Knee Implant Device

Abstract

A joint prosthesis particularly useful in total knee replacement, and capable of providing controlled motion about three axes corresponding to the capabilities of a normal knee. A dual centered pivot with contacting arcuate support blocks provides for a combination of rotational and translational movement during knee bending movements. Axial rotation of the femur (upper leg) relative to the tibia (lower leg) is also possible through the normal range of movements, and a bias toward the neutral position is provided to signal the patient that such rotation exists. Flexure or bending of the joint in an axis transverse to the normal knee axis is also provided with a resilient bias toward the aligned orientation. The joint is secured to the bone structure by self tapping connector screws. The connector screws are locked in place by outrigger screws. The entire knee joint is enclosed in a flexible encapsulating cover to prevent damage to adjacent tissues and contamination of body fluids.

Description

BACKGROUND OF THE INVENTION

Numerous joint structures for knee endo-prosthesis and artificial joints have been proposed. The most common such joint prosthesis employs a single pivot bearing. The use of a single pivot bearing is primarily prompted by simplicity, since a single pivot does not duplicate the actual movements in a normal knee resulting in an abnormal gait and in high stresses. Further, such joints are not capable of bending to the full 120 to 135 degrees of rotation corresponding to normal knee capability without pinching tissue. Further, such structures have been susceptible to breakdown, particularly at the point of attachment to skeletal structure. Additionally, they may damage the adjacent tissues by entrapment of tissues in the hinge mechanism. Those prior art devices which have been proposed to provide for knee movement in three axes have been unduly complex, or have required the removal of such a large quantity of bone as to destroy the attachment points for some of the ligaments that controlled knee movement.

Therefore, it is desirable to have a knee prosthesis useful in total knee replacement, that is relatively strong and stable, and which closely duplicates the rotational and translational constraints and capabilities of a normal knee. Such a knee is particularly to be desired if it provides for attachment to the bone structure with the removal of a minimum amount of ligaments and other supportive tissue, and without substantial weakening of the bone structure. It is further desirable in such a knee that a natural feel be provided in those motions that result in resistance in the normal knee. A still further desirable characteristic of such a knee is the protection of the body tissue surrounding the prosthesis from damage by contact with the moving parts and the exclusion of body fluids from the knee structure to avoid chemical contamination of the body or corrosive damage to the knee joint.

SUMMARY OF THE INVENTION

An exemplary embodiment of the invention utilizes a dual centered pivot. However, it is to be understood that the invention is applicable to knee prosthesis incorporating more than two pivots in applications where such additional complexity is justified by the additional flexibility attainable. The pivot bearing comprises a pair of pivot pins carried in a pivot shield for supporting the structure of the apparatus. Each pivot pin carries an arcuate support block with opposed arcuate surfaces in a combination of rolling and sliding contact during the knee bending function to produce the combined bending and translational movements. A connector block is fitted over the pivot pins through an enlarged mounting opening having a curved surface and a flat surface. The enlarged opening provides for a degree of relative rotation between the upper leg and lower leg portions of the device. Since the rotation takes place by twisting of the pivot pins across the curved surfaces of the connector block mounting openings, the pivoting results in an axial translation as well as a rotation. The translation has the effect of compressing a spring washer and thereby providing a spring bias. In use, the patient senses the spring bias and thereby is provided with a sensation of misalignment in the knee. The spring washer also serves to simulate the "screw-in" effect. As weight is placed on the knee in the aligned position, the spring washers on the roller blocks are compressed and flattened against the connector block. This results in the knee structure becoming quite rigid and also provides good cushioning.

The joint structure is secured to the bone structure in the case of a total knee prosthesis through self tapping screws and a bonded saddle. The connector screw shape is a highly pitched undercut thread which may be screwed into the central portion of the femur and tibia to produce a sound support for the knee joint structure. Three locking screws or outriggers are employed to lock the attaching screw and saddle in position and prevent loosening in use. The connector block is pinned to the screw and the pin locked in place by a resiliently latched lock slide.

The joint structure is of a size that permits it to be installed within the confines of the original bone dimensions. For this purpose, the bone is surgically configured to the exterior dimensions of upper and lower saddles. The saddles are cemented in position. The saddles replace the removed hard bone surface and thereby retain the monocoque reinforcing effect and maintain adequate structural strength. Through the use of this technique, it is not necessary to detach tendons or ligaments, and other tissue adjacent to the joint and therefore these structures remain to provide stability and control, and to strengthen the musculature surrounding the prosthesis.

The final motion provided for in the joint will be referred to as a tilting in the lateral plane of the joint, and is accomplished by mounting the connector screw to the pivot bearing through a connector pin. The connector screw is held by the pin in a socket in a connector block. The socket is filled by material having sufficient resiliency to permit the eight to ten degrees of tilting that duplicates that obtainable in normal knees. The resilient material is the same silicone rubber or other flexible substance used in providing an encapsulation for the entire joint structure. Encapsulating material is formed in two halves and joined to the pivot shield around the periphery at the central portion of the shield. The material is bonded to the metal to provide a permanent seal against the admission of body fluids. Sufficient material is provided to form a fold on the front face of the knee to permit knee bending through the full travel desired. The rear face is provided with paired opposed recesses to insure that the bending is always along the same line.

It is therefore an object of the invention to provide a new and improved joint prosthesis.

It is another object of the invention to provide a new and improved joint prosthesis which closely approximates the motions obtainable in normal knees.

It is another object of the invention to provide a new and improved joint prosthesis which shields the motion of moving parts.

It is another object of the invention to provide a new and improved joint prosthesis which is sealed from the body tissues and fluids.

It is another object of the invention to provide a new and improved joint prosthesis which has stable motion.

It is another object of the invention to provide a new and improved joint prosthesis that provides a positional pressure during axial rotation and tilting.

It is another object of the invention to provide a new and improved joint prosthesis that is relatively small in overall dimensions.

It is another object of the invention to provide a new and improved joint prosthesis which is high in structural strength.

It is another object of the invention to provide a new and improved joint prosthesis which includes provision for secure attachment to bone structure.

It is another object of the invention to provide a new and improved joint prosthesis which may be removed as necessary with minimal damage to the bone or tissue.

It is another object of the invention to provide a new and improved joint prosthesis that may be easily installed by relatively simple surgical procedures.

It is another object of the invention to provide a new and improved joint prosthesis that provides a screw-in effect to mimic normal knee action.

It is another object of the invention to provide a new and improved joint prosthesis with provision for reinforcing the bone which is cut away for joint installation.

It is another object of the invention to provide a new and improved joint prosthesis that may be installed without the removal of any ligaments secured to the distal or proximal surfaces of the femur or tibia except the anterior and posterior cinciate ligaments.

It is another object of the invention to provide a new and improved joint prosthesis that locks in the upright or aligned position.

Other objects and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout and in which:

FIG. 1 is a side elevation view of a knee joint prosthesis with portions of the leg bones indicated in broken line.

FIG. 2 is a rear elevation view of the joint with portions of the flexible encapsulating material cut away.

FIG. 3 is a sectional view taken on line 3--3 of FIG. 2.

FIG. 4 is a sectional view taken on line 4--4 of FIG. 3.

FIG. 5 is a sectional view taken on line 5--5 of FIG. 3.

FIG. 6 is a sectional view taken on line 6--6 of FIG. 5.

FIG. 7 is an enlarged prospective view of a connector pin and lock slide.

FIG. 8 is a side elevation view partially cut away showing the bending action.

FIG. 9 is a sectional view taken on line 9--9 of FIG. 5.

FIG. 10 is a sectional view similar to FIG. 9 showing the rotational action.

FIG. 11 is a rear elevation view partially cut away showing the compression effect of the rotation.

Referring now to the drawings and particularly to FIGS. 1 and 2, the joint prosthesis 10 of the invention is illustrated. The joint is shown as being secured to the femur 12 and tibia 14 by connector screws 16 and 18. The connector screws are secured in position by outrigger screws 20. Saddles 22 and 24 are employed by fitting them within the cavity created through the condyles of the tibia and femur, and cementing them to the soft bone thereby maintaining the monocoque strength of the original bone structure. The saddles have arcuate facing surfaces 23 and 25 to permit maximum bone contact without interference during knee bending action.

A pivot shield 26 mounts pivot pins 28 and 30 which are held in position through the pivot shield by retainers 32. The pivot pins 28 and 30 carry upper and lower connector blocks 34 and 36. The entire joint structure is encapsulated by a flexible encapsulation member 37 of silicone rubber including upper and lower portions 39 and 40.

Referring now most particularly to FIG. 3, there is illustrated the pivot shield 26 which, at its rear facing edge, has a rear portion 44 of a peripheral channel to capture the locking portions of the upper and lower encapsulation members 39 and 40. The front face of the pivot shield has the corresponding front portion 46 of the channel. The pivot shield 26 has rear facing arcuate portions 50 and 52 which cooperate to stabilize the movements of the connector blocks as is described more fully hereinafter.

The upper and lower connector blocks 34 and 36 are identical and will be described by reference to connector block 34. The connector block has an axial bore 54 for receiving the arcuate support block 60. The arcuate support block 60 is constrained within the support block bore 54 to axial movement and is resiliently biased away from the bottom of the bore 54 by a spring washer 68 centered over a protrusion 64 on the support block. The connector block 34 has channels 61 and 62 to provide attachment and bonding points for the encapsulation material 37 and a socket 58 which receives the connector screw 16. The socket 58 has inclined sides as is best illustrated in FIG. 5 and therefore receives an excess amount of the silicone rubber 94 to provide for up to 10 degrees of tilting movement of the connector screw 16 relative to the connector block 34. The connector screw 16 and block 34 are secured together by a connector pin 80, and the assembly retained in position by a lock slide 82.

A connector block slide 150 is received around the lower portion of connector block 34. The slide 150 moves along the connector block when pressure is placed on the knee in the aligned position to accommodate movement of the roller blocks 60 in bore 54. The connector block slide is carried on pin 28. The surface 56 on slide 150 contacts the pivot shield inner surface 50 during approximately the first 20 degrees of bending in the joint, after which the surface 56 rotates out of contact to permit axial rotation.

The connector screw 16 has threads 86 which are highly undercut and have a pitch of approximately 37.degree. so that the screw is self tapping. The screw is held locked into the bone by a plurality of outriggers 20 which are secured in threaded bores near the end of the connector screw. The connector screw carries a flange 17 which is received in a recess in the attachment pad 23 of the saddle 22. Pad 23 of saddle 22 also includes a plurality of angulated bores 88 which receive the outrigger screws 20 and are aligned so as to position the outrigger screws for their eventual insertion into threads in the outer circumference of the connector screw 16. The mounting of the screw results in the primary stress being transferred in tension and permits the use of caboneous silicon alloyed isotopic carbon with its desirable non-reactivity to the histology of the body. The pad 23 and screw 16 have a lateral inclination of approximately 11 degrees to duplicate the angulation of the femur.

The silicone rubber is bonded in the various channels directly to the metal. The members 39 and 40 are provided with folds 43 and 45 on the front of the knee joint to permit full bending. The rear face is provided with opposed paired indentation 123 and 125 on the members 39 and 40 respectively which provides extra silicone rubber for flexure. As is illustrated in FIGS. 8 and 9, the indentations 123 and 125 are substantially of flattened conical configuration. During bending the conical indentations 123 and 125 are contacted by the connector blocks 34 and 36. This contact pushes the indentations 123 and 125 outwardly and thereby provides extra silicone rubber substantially along a line connecting the apexes of the cones. The extra silicone rubber insures that the bend line will be regular and will be consistently along the same line. The extra silicone rubber 94 filling in the sloping sides of socket 58 in the connector clock permits eight to ten degrees of relative rotation about pin 80.

Referring to FIG. 7 the connector pin 80 is illustrated as including a dovetail portion 100 which cooperates with the dovetail portion 102 on the lock slide 82. The lock slide is retained in position in the connector block slide recess 115 by the shoulder 106. The shoulder 106 is held in an expended position by the wedge member 105. The wedge member itself is held in axial position by engagement with shoulders 107 on slide tumblers 109.

IMPLANTATION AND USE

As provided for implantation, the device of the invention would have an assembled pivot structure and bonded encapsulation. However, the connector screws 16 and saddles 22 and 24 would be left disassembled. The natural knee is surgically exposed and bone is removed from the femur and tibia to produce a cavity configuration corresponding to the exterior configuration for the upper and lower saddles 22 and 24. The saddles are temporarily put in place and holes for the outrigger screws 20 are drilled in the bone structure by the use of the holes 88 as a guide. The central bore for the connector screws 16 is also drilled at this time. Then the saddles are removed and the connector screws turned into place. The connector screws are highly pitched and are therefore self tapping in the soft central bone structure. With the screws in place, the saddles are positioned against the connector screw flanges 17 and cemented to the cavity in the bone structure using methyl methacrylate or similar cement. By securing the saddles over the soft bone where hard bone has been removed, the monocoque reinforcing effect is retained. Then outrigger screws 20 are screwed in place through the drilled holes in the bone, and into the threaded bores near the end of the connector screws 16. The screws hold the saddle against the flange 17 and thus binds the connector screw and saddle into an integral unit for transferring tension, compression, rotational and bending forces.

With the connector screws in place, it is now possible to attach the joint structure through the connector blocks 34 and 36. The connector pin ends are received in the connector block sockets 58 and the pivot pin 80 inserted through the connector screw mounting hole and into the opposite side of the connector block. The pivot pin 80 is retained in position by the lock slide 82 which engages the dovetail portion 100 on pin 80. The lock slide is retained in the connector block 34 by squeezing the lock slide with a special purpose tool and allowing the shoulder 106 to pass within the lock slide recess 115 in the connector block 34, and then releasing pressure on the tool to allow the shoulder 106 to engage the corresponding shoulder on the channel in the lock slide recess 115. The lock slide 82 is fixed against removal by the installation of the wedge member 105 which engages the shoulders 107 on the end tumblers 109 when it is fully inserted.

When the installation is complete, the incision may be closed. The post operative recuperative period is minimized by the fact that minimum tissue damage takes place during the operation. The bone structure grows in and around all of the undercut threads on the connector screws 16, and in and around the outrigger screws 20. Thus a firm connecting support to the sound bone structure is provided. The saddles 23 and 24 also transfer load to the bone through the cemented surfaces which heal rapidly.

After recuperation, the joint is ready to operate in a manner closely approximating the natural knee joint.

FIG. 3 illustrates the erect knee position. It will be noted that the flat end surfaces of the roller blocks 60 are in contact, and that the surfaces 56 on the connector blocks contact the curved inner faces 50 and 52 of the pivot shield 26. Thus the knee is locked. Rotational and other loads are transferred without joint movement.

Referring to FIG. 8, the configuration of the knee bending is illustrated. The surface 56 is now out of contact with the curved inner face 52 of the pivot shield. The rotation of the surface 56 away from the pivot shield 26 permits relative axial rotation of the tibia and femur, such as takes place in normal knees after approximately 20 degrees of bending. Rotation is accommodated on the curved arcuate surface 122 of enlarged opening 120. FIG. 10 illustrates the relative position of the pivot pin 28 relative to the connector block 36 during joint rotation. FIG. 11 is illustrative of the effect of rotation on the spring washer 68. The pivot pin 28 is shown as rotating along the arcuate surface 122 so that it is out of contact with the very bottom portion thereof, and is positioned midway in the axial length of the opening 120. A total of plus or minus 20 degrees is provided. The spring washer 68 is partially compressed thereby creating a bias and giving the user a positional reference whereby a resistance sensation is produced corresponding with knee rotation.

Lateral tilting is accommodated by the socket 58 which has sloping sides to accommodate extra silicone rubber 94. The rubber serves to provide a positional sensation to the user during the lateral flexing action in a manner similar to that employed in axial rotation.

The entire mechanism is encased in the encapsulation 37 thereby excluding the tissues and fluids from the mechanism and preventing contact or possible pinching between any of the moving parts. The encapsulation serves as a surface on which the patella may slide so that the important patellar functions are retained. The action of the encapsulation during bending is illustrated in FIG. 8 wherein the folds 43 are partially extended and the folds are being created in the rear face of the encapsulation pairs 39 and 40 along a regular bend line under the influence of indentations 123 and 125. With maximum knee extension the connector blocks will contact the rear portion of the pivot shield 26 limiting the total travel to the selected figure of approximately 135.degree.. FIG. 8 also illustrates that during bending, contact is maintained between the roller surfaces and therefore extra stability is provided in the movement.

Should it ever become necessary to remove the joint for repair or replacement, the surgeon would remove the lock slides in reverse of the above described locking procedure and back off the outrigger screws 20 to make it possible to remove the connector screws 16. This would be accomplished with minimum bone damage because it is not necessary to break the bone in order to remove the screw once the outriggers are removed.

Claims

Having described my invention, I now claim.

1. A joint prosthesis comprising:

joint means,

attachment means for securing said joint means between relatively movable skeletal members,

said joint means for constraining said skeletal members to a combination of relative rotation and translation,

said joint means comprising at least two axially spaced pivot bearings incorporating two pivot pins, a common pivot frame, and two connector blocks,

said two pivot pins spaced axially in said joint means and carried on said common pivot frame,

said pivot bearings being connected to said attachment means through said connector blocks,

said connector blocks having an axial bore and receiving said pivot pins through a transverse opening through said axial bore.

2. The joint prosthesis as claimed in claim 1 wherein:

said transverse opening in said connector block is enlarged to provide a limited pivoting freedom of movement for said pivot pins in said connector block.

3. The joint prosthesis as claimed in claim 2 wherein said opening in said connector block has an arcuate surface for producing an axial translation of said connector block relative to said pivot pin upon axial rotation of said pivot pins.

4. The joint prosthesis as claimed in claim 1 wherein:

said attachment means comprise a connector screw and each connector block is secured to said connector screw by a connector screw pivot pin received in a transverse bore through said connector screw and in said connector block.

5. The joint prosthesis as claimed in claim 4 wherein said connector screw is received in an axial socket in said connector block,

said axial socket having radially opposed sloping sides,

the radial line connecting said sloping portions being substantially perpendicular to the axis of said connector screw pivot pin.

6. The joint prosthesis of claim 1 wherein said axial bore in said connector blocks accommodate opposed roller blocks carried on said pivot pins,

said opposed roller blocks having a face-to-face contact in the axially aligned orientation for said joint means, and having curved surfaces in contact during bending movement of said knee.

7. A joint prosthesis according to claim 1 wherein:

said connector block includes an arcuate surface which contacts the inner face of said pivot frame in the axially aligned orientation of said joint means,

said arcuate surface on said connector block being pivotally moved away from said inner face after a pre-determined amount of bending in said joint means to allow limited relative axial rotation.

8. The joint prosthesis of claim 7 wherein:

said arcuate surface sccommodates relative axial rotation of plus or minus 20.degree..

9. The joint prosthesis of claim 2 wherein:

said connector blocks have slide portions around the inner ends of said connector blocks.

said slide portions accommodating limited relative axial translation between said connector block and said slide.

10. The joint prosthesis of claim 9 wherein:

said slide portions contacting the inner face of said pivot frame during approximately the first 20.degree. of bending in said joint means.

11. In a joint prosthesis for providing relative movement between skeletal members that improvement comprising:

attachment means comprising a connector screw adapted to be threaded into the interior axial portion of said skeletal members,

outrigger screws threaded into said connector screw near the terminal end thereof at an acute angle to the longitudinal axis of said connector screw and adapted to pass through bone of said skeletal members.

12. In a joint prosthesis for providing a mechanism for relative movement between skeletal members, that improvement comprising:

a joint mechanism,

an attachment system comprising a pair of saddle means comprising substantially U-shaped saddle members with an attachment pad at the base of said U-shaped saddle members,

said saddle means adapted to be cemented to bone structure and secured to said joint mechanism through said attachment pad,

a plurality of bores through said attachment pad,

said bores having an axis at an acute angle to the axis of a central bore through said attachment pad.

13. Apparatus for use in a joint prosthesis comprising:

joint means for producing a combined rotation and translation,

said joint means comprising at least two spaced pivot bearings,

said pivot bearings comprising pivot pins carrying, for rotation, upper and lower connector block means,

said connector block means for securing said joint means to relatively movable limbs,

each of said pivot pins carrying arcuate support blocks,

said support blocks having cooperating surfaces in contact during rotation about the axis of said pivot bearings,

said connector block means includes a connector screw pivot pin and a transverse bore for securing said connector block to a connector screw,

connector screw pivot pin locking means comprising a locking slide having a dovetail groove over a portion of one face thereof for receiving a dovetail extension on said connector screw pivot pin,

said lock slide having a locking shoulder for engaging a shoulder in the lock slide recess in said connector block, and having a wedge lock for locking said shoulder into interference with said slot.

14. The joint prosthesis of claim 13 wherein:

said connector block receives said connector screw in a socket with inclined sides to accommodate up to 10.degree. of tilting movement.