5,863,295
`[11] Patent Number:
`[19]
`United States Patent
`
`Averill et al.
`[45] Date of Patent:
`Jan. 26, 1999
`
`U8005863295A
`
`[54] PROSTHETIC DEVICE AND METHOD OF
`IMPLANTATION
`
`4,608,053
`4,718,915
`4,955,912
`
`8/1986 Keller .
`1/1988 Epinette.
`9/1990 Berchem.
`
`[75]
`
`Inventors: Robert G. Averill, Ringwood; Robert
`C. Cohen, Rockaway Township; Rafail
`Zubok Midland Park all ofNJ
`’
`’
`'
`'
`,
`Implex C0rp0rat10n, Alendale, N.J.
`
`.
`[73] Ass1gnee:
`
`[21] Appl. No.2 844,443
`.
`Filed:
`
`[22]
`
`Apr. 18, 1997
`
`Related US. Application Data
`
`[62] Division of Ser. No. 636,727, Apr. 23, 1996, Pat. No.
`5,702,487, which is a continuation of Ser. No. 252,450, Jun.
`1 1994
`b
`d
`d.
`’
`’a a“ (me
`Int. Cl.6 ........................................................ A61F 2/36
`[51]
`[52] us. Cl. ............................................. 623/23
`
`[58] Field of Search
`606/80 85‘ 623/22
`623/23
`
`[56]
`
`References Cited
`
`U~S- PATENT DOCUMENTS
`4064567 12/1977 Burstein et a1.
`.
`4,514,865
`5/1985 Hams .
`4,530,116
`7/1985 Frey .
`4,549,319
`10/1985 Meyer .
`
`‘
`
`4/1991 Smith ~
`570077931
`5/1991 ZOIman et al'
`530183285
`7/1991 BIOOkS'
`590359717
`5,061,287 10/1991 Feiler.
`5,092,899
`3/1992 Forte.
`.
`5,092,900
`3/1992 Marchetti et a1.
`5,108,405
`4/1992 Mikhail et a1.
`........................... 606/80
`5,108,437
`4/1992 Kenna .
`5,147,408
`9/1992 Noble et a1.
`5,169,401
`12/1992 Lester et a1.
`5,171,275
`12/1992 Ling et a1.
`.
`5,342,363
`8/1994 Richelsoph ................................ 606/80
`
`.............................. 606/85
`.............................. 606/80
`
`Primary Examiner—Debra S~ Brittingham.
`Attorney) Agent, 07‘ FWm—Plevy & ASSOClateS
`[57]
`ABSTRACT
`
`A hip Prosthesis for implanting into the medullary canal of
`a femur, which comprises a stem for implanting into the
`canal of the femur, the stem having a proximal end and a
`distal end, the stem also including a proximal locking zone
`substantially adjacent the proximal end, the proximal lock-
`ing zone including a proximal locking surface which cir-
`cumferentially press-fits Within the canal of the femur and a
`neck extending at an angle from the proximal end of the
`stem for receiving the femoral head of the prosthesis.
`
`6 Claims, 9 Drawing Sheets
`
`
`
`Page 1 of 14
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`ZIMMER EXHIBIT 1012
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`ZIMMER EXHIBIT 1012
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`US. Patent
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`Jan. 26, 1999
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`Sheet 1 0f 9
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`5,863,295
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`US. Patent
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`Jan. 26, 1999
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`Sheet 2 0f 9
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`5,863,295
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`FIG. 2
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`r”
`L32?
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`FIG 3
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`F“
`L32
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`28
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`/\
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`12
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`468
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`48
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`FIG. 5
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`460
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`US. Patent
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`Jan. 26, 1999
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`Sheet 3 0f 9
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`5,863,295
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`FIG. 6
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`US. Patent
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`Jan. 26, 1999
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`Sheet 4 0f 9
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`5,863,295
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`FIG. 7
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`US. Patent
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`Jan. 26, 1999
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`Sheet 5 0f 9
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`5,863,295
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`FIG.
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`8
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`US. Patent
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`Jan. 26, 1999
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`Sheet 6 0f 9
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`FIG. 9
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`FIG. 10
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`FIG.
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`11
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`FIG.
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`12
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`Jan. 26, 1999
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`Sheet 7 0f 9
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`FIG.
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`13
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`86
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`FIG.
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`14
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`1..
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`r.O‘.4
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`PD7
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`
`Pkg
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`{I'll-.AMWMIIIWAEI’AIIE
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`FIG.
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`15
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`Jan. 26, 1999
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`Sheet 8 0f 9
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`FIG. 15
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`FIG. 17
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`US. Patent
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`Jan. 26, 1999
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`Sheet 9 0f 9
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`FIG. 18
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`FIG. 19
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`5,863,295
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`1
`PROSTHETIC DEVICE AND METHOD OF
`IMPLANTATION
`
`This is a Divisional of application Ser. No. 08/636,727,
`filed on Apr. 23, 1996 for PROSTHETIC DEVICE AND
`METHOD OF IMPLANTATION now US. Pat. No. 5,702,
`487, which is a continuation of Ser. No. 08/252,450, filed
`Jun. 1, 1994 for PROSTHETIC DEVICE AND METHOD
`OF IMPLANTATION, now abandoned.
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to a prosthetic
`device and in particular, to a prosthetic bone implant which
`is implanted into a proximal femur in a press-fit manner.
`BACKGROUND OF THE INVENTION
`
`Prosthetic devices are utilized for replacing load-carrying
`skeletal members, such as the human hip, which are ren-
`dered non-functional due to acute arthritis, fracture, resec-
`tions for malignancy or malformation. Such procedures have
`become more commonplace not only in human beings but
`also in animals such as dogs.
`Hip joints are commonly repaired by total joint replace-
`ment with artificial components. Such hip prostheses typi-
`cally include a femoral portion or component which is
`implanted in the femur and an acetabular component which
`is secured to the pelvis. The femoral component includes a
`head which articulates in a socket formed in the acetabular
`component.
`With prostheses, especially a hip prosthesis, it is desirable
`to provide a rigid fixation of the prosthesis in order to
`provide long term stabilization, to minimize bone-implant
`micromotion, and to minimize the occurrence of
`complications, such as pain, after surgery.
`Many known prosthetic devices require rigid fixation
`through the use of cement for the embedment of the pros-
`thesis into the bone structure. These types of devices,
`however, display a number of disadvantages; during the
`installation of the prosthesis, it is typically necessary to wait,
`after sealing the shaft, until the cement has acquired suffi-
`cient resistance by polymerization before proceeding. Dur-
`ing setting of the cement, the cement releases heat and can
`cause damage to surrounding tissue. The presence of the
`cement also inhibits the ingrowth of bone into the prothesis.
`Another problem associated with prior art cemented pros-
`theses is that they are designed to be firmly attached along
`their entire length. In the case of a hip prosthesis, the entire
`length of the stem of the femoral component
`is either
`cemented to the intramedullary canal of the femur to insure
`adequate stability. This causes compressive and other
`stresses created in and through the stem, when the leg is
`used, to be transferred to the femoral bone near the distal end
`of the prosthetic stem not uniformly along its length. The
`fixation created between the cement and the portion of the
`bone surrounding the lower portion of the stem transfers the
`forces developed through the ball joint to the lower portion
`of the femur and bypasses its proximal end. Over time, that
`portion of the femur is subject to deterioration of osteoporo-
`sis and thinning of the bone. As a result, the proximal end of
`the femur essentially loses density causing eventual loosen-
`ing of the stem of the prosthesis within the bone. The
`problems associated with cemented implants have resulted
`in the development of implants which are inserted into the
`bone canals to obtain a press-fit arrangement.
`In prostheses which are designed to be press-fitted, par-
`ticularly in the case of press-fit hip femoral stems, two issues
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`affect the clinical performance of the implant. These issues
`are initial implant stability and bone reactions. Astem design
`should focus on the tightest fit
`to resist subsidence and
`torsional forces and micromotion. The bone should be
`
`loaded most proximally in press-fit applications when good
`bone quality is encountered to stimulate appropriate bone
`remodeling, for continued implant support, and reduced
`stress-shielding of that critical region.
`The present invention provides an improved geometry of
`the stem in the proximal bone region by a modification
`involving the shape of the implant and its interaction with
`the preparation instruments.
`In prior art press-fit implants, an interference fit is pro-
`vided by a slightly undersized preparation where the anterior
`and posterior faces of the proximal implant do not compress
`much bone relative to the medial and lateral portions. The
`anterior and posterior faces on many of the prior art implants
`are parallel sided providing no resistance to subsidence.
`Torsionally, the resistance can be minimal due to the lack of
`bone quality and contact. With a slightly tapered anterior and
`posterior face, the bone is slightly compressed in an inter-
`ference fit. The angle defined by the tapered faces of typical
`prior art implants is approximately 3 degrees. Due to this
`slight angle, a linear distance corresponding to the implan-
`tation axis provides little outward displacement. Hence, the
`bone is not compressed to any great extent, which in turn,
`may contribute to less than optimal
`initial stability.
`In
`addition,
`the slight angle is not optimal
`in transferring
`compressive loads to the bone with most of the initial loads
`going to the medial proximal portions. Increased anterior/
`posterior loading occurs only when bone ingrowth occurs
`and bony remodeling occurs over a broad, mostly medial
`area. The present
`invention includes a geometry in the
`proximal region about the stem which provides a greater
`angle on the anterior and posterior faces of the stem. The
`angle on the anterior/posterior sides is at least double that of
`the prior art tapered stems and is located in a more proximal
`location.
`
`locking zone of the present
`The improved proximal
`invention initially loads the bone more proximally and
`compresses the bone (in an interference fit) to a greater
`extent than prior art stems. This provides for densification of
`bone about the stem, greater resistance to subsidence, and
`greater resistance to torsional forces. In addition, the den-
`sification of bone potentially inhibits the transfer mechanism
`for implant debris to the boundary surrounding the implant/
`bone interface. A reduction in the incidence of lysis is also
`a potential benefit.
`To aid in retaining the stem of the present invention, a
`bio-active material or the like, may be applied to the surfaces
`in the proximal locking zone. This material and such allow
`for bony ingrowth into the material which enhances the
`fixation of the prosthesis within the femur.
`invention to
`It
`is,
`therefore, an object of the present
`provide a prosthesis which will transfer the forces generated
`in the upper portion of the stem to the proximal portion of
`the femur through an effective angle and thereby eliminate
`deterioration of the bone in that area.
`
`It is a further object of the invention to provide a novel
`method of implanting a femoral stem which prepares the
`intramedullary canal for the novel geometry of the present
`invention.
`
`SUMMARY OF THE INVENTION
`
`According to the invention, a hip prosthesis for implant-
`ing into the medullary canal of a femur comprises a stem for
`
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`5,863,295
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`3
`implanting into the canal of the femur, the stem having a
`proximal end and a distal end, the stem also including a
`proximal locking zone substantially adjacent the proximal
`end, the proximal locking zone including a proximal locking
`surface which circumferentially press-fits within the canal of
`the femur and a neck extending at an angle from the
`proximal end of the stem for receiving the femoral head of
`the prosthesis.
`The stem further defines a longitudinal axis. The proximal
`locking surface and the longitudinal axis define a proximal
`locking angle therebetween. This proximal locking angle on
`the anterior and posterior portions of the proximal locking
`surface, can range anywhere between 5 and 10 degrees,
`however, 7 degrees is preferred.
`The proximal locking surface extends circumferentially
`about said stem and can comprise a layer of material which
`promotes growth of natural bone tissue into the layer of
`material for enhancing the attachment of the prosthesis to
`the femur. This layer can comprise a synthetic bone material
`such as hydroxyapatite or in another embodiment of the
`invention, a layer comprising a plurality of beads coating the
`proximal locking surface.
`Also according to the invention, a method for implanting
`a prosthesis stem into a medullary canal of a femur, the
`prosthesis having a proximal locking zone which presents a
`geometric profile for press-fit engagement within the canal,
`the method comprising the steps of resecting a portion of the
`bone using a template as a guide, reaming a bore along the
`medullary canal of the bone, inserting a trial implant into the
`bore to prepare the bore for the geometric profile of the
`proximal locking zone of the stem removing the trial implant
`from the bore, and inserting the prosthesis into the bore, the
`proximal locking zone of the prosthesis engaging the bore in
`a press-fit engagement to securely lock the prosthesis into
`the bore for in the medullary canal of the bone.
`The step of reaming includes a first reaming with a first
`cylindrical reamer of a given diameter and a second reaming
`with a tapered reamer after the first reaming, to prepare the
`bore for the geometric profile of the prosthesis stem. The
`step of reaming can also include a second reaming with a
`second cylindrical reamer having a diameter substantially
`greater than the diameter of the first cylindrical reamer.
`The trial implant includes a proximal locking zone which
`presents a geometric profile substantially like the geometric
`profile of the locking zone of the stem, the geometric profile
`of the trial implant being of a size which is slightly less than
`a size of the geometric profile of the stem to prepare the bone
`for the interference fit.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Reference is now made to the accompanying figures in
`which:
`
`FIG. 1 is an anterior elevational view of the hip implant
`prosthesis of the present invention;
`FIG. 2 is a cross-sectional view taken along line 2—2 of
`FIG. 1;
`FIG. 3 is a cross-sectional view taken along line 3—3 of
`FIG. 1;
`FIG. 4 is a magnified anterior elevational view of the
`proximal locking zone;
`FIG. 5 is a magnified lateral elevational view of the
`proximal locking zone;
`FIG. 6 is a lateral elevational view of the hip implant
`prosthesis of the present invention;
`FIG. 7 is an anterior elevational view of an alternative
`
`embodiment of the present invention without a plurality of
`beads;
`
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`FIG. 8 is an anterior elevational view of the embodiment
`
`shown in FIG. 7 with a plurality of beads attached to the
`proximal locking surface;
`FIG. 9 is a fragmentary view of the proximal end of a
`femur showing the neck and head thereof in dashed lines,
`representing the portion of the femur resected in order to
`implant the prosthesis of the present invention;
`FIG. 10 is an elevational view of the cylindrical reamer;
`FIG. 11 is a fragmentary cross-sectional view of the
`proximal end of the femur illustrating the cylindrical ream-
`ing tool of FIG. 10;
`FIG. 12 is a cross-sectional view similar to that of FIG. 11
`
`showing the bore in the medullary canal following the
`reaming with the cylindrical reamer;
`FIG. 13 is a cross-sectional view similar to FIG. 11 but
`
`illustrating the use of a rasp to set the initial geometry of the
`bore for the prosthesis;
`FIG. 14 is a cross-sectional view similar to FIG. 12 but
`
`illustrating the geometry of the bore in the medullary canal
`following the step of reaming with the rasp;
`FIG. 15 is an elevational view of the rasp shown in FIG.
`13;
`FIG. 16 is a cross-sectional view similar to FIG. 13 but
`
`illustrating the use of a trial implant to set the final geometry
`of the bore for the prosthesis;
`FIG. 17 is a cross-sectional view similar to FIG. 14 but
`
`illustrating the final geometry of the bore in the medullary
`canal following the step of inserting the trial implant;
`FIG. 18 is an elevational view of the trial stem implant
`and trial neck implant shown in FIG. 16;
`FIG. 19 is a cross-sectional view illustrating the prosthe-
`sis implanted into the bore formed in the medullary canal of
`the femur.
`
`DETAILED DESCRIPTION OF THE DRAWINGS
`
`In the description which follows, it should be understood
`that any reference to either orientation or direction is
`intended only for the purpose of illustration and is not in any
`way intended to be a limitation of the scope of the present
`invention.
`
`the term “proximal” references to the
`As used herein,
`portion of the prothesis positioned closest to the heart. and
`the term “distal” refers to the portion of the prothesis
`positioned farthest from the heart. Also used herein, are the
`terms “anterior”, which references the portion of the pros-
`thesis facing toward the front of the body, and the term
`“posterior”, which references the portion of the prosthesis
`facing toward the rear of the body. It should be understood,
`however, that because the device may be used in either the
`right or left femur, the “anterior” portion of the prosthesis
`can also become the “posterior” portion of the prosthesis and
`visa versa.
`
`is the term “press-fit”, which is
`Further used herein,
`defined as a mechanical engagement
`formed by two
`components, at least one of which is deformable, where the
`adjacent boundary lines of the two components overlap and
`interface with each other such that the two components must
`be forced into a position adjacent each other which produces
`a locking force developed over the area of contact between
`the two components.
`Referring to FIG. 1, there is shown a side elevational view
`of a prothesis according to the present invention designated
`by the numeral 10. The prothesis of FIG. 1 is designed as a
`femoral component of a hip prosthesis. It is understood,
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`5,863,295
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`5
`however, that the prothesis according to the present inven-
`tion can be configured into any other type of implantable
`prosthetic device. For example, the prosthesis of the present
`invention can be configured as a humeral component of a
`shoulder prosthesis. In any event, the prosthesis shown in
`FIG. 1 is configured as the femoral component of a hip
`prosthesis and is dimensioned to be press-fitted within a bore
`formed in the femoral intramedullary canal. The prothesis
`generally includes a stem 12 having a proximal end 16 and
`a distal end 18, and a neck 36. The prosthesis 10 further
`includes a lateral side 25 and a medial side 27. The stem 12
`
`defines a longitudinal axis 14 wherein the neck 36 extends
`medially, at approximately an angle 16 relative to the
`longitudinal axis 14, from the proximal end 17 of the stem
`12.
`
`A spherically shaped driver recess 20 is formed in the
`proximal end 16 of stem 12. The driver recess 20 provides
`an area for the placement of an impaction tool (not shown)
`which is used to drive the prosthesis into the bore formed in
`the canal of the femur.
`
`Starting at the proximal end 16 and extending distally
`therefrom is a tapered portion 22 which defines a proximal
`locking zone 24 and a recessed medial pocket 50, both of
`which will be discussed in greater detail below. The tapered
`portion 22 extends distally from the proximal locking zone
`24, merging into a cylindrical portion 26. The free end of the
`cylindrical portion 26 forms the distal end 18 of the stem 12.
`The distal end 18 of the stem 12 tapers down from the
`cylindrical portion 26 to a generally spherical tip portion 19.
`FIGS. 2 and 3 illustrate the changing cross-sectional
`shape of the tapered portion 22 at respective lines 2—2 and
`3—3. The cross-sectional shape of the tapered portion 22 of
`stem 12 at line 2—2 (FIG. 2), presents a greater medial-
`lateral dimension 28 as compared with the overall anterior-
`posterior dimension 30 (as measured on the lateral side). The
`cross-sectional shape of the tapered portion 22 changes
`significantly such that the medial-lateral dimension 28 and
`anterior-posterior dimension 30 defines an almost circular
`cross-section at line 3—3, (FIG. 3) approaching the distal
`end of the tapered portion 22. Also, the anterior-posterior
`width 30 adjacent the lateral side of the tapered portion 22
`becomes substantially greater in width, moving proximally,
`than the corresponding anterior-posterior width 32 adjacent
`the medial side.
`
`Referring again to FIG. 1, the neck 36 of the prosthesis 10
`is tapered and includes a peg portion 38. The proximal end
`of the stem 12 merges into the distal end of neck 36 forming
`a first circumferential fillet at 40. The neck 36 converges
`proximally as it merges into the tapered portion 38 forming
`a second circumferential fillet at 42. The tapered portion 38
`is slightly tapered in the distal to proximal direction and
`includes a chamfer 44 at the proximal end of the tapered
`portion 38. The tapered portion 38 is adapted to receive the
`femoral bearing head portion of the prosthesis (not shown).
`Still referring to FIG. 1, there is illustrated the proximal
`locking zone 24 portion of the stem 12. The proximal
`locking zone 24 is comprised of four proximal
`locking
`surfaces 46A, 46B, 46C, and 46D which extend circumfer-
`entially about the proximal portion of the tapered portion 22
`of stem 12. Proximal locking surfaces 46A. 46B, 46C and
`46D step down at circumferential step 48 to meet
`the
`remaining portion of tapered portion 22.
`The details of the proximal locking zone 24 are best
`illustrated by referring to FIG. 4. Locking surface 46A
`extends between locking surfaces 46B and 46C (not visible)
`and presents a conically shaped surface on the lateral side of
`the prosthesis. Locking surface 46D extends between lock-
`ing surfaces 46B and 46C and presents a curved surface on
`the medial side of the prosthesis. Locking surfaces 46B and
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`46C are planar and are located respectively on the anterior
`and posterior sides of the prosthesis.
`The anteriorly and posteriorly located locking surfaces
`46B and 46C each lie in a plane that defines a locking angle
`52 which ranges between 5 and 10 degrees and preferably 7
`degrees relative to longitudinal axis 14. (see also FIG. 5).
`Angle 52 is best illustrated in FIG. 5 where the prosthesis
`has been rotated 4.3° about the longitudinal axis 14.
`Referring again to FIG. 4, the conically shaped surface
`presented by the laterally located locking surface 46A tapers
`at the same locking angle 52 as locking surfaces 46B and
`46C, i.e., between 5 and 10 degrees and preferably 7 degrees
`relative to longitudinal axis 14 as stated above. The curved
`surface presented by the medially located locking surface
`46D follows the general taper of the medial portion 22 of the
`stem segment and presents a slightly round surface. This
`configuration provides an uninterrupted continuum of lock-
`ing surfaces 46B and 46C.
`Referring now to FIG. 6, there is shove the lateral side of
`the prothesis of the present invention. FIG. 6 clearly illus-
`trates the angle defined by proximal locking surfaces 46B
`and 46C and the anterior-posterior tapering of the remaining
`portion of the tapered portion 22.
`The prosthesis shown in FIGS. 1—6 is intended to be
`implanted by a press-fit engagement which does not utilize
`a cement for locking into place. As such, a layer(s) of
`bio-active material or “synthetic bone” material is deposited
`on the proximal locking surfaces 46A, 46B, 46C, and 46D
`which allow the prosthesis to become permanently attached
`via a mechanism which includes growth of the natural bone
`tissue within the cortex of the bone into the layer(s) of
`bio-active material. The synthetic bone material is generally
`plasma-sprayed on the prothesis. The preferred choice of
`synthetic bone material can be any well known ceramic
`comprising at
`least one artificial apatite in the form of
`hydroxyapatite (Ca50H(P04)2). This material can be applied
`in multiple layers and the layers themselves can be com-
`posed of different materials. The layer of synthetic bone is
`designed to be highly compatible with natural bone tissue.
`Referring now to FIG. 7 there is shown an alternative
`embodiment of the present
`invention designated by the
`numeral 60. The embodiment of FIG. 7 is substantially
`identical
`to the embodiment of FIGS. 1—6 except
`that
`proximal locking surfaces 62A, 62B, 62C (not visible), and
`62D are recessed and bounded by a circumferentially
`extending proximal ridge 64 and a circumferentially extend-
`ing distal ridge 66. The proximal
`locking surfaces are
`recessed to receive a plurality of beads 67 which act like a
`porous coating for receiving the ingrowth of the natural bone
`tissue. The beads can be made from any suitable material
`such as cobalt chromium or the like. The beads are bonded
`to the proximal locking surfaces 62A, 62B, 62C, and 62D by
`sintering as shown in FIG. 8. Note that the medial pocket 50
`can also receive a coating of beads if desired, as shown at 68
`in FIG. 8, in order to further provide for the ingrowth of
`natural bone tissue.
`
`The prosthesis of the present invention can be manufac-
`tured from titanium alloy, cobalt-chromium alloy or any
`other suitable material well known in the art. The prosthesis
`can be made by forging, casting and/or machining opera-
`tions or any other well known technique.
`Referring now to FIGS. 9—19, the apparatus employed in
`the method of implanting the prosthesis of the present
`invention is illustrated. Each tool of the apparatus will be
`explained in connection with the description of the method
`in which the apparatus is used, which follows.
`Starting with FIG. 9, the proximal end of the femur 70 is
`presented and the femoral neck 72 is removed using a
`femoral template (not shown) for determining the area to
`resect.
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`5,863,295
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`A first cylindrical reamer 82 having straight flutes 84 as
`shown in FIG. 10. The first cylindrical reamer 82 is inserted
`in the postero-lateral portion of the resected surface of the
`femoral neck 72 and enters the medullary canal 74 to form
`a bore 76 as shown in FIGS. 11 and 12. The cutting flutes 84
`of the first cylindrical reamer 82 align the reamer within the
`medullary canal 74. Successively greater diameter reamers
`may be used until the desired diameter bore is achieved
`which is intended to create a line to line fit with the implant
`stem.
`
`Proximal shaping of the bore 76 for the geometry of the
`stem of the prosthesis is implemented as shown in FIGS. 13
`and 14 using a tapered rasp 86 having circumferential
`cutting teeth 88. As best shown in FIG. 15, the tapered rasp
`86 has a profile which is substantially like that of the
`prosthesis but without the flare characterized by proximal
`locking surfaces 46A, 46B, and 46C of prosthesis 10. The
`tapered rasp 86 is inserted and driven into bore 76 as shown
`in FIG. 13.
`
`Once the tapered rasp 86 is removed, the final geometry
`of the bore 76 is formed using a trial implant 90 as illustrated
`in FIG. 18. The neck 92 and stem 94 of the trial stem implant
`90, which are manufactured as separate components, each
`have a shape and profile which is substantially identical to
`that of the prosthesis. The trial stem implant 90 includes a
`proximal locking zone 96 which includes a proximal locking
`surface 98 with a knurled finish 100 which is designed to
`prepare the proximal region 78 of the bore 76 for the
`proximal locking surface of the prosthesis. The trial implant
`90 is inserted and driven into the bore 76 as shown in FIG.
`16. The illustration of FIG. 17 shows how the proximal
`locking surface 96 of the trial implant crushes the bone in the
`proximal region 78 of bore 76 and provides a slightly
`undersized dimension relative to the prosthesis. This results
`in a press-fit engagement between the prosthesis and the
`bore 76 when the prosthesis is driven into the medullary
`canal 74.
`
`After the trial implant 90 has been removed from the bore
`76, the prosthesis 10 is ready to be implanted. As illustrated
`in FIG. 19, the prosthesis 10 is inserted into the bore 76 and
`driven into the bore 76 using an impaction tool (not shown)
`the end of which is placed into the driver recess 20. The
`prosthesis 10 is driven into the bore 76 until the proximal
`locking surface is firmly engaged with the proximal region
`78. The improved proximal locking zone of the present
`invention initially loads the proximal-most portion of the
`bone and greatly compresses the bone thereat. This provides
`for densification of bone about the stem, greater resistance
`to subsidence, and greater resistance to torsional forces. In
`addition, the densification of bone potentially inhibits the
`transfer mechanism for implant debris to the boundary
`surrounding the more distal implant/bone interface. Areduc-
`tion in the incidence of lysis is also a potential benefit.
`While it is presently contemplated that the present inven-
`tion is a hip prothesis, as described herein,
`the present
`invention is not
`limited to uses as a hip prothesis and
`consequently, may be used as a prosthetic implant of any
`type. Further, while the present invention is particularly well
`suited for press-fit implantation, the present invention is not
`limited to such, and therefore, embodies implantation in any
`suitable manner. Further, other methods of creating a porous
`surface on the prosthesis for providing bone ingrowth may
`be employed and can include porous fiber metal structures
`such as metal meshes or porous pads which are wrapped
`around the prosthesis. These and other such methods are
`contemplated in the present invention for the purpose of
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`enhancing the fixation of the prosthesis within the femur.
`Any variations or modifications to the invention described
`herein are intended to be included within the scope of the
`invention as defined by the appended claims.
`We claim:
`
`1. A method for implanting a prothesis stem having a
`proximal and a distal end into a medullary canal of a femur,
`said prothesis stem having a proximal locking zone substan-
`tially adjacent said proximal end which presents a geometric
`profile for press-fit engagement within said canal, said
`method comprising the steps of:
`a) resecting a head and neck portion of said femur;
`b) reaming a bore along said medullary canal of said
`femur;
`c) inserting a trial implant into said bore to prepare said
`bore for said geometric profile of said proximal locking
`zone of said stem, wherein said proximal locking zone
`of said stem is substantially adjacent said proximal end
`of said stem and having a geometric profile substan-
`tially similar to and of a size less than said geometric
`profile of said prosthesis stem, wherein said proximal
`locking zone includes an outwardly flared circumfer-
`ential proximal locking surface which extends about
`said proximal end of said stem, said proximal locking
`surface circumferentially press-fits within the canal of
`the femur, wherein said outwardly flared circumferen-
`tial proximal locking surface includes a first planar
`locking surface on an anterior side of said prosthesis, a
`second planar locking surface on a posterior side of
`said prosthesis, and a convex locking surface extending
`between and merging into said first and second planar
`locking surfaces on a lateral side of said prosthesis;
`d) removing said trial implant from said bore; and
`e) inserting said prosthesis stem into said bore, said
`proximal locking zone of said prosthesis stem engaging
`said bore in a press-fit engagement to securely lock said
`prosthesis stem into said bore in said medullary canal
`of said femur.
`
`2. The method according to claim 1, wherein said step of
`reaming includes a first reaming with a first cylindrical
`reamer of a given diameter.
`3. The method according to claim 2, wherein said step of
`reaming further includes a second reaming with a tapered
`reamer after said first reaming, to prepare said bore for said
`geometric profile of said prosthesis stem.
`4. The method according to claim 2, wherein said step of
`reaming includes a second reaming with a second cylindrical
`reamer having a diameter substantially greater than said
`diameter of said first cylindrical reamer.
`5. The method according to claim 4, wherein said step of
`reaming further includes a third reaming with a tapered
`reamer after said second reaming, to prepare said bore for
`said geometric profile of said prosthesis stem, and wherein
`said trial implant includes a proximal locking zone which
`presents a geometric profile substantially like said geometric
`profile of said locking zone of said stem, said geometric
`profile of said trial implant being of a size which is slightly
`less than a size of said geometric profile of said stem.
`6. The method according to claim 1 wherein said proximal
`locking surfaces of said trial
`implant are recessed and
`bounded by a circumferentially extending proximal ridge
`and a circumferentially extending distal ridge.
`*
`*
`*
`*
`*
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