The present invention relates to medical orthopaedic

instrumentation and more particularly relates to an improved bone cutting instrument.

Many orthopaedic surgical instruments require the use of an

elongated rod, plate or bar for alignment purposes. During surgery,

this rod can be supported in parallel relationship with a patient's long bone such as for example a patient's tibia or femur. Cutting instruments are often adjustably mounted upon such an alignment

rod. It is common to attach tibial or femoral cutting blocks in a

sliding manner upon an alignment rod.

One of the most common methods of affixing a tibial cutting block, femoral cutting block or like orthopaedic instrumentation to an

alignment rod is a threaded set screw or set bolt that is mounted at

the opening in the block through which the rod is mounted. In order

to tighten the instrument to a selected position on an alignment rod, the user simply tightens the bolt or set screw so that it engages the outer surface of the rod. In order to move the instrumentation with

respect to the rod, the user simply loosens the bolt to disengage it

from the rod.

One of the problems of set screw type locking mechanisms is

that they tend to loosen very easily. An improved locking mechanism would be desirable in providing a firm locking arrangement between an orthopaedic surgical instrument that is

used for cutting patient's bone tissue and an elongated alignment

rod.

According to the invention, a surgical instrument system comprises a first surgical instrument and a second surgical instrument which is movable with respect to said first instrument;

said second instrument comprising a locking member which forms a

connection with said first instrument whereby to secure said second

instrument in a selected position with respect to said first instrument; said locking member comprising a cam member pivotally mounted

on said second instrument for rotation about said pivot; said cam member comprising a handle portion for enabling a user to rotate

said cam, and a cam body portion having a bearing surface which is

arranged to engage said first surgical instrument upon rotation of said cam member.

The present invention provides an improved surgical

instrument system comprising for example a cutting block body that

slides upon an elongated linear alignment rod. A locking member carried by the block body can form a connection with the rod at a selected position along the rod.

The locking member is in the form of a cam that rotates about a pivot pin on the second instrument body. The cam includes a handle portion that enables the user to rotate the cam about its pivot.

The locking member also includes a bearing surface that engages the first instrument when the cam member is in a locked position. The user can apply force to the handle portion when locking the cam bearing surface to the first instrument.

A portion of the cam preferably includes a slot that extends circumferentially about the pivot.

The slot provides a cam locking arrangement which provides the advantage that the manufacturing tolerances of the cam arrangement are not critical to its performance . This is because the slot may allow a portion of the cam to deflect resiliently in the manner of a spring when force is applied to the bearing surface. The deflection creates a small opposing force in the cam which serves to urge the bearing surface into contact with the first instrument to provide a firm engagement between the first and second instruments to lock them into a desired position relative to each other.

The slot is preferably positioned radially in between the pivot

pin and the periphery of the locking member in the region of the

bearing surface. The slot has a closed end portion and an open

end portion. The open end portion communicates with the locking member periphery at a position which is preferably spaced away from the bearing surface.

The slot preferably extends along a curved path

circumferentially about the locking member so as to generally track the bearing surface in the region adjacent the bearing surface.

In the preferred embodiment, the slot extends at least ninety

degrees (90°) circumferentially about the pivot.

The slot is preferably curved, but a portion of the slot adjacent the bearing surface can be "S" shaped.

The locking member has a center of rotation defined by the

pivot pin. The pivot pin extends between two flanges that are an integral portion of the second instrument.

The slot is preferably very narrow (e.g. 0.014 inches thick),

being between about 0.006 and 0.10 inches in thickness. The cam

is preferably about one to three inches long. In the preferred embodiment, the slot is generally of a uniform thickness along its entire length.

The first instrument may comprise an alignment rod which is preferably a cylindrically shaped rod having a portion that is flat. Thus, the rod provides a flat longitudinally extending linear surface thereon for receiving the bearing surface of the cam. The alignment rod can be a rectangular or square shaped plate like distal cutting block stylus. However, it should preferably have at least one flat surface.

The bearing surface of the cam which engages the first

instrument as the cam is rotated may be shaped to provide a peak force between the cam and the first surface which must be exceeded to move the cam to its engaged position in which the first and second instruments are locked together. This may conveniently be achieved by providing a pair of outwardly inclined surfaces, which may be generally flat, such that the peak force occurs when the intersection between the inclined surfaces bears against the first instrument. Thus, in moving from disengaged to engaged position

the force required to move the cam peaks just before the fully engaged position is reached so that the locking member cannot be

inadvertently moved out of the locked position without reapplying the peak force.

The deflecting force on the part of the cam between the slot

and the bearing surface reaches a maximum when the peak force is applied. Preferably the slot relaxes slightly from its peak deflection

when the locking member is fully engaged so that the peak

deflection force must again be applied to unlock the locking member.

For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description of a preferred embodiment which is given as an example only, taken in conjunction with the accompanying drawings, in which

like parts are given like reference numerals, and wherein:

FIGURE 1 is a perspective view of the preferred embodiment

of the apparatus of the present invention;

FIGURE 2 is another perspective view of the preferred embodiment of the apparatus of the present invention;

FIGURE 3 is a schematic view of the preferred embodiment

of the apparatus of the present invention illustrating the cam locking

member;

FIGURE 4 is another schematic, perspective view of the preferred embodiment of the apparatus of the present invention illustrating the cam locking member;

FIGURE 5 is a perspective view of the preferred embodiment

of the apparatus of the present invention;

FIGURE 6 is bottom schematic, partial cut away view of the preferred embodiment of the apparatus of the present invention illustrating the locking cam and its engagement with the alignment

rod;

FIGURE 7 is a bottom view of the preferred embodiment of the apparatus of the present invention showing the locking cam in a relaxed, unlocked position; and

FIGURE 8 is a bottom plan view of the preferred embodiment

of the apparatus of the present invention illustrating the locking cam

in a locked, engaged position.

Figures 1-2 and 5 show generally the preferred embodiment of the apparatus of the present invention designated generally by

the numeral 10. Knee cutting instrumentation 10 includes an

elongated linear rod 11 having end portions 12, 13, flat

longitudinally extending surface 14, and instrument block body 16.

Rod 11 has an elongated rod linear axis 15 that can be

aligned by a surgeon with a desired bone that is to be cut as part of

a surgical procedure. For example, the rod 11 and its linear axis 15 can be aligned with the central longitudinal axis of a patient's tibia or

with a patient's femur. Such a rod 11 can be aligned with the

mechanical axis or with the anatomical axis of a patient's bone if

desired.

Instrument body 16 can provide one or more cutting guide

surfaces 17 thereon. These guide surfaces 17 aid a surgeon by holding a saw blade in a plane while making an appropriate cut on

the patient's bone tissue such as for example a patient's proximal tibia, distal femur, or the like.

Instrument block body 16 can also provide a number of

openings 18 through which pins or screws can be inserted and then

into underlying bone tissue. Such pins or screws are used for rigidifying the block body 16 relative to the patient's bone tissue once alignment is completed using rod 11.

A plurality of bores 19, 20, 21 are provided through body 16 as shown in Figure 1. The central bore 20 is cylindrically shaped to receive and conform generally to the outer surface of rod 11. A cam locking member 25 is positioned at or near bore 20 for engaging rod

11.

Instrument block body 16 provides a pair of square flanges

22, 23 that are integrally connected thereto as shown in Figures 1-2.

Each flange 22, 23 has an opening that receives rod 11. Flange 23 has opening 45.

Flanges 22, 23 are spanned by a pivot pin 24 that carries cam locking member 25. The flanges 22, 23 provide flat surfaces

26, 27 that are parallel positioned and accept corresponding flat

surfaces 41 , 42 of cam locking member 25. During use, the surgeon slides the instrument block body 16 upon rod 11 to a desired location between the ends 12, 13 of rod 11. The surgeon then

grabs a handle portion 28 of cam locking member 25 then rotates

the handle 28 toward the instrument body 16 in the direction shown

by curved arrow 43 in Figure 7. This causes a bearing surface 30 portion of cam locking mechanism 25 to engage the flat longitudinally extending surface 14 of rod 11 as shown in Figures 5-

6.

Figures 3-4 show more particularly the construction of the

cam locking member 25. Cam locking member 25 has flat parallel surfaces 41 , 42 and an elongated slot 37 that extends between surfaces 41 and 42. The slot 37 is preferably of a uniform thickness

of between about 0.006 to 0.100 inches. It can be wire cut with a

EDM machine. Cam locking member 25 includes a handle portion

28 with a pair of spaced apart flat surface 33, 34. A flat surface 32

is generally perpendicular to the surface 33. Flat surface 31 is

angled with respect to surface 34, preferably forming an obtuse angle therewith in Figure 3. An arcuate surface defines bearing surface 30 as shown in Figure 3. The bearing surface 30 extends

between edges 35, 36.

The elongated slot 37 extends between closed end portion

38 and open end portion 40 as shown in Figures 3 and 4. An "S" shaped portion 39 is provided closest surface 32. Further, the "S" shaped portion 39 of slot 37 is positioned adjacent to bearing

surface 30.

When the surgeon rotates the handle 28 in the direction of arrow 43, the bearing surface 30 also rotates into engagement with the rod 11 and more particularly its flat surface 14. Continued

rotation of the handle 28 in the direction of arrow 43 causes the

bearing surface 30 to very tightly engage the surface 14 of rod 11. This action produces compression in locking member 25 between pivot pin 24, bearing surface 30 and flat surface 14.

In order to minimize tolerances, the wire cut slot 37 allows a

portion 44 of cam locking member 25 to flex. The portion 44 is that portion of cam locking member that is bounded by the slot 37, bearing surface 30, and surfaces 41 and 42.

Bearing surface 30 is not smoothly curved. It is formed of two relatively flat surfaces 46, 47 which are outwardly inclined with

respect to each other, forming an obtuse angle at their intersection point 48. As the cam handle is rotated from a disengaged position, shown in fig 7, in the direction of arrow 43 to an engaged position, sown in fig 8, surface 46 is brought into engagement with the flat

surface 14 of the rod ^" ! 1. The force required to move the cam then increases, due to the angle of surface 46, until a peak force is

reached when the cam has been rotated until intersection point 48 engages the rod. This is also the point at which maximum deflection of flex portion 44 occurs. Further rotation of the cam handle brings surface 47 into engagement with the rod which, due to its angle,

allows a very small reduction of both the rotational force and

deflection of flex portion 44. This ensures that the cam may not be rotated to its disengaged position without applying the peak rotational force again and therefore offers some security against unlocking the instrument inadvertantly.

The present invention thus provides a simple yet reliable cam locking arrangement for locking an instrument block body 16 to an elongated alignment rod 11. The present invention solves this

problem by providing a unique cam locking arrangement that allows flexibility when the surgeon desires a connection between the cam

locking member 25 and the rod 11 at a particular location not withstanding imperfections in manufacture or in assembly.

The following table lists the parts numbers and parts

descriptions as used herein and in the drawings attached hereto. Part Number Description

10 knee cutting instrumentation

11 rod

12 end

13 end

14 flat longitudinal surface

15 rod linear axis

16 instrument body

17 cutting guide surface

18 opening

19 bore

20 bore

21 bore

22 flange

23 flange

24 pivot pin

25 cam locking member

26 flat surface

27 flat surface

28 handle

29 pivot opening

30 bearing surface

31 flat surface

32 flat surface

33 flat surface

34 flat surface

35 edge

36 edge

37 wire cut slot

38 end portion

39 S shaped portion

40 open end

41 flat surface

42 flat surface

43 arrow

44 flex portion

45 opening

46 bearing surface

47 bearing surface

48 intersection point