Patent Application
20090157192
Implantation of a replacement joint is an increasingly common treatment for joint failures caused by injury or disease. One of the most commonly replaced joints is the hip. Known hip replacement joints include a large hemispherical acetabular component to replace the acetabulum in the pelvis and a femoral component having a head portion that is received in the acetabular component. The replacement procedure involves using a large bone reamer to create a hemispherical pocket in the pelvis into which the acetabular component is seated. The femoral component, in turn, is attached to the end of the femur. The replacement joint components are inserted through an incision in the patient's body. This incision often must be relatively large in order to accommodate the relatively large acetabular component. As is well known, a larger incision can lead to increased stress on the patient.
Because the pocket in the pelvis in which the acetabular component seats is hemispherical, the acetabular component is capable of rotating relative to the pelvis with two degrees of freedom before it is affixed in place. The acetabular component can be secured in place using cement or bone screws. In order to ensure proper fit, and hence operation, of the replacement joint, the acetabular and femoral components should be sized and oriented to match the bone structure of the patient. However, until it is secured in place, the acetabular component is capable of rotating relative to the pocket in the pelvis. Thus, getting the acetabular component into the proper alignment is very difficult and often the final alignment is merely an estimate or educated guess by the surgeon as to the proper position. Unfortunately, if the acetabular component is misaligned, problems can arise with the replacement joint including a limited range of motion or a joint dislocation.
The invention provides a replacement joint for a human body and a method of installing such a replacement joint. A ball portion of the replacement joint is installed on an end of a first bone. A receptacle having an engagement surface that has an aspherical configuration is formed in a second bone. A socket portion of the replacement joint is inserted in the receptacle so as to receive the ball portion on the first bone. The socket portion has an engagement surface with an aspherical configuration complementary to the engagement surface of the receptacle in the second bone. The configurations of the engagement surfaces of the socket portion and the receptacle in the second bone are such that inserting the socket portion in the receptacle in the second bone provides the socket portion with at least four degrees of constraint.
Referring now more particularly to
For a total hip replacement, the prosthetic joint includes both a ball portion 12 and an acetabular or socket portion 14. In this case, the ball portion 12 can include a stem or other connecting portion for connecting the ball portion 12 to the femur 16 and a generally spherical ball supported on the connecting portion (see e.g.,
For receiving the ball portion 12 at the end of the femur 16, the socket or acetabular portion or component 14 of the prosthetic joint 10 defines a generally hemispherical pocket or cup within which the ball portion 12 can move with three degrees of freedom. The acetabular socket component 14 is attached to the patient's pelvis 18 and in particular is mounted in a cavity or receptacle 20 that is formed in the pelvis 18. As will be appreciated from the following description, the acetabular socket component 14 of the present invention is equally applicable to total hip replacement procedures in which the end of the femur is replaced with a completely new ball portion as well as partial hip replacement procedures where a new prosthetic acetabular socket is installed and the entire original femur head is maintained or a only a portion of the original femur head is replaced.
Current replacement acetabular sockets only have three degrees of constraint when they are placed in the mating cavity formed in the bone. In particular, as noted above and as shown in
According to the present invention, to enable a surgeon to more precisely align and orient the acetabular component relative to the patient's pelvis, the acetabular socket component 14 and the receptacle 20 in the patient's pelvis 18 are configured such that at least four degrees of constraint are provided when the acetabular socket component is inserted in the receptacle. This is accomplished by providing the acetabular socket component 14 and, in turn, the mating receptacle 20 formed in the pelvis with complementary aspherical configurations. More specifically, the acetabular socket component 14 and the mating receptacle 20 have engagement surfaces with complementary aspherical configurations (i.e., non-spherical or non-hemisherical) that interengage one another so that the receptacle 20 formed in the pelvis better grips and retains and the acetabular socket component 14 and in such manner that rotation of the actetabular socket component 14 relative to the pelvis 18 is prevented. As a result, a surgeon is able to position the acetabular socket component 14 in a highly precise manner, which should lead to a reduction in subsequent problems, including dislocations, with the replacement joint 10.
Any configuration that provides the necessary minimum of four degrees of constraint can be used for the engagement surfaces of the acetabular socket component 14 and the receptacle 20 in the pelvis. For example, according to one relatively simple embodiment shown in
The acetabular socket component 14, as well as the ball portion 12, can be constructed of any suitable medically implantable materials such as metals, ceramics or plastics. Moreover, in a known manner, the ball and acetabular socket components 12, 14 could be provided with porous surfaces that would allow bone growth into the implant itself thereby helping improve retention of the replacement joint. The components of the replacement joint also could be provided with a surface coating that stimulates bone growth around the implant.
More complex shapes could also be used for the engagement surface of the acetabular socket component 14. Moreover, to allow the acetabular component 14 to be fed into the pelvis region of a patient using a smaller incision, thus making the hip joint replacement procedure less invasive, the component 14 could be divided into a plurality of smaller elements 22. In such a case, the receptacle 20 for the acetabular socket can also be divided into a plurality of cavities 24 each of which receives a respective element 22 of the acetabular socket. Again, in order to allow for precise placement and orientation of all of the elements of the acetabular socket component 14, each element 22 and each mating cavity 24 of the receptacle 20 can have complementary aspherical configurations that provide each element with at least four degrees of constraint when inserted into its respective cavity. An illustrative embodiment of such an arrangement is shown in
In the embodiment of
The acetabular socket 14 of the present invention and any sub-elements 22 thereof can be secured in the receptacle 20 in the pelvis 18 using any suitable means including for example cement and/or one or more bone screws. Alternatively, one or more mechanical engagement features could be formed directly into the acetabular socket 14 and mating receptacle 20. For example, as shown in the embodiment illustrated in
The receptacle 20 and/or receptacle cavities 24 in the bone for receiving the one or more elements 22 of the acetabular socket 14 of the invention can be formed using conventional bone cutting tools. It is particularly advantageous if these bone cutting tools are supported and manipulated by medical robots or manipulators. As is known, such robots and manipulators can provide a number of advantages to both patients and medical practitioners. In particular, a robot or manipulator can enhance the dexterity of a surgeon/operator and even allow the surgeon to manipulate the tool in ways the surgeon would not be capable of achieving when using his own hands.
The robots or manipulators that can be used to help install the replacement joint 10 of the present invention can be master-slave controlled manipulators in which the surgeon inputs and/or movement signals to the “slave” manipulator via a master or haptic interface that operates through a controller or control console. Alternatively, the robot or manipulator can be a unit that is intended to be pre-programmed with the required tool movements before the surgical procedure thereby eliminating the need for a slave robot or manipulator. Of course, the robot or manipulator can be designed to operate using a combination of these two concepts with some of the required tool movements being pre-programmed and with the surgeon providing other positioning or movement signals during the actual procedure through a slave manipulator. Whether or not a haptic interface is provided, the manipulator would be under the control of a surgeon in some manner.
As will be appreciated, the one or more cavities 24 in the bone for receiving the one or more elements 22 of the acetabular socket component 14 have relatively complex shapes, particularly as compared to the bone reamer formed hemispherical cavities used to receive conventional replacement acetabular sockets. For example, the embodiment of the invention illustrated in
An illustrative embodiment of a robotic surgical system including a master-slave manipulator 36 that can be used installing the replacement joint 10 of the present invention and in particular cut the cavity or cavities 22 for receiving the acetabular socket component 14 is shown schematically in
Based on the signals provided by the controller 42, the manipulator 36 executes the desired movement or operation of the tool 34. Thus, any desired dexterity enhancement can be achieved by setting up the controller 42 to perform the appropriate adjustments to the signals sent from the haptic interface 38. For example, this can be accomplished by providing the controller 42 with software which performs a desired dexterity enhancement algorithm. Software dexterity enhancement algorithms can include position scaling (typically downscaling), force scaling (up-scaling for bone and cartilage, downscaling for soft tissue), tremor filtering, gravity compensation, programmable position boundaries, motion compensation for tissue that is moving, velocity limits (e.g., preventing rapid movement into brain, nerve or spinal cord tissue after drilling through bone), and, as discussed in greater detail below, image referencing. These and other examples of possible algorithms are well known in the field of robotics and described in detail in published literature. The ZMP SynqNet® Series Motion Controllers which employ the SynqNet system and are available from Motion Engineering of Santa Barbara, Calif. are one example of a suitable controller for use with the present invention (see www.synqnet.org and www.motioneng.com). Another example of a suitable controller is the Turbo PMAC available from Delta Tau Data Systems of Northridge, Calif.
The robotic surgical system could further have an associated intra-operative positioning sensing or navigation system 44. The navigation system 44 can be configured to monitor not only the position of the tool 34 but also the position of the bone in which the acetabular socket component 14 is to be implanted (e.g., the pelvis) during the joint replacement procedure. The navigation system 44 also can also be configured to monitor the position of the femur during the procedure including during procedures in which a ball portion is being installed on the femur. The position information regarding the tool 34, the femur 16 and the pelvis 18 generated by the navigation system 44 can be communicated back to the controller 42 such that the “real time” position of the tool and the relevant bones can be taken into account in whatever control algorithms are being executed by the controller. Moreover, the navigation system 44 and controller 42 can be configured so to be able to predict the final position of the femur after it is engaged with the acetabular socket component.
With an intra-operative navigation system 44, one of the first steps of the joint replacement procedure can be determining the desired position for the acetabular socket component 14 in the pelvis 18 and then inputting information concerning that desired position into the navigation system 44 and/or controller 42. This can also be done for the ball portion 12 if one is to be installed. This information can then be used by the controller 42 and navigation system 44 to help direct operation of the manipulator 36 during the procedure. Moreover, during the procedure the navigation system 44 and controller 42 can constantly monitor the position of the tool 34 and bones 16, 18 relative to the initial desired position for the replacement joint components and adjust as necessary the control algorithms or provide any necessary warning signals. Those skilled in the art will appreciate that any three dimensional, six degree of freedom position tracking or navigation technology can be used for the navigation system such as optical triangulation or electromagnetic tracking. Such systems are well known in the field of neuro, spine and other types of surgery.
The intraoperative navigation system 44 can further include an image guidance system 46 so that as replacement procedure is performed the position of the tool 34 can be rendered against a preoperative image (e.g., magnetic resonance, computerized tomography, ultrasound or x-ray). If desired, during the procedure, the image data against which the position of the tool is rendered can be updated to provide real time image data using, for example, CT, MR or the like. A combined image guidance and position tracking system is the StealthStation® system available from Medtronic of Minneapolis, Minn.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
