement axis (SDA) concept. A three-dimensional sonic digitizer was utilized in a study of the dominant wrist of 15 normal subjects to determine the location and orientation of the SDAs based on the endpoints of flexion-extension motion (FEM) and radial-ulnar deviation (RUD) of the hand. The length of the common perpendicular between the SDAs of FEM and RUD was as large as 6 mm in some individuals; however, in some subjects the FEM SDA was distal of the RUD SDA while in others it was proximal. Considering the group of 15 subjects, the SDAs of FEM and RUD for the normal group nearly intersect in the head of the capitate in the neutrally positioned wrist and forearm.

The Three-dimensional Rotational Behaviors of the Carpal Bones

The rotational behaviors of the carpal bones of ten fresh cadaver forearms were determined using a three-dimensional sonic digitizer, as the hands were passively moved through planar constrained motions. Changing forearm orientation from supination to pronation results in an increase in the magnitudes of extension of the proximal and distal carpal row bones and a reduction in the magnitudes of flexion of the distal carpal row bones. The included angles between each carpal bone screw displacement axis (SDA) and third metacarpal SDA for corresponding intervals of motion are significantly greater than zero, regardless of forearm orientation. The included angles of the proximal carpal row bones are significantly greater than those of the distal carpal row bones during third metacarpal radial-ulnar deviation. The carpal bone rotation magnitudes are significantly attenuated relative to the prescribed rotation magnitudes of the third metacarpal, with the exception of the trapezoid during third metacarpal extension. The rotational attenuation is greatest in the proximal carpal row bones and is most pronounced during third metacarpal flexion-extension motion and ulnar deviation. Evidence from this investigation favors a carpal row concept of wrist motion, as opposed to a carpal column model.

The scapholunate ligament

The effects of scapholunate ligament sectioning on scaphoid and lunate bone three-dimensional kinematics were analyzed using a sonic digitizer method. Carpal bone motions were described using a screw displacement axis concept. After scapholunate ligament sectioning, few significant kinematic changes were observed in the orientation of the screw displacement axes or in carpal bone rotation about the screw displacement axes. The angles between the screw displacement axes of the scaphoid and lunate bones were only minimally affected, indicating that the two bones continued to track well relative to each other. The results indicate that sectioning of the scapholunate ligament does not result in a major disturbance of scaphoid and lunate bone motions.

An investigation of carpal bone motion using a three-dimensional sonic digitizer

Normal carpal kinematics were studied in 22 cadaver specimens using a biplanar radiography method. The kinematics of the trapezium, capitate, hamate, scaphoid, lunate, and triquetrum were determined during wrist motion in sagittal and coronal planes. The results were expressed using the concept of the screw displacement axis and converted to describe the magnitude of rotation about and translation along three axes (X-axis: pronation-supination axis, Y-axis; flexion-extension axis, and Z-axis: radial-ulnar deviation axis) commonly used for the wrist. The orientation of these axes is expressed relative to the radius.Within the proximal carpal row, considerable differences of carpal behavior around the Y-axis were observed during sagittal plane motion of the wrist. The scaphoid exhibited the greatest magnitude of rotation, and the lunate the least. The magnitude of rotation of the carpal bones around the X-axis during sagittal plane motion of the wrist was small. The proximal carpal bones exhibited some ulnar deviation in 60° of wrist flexion. During coronal plane motion of the wrist, the magnitude of radial-ulnar deviation of the distal carpal bones was mutually similar and generally of a greater magnitude than that of the proximal carpal bones. The proximal carpal bones experienced some flexion during radial deviation of the wrist and extension during ulnar deviation of the wrist. Translation was generally minimal in all carpal bones throughout wrist motion.This study reports results from the largest cadaver wrist kinematics study completed to date. The accuracy of the current method was improved when compared to previous studies. A sufficient number of specimens to allow statistical comparison was used and minimal interspecimen variability was noted. This study enabled a precise description of quantitative analyses of normal carpal kinematics relative to the radius.