The Collaborative International Dictionary of English v.0.48:

Wrench \Wrench\, v. t. [imp. & p. p. Wrenched; p. pr. & vb. n.
   Wrenching.] [OE. wrenchen, AS. wrencan to deceive,
   properly, to twist, from wrenc guile, deceit, a twisting.
   ????. See Wrench, n.]
   [1913 Webster]
   1. To pull with a twist; to wrest, twist, or force by
      violence.
      [1913 Webster]

            Wrench his sword from him.            --Shak.
      [1913 Webster]

            Forthwith this frame of mine was wrenched
            With a woeful agony.                  --Coleridge.
      [1913 Webster]

   2. To strain; to sprain; hence, to distort; to pervert.
      [1913 Webster]

            You wrenched your foot against a stone. --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wrenching
    adj 1: causing great physical or mental suffering; "a wrenching
           pain" [syn: racking, wrenching]