Employees were rigging down a power swivel at a well site. They placed the power swivel in a trailer and were preparing to remove the Kelly valve and cross-over subs. The operator came down from the drillers console, set the power swivel's control panel down in front of the draw works, and then went to get a kink out of a hydraulic hose. The hose caused the control panel to flip over, engaging the power swivel. The injured employee placed a 48" pipe wrench onto a sub. When the power swivel engaged, the wrench swung and struck the injured employee's left knee. The employee's knee was dislocated and they sustained soft tissue damage to the ACL and MCL.