( 14) has classified wrist instability into acute (6 weeks, little primary healing potential). Dynamic instability requires certain maneuvers to occur with stress, and motion fluoroscopy is often required for diagnosis. Static instability is present at rest and can be diagnosed on routine AP and lateral radiographs. There are two main carpal instability patterns: static and dynamic. C: Dorsal ligaments: (16) radiotriquetral (17) triquetrum-scaphoid-trapezium-trapezoid, also known as the dorsal intercarpal ligament (18) dorsal scapholunate (19) dorsal lunotriquetral and (20) dorsal transverse interosseous ligaments of the distal row.Ĭarpal instability is defined as the inability to bear physiologic loads without losing the normal carpal alignment ( 13). B: Palmar deep ligaments: (8) short radiolunate (9) ulnolunate (10) ulnotriquetral (11) palmar scapholunate, (12) palmar lunotriquetral, (13) triquetral-hamate-capitate, also known as the ulnar limb of the arcuate ligament (14) dorsolateral scaphotrapezial and (15) palmar transverse interosseous ligaments of the distal row. A: Palmar superficial ligaments: (1) radioscaphoid, (2) radiocapitate, (3) long radiolunate, (4) lunocapitate, (5) scaphocapitate, (6) pisohamate, and (7) flexor retinaculum or transverse carpal ligament. These drawings do not aim to replicate the exact shape and dimensions of the actual ligaments, nor their frequent anatomic variations. Schematic representation of the most consistently present wrist ligaments. With those preliminaries out of the way, in the next video we move on to representing the orientation of a rigid body.Fig 24-1. If you align the thumb of your right hand with the axis of rotation, positive rotation is the direction that your fingers curl. Positive rotation about an axis is defined by the right-hand rule. Even if the body is moving, when we talk about the body frame, we mean the stationary frame coincident with the frame attached to the body at a particular instant in time. In this book, all frames are considered to be stationary. The configuration of the body is given by the position of the origin of the body frame and the directions of the coordinate axes of the body frame, expressed in the space-frame coordinates. If I want to represent the position and orientation of a body in space, I fix a frame to the body and fix a frame in space. You can create a right-handed frame using your right hand: your index finger is the x-axis, your middle finger is the y-axis, and your thumb is the z-axis. All frames are right-handed, which means that the cross product of the x and y axes creates the z-axis. A frame consists of an origin and orthogonal x, y, and z coordinate axes. Rigid-body configurations are represented using frames. This approach may be new to you if you haven't taken a course in three-dimensional kinematics before. In other words, our representation of a configuration will not use a minimum set of coordinates, and velocities will not be the time derivative of coordinates. As discussed in the last chapter, we'll use implicit representations of configurations, considering the C-space as a surface embedded in a higher-dimensional space. In Chapter 3, we learn representations of configurations, velocities, and forces that we'll use throughout the rest of the book.
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