Patent Application
20070073303
The present invention relates generally to surgical saws and, more particularly, to powered circular saws and blades for precision cutting of bone.
Powered surgical saws are utilized in many operations in orthopedic surgery, especially during total-joint replacement procedures. For total-knee replacement surgery, accurate bone cuts are required to ensure optimal implant alignment to maximize durability and function of the artificial joint.
Conventional total-knee replacement tools include cutting blocks (cutting guides) containing a slot and powered oscillating saws. The slot of the cutting blocks permit passage of the oscillating saw blade, thereby guiding the angle and position of the intended bone cut.
Oscillating saws are utilized to cut bone in many surgical procedures, including total-knee replacement and total-hip replacement surgery. The saw blades attached to oscillating saws are long and narrow, allowing the surgeon to cut thick pieces of bone with the limited exposure offered with routine surgical approaches.
Oscillating saws are inherently inefficient cutting tools, however, requiring considerable manual force to cut hard materials such as bone. The saw blades vibrate, whip and deflect, leading to gouging of bone, and imprecise cuts. Though the cutting teeth must oscillate to cut bone, oscillation of the shank of the saw blade can damage soft tissues, particularly with minimally invasive surgical approaches.
The typical length of oscillating saw blades are about 3½ inches in length, limited by deflection of the blade beyond this length. However, the combination of the cutting guide and bone may be thicker than 3½ inches. Metallic debris is often generated from the oscillating blade scraping on the cutting block. Vibration of the blade on the cutting block can loosen or shift the cutting block, leading to excess bone removal. Binding of the saw blade within bone can result in kickback, potentially injuring vital structures such as ligaments, tendons, nerves and blood vessels. In addition, the deflected saw blade can injure the surgeon or assistant's hands, exposing them to possible blood-borne pathogens.
To alleviate these problems, alternative bone-cutting systems have been developed. As one example, U.S. Pat. No. 5,725,530 describes a surgical saw including a saw assembly driven by a powered surgical handpiece. The system includes a pair of parallel, co-planar guide arms, a pair of flexible, endless cutting bands disposed around the guide arms, respectively, and a drive mechanism for driving the cutting bands around the guide arms in a cutting direction. The cutting bands each include a plurality of spaced cutting teeth connected to one another by flexible band segments. The cutting bands are driven by the drive mechanism relative to the guide arms in opposite directions along defined paths to cut anatomical tissue at distal ends of the guide arms. A method of resecting bone includes the steps of driving the cutting bands relative to the guide arms in the cutting direction along the defined paths and inserting the distal ends of the guide arms in the bone to resect the bone along the plane of the guide arms.
Although systems such as the one just described do away with an oscillating blade, the assembly is complex, leading to increased cost or possible mechanical problems. Circular saws are efficient cutting tools which afford great precision in cutting hard substances. The drawbacks of circular saw blades are that they have limited travel, practical only for cutting relatively thin structures, and have a broad cutting base, requiring exposure of a large segment of the substance being cut.
This invention resides in a power cutting saw system affording greater efficiency and improved precision in cutting bone. Broadly, the system exhibits the cutting efficiency of a circular saw, but retains the practical dimensions of an oscillating saw blade.
According to the invention, a circular saw blade, available in a variety of diameters, is positioned at the end of a narrow, low-profile elongated support. The support houses a drive assembly that efficiently transmits power from a standard hand-held portable saw to the blade. The support can rest on modified saw guides for total joint procedures, providing the surgeon with a compact, efficient and precise bone-cutting tool.
In the preferred embodiment the circular saw and support are single-use disposable units, available in a variety of lengths and widths. In an alternative embodiment, twin blades are used to eliminate changes in height between the blades and the support.
Turning now to the figures,
Although in the preferred embodiment the saw blade is belt-driven, other mechanisms may be used, including meshing gears, as well as direct drive to the teeth 104 of the blade 102. With respect to the teeth 104, any configuration suitable for bone cutting may be utilized, as the invention is not limited in this regard. For example, the teeth currently used on oscillating saws may be applicable, as well as other configurations known to those of skill in the art.
In terms of materials, the blade 102 and support 120 are made of any suitable durable and rigid material, such as metal. Nor is the invention limited in this regard, since it may be possible to use hard plastics for various components as well. This may be advantageous for single-use disposable versions of the invention.
Although the top of the assembly includes a slight stair-step in terms of height between the blade 102 and the pulley 108, the bottom of the assembly is flat, allowing the surgeon to rest the support 120 onto existing or modified saw guides for various surgical procedures, including total-joint replacement. Little vibration occurs between the novel circular saw/support and the cutting guide since only the exposed tip of the circular saw moves. Since the platform does not vibrate on the cutting block, there is less metallic debris formed, and less deviation from the intended course. Precise bone cuts are thereby facilitated, providing a safe and stable cutting instrument for the surgeon.
It is anticipated that different assemblies of the type shown in
