The Collaborative International Dictionary of English v.0.48:

Sprain \Sprain\ (spr[=a]n), v. t. [imp. & p. p. Sprained
   (spr[=a]nd); p. pr. & vb. n. Spraining.] [OF. espreindreto
   press, to force out, F. ['e]preindre, fr. L. exprimere. See
   Express, v. t., and cf. Spraints.]
   To weaken, as a joint, ligament, or muscle, by sudden and
   excessive exertion, as by wrenching; to overstrain, or
   stretch injuriously, but without luxation; as, to sprain
   one's ankle.
   [1913 Webster]