noun
double-jointed
Describes a person whose joints are unusually flexible, allowing them to bend further than normal. Often used in medical or everyday contexts.
彼女は二重関節で、指が普通よりずっと反る。
She is double-jointed, and her fingers bend back much further than normal.
二重関節の人は、関節が外れやすいことがある。
People who are double-jointed may be prone to dislocating their joints.
柔軟 means general flexibility, while 二重関節 specifically refers to hypermobile joints.
Compound of 二重 (double) and 関節 (joint). The term is a direct calque of the English 'double-jointed'.