Typically, spinal surgical procedures used, for example, to provide stabilization, fusion, or to correct deformities, require large incisions and substantial exposure of the spinal areas to permit the placement of surgical implants such as, for example, various forms of screws or hooks linked by rods, wires, or plates into portions of the spine. This standard procedure is invasive and can result in trauma, blood loss, and post operative pain. Alternatively, fluoroscopes have been used to assist in placing screws beneath the skin. In this alternative procedure at least four incisions must be made in the patient's back for inserting rods or wires through previously inserted screws. However, this technique can be difficult in that fluoroscopes only provide two-dimensional images and require the surgeon to rotate the fluoroscope frequently in order to get a mental image of the anatomy in three dimensions. Fluoroscopes also generate radiation to which the patient and surgical staff may become over exposed over time. Additionally, the subcutaneous implants required for this procedure may irritate the patient. A lever arm effect can also occur with the screws that are not connected by the rods or wires at the spine. Fluoroscopic screw placement techniques have traditionally used rods or plates that are subcutaneous to connect screws from vertebra to vertebra. This is due in part to the fact that there is no fluoroscopic technique that has been designed which can always adequately place rods or plates at the submuscular region (or adjacent to the vertebrae). These subcutaneous rods or plates may not be well tolerated by the patient. They also may not provide the optimal mechanical support to the spine because the moment arm of the construct can be increased, thereby translating higher loads and stresses through the construct.
A number of different types of surgical navigation systems have been described that include indications of the positions of medical instruments and patient anatomy used in medical or surgical procedures. For example, U.S. Pat. No. 5,383,454 to Bucholz; PCT Application No. PCT/US94/04530 (Publication No. WO 94/24933) to Bucholz; and PCT Application No. PCT/US95/12894 (Publication No. WO 96/11624) to Bucholz et al., the entire disclosures of which are incorporated herein by reference, disclose systems for use during a medical or surgical procedure using scans generated by a scanner prior to the procedure. Surgical navigation systems typically include tracking means such as, for example, an LED array on the body part, LED emitters on the medical instruments, a digitizer to track the positions of the body part and the instruments, and a display for the position of an instrument used in a medical procedure relative to an image of a body part.
Bucholz et al. WO 96/11624 is of particular interest, in that it identifies special issues associated with surgical navigation in the spine, where there are multiple vertebral bodies that can move with respect to each other. Bucholz et al. describes a procedure for operating on the spine during an open process where, after imaging, the spinous process reference points may move with respect to each other. It also discloses a procedure for modifying and repositioning the image data set to match the actual position of the anatomical elements. When there is an opportunity for anatomical movement, such movement degrades the fidelity of the pre-procedural images in depicting the intra-procedural anatomy. Therefore, additional innovations are desirable to bring image guidance to the parts of the body experiencing anatomical movement.
Furthermore, spinal surgical procedures are typically highly invasive. There is, thus, a need for more minimally invasive techniques for performing these spinal procedures, such as biopsy, spinal fixation, endoscopy, spinal implant insertion, fusion, and insertion of drug delivery systems, by reducing incision size and amount. One such way is to use surgical navigation equipment to perform procedures percutaneously, that is beneath the skin. To do so by means of surgical navigation also requires apparatus that can indicate the position of the spinal elements, such as, for example the vertebrae, involved in the procedure relative to the instruments and implants being inserted beneath the patient's skin and into the patient's spine. Additionally, because the spinal elements naturally move relative to each other, the user requires the ability to reorient these spinal elements to align with earlier scanned images stored in the surgical navigation system computer, to assure the correct location of those elements relative to the instruments and implants being applied or inserted percutaneously.
In light of the foregoing, there is a need in the art for apparatus and minimally invasive procedures for percutaneous placement of surgical implants and instruments in the spine, reducing the size and amount of incisions and utilizing surgical navigation techniques.