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mds21636.mpg13602K Segment 1.Case, slow playing, right hand. The index does not properly extend to pluck the strings. Strong agonistic-antagonistic cocontractions in the thumb with hyperflexion of the IP joint in static posture. When the thumb plucks a string, the cocontractions become significantly less or disappear. When the index plucks strings while keeping contact with the thumb, the fingertips of thumb and index remain forcefully pressed to together. When the thumb strikes a string, contact with the index is easily released and the thumb can well strike the string. In the occasion that the thumb does keep contact with the index during thumb stroke, the contact forces are visibly low. Segment 2.Case, fast playing, right hand. Neither index nor thumb has significant dystonic symptoms. Playing is very fast and finger strokes are regular. However, thumb movements are jerky. Thumb strokes originate mainly at the CMC1, with the thumb moving as a stick, with a large trajectory component perpendicular to the plane of the strings. Hesitations in playing are caused by thumb, not index. Segment 3.When the right hand thumb is flexed with active Flexor Pollicis Longus, i.e., with an actively flexing IP joint, the MCP joint can be normally flexed. Segment 4.Test of function of Flexor Pollicis Brevis (FPB): MCP1 flexion with relaxed IP joint. Part 1 (left hand): Normal MCP1 flexion, indicating normal FPB function. Part 2 (right hand): Impossibility to flex the MCP1 joint without cocontracting Flexor and Extensor Pollicis Longus.

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