The powered saw is an important powered tool that a surgeon employs in order to perform certain surgical procedures. A typical powered saw has a handpiece in which is housed either an electrically or pneumatically driven motor. The motor is attached, through a drive shaft, to a head, also part of the handpiece. The head is adapted to removably receive a saw blade. The actuation of the motor causes movement of the head and the attached saw blade. This movement of the saw blade is what gives the blade the power to cut through the tissue it is employed to separate. Powered surgical saws are able to cut through both hard and soft tissue much faster, and with greater accuracy, than the manually operated saws that they have replaced. Also, it should be clear that the physical effort a surgeon has to employ to operate a powered surgical saw is much less than that used when cutting tissue with manual saws.
Many surgical saws are designed to be used with flat saw blades. Typically, this type of saw blade has a base that is designed to seat in a complementary slot or opening formed in the head. The saw base has one or more openings or slots in which coupling members integral with the head seat in order to lock the blade to the head. Extending from the base, the saw blade has a main body. The leading edge of the main body is formed with teeth that perform the actual cutting action.
Many surgical saws are designed so that their heads and complementary blades engage in a repetitive right-left-right-left oscillating motion. More specifically, the head of an oscillating motion saw moves in either a sagittal pattern or in oscillatory pattern. When a blade is moved sagittally, it pivots in a plane that is parallel to the axis of the handpiece. When a blade is moved in an oscillating pattern, it pivots back-and-forth in a plane that is angled to the longitudinal axis of the handpiece.
Over the past few years, it has become popular to provide powered surgical saws with heads that have tooless mechanisms for coupling the saw blades to the saws. These mechanisms often have some sort of spring loaded device for holding the head coupling members in position so that they lock the saw blade in place. The coupling member is displaced from the locked state to the release state by the depression of a button also built into the saw head. One advantage of these assemblies is that they make replacing saw blades, which often occurs during surgery, a relatively simply task. All one has to do is depress the button in order to move the coupling member to the unlocked state; the surgical personnel then remove one blade and insert a new blade. Still another advantage of these assemblies is that they eliminate the need to bring another tool, either a small wrench or a key, into the surgical suite. The elimination of this tool eliminates the need to have to sterilize it before an operation and the need to have to account for its presence.
While current surgical saws, with their tooless heads, have proven to be useful surgical tools, there is a disadvantage associated with their use. When an oscillating motion saw with this type of head is actuated, it generates a significant amount of noise. This is because current saw blades do not tightly fit into the saw head slots in which they seat. There are two reasons for this. First, these saw heads and their complementary blades are inherently dimensioned so that there is a small interstitial gap between the blade and the adjacent walls of the saw head that define the complementary slot. This gap is necessary to ensure that the base of the saw can be quickly slide into and removed from the slot. Secondly, there is a slight gap due to the inherent manufacturing impressions that develop during the fabricating of these components. Consequently, each time a saw head changes its direction of motion, the inertial movement of the saw blade, which is still travelling in the first direction, causes the side of the blade to abut against the adjacent surface of the saw head. Each time this motion occurs, noise is produced. These saw blades typically oscillate back-and-forth at a rate of 10,000 to 20,000 cycles/min. The cumulative noise produced by the saw blade repetitively striking the interior walls of the saw head in which it is seated is quite noticeable.
There have been some attempts to provide saw head-and-blade assemblies designed to minimize the noise produced when these components are actuated. In one such assembly, the saw head is provided with outwardly tapered pins and the base of the saw blade is provided with holes in which the pins seat. This arrangement is intended to provide a tight fit between the pins and the adjacent section of the saw blade through which the pins seat. By providing this tight fit, the post-insertion play of the saw blade is reduced. The reduction in this play reduces the incidence of the blade striking the interior walls of the saw head and the noise generated by such action. This assembly has served to minimize the noise associated with the actuation of a surgical saw. However, there are several limitations associated with this assembly. It is costly to precision machine the tapered pins used to hold the saw blade in the head. Moreover, these pins, are subject to wear and can wear at an uneven rate. Over time, as a result of this uneven wear, the saw blade may unevenly seat on the pins. This uneven seating can cause a deformation of the planar alignment of the blade and its teeth. Also, over time, the wear can cause the blades to seat lower and lower on the pins. This can make removal of the blade difficult.