WO2012020460A1

WO2012020460A1 - Real time knee balancer

Info

Publication number: WO2012020460A1
Application number: PCT/JP2010/005062
Authority: WO
Inventors: Masahisa Tanimoto; Yoshihiro Aoki; Tetsuya Kiyono
Original assignee: Johnson and Johnson KK
Current assignee: Johnson and Johnson KK
Priority date: 2010-08-13
Filing date: 2010-08-13
Publication date: 2012-02-16
Anticipated expiration: 2013-02-13
Also published as: JP5642878B2; JP2013537452A

Abstract

A balancer includes a base plate (3) having a gap scale (25), a slider (7) having a gap pointer (65n) and an angular scale (65) and being movable translationally and vertically with respect to the base plate (3), a top plate (5) having an angular pointer (51), being swingable with respect to the slider (7) and vertically movable together with the slider(7), and a resilient member (9) biasing the top plate (5) upwards with respect to the base plate (3). When a biasing force of the resilient member (9) causes the base plate (3) to engage the tibia and the top plate (5) to engage the femur, cooperation of the gap scale (25) of the base plate (3) and the gap pointer (65n) of the slider (7) indicates a vertical position of the top plate (5) with respect to the base plate (3), while cooperation of the angular scale (65) of the slider (7) and the angular pointer (51) of the top plate (5) indicates an inclination of the top plate (5) with respect to the base plate (3).

Description

REAL TIME KNEE BALANCER

The present invention relates to an apparatus capable of measuring the gap and the balance between the femur and the tibia in execution of a total knee replacement, and more particularly, to an apparatus capable of measuring with ease and in real time the gap and the balance under load.

During the artificial knee joint replacement, measurement of the gap and balance between the femur and the tibia may be required, and various apparatuses related to such measurement have been proposed.

Patent Citation 1 discloses an apparatus that has a ratchet type screw jack made up of a jack base portion and a jack movable portion, and fixes an engaging plate extending long from the jack base portion at the tibia by nails while placing a swingable supporting plate similarly extending long from the jack movable portion below the femur, uses a torque wrench to lift the supporting plate with the jack function and push up the lower surface of the femur.

According to the apparatus disclosed in Patent Citation 1, the jack is opened with the torque wrench until the torque reaches a predetermined value, and after lifting up the supporting plate (i.e., the lower surface of the femur) to a certain height position, the amount of swing of an arm extended towards the jack from the supporting plate is read from an angle scale provided on the jack, giving the balance between the femur and the tibia.

Patent Citation 2 discloses an apparatus including a lower member, a swingable upper member, a coil spring disposed between the upper and lower members, and an eccentric shaft for locking the upper and lower members at the closest position to each other, a scale serving both as a gap indicator and an angular indicator being provided on the lower member and a pointer for pointing at the scale being provided on the upper member.

According to the apparatus disclosed in Patent Citation 2, adjustment and checking of the ligament balance can be achieved by setting the upper and lower members locked at the closest position to each other between the femur and the tibia, and vertically expanding the upper and lower members by unlocking them, and reading the scale (the lower member) pointed at by the pointer (the upper member).

Japanese Patent No. 4095919 (U.S. Patent No. 7,156,853) Japanese Unexamined Patent Application, First Publication No. 2008-183083

The apparatus disclosed in Patent Citation 1 sets the gap and reads the angle at that point rather than measuring the gap, due to the construction employing the jack, and differs in the required application and function. The left-right asymmetry requires left and right apparatuses to be separately prepared, generating concerns about cost. Further, the construction in which the scale is read at the jack remote from the measuring target makes accurate measurements fairly difficult. Furthermore, the construction, which is difficult to make compact and lightweight, generates concerns about burden on the operator (the surgeon or the like) and the subject (the patient).
In actual measurement, measurements may be performed sequentially at various desired angles within the range from flexion to extension of the knee joint, and in such a case, the problems arises of having to repeat a cycle of opening the jack, measuring, and closing the jack for every measurement, which is a cumbersome procedure.

Due to the construction in which the scale serves both as a gap indicator and as an angle indicator, the apparatus disclosed in Patent Citation 2 requires a considerable proficiency to timely and accurately measure (separately read) both of them. Further, the large freedom of movement in the upper member makes for poor reproductivity in the readings of the scale. Furthermore, since it appears to lack a mechanism or consideration for slowing down the rapid expansion (moving away) of the upper and lower members when unlocked, there are concerns about unintentional damage to the femur and tibia.

It should be noted that, for the development and improvement of the total knee replacement, the associated companies of the applicant of the present invention (DePuy companies) provided CAS Ligament Tensor (Product Number: 129901080) to the market, and it has been well received. The Ligament Tensor may be the same as the present invention in that it is inserted between the femur and the tibia to move apart the two, but, it does not have its own measuring functions and is used in combination with a navigation system. The present invention can be described as a creation of a very unique idea on an extension of this technology.

In light of the above, an object of the present invention is to provide an apparatus capable of measuring in real time and accurately the gap and the balance between the femur and the tibia without the use of a navigation system.

A first aspect of the invention is characterized by a balancer insertable between a femur and a tibia, including:
a base plate having a gap scale,
a slider having a gap pointer and an angular scale and being movable translationally and vertically with respect to the base plate,
a top plate having an angular pointer, being swingable with respect to the slider, and vertically movable together with the slider, and
a resilient member biasing the top plate upwards with respect to the base plate,
wherein, when a biasing force of the resilient member causes the base plate to engage the tibia and the top plate to engage the femur, cooperation of the gap scale of the base plate and the gap pointer of the slider indicates a vertical position of the top plate with respect to the base plate, and at the same time, cooperation of the angular scale of the slider and the angular pointer of the top plate indicates an inclination of the top plate with respect to the base plate.

A second aspect of the invention is characterized in that, in the first aspect, the top plate is connected to the slider via a shaft and is swingable around the shaft.
A third aspect of the invention is characterized in that, in the first aspect, the resilient member is arranged between the base plate and the top plate.

A fourth aspect of the invention is characterized by a balancer insertable between a femur and a tibia, including:
a base plate having a gap scale on each of the left and right sides,
a slider having a gap pointer and an angular scale on each of the left and right sides, the slider being translationally and vertically movable with respect to the base plate,
a top plate having an angular pointer on each of the left and right sides, the top plate being swingable with respect to the slider and vertically movable together with the slider, and
a resilient member arranged in each of the left and right sides of the balancer to bias the top plate upwards with respect to the base plate,
wherein, when a biasing force of the resilient member causes the base plate to engage the tibia and the top plate to engage the femur, cooperation of the gap scale of the base plate and the gap pointer of the slider indicates a vertical position of the top plate with respect to the base plate, and at the same time, cooperation of the angular scale of the slider and the angular pointer of the top plate indicates an inclination of the top plate with respect to the base plate.

A fifth aspect of the invention is characterized in that, in the fourth aspect, the top plate is connected to the slider via a shaft and is swingable around the shaft.
A sixth aspect of the invention is characterized in that, in the fourth aspect, the resilient member is arranged between the base plate and the top plate.

A seventh aspect of the invention is characterized by a handle for vertically pinching a balancer according to any one of the first to sixth aspects, including: a pair of bar members, one of the bar members having a first end portion for depressing the top plate from above, the other of the bar members having a second end portion insertable into an opening formed in the base plate.
An eighth aspect of the invention is characterized in that, in the seventh aspect, the first end portion is bifurcated and has a rounded contacting portion for contacting the top plate, and the second end portion is formed into a straight flat plate having a cross-section complementary to a cross-section of the opening.

A ninth aspect of the invention is characterized by a shim to be attached to a balancer according to any one of the first to sixth aspects, the shim having a predetermined thickness.
A tenth aspect of the invention is characterized in that, in the ninth aspect, a top surface of the shim is attached to an under surface of the base plate through a male-female type fitting portion.
An eleventh aspect of the invention is characterized in that, in the ninth aspect, an under surface of the shim is attached to a top surface of a tilt plate through a male-female type fitting portion.
A twelfth aspect of the invention is characterized in that, in the ninth aspect, a top surface of the shim is provided with a protrusion for preventing the shim from falling off.

A thirteenth aspect of the invention is characterized by a tilt plate to be attached to a balancer according to any one of the first to sixth aspects, the tilt plate including a thinner side and a thicker side to form a predetermined inclination angle.
A fourteenth aspect of the invention is characterized in that, in the thirteenth aspect, a top surface of the tilt plate is provided with a male-female type fitting portion for attachment to an under surface of the base plate and/or the shim.

The disadvantages described above can be solved successfully. Specifically, according to the present invention, the gap and balance between the femur and the tibia can be simply and accurately measured in real time without using a navigation system.

These and other objects, features, and effects of the present invention will become apparent to one skilled in the art from the description of the embodiment of the present invention, as illustrated in the accompanying drawings, and appended claims.

FIG. 1 is an exploded perspective view of a balancer according to an embodiment of the present invention as seen from diagonally forward right. FIG. 2 is an exploded perspective view of the balancer according to the present embodiment as seen from diagonally backward left. FIG. 3 is a plan view of a base plate. FIG. 4 is a front view of the base plate. FIG. 5 is a side view of the base plate. FIG. 6 is a perspective view of the base plate as seen from diagonally forward right. FIG. 7 is a perspective view of the base upside down. FIG. 8 is a plan view of a top plate. FIG. 9 is a front view of the top plate. FIG. 10 is a cross-sectional view of the top plate taken along line X-X and seen in the direction of the arrows in FIG. 9. FIG. 11 is a bottom view of the top plate. FIG. 12 is a perspective view of the top plate as seen from diagonally forward right. FIG. 13 is a perspective view of the top plate upside down. FIG. 14 is a front view of a slider. FIG. 15 is a cross-sectional view of the slider taken along line XV-XV and seen in the direction of the arrows in FIG. 14. FIG. 16 is a perspective view of a handle. FIG. 17 is a perspective view of one of the bar members constructing the handle. FIG. 18 is a perspective view of the other one of the bar members constructing the handle. FIG. 19 is a front view of a shim. FIG. 20 is a side view of the shim. FIG. 21 is a perspective view of the shim as seen diagonally forward right. FIG. 22 is a perspective view of the shim upside down. FIG. 23 is an exploded view of an assembly of the balancer, the shim and the tilt plate as seen from the front. FIG. 24 is an exploded view of the assembly of the balancer, the shim and the tilt plate as seen from the side. FIG. 25 is an exploded perspective view of the assembly of the balancer, the shim and the tilt plate as seen from diagonally forward right. FIG. 26 is an exploded perspective view of the assembly of the balancer, the shim and the tilt plate as seen from diagonally backward left. FIG. 27 is a view of the balancer set between the femur and the tibia as seen from the front.

FIG. 1 is an exploded perspective view of a balancer 1 according to an embodiment of the invention as seen from diagonally forward right, and FIG. 2 is an exploded perspective view of the balancer 1 of the present embodiment as seen from diagonally backward left.

The arrow X in FIG. 1 indicates a width direction (left-right direction)of the balancer, the arrow Y the depth direction (front-back direction) of the balancer, and the arrow Z the height direction (thickness direction) of the balancer.

The balancer 1 according to the present embodiment is, for example, a measuring apparatus to be inserted between the femur and the tibia in a total knee replacement operation and essentially includes a base plate 3 that is to be located on the tibia side, a top plate 5 that is to be located on the femur side, a slider 7 coupled to the top plate 5, and a pair of coil springs (resilient members) 9 disposed between the base plate 3 and the top plate 5 to bias them to move apart from each other.

The balancer 1 of the present embodiment is also accompanied by a handle 11 (FIG. 16) for reliably grasping the balancer 1 for the above-mentioned insertion, a shim 13 (FIG. 19) for making it possible to deal with small and large sizes of the gap between the femur and the tibia, and a tilt plate 15 (FIG. 23) for making it possible to deal with the inclination in the anterior posterior direction of the above-mentioned gaps.

These components may be made of, for example, suitably heat-treated, precipitation hardened stainless steel (concretely, e.g., SUS 630) which has an excellent balance of hardness and corrosion resistance.

(1) Base Plate
Referring to FIGS. 3 to 7, the base plate 3 has a substantially kidney shape or a substantially broad-bean shape when viewed from above and preferably has a size nearly the same as that of the proximal end surface of the tibia.

Substantially the center of each of the left and right sides of the top surface of the base plate 3 is provided with a cylindrical raised portion 21 for holding the coil spring 9.
At the anterior side of the top surface of the base plate 3, a pair of upstanding portions 23 (23a, 23b) is provided to stand symmetrically a predetermined distance spaced apart in the horizontal direction.

The opposing vertical surfaces of the

upstanding portions

23a, 23b slidably engage with the corresponding surfaces of the slider 7, which will be described later, thereby guiding translational movement of the slider 7 in the vertical direction (Z direction back and forth).
The front surface of each upstanding portion 23 is provided, along the vertically extending outer edge, with a gap scale 25 (25a, 25b) (in the drawings, scale marks or nicks at 1 mm intervals) and numerical characters for the scale (in the drawings, 8, 10, and 12).

On substantially the center of the top surface of the base plate 3, a substantially rectangular parallelepiped guide post 29 for guiding the translational movement of the top plate 5 in the Z direction is vertically provided.
The front surface of the guide post 29 is formed with a vertically elongated opening 31 that penetrates the guide post 29 in the Y direction.

A shaft 47 of the top plate 5 (which will be described later) fits into the vertically elongated opening 31, and as the top plate 5 translationally moves in the vertical direction (Z direction, back and forth), the shaft 47 hits the upper and lower inner ends of the vertically elongated opening 31 to limit the movement in the vertical direction (Z direction) to a certain distance. In other words, the length of the vertically elongated opening 31 determines the maximum stroke length of the translational movement (Z direction) of the top plate 5.

Further, in the front surface of the guide post 29, below the vertically elongated hole 31, a horizontally elongated opening 33, which penetrates the guide post 29 in the Y direction in the same manner, is formed. The horizontally elongated opening 33 receives one of the two ends of the handle 11, which will be described later, for grasping the balancer 1.

Further, a wall surface 26 of the guide post 29 and a wall surface 44 of the top plate 5 engage to guide the translational movement and, at the same time, a wall surface 27 of the guide post 29 and a wall surface 45 of the top plate 5 engage to guide the translational movement, thereby restraining rotation of the top plate 5 within the Y-Z plane. This allows more stable measurement.

The bottom surface (under surface) of the base plate 3 is provided with a plurality of protrusions 35 (four in the illustrated configuration) for positioning and connecting the shim 13 and the tilt plate 15, which will be described later. These protrusions are stuck into the end surface of the tibia for fixation of the base plate.

(2) Top Plate
Referring to FIGS. 8 to 13, similarly to the base plate 3, the top plate 5 is of substantially kidney shape or broad-bean shape when viewed from above.

Substantially the center of each of the left and right sides of the under surface (bottom surface) of the top plate 5 is provided with a raised portion 41 having a circular cylindrical form with a diagonally cut top for holding the coil spring 9.

Substantially the center of the top surface of the top plate 5 is provided with a rectangular opening 43 that penetrates the top plate 5 in the Z direction (vertical direction). This rectangular opening 43 fittingly receives the guide post 29 of the base plate 3.

The center of the rear inner face in the Y direction of the rectangular opening 43 is provided with a holding hole that receives and holds the rear end of the shaft 47 extending in the Y direction, and the corresponding front inner face in the Y direction is provided with a through hole that holds the front of the shaft 47.

The shaft 47 is fixedly supported by the top plate 5 via these two holes and the shaft end located on the front side forwardly protrudes a certain length from the front end surface of the top plate 5. The slider 7 is mounted on the thus-protruding shaft portion.

Specifically, the coil springs 9 are set on the base plate 3, the guide post 29 is passed through the rectangular opening 43, and the top plate 5 is moved closer to the base plate 3 against the biasing force of the coil springs 9, and when the front through hole and the rear holding hole of the top plate 5 and the vertically elongated opening 31 of the guide post 29 (and a central opening 57 of the slider 7) are aligned as seen from the front side, the shaft 47 is fitted to the top plate 5.

The left and right sides of the front surface of the top plate 5 are each provided with a single pointing mark or nick 51 (51a , 51b) (hereinafter referred to as an angular pointer) for pointing at an angular scale (which will be described later) on the slider 7.

(3) Slider
Referring to FIGS. 14 and 15, the slider 7 includes a rectangular thick plate portion 59, which has at its center the central opening 57 that penetrates in the anterior posterior direction (Y direction), and thin plate portions 61 at both left and right sides, which extend horizontally outwards from both sides of the thick plate portion 59 and have edges (outer boundary) formed by an arc whose center is the central opening 57.

The central opening 57 of the slider 7 is, as described previously, fitted rotatably relative to the shaft 43 that projects from the front end surface of the top plate 5.

The thick plate portion 59 has opposing vertical surfaces on both sides in the horizontal direction, and each vertical surface slidably engages, as described above, with the corresponding vertical surface of the

upstanding portions

23a and 23b of the base plate 3.

The front surface of each thin plate portion 61 is provided, along its outer edge, with an angular scale 65 (in the drawing, scale marks or nicks at 1 degree intervals) and numerical characters for the scale (in the drawing, +5 and -5).

The vertically center (horizontal position) scale mark 65n in each of the left and right

angular scales

65a and 65b is formed thicker and longer than others. This scale mark 65n forms a gap pointer (65n) for pointing at the gap scale 25 on the upstanding portion 23 of the base plate 3.

(4) Coil Spring
In the present embodiment, the coil springs 9 are used. However, springs, rubbers, or the like of other forms may be used provided that they can bias the base plate 3 and the top plate 5 to move apart (to be spaced apart) relative to each other.

(5) Handle
Referring to FIGS. 16 to 18, the handle 11 is a tool for grasping the balancer 1 to insert it between the femur and the tibia, and pinches the base plate 3 and the top plate 5 against the biasing force of the coil springs 9, reducing the overall thickness to achieve easy insertion.

The handle 11 has a construction such that two substantially S-like

shape bar members

71, 73 are crossed and connected at a crossed section by means of a pin 75.

The front side of one of the bar members 71 is bifurcated so that the left and right can be pressed in a well-balanced manner when depressing the top surface of the top plate 5 downwards, and the front end portion 71a (pressing portion or contacting portion) is rounded to be able to make point or line contact for minimizing the generation of unnecessary component forces during the pressing.

For easy insertion and withdrawal from the horizontally elongated opening 33 formed in the front surface of the guide post 29 of the base plate 3, the front end side of the other bar member 73 is provided with a straight flat plate portion 73a having a complementary and similar cross-section.

(6) Shim
Referring to FIGS. 19 to 22, when inserting the balancer 1 between the femur and the tibia, if the gap is larger than usual, the shim 13 temporarily forms an overall balancer thickness that corresponds to the gap.

The illustrated shim 13 has a thickness of 2.5 mm. As a matter of course, alternatively or additionally, shim having other thickness, e.g. thickness of 5.0 mm and 7.5 mm, are provided.

The top surface of the shim 13 is provided, for attachment of the shim 13 to the base plate 3, with four fitting holes 81 that receive the four protrusions 35 provided on the under surface of the base plate 3.

The under surface of the shim 13 is provided with three protrusions 85 for attachment of the tilt plate 15.

Further, the top surface of the shim 13 is provided with a C-like shape protruding portion 89. This protruding portion 89 is constructed to enter within the base plate, when the shim 13 is attached to the under surface of the base plate 3, through an opening 37 (FIG. 7) formed in the base plate under surface so as to communicate with the horizontally elongated hole 33 and substantially align with the horizontally elongated hole 33.

In addition, it is constructed so that, when the flat plate portion 73a of the front end of the handle 11 enters the horizontally elongated hole 33 of the base plate 3, the protruding portion 89 is caught by the flat plate 73a, and the detachment (falling) of the shim 13 can be reliably prevented.

(7) Tilt plate
Referring to FIGS. 23 to 26, the illustrated tilt plate 15 has a top surface forming an attachment surface for the base plate 3 or the shim 13 (the illustrated shim has a thickness of 5 mm), and has a thinner front side, a thicker rear side, and an inclination of 5 degrees. As a matter of course, alternatively or as needed, the tilt plate may have a different inclination angle (e.g., 10 degrees, 15 degrees or the like).

The top surface (attachment surface) of the tilt plate is provided with four fitting holes 91, into which the four protrusions 35 protruding from the base plate under surface can fit for the connection with the base plate 3, and also provided with three fitting holes 93 into which the three protrusions 85 projecting from the shim under surface can fit for the connection with the shim 13. For standardization, these seven

protrusions

35, 85 may have the same outer diameter, and similarly, the seven

fitting holes

91, 93 may have the same inner diameter.

Hereinafter, the use of the balancer 1 (and/or the shim and the tilt plate) of the present embodiment having the construction as above will be briefly described.

Prior to insertion of the balancer 1 between the femur and the tibia, the flat plate portion 73a of the handle 11 is first inserted into the horizontally elongated opening 33 of the guide post 29 of the base plate 3 and the top surface of the top plate 5 is depressed by the other front end portions 71a of the handle 11 to minimize the overall thickness of the balancer. In other words, the base plate 3 and the top plate 5 are located to be closest to each other.

The construction, which enables the balancer 1 to be grasped in such a reduced thickness, allows for very easy insertion of the balancer 1 into the gap between the femur and the tibia.

It should be noted that in cases that the above-mentioned gap is larger and/or more inclined than supposed, it is preferable to attach the shim 13 and/or the tilt plate 15 in advance.

As discussed above, when the shim 13 is attached, the novel interconnecting structure of the protruding portion 89 of the shim 13, the horizontally elongated opening 33 of the base plate 3, and the flat plate portion 73a of the handle 11 can reliably prevent the falling of the shim 13.

Further, regardless of the existence of the shim 13, the handle 11 can grasp the balancer 1 with the usual opening angle, which may considerably improve work efficiency and performance.

Gradual release of the grasping force of the handle 11 against the balancer 1 inserted into the gap between the femur and the tibia causes the distance between the base plate 3 and the top plate 5 to increase due to the biasing force of the coil spring 9, leading to the base plate 3 abutting and engaging with the tibia side and top plate 5 abutting and engaging with the femur side.

During the above, as discussed previously, the slider 7 and the shaft 47 move translationally upwards with respect to the base plate 3 while the top plate 5 moves upwards together with the slider 7 and the shaft, but swingably around the shaft 47.

The gap (dimension or distance) between the tibia and the femur can be visually confirmed (measured) with ease from the gap scale 25 (25a, 25b) of the base plate 3 (the upstanding portion 23) and the gap pointer 65n of the slider 7 pointing at the gap scale.

On the other hand, the inclination or balance of the femur against the tibia can be visually confirmed (measured) with ease from the angular scale 65 (65a, 65b) of the slider 7 and the angular pointer (pointing mark) 51 (51a, 51b) of the top plate 5 pointing at the angular pointer.

As above, on setting the balancer 1 into the gap between the femur and the tibia, the two visual confirmation (measuring) operations become possible.

As described hereinabove, according to the balancer of the present embodiment, an apparatus configuration corresponding to the opening and inclining conditions between the tibia and the femur can be achieved instantly, and the balancer can be set very simply and easily between the tibia and the femur and, in addition, real time measurement of the dimension and inclination (balance) between the two bones can be performed at the moment the balancer is set.

Further, the whole balancer can be constructed very compact and lightweight, allowing considerably improved operability and keeping damage to the subject to a minimum.

It should be noted that, in the present embodiment, the balancer is made up of a left-right symmetrical structure, and hence, when it is set between the femur and the tibia, measurements can be made from the combination of the scale and pointer on one side even if the combination of the scale and pointer on the other side cannot be visually confirmed due to an obstacle on that side. That is, suitable measuring operation can be realized. This allows measurements with the patella returned to its original position, resulting in reproduction of a situation closer to that of an actual knee joint.

Now, FIG. 27 shows the balancer 1 of the present embodiment actually set between the femur F and the tibia T. In this figure, the femur F and the tibia T are in an extended condition, and the (unillustrated) patella is in its original location (non-everted position).

As can be clearly seen from FIG. 27, according to the balancer 1 of the present embodiment, proper and quick measurement is possible for the knee (the femur and the tibia) that has no patella eversion and is functionally and physiologically in its natural conditions. As a matter of course, a similar measurement is possible for a knee (the femur and the tibia) in a flexed condition.

The present invention itself, however, is not limited to constructing balancers in a left-right symmetrical structure. For example, the balancer may be constructed in a left-right asymmetrical structure. In conclusion, the required measurements are possible provided that the scale and pointer combination is provided on either of left and right sides of the balancer.

The embodiment described above is a representative one of the present invention, provided for illustrative purposes, and not intended to limit the scope of the present invention. The elements, materials, and various means illustrated and described in the present specification are not limiting, but may be changed or modified within the scope of the present invention and are limited solely by the following appended claims.

1 balancer
3 base plate
5 top plate
7 slider
9 coil spring
11 handle
13 shim
15 tilt plate
21, 41 raised portion
23, 23a, 23b upstanding portion
25, 25a, 25b gap scale
26, 27 wall surface
29 guide post
31 vertically elongated hole
33 horizontally elongated hole
35 protrusion
37 opening
43 rectangular opening
44, 45 wall surface
47 shaft
51 angular pointer (pointing mark)
57 central opening
59 thick plate portion
61 thin plate portion
65, 65a, 65b angle scale
65n gap pointer (scale mark)
71, 73 bar member
71a front end
73a flat plate portion
75 pin
81, 91 fitting hole
85 protrusion
89 protruding portion

Claims

A balancer (1) insertable between a femur and a tibia, comprising:
a base plate (3) having a gap scale (25);
a slider (7) having a gap pointer (65n) and an angular scale (65) and being movable translationally and vertically with respect to the base plate (3);
a top plate (5) having an angular pointer (51), being swingable with respect to the slider (7), and vertically movable together with the slider (7); and
a resilient member (9) biasing the top plate (8) upwards with respect to the base plate (3),
wherein, when a biasing force of the resilient member causes the base plate (3) to engage the tibia and the top plate (5) to engage the femur, cooperation of the gap scale (25) of the base plate (3) and the gap pointer (65n) of the slider (7) indicates a vertical position of the top plate (5) with respect to the base plate (3), while cooperation of the angular scale (65) of the slider (7) and the angular pointer (51) of the top plate (5) indicates an inclination of the top plate (5) with respect to the base plate (3).
The balancer (1) according to claim 1, wherein the top plate (5) is connected to the slider (7) via a shaft (47) and is swingable around the shaft (47).
The balancer (1) according to claim 1, wherein the resilient member (9) is arranged between the base plate (3) and the top plate (5).
A balancer (1) insertable between a femur and a tibia, comprising:
a base plate (3) having a gap scale (25a, 25b) on each of the left and right sides;
a slider (7) having a gap pointer (65n, 65n) and an angular scale (65a, 65b) on each of left and right sides, the slider (7) being translationally and vertically movable with respect to the base plate (3);
a top plate (5) having an angular pointer (51a, 51b) on each of left and right sides, the top plate (5) being swingable with respect to the slider (7) and vertically movable together with the slider (7); and
a resilient member (9) arranged in each of left and right sides of the balancer (1) to bias the top plate (5) upwards with respect to the base plate (3),
wherein, when a biasing force of the resilient member causes the base plate (3) to engage the tibia and the top plate (5) to engage the femur, cooperation of the gap scale (25a, 25b) of the base plate (3) and the gap pointer (65n, 65n) of the slider (7) indicates a vertical position of the top plate (5) with respect to the base plate (3), while cooperation of the angular scale (65a, 65b) of the slider (7) and the angular pointer (51a, 51b) of the top plate (5) indicates an inclination of the top plate (5) with respect to the base plate (3).
The balancer (1) according to claim 1, wherein the top plate (5) is connected to the slider (7) via a shaft (47) and is swingable around the shaft (47).
The balancer (1) according to claim 4, wherein the resilient member (9) is arranged between the base plate (3) and the top plate (5).
A handle (11) for vertically pinching a balancer (1) according to any one of claims 1 to 6, comprising:
a pair of bar members (71, 73), one of the bar members (71) having a first end portion (71a) for depressing the top plate (5) from above, the other of the bar members (73) having a second end portion (73a) insertable into an opening (33) formed in the base plate (3).
The handle (11) according to claim 7, wherein
the first end portion (71a, 71b) is bifurcated and has a rounded contacting portion for contacting the top plate (5), and
the second end portion (73a) is formed into a straight flat plate having a cross-section complementary to a cross-section of the opening (33).
A shim (13) to be attached to a balancer according to any one of claims 1 to 6, the shim (13) having a predetermined thickness.
The shim (13) according to claim 9, wherein a top surface of the shim (13) is attached to an under surface of the base plate (3) through a male-female type fitting portion (81).
The shim (13) according to claim 9, wherein an under surface of the shim (13) is attached to a top surface of a tilt plate (15) through a male-female type fitting portion (85).
The shim (13) according to claim 9, wherein a top surface of the shim (13) is provided with a protrusion (89) for preventing the shim from falling off.
A tilt plate (15) to be attached to a balancer according to any one of claims 1 to 6, comprising:
a thinner side and a thicker side to form a predetermined inclination angle.
The tilt plate (15) according to claim 13, wherein a top surface of the tilt plate (15) is provided with a male-female type fitting portion (91, 93) for attachment to an under surface of the base plate (3) and/or the shim (13).