Surgery – Instruments – Stereotaxic device
Reexamination Certificate
1999-02-09
2001-11-27
Reip, David O. (Department: 3731)
Surgery
Instruments
Stereotaxic device
Reexamination Certificate
active
06322567
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 bons such that the unwanted bone motion can be compensated for in real time during surgery on the bone.
In a preferred aspect, the present invention provides a method of tracking and compensating for bone motion when operating on a bone with a surgical robotic cutting arm, comprising; initially registering the surgical robotic cutting arm to the bone (ie: determining the initial spatial relationship between the surgical robotic cutting arm and the bone), tracking bone motion with a bone motion detector; and compensating for the bone motion by updating the registration between the surgical robotic cutting arm and the bone as the bone moves. (Initially registering the surgical robotic cutting arm to the bone comprises determining the initial spatial relationship between the surgical robotic cutting arm and the bone such that the surgical robotic arm can be positioned to operate at a desired location or locations on the bone).
In certain preferred aspects, the system of tracking bone motion includes tracking both translational and rotational movements of the bone with a bone motion detector. In alternate preferred aspects, the system of tracking bone motion includes tracking only translational movements of the bone with a bone motion detector.
An important advantage of the present invention is that compensation for bone motion is made during surgery such that the surgical team is not forced to terminate the cutting procedure, re-register the surgical robotic arm to the bone, and then re-start the cutting procedure each time the bone moves. Instead, the present system enables the surgical robotic arm to continue to accurately cut the cavity into the bone, even during bone motion.
Determining the initial spatial relationship between the surgical robotic arm and the bone can be accomplished in a variety of ways using radio-opaque marker pins. For example, prior to surgery, the marker pins are attached to the bone 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 pre-surgical image, 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). Thereafter, 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.
An advantage of this registration method is that bone motion can be detected as the surgical robotic arm is initially registered to the bone, as follows. The spacing of the marker pins with respect to one another is initially determined at the time when these marker pins are first viewed in the pre-surgical image of the bone. As the surgical robotic arm is brought into contact with each of these marker pins in turn during the registration process, bone motion detection is achieved by observing any apparent deviations in the relative spacing among the various marker pins. In particular, should the relative spacing between a first and a second marker pin be found to be different from that which was initially observed in the bone image, this would indicate bone motion during the interval of time during which the surgical robotic arm is moved from contacting the first marker pin to contacting the second marker pin. The detection of such bone motion during initial registration can be used to shut down the registration process such that the bone can be re-stabilized prior to re-commencement of the registration process.
Alternatively, when tracking bone motion with a bone motion detection system during the initial registration of the surgical robotic arm to the bone, (for example, by tracking bone motion with a passive mechanical arm secured at its distal end to the bone), the registration process need not be interrupted and re-started, even if bone motion occurs during the initial registration process, as will be explained.
Since the marker pins remain at fixed locations on the bone as the bone moves, an advantage of the above marker pin approach to registering the surgical robotic arm to the bone is that only the position of the marker pins needs to determined with respect to the surgical robotic arm, (subsequent to determining the position of the marker pins with respect to the bone).
Another advantage of the above approach to registering
Cohan Steven M.
Mittelstadt Brent D.
Ho (Jackie ) Tan-Uyen T.
Integrated Surgical Systems, Inc.
Reip David O.
Townsend and Townsend / and Crew LLP
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