Devices and methods for performing percutaneous surgery under direct visualization through a single cannula are shown. A device includes an elongated cannula sized for percutaneous introduction that defines a working channel between its ends. The working channel is sized to receive one or more surgical tools therethrough. A clamp assembly is engaged to the outer surface of the cannula. The clamp assembly includes a viewing element receiving portion and a viewing element includes a clamp assembly engaging portion for removably engaging the viewing element to the clamp assembly. In one embodiment, the receiving portion defines a receptacle for receiving a dovetail included on the engaging portion of the viewing element. The receiving portion may also include a pivotable clip for removably engaging a protuberance of the engaging portion. The clamp includes a mechanism that allows translation, rotation, and removal of the clamp assembly and the viewing element with respect to the cannula. The cannula may also be engaged to a flexible arm that is securely mounted in order to stabilize the position of the cannula at the surgical site.