Oval dilator and retractor set and method

Access to a greater area of surgical site with minimally invasive procedure is obtained by using two sets of sequentially placed tissue dilators oriented with their axes in a plane parallel to the spinal axis and a final non-circular dilator encompassing the two sets, followed by a non-circular tubular retractor providing a working channel extending longitudinally of the spine.

BACKGROUND

The present invention relates to instruments and methods for performing tissue retraction for surgeries using minimally invasive procedures.

Traditional surgical procedures for pathologies located within the body can cause significant trauma to the intervening tissues. These procedures often require a long incision, extensive muscle stripping, prolonged retraction of tissues, denervation and devascularization of tissue. These procedures can require operating room time of several hours and several weeks of post-operative recovery time due to the destruction of tissue during the surgical procedure. In some cases, these invasive procedures lead to permanent scarring and pain that can be more severe than the pain leading to the surgical intervention.

U.S. Pat. No. 5,792,044 issued to Kevin T. Foley et al. provides rather extensive background information pertaining to percutaneous surgery. FIGS. 10athrough 10iof that patent depict, and column 10 at lines 11 and following of the patent describe, steps of a method for access to a surgical site in the spine. As described, it begins with the insertion of a guide wire followed by a series of successfully larger dilators installed in sequence to dilate the soft tissues. Then, following installation of the largest dilator deemed necessary, a cannula (retractor) is advanced over the largest dilator for providing a working channel from the skin of the patient to working space adjacent the spine. The retractor can be secured in place by any of the many suitable means known in the art, several of which are mentioned in the patent. It is desirable to be able to use the working channel provided by the retractor, for surgical tools, for viewing devices and for inserting and manipulating fixation elements to the maximum extent possible for desired placement and fixation. Some such items or combinations of items dictate the inside diameter needed in the retractor.

It is sometimes desirable to have working space at the spine extending a greater distance axially of the spine than transversely. However, to provide such access through the typical circular retractors using the above-mentioned dilation techniques, could require a diameter so great as to cause significant trauma to the intervening tissues during placement of the dilators and the tubular retractor.

The development of minimally invasive percutaneous procedures has yielded a major improvement in reducing recovery time and post-operative pain because minimal dissection of tissue (such as muscle tissue, for example) is required. Minimally invasive surgical techniques are desirable for spinal and neurosurgical applications because of the need for access to locations within the body, and the danger of damage to vital intervening tissues. While developments in minimally invasive surgery are steps in the right direction, there remains a need for further development in minimally invasive surgical instruments and methods.

SUMMARY

One aspect of the present invention is providing a minimally invasive but an optimally oriented working channel for access to spinal surgery sites at the spine.

Another aspect is providing an improved shape of working channel.

Another aspect is providing a way to access greater working space adjacent the spine with minimal trauma to tissue between the skin and the spine.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

With reference toFIGS. 1A–1C, lumbar vertebrae L3, L4and L5are illustrated schematically with the planned surgical site being at the L4–L5joint through a posterion approach. The tubular retractor11according to the illustrated embodiment of the present invention is shown in place with its distal end12contacting the laminae of L4and L5at the site where the intervertebral disc13will be addressed. The oval dilator14is shown receiving the retractor11. Tubular retractor11and oval dilator14can also be positioned at other locations along the spine and in other approaches to the spine, including lateral, postero-lateral, antero-lateral and anterior approaches.

Current tissue dilation practice with a single guide wire and a sequence of dilators positioned over the single guide wire is shown and described in a publication entitledMETRx Microdiscectomy Surgical Technique, published in 2001 by Medtronic Sofamor Danek of Memphis, Tenn., USA, the entire contents of which publication are incorporated herein by reference. The METRx™ System for microdiscectomy, marketed by Medtronic Sofamor Danek, USA of Memphis, Tenn., includes a set of circular dilator tubes in diameters from 5.3 mm to 16.8 mm that are positioned one over the other to receive a circular retractor of desired size.

The present invention can be practiced with or without guide wires. An example of the present invention with guide wires will be described first. So, referring now toFIGS. 2A through 2G,FIG. 2Ashows a couple of guide wires16and17which are vertically spaced. Using conventional visualization technique, these wires are inserted through an incision in the skin at18and advanced through tissue to spinal bone at points19and21, for wires16and17, respectively, on the vertebrae. If desired, they can be advanced forcefully enough to become anchored at an appropriate spacing in a bony face or faces, depending upon the specific site to which the surgery is addressed. It is further contemplated that guide wires16and17could be anchored to bone and/or tissue at other locations of the posterior spine and in locations to accommodate other approached to the spine.

At a spinal surgery site, the spine has an axis in a direction from head toward feet which may be referred to hereinafter as a primary axis. At the site illustrated herein, the primary axis is designated by the line22. According to one feature of the invention, the cross-sectional shape of the tubular retractor11is non-circular, and has a generally elliptical or oval shape having a major axis parallel to the axis22of the spine. Accordingly, the wire-to-bone contact points (or anchor points, if desired) are on an axis or line23parallel to axis22of the spine at the surgery site. By orienting the major axis parallel to or in the general direction of axis22, access can be provided to multiple vertebral elements through a single working channel. For example, inFIG. 1C, access to each of the vertebrae L4and L5can be provided through the working channel of oval tubular retractor11to accommodate procedures and/or implant insertion into each of the vertebrae L4and L5with little or no repositioning of the distal end of oval tubular retractor11.

Following installation of the guide wires, the first pair of dilators24and26is installed on the wires16and17, respectively. Each of the dilators is a circular tube with a central aperture throughout its length and sized to enable sliding the dilator along the length of the guide wire until the rounded distal end for tube24, for example, engages a bony face or other tissue at point19or tissue adjacent the surgical site. A series of grooves24G is provided in each tube near the proximal end such as24P, the series extending from adjacent the proximal end toward the distal end a short distance, to facilitate grasping the tube during insertion and later when removed from the body.

Following insertion of the dilators24and26, and the distal ends against the bone or other tissue, larger dilators27and28are placed on the dilators24and26, respectively, and advanced along them until abutment of their distal ends, such as27A for dilator27, with bone or other tissue adjacent the surgical site. These dilators are similar to dilators24and26except for the larger size and shorter length.

Then dilators29and31are placed over and advanced along dilators27and28, respectively, until the distal ends29A and31A of these dilators contact the bone or other tissue adjacent the surgical site.

Then dilators32and33are installed and advanced over the dilators29and31, respectively, and advanced along until their distal ends32A and33A contact the bone or other tissue adjacent the surgical site.

As each of the aforementioned dilators (which may be referred to as “precursor dilators”) is placed, the soft tissue is dilated with minimal trauma. Also, the set of dilators is oriented such that a plane containing the longitudinal axes of all of them, also contains the line23which is parallel to the spinal axis22and may, in some instances, be co-planar with the spinal axis22, depending upon the direction of access desired by the surgeon.

After insertion of the last set of the circular precursor dilators, oval dilator14, according to the illustrated embodiment of the invention, is installed. It is advanced over the dilators32and33until the distal end14A thereof is located where the surgeon desires, which can be in contact with the laminae of at least one of the vertebrae or adjacent other paraspinous tissue and/or other portions of the vertebral bodies. Following the seating of the oval dilator14, the oval tubular retractor11according to the invention is advanced along the oval dilator14until its distal end12contacts or is proximate bone or paraspinous tissue at the surgery site.

Following positioning of the oval tubular retractor11, the precursor dilators, and guide wires if not already removed, can be removed in any desired sequence or as a group, depending upon the convenience of the surgeon. The staggered lengths and gripping surfaces near the proximal ends thereof facilitate this. Once these dilators and oval dilator14have been removed, the oval tubular retractor11remains in place, providing a working channel through which viewing devices, instruments, fixation devices and materials may be passed. Some examples of the type of viewing systems that can be used with the tubular retractor of the present invention are those that are available with the above-mentioned METRx System, which includes microscopic viewing systems positioned over the proximal end of the retractor, and endoscopic viewing systems positioned through the retractor. Tubular retractor11could also be used with other viewing systems, such as those that include an endoscope positioned to the surgical site through a second portal and/or fluoroscopic viewing systems.

Referring now toFIG. 3, the combination shown is much like that ofFIG. 2G, but a mounting bracket38is shown on the oval tubular retractor11. The mounting bracket can be secured to a flexible arm or other device mounted to the surgical table or other fixture in the operating room.

FIG. 5shows the tubular retractor11and bracket38and the oval internal shape of the tube and which becomes the working channel in the patient's body. In this illustrated embodiment, the tube cross section is somewhat elongate with relatively straight sides and round ends. Accordingly this oval has a major axis39, and a minor axis41perpendicular to the major axis. When this retractor is in place at the surgery site, the axis39is in the same plane as line23(FIG. 1).

While the longitudinal axis42of the oval tubular retractor is intended to bisect a line between points19and21in the vertebrae, and the axis39lies in a plane containing the longitudinal axis42and parallel to a plane containing the primary spinal axis22at the site of the surgery, it is conceivable that the axis39will not be perfectly parallel to axis22. This would be the case if it is found preferable to tip the axis42slightly in a vertical plane to avoid interference with and the necessity for removal of some bony structure or tissue material for access to the surgical site. It may also be desired to reposition the distal end12of oval retractor11from its initial insertion position over paraspinous tissue located outside the location of the working channel of oval retractor11by manipulating oval retractor11through the skin and tissue of the patient.

Referring now theFIG. 6, the oval dilator14is shown with the oval retractor11slid partway between the distal end14A and proximal end14P of the oval dilator. Since the pair of circular cross-section dilators32and33present a grooved contour or valley at their junction and along their entire length, a volume of tissue along each side of the pair might not be entirely dilated at the time for installation of the oval dilator14. Therefore, the oval dilator is provided with a pair of longitudinally extending internally projecting ribs14B and14C as shown inFIG. 6and extending from the proximal end14P to the distal end14A. To facilitate dilation of the above mentioned volume of tissue as the oval dilator is inserted, the leading internal edge of each of the ribs14B and14C is curved, as is the contour of the entire leading edge of the oval dilator14, as shown inFIG. 7.

The thickness of the tube wall section at the ribs14B and14C relative to the wall thickness at the top and bottom of the oval dilator is indicated by the dashed lines14L inFIG. 7. Ribs14B and14C can extend into the channel of dilator14, and facilitate alignment of oval dilator14along the pair of adjacent circular cross-section dilators32and33.

The externally projecting perimetrical flange11F on the oval retractor provides a useful feature on which the bracket38or some other sort of bracket, if desired, can be incorporated at the point of manufacture of the retractor. Viewing instruments and/or other surgical instruments can be mounted to the oval retractor11on flange11f.

The invention can be practiced without guide wires, if desired. Following an incision, the first dilator tube is inserted and guided using fluoroscopy or other visualization technique until its distal end contacts vertebral bone or other tissue at the desired location. Then, through the same incision, the second dilator tube is inserted, side-by-side with the first and advanced to contact of its distal end with the bone. Then a third dilator is installed on the first dilator and advanced to contact its distal end with the bone. Then a fourth dilator is installed on the second dilator and advanced to contact of its distal end with the bone. This process continues in the same manner as described above until the dilation is sufficient to accommodate the size of oval tubular retractor to be used. As each set of dilators is inserted, it can contact the wall of the adjacent dilator and provide an additional separation between the side-by-side dilators that corresponds to about one-half of the increase in the external diameter of the dilator being inserted over the external diameter of the dilator receiving the inserted dilator.

The materials used in the guide wires, dilators and retractor can be stainless steel, aluminum, plastic, or any other material suitable for surgical instruments. The material can be opaque, translucent or combinations thereof. Specific examples of circular dilator tube diameters useful with the present invention and found in the above-mentioned publication are: 5.3 mm, 9.4 mm, 12.8 mm, 14.6 mm, and 16.8 mm, and one specific example guide wire diameter is 0.062 inch. Other dilator and guide wire diameters are also contemplated.

One example of dimensions of the major and minor axes of the oval tubular dilator14of the present invention may be 40 mm and 20 mm, respectively. A smaller one may be 28 mm and 14 mm, respectively. Other sizes may be provided if desired. Oval tubular retractor11would have internal dimensions so that they slidably fit the oval dilators which slidably fit the round dilators as described above. Examples of lengths may be 3 cm to 9 cm. The length chosen will usually be the shortest that provides access to the surgical site or working space adjacent the spine, such as, for example, the vertebra lamina while allowing maximum mobility of instruments in the working channel. The oval retractors11can be provided in a set or kit of oval retractors11having various lengths from which the surgeon can select.