Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA
The thumb is crucial to the overall function of the hand, with amputation leading to about 40% impairment. Because of value of thumb, reimplantation at any level is recommended. It also accounts to around 22% disability of the individual as a whole
The thumbs actions are flexion, extension, abduction(palmar and radial), adduction and opposition.
Abduction is defined as motion away from second metacarpal and adduction is motion towards second metacarpal. It occurs at the carpometocarpal joint. It can occur in two planes, parallel to the palm of the hand and perpendicular to the palm of the hand.
Flexion extension occurs at MCP, IP and CMC.
Opposition have several actions –
Palmar abduction that transitions to adduction at CMC joint.
Rotation at CMC joint.
Flexion at CMC, MCP AND IP joint.
Complete opposition is measured as tip of the thumb touching either the base of the 5th digit or tip of the little finger. These two actions can be used to find deficiencies in opposition. Another way is by measuring from flexor crease of IP joint to the distal palmar crease over the 3rd metacarpal. It can also be tested by making the thumb touch different parts of the palm.
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