Normal wrist motion consists of following movements
- Flexion – When the hand and wrist is moved toward palmar surface of forearm
- Extension – When the hand and wrist is moved toward dorsal surface of forearm
- Radial deviation – Hand is deviated towards radial side
- Ulnar Deviation – Hand is deviated towards radial side
- Axial rotation around the distal radioulnar joint
Normal wrist motion has a range of flexion and extension as 65-70 degrees. Radial deviation wrist motion is 20 degrees and ulnar deviation is 40 degrees. Out of total deviation, carpal bones contribute about 10 degrees of rotation while rest is contributed by forearm [about 140 degrees]
The wrist motion is as a result of complex arrangements between the two carpal rows. Wrist’s versatility mostly is due to the intercalated three-bone system of the proximal carpal row.
For radioulnar deviation the proximal row undergoes a secondary angulation in the sagittal plane [A plane that divides body into left and right equal halves] in addition to the synchronous motion in the coronal plane.
During radial deviation scaphoid undergoes flextion as the trapezium comes towards the radius. Scapholunate ligament transmits this motion the lunate and triquetrum.
With movement in opposite direction towards neutral and further to ulnar deviation the proximal row extends and supinates.
With ulnar deviation, scaphoid extends. Proximal migration of the hamate forces the triquetrum to displace palmarly and extend and lunate comes along.
By varying the length and contour, the proximal carpal row permits extensive excursion of the wrist and at the same time maintains stability.
Disruption of the mechanism due to a fracture or ligamentous injury results in instability of the wrist due to loss of synchronicity and change in contact pattern of carpal bones.
Instability of the wrist, over time result in arthritis of the wrist.
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