Traditional surgical procedures often require a long incision, extensive muscle stripping, and prolonged retraction of tissues to access the desired surgical site as well as denervation and devascularization of surrounding tissue. This is particularly the case with spinal applications because of the need for access to locations deep within the body. Such surgical procedures can cause significant trauma to intervening tissues and potential damage to good tissue due to the amount and duration of tissue retraction, resulting in increased recovery time, permanent scarring, and pain that can be more severe than the pain that prompted the original surgical procedure. This is further exacerbated by the need to make a large incision so that the surgeon can properly view the areas inside the body that require attention.
Endoscopic, or minimally invasive, surgical techniques allow a surgical procedure to be performed on a patient's body through a smaller incision in the body and with less body tissue disruption. Endoscopic surgery typically utilizes a tubular structure known as a cannula (or portal) that is inserted into an incision in the body. A typical cannula is a fixed diameter tube, which a surgeon uses to hold the incision open and which serves as a conduit extending between the exterior of the body and the local area inside the body where the surgery is to be performed. Thus, cannulae can be used for visualization, instrument passage, and the like.
The typical cannula, however, presents at least two disadvantages. First, insertion of the cannula typically requires an incision. Although this incision is often relatively smaller than incisions made for surgical procedures performed without a cannula, there is still trauma to healthy tissue. There also may be a need to dilate the tissue prior to insertion of the cannula. Additionally, endoscopic surgical techniques may be limited by the size of the cannula because some surgical instruments, such as steerable surgical instruments used in posterior discectomies, are sometimes larger than the size of the opening defined by the cannula. Therefore, there is a need for a surgical site access system that can be inserted with minimal incision of tissue yet still provide an entrance opening and conduit sized for sufficient instrument passage and operation.