AU729426B2 - Tibial resection instrument - Google Patents

Description

P:\OPER\PHH\87857-9g.AW.DOC 24/11/00 lA- Tibial Resection Instrument The present invention relates to orthopedic surgical instruments and more particularly relates to a tibial cutting guide instrument for resecting the patient's proximal tibia for installing a knee prosthesis.

In knee joint replacement surgery, a surgeon typically affixes two prosthesis components to the patient's femur and tibia. These replacement components are typically known as the femoral component and the tibial component.

The femoral component is placed on a patient's distal femur after the surgeon makes a plurality of surgical cuts. One common type of femoral prosthesis has a J-shape. A femoral prosthesis is usually metallic, having a highly polished outer femoral articulating surface.

A common type of tibial prosthesis uses a laterally extending tray that is shaped to conform to •the patient's proximal tibia after the proximal tibia has been cut transversely by the surgeon.

The tibial prosthesis also includes a stem or plug that extends generally perpendicular to the tray from the center of the tray. The stem is placed in a surgically formed opening that extends S•into the patient's intramedullary canal from the transverse cut formed on the proximal tibia.

A plastic polymeric insert is attached to the tibial tray. This insert provides a tibial articulating surface that articulates with the femoral articulating surface as the patient's tibia moves through a full range of motion with respect to the patient's femur.

25 One of the problems with knee joint replacement surgery is that of accurately fitting the patient.

Each patient has a different bone structure and geometry. Even though the surgeon uses x-rays to study a particular patient's anatomy at the knee, the surgeon does not have a perfect appreciation of the patient's anatomy until after the knee has been surgically exposed and the surgeon begins to make cuts on the femur and the tibia.

P:\OPER\PHH\87857-98.AME.DOC 24/11/00 -2- Knee prosthetic components are not available in infinite sizes. The surgeon must examine the patient's anatomy, make the requisite surgical cuts and install prosthesis components that fit.

When the surgeon uses bone cement to fix the prosthesis in place, any inconsistencies in the prosthesis fit may, to some extent, be compensated by the bone cement. However, in instances where bone cement is not used, but rather the ingrowth of natural bone is relied on to fix the prosthesis in place, the fit of the prosthesis must be exceptionally good. There is therefore a need to provide tibia resection apparatus which ensures an improved fit for the prosthesis.

It is an object of the present invention to meet this need.

A number of tibial components have been patented that relate to tibial components having a tray, a plastic insert with articulating surface, and a stem portion that provides initial fixation when the prosthesis is implanted. Other patents have issued that relate to cutting instrumentation for preparing the patient's proximal tibia to receive a tibial prosthetic insert as part of knee joint replacement surgery.

US patent 4,016,606 discloses a knee prosthesis that includes a tibial component with a tray and •with a stem adapted to be received in a longitudinal bore in the patient's femur. The stem has 20 one end that is integral with a depending generally spheroidal surface having generally the same radius as the radius of the spheroidal depression in the insert.

In US patent 4,601,289 there is disclosed a femoral trial prosthesis/rasp assembly used in hip implant surgery. The assembly includes a handle that grips the combination trial prosthesis/rasp 25 in a secure manner by clamping over and locking on to a post on the trial prosthesis/rasp which later serves as a mounting piece for a femoral prosthesis head used in trial reductions.

US Patent 4,938,769 discloses a tibial prosthesis for use during a total knee arthroplasty procedure which includes a modular two part tibial component comprising an in-bone anchorage assembly to which is removably attached a tibial tray adapted to receive and retain a bearing insert. Removal of the tray permits access to the interface between the bone and anchorage P:\OPER\PHH\S87857-98.AMEDOC 24/11/00 -3assembly in the event removal or revision are necessary. In preferred embodiments, the invention affords hybrid fixation of the tibial prosthesis in that bone cement for immediate fixation and adaptation for longer term bone ingrowth are featured. The patent also discusses the use of porous coatings to enhance fixation.

US Patent 4,938,769 further discloses an end bone anchorage assembly for a tibial prosthesis that includes an axially elongated central stem and a plurality of elongated fixation pegs spaced from the stem. The stem and the pegs have proximal and distal ends. The proximal ends of the stem define and attachment table. A plurality of structural links interconnect the pegs and the stem. Means is provided for removably attaching a tibial tray to the assembly wherein each of the pegs is connected to the stem by the structural link.

US Patent 5,080,675 discloses a tibial component for a replacement knee prosthesis comprising a tibial tray for connection to a suitably prepared tibia, the tray carrying fixed lateral and medial condylar bearing components. Only the medial component has a shock absorber located beneath it.

US Patent 5,137,536 issued to Tomishisa Koshino describes a tibial component for an artificial knee joint. The tibial component includes a plate section having an upper surface and a pair of 20 bearing surfaces parts that are adapted to be in sliding contact with a femoral component. A stem portion extends downwardly from a lower surface of the plate section. A pair of blade like members extend obliquely and posteriorly from the stem. The plate section has a lower surface with a plurality of elongated grooves for improving affinity with respect to the surrounding bone, the grooves including a first group of grooves and a second set of group of grooves 25 extending perpendicularly to the first group of grooves.

.1 US Patent 5,246,459 discloses a modular tibial support peg operable to secure a tibial component of a knee joint prosthesis to a tibia having a groove. The modular tibial support peg includes a cylindrical body with a ridged outer surface operable to engage the groove in the tibia. The modular tibial support peg further includes a plurality of spikes extending inferiorly from the cylindrical body. The spikes are operable to engage the tibia at the inferior end of the P:\OPER\PHH\87857-98.AME.DOC 24/11/00 -4groove.

According to the present invention, there is provided a tibial cutting guide instrument for resecting a patient's proximal tibia to receive a tibial prosthesis comprising: an instrument body having mounting means for attaching the instrument body to a patient's proximal tibia; said mounting means including a rod that can track the patient's intramedullary canal so that the rod enables the surgeon to reference surgical cuts with respect to the patient's intramedullary canal; the instrument body having at least one cutting guide for guiding a surgeon's cutting blade during cutting of the patient's proximal tibia; and adjustable stylus means carried by the instrument body for setting a depth of cut at either of the patient's medial and lateral condylar surfaces, said adjustable stylus means comprising two probes that are adjustably mounted on the instrument body.

The instrument of the present invention facilitates improved preparation of a patient's proximal S: tibia with a surgical saw by guiding the saw when shaping the patient's proximal tibia with cuts to receive a tibial implant.

20 Preferably, the probes are generally parallel.

Preferably, the probes are independently adjustable relative to the instrument body, and adjustment of a selected probe relative to the instrument body conveniently also adjusts the distance between the selected probe and the cutting guide(s). The instrument body may further comprise indicia means for indicating the distance between each probe and the cutting guide(s).

Advantageously, each probe has a toothed rack thereon and the instrument body carries means for engaging a selected tooth of the toothed rack. The instrument preferably comprises means for locking the or one of the stylus probes to the instrument body at a selected position along the length of the probe.

The instrument may be provided with, for example, one or two cutting guides.

P:\OPER\PHH\87857-98.AME.DOC 24/1 1/00 The or each cutting guide preferably comprises a cutting guide slot, and the or each guide slot may define a plane that transversely intersects the rod.

In one example of a use of a preferred embodiment of an instrument in accordance with the invention, the patient's tibial intramedullary canal is first drilled to receive an intramedullary rod. The surgeon then places the rod in the intramedullary canal and mounts the cutting guide instrument on the rod above the patient's proximal tibia. The cutting instrument has transverse cutting guide surfaces for guiding a surgical saw during an initial cutting of the proximal tibia.

The adjustable stylus means references the proximal tibia before cutting begins. The surgeon then sets a selected depth of cut with the adjustable probes and engages the proximal tibial surface with the two probes.

After the depth of cut has been set using the stylus means, the proximal tibia is cut with a first transverse cut. During this first cut, the saw tracks the cutting guide surfaces and then engages the proximal tibial bone tissue. The cutting instrument with the stylus means is then removed.

A second cutting instrument may then be mounted on the rod above the patient's proximal tibia.

The second cutting instrument has guide surfaces externally of the proximal tibia for guiding •a surgical saw blade and a cutter thereon that includes multiple blades for cutting longitudinally 20 into the proximal tibial. After the secondary cutting instrument is positioned to a selected depth within the proximal tibia, a secondary transverse cut is made on the proximal tibia using the secondary cutting instrument. The saw first tracks the guide surfaces externally of the proximal tibia and then tracks a cutting guide surface on the blades.

Preferably, the primary and secondary cuts are made generally perpendicular to the rod and thus S. to the patient's intramedullary canal.

The cutter on the secondary cutting instrument may include a plurality of flat blades that are thrust completely into the patient's proximal tibial bone tissue. The blades are imbedded in the proximal tibia. The top surface of the cutter blades may be slightly below the surface of the first transverse cut. This allows the surgeon to use the secondary cutting instrument to track not only P:\OPER\PHH\87857-98.AME.DOC 24/11/00 -6the secondary cutting instrument externally of the tibia but also to track a guide surface provided on the upper surface of the cutter blades that have been imbedded in the patient's proximal tibial bone tissue.

One embodiment of an instrument in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a perspective schematic view illustrating preliminary tibial preparation; FIGURE 2 is a schematic perspective view illustrating attachment of an ankle clamp and the preferred embodiment of the instrument of the present invention illustrating the tibial cutting block and tibial stylus portions thereof; FIGURE 3 is a perspective view illustrating the tibial cutting block and the tibial stylus portion of the instrument shown in Figure 2; FIGURE 4 is a fragmentary perspective view illustrating a cutting of the proximal tibial using the tibial cutting block shown in Figure 3; FIGURE 5 is a perspective exploded view illustrating the tibial cutting block and the tibial stylus portion of the instrument of Figure 2; FIGURE 6 is an exploded perspective view illustrating the tibial stylus portion shown in Figure 20 FIGURE 6A is a sectional elevational fragmentary view illustrating the tibial stylus portion shown in Figure 6; FIGURE 7 is a top view illustrating the tibial stylus portion shown in Figure 6; FIGURE 8 is partial section view illustrating the tibial stylus portion shown in Figure 6; FIGURE 9 is partial perspective view of the tibial stylus portion shown in Figure 6; FIGURE 10 is a fragmentary view of the tibial stylus portion shown in Figure 6; FIGURE 11 is another fragmentary sectional view of the tibial stylus portion shown in Figure 6; FIGURE 12 is a view similar to Figure 8; FIGURE 13 is a front elevational view of the tibial cutting block shown in Figure FIGURE 14 is a top view of the tibial cutting block shown in Figure PAOPER\P-IJ\87857-9S.AME.DOC 24/11/00 -7- FIGURE 15 is a sectional view of the tibial cutting block shown in Figure FIGURE 16 is a partial sectional view of the tibial cutting block shown in Figure FIGURE 17 is a perspective view illustrating placement of an embodiment of a tibial secondary prep-guide portion used after an instrument according to the present invention; FIGURE 18 is a perspective view illustrating the tibial secondary prep-guide of Figure 17 and a secondary finishing of the proximal tibia; FIGURE 19 illustrates installation of a trial tibial prosthesis in the patient's proximal tibia; FIGURE 20 illustrates the trial femoral prosthesis and the trial tibial prosthesis installed respectively on the patient's distal femur and proximal tibia and prior to rotation to the tibial trial prosthesis; FIGURE 21 is a perspective view of the tibial secondary prep-guide portion of Figure 17; FIGURE 22 is a frontal elevational view of the tibial secondary prep-guide of Figure 17; and FIGURE 23 is an elevational side view of the tibial prep-guide of Figure 17; Figures 1-4 illustrate a preliminary preparation of the patient's distal tibia as part of knee joint replacement surgery. In Figure 1, the patient's tibia 10 is shown as is the proximal tibia 11. A 20 drill 13 is used to track the patient's intramedullary canal 12 for receiving a reamer 21. Also shown in Figure 1 is the patient's femur 14 that has already been surgically prepared to receive a trial femoral prosthesis. The distal femur 15 is typically prepared with anterior and posterior cuts that are parallel to each other, a distal cut that is generally perpendicular to the anterior and posterior cuts, and diagonally extending chamfer cuts that extend between the distal cut and the 25 respective posterior and anterior cuts.

In Figure 2, an ankle clamp 16 has been installed at the patient's ankle 17 and with an alignment sleeve 18 that is positioned generally parallel to the patient's tibia. The sleeve 18 provides a coupling 19 for forming a connection with the bottom of a tibial cutting guide 20. Ankle clamps 16 are commercially available and can be seen for example in the Steele patent 5,197,944.

P:OPER\PHH\87857-98AMEDOC 24/11/00 -8- In Figure 3, the tibial cutting guide 20 can be seen placed adjacent the patient's proximal tibia 11. In Figures 3 and 5-6, the tibial cutting guide 20 can be seen attached to the tibial stylus and the assembly of cutting guide 20 and stylus 50 being attached to reamer 21 mounted in the patient's intramedullary canal. Stylus 50 is shown more particularly in Figures 5-12. Cutting block 20 is shown more particularly in Figures 13-16.

Cutting block 20 includes a block body 22 that includes a pair of upper flanges 23 and a pair of lower flanges 24. Slots 25, 26 extend between the upper flanges 23 and the lower flanges 24.

The slots 25, 26 provide a guide for a flat cutting blade such as the cutting blade 73 shown in Figure 4 which can be a commercially available powered saw. The saw blade 73 cuts through the patient's proximal tibia 11 as shown in Figure 4 along a line 74 that is generally perpendicular to the patient's intramedullary canal. In Figure 4, the block 20 has been attached to the proximal tibia 11 using a plurality of bone spikes Tibial cutting block 20 further provides a center portion 27 that can be used to attach the cutting block 20 to the tibial stylus 50 and to ankle clamp 16 at coupling 19. The cutting block body 22 provides a lower attachment portion 28 having a plurality of cylindrical bores 29 therethrough as shown in Figures 13 and 14. These cylindrical openings 29 provide a cylindrical shape that corresponds generally to the outer configuration of a bone spike 30. One or more bone spikes 20 can be placed through a corresponding plurality of the openings 29 for affixing the block 20 to the patient's proximal tibia after alignment has been accomplished using elongated reamer rod 21 placed in the patient's intramedullary canal, the stylus 50, and ankle clamp 16.

o* Vertical rod 31 extends from coupling 19 to center portion 27 oftibial cutting block 20. A set screw 32 threadably engages opening 33 of central portion 27 of cutting block 20. Cylindrical socket 34 receives the upper end of vertical rod 31. The set screw 32 can be tightened against the rod as it occupies the cylindrical socket 34.

An upper cylindrically-shaped internally threaded opening 35 allows the cutting block 20 to be attached to tibial stylus 50. Vertical post 36 extends between stylus 50 and cutting block The post 36 has a central longitudinal axis that is perpendicular to the plane defined by slots P:\OPER\PHH\87857-98.AME.DOC 24/11/00 -9- 26. Further, the central longitudinal axis of post 36 is parallel to the central longitudinal axis of reamer rod 21 that is mounted in the patient's intramedullary canal. The post 36 has a lower end 37 with a pair of flanges 38, 39 having a recess 40 therebetween.

An upwardly projecting portion 41 of the center portion 28 of cutting block 20 registers in the recess 40. Further, the flanges 38, 39 closely conform to the projecting portion 41 upon assembly. A threaded connection can be used to form a connection between the threaded opening 35 and bolt 49 that extends through vertical bone 46 of vertical post 36. A bolted connection can be used to assemble the vertical post 36 to the cutting block 20, for example.

A pair of shoulders 44, 45 at the upper end of vertical post 36 register in an elongated slot 53 on tibial stylus 50. The upper end 43 of post 36 has a transverse cross section that corresponds in size and shape to the transverse cross section of the longitudinally extending slot 53. Slot 53 extends through horizontal beam 51 of tibial stylus 50. The slot 53 communicates with a longitudinal opening 52 in the upper surface of the horizontal beam 51. A transverse probe holder 54 extends at generally right angles to the beam 51. A bushing 55 extends upwardly from the connection between beam 51 and probe holder 54. The bushing 55 provides a vertical open ended bore 56 that receives reamer 21. Set screw 57 can be used to tighten bushing 55 and the entire tibial stylus 50 to reamer 21. Internally threaded opening 70 receives the set screw 20 57.

•Probe holder 54 includes a pair of sides 58, 59 each having an elongated vertically extending probe 60, 61 respectively. The probe holder 54 has an upper generally flat surface 62 that is Soo*.: o perpendicular to the central longitudinal axis of bore 56 and to the central longitudinal axis S 25 reamer rod 21. Each probe 60, 61 moves vertically in an opening 66, 67 respectively. A pair of horizontal openings 68, 69 carry detent locking members 63, 64 respectively. The detent locking members 63, 64 can be spring loaded with springs 97, 98. Each of the detent locking members 63, 64 have openings that allow the probes 60, 61 to pass therethrough. Each probe 61 provides a rack having a plurality of vertically spaced teeth 76 thereon (see Figure 6).

Spaces between the teeth 76 are engaged by the respective detent locking member 63, 64 at stop 96 when they are released, thereby affixing the position of each of the probes 60, 61 relative to P:\OPER\PHIH\87857-98.AME.DOC 24/11/00 the probe holder 54. A stop pin 101 holds each detent locking member 63, 64 in its opening 68, 69.

Longitudinal opening 52 is surrounded by side walls 72 and by longitudinally extending shoulders 71. This allows the placement of a bolt 49 into slot 52 and through the center of vertical bore 46 of vertical post 36 for attaching to threaded opening 35. Further, the head 43 of the bolt 49 rests on the shoulder 71 transferring load thereto.

In Figures 17-18 and 21-23, there can be seen tibial secondary prep guide 75 which is used after removal of and initial cutting of the tibia using the cutting block 20 and stylus 50. Guide 75 has an instrument body 76 that includes a pair of spaced apart vertical posts including the post 77 and the post 82. Post 77 carries a cylindrical cutting element 78 with a plurality of circumferentially spaced and radially extending cutting blades 79-81. The post 82 supports a pair of flanged portions including upper flanges 83 and lower flanges 84.

A pair of flat cutting blade guide slots 85, 86 are positioned between the upper flanges and the .0 lower flanges 83, as shown in Figures 21-23. During use, the surgeon places the tibial secondary prep guide over the reamer 21 that is installed in the patient's intramedullary canal.

This registers the three cutting blades 79-81 and the cylindrical cutting element 78 at the center 20 of the patient's proximal tibia 11, as shown in Figure 17.

.The surgeon hammers the flat side 88 of instrument body 76 driving the cutting blades 79-81 into the proximal tibia 11 as shown in Figures 17-18. The surgeon hammers the surface 88 until the blades 79-81 are just beneath the surface of proximal tibia 11 as shown in Figure 18. This allows the surgeon to shave a layer of tissue from proximal tibia 11 with great precision. The saw blade 89 is supported not only by the flanges 83, 84, but also by the upper surfaces 90 of Sblades 79-81 which are in a common plane with the upper surface 91 of the flange 84, as shown in Figure 31. The dotted line 102 in Figure 21 shows the path taken by saw blade 89 to secondarily cut the proximal tibia.

After the secondary cut is made to the proximal tibia 11, a trial prosthesis can be installed on P:\OPER\PIH\87857-98.ANE.DOC 24/11/00 -11 the patient's distal tibia 11. In Figures 19-20 a tibial trial prosthesis 92 is shown as installed into the patient's intramedullary canal 12. The tibial trial prosthesis 92 can include three components, a metallic plate or tray 93, a stem or plug 94, and a plastic trial insert 95. In Figure a tibial prosthesis 92 has been installed by the surgeon on the patient's proximal tibial 11.

The surgeon has also installed a trial femoral prosthesis 100 on the distal femur The following table lists the parts numbers and parts descriptions as used herein and in the drawings attached hereto.

.4

*OS

o Seoo

S

P:\OPER\PHM\87857-98.AME.DOC 24/11/00 12 S S es S S S S

S.

S

'*SSS*S

0

*SSS

S

*SSS

Part Number 11 12 13 14 16 17 18 19 20 21 22 23 24 25 26 27 28 29 PARTS LIST Description tibia proximal tibia intramedullary canal drill femur distal femur ankle clamp ankle alignment sleeve coupling tibial cutting guide elongated reamer rod cutting block body upper flange lower flange horizontal slot horizontal slot center portion attachment portion cylindrical bores P:\OPER\PMH878S7-9g.AME.DOC -24/l1/00 -13 bone spikes 31 vertical rod 32 set screw 33 internally threaded opening 34 cylindrical socket internally threaded opening 36 vertical post 37 lower end 38 flange 39 flange recess 41 projecting portion 43 head 44 shoulder 45 shoulder *46 vertical bore 47 recess 0 0 48 recess 49 bolt tibial stylus 51 horizontal beam 51 horizontal beam P:\OPER\PHH\87857-98.AME.DOC 24/11/00 14- 52 longitudinal opening 53 longitudinal opening 54 probe holder bushing 56 vertical open ended bore 57 set screw 58 side 59 side probe 61 probe 62 flat surface 63 detent locking member oo

S

64 detent locking member 55 °65 bolted connection 66 opening 67 opening **68 horizontal opening 69 horizontal opening 70 internally threaded opening 71 longitudinally extending shoulder 72 side wall 73 saw blade P:\OPER\PH-H\87857-98.AME.DOC 24/1100 74 transverse cut tibial secondary prep guide 76 body 77 vertical post 78 cylindrical cutting element 79 blade blade 81 blade 82 vertical post 83 upper horizontal flange 84 lower horizontal flange 85 cutting guide slot @0 o: 86 cutting guide slot g.

87 open ended vertical bore 88 flat surface 89 blade upper surface 91 upper surface 92 trial prosthesis 93 tray 94 stem insert P:\OPER\PHH\87857-98.AME.DOC -24/11/00 -16- 96 stop 97 spring 98 spring 99 opening 100 opening 101 stop pin 102 transverse cutting plane Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

The reference to any prior art in this specification is not, and should not be taken as, an 10 acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

but not the exclusion of any other integer or step or group of integers or steps.

S".o.

Se

Claims (12)

1. A tibial cutting guide instrument for resecting a patient's proximal tibia to receive a tibial prosthesis comprising: an instrument body having mounting means for attaching the instrument body to a patient's proximal tibia; said mounting means including a rod that can track the patient's intramedullary canal so that the rod enables the surgeon to reference surgical cuts with respect to the patient's intramedullary canal; the instrument body having at least one cutting guide for guiding a surgeon's cutting blade during cutting of the patient's proximal tibia; and adjustable stylus means carried by the instrument body for setting a depth of cut at either of the patient's medial and lateral condylar surfaces, said adjustable stylus means comprising two probes that are adjustably mounted on the instrument body.

2. The instrument of claim 1 wherein the probes are independently adjustable relative to the instrument body. 20

3. The instrument of claim 2 wherein adjustment of a selected probe relative to the instrument body also adjusts the distance between the selected probe and the cutting guide(s).

4. The instrument of any one of claims 1 to 3 wherein the probes are generally parallel.

The instrument of any one of claims 1 to 4 wherein the instrument body further comprises indicia means for indicating the distance between each probe and the cutting guide(s).

6. The instrument of any one of claims 1 to 5 wherein each probe has a toothed rack thereon, and the instrument body carries means for engaging a selected tooth of the toothed P:\OPER\PHH\87857-98.AME.DOC 24/11/00 18 rack.

7. The instrument of any one of claims 1 to 6 further comprising means for locking a stylus probe to the instrument body at a selected position along the length of the probe.

8. The instrument according to any one of claims 1 to 7 wherein said instrument is provided with one cutting guide.

9. The instrument according to any one of claims 1 to 7 wherein said instrument is provided with two cutting guides.

The instrument according to any one of the preceding claims wherein the or each cutting guide comprises a cutting guide slot.

11. The instrument of claim 10 wherein the or each guide slot defines a plane that transversely intersects the rod.

12. A tibial cutting guide instrument according to claim 1 and substantially as herein •e described with reference to the accompanying drawings. SDATED this 24th day of November, 2000 25 SMITH NEPHEW, INC. By DAVIES COLLISON CAVE Patent Attorneys for the applicant