System and method for ligament graft placement

[0002] This application is a continuation of prior application No. PCT/EP99/01778 filed Mar. 17, 1999, which is incorporated herein by reference in its entirety.

[0003] The present invention relates to a method and system for computerized in-situ planning and guidance of ligament graft placement.

[0004] Treatment of injuries and other conditions associated with a joint of an individual often involves the re-attachment or reconstruction of one or more ligaments. For example, anterior cruciate ligament (ACL) rupture is a very common sports-related injury. Ligament reconstruction with autogenous graft using a minimally invasive endoscopic approach has become a standard therapy in ACL replacement. Endoscopic surgical approaches seek to minimize trauma to the individual.

[0005] Unfortunately, approximately 40% of ACL ligaments are improperly located, e.g., misplaced as a result of reconstructions performed by traditional endoscopy. Such improper ligament placement can lead to premature degeneration of knee structures, which degeneration can eventually necessitate total knee joint replacement. To facilitate proper ligament placement, a practitioner is preferably able to identify and locate anatomical landmarks associated with the joint. For example, proper ligament reconstruction or positioning involves steps such as the drilling of tunnels that are properly placed with respect to the anatomical landmarks, avoiding the impingement of ligaments and surrounding tissues, ensuring that ligament elongation does not exceed 10% (collagen fibre ruptures beyond 10% elongation), selecting proper graft tension and position to restore knee stability; and obtaining proper graft fixation in good quality bone.

[0006] A portion of ligament misplacements are attributable to the restricted, local endoscopic view, which fails to provide surgeons with a global overview of ligament position, such as that seen in traditional postoperative X-rays. For example, the endoscopic view limits a surgeon's ability to identify landmarks, which would otherwise assist in proper ligament placement.

[0007] A method for determining the femoral point of graft attachment during ACL replacement is disclosed in European Patent Application No. 0603089 to Cinquin et al. The disclosed method concerns the determination of a femoral point of graft attachment with respect to a tibial graft attachment point such that the distance between these two points remains invariant during knee flexion and extension. The positions within an on-site three-dimensional coordinate system of a reference and a pointer, which are both provided with energy emitting markers, are determined by means of a three-dimensional position measurement system, such as the OPTOTRAK position measurement system, Northern Digital, Waterloo, On. The position measurement system measures the position of the markers with respect to the on-site three-dimensional coordinate system. Therewith, the position of the tip of the pointer is determinable by means of a computer.

[0008] The Cinquin method comprises the steps of (1) attachment of a first reference at the tibia; (2) positioning of the pointer tip at a previously determined point T₁and measuring the position of the pointer tip with respect to the first reference; (3) Positioning of the pointer tip at several points P₁at the trochlea of the femur close to that position where the invariant point is expected; (4) Calculation of the distances of point T₁and each of the points P1; (5) Displacement of the femur with respect to the tibia and calculation of the variations of the distances between T₁and each of the points P₁; (6) Selection of that point P₁among points P₁which shows the most invariant distance.

[0009] The Cinquin method measures knee movement to obtain a “functional” placement of the ligament that respects certain elongation criteria. The disadvantage of this method is that anatomical placement criteria such as a general overview of graft position with respect to the whole anatomy of the joint are not obtained.

[0010] The present invention is related to a ligament replacement system, which allows both consideration of functional and anatomical criteria in a variety of graft types, surgical philosophies and surgical techniques. The system preferably provides realtime computerized in-situ planning and guidance of ligament graft placement. Most preferably, the system provides planning and guidance for anterior cruciate ligament insertion.

[0011] One embodiment of the system comprises a position measurement device in communication with a computer to determine the position and orientation of objects in a three dimensional coordinate system. The three dimensional coordinate system includes at least one organ, such as a femur or tibia, of an individual. Objects to be tracked comprise at least three markers, which can be configured to emit, receive, or reflect energy, such as light or acoustic energy. For example, energy emitters can include light sources, such as light emitting diodes emitting in the visible or infrared, acoustic transmitters, or conductive coils suitable for establishing a detectable magnetic field. Energy receiving means include light detectors, such as photodiodes or charge coupled devices. Microphones or Hall-effect elements may also be used.

[0012] To sense the position of energy emitting markers, the system includes at least three energy detecting elements, such as three light detectors. The three energy detecting elements cooperate with the energy emitting markers to determine the position of each marker associated with an object to be tracked. Based on the respective positions of markers associated with the tracked object, the position and orientation of the tracked object are determined.

[0013] The system preferably includes a plurality of reference bodies, which can be used to determine the position and orientation of an organ of an individual. The reference bodies are preferably rigid, having at least three markers each. Each reference body preferably comprises an attachment element, such as a screw or pin, with which the reference bodies can be attached to an organ, such as a bone. For example, respective reference bodies can be attached to the femur and tibia. In one embodiment, the reference markers are fiducial markers.

[0014] The system also includes a pointer and an endoscope. The pointer includes markers, which allow the position and orientation of the pointer to be determined. The pointer includes a pointer tip having a known spatial relationship to the markers. Thus, the position of the pointer tip can be determined from the positions of the markers. The endoscope preferably includes markers that allow the position and orientation of the endoscope to be determined in the three dimensional coordinate system. In a preferred embodiment, the pointer and endoscope are integral with one another.

[0015] The computer is configured to determine the position and orientation of the reference bodies, endoscope, and pointer based upon the position and orientation of the associated markers. The pointer and the endoscope are preferably configured as a one-piece computer-integrated endoscopic instrument.

[0016] An embodiment of the system includes a medical imaging device, which preferably includes an X-ray source and an X-ray receiver, for gathering medical image data, which is transferred to the computer either directly in numerical format or upon digitizing a radiographic film of the image. The computer is configured to process the image such as by magnifying a portion of the image. The imaging device can be used preoperatively and/or intraoperatively.

[0017] In a preferred embodiment, the system includes an ultrasound device, having associated markers, which allow the position and orientation of an ultrasound head of the ultrasound device to be determined as discussed above. The ultrasound device is in communication with the computer, which can process and display ultrasound data acquired by the ultrasound device. In a preferred embodiment the ultrasound device is an A-mode ultrasound device configured to emit and receive an ultrasound beam along a preferably known axis to allow realtime signal processing and or display of ultrasound data.

[0018] The computer is preferably configured, such as with a memory or software, to display a three-dimensional representation of the connection between ligament attachment points determined using the pointer. When ligament attachment points are identified, the computer can display a preferably three dimensional representation of the connection between ligament attachment points previously determined using the pointer or ultrasound device. The computer is preferably configured to display a ligament during knee flexion and extension.

[0019] One embodiment of the system further comprises a drilling device having at least three markers. The drilling device has a drill tip having a known spatial relationship relative to the markers. The drilling device markers allow the position and orientation of the drilling device and drill tip to be determined in the three dimensional coordinate system. Thus, the position of the drill tip can be determined relative to a predetermined location of a patient's bone. For example, the drill tip can be positioned relative to the bone as previously planned using the computer. The computer is preferably configured to allow at least one of the image data and ultrasound data to be used to plan the position and orientation (path) of a hole to be drilled. The path of a hole being bored by the drill can be monitored and displayed by the computer. Thus, the actual path can be compared to the previously planned drill path to allow the practitioner to minimize deviations between the actual procedure and the preoperative plan. In one embodiment the drill is guided to allow the computer to control the drilling path.

[0020] Another embodiment of the invention relates to a method for ligament reconstruction. The method comprises obtaining medical image data, such as at least one X-ray of a joint associated with the ligaments. For example, if the ligaments of the knee are to be reconstructed, the medical image data comprises respective portions of both the femur and tibia. The medical image data is transferred to a computer. Based upon the medical image data, ligament graft placement with respect to anatomical landmarks of the first and second bones is determined based upon computer manipulation of the medical image data. Preferably the medical image data are prepared as one or more templates.

[0021] The positions of the landmarks, such as points, on the surface of first and second bones of an individual are determined with respect to a three dimensional coordinate system. In a preferred embodiment, the first and second bones are respectively the femur and tibia of an individual. The determination of the landmark positions preferably comprises use of at least one of an ultrasound device and a pointer.

[0022] The ultrasound device, which is in communication with the computer, is used to provide ultrasound data of the first and second bones. The ultrasound device includes markers that allow a position measuring device to determine the position and orientation of the ultrasound device to be determined in the three dimensional coordinate system. The ultrasound data preferably comprises data indicative of the position of landmarks of the first and second bones. For example, the ultrasound data preferably comprises data indicative of a position of at least one of the posterior femoral and tibial condyles.

[0023] The pointer comprises a pointer tip, which can be positioned relative to a landmark. The position measurement system is used to determine the position and orientation of markers associated with the pointer. Based on the known position and orientation of the markers of the pointer, the position and orientation of the pointer tip can be determined. The position of the landmark on the surface of the first and second bones are determined based on the spatial relationship between the pointer tip and the landmark.

[0024] Based upon the landmark position data, a mathematical relationship between the intraoperative position of the first and second bones and an image of the first and second bones from at least one of the medical image data and ultrasound data is determined. Preferably, reference bodies having markers are associated with the first and second bones to allow the position and orientation of the bones to be determined in the three dimensional coordinate system. The placement of a ligament graft is determined functionally and anatomically based upon the locations data, medical image data, and ultrasound data.

[0025] The present invention is described below in relation to FIG. 1, which shows a ligament reconstruction system according to the invention.

[0026] Referring to FIG. 1, a ligament reconstruction system 25 is configured for performing ligament reconstruction or other restorative procedure involving a joint, such as a knee, of an individual. System 25 preferably includes a positioning measuring device 14, which is configured to determine the position and orientation of an object in a three dimensional coordinate system 20, which preferably includes at least a first and second bone of an individual. The first and second bones are preferably the individual's femur 8 and tibia 9.

[0027] Determining the position and orientation of an object is referred to herein as “tracking” the object. Tracking an object preferably involves determining the position of at least two and preferably three or more markers associated with the object. The markers preferably have a known spatial relationship relative to the object to be tracked. Based on the known spatial relationship, the position and orientation of the object can be determined based upon the positions of the associated markers. Device 14 is in communication with computer 3 to allow the position and orientation of a tracked object to be thereby displayed.

[0028] In a preferred embodiment, the markers are configured to emit energy and position measuring device 14 is configured with at least three energy detection elements 29 to detect energy emitted by the markers. For example, energy emitting markers can include light sources, such as light emitting diodes, which emit in the visible or infrared, acoustic transmitters, or conductive coils suitable for establishing a detectable magnetic field. The energy detection elements can include, for example, light detectors 29, such as photodiodes or charge coupled devices. A suitable position measurement device is the OPTOTRAK 3020 available from Northern Digital, Canada. The OPTOTRAK device tracks the position of infrared light emitting diodes, which are positioned in a known spatial relationship to objects to be tracked. It should be understood, however, that tracking can be accomplished where the markers are configured to detect energy and the position measuring device is configured to emit energy to be detected by the markers.

[0029] A drilling device 15 having at least three markers 6 is an example of an object trackable by position measuring device 14. The drilling device has a drill tip 17 having a known spatial relationship relative to markers 6. Position measuring device 14 determines the position and orientation of markers 6 in the three dimensional coordinate system. Based upon the known spatial relationship between drill tip 17 and markers 6, the position of drill tip 17 is determined.

[0030] Computer 3 is preferably configured to allow at least one of medical image data and ultrasound data, which are described below, to be used in planning the position and orientation (path) of a hole to be drilled in a bone. The path of a hole being bored by the drill can be monitored and displayed by the computer. Thus, the actual path can be compared to the previously planned drill path to allow the practitioner to minimize deviations between the actual procedure and the preoperative plan. In one embodiment the drill is guided to allow the computer to control the drilling path.

[0031] Ligament reconstruction system 25 also includes a plurality of reference bodies 4, 5, for determining the position and orientation of an individual's bone in the three dimensional coordinate system. The reference bodies 4, 5 are preferably rigid and include respective markers 27, 28, which are preferably configured to emit energy. Each reference body 4, 5 preferably includes a respective attachment element, such as pins or screws 32, 33, with which the reference bodies can be releasably attached to a bone. For example, reference body 4 is shown as being attached to femur 8. The position and orientation of femur 8 can be determined based upon the position and orientation of markers 27 attached thereto.

[0032] System 25 also includes a pointer 10 and endoscope 11, which cooperate to allow a practitioner to digitize landmarks of the femur 8 and tibia 9. Digitizing a landmark comprises determining the position of the landmark in the three dimensional coordinate system, as discussed below. Pointer 10 includes markers 35, which allow the position and orientation of the pointer to be determined in the three dimensional coordinate system. The pointer preferably includes a pointer tip 16 having a known spatial relationship to the markers 35. Based upon the known spatial relationship, the position of the pointer tip 16 can be determined from the position and orientation of the markers 35.

[0033] To digitize a landmark, such as a point associated with an individual's bone, pointer tip 16 is positioned to have a known spatial relationship to the landmark to be digitized. Preferably, pointer tip 16 is positioned to touch the landmark. A display 12 of endoscope 11 allows the practitioner to visualize the pointer tip 16 and the landmark. Display 12 can be integrated with a display of computer 3. The position in the three dimensional coordinate system of the landmark to be digitized is determined from the position of pointer tip 16, which is determined as described above. In a preferred embodiment, the pointer and endoscope are integrated. The integrated pointer-endoscope includes an endoscopic palpation hook 16′.

[0034] Certain landmarks, such as the posterior femoral and tibial condyles, are difficult to obtain by direct digitization with the pointer 10. For this reason, the device according to the invention preferably includes an A-mode ultrasound device 13 equipped with markers 36. Ultrasound device 13, which is in communication with computer 3, determines the distance between an ultrasound device head 18 and an intersection point 19 of an ultrasound beam 34 with the surface of a bone. Because the position and orientation of ultrasound device head 18 is determined by position measuring device 14, the orientation of beam ultrasound beam 34 can also be determined. The orientation of ultrasound beam 34 and the distance of ultrasound device head 18 from intersection point 19 are used to determine the position of intersection point 19 within the three-dimensional coordinate system 20 by means of a coordinate transformation performed via the computer 3.

[0035] Intraoperatively measured landmarks on the surface of a patient's bone are used to establish a mathematical relationship between the intraoperative position of the bone and an image of the bone as represented by the medical image data. Such a transformation of coordinates on the medical image may be computed into coordinates within the on-site three dimensional coordinate system 20 therewith allowing functional and anatomical considerations of the graft placement.

[0036] System 25 includes a medical imaging device 26 for obtaining medical image data. Medical imaging device 26 preferably includes an X-ray source 1 and an X-ray receiver 52 suitable for acquiring medical image data in the form of X-rays of a patient's anatomy. Alternatively, the medical image data can comprise images obtained using with other imaging technologies such as magnetic resonance. In any case, the medical image data can be obtained pre-operatively and/or intra-operatively. Preoperative medical image data will typically be available in either numerical or analog formats. Where the medical image data are available in numerical format, such as in digitized format, the medical image data can be transferred directly to a computer 3. Where the medical image data are available in an analog format, such as a radiographic image, the image can be scanned, digitized and transferred to computer 3.

[0037] To obtain intra-operative medical image data, medical imaging device 26 preferably includes a fluoroscope. Intra-operative medical image data are preferably obtained of standard orientations, such as, for example, anterior-posterior and medial-lateral orientations. The medical image data preferably include an image of a sizing element, such as a ruler having radio-opaque markings. Images of the radio-opaque markings appear in the medical image data. Computer 3 is configured to determine the magnification of the medical image data, such as an image of a knee, based upon the images of the radio-opaque markings.

[0038] Computer 3 may be used to display an image 8′ of the femur and an image 9′ of the tibia. When ligament attachment points are identified, the computer can display a preferably three dimensional representation of the connection 40 between ligament attachment points previously determined using the pointer or ultrasound device. The medical image data are preferably prepared as X-rays templates. Desired ligament placement with respect to anatomical landmarks, e.g. the medial and lateral condyles or the trochlea, can be planned directly on the medical image displayed via computer 3 through manipulations of the templates.

[0039] While the above invention has been described with reference to certain preferred embodiments, it should be kept in mind that the scope of the present invention is not limited to these. Thus, one skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the claims set forth below.