The present inventions relate to devices used in orthopedic spinal surgical procedures. Specifically, the inventions improve upon spinal implant assemblies with a self-tapping exit flute for easier bone screw removal and a tool for pulling the spinal rod through spinal connector assemblies.
Back pain is a commonly reported medical aliment. It is most frequently associated with degenerative changes in the spinal vertebra. Most of the 30 million U.S. patients who report back pain each year resolve their pain with conservative treatment (e.g., rest and exercise). Nonetheless, approximately 15 percent or 4.5 million fail conservative therapy and are left with debilitating pain. Out of these, approximately 500,000 people opt for spinal surgery. In addition to alleviating pain, spinal surgery seeks to minimize damage to adjacent supportive muscle and skeletal components. Although other dynamic treatment options are becoming available, spinal fusion is the most common surgical procedure.
Several techniques and systems have been developed for correcting and stabilizing the spine (e.g., to facilitate spinal fusion). Over the years, spinal and orthopedic implants have evolved toward progressively stronger, stiffer and better devices, as it is presumed that increased construct rigidity optimizes bone fusion and provides more rapid and robust healing. The most widely used systems use a bendable rod that is placed longitudinally along the length of the spine. Such a rod is bent to follow the normal curvature of the spine whether it is the normal kyphotic curvature for the thoracic region or the lordotic curvature for the lumbar region. In such a procedure, a rod is attached to various vertebrae along the length of the spinal column by a number of bone anchor assemblies. A bone anchor element may be a hook that engages the vertebra laminae or a spinal bone screw threaded into the vertebral bone.
In traditional rigid stabilization systems, the rod is situated on opposite sides of the spine or spinous processes. Numerous bone screws are then screwed into the pedicles of the vertebral bodies. Rods are affixed to these bone screws so corrective and stabilizing forces are applied to the spine. After stabilization, the vertebra is typically decortified where the outer cortical bone is removed to provide a foundation for bone grafts. Over time, these bone grafts fuse the damaged vertebrae together.
A good example of rod spinal fixation is the TSRH® Spinal System sold by Medtronic Sofamor Danek Inc. The TSRH® Spinal System incorporates elongated rods, hooks, screws and bolts that are configured to create segmented constructs through the spine. In earlier versions, the vertebral hooks and bone screws were perpendicularly attached below the spinal rod at a fixed orientation. When introduced, the TSRH® Spinal System was a significant advance over prior systems. It provided the surgeon far more versatility, stronger fixation and easier implantation. Nonetheless, it also required the surgeon to make significant changes to the contour of the rod. If bent correctly, a bone fastener, such as a hook or screw, could be connected to the rod through lateral eyebolts adjacent to the rod.
One drawback to the original TSRH® spinal systems was that these lateral eyebolt fasteners met the rod at various angles making installation of the spinal rod very difficult. To solve this problem, the TSRH® Variable Angle Screw in U.S. Pat. No. 5,261,909 by Sutterline et al. utilized the same TSRH® eyebolt to connect the spinal rod but incorporated a washer. This washer engaged the spinal rod through a groove on one surface of the washer. More importantly, it added two opposing radially splined surfaces so that the fastener could move at variable angles relative to the spinal rod. Finally, a nut threaded onto the post of the eyebolt clamped all the components together to complete the assembly. Such a variable angle screw configuration allowed the bone screw to pivot in a single plane parallel to the plane of the spinal rod thereby eliminating one of the many angles that needed to be negotiated to meet the rod.
The variable angle screw system of U.S. Pat. No. 5,261,909 presented a significant advance over the prior rod-based implant system. It was also relatively compact and required a minimal number of parts, yet was able to accomplish a solid fixation of the bone fastener so that the rod had a wider range of angular orientations. A drawback, however, was that the eyebolt-nut combination required side tightening of the nut to clamp the systems together. This side tightening required a large surgical area around the spine to accommodate a wrench. To address this difficulty, a top-tightening assembly was disclosed in U.S. Pat. No. 5,282,801 to Sherman. In this patent, the clamp assembly replaced the eyebolt and nut with a T-bar against the head of the variable angle bone fastener. While the original TSRH® Spinal System relied upon tightening a nut against the variable angle bone screw, the top-tightening approach of U.S. Pat. No. 5,282,801 utilized a set screw that pushed the spinal rod into an interlocking washer, and ultimately against a complementary spline face of the variable angle screw. With this system, the variable angle capability was retained while a useful top-tightening feature was added.
With the addition of the top-tightening capability, the TSRH® Spinal System provided surgeons with a great deal of flexibility in the placement and orientation of bone fasteners. Although these variable angle components now greatly reduced the need to manipulate and bend the spinal rod, a certain amount of shaping or contouring of the spinal rod was still required. Specifically, the rod had to be shaped so that the point of attachment of the bone fastener to the rod was the same distance from the vertebral body as the splined or inter-digitating portion of the bone fastener. To do so, a vertical or height adjustment of the bone screw was necessary to ensure that the variable angle components were properly aligned with each other when the assembly is clamped together. If there was height difference between the bone screw and the rod, it was made up by threading or unthreading the bone screw either up or down.
To overcome this bone screw adjustment drawback, a system was developed to provide vertical adjustability. If the height difference between the rod and bone screw was close, the new system would allow a rod to be situated at any distance from the spine and/or oriented with a pre-set contour regardless of the location of the fastener. With the addition of a complementary splined surface to the bone washer described in U.S. Pat. No. 5,643,263 to Simonson, the TSRH® Spinal System now allowed a surgeon to easily engage a bent spinal rod to any type of fixation element for final tightening. Furthermore, various sized rods and screws could now be fixed in almost any angulation. With its vertical height adjustment ability, the widest angulations of any spinal bone anchor system can be met. Furthermore, it can also engage a rod or bone screw of any size or configuration without switching its connectors. The current TSRH® Spinal System allows a surgeon to easily engage a bent spinal rod to any type of fixation element.
The rotation ability of the spinal system assembly 2 is also shown in
Along with variable-sized washers 4, 8 and the 160° medial-lateral flexibility of the bone screws, the TSRH® Spinal System can also undergo a medial-lateral adjustment. In doing so, the engagement of laterally placed screws is now possible. This is especially important during multi-level rod constructs between the vertebrae. With the radially splined ridges 12, various sized washers and the smooth bone screw shank 14, the anatomic placement of pedicle screws can be made with minimal rod contouring. Such a configuration also minimizes any forced preloading or stressing of the screw-to-rod interface. With respect to other assemblies, no other spinal system assembly has all of these characteristics and abilities.
As the prior art illustrates, spinal fixation devices are constantly being improved. Whereas a rod 36 shown in
Another common issue among all spinal system assemblies is bone screw pullout. After extensive wear, bone screws may weaken or begin to pullout. As a result, spinal system assemblies may begin to slip along their rods and bone screws. When the vertebral bone is strong and healthy, the initial fixation of traditional spinal and orthopedic screws is excellent, with more than adequate strength to resist pullout. With dense, sclerotic or osteoporotic bone, micro-motions resulting from the normal range of motion with the skeletal system may lead to a progressive degradation from the initially implanted state. Should the bone fail to heal, these micro-motions can persist and cause the metallic screw to oscillate within the softer cancellous bone. When subjected to persistent toggling, the modulus mismatch of the metal to cortico-cancellous bone interface may cause the bone screw to become loose.
A lot of time and preparation typically goes into inserting a bone screw into the cortical and cancellous bone of the vertebra. This includes preparing the pedicle canal, determining the screw length and tapping the pedicles with screws. This is particularly true for dense, sclerotic or osteoporotic bone. In healthy bone, some pedicle screws with self-tapping entry flutes at their distal or cutting end can easily penetrate the bone until its last thread is flush with the bony surface (see
So as to not obscure screw alignment and placement, decortication is usually performed after the bone screws are set. When decortication is complete, cortico-cancellous bone grafts are firmly pressed in place to form a bone fusion bed. Although there are many types of segmental spinal fusion (dorsolateral intertranverse, posterior lumbar interbody, anterior lumbar interbody, etc.), the basic technique is very similar. Prior to placement of the bone graft, a fusion bed is thoroughly prepared by decortication of the bony surface to expose the underlying cancellous core. This usually includes the transverse processes, the facet joints and the par interarticularis. Decortication is performed with a variety of instruments such as a burr or curette. For a short-term segment fusion, unilateral posterior iliac crest harvesting provides adequate bone for grafting. For longer complex fusion, bilateral iliac crest bone harvesting may be necessary. Such bone graft is carefully applied to the decorticated surfaces in a continuous fashion, forming a bridge from one segment to the next.
A portion of the fusion process can be seen in
After decortication, cortico-cancellous bone graft 44 is firmly pressed on the bone fusion bed prior to the placement of the connectors 5 and rod 20 constructs. After the rod, connectors and bone screw are assembled; the normal curvature is obtained through segmental distraction and compression of the spine. After several adjustments and provisional tightenings, the surgeon performs the final tightening.
Over time, the cortico-cancellous bone graft fuses the vertebrae together. While the vertebrae are fusing, the main objective of spinal implants is to stabilize the spine until such time that fusion is complete. Once fused, the spinal implants become secondary. In general, most spinal implants are left behind and not removed because of the risk of surgery to do so. There are, however, many situations that require implant removal and this is particularly true during bone screw pullout. Classically, screw pullout, dislodgement and breakage are the main cause of implant failure. Such bone screw failure results in a weakening of mechanical strength for the overall construct. It also lowers the biological potential for bone healing. A need therefore exists to more easily remove bone screws especially through the newly laid cortico-cancellous fusion bed.
In summary, there is a need in the industry for continual improvements in devices, implants and tools used in orthopedic spinal surgical procedures. In particular, improvements need to be made in removing existing spinal system assemblies, especially bone screws. For spinal system assemblies, where the rod is threaded through connector apertures, a need exists to help pull the rod through the connectors. The present invention describes improvements in these areas for many makes and models of spinal implants on the market today.
The present invention provides improvements to bone screws, rods and tools used in orthopedic spinal surgical procedures. Specifically, the present invention improves the spinal system assemblies with one or more exit flutes on the bone screw and tools for pulling the spinal rod through the spinal system assembly.
A self-tapping exit flute is a cutting flute at the proximal end of a bone screw (i.e., next to the bone screw shank). If bone screw removal is needed, the self-tapping exit flute of the present invention permits a cleaner removal of the screw through the previously tapped cortical and cancellous bone of the vertebra and, more importantly, through the newly laid and fused bone created by the cortico-cancellous bone graft. Such a self-tapping exit flute may prevent cracking or disruption of the bone fusion bed, especially if a healthy fusion bed is maintaining its strength and integrity.
A second embodiment pertains to spinal system assemblies where the rod is threaded through apertures of connectors or washers. Rather than pushing rods through the apertures, a pulling tool is used to help pull the rod through the connector washer apertures. One preferred embodiment is a flexible thread, string or wire attached to the distal end of a spinal rod. This flexible thread is attached to a needle-like probe. The probe helps the surgeon insert the flexible thread into and through the connector washer apertures. Once the probe is through the connector, an attachment mechanism on the probe connects to a pulling tool with a handle. In one embodiment, the distal end of the pulling tool attaches or snaps onto the probe by a hooking device. The surgeon then pulls the rod through the apertures of the connector washers by a rod puller. In combination with a pushing tool, a pulling tool may facilitate the placement of the spinal rods through the connector washers.
A self-tapping exit flute of the present invention is shown in
A close-up of the self-tapping exit flute is shown in
Referring to
As illustrated in
There are various ways to connect the flexible thread 70 to the spinal rod 20. As shown in
Although the rod 20 can be pulled through the apertures 6 of the connector assemblies 5 by a surgeon pulling on the probe 66, there may be circumstances to have additional pulling and gripping force. As shown in
As shown in
The entire rod puller assembly is shown in
In the foregoing specification, the invention has been described with reference to specific preferred embodiments and methods. It will, however, be evident to those of skill in the art that various modifications and changes may be made without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than restrictive, sense; the invention being limited only by the appended claims.
This application claims the benefit of priority under 35 USC 119(e) of U.S. Provisional Application No. 61/370,427, filed on Aug. 3, 2010, which is incorporated herein by reference in its entirety for all purposes.
Number | Date | Country | |
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61370427 | Aug 2010 | US |