Methods for manufacturing skeletal implants

This application claims priority from United States provisional application Serial No. 60/173,646, filed Dec. 30, 1999, which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to methods and instrumentation for manufacturing an implant, and more particularly to methods and instrumentation for manufacturing and inspecting an intervertebral implant formed from cadaveric human or animal bone.

2. Background to Related Art

Intervertebral implants which are formed from cadaveric human or animal bone (“bone”) are well known in the art. Intervertebral implants formed of bone having a threaded dowel configuration, i.e., cylindrical, are also well known. The manufacturing or machining of a threaded intervertebral bone dowel is an involved process which includes at least a drilling or coring step, a milling step, a tapping step and a threading step. Due to the anatomical limitations of bone, each of the manufacturing steps must be precisely performed to produce a dowel having the requisite dimensions suitable for implant use. Typically, the entire manufacturing process is performed before the dowel is evaluated or inspected for suitability for implant use. Thus, where donor bone is not suitable for dowel manufacture or the donor bone has been improperly machined, much time and effort is needlessly wasted in performing additional manufacturing steps on a dowel which will never be useable as an implant.

Accordingly, a continuing need exists for methods and instrumentation for precisely manufacturing a bone dowel from a bone and for quickly identifying unsuitable bone early in the machining process to avoid undue waste of time and effort.

SUMMARY

In accordance with the present disclosure, instrumentation for manufacturing a bone dowel from human or animal cadaveric bone and instrumentation for evaluating the suitability of the bone and/or dowel for implant use after each step of the manufacturing process is provided. Such instrumentation for manufacturing a bone dowel includes a blanking or coring apparatus, a milling apparatus, a threading apparatus and a tapping apparatus. A series of gauges are provided to inspect and determine the suitability of the bone dowel at each step of the manufacturing process. By inspecting the dowel being manufactured after each step of the manufacturing process, time and effort which is needlessly wasted during completion of the manufacturing of dowels which are unsuitable for implant use (due to unsuitable bone and/or inaccurate machining of bone) can be avoided.

Instrumentation for more accurately positioning bone and the partially manufactured dowel into the instrumentation for machining the dowel is also provided. Such instrumentation includes a gauge for positioning a piece of bone in relation to the coring apparatus, and mounting blocks for securing the partially manufactured dowel in relation to the milling, threading and tapping apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the presently disclosed instrumentation for manufacturing and evaluating intervertebral implants are described herein with reference to the drawings, wherein:

FIG. 1

is a perspective of one preferred embodiment of the presently disclosed blanking or coring apparatus;

FIG. 1A

is a perspective view of the presently disclosed Shimp gauge;

FIG. 2

is a perspective view of a bone dowel formed by the coring apparatus shown in

FIG. 1

;

FIG. 3

is a perspective view with parts separated of a holding block of the presently disclosed dowel milling apparatus;

FIG. 4

is a perspective view of the holding block shown in

FIG. 3

in the assembled condition;

FIG. 5

is a side view of the holding block shown in

FIG. 3

;

FIG. 6

is a perspective view of one preferred embodiment of the presently disclosed milling apparatus;

FIG. 7

is a perspective view of the bone dowel formed by the milling apparatus shown in

FIG. 6

;

FIG. 8

is a perspective view of the slot milling bit of the milling apparatus shown in

FIG. 6

;

FIG. 9

is a perspective view of the support blocks of the second adjustment vise of the coring apparatus shown in

FIG. 1

;

FIG. 10

is a side view of the support block shown in

FIG. 9

;

FIG. 11

is a backside view of the support block shown in

FIG. 9

;

FIGS. 12

a

-

12

c

are perspective, front and side views of one embodiment of the presently disclosed wall thickness GO/NO GO gauge;

FIG. 13

is a perspective view of one embodiment of the presently disclosed slot width GO/NO GO gauge;

FIG. 14

is a perspective view of one embodiment of the presently disclosed outer diameter and length gauge;

FIG. 15

is a perspective view of one embodiment of the presently disclosed pilot hole gauge;

FIG. 16

is a perspective view with parts separated of one embodiment of the presently disclosed drilling holding block;

FIG. 17

is a perspective view of the bone dowel after the pilot hole has been drilled and tapped;

FIG. 18

is a perspective of the holding block shown in

FIG. 16

in the assembled condition;

FIG. 19

is a perspective view of one embodiment of the presently disclosed tapping holding block;

FIG. 20

is a perspective view of the presently disclosed dowel threading tool;

FIG. 21

is a perspective view of a presently disclosed dowel thread gauge; and

FIG. 22

is a perspective view of a threaded bone dowel after the outer surface has been threaded using the dowel threading tool shown in FIG.

20

.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The embodiment of the methods and apparatus disclosed herein are discussed in terms of skeletal implantation and related instrumentation. It is contemplated that the present methods and apparatus for manufacturing implants find application in spinal implantation procedures whereby a fusion implant is placed into a receiving bed formed in an intervertebral space.

In one particular embodiment in accordance with the principles of the present disclosure, a procedure is described for machining and inspecting fusion implants including threaded cortical dowels. It is contemplated that the procedure may include processes such as coring a dowel, milling a dowel, tapping a dowel and threading a dowel. These processes are described in greater detail below.

Referring now in detail to the drawings wherein like reference numerals identify similar or like components throughout the several views,

FIG. 1

illustrates aspects of a process for coring a bone dowel using a dowel coring apparatus

10

.

Coring of a Dowel

A pneumatic dowel blanking or coring apparatus

10

is prepared and set up for operation prior to the coring process by connecting an air supply line

12

of dowel coring apparatus

10

to an air supply. The dowel coring apparatus

10

includes a drill press

11

. Typically, an air pressure of 100 psi and above is utilized to drive a dowel cutter

24

, although coring apparatus using lesser pressures may also be used. Dowel coring apparatus

10

is also attached to a water supply (not shown) for irrigation.

A bone shaft

14

is selected for producing the threaded cortical dowels. Bone shaft

14

is preferably a long bone shaft, i.e., the shaft of a femur, ulna, radius, tibia or fibula, although other bone may also be used. A cortical shaft portion

16

of bone shaft

14

includes a medullary canal

18

which is examined to determine the appropriate size dowel cutter to be used. The dowel cutter includes a hollow cylindrical bit which must be greater in diameter than the medullary canal of bone shaft

14

. It is contemplated that dowel cutter sizes such as, for example, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, etc., maybe used.

After the appropriate size dowel cutter

24

is selected, it is secured to dowel coring apparatus

10

. Dowel cutter

24

is secured to shaft

26

of dowel coring apparatus

10

in a known manner and includes an annular serrated edge

14

. Dowel cutter

24

is configured to penetrate bone shaft

14

to blank a dowel.

Bone shaft

14

is placed into a vise assembly

28

of dowel coring apparatus

10

so that a targeted portion of shaft

14

may be blanked to produce the dowel. A first adjustment vise

30

positions bone shaft

14

along at least one axis so that canal

18

is centered with dowel cutter

24

. First adjustment vise

30

is manipulated by knob

31

to adjust positioning of bone shaft

14

relative to dowel cutter

24

.

A second adjustment vise

32

secures and stabilizes bone shaft

14

in position for coring. Second adjustment vise

32

includes support blocks

31

a

and

31

b

and inserts

34

a

and

34

b

. One insert is supported on each support block. Each support block is rotatably secured to vise

32

and each insert is vertically adjustable in relation to a respective support block to facilitate securement of the irregular shape of bone shaft portion

16

within vise

32

. Second adjustment vise

32

is manipulated by rotating knob

33

to advance insert

34

a

towards insert

34

b

to clamp shaft portion

16

therebetween. It is contemplated that the components of the first and second adjustment vises may be movable by motorized means. Referring to

FIGS. 9-11

, inserts

34

a

and

34

b

have angled cavities

36

configured to receive bone shaft

14

. It is contemplated that angled cavities

36

may have alternate angular configurations or may comprise other geometric configurations such as, for example, elliptical, parabolic, etc.

As illustrated in

FIG. 1A

, a shimp gauge

38

can be employed for properly aligning dowel cutter

24

with bone shaft

14

. Shimp gauge

38

includes flexible walls

39

a

and

39

b

which are positioned on opposite sides of and snap onto dowel cutter

24

. Gauge

38

includes a cross hair

40

for aligning dowel cutter

24

with the center of the medullary canal

18

of bone shaft

14

. More specifically, with gauge

38

positioned about dowel cutter

24

, knob

31

can be turned to adjust the position of bone shaft

14

with respect to dowel cutter

24

. Bone shaft

14

should be positioned such that cross hair

40

is aligned with and positioned in front of the medullary canal at bone shaft

14

. A window cavity

42

is formed about cross hair

40

and allows for a visual determination of the adequacy of thickness of cortical shaft portion

16

, i.e., the cortical thickness of bone shaft

14

should cover the space between cross hair

40

and the edge

42

′ of window

42

. To assist in visualization of canal

18

during subsequent cuts, it is suggested to remove bone shaft

14

from vise assembly

28

and saw off the previously cut end of cortical shaft portion

16

.

Referring back to

FIG. 1

, during operation, the air and water supplies connected to dowel coring apparatus

10

are activated. As a safety feature, the air and water supplies are activated only after dowel cutter

24

is installed. A handle

44

of dowel coring apparatus

10

is manipulated, such as, for example, by gradually being pulled down in the direction indicated by arrow “A”, until dowel cutter

24

, which is rotating, passes through bone shaft

14

. Handle

44

is thereafter released. It is contemplated that manipulation of handle

44

should be performed slowly because cutting too fast may result in off-center drilling, resulting in possible damage to the bone dowel. It is further contemplated that the components of the dowel coring apparatus may be movable by motorized means.

Referring to

FIG. 2

, a bone dowel

46

is produced and is disposed within dowel cutter

24

. Bone dowel

46

, which comprises a cylindrical bone blank having a throughbore defined by medullary canal

18

, may be removed from dowel cutter

24

by hand or by the use of compressed air.

Referring to

FIGS. 12A-12C

, an in process check of the sidewall thickness of bone dowel

46

is performed to determine the adequacy thereof. Bone dowel

46

is rinsed in water to remove loose bone particles from its exterior and medullary canal

18

. The cortical sidewall thickness of bone dowel

46

is checked using a gauge, such as the universal Wall Thickness Go/No Go gauge

48

. Using a gauge end

50

, which is suitably marked, e.g., “wall”, medullary canal

18

of bone dowel

46

is positioned about post

52

such that the thinnest portion of the bone wall defined between medullary canal

18

and the outer circumference of bone dowel

46

is permitted to freely fall between gauge post

52

and sidewall

54

of gauge

48

. Bone dowel

46

should not be forced or pushed between gauge post

52

and sidewall

54

, as a false measurement for adequacy of the bone dowel may be taken. If the dowel falls to the bottom of post

52

, the bone wall is too thin, and the bone dowel is rejected. This adequacy procedure is repeated for the opposite side of canal

18

. If the bone dowel wall is unacceptable, i.e., rejected, bone shaft

14

should be rechecked for centering and/or a different size, i.e., larger, dowel cutter should be used. It is contemplated that reassessment of the suitability of the donor for bone dowel production may be reconsidered. If bone dowel

46

is acceptable, proceed in the manufacturing method.

Referring again to

FIGS. 12A-12C

, an in process check of cortical face wall thickness may be checked using the universal Wall Thickness Go/No Go gauge

48

. Using gauge end

56

, which is suitably marked, e.g., “Face”, medullary canal

18

of bone dowel

46

is positioned onto post

58

with one end of dowel

46

positioned against face wall

60

of gauge

48

at its thinnest point. Bone dowel

46

is permitted to freely fall between gauge post

58

and face wall

60

. For the reasons discussed above, bone dowel

46

should not be forced or pushed between gauge post

58

and face wall

60

. If bone dowel

46

falls to the bottom of post

58

, it is rejected, i.e., the wall thickness is insufficient for dowel use. If the face wall thickness of bone dowel

46

is unacceptable, bone dowel

46

is rejected and placement of bone shaft

14

in dowel coring apparatus

10

should be checked. If the bone dowel is rejected, the suitability of the donor bone for bone dowel production may be reconsidered. If bone dowel

46

is acceptable, proceed in the manufacturing method.

Referring to

FIG. 14

, an in process check of the outside diameter and length of bone dowel

46

is performed to determine the adequacy thereof. Bone dowel

46

is placed in an appropriate outside diameter and length Go/No Go gauge

62

. Bone dowel

46

is inserted into the No Go end

64

of gauge

62

. If bone dowel

46

is acceptable (does not fit in No-Go end

64

) proceed to check bone dowel

46

in the Go end

66

of gauge

62

by inserting bone dowel

46

into the Go end

66

of gauge

62

so that a slot of bone dowel

46

mates on a gauge boss

68

and medullary canal

18

is visible in window

70

. If bone dowel

46

fits in the Go end

66

of gauge

62

, the outside diameter is acceptable. If the outside diameter is acceptable, the length of bone dowel

46

can be checked by viewing length marker

72

to determine if the length falls within an acceptable range. If the length is acceptable, bone dowel

46

is acceptable. If bone dowel

46

fails, bone dowel

46

is rejected and dowel coring apparatus

10

should be checked. If the diameter of bone dowel

46

is acceptable, but the length is too long, bone dowel

46

is cut to a proper length and rechecked. If the length of bone dowel

46

is too short, bone dowel

46

is rejected.

The results of the above mentioned in-process checking procedures may be recorded on an attached log or the like.

Milling of Slot and Face

Referring to

FIGS. 3-8

, a dowel milling apparatus

74

is prepared and set up for operation during the manufacturing process by connecting an air supply

75

to dowel milling apparatus

74

(FIG.

6

). Typically, a pressure of 100 psi and above is utilized, although milling apparatus requiring lower air pressures may also be used. A water supply (not shown) is connected to dowel milling apparatus

74

for irrigation.

Referring to

FIGS. 6 and 8

, a face and slot milling bit

76

is secured to dowel milling apparatus

74

. As a safety feature, air supply

75

should not be connected to apparatus

74

until the bit is secured to the dowel milling apparatus

74

. Moreover, the water supply should only be turned on when using dowel milling apparatus

74

.

Referring to

FIGS. 3-5

, bone dowel

46

is inserted into an appropriately sized holding block

78

. Bone dowel

46

is positioned in holding block

78

such that canal

18

is visible through block window

80

and the slot is milled approximately perpendicular to canal

18

. The depth of bone dowel

46

as seated in block

78

is set with use of a guide

82

attached to block

78

, as shown in FIG.

5

. Set screws

84

are tightened so that block

78

holds bone dowel

46

securely in place. Up to three bone dowels can be placed into holding block

78

at one time. It is contemplated that holding block

78

may be alternately configured to hold a single or multiple number of bone dowels.

Referring back to

FIG. 6

, holding block

78

is inserted into a pre-centered vise

86

positioned on dowel milling apparatus

74

and vise

86

is secured.

Dowel milling apparatus

74

is activated by activating the water and air supplies. A handle

88

is manipulated to feed block

78

throughface and slot milling bit

76

in the forward and reverse directions. It is contemplated that bone dowel

46

should only pass through face and slot milling bit

76

forwards and reverse once. It is further contemplated that bone dowel

46

should not have reverse movement until face and slot milling bit

76

is completely clear of the last bone dowel in block

78

. It is envisioned that prior to stopping dowel milling apparatus

74

, face and slot milling bit

76

is clear of bone dowel

46

. Dowel milling apparatus

74

is deactivated and holding block

78

is removed from vise

86

.

Referring to

FIG. 7

, after the milling step described above, bone dowel

46

has a milled slot

90

and smooth face

91

. Slot

90

is oriented substantially perpendicular to medullary canal

18

. Bone dowel

46

may be removed from block

78

.

Referring to

FIG. 13

, an in process check of the slot width is performed using the universal Slot Width Go/No Go Gauge

102

. Go side

104

of gauge

102

is inserted into slot

90

of bone dowel

46

so that it extends through the entire length of slot

90

. If gauge

102

extends through the entire slot, it is acceptable. If it does not extend through the entire slot, bone dowel

46

is rejected. If bone dowel

46

is acceptable, proceed to check a No Go side

106

in the same manner. No Go side

106

should not fit into slot

90

. Thus, if it does, slot

90

is too wide and bone dowel

46

is rejected. If No Go side

106

does not fit into slot

90

, it is acceptable. If slot

90

is rejected, milling apparatus

74

should be checked. If bone dowel

46

is acceptable, proceed in the manufacturing process as follows.

Referring to

FIG. 16

, bone dowel

46

is placed in a holding block

92

for drilling and tapping an insertion tool engaging bore

95

. Bone dowel

46

is positioned with milled slot

90

on top. Up to three bone dowels can be placed into holding block

92

at one time. It is contemplated that holding block

92

may be alternately configured to hold a single or multiple number of bone dowels. Referring to

FIG. 17

, holding block

92

includes a drill centering device

93

having a guide bore

97

to facilitate proper positioning of a pilot hole drill bit

94

for drilling hole

95

in bone dowel

46

.

Drill centering device

93

includes a drill guide

96

which defines guide bore

97

and cooperates with pilot hole drill bit

94

for drilling pilot hole

95

. Pilot hole drill bit

94

is secured to an electric drill or the like. Manual activation of pilot hole drill bit

94

is also contemplated.

Pilot hole drill bit

94

is inserted through guide bore

97

to drill pilot hole

95

. Drill bit

94

is rotated clockwise until drill bit

94

is observed through a holding block window (not shown) inside canal

18

of bone dowel

46

and drill bit

94

turns freely. Pilot hole drill bit

94

is removed by rotating drill bit

94

counter clockwise. Pilot hole drill bit

94

should not be advanced such as to engage the opposite wall of canal

18

.

Referring to

FIG. 15

, an in process check of pilot hole

95

of bone dowel

46

is performed to determine the adequacy of the inner diameter thereof. To accomplish this, pilot hole

95

is visually checked to ensure that it is approximately centered and that it passes into canal

18

. Next, the inner diameter of pilot hole

95

is checked with Pilot Hole Pin Gauge

97

. To accomplish this, end

98

of gauge

97

is inserted into pilot hole

95

. Insertion should not be forced. If end

98

extends though pilot hole

95

and into canal

18

, the diameter of pilot hole

95

is too large and bone dowel

46

is not acceptable. If pilot hole

95

does not extend into canal

18

, it can be drilled through using a hand held tool and rechecked for proper inner diameter, as discussed above.

Referring to

FIG. 19

, pilot hole

95

is now threaded. To accomplish this, a tap centering device

101

is secured to mounting block

92

. Tap centering device

101

is similar to drill centering device

93

except that guide bore

97

′ is larger than guide bore

97

to allow passage of tap

99

. A tap

99

is inserted through guide bore

97

′ of device

101

to thread pilot hole

95

of bone dowel

46

. Tap

99

is removed after this is accomplished by manually twisting tap

99

counter clockwise from guide bore

97

′. It is contemplated that tap

99

may be operated by motorized means. It is further contemplated that tap

99

should not be inserted so far as to engage the opposite wall of canal

18

.

Bone dowel

46

can now be removed from holding block

92

. Bone dowel

46

is rinsed in water to remove loose bone particles from its exterior and medullary canal

18

. Referring to FIG.

18

, bone dowel

46

now includes internally threaded pilot hole

95

. Referring again to

FIG. 15

, an end

100

of gauge

97

may be used to check the adequacy of the threads of pilot hole

95

.

An in-process check of the cortical face wall thickness of bone dowel

46

may be conducted using the universal wall thickness Go/No Go gauge

48

, similar to that described above with regard to

FIGS. 12

a

-

12

c

. If the face wall thickness of bone dowel

46

is unacceptable, reject bone dowel

46

and recheck slot and face milling bit

76

and placement in holding block

78

. Also reassess the suitability of the donor bone being used for dowel production. If acceptable, proceed in the manufacturing process.

Threading

Referring to

FIGS. 20 and 21

, bone dowel

46

can now be externally threaded. A threading tool

108

is prepared and set up for operation during the manufacturing process. A water supply (not shown) is connected to threading tool

108

for irrigation. It is contemplated that the water supply should be activated only when threading tool

108

is in use. It is further contemplated that threading tool

108

may be configured for a variety of different size bone dowels, such as, for example, 14 mm, 16 mm, 18 mm, 20 mm, etc. Bone dowel

46

is positioned onto a loading shelf

110

within threading tool

108

through a window

112

formed in tool

108

. Threading tool

108

includes a plurality of circumferentially spaced inserts

114

having teeth for engaging and threading the exterior cylindrical surface of bone dowel

46

. A driver

116

engages the slotted end of bone dowel

46

to drive bone dowel

46

through threading tool

108

to form the threads on the exterior of bone dowel

46

. Bone dowel

46

is placed onto driver

116

such that a tang

118

located at an end of driver

116

engages slot

90

of bone dowel

46

.

Tang

118

is configured to engage slot

90

of bone dowel

46

to manually advance bone dowel

46

through tool

108

by turning a handle

120

clockwise. When bone dowel

46

has passed entirely through threading tool

108

, it will discharge from tool

108

into a cradle or the like (not shown) positioned at one end of tool

108

. Bone dowel

46

should not be backed through threads

114

of tool

108

once it has passed through initially, nor should bone dowel

46

be run through twice. Referring to

FIG. 21

, bone dowel

46

now includes external threads

122

.

Referring to

FIG. 22

, an in process check of threads

122

of bone dowel

46

is performed to determine the adequacy thereof. To accomplish this, dowel threads

122

are checked using thread check gauge

124

which includes verifying threads

126

. Verifying threads

126

are aligned with dowel threads

122

and threads

122

of bone dowel

46

are visually checked for gaps, unevenness, and improper fit. If gauge

124

fits threads

122

without gaps and unevenness, threads

122

are acceptable. If threads

122

are unacceptable, bone dowel

46

is rejected and threading tool

108

is inspected for quality and adjusted. If threads

122

are acceptable, proceed in the manufacturing process as follows:

An in-process check of the outside diameter and length of bone dowel

46

may be conducted using outside diameter and length gauge

62

, similar to that described above with regard to FIG.

14

. After completion of the above method, each acceptable bone dowel

46

is sterility tested, measured and packaged for use.

It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the double sided gauges shown in

FIGS. 14-17

can be formed as two separate gauges. The gauges may also be provided in a kit for forming bone dowels having any desired dimensions. Moreover, the coring and milling apparatus can be electrically, hydraulically, or pneumatically actuated apparatus. Therefore, the above description should not be construed as limiting but exemplifications of the various embodiments. One skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.