Tibial spacer saw guide

A tibial spacer saw guide for guiding the resection of a bony defect of the lateral or medial condyle of the proximal tibia to accommodate a spacer to be implanted beneath a tibial baseplate of a tibial prosthesis. The saw guide includes a plate having a plurality of locating holes corresponding in spacing and location to pins extending from the inferior surface of the tibial baseplate. The plate has medial and lateral guide edges for guiding a sagittal osteotomy where the guide edges are located relative to the locating holes, and thus relative to the pegs of the tibial baseplate. The saw guide also includes an anterior block extending from the plate and having a plurality of slots for guiding a horizontal osteotomy for the spacer of selected depth. The plate rests on an initially resected surface, and thus the horizontal osteotomy for the spacer is located relative to the initial osteotomy surface. The block is repositionable relative to the plate such that the saw guide can be used for both medial and lateral spacers of both the left and right tibias.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to surgical instruments used during 
implantation of orthopedic joint replacement prostheses, and relates more 
particularly to a saw guide for guiding the resection of bony defects of 
the proximal tibia to accommodate a spacer used with a tibial component of 
a knee prosthesis. 
2. Background Information 
Total knee joint replacement surgery involves replacing the natural 
articulating surfaces of the femur and tibia with prosthetic components 
formed of biocompatible materials providing artificial articulating 
surfaces. The femoral component is often formed of a biocompatible metal 
such as titanium or a titanium alloy, or a cobalt-chrome alloy, with an 
articulating surface that is highly polished. The tibial component is 
often formed of a biocompatible metal baseplate and a smooth articulating 
surface attached to the metal baseplate that is formed of a material such 
as ultra-high molecular weight polyethylene that provides low friction and 
a low wear rate in combination with the metal articulating surface of the 
femoral component. 
Each of the femoral and tibial components include, in addition to the 
mutually articulating surfaces, respective femur and tibia bone engaging 
surfaces. The bone engaging surfaces are often planar, or combinations of 
planar surfaces, and it is therefore necessary to resect the distal end of 
the femur and the proximal end of the tibia to provide complementary 
shaped planar bone surfaces for close fitting engagement with the planar 
bone engaging surfaces of the prosthetic components. In the case of the 
tibia, it is generally sufficient to provide a single, generally 
horizontal planar osteotomy of the proximal tibia to form a planar surface 
that mates with and engages a single planar inferior surface of the tibial 
base plate. In some cases, however, bony defects of the proximal tibia 
affect one of the lateral and medial condyles to a greater depth than the 
other. While it would be possible to perform a single planar osteotomy of 
the proximal tibia at a depth sufficient to resect the greater bony 
defect, this has the effect of resecting more bone than is desirable from 
the less affected side. It is therefore preferable to perform an initial 
planar osteotomy of the minimum depth necessary to resect the less 
affected side of the proximal tibia to provide good seating of the tibial 
base plate. A second generally horizontal osteotomy of the more affected 
side can be performed to resect that side of the proximal tibia to a 
greater depth to remove the bony defect. A spacer can then be inserted 
between the inferior surface of the tibial base plate and the deeper 
planar bone surface. A vertical sagittal osteotomy intersecting the first 
and second planar osteotomies will also be necessary to completely resect 
the bone on the more affected side. 
Because of the desirability of providing good prosthesis-to-bone contact, 
it is necessary that the osteotomies referred to above be performed with 
relative precision. The vertical sagittal osteotomy should be located 
accurately in the medial-lateral direction to ensure alignment and close 
spacing between the inner edge of the tibial spacer and the vertical bone 
surface. The two horizontal planar osteotomies of the proximal tibia 
should lie in planes that are parallel to one another or otherwise conform 
to the relationship between the upper and lower surfaces of the spacer. In 
addition, the vertical spacing between the horizontal osteotomy planes 
should accurately conform to the thickness of the spacer. While the 
surgeon will have some latitude during surgery to select the thickness of 
the spacer to be used to correct for the bony defect that is being 
resected, for reasons of practicality the spacers will usually be 
available in only a few standard thicknesses. It would therefore be 
desirable to provide a tibial spacer saw guide that can accurately guide 
the saw blade during resection of the proximal tibia to ensure a good fit 
of the spacer. 
One example of a tibial prosthesis with which the present invention can be 
used advantageously is the prosthesis described in U.S. Pat. No. 
4,963,152, issued Oct. 16, 1990, and assigned to Intermedics Orthopedics, 
Inc. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention, a saw guide is provided 
for guiding a saw blade for resecting a medial or lateral bony defect of 
an initially resected tibial plateau to accommodate a spacer to be 
implanted beneath the inferior surface of a tibial base plate. The tibial 
base plate has a first pair of medial pegs and a second pair of lateral 
pegs adapted to be received in corresponding pairs of medial and lateral 
peg holes drilled in the initially resected tibial plateau. The saw guide 
includes a plate having an inferior surface for engaging the initially 
resected tibial plateau in first and second orientations. The plate 
includes a first pair of locating holes for receiving pins therethrough 
spaced and arranged to align with the pair of medial peg holes in the 
medial side of the initially resected tibial plateau when the plate is in 
the first orientation, and a second pair of locating holes for receiving 
pins therethrough spaced and arranged to align with the pair of lateral 
peg holes in the lateral side of the initially resected tibial plateau 
when the plate is in the second orientation. The plate further includes a 
lateral guide edge for guiding a saw blade for making a sagittal osteotomy 
when the plate is in the first orientation, the lateral guide edge being 
spaced and oriented relative to the first pair of locating holes. The 
plate further includes a medial guide edge for guiding a saw blade for 
making a sagittal osteotomy when the plate is in the second orientation, 
the medial guide edge being spaced and oriented relative to the second 
pair of locating holes. A block is attached to the plate anteriorly of the 
tibial plateau and extends generally in the medial-lateral direction, the 
block including at least one saw guide surface for guiding a saw blade for 
making a generally horizontal osteotomy of one of the medial or lateral 
sides of the tibial plateau, the saw guide surface being displaced from 
the inferior surface of the plate a distance substantially equal to the 
thickness of the spacer to be accommodated. The peg holes drilled in the 
initially resected tibial plateau serve as a reference for locating the 
sagittal osteotomy, and the initially resected surface of the tibial 
plateau serves as a reference for locating the generally horizontal 
resection to accommodate the spacer, thereby assuring accurate fit of a 
spacer which is dimensioned relative to the pegs and undersurface of the 
tibial base plate. 
It is an object of the present invention to provide an instrument for 
accurately guiding a saw blade to perform osteotomies of the proximal 
tibia to resect bony defects to accomodate a spacer to be received 
inferiorly of a tibial prosthesis. Other objects and advantages of the 
present invention will be apparent from the following descriptions of a 
preferred embodiment with reference to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, there is shown a prior art tibial baseplate 10 
comprising the metal portion of a two-piece asymmetric prosthetic tibial 
component, wherein the second portion (not shown) comprises a plastic 
tibial insert that engages the superior surface 12 of baseplate 10 and 
provides a bearing surface for articulation with a femoral component. 
Tibial baseplate 10 is designed to approximate the natural anatomic shape 
of the tibial plateau. Projecting perpendicularly from the inferior 
surface 14 are four cylindrical pegs, including medial-posterior peg 16, 
medial-anterior peg 18, lateral-posterior peg 20, and lateral-anterior peg 
22. Between the pair of medial pegs 16, 18 and the pair of lateral pegs 
20, 22, are two countersunk holes 24 and 26 on the anterior-posterior 
centerline 28, which accept fully-threaded cancellous bone screws (not 
shown). Tibial baseplate 10 is described further in U.S. Pat. No. 
4,963,152, which description is hereby incorporated by reference. 
Referring to FIG. 3, there is illustrated tibial spacer saw guide 30 which 
is useful for preparing the tibial plateau to receive a tibial baseplate 
of the general type shown in FIGS. 1 and 2, i.e., a tibial baseplate 
having a pair of medial pegs and a pair of lateral pegs extending from the 
inferior surface. More particularly, saw guide 30 is useful for resecting 
a bony defect of the medial or lateral condyle of the tibia to receive a 
spacer 32 to be placed beneath the inferior surface of the tibial 
baseplate 10, as shown in FIG. 4. Spacer 32 includes a pair of holes 
therethrough through which the corresponding pair of medial or lateral 
pegs of tibial baseplate 10 are received. Thus, spacer 32 is located 
relative to the pegs of the tibial baseplate. 
Tibial spacer saw guide 30 includes two principal components, plate 34 and 
block 36. 
Plate 34 is a generally rectangular flat plate having a substantially 
planar inferior surface 38 and a substantially planar superior surface 40. 
Plate 34 is bounded by a lateral guide edge 44, a medial guide edge 46, 
and end edges 48 and 50. A longitudinal rectangular groove 52 in inferior 
surface 38 of plate 34 extends the length of plate 34 and is open at end 
edges 48 and 50. A longitudinal slot 54 extends substantially the length 
of plate 34 and is aligned with groove 52. Slot 54 extends through plate 
34 from superior surface 40 to the bottom wall of groove 52. In each 
corner of plate 34, there is situated a pair of locating holes for 
receiving therethrough locating pins 56 and 56. Right medial locating 
holes 60 and 62 are situated proximate the corner defined by end edge 48 
and medial guide edge 46. Right lateral locating holes 64 and 66 are 
situated proximate the corner defined by end edge 48 and lateral guide 
edge 44. Left medial locating holes 68 and 70 are situated proximate the 
corner defined by end edge 50 and medial guide edge 46. Left lateral 
locating holes 72 and 74 are situated proximate the corner defined by end 
edge 50 and lateral guide surface 44. Associated with each pair of medial 
or lateral locating holes is a third stabilizing hole situated on the same 
side of groove 52. Stabilizing hole 76 is associated with locating holes 
60 and 62. Stabilizing hole 78 is associated with locating holes 64 and 
66. Stabilizing hole 80 is associated with locating holes 68 and 70. 
Stabilizing hole 82 is associated with locating holes 72 and 74. Block 36 
is a generally elongated rectangular block having a planar superior 
surface 90, inferior surface 92, sides 94 and 96,7 and ends 98 and 100. A 
rectangular tongue 102 extends from superior surface 90 transversely to 
block 36 proximate end 100. Tongue 102 is sized and dimensioned to be 
received in groove 52 of plate 34 in a close-fitting but slidable 
relationship. Planar superior surface 90 of block 36 engages planar 
inferior surface 38 of plate 34 such that block 36 is maintained 
substantially parallel to plate 34. Tongue 102 interacts with groove 52 to 
maintain the longitudinal axis of block 36 substantially perpendicular to 
the longitudinal axis of plate 34. Saw guide slots 104 and 106 extend 
through block 36 from side 94 to side 96, and extend to end 98. Slot 104 
is parallel to superior surface 90 and displaced 4 mm therebelow. Slot 106 
is also parallel to superior surface 90 but is displaced 8 mm therebelow. 
Each of slots 104 and 106 are sized to received therethrough a saw blade 
107 such that the saw blade can reciprocate in the lateral-medial 
direction and can be displaced in the anterior-posterior direction, but is 
restrained from motion in the vertical direction. A pair of stabilizing 
holes 108 and 110 extend through block 36 from side 94 to side 96 and are 
provided to optionally receive stabilizing pins 112 and 114 therethrough. 
A thumbscrew 116 having a knurled knob 118 includes a threaded shaft that 
extends through longitudinal slot 54 of plate 34 and is received in a 
correspondingly threaded bore in the superior surface of tongue 102 of 
block 36. When thumbscrew 116 is tightened, the superior surface 90 of 
block 36 is drawn into tight engagement with the inferior surface 38 of 
plate 34 to prevent relative movement between plate 34 and block 36. When 
thumbscrew 116 is loosened slightly, block 36 can be slid from one end of 
plate 34 to the other, with tongue 102 sliding in groove 54. When 
thumbscrew 116 is loosened to a greater extent, block 36 can be rotated 
180.degree. about the axis of thumbscrew 116 and positioned to extend in 
the opposite direction from that illustrated. Thus, it will be understood 
that block 36 can be oriented in any one of four possible orientations 
relative to plate 34. In addition, within any one general orientation, 
some repositioning in the anterior-posterior direction is permitted by 
loosening thumbscrew 116. 
Referring in particular to FIG. 3, use of tibial spacer saw guide 30 cain 
be described as follows. Using a tibial cutting guide as generally 
understood in the prior art, an initial osteotomy of the proximal tibia is 
performed to resect the least involved condyle of the tibial plateau to 
leave a flat proximal bone surface 117. It should be understood that the 
initial osteotomy is generally similar to the osteotomy that would be 
performed in the prior art technique, except that the initial osteotomy 
will not completely resect the bony defect of the most affected side 
because the natural tibial plateau on the most affected side will be below 
the level of the initial osteotomy. After checking the initially cut 
surface 117 for flatness, a proximal tibial drill guide as known in the 
prior art is selected from among several sizes available, and the best 
fitting drill guide is positioned onto the initially cut surface of the 
proximal tibia. The drill guide has six holes corresponding in location to 
pegs 16, 18, 20 and 22, and screw holes 24 and 26, of a correspondingly 
sized tibial baseplate 10 of FIG. 1. Holes are drilled in the tibial 
plateau at the site of each of the drill guide holes. So far the procedure 
has been similar to the prior art technique note: involving spacers and 
has not yet utilized the apparatus of the present invention. 
At this point, the present invention comes into use. For the purposes of 
the present description, it should be assumed that the greater bony defect 
involves the lateral condyle of the right tibia, and use of saw guide 30 
will be described with that assumption, as illustrated in FIG. 3. The 
drill guide is removed and the pair of medial holes corresponding in 
location to pegs 16 and 18 of tibial baseplate 10, in the non-defective 
side of the initially resected surface, are filled with smooth guide pins 
56 and 56. The associated hole on the medial side of the resected tibial 
surface corresponding to screw hole 24 of tibial baseplate 10 is filled 
with a stabilizing pin 119. 
Block 36 is assembled to plate 34 proximate end 50 so as to extend 
laterally in the medial-lateral direction. Plate 34 is placed over pins 
56, 58 and 119 such that the pins pass through holes 60, 62 and 76, 
respectively, and plate 34 is lowered until inferior surface 38 rests 
flush against initially resected surface 117 of the proximal tibia. When 
so placed, block 36 is disposed anteriorly of the tibia. One or more pins 
112 and 114 can optionally be inserted through holes 108 and 110 in block 
36 and driven into the anterior surface of the tibia to provide additional 
fixation and stability of saw guide 30 relative to the proximal tibia. A 
vertical sagittal osteotomy is made using, for example, a one inch wide 
saw blade 120 held flush against lateral guide edge 44. The vertical 
osteotomy is made approximately 4 mm or 8 7216 mm deep, depending on the 
size of the defect and the size of the spacer that has been selected. 
Preferably, following completion of the vertical osteotomy, a free saw 
blade is left imbedded in the bone to act as a protector to avoid 
undercutting the non-involved tibial plateau surface when the horizontal 
osteotomy is performed. As used herein, the term "horizontal osteotomy" 
refers to an osteotomy that is generally transverse to the longitudinal 
axis of the tibia assuming that the longitudinal axis of the tibia is 
oriented vertically. The term "horizontal" includes not only orientations 
substantially perpendicular to the longitudinal axis of the tibia, but 
also orientations deviating from true horizonal at angles up to about 
45.degree.. A horizontal osteotomy is made using a similar saw blade 107 
inserted through either slot 104 or 106, depending on the size of the 
defect and the size of the spacer that has been selected. The saw blade is 
moved in the anterior-posterior direction and in the medial-lateral 
direction until the affected side has been completely resected, as shown 
in FIG. 3. Saw guide 30 and pins 56, 58 and 119, and pins 112 and 114, if 
used, are then removed from the tibia. 
Following testing with a trial spacer and trial tibial base plate, and 
trial femoral component, the spacer 32 (FIG. 4) is secured to the inferior 
surface of the prosthetic tibial base plate using bone cement or other 
securing means as may be desired, and the composite base plate and spacer 
are placed on the prepared surface of the tibia and secured in place with 
a pair of cancellous bone screws received through screw holes 24 and 26 of 
tibial baseplate 10. An appropriately sized polyethylene tibial insert 122 
(FIG. 4) is placed on the superior surface 12 of tibial baseplate 10, 
followed by implantation of the femoral component on the appropriately 
prepared distal femur. 
It should be understood that the above-described procedure could also be 
performed to resect the medial condyle of the right tibia, or the medial 
or lateral condyle of the left tibia, using the same saw guide 30. For 
instance, by reversing the orientation of block 36 so that end 98 extends 
medially in the medial-lateral direction, and by using locating holes 64, 
66 and 78 of plate 34 to fix plate 34 to the lateral side of the tibial 
plateau, the medial side of the right tibia could be resected to 
accommodate a spacer. In addition, by moving block 36 proximate end 48 of 
plate 34 and rotating plate 34 so that block 36 is disposed anteriorly of 
the tibia, saw guide 30 can be used on the left tibia. To assist the 
physician in orienting block 36 properly relative to plate 34, saw guide 
30 is provided with alignment indicia. For example, end edge 50 is 
provided with a pair of scribe marks 124 and 126 disposed on opposite 
sides of groove 52 and labeled "R LAT" and "R MED", respectively. Another 
scribe mark 128 on side 96 of block 36 aligns with scribe mark 124 when 
block 36 and plate 34 are oriented as shown in FIG. 3. This indicates that 
saw guide 30 is set up for guiding an osteotomy of the right lateral 
proximal tibia. The vertical sagittal osteotomy is guided by lateral guide 
edge 44 labeled "LATERAL CUT SURFACE." Another scribe mark (not shown) 
corresponding to scribe mark 128 is located on side 94 of block 36 and 
aligns with scribe mark 126 when saw guide 30 is set up for guiding an 
osteotomy of the right medial proximal tibia. In that case, the vertical 
sagittal osteotomy is guided by guide edge 46 labeled "MEDIAL CUT 
SURFACE." In analogous fashion, scribe marks corresponding to scribe marks 
124 and 126 are disposed on end edge 48 of plate 34, but are labeled "L 
LAT" and "L MED." It should be understood that regardless of which tibia 
is involved, lateral guide edge 44 will always be used for the sagittal 
osteotomy for a lateral spacer, and medial guide edge 46 will always be 
used for the sagittal osteotomy for a medial spacer. It should further be 
understood that the vertical sagittal cut is located particularly 
accurately because the lateral guide edge is positioned relative to the 
locating holes, which in turn correspond to the location of the pegs on 
the inferior surface of the tibial baseplate. Thus, insofar as the spacers 
themselves are dimensioned relative to the tibial baseplate pegs, the 
medial-lateral fit between the spacer and resected bone is quite good. 
Similarly, the horizontal osteotomy guide slots are located relative to 
the inferior surface of the plate 34, which corresponds to the inferior 
surface of the tibial baseplate. Thus, insofar as the spacers themselves 
are dimensioned relative to the inferior surface of the tibial baseplate, 
the superior-inferior fit between the spacer and resected bone is likewise 
quite good. 
While the present invention has been illustrated and described with 
particularity in terms of a preferred embodiment, it should be understood 
that no limitation of the scope of the invention is intended thereby. The 
scope of the invention is defined only by the claims appended hereto. It 
should also be understood that variations of the particular embodiment 
described herein incorporating the principles of the present invention 
will occur to those of ordinary skill in the art and yet be within the 
scope of the appended claims. For example, while slots 104 and 106 of 
block 36 of the preferred embodiment are illustrated as being 
substantially parallel to inferior surface 38 of plate 34, it should be 
understood that slots 104 and 106 can be disposed at an acute angle up to 
about 45.degree. sloping downwardly and away from the plane of plate 34 in 
the medial-lateral direction. Such an orientation would allow a horizontal 
osteotomy to be performed to accommodate a wedge-shaped spacer.