EMPLOYEE WAS USING A 24"" CRESCENT WRENCH TO LOOSEN A RUSTED TURNBUCKLE THAT WAS SECURED IN A BENCH VISE. AS HE PULLED BACK ON THE WRENCH HANDLE WITH BOTH ARMS, THE WRENCH CAME OFF THE TURNBUCKLE CAUSING THE EMPLOYEE TO LOSE HIS BALANCE AND TURN HIS LEFT ANKLE. THE LEG FRACTURED AT THE BASE OF THE LEFT FIBULA.