Ask the Experts: helping double-jointed students

The dilemma I have a new student, quite advanced, who has a double-jointed left thumb, and plays with it in a locked ‘L’ position (pictured). I am afraid that this may affect shifting, intonation and vibrato, and I feel she should relearn her left-hand position with a relaxed curved thumb. Would you agree? If so, what would be the best way to encourage her to practise in a different way? One curious thing is that in moving to third position, she will actually go to fourth position, and play with the hand leaning back to get the third-position notes.

MIMI ZWEIG The double-jointed thumb is always a difficult nut to crack. On the positive side, double-jointed students have the advantage of flexible knuckles that facilitate a warm vibrato. If the thumb can remain loose and slide gently along the fingerboard during shifts...