As is known in the medical field, the cannula is utilized for creating a passage extending from the exterior into a cavity in the patient to a particular location where the surgical procedure is to be performed.  For example, in current day practices lumbar discectomy whose objective is to decompress the affected nerve root, endoscopic and micro endoscopic techniques are often used.  These techniques are becoming popular inasmuch as the patient benefits from the small incision, limited tissue disruption, better visualization and illumination all of which shortens the hospital stay and hastens recovery.  One of the techniques for performing the lumbar discectomy is the use of tubular retractor (a specific cannula) which allows for laminotomy, deical facetectomy, foraminotomy, nerve root retraction and disectomy.  A typical procedure is to advance a guidewire through a small incision which is advanced to the inferior edge of the superior lamina.  A small incision is then made that extends either cranially or caudally.  A calnulated dilator is then inserted over the guidewire.  Larger diameter cannulated dilators are sequentially inserted over each other to increase the opening into the body cavity.  Typically the guide wire is removed after the first cannulated dilators installed and eventually the cannulated dilators are all removed after the, tubular retractor has been inserted over the largest of the cannulated dilators.  Once these procedures are accomplished, the tubular retractor is locked into position by a retractor clamp that is clamped to a retractor clamping arm which is fixed to a rigid member such as the operating table.  This provides an unencumbered zone where the surgeon can perform the medical procedure that was intended to be performed. 
As is well known in this field of technology, the cannulated dilators and tubular retractors are made from surgical metal material and are sized for the largest depth that is anticipated in the surgical procedure.  Hence, whether the depth is 10 millimeters (mm), 20 mm, 30 mm, etc.  Measured from the exterior of the cavity to the most interior position in the cavity (inferior edge of the superior lamina) the tubular retractor that may be available for use ii the surgical procedure could be 100 mm or larger.  The additional or excess length of the dilator retractor is not only cumbersome to use, it is unnecessary and undesirable. 
This invention obviates this problem by providing the necessary elements that allow the dilator retractor (cannula) to be cut to size once the incision and diameter of the cavity has been established.  Hence, in the surgical procedure described above the last cannulated dilator in the procedure in accordance with this invention includes indicia of a graduated vertical scale on the tubular wall, preferably in millimeters that is viewed by the user.  A cannula or dilator retractor, which basically is a cylindrical tube made from a plastic or synthetic material in one preferred embodiment or surgical metal in another embodiment which is easy to cut and which is transparent in one embodiment and opaque in another is provided in the largest length contemplated in this particular procedure or alternatively is pre-sized in a series of sized cannulas.  A template that has a diameter that is slightly smaller than the diameter of the dilator retractor made from a soft plastic material such as Teflon material that may include graduated annular grooves that are graduated vertically in scale that is commensurate with the indicia scale on the cannulated dilator.  Or alternatively, the dilator retractor may also include on the wall indicia corresponding to the indicia on the cannulated dilator.  Hence, the surgeon or user merely has to count the annular grooves or the indicia on the wall of the dilator retractor to match the depth of the cavity and with a cutter, cut through the delator retractor which will provide a cannula that is acceptable to the surgeon without the unnecessary length that has heretofore presented a problem. 
An annular retractor clamp is provided to fit over the top of the dilator retractor which obviously is sized to accommodate the width of the retractor clamp which, in turn, is utilized to mate with a rigid holder that is clamped to a rigid member such as the operating table or other convenient member to secure the cannula in place. 
This invention also contemplates a tool for insertion of the cannulated dilator and a tool for the insertion of the dilator retractor into the body cavity.  The tool for insertion of the cannulated dilator is a rectangular shaped planar member that removably fits the cannulated dilator and serves to provide leverage for the surgeon to turn the dilator retractor while it is being inserted into the body cavity to reach its ultimate destination.  A tool for insertion of the dilator retractor is generally a pusher which may be made integral with the template includes an inner bore that is slightly larger than the outer diameter of the cannulated dilator and includes a flat bottom surface that overlies the top end wall surface of the dilator retractor so that the pusher provides leverage for the surgeon to slide the dilator retractor over the scaled cannulated dilator until it reaches the final destination in the body cavity. 
As an alternate to the use of the cutter and template, it is contemplated within the scope of this invention, that a series of different length dilator retractors will be made available so that the surgeon after making the measurement of the depth of body cavity with the cannulated dilator will select the dilator retractor that most closely matches the size desired.