Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-12-09
2002-08-06
Smith, Ruth S. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S429000, C606S130000
Reexamination Certificate
active
06430434
ABSTRACT:
TECHNICAL FIELD
The present invention relates to surgical bone cutting systems and more particularly to systems for detecting or tracking bone motion during surgery.
BACKGROUND OF THE INVENTION
When performing robotically assisted total hip replacement surgery, (for example, when cutting a cavity into a patient's femur bone for the insertion of an artificial hip joint therein), it is very important to minimize the effects of bone motion. Successful hip replacement surgery, particularly when using cementless implants, relies on the highly accurate creation of the cavity within the proximal (upper) end of the femur for receiving the implant. Deviations of less than plus or minus 1 mm from the planned cavity placement and dimensions are desirable.
Accordingly, to minimize the effects of unwanted bone motion on cutting accuracy, it has been desirable to attempt to prevent bone motion to the maximum degree possible by firmly anchoring the bone while the surgical bone cutter is operating on the bone. Typically, unwanted bone motion has been restrained by the use of fixators which hold the bone in position as firmly as is possible. Unfortunately, there are practical limits as to how securely the bone can be held in position by a fixator. For example, for many surgical procedures it is necessary for the surgical team to hand hold retractors for surgical access. Changes in the forces applied to the bone by these hand held retractors can cause unwanted bone motion. Moreover, in many cases the surgical team does not know whether additional retraction is required until after the bone cutting procedure has commenced. As such, it is typically necessary to modify or slightly change the retraction forces on the bone during the course of the bone surgery. This can have the undesirable effect of causing unwanted bone motion, leading to inaccuracies in cutting the bone. In addition, under some conditions, such as to provide optimal cutting access, it may even be desirable to move the bone slightly during surgery. This further complicates the problem of cutting inaccuracies caused by unwanted bone motion thereafter.
Small amounts of bone motion cause the surgical operative site to “drift”, thereby causing undesirable implant cavity placement errors as the bone moves while a robotic bone cutter is cutting the implant cavity in the bone. Larger amounts of bone motion can cause serious cutting inaccuracies and are indicative of the bone fixation or retraction system becoming unstable. Should such larger amounts of bone motion occur, it is then necessary to immediately shut down the cutting operation and restart the cutting procedure after re-locating the position of the bone with respect to the cutting device. Specifically, the surgical team is required to remove the cutting device and its accompanying gas supply hose and irrigation, re-determine the position of the bone with respect to the cutting device, and then reinstall the cutter, gas supply, and irrigation systems before continuing with the bone cutting procedure. This can be very time consuming and frustrating for the surgical team.
SUMMARY OF THE INVENTION
As discussed above, unwanted bone motion can generate cutting inaccuracies during bone surgery. Such unwanted bone motion cannot be completely eliminated during bone surgery. Accordingly, the present invention provides a system to minimize the effects of unwanted bone motion by tracking the motion of the bone such that the unwanted bone motion can be compensated for during surgery on the bone.
The present invention provides a method for re-registration between a robotic coordinate system and an image data set, comprising: providing an image data set that has been registered within the robotic coordinate system based upon an initial bone position within the robotic coordinate system; locating at least three conserved points fixed relative to the initial bone position prior to a detectable change in bone position from the initial bone position; relocating the same at least three conserved points after bone motion may have occurred thereby determining changes in the position of the three conserve points; and re-registering the image data set within the robotic coordinate system based on the changes in position of the three conserved points.
In the present invention, intraoperatively attached fiducial markers are used to determine the position and orientation of the bone and to track bone motion over time. The intraoperatively attached fiducial markers are used to define at least three conserved points which are fixed relative to the bone. Bone motion is tracked over time by tracking the motion of the at least three conserved points over time.
In the present invention, the at least three conserved points (which are fixed relative to the bone), are located and tracked within the coordinate system of the surgical robotic arm subsequent to initially registering an image data set of the bone to the surgical robotic arm.
In one preferred aspect of the invention, the three conserved points are defined by two implanted fiducial markers. Preferably, at least one fiducial is implanted after the image data set of the bone, (which represents the shape of the bone), has been created.
First, the surgical robotic arm is registered to the bone. Initially registering the surgical robotic arm to the bone comprises determining the initial spatial relationship between the surgical robotic arm and the bone, (wherein the shape of the surface of the bone is preferably represented by an image data set).
The registration of the surgical robotic arm to the image data set of the bone can be accomplished using a variety of techniques. In certain aspects of the present invention, a variety of techniques using radio-opaque marker pins can be used.
For example, as is described in provisionally filed Patent Application entitled Bone Motion Tracking System, U.S. patent application Ser. No. 60/112,319 filed Dec. 14, 1998, and in non-provisionally filed U.S. patent application Ser. No. 09/247,818 filed on Feb. 9, 1999, incorporated herein by reference in their entirety for all purposes, marker pins are attached to the bone prior to surgery and a pre-surgical image of the bone with the marker pins attached is taken. The pre-surgical image can preferably be generated by computerized tomography (CT), digital radiography, or the like. From the image data set representing the pre-surgical image of the bone, the spatial relationship of the bone with respect to the marker pins can be determined, (ie: the position and orientation of the bone can be determined by knowing the position and orientation of the marker pins). In one aspect, the surgical robotic arm is registered to the bone by being moved to contact each of the marker pins in turn. As such, the position of each of the marker pins will be sequentially recorded in terms of the surgical robotic arm's co-ordinate system, thereby registering the surgical robotic arm to the bone. In other aspects, a digitizer arm, (which may comprise an articulated passive mechanical arm), is registered to the bone by being moved to contact each of the marker pins in turn. In this aspect, the digitizer arm is first registered to the robotic arm's coordinate system.
Alternatively, the present surgical robotic arm can be registered to the bone using marker pins by the system described in co-pending application Ser. No. 09/022,643, filed Feb. 12, 1998 now abandoned, and incorporated herein by reference in its entirety for all purposes, which describes a method and system for transforming a bone image into a robotic coordinate system based upon registering between the robotic coordinate system and the image data set: (1) two positional coordinates axially spaced apart along the bone and (2) a directional vector passing through at least one of the positional coordinates.
In alternate approaches, the present surgical robotic arm can be initially registered to the bone without the use of fiducial marker pins. For example, the initial position and orientation of the bone may be determined
Integrated Surgical Systems, Inc.
Smith Ruth S.
Townsend and Townsend / and Crew LLP
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