What is an habitual sudden twitching of the hinder leg of a horse, or an involuntary or convulsive contraction of the muscles that raise the hock. [Written also springhalt.] called?

stringhalt — An habitual sudden twitching of the hinder leg of a horse, or an involuntary or convulsive contraction of the muscles that raise the hock. [Written also springhalt.]. (Webster's 1913.)