WO2003021552A2

WO2003021552A2 - Surgical tool assembly and method of practising bone surgery

Info

Publication number: WO2003021552A2
Application number: PCT/GB2002/003931
Authority: WO
Inventors: Robert Smith; James Robert Hewit; Alan Peter Slade; Stuart Brown
Original assignee: University Of Dundee
Priority date: 2001-08-31
Filing date: 2002-08-30
Publication date: 2003-03-13
Also published as: GB0121113D0; AU2002324132A1; WO2003021552A3

Abstract

There is disclosed a method of practising a bone cutting operation on an artificial prototype (44) of a bone (12). The method includes the steps of obtaining a three-dimensional (3D) image (42) of a patient's bone (12); manufacturing a three-dimensional prototype (44) of the patient's bone (12) according to the image (42); immobilising the bone prototype (44); positioning a cutting device (58) relative to the bone prototype (44); carrying out a selected practice cutting operation on the bone prototype (44) using the cutting device (58); and inspecting one or more practise cuts made during the practise cutting operation, to determine whether a corresponding cutting operation would be appropriate for conducting surgery on the patient's bone (12). There is also disclosed a surgical tool assembly (66) for carrying out the practise cutting operation.

Description

SURGICAL TOOL ASSEMBLY AND METHOD OF PRACTISING BONE SURGERY

The present invention relates to a surgical tool assembly and to a method of practising a bone cutting operation. In particular, but not exclusively, the present invention relates to a method of practising a bone cutting operation on an artificial prototype of a bone.

The life expectancy in Western economies is increasing with a concomitant rise in the incidence of age related diseases. Joint diseases, such as osteoarthritis are more common in the ageing population and result in pain and impaired mobility of the joint. Where such joint disease occurs in the lower, limbs, the personal mobility of the patient is frequently impaired. Considerable health service resources are consumed in controlling the consequences of pain and immobility; it is believed that it may be more cost effective to treat the joint disease directly. Surgical intervention frequently involves total hip or total knee replacement (TH/TKR) , using prosthetic joint components. This treatment has met with widespread success and increasing popularity. The availability of reliable prosthetic joint replacement surgery is attractive to other age groups who suffer pain and immobility in the joints of the lower limb as a result of congenital deformity, trauma or disease. However, the typical life span of less than 12 years for a total knee replacement, and the limited number of revisions (typically two) possible means that TKR is usually an unsuitable treatment for patients in the early or middle years of life. Alternative treatments to extend the life of the joint to an age where prosthetics offer a viable solution are desired. One such treatment is to surgically realign the joint surfaces so that loads through the joint are directed through healthy joint tissues and along the natural load-bearing path. This intervention is known as osteotomy. There are cost and other disadvantages relating to both knee replacement and osteotomy surgery.

Most morbidity (the requirement to carry out revisions) in TKR is attributable to loosening between the prosthetic component and the bone. The elimination of loosening is at least partly dependent upon the accuracy with which the bone stock can be selected and prepared to accept the prosthesis. Current surgical systems for preparing the bone employ jigs and fixtures which are secured around the surgical site and possess alignment features corresponding to palpable landmarks at the ankle and hip. The accuracy in placing these jigs is typically judged to be around 1-4°. Further, the surgical plan for the placement of the prostheses depends upon the surgeon' s empirical pre-operative judgement of the desired geometrical alignment of the joint and his intra-operative assessment of the viability of bone stock, both of which judgements can effect the loosening prognosis.

Osteotomies are rarely performed in the United Kingdom, since the surgery demands very high levels of skill and training. In particular, the surgeon must be able to plan and execute a three-dimensional adjustment to the alignment of the bone axes using only two-dimensional x- rays as a guide and with minimal visibility of the surgical site through the incision. The success rate of osteotomy around the knee is typically around 33-73% and the morbidity is affected by non-/delayed union, infection and fixation failure.

It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a method of practising a bone cutting operation on an artificial prototype of a bone, the method comprising the steps of: obtaining a three-dimensional image of a patient's bone; manufacturing a three-dimensional prototype of the patient's bone according to the image; immobilising the bone prototype; positioning a cutting device relative to the bone prototype; carrying out a selected practise cutting operation on the bone prototype using the cutting device; and inspecting one or more practise cuts made during the practise cutting operation, to determine whether a corresponding cutting operation would be appropriate for conducting surgery on the patient's bone.

It will be understood that the method is a method of practising a bone cutting operation outwith the human or animal body.

Preferably, the cutting device is positioned by establishing one or more points of reference on the bone prototype and positioning the cutting device with respect to said one or more points of reference. The bone prototype points of reference may correspond to points of reference previously established on the patient's bone. Thus, the location of the points of reference on the bone prototype are identical to the respective locations of the previously established points of reference on the patient's bone. Accordingly, when a patient's bone is subsequently immobilised, the cutting device may be positioned in an identical location with respect to the patient's bone as it was to the bone prototype. A surgical operation may therefore be carried out on the patient's bone which is identical to the selected, optimum practise cutting operation.

Thus, the present invention is particularly advantageous in that it allows a practice operation to be carried out on a prototype of a patient's bone, such that the optimum cutting operation may be performed on the patient following satisfactory conclusion of practice operations. In particular, this allows the optimum angle, depth, extent and number of cuts to be determined in practice operations on bone prototypes which mirror the patient's bone.

It will be understood that references herein to cutting, a cutting operation, a cutting device or cutting tool are to the removal of material from a bone or a bone prototype by any suitable operation such as sawing, drilling or the like.

The three-dimensional (3-D) image of the patient's bone may be obtained through a computed tomography (CT) scan, magnetic resonance imagery (MRI) scan and/or or by X- ray. The 3-D image may be obtained from a number of two- dimensional images; where the image is obtained by X-ray, at least two X-rays of the patient's bone may be taken on planes disposed at 90° to each other. Data obtained from the CT, MRI or X-ray scan may be converted into a three- dimensional image using appropriate computer software.

One or more, in particular two, pins may be fixed subcutaneously to the patient's bone prior to obtaining the three-dimensional image. Said one or more pins may be fiducial pins which may provide one or more points of reference for the patient's bone. Thus it will be understood that when the three-dimensional prototype of the patient's bone is manufactured, the prototype includes fiducial pins, which may both provide fixing points for restraining the bone prototype and points of reference to aid the practice cutting operation.

The 3-D prototype bone may be manufactured in a rapid prototyping process such as a stereolithography, selective laser sintering, fused deposition modelling, laminated object modelling, thermojet, or three-dimensional printing process. The bone prototype may be manufactured of a plastics material such as a polymer, for example, an ABS plastic, a laser-cured photosensitive resin, a water activated starch powder or any other bone analogue.

The bone prototype may be immobilised by coupling a jig to the bone prototype, in particular to the one or more pins, and by mounting the jig on a surgical table.

Conveniently, the cutting device is positioned with respect to points of reference such as the one or more pins and/or part of the jig. The cutting device may be orientated by detecting the location of the points of reference and adjusting the position of the cutting tool accordingly.

Preferably, the practice cutting operation comprises an automated operation, such as a robot assisted bone cutting operation. The step of carrying out the selected practice cutting operation may comprise the step of programming an automated surgical tool assembly to carry out the cutting operation and subsequently activating the surgical tool assembly. The method may still further comprise the step of emulating the practice cutting operation using an emulator, such as a light source which casts a visible reference line on the bone prototype, to indicate the direction of the cut to be performed. Alternatively, the step of carrying out the selected practice cutting operation may comprise a surgeon carrying out a manual cutting operation using a hand-held cutting tool .

According to a second aspect of the present invention, there is provided a surgical method comprising the steps of: obtaining a three-dimensional image of a patient's bone ; manufacturing a three-dimensional prototype of the patient's bone according to the image; immobilising the bone prototype; positioning a cutting device relative to the bone prototype; carrying out a selected practise cutting operation on the bone prototype using the cutting device; inspecting one or more practise cuts made during the practise cutting operation, to determine whether a corresponding cutting operation would be appropriate for conducting surgery on the patient's bone; and subsequently conducting a cutting operation on the patient's bone.

The method may further comprise immobilising the patient' s bone and positioning the cutting device relative to the patient' s bone in the same fashion as for the bone prototype according to the determined appropriate practice operation. Thus, the cutting operation conducted on the patient's bone may correspond exactly to the determined appropriate practice operation.

According to a third aspect of the present invention, there is provided a surgical tool assembly for use in the method of the first aspect of the present invention, the assembly comprising: a cutting device including a movable cutting tool; immobilising means for immobilising the bone prototype during a cutting operation and to allow registration of the location of the bone prototype with respect to the cutting tool; operation planning means including software for generating an operational cutting plan for cutting the bone prototype and for storing a selected cutting plan; and drive means for moving the cutting tool along a cutting path according to the stored operational cutting plan, to cut the bone prototype.

According to a fourth aspect of the present invention, there is provided a surgical tool assembly as claimed in claim 27. Preferably, the surgical tool assembly comprises a robotic surgical tool assembly, where the drive means may comprise a support such as an arm which is moveable in three planes of motion. Thus, advantageously, the cutting tool may be placed in any desired location with respect to the bone prototype for carrying out a cutting operation.

The cutting tool may comprise a saw having at least one oscillating blade. The cutting tool may include two saw blades overlapping such as rotary or back and forth oscillating blades, each of the blades mounted for relative movement with respect to one another. Alternatively, the cutting tool may comprise a drill or any other cutting or abrading tool.

The immobilising means may comprise a mounting assembly forming part of or being mountable to a surgical table and including one or more clamps for receiving and restraining the bone prototype. One or more, preferably two, pins may extend from the bone prototype, and the immobilising means may further comprise a jig rigidly coupled to at least two such pins. The or each pin and/or the jig may form part of a bone prototype assembly. The or each clamp may receive the jig or a pin extending from the bone prototype, the jig and/or the pin providing one or more points of reference to indicate the location of the bone prototype with respect to the cutting tool. Alternatively, the surgical tool assembly may include detection means for detecting the location of one or both of the immobilising means and the bone prototype, for orienting the cutting tool with respect to the bone prototype. The detecting means may comprise a light source and a light detector, such as a laser and a photo sensitive sensor, respectively.

The operation planning means may comprise an integrated processor or a computer interfaced with the cutting device and may include software which enables a three-dimensional image of the patient's bone to be produced and an operational cutting plan including one or more cutting paths into the bone to be defined and stored. The surgical tool assembly may further comprise a cutting tool emulator for simulating a cut to be made by the cutting tool. The emulator may comprise a light source such as a laser.

There follows a description of embodiments of the present invention, by way of example only, with reference to the accompanying drawings, in which:

Figs. 1A-1H are schematic illustrations of the steps in a method of practising a bone cutting operation, in accordance with an embodiment of the present invention;

Figs. II and 1J are schematic illustrations of a subsequent operation on a patient's bone; and

Figs. 2A-2C are perspective views of a surgical tool assembly in accordance with an embodiment of the present invention, shown during various stages of cutting a simulated bone. Referring firstly to Figs. 1A-1H, there are shown schematically various stages during a method of practising a bone cutting operation on an artificial prototype of a bone .

In Fig. 1A, an upper part of a patient's leg 10 is shown. For clarity, only the femur bone 12, which extends between the pelvis region 14 and the knee 16, is shown. In a pre-operative procedure, a jig 18 is secured to the femur 12 through two fiducial pins 20 and 22, which are mounted in holes drilled in the femur 12 in a known fashion. The jig 18 is rigid and connects the fiducial pins 20 and 22 together through coupling blocks 24 and 26 and a connecting rod 28. Two short arms 30 and 32 extend from the coupling block 20 and points of reference (POR's) 34 and 36 are provided at respective ends of the arms 30 and 32. As will be described below, these points of reference 34 and 36 allow registration of the bone location with respect to a cutting device (not shown in Fig. 1A) during a cutting operation.

When the jig 18 has been securely fitted to the femur 12, a three-dimensional image of the femur bone 12 and jig 18 is obtained, as illustrated in Fig. IB and indicated generally by reference numeral 38. The image 38 is obtained by taking a CT scan, MRI scan or x-rays of the femur 12 and jig 18. In one embodiment, the image is obtained by taking orthogonal anteroposterior (midline front to back) and mediolateral (midline left to right) views of the femur 12 and jig 18. The bone outline is then "digitised" by recording the outline co-ordinates of the femur 12 and jig 18 from the 2-D x-ray images and plotting the co-ordinates using a computer aided design package, such as AutoCad, using a processor 40, as shown in Fig. 1C. The digitised image 42 is illustrated in Fig. ID.

By feeding the data from the computer software into a rapid prototyping machine, such as a selective laser sintering machine (not shown) , which sinters a polymer powder using a C0₂ laser, a 3-D rapid prototype 44 of the patient's femur 12 and the jig 18 is obtained, as illustrated in Fig. IE. The protyped femur, jig and jig components are indicated by the same reference numerals with the adition of the superscript'.

The prototype 44 is then immobilised by mounting in a mounting assembly 46 (Fig IF) on an operating table 48, which includes clamps 50 and 52 that receive the connecting rod 28' of the prototyped jig 18'. Once the prototype 44 has been securely mounted to the operating table 48, the position of the prototype 44 with respect to the cutting device is registered in a registration process. This is done by directing the cutting device to automatically detect the location of the POR 34' and 36' on planes defined in the X, Y and Z directions illustrated in Fig. 1G. This allows the selected cutting operation to be performed, as will be described below. Fig. 1G also illustrates a cutting emulator in the form of a light source such as a laser 54, which forms part of the cutting device. The laser 54 projects a visible light beam, illustrated at 56, onto the surface of the prototype femur 12 ' , to indicate the programmed cuts 64 to be performed on the prototype 44. This allows the selected cutting operation to be verified before a cut is made.

A subsequent cutting operation is illustrated in Fig. 1H, where a cutting tool of a cutting device, in the form of a sagittal saw 58 having saw blades 60 and 62, is shown in the process of making the cuts 64. After the cuts 64 have been made in the prototype femur 12', the surgeon inspects the cuts to determine whether a corresponding cut would be appropriate for the patient. If the surgeon finds that corresponding cuts made on the femur 12 of the patient would not be appropriate, the surgeon may select an alternative operating procedure, for example having longer, deeper or more angled cuts and may carry out a further practice operation on a second prototype 44 by repeating the steps illustrated in Figs IF to 1H. It will be noted that, following manufacture of a first prototype 44, further prototypes may be made in the same fashion in a rapid prototyping process, or a mould may be constructed from the first prototype 44, such that subsequent casts may be taken. When the surgeon is happy with the selected procedure, a surgical operation may then be carried out on the patient's femur 12 by repeating the (optional) emulating and cutting steps of Figs 1G and 1H on the patient's femur 12.

This is illustrated in Fig. II and 1J, where the patient's femur 12 carrying the jig 18 has been securely fastened to the operating table 48 by the mounting assembly 46, in the same position and orientation as the prototype 44. This is verified by determining the location of the POR 34 and 36, which are in an identical location on the patient's femur 12 as the corresponding POR 34' and 36' on the prototyped femur 12 ' . The surgeon can then be sure that the optimum surgical operation may be performed on the patient .

Figs . 2A to 2C are more detailed views of various stages in the practice bone cutting operation described above. Figs. 2B and 2C illustrate a surgical tool assembly of the present invention, in the form of an automated surgical saw, indicated generally by reference numeral 66.

Like components of the assembly 66 illustrated in

Figs. 2A to 2C with the assembly parts shown in Figs. 1A to 1J share the same reference numerals with the addition of the letter "a". In Fig. 2A, a shaped test member 12a, which is curved to simulate shapes found in human bones, is fixed to a jig 18a, and a proposed cut 64a is projected onto the surface of the member 12a by an emulator laser 54a (Fig. 2B) , which is mounted on a support arm 68 of the tool assembly 66.

In Fig. 2C, a saw 58a is shown mounted on the arm 68 for carrying out the cutting operation along the line projected by the emulator 54a, and is shown immediately prior to commencing cutting of the member 12a. Associated with the surgical saw 66 is operation planning means in the form of an associated computer or an integrated processor

(not shown) which controls the operation of the saw 66.

Software such as DASYLab (Registered Trade Mark) version 5.0 (created by DATALOG of Germany) employs graphical user interfaces (GUI's) to allow the surgeon to construct data acquisition and control programs from a range of preprogrammed functional modules. This allows the surgeon to plan the operation and once the appropriate plan has been selected, the cutting paths of the operation are emulated using the laser 54a and then subsequently carried out using the saw 58a.

Various modifications may be made to the foregoing within the scope of the present invention.

Claims

1. A method of practising a bone cutting operation on an artificial prototype of a bone, the method comprising the steps of: obtaining a three-dimensional (3D) image of a patient's bone; manufacturing a three-dimensional prototype of the patient's bone according to the image; immobilising the bone prototype; positioning a cutting device relative to the bone prototype; carrying out a selected practice cutting operation on the bone prototype using the cutting device; and inspecting one or more practise cuts made during the practise cutting operation, to determine whether a corresponding cutting operation would be appropriate for conducting surgery on the patient's bone.

2. A method as claimed in claim 1, wherein the cutting device is positioned by establishing at least one point of reference on the bone prototype and positioning the cutting device with respect to said at least one point of reference .

3. A method as claimed in claim 2, wherein the at least one bone prototype point of reference corresponds to a point of reference previously established on the patient's bone.

4. A method as claimed in any preceding claim, wherein the 3-D image of the patient's bone is obtained through a computed tomography (CT) scan, magnetic resonance imagery (MRI) scan and/or or by X-ray.

5. A method as claimed in claim 4, wherein the 3-D image is obtained by taking at least two X-rays of the patient's bone on planes disposed at 90° to each other.

6. A method as claimed in claims 4 or 5, wherein data obtained from the CT, MRI and/or X-ray scan is converted into a 3-D image using computer software.

7. A method as claimed in any preceding claim, wherein at least one pin is fixed subcutaneously to the patient's bone prior to obtaining the three-dimensional image.

8. A method as claimed in claim 7, wherein there are two pins, and wherein said pins are fiducial pins which provide points of reference for the patient's bone.

9. A method as claimed in any preceding claim, wherein the 3-D prototype bone is manufactured in a rapid prototyping process .

10. A method as claimed in any preceding claim, wherein the bone prototype is immobilised by coupling a jig to the bone prototype.

11. A method as claimed in claim 10 when dependent on claim 8, further comprising coupling the jig to the at least one pin, and mounting the jig on a surgical table.

12. A method as claimed in claim 11, further comprising positioning the cutting device with respect to additional points of reference on the jig.

13. A method as claimed in any preceding claim, wherein the practice cutting operation is an automated operation, and wherein the step of carrying out the practice cutting operation comprises programming an automated surgical tool assembly to carry out the cutting operation and subsequently activating the surgical tool assembly.

14. A method as claimed in any preceding claim, wherein the method further comprises the step of emulating the practice cutting operation using an emulator.

15. A method as claimed in claim 14, wherein the operation is emulated using a light source which casts a visible reference line on the bone prototype, to indicate the direction of the cut to be performed.

16. A method as claimed in any one of claims 1 to 12, wherein the step of carrying out the selected practice cutting operation comprises a surgeon carrying out a manual cutting operation using a hand-held cutting tool.

17. A surgical tool assembly for use in the method of claim 1 the assembly comprising: a cutting device including a movable cutting tool; immobilising means for immobilising the bone prototype during a cutting operation and to allow registration of the location of the bone prototype with respect to the cutting tool; operation planning means including software for generating an operational cutting plan for cutting the bone prototype and for storing a selected cutting plan; and drive means for moving the cutting tool along a cutting path according to the stored operational cutting plan, to cut the bone prototype.

18. An assembly as claimed in claim 17, wherein the surgical tool assembly comprises a robotic surgical tool assembly, where the drive means comprises a support which is moveable in three planes of motion.

19. An assembly as claimed in either of claims 17 or 18, wherein the cutting tool comprises a saw having two overlapping saw blades, each of the blades mounted for relative movement with respect to one another.

20. An assembly as claimed in any one of claims 17 to 19, wherein the immobilising means comprises a mounting assembly mountable to a surgical table and including at least one clamp for receiving and restraining the bone prototype .

21. An assembly as claimed in claim 20, wherein at least one pin extends from the bone prototype, and the immobilising means further comprises a jig rigidly coupled to the at least one pin.

22. An assembly as claimed in claim 21, wherein the at least one pin and the jig form part of a bone prototype assembly, the at least one jig clamp receiving the jig or a pin extending from the bone prototype, the jig and/or the pin providing at least one point of reference to indicate the location of the bone prototype with respect to the cutting tool.

23. An assembly as claimed in any one of claims 17 to 21, wherein the surgical tool assembly includes detection means for detecting the location of one or both of the immobilising means and the bone prototype, for orienting the cutting tool with respect to the bone prototype.

24. An assembly as claimed in claim 23, wherein the detecting means comprises a light source and a light detector.

25. An assembly as claimed in any one of claims 17 to 24, wherein the operation planning means comprises an integrated processor or a computer interfaced with the cutting device; and software which enables a 3-D image of the patient's bone to be produced, and an operational cutting plan including at least one cutting path into the bone prototype to be defined and stored.

26. An assembly as claimed in any one of claims 17 to 25, wherein the assembly further comprises a cutting tool emulator for simulating a cut to be made by the cutting tool.

27. A surgical tool assembly comprising: a cutting device including a movable cutting tool; immobilising means for immobilising a three- dimensional prototype of a patient's bone during a practice cutting operation and to allow registration of the location of the bone prototype with respect to the cutting tool; operation planning means including software for generating an operational cutting plan for cutting the bone prototype and for storing a selected cutting plan; and drive means for moving the cutting tool along a cutting path according to the stored operational cutting plan, to cut the bone prototype.

28. A surgical tool assembly as claimed in claim 27, for use in subsequently cutting the patient's bone according to the stored operational cutting plan.