CA2243152C

CA2243152C - Diaphysial cortical dowel

Info

Publication number: CA2243152C
Application number: CA002243152A
Authority: CA
Inventors: Kevin Carter; David Dulebohn; Nicholas E. Grivas; Jamie M. Grooms
Original assignee: University of Florida Tissue Bank Inc
Current assignee: RTI Biologics Inc
Priority date: 1996-01-16
Filing date: 1997-01-16
Publication date: 2004-03-30
Anticipated expiration: 2017-01-16
Also published as: US6096081A; US5814084A; DE69715817T2; AU1700597A; ATE224680T1; DE69715817D1; WO1997025945A1; EP0876129B1; AU704228B2; HUP9902187A3; EP0876129A1; CA2243152A1; PL328226A1; ES2186865T3; CZ220698A3; JP2000503231A; JP3935506B2; HUP9902187A2

Abstract

A dowel (300) is provided by obtaining a plug from the shaft (diaphysis) of various tong bones. The dowel (300,) has an infra-medullary canal (30) which can be packed with any of a variety of osteogenic materials. The dowel (300) has a cortical surface (10) into which an instrument attachment hole (15) may be machined and onto which an alignment marl; (16) may be inscribed for proper orientation of the infra-medullary canal (30) or a driver slot (56) which may be used to assist in further machining of the bone dowel (300).

The dowel (300) has a chamfered insertion end and has improved biomechanical and vertebral fusion induction properties as compared to standard dowles known in the art. A threaded (31) or grooved (32) dowel (300) and an apparatus (400) for efficient production thereof are also provided.

Description

DESCRIPTION
DIAPHYSIAL CORTICAL DOWEL
Backxaround of the Invention i. Field of the Invention: "fhe invention provides a novel dowel machined from the cortex of bone diaphyses and methods of use thereof.
ii. Ba und: It is common for patients presenting with spinal trauma or pathology to require the fusia~n of two or more vertebra. In the art, a standard solution to this problem is to create a cavity between two adjacent vertebra to aooept the insertion of a dowel made.from bone or another material. For this purpose, a dowel ;lrnown as the Cloward Dowel has been in use for mmy years.
That device is a generally circular pin made by drilling an allogeneic or sutogenic plug from the cancellous bone of the ilium (i.e., the hip bone). As such, this bone has two cortical surfaces (i.e., it is bicmtical) and has an open, latticod or porous structure between the two cortical surfaces.
Unfortunately, such dowels have very poor biomechanical properties, principally being susceptible to compnssian. Accordingly, such dowels present the major danger of collapsing prior to fusion of the adjacent vertebra be<wan which such a dowel is inserted.
A dowel of greater biamochaztical properties has bees produced from allogeneic femoral or tibial conldyles (i.e., the rounded prominence at the end of the femur or tibia where such bones ertica~late with other bones). The result of drilling a plug from such a coadyle is a unicortical dowel.
Such unicactical dowels ate available from most tissue banks, including the University of Florida Tissue Bank, Inc., (see, far example, our Allograft Catalog, product numbers 280012, 280014, and 280016; this catalog and these products are available on request by calling 904-462-3097, or by calling 1-800-0AGRAFT, or by writing to the University of Florida Tissue Bank, Inc., 1 Progress Boulevard., P.O. Box 31, S. Wing, Alachua, Florida 32615). While such unicortical dowels represent a major advance over the bicortical dowels of Cloward, described above, from a biomechanical point of view, the biomechanical properties of the diaphysial cortical dowel of the instant invention is expoc~d to rat a substantial improvement over the unicortical dowels, due to the greater density of source bone, as will be evident from a reading of the full disclosure which follows.

In addition to the known ~;loward and unicortical dowels, a number of United States Patents have beers found dealing with the general area of dowels for achieving vertebral fusions. Thus, for example, U.S. PateW No. 5,0I5,247 discloses a threaded spinal implant which, when placed between two adjacent vertebrae, directly participates and is inwrporated in the ensuing fusion. The implant is made of a hollow metal casing which is filled with osteogenic material. A
plurality of perforations are provided in the casing so that bone can grow into and out of the implant.
Metal threads and tabs are provided to insc,~rt and prevent backing out of the implant, respectively.
However, that implant is made out of metal and thus is a foreign object which is inserted into the spine and is thus never fully incorporated into the fusion. Furthermore, as the implant is preferably made of titanium, production of the implant requires the use of specialized metal molding and machining, and production of the implant material itself, which is expensive.
In U.S. Patent No. 4,6?7,853, a method of producing a prosthesis for replacement of articular cartilage and the prostheses so produced is disclosed. The prostheses of the '853 patent, principally designed for articulating cartilage replacement, are anachined from allogenic or xenogencic bone segments and then demiz~alized to produce a bone fragment with a spongy texture similar to natural cartilage. The prostheses are also farmed to render the material non-antigenic.
While the methods of the '853 patent may be used to alter the properties of the diaphysiai cortical dowel of the instant invention, thre '853 patent does not teach or suggest the novel device and method of the instant invention.
In U.S. Patent No. 5, 03,049, a flexible prosthesis and a method for making such prostheses are disclosed. 'The pry inchuies machining a bone, demineraliziag the bone to impart a desired degree of flexibility, and tanning to render the material non-antigenic. This patent is gay ~ ;a a to the di,ae found in the '853 patcat discussed above, except that the particular applicability of the disclosed process to the production of an outer ear prosthesis is emphasized.
In U.S. Patent No. 5,306,303, a bore induction method is disclosed which consists of implanting a bone morphogrnetic, protein-free cxraanic in the soft tissue or bore of an animal. The ceramic disclosed as preferable is calcium phosphate and the use of such material for achieving spinal interveatebral joist fusions (disk arthroplasty) is suggested. The material and product of the '303 patens, aside from its possible use for a purpose similar to that for which the instant product is designed, bears little or no resemblance to the instant invention.
In U.S. Patent No. 5,171,279, a method for subcutaneous suprafascial pedicular internal fixation of vertebra; of the spine is disclosed to facilitate graft fusion.
The method included excision WO 97!259'15 PCT/US97/00630 of the uucieus of an affected disc, preparation of a bone graft, instrumentation of the vertebrae for fixation, and introduction of a bone gra$ into the resected nuclear space.
Metallic fixation hardware is disclosed as the principal aspect of the claimed invention. Accordingly, aside from dealing with the same general problem, the invention disclosed and claimed in the '279 patent bears Little resemblance to the diaphysial cortical dowel and method of the instant invention.
Accordingly, having reviewed many solutions attempted in the field prior to the instant disclosure, it is concluded that there remains the need for a vertebral fusion graft which has superior biomechanical and vertebral fusion promoting properties. The instant invention provides such a graft as well as a method for making and using the graft.
Brief Summary of the Invention The diaphysial cortical dowel of this invention is a graft useful in cervical or thoracic and Lumbar fusions. For cervical fnsions, the dowel is preferably obtained from the allogeneic fibula, radius, ulna and occasionally, from small humeri. The dimensions of such dowels are typically between about 8-15 mm in length (depth) and about 10-14 mm in diameter. For thoracic and lumbar fusion.C, the dowel is preferably obtained from the humerus, femur or tibia.
The dimensions of such dowels are typically between about 10-30 mm in length (depth) and about 14-20 mm in diameter.
In each case, the dowel is obtained as a transverse plug from the diaphysis of these bones.
Accordingly, each dowel has the feature of having the natural infra-medullary canal of the source bone forming a cavity through the dowel, perpendicular to the length of the dowel, which can be pre-packect with allogeneic cancellous bone, autogenous bone fragments, hydroxyapatite, bioglass, mixtures of these elements or any other bioceramic or osteogenic material to promote rapid fusion of the vertebrae between which the dowel is inserted. Such dowels are generally referred to herein as "diaphysial" cortical dowels. Unlike prior bone grafts, the present invention provides a generally cylindrical dowel of cortical bone having a canal through the dowel generally perpendicular to the long a~;is of the dowel.
The method for preparing and using the diaphysial cortical dowel of this invention comprises the steps of obtaining a plug from the diaphysis of an appropriate donor bone or a plug from an alternate acceptable cortical bone source through which a perpendicular canal may be machvied. Typically, the donor will have been extensively screened for communicable diseases, cancer, and at-risk behavior prior to acceptance of the donor bone for dowel formation. The plug is then, machined, preferably in a class 10 clean room, to the dimensions desired. Optionally, a groove is inscribed on the circumference of the dowel to prevent backing-out of the dowel. Another option is to inscribe a thread onto the cylindrical surface (circumference) of the dowel to improve fixation and prevent backing out. Chamfering of the forward end of the dowel which is to be inserted into a cavity formed between adjacent vertebrae is also preferred. The curvature of the chamfered end aids in the ease of insertion. Preferably, an instrument attachment hole is machined in the opposite end of the dowel from the chamfered end. Preferably, a score mark is inscribed on the cortical end into which the instrument attachment hole is machined so that the surgeon can align the infra-meduklary canal so that the canal is parallel with the length of the recipient's spinal column.
In use, the surgeon creates a cavity between two adjacent vertebra that are to be fused. The autogenous bone fragments may be collected and packed into the infra-medullary canal of the diaphysial cortical dowel, or the dowel may be used with a pre-packed osteogenic composition. The dowel is mounted on an instrument via the instrument attachment hole and carefully inserted into the cavity created between the adjacent vertebrae to be fused. Over a period of several months, it is found that substantial fusion of the adjacent vertebrae occurs.
Accordingly, it is one object of this invention to provide a diaphysiak cortical dowel made from bone for insertion between vertebrae to be fused.
Another object is to improve patient incidence of safe and satisfactory fusion.
Another object of this invention is to provide a dowel for vertebral fusions which has improved biomechanical properties over standard Cloward Dowels and unicortical dowels known in the art.
Another object of this invention is to provide a dowel with improved osteogenic and vertebral fusion promoting capacity.
Another object of this invention is to provide a dowel with a natural canal running therethrough to accept packing having osteogenic properties.
Another object of this invention is to provide a method for making a novel diaphysial cortical dowel.
2S Another object of this invention is to provide a method for using the novel diaphysial cortical dowel of this invention.
Additional objects and advantages of the diaphysial cortical dowel of this invention will become apparent from the full disclosure which follows.
Brief Summary of the Figures Figure 1A depicts the structure of a standard unicorticak dowel known in the art.
Figure 1B depicts the structure of a standard Cloward Dowel known in the art.

Figure 1C depicts the structure of one embodiment of the diaphysial cortical dowel of this invention.
Figure 2A depicts the ACF dowel with the instrument attachment hole and score mark.
Figure 2B depicts the ATIF or ALIF dowel with the instrument attachment hole and score 5 marl:.
Figure 3A and 3B depict one embodiment of this invention in which the dowel is threaded.
Figure 3C and 3D depict one embodiment of this invention in which the dowel is grooved.
Figure 4A is a side view of a dowel "blank" of this invention.
Figure 4B is an end-on view of the dowel "blank".
Figure SA is a threaded dowel of this invention.
Figure SB is an end-on view of the threaded dowel.
Figure SC is a detail of one embodiment of the thread of one embodiment of the threaded dowel of this invention.
Figure 6A is a top plan view of one embodiment of a dowel threader of this invention.
Figure 6B is a side view of the dowel threader of this invention.
Figure 6C is an end-on view of the dowel threader of this invention showing the elements of the cutter assembly.
Figure 7A is a detailed view of a single tooth of one cutter blade of the dowel threader.
Figure 7B is an end-on view of the tooth profile.
Figure 7C is a global side view of a cutter blade.
Figure ?D is a detailed side view of cutter blade 421.
Figure ?E is a detailed side view of cutter blade 422.
Detailed Description of the Invention The diaphysial cortical dowel of this invention is a graft useful in cervical or thoracic and lumbar fusions. For cervical fusions, the dowel is preferably obtained from the fibula, radius, ulna and occasionally, from small humeri. The dimensions of such dowels are typically between about 8-15 mm in length (depth) and about 10-14 mm in diameter. For thoracic and lumbar fusions, the dowel is preferably obtained from the humerus, femur or tibia. The dimensions of such dowels are typically between about 10-30 mm in length (depth) and about 14-20 mm in diameter. In each case, the dowel is obtained as a transverse plug from the diaphysis of these long bones. Preferably, the bone plug.; are obtained using a diamond or hard metal tipped cutting bit which is water cleaned and cooled. (:onunercially available bits (e.g core drills) having a generally circular nature and an internal v~icant diameter between about 10 mm to about 20 mm are. amenable to use for obtention _. ,ø~ Sa.~.SUBST1TUTE._SHEET (RULE 26) a G
of these bone plugs. Such cure drills arc available. for example, ti~om Starlite, Inc. A machine for obtention of cndu- and cur'tla,ll duw'cls consists of a pneumatic driven miniature lathe which is fabricated li-om stainless steel and anodized aluminum. It has a spring loaded carriage which travels parallel to the cutter. The carriage rides on two runners which are I .0 inch (?.~-t cm) stainless rods and has a travel distance of approximately 8.0 inches (?0.33 cm). One runner has set pin holes on the runnin~~ rod which will stop the carriage from movin~~ when the set pin is placed into the desired hole.
The carriage is moveable from side to side with a knob which has ~~raduatiuns in metric and in En~~lish.
This allows the 'raft to be positioned. On this carriage is a vice with clamps the ;raft and holds it in place while the dowl is b~in~~ cut. The vice has a cut out area in the jaws to allow clearance for the cutter. The lathe has a drive system which is a pmumatic motor with a valve controller which allows a desired RPM to be set.
First, the carria~=a is manually pulled back and lucked in place with a set pin. Second, the =raft is loaded into the vice and is alit=ned with the cutter. Third. the machine is stared and the RPM is set. by using, a f~nob on the valve control. Fourth. the set pin, which allows the graft to be loaded onto I~ the cutter to cut the dowel. Once the cutter has cut all the way through the ~~raft the carria~~e will stop a on a set pin. Fifth. sterile water is used to eject dowel out of the cutter. ;
It is fully autoclavable and has a stainless steel vice and'ur clamping fixture to hold ~gratts for cutting=
dowels. The 'raft can be positioned to within 0.001" (0.03 mm) of an inch which creates dowel uniformity durin~~ the cutting process.
''0 The cutter used in conjunction with the above machine can produce dowels ran~~in!; from ~
mm to 30 mm diameters and the sizes of the cutters are 10.6 mm: I I.0 mm. 1 ~'.0 mm: 13.0 mm: I-t.0 mm: 16.0 mm: and 18.0 mm. The composition of the cutters is stainless steel with a diamond powder cuttings surface mhich produces a very smooth surface on the wall of the dowels. In addition. sterile water is used to cool and remove debris from draft and!ur dowel as the dowel is bein' cut (hydro ~5 infusion). The water travels down throu~'h the center of the cutter to irr~~gate as w~el( as clean the dowel under pressure. In addition. the water aides in ejecting the dowel from the cutter.
Plu~'s having' a depth of about 8 mm to about 30 mm are generally acceptable, with appropriate gradations in length and diameter naturally being available at the option of the machinist.
Accordingly, for cervical dowels. also referred to herein as anterior cervical fusion or ACF dowels.
30 len~~ths of 8 mm, 9 mm. up to about I ~ men are desirable. Dowels of ditTerin~ diameter are most conveniently obtained as follows:
Diameter Source 10.6-I I mm fibula se ~,~~r,~s~~~~ SHEET

_ 7 I2 mm radius I4 mm ulna 14+ mm small humeri Dowels for thoracic and lumbar fusions, also referred to herein as anterior thoracic inner body fission (ATIF) and anterior lumbar inner body fusion (ALIF) dowels, respectively, having a depth of between about 10 - 30 mm, and preferably between about 15-24 mm, are generally acceptable, depending on the needs of a particular patient. Dowels of differing diameter for thoracic and lumbar fi>sions are most conveniently obtained as follows:
Diameter ours 14-16 mm humerus 16-18 mm femur I8-20 mm tibia In every case, a consenting donor (i.e., a donor card or other form of acceptance to serve as a donor) is screened for a wide variety of communicable diseases and pathogens, including human immunodeficiency virus, cytomegalovirus, hepatitis B, hepatitis C and several other pathogens.
These tc,~sts may be conducted by any of a number of means conventional in the art, including but not limited oo ELISA assays, PCR assays, or hemagglutination. Such testing follows the requirements of (l) American Association of Tissue Banks, Technical Manual for Tissue Banking, Technical Manual - Musculoskeletal Tissues, pages M19-M20; (ii) The Food and Drug Administration, Interim. Rule, Federal Register / Voi. 58, No. 238 / Tuesday, December 14, 1993 / Rules and Regulations / 655 l 7, D. Infectious Disease Testing and Donor Screening;
(iii) MMWR / Vol. 43 / No. RR-8, Guidelines for Preventing Transmission of Human Immunodeficiency Virus Through Transplantation of Human Tissue and Organs, pages 4-7; (iv) Florida Administrative Weekly, Vol.
I0, No. 34, August 21, 1992, 59A-L001-OI4 59A-1.005(12)(c}, F.A.C., (12) (a) -(h), 59A-1.005(15), F.A.C., (4) (a) - (8). In addition to a battery of standard biochemical assays, the donor, ar their next of kin, is interviewed to ascertain whether the donor engaged in any of a number of high risk behaviors such as having multiple sexual partners, suffering from hemophilia, engaging in intravenous drug use etc. Once a donor has been ascertained to be acceptable, the bones useful for obtention of the dowels as described above are recovered and cleaned. The f nal machined product may be stored, frozen or freeze-dried and vacuum sealed for later use.
Since the dowels are obtained from transverse plugs across the diaphysis of long bones, each dowel has the feature of having the natural infra-medullary canal of the source bone forming a cavity through the dowel perpendicular to the length of the dowel. The canal cavity in the long bone is, in vivo, filled with bone-marrow. in the standard Cloward Dowel and unicortical dowels known in the art, no such natural cavity e~sts and the cancellous bone that forms the body of such dowels tends to be too brittle to accept machining of such a cavity. The instant dowels, by the nature of their origin, are almady available with such a cavity. Naturally, based on this disclosure, those skilled in the art will recognize that other prone sources could be used which do not have the infra-medullary canal, and if su~cie;nt strength is inherent to the bone, such a canal could be machined. Accordingly, such an extension of this invention should be considered as an obvious variant hereof and comes within the claims appended hereto. The marrow is removed from the infra-medullary canal of the diaphysial plugs and the cavity is cleaned. The cavity can then be packed with autogenous bone &agmeuts from the recipient (i.e., when the cavity between adjacent vertebrae is formed, the removed bone fragments can be used as an autogenous packing), hydroxyapatite, BIOGLASS~, mixtures of these elements or any other osteogenic material to promote rapid fusion of the vertebrae between which the dowel is inserted. Bioactive glasses are generally composed of SiOz, Na,O, CaO, and P205. A preferred bioactive glass, BIOGLASS~ 4555 contains these compounds in the following respective weights: 45%, 24.5%, 24.4%, and 6%. As is evident from a review of Arr Introduction to Bioceramics, edited by Larry L. Hench and June Wilson (World Scientific Publishing Co. Pte.
Ltd, 1993, volume I), there is a vast array of bioceramic materials, including BIOGLASS~, hydroxyapatite and calcium phosphate campositions known in the art which can be used to advantage for this purpose.
The methcxl for preparing and using the diaphysial cortical dowel of this invention comprises the steps of obtaining a plug from the diaphysis of an appropriate donor bone. As describai above, the donor will have been extensively screened for communicable diseases, cancer, and at-risk behavior prior to acceptance of the donor bone for dowel formation. The plug is then machined, preferably in a class L O clean room, to the dimensions desired. The machining is preferably conducted on a Iathe such as a jeweler's lathe or machining tools may be specifically designed and adapted f~ this purpose. Specific tolerances for the dowels and reproduceability of the product dimensions arse important features for the sucetssful use of such dowels in the clinical setting. Optionally, a groove 3Z (see figure 3B) is inscribed on the cylindrical surface (circumference) of the dowel to prevent backing-out of the dowel, thereby foaming a "rib" on the dowel which acts as a stop. Another option is to inscribe a thread 31 {see figure 3A) onto the circumference of the dowel. Machining of such grooves and threads on standard Ctowai~d Dowels and even on unicortical dowels known in the art is difficult if not impossible due to the brittle cancellous nature of'such dowels. Accordingly, the dowels of this invention have the advantage of having very good biomechanical properties amenable to such machining.

The forward end of the dowel which is to be inserted into a cavity formed between adjacent vertebrae is preferably chamfered by appropriate abrasive means known in the art such as machining, filing or sanding. 'fhe curvatwc of the chamfered end aids in the ease of insertion. The tolerance for the chamfering is fairly liberal and the desired object is merely to round or slightly point the end of the dowel that is to be inserted inta the cavity formed between adjacent vertebrae to be fused.
Preferably, opposite the chamfered end, an instrument attachment hole is machined, for example by drilling andJor tapping. It is preferable that this end have a generally flat surface to accept the instrument for insertion of the dowel into the recipient.
Preferably, the dowel will be of such dimensions as to fit standard insertion tools, such as those produced by Midas-Rex, Inc. In addition, it is preferred that a score mark be inscribed on the instrument attachment site of the dowel so that the surgeon cut align the infra-medullary canal so that the canal is parallel with the length of the recipient's spinal column. With the aid of the scare mark, once the dowel is inserted into the intervertebral cavity that is formed by the surgeon, and the canal is no longer visible, proper alignment is possible.
Referring W Figure 1, there is shown, in Figure 1A the standard unic~tieal dowel 100 hwn in the art, having a cortical surfaoc 10, a drilled and/or tapped inset attachment hole 15, and a body of brittle: cancellous bcane 20.
In Figure 113, thane is shown the standard bicortical dowel 200 known in the art having two cortical surfaces 10,, a drilled andlor tapped instrument attachment hole 15, and a body of brittle cancellous bone Z0.
In Figure 1 C, one embodiment of the novel dowel 300 of this invention is shown having a cortical surface 10 into which an ir~stnmnent attachment hole 15 and aligtun~t score mark 16 may be machined (not shown as these elemtnts are optional but preferned). Also shown is the inlary canal 30 and the chamfered insertion exrd 40 (also optional but preferred). Also not shown but easily i»ribod dire to the str~g~ of the dowel 300 are citcumferaitial (annular) ribbing or threads.
Rcfemng to Figure 2, there is s6awn the ACF dowel in Figure 2A and the ATIF or the ALIF
in Figure 2B. Also shown, in additbon to what is shown in Figure 1, arc the score mark 16 and the iast hole 15.
In figures 3A and 3B, the threaded 31 and grooved 32 dowel of this invention are shown.
While those skilled in the art would know how to prepare a grooved or threaded dowel of this invention based on the foregoing disclosure and the disclosure of U.S. Patent No. 5,814,084, one specific technique tim preparation of~ preferred embodiments of this invention is discussed herewith.
With reference to Figure 4A, there is provided a side view of a diaphysial cortical dowel of this invention, which may be used as is. ur which may b a Ilunhvr machined to have ~.:rouves or threads. For purposes of illuswatiun only, specific dimensions ufduwel diameter. length and tlwead pitch are provided. Those skilled in the art will reco~,niae that thw specifics may be appropriately scaled, depending un the size of the dowel required tbr any ~_imn application.
5 In the schematic view provided in tiuure -tA, a blank Juml is reprzsented which may be used to machine an I 8mm diameter by 28mm Iw~~th threaded duwc:l. Various features of the dowel blank are shown: the cortical bon a 10. the tapped instrument attachment hole 15. the infra-medullary canal 30, and the chambered forward and of the dowel. -l0. Fur illustrative purposes. the following dimensions are also provided in inches and.'ur millimeters: 50 - 0.630" ( l6.Omm): 51 - 0.100"
10 (3.~-lrnm): ~.2 - 3.~ I''" ( f 3mm): ~3 - 1.03-4" (?6mm): ~.1- 0.60" ( I
.3nun); ~~ _ 0.1 ~Gl" (3.8nun):
56 - 0.317" (~.~mm).
In fissure -tB, an end-un view ufthe dowel blank turn thv inau~ument-attachment pule 15 (rear) end ofthe dowel is pruv ided. For illustrative purposes, the following dimensions are provided:
57 - 0.7087" ( 18mm).
I~ r In figure ~A. there is provided a view of the threaded dowel. Fur illustrative purposes. the follow ing dimensions are provided:
For the intramedullary cana1.30 a re_ular or irregular hole having! a diameter s8 no greater than about 0.~~ 1" ( I-tram) is preferred to avoid the walls of the dowel ti-um bein';
too thin. and so that a minimum wall thickness 59 at the rout ufthe thread. un both sides of the canal. is preferably -tnun or more. In ti~~ure ~B. an end-un view, ti-om the orientation ofthe double arrows shoran. shows the instrument attachment hole 1: and score mark l6 ur driver clot ,6. In figure ~C. there is shown a detail ofone embodiment of the thread. In this embodiment. a ri~~ht hand thread with ten threads per inch at a heli~c angle at the root diameter ofabout 2.8892° is provided as follows: the pitch 60 -0. I Op" (2.6mm); the thread an~~le 61 - 60°: the thread crest width 62a - 0.025' (0.6-fmm): the thread hei~_~u 63 0.039" ( I mm): and the radius of the various thread an~_le as it changes 6-1 is typically about 0.010" (0.35~tmm). Those skilled in the art will recognize that the fore~'oin'; specifics. '.v;i:e preferable, may be modified depending= on the particular sur';ical requirement ofa liven application.
Those skilled in the art will also recognize that any number of different means may be employed to produce the threaded or grooved embodiments of the dowel of this invention. However.
in one preferred embodiment, with reterencv to figure 6A, there is shown a top view ofa thread cutter -100. in this embodiment. there is provided a handle -tU 1 attached to a drive shaft .102 having a threaded portion -t03 or a graduated sediment means ter controlled incremental advancement of thv drive shaft -102 upon rotation of the handle -401. Support tmans -40-t and -405 are provided for ali~=nment and support ofthe shaft -t02. with either ur both support means having mat=hind threads.
3~ (in this illustration. only support means -l05 would hove matching threads, while support means -t0-1 ~t t~l,,tnri'1 ~~C~~
~I'. .: i: JJ

WO 971259.45 PCT/US97/00630 would have a hole which may have bearings to assist in rotation of the handle 401 and shaft 402), or like graduated segment means for controlled incremental advancement of the drive shaft 402. At the terminal end 406 of the drive shaft 402, there is provided a protruding element 407 which corre;;ponds in width to the driver slot 56 on the rear end of the dowel of this invention. At 408, there is provided a housing for the cutter assembly described further below.
The supports 404 and 405 and the housing 408 for the cutter assembly are all mounted on a steady, solid, preferably weighty base unit 409 via screws, welding, or like attachment means at 410 a-f.
Referring now to figure 6B, there is provided a side view of this embodiment of the thread cutter 400, with like elements described above being similarly numbered. The following additional elemelits are evident from this view: cutter blades assembly 420 (comprising cutter blades 421 and 422 arid guide plates 424 and 425, see Figure 6C), is shown afFxed to the cutter assembly housing 408, and an approximate travel distance 41I from the fully backed out terminal end of the drive shaft 406, to the end of the cutter assembly 420 is shown. This distance must be sufficient to allow insertion of a dowel blank and advancement of the blank through the cutter assembly 420 to allow a fully threaded dowel to emerge from the cutter assembly.
In figure 6C, an end-on view (from the direction shown by the double arrows in Figure 6B) of the cutter assembly 420 and cutter assembly housing 408 is provided. The elements of this embodiment of the cutter assembly are now described in further detail:
corresponding 421 and 422 cutter blades are held in place in the housing 408 by fixation wedges 423a and 423b while guide plates 424 and 425, having no cutting teeth, are held in place by fixation wedges 423c and 423d.
Fixation wedges 423a-d are held in place by screws 426a-d. The foregoing arrangement is preferred, as it allows for easy disassembly of the cutter assembly, removal of the cutter blades, cleaning of the various components, and if desired, sterilization by autoclaving, chemical, irradiative or like means. It should be noted that the cutter blades 42I and 422 and guide plates 424 and 425 may b~, fixed in place by increasing the tension created by tightening screws 426a-d, which draws the fixation wedges 423a-d into the housing 408, thereby clamping these elements in place.
Naturally, based on this disclosure, those skilled in the art will be able to develop equivalents of the cutter ~~ssembly system described herein, such as by use of wing-nuts, welding or like means to affix these various elements in appropriate cutting relationship to each other, without departing from the heart of this invention.
For purposes of illustration, the following additional features shown in figure 6C are noted:
the diameter of the dowel that may be threaded according to this device is defined by the diameter of the aperture 427 created between the cutter blades 421 and 422 and the guide plates 424 and 425.
It will be recognized by those skilled in the art that all of the foregoing elements should preferably ~' !~ js!'~f3 j'1 ~. ~~~:~2_~.~~t~'v'~~4~~

. CA 02243152 1998-07-15 I?
be ma«ufactured from durable nutterials smh as -l-t0 stainless sml. ur like materials. In particular. the cuttings surfaces -121a and -t22a ut the blatlm -42! antJ -t22. ~Iwribud in ~ruate;r ~ictail below. ,tre made from hard metal. It should further he: noted that tht: cutting ~d~~es -121a and -1''?n are disposed in' relation to each other so that thm ore un axis.
With reference to figure 7. greater dW ail regarding the cutW r blade, 421 and -t'_. is providW:
Figure 7A provides a detail of the cutter. which maintains trw tooth IUI'ITl tivm top to bottom. sU that Ilte cutter can be sharpened by surface ~=rindin '= the lace. This is achieved by wire-cutting=the teeth such that tht:re is about a ~° incline 62c beUveen the dcscendin'~ vertices at the li-ont and rear uFeach tooth, l0 and about an :3° incline 62d bmveen the liwnt and rear uf~the top ufeach tuutlt. This aspect can best he seen in cutter blade end-un v iew 'L3. Also. the thicl.ness ufthe cutter blade. 62e. preferably about 0.100' (~'.5-Imm), can be seen in that ti~_ure.
As noted in ti~=ore >C. thmn~=le 61 in ti~ure 7A is preferably about 60°. The w idth of the top of the tooth 62b is preferably about 0.0'_x" (0.63~mm). The pitch 60 is preferably about 0.100"I
(?.~mrn). tn ti~~ure 7C, there is shown an overall view ut the cutter blades -421 ur 42? which are assembled in tln~ cutter assembly h~u5in~ 408. Fur illustrative purpo,es. the fullowin~; dimensions are provid:d: The entire lun~th of the cu«er blade 421 b is about I .6>0"' (-1.=cm). Fixation win ~s 421c and -t21 d are provided to allwv proper seatin_~ uFthe cutwr blade upon insertion into the housing -408. r1t ~, a line is provided on cutter blades 42land 422. which allows tar appropriate registration between cutter blades 421 and 4~2 during manufacture thereof. Upon insertion into the housin~=408. it is critical that the blades and the teeth thereon are appropriately re_istcred su that as blade 421 cuts into the bone dowel as it is rotationally advanced through the cutter assembly 420, blade 423 is appropriately ~ituatc:d so that its matchin'; teeth are in phase with the thread inscribed by the teeth on blade 421. This is accomplished by a combination of the fixation wings -1214 and 421c properly seatin~~ in the hosin~~ -t08 ,;
such that the wall 421e abuts the Ilottslll~~ 408 and the huusin~= 40$ walls about the insides ofwin~gs -121d and 421c.~
In figure 7D, there is provided a top view ufmtting ed_e-t2la. As can be seen.
in this -embodiment of the invention. the cutter blade 421 has twelve cuttings teeth.
numbered in the ti~ure 431--1-12. As a dowel blank is fed into the cutter assembly, it first encounters a truncated tooth at 431, and at 30 every subsequent tooth, the hei'_ht ul~thv tooth is incremented by about 0.00-t" (0.1 nun), startin~~ from about 0.003" (O.~mm) at 431. until the final tooth h~i~.:ht is reached. in this example. of 0.039" ( I mm) at .l-tl and .t.t2. The truncated teeth 431-.1-t0 teed into the duvvel bein'; cut alone_ the 30° line so that the teeth cut on only two sides. The dotted line 4-t3 ,bows the final pitch and form that the cutter will cut in the bone dowel. Similar to the fure_oing deacriptiun ti>r li__ure 7D above, the cutting_ ed<~e 422a is shown in ~~reater detail in ti~_ure,7G, with vli:ven weth -t,l-.i61 spread over the len~~th ofthe ' . ._..~Lr;~ C F
~J

blare. At -t5t, the first tooth at U.()()-t" (().I mm) in this ~xamplc is encountered by the blank and at each successive tuutlt. an increase ul~ahuut 0.0t)-4" (O.Imm) is madmntil the !final tooth height of about O.U39" ( 1 mm) reach ed ;u 4b0 ,end -461. main. tIm dutW d line; -t-13 shows the linal pitch and ti>rm that the cutter will cut in the bone dowel.
In operation. based un the luryoin~ description. it will by appreciated that the cutter blades -l21 and -t22 are placrd into the lu~usin_ -t08. clamped into plave via the tivatiun wedgies .123 and the screws -t36, atur the blades haev hten properly seated and the two blades arc perfectly aliened. :~ blank ducal is then loaded into the urilice 427 and the drive shaft with the protrudin~~ element -107 is inserted into the driver slut 56 ~>f the ducal 300. Fur this purpose. the IU score mark Ib may be nrschined us a ~,ruuve (driver slot ;b) which mates with the protrudin~~
element -107 such that rotational torque may be transmitted to the dowel. The ~=roove may be oriented parallel to. perpendicular tu. or at any other desired uriwtation w ith respect to the intramedullary canal of the dowel. The handle -lU I is turned. ti~rcin~_ the dowel to rotate and adv,mce incrementally thruu_h the cutter assembly -t20. thereby inscribing=
the thread defined by the ;;utter blades -121 and 423 into the cylindrical surface (circumtcrence) uftlu~ dowel.
As noted above, those skilled in the art will r~co~_ni~e that modifications to the specifics of the device described above w ill allow fur the preparation of varied thread ur _rooves in the circumference of the dowel. Fur example. to tbrm a ~rouw in a dowel. the ducal could be mounted in a lathe. such as those known in the art and commercially available.
fur example from ''U SHERLINE i RODUCTS lVC-. Sr\N V1:~RCOS. C:~I.IFORNIA ~)'_'U69, and a cutter blade applied as the dowel is rotated.
Advanta~~eously. the dowel ofthis invention may be conveniently incorporated into known fusion procedures. In one use. the surgeon creates a cavity between adjacent vertebrae that are to be fused. using cowentional surgical procedures. The autu~;enuus bpne fra~~ments ~5 produced in the formation of the we iU may be collected and packc;d into the it~tra-medullary canal of the diaphysial cort;m~ dowel. ur the dowel may bmsed with a pre-packaged osteo~~enic composition. A dowel ufthe appropriate dimensions is selected by the sur~~eon.
based on the size of the cavity created and the needs uftie partic:u(ar patient underguin~ the fusion. The dowel is mounted on an instrument via the instrument attachment hole and carefully inserted into the 30 cavity created between the adjacent vertebra to be fused. Fur cervical Fusions. only one dowel is needed. Fur lumbar fusions, Uvo domls may be required. In any event, the duw;;ls may be applied laparoscopically-usin~~ currently available insUwmentatiun. Over a period ot~several months, it is found that substantial fusion ufthe adjacent mrtebrae occurs.
r ,, s:_: ;~y,_-", ~,i~t_S=t ntr,..,; -While the foregoing description describes this invention, those skilled in the art v~itl recognize that any of a number of variations on the basic theme disclosed herein can be made. Thus, for example, differing shapes can be made from the diaphysis of various bones and could be used for other orthopaedic purposes than vertebral fusions. In addition, any of a number of known bone treatments can be applied to the dowel of this invention to alter its properties. For example, the methods disclosed in U.S. Patent Nos. 4,627,853; 5,053,049; 5,306,303; and 5,171,279 can be adapted and applied to the invention disclosed herein.
Having generally described the dowel of this invention, its mode of manufacture and use, the following specific examples are provided Example 1- Biomechanical Testing of ACF Dowels P~tr~ose: 'fo descxibe the results from the compression testing of ACF dowels.
Materials: lnstron Machine, ACF Dowels, Graph Recording Paper, Pen.
Procedure: The procedure utilized the above materials to compress the ACF
dowels to failure and calculate: their rupture modules.
Preparing_thc dowel for compression:
- Wipe the residua! moisture from the surface of the dowel.
- Set lnstron for desired full scale load, crosshead speed, and paper speed.
- Position dowel under compression head with hole up.
Testing,Drooedtu~es:
- Start the graph Paper to record the composition load.
- Start the lnstroa to compress the ~wcl.
- Stop and release the load when failure is achieved or the machine is at a maximum compression load and tl~e dowel does not fail.
The dowels were all ca~ressod to faih~. The results from the testing is included in the data below.

Maximum Load Minimum Load Mean Load Median 383 kg 200 kg 267.14 kg 264 kg 3743 Newtons 1960 Ntwtaos 2618 Newtons 2587 Ne~wtons Example 2 - Biomechanical Testing_of ATIF do ALIF Dowels P~ : To descxibe the results from the compression testing of the ATIF & ALIF
dowels.

Materials: Instron Machine, ATfF & ALIF Dowels, Graph Recording Paper, Pen.
Procedure: The procedure utilized the above materials to compress the dowels to failure and calculate their rupture modulus.
Preps the dowel for compression:
5 - Wipe the residual moisture from the surface of the dowel.
- Set lnstron for desired full scale load, crosshead speed, and paper speed.
- Position dowel under compression head with the hole up.
Testing procedures:
- Start the graph paper to record the compression load.
10 - Start the instron to compress the dowel.
- Stop and release the load when failure is achieved or the machine is at a maximum compression load and the dowel does not fail.
Results: The AT7F & ALIF dowels were tested in the above manner and did not fail with a compression load of 500 kg (4900 Newtons). This is the Instron's maximum load.
I xample 3 - Cervical Fusion Using Diapl~sial Cortical Dowel Preoperative Diagnosis. Ruptured cervical disc and spondylosis CS-6.
Postoperative Diagnosis. Same.
Operative Procedure. Anterior cervical discectomy and fusion CS-6.
After satisfactory general endotracheal anesthesia in the supine position, the patient was prepped and draped in the routine fashion. Incision was made in the skin length of the neck and carried through the platysma muscle. Dissection was carried down to expose the anterior vertebral column and the appropriate space identified by x-ray. Discectomy and foraminotomy were then perfonned and there was found a central, extruded fragment of disc toward the right side. When adequate decompression had been achieved, a bone dowel was cut from bone bank fibula and counter-sunk between the vertebral bodies to afford distraction. The wound was then irrigated with Bacitreicin and closed in layers with Dexon and steri strips.
Postoperative evaluation and subsequent patient monitoring revealed successful operative outcome and good vertebral fusion.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and thf: scope of the appended claims.
'~ .'t li~;~"t~~ ', C"~~3 l t=?;?l~~t~:~

References U.S. Patent No. 5,015,247 U.S. Patent No. 4,627,853 U.S. Paccnt No. 5,053,049 U.S. Patent No. 5,306,303 U.S. Patent No. 5,171,279 University of Florida Tc~sue Bank, lnc, Allograft Catalog.
An Introduction of Bioceramics, Hencl~, Larry L., June Wilson (eds.), World Scientific Publishing Co. Pte.
Ltd., volume 1 1;1993) Bone Graft Surgery in Disease, Injury and Deformity, Albct, D. Applcton-Century Company, Inc. ( 1940) Vich,J. Neurosurg. 63:'750-753 (198 ~) Vicki, U.S. Patent No. 4,877,020

Claims

THE EMBODIMENTS Of THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OK PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A diaphysial cortical bone dowel comprising a transverse bone plug obtained from a transverse cut in the diaphysis of a long bone having an infra-medullary canal, said plug having a canal running therethrough, wherein said canal is defined by the intra-medullary canal of said long bone and wherein said plug retains the natural architecture surrounding said infra-medullary canal.

2. The diaphysial conical dowel of claim 1 having a chamfered end.

3. The diaphysial cortical dowel of claim 2 wherein the end opposite the chamfered end has an instrument attachment hole machined therein.

4. The diaphysial cortical dowel of claim 3 wherein the end having the instrument attachment hole also has a sore mark inscribed therein.

5. The diaphysial dowel of claim 1 further comprising an external feature machined into the circumference of the dowel.

6. The diaphysial cortical dowel of claim 5 wherein said feature includes a groove.

7. The diaphysial comical dowel of claim 5 wherein said feature includes threads formed along a portion <>f the length of the dowel.

8. The diaphysial cortical dowel of claim 1 having a length of between 8 mm and about 30 mm.

9. The diaphysial cortical dowel of claim 8 having a diameter of between about mm and about 24 mm.

10. The diaphysial cortical dowel of claim 1 further comprising an osteogenic composition packed within said canal.

11. The diaphysial cortical dowel of claim I 0 wherein said osteogenic composition is autogenous bone, hydroxyapatite, bioglass, a calcium phosphate ceramic or a mixture of these.

12. The diaphysial cortical dowel of claim 1 obtained as a transverse plug from the shaft of a donor's fibula, radius, ulna, humerus, femur or tibia.

13. The diaphysial cortical dowel of claim 1 prepared by a process which comprises machining a transverse plug from a transverse cut in the diaphysis of a donor's fibula, radius, ulna, humerus, femur or tibia. said plug having a diameter of between about mm and about 24 mm and a length of between about 8 mm and about 30 mm such that the resulting plug retains the natural architecture surrounding the canal running therethrough, wherein said canal is defined by the intra-medullary canal of said long bone.

14. The diaphysial cortical dowel of claim 13 wherein said process of preparation further comprises chamfering one end of said plug to form a generally curved surface for ease of insertion of the dowel into an intervertebral cavity.

15. The diaphysial cortical dowel of claim 14 wherein said process of preparation further comprises machining an instrument attachment hole into the end of the dowel opposite the chamfered end sand inscribing a score mark on the instrument attachment end of the dowel to allow for proper alignment of the intra-medullary canal.

16. A method of making a dowel which comprises machining a transverse plug as a transverse cut across the diaphysis of an isolated bone selected from a fibula, a radius, an ulna, a humerus, a femur and a tibia, said plug having a diameter of between about 10 mm and about 24 mm and a length of between about 8 mm and about 30 mm such that the resulting plug has, running through it, perpendicular to the long axis of the plug, a canal defined by a portion of the natural intra-medullary canal of the isolated bone.

17. The method of claim 16 further comprising chamfering one end of said plug to form a generally curved surface for ease of insertion of the dowel into an intervertebral cavity.

18. The method of claim 16 further comprising machining an instrument attachment hole into the end of the dowel opposite the chamfered end.

19. The method of claim 18 further comprising inscribing a score mark on the instrument attachment end of the dowel to allow for proper alignment of the intra-medullary canal.

20. Use of a diaphysial dowel according to any one of Claims 1-12 to fuse vertebrae.

21. An implant for insertion into at least one bore formed between opposing vertebrae of a spine where the vertebrae are separated by a space and each vertebra has end plates, the implant comprising:

(a) a solid generally cylindrical body having a first and a second end, and an outer surface, opposing sides and a longitudinal axis;
(b) the body having threads on a portion of the outer surface between the first and second end, the threads configured for threading into bone:

(c) the body including at least one through canal perpendicular to the longitudinal axis positioned between opposing sides, the through canal containing a biocompatible porous material for allowing the growth of bone through the canal; and (d) the through canal being positioned between generally opposing sides of the body so as to provide contact between the biocompatible porous material and the end plates of the opposing vertebrae when the implant is inserted into at least one bore formed between opposing vertebrae;
provided that said implant is composed substantially of cortical bone, that said implant comprises a transverse plug obtained from a transverse cut across the diaphysis of a long bone, and that said canal is defined by the infra-medullary canal of a long bone, and wherein said body retains the natural architecture surrounding said infra-medullary canal.

22. A method for making an implant for insertion into a space formed between adjacent vertebrae comprising, obtaining a plug of substantially cortical bone by cutting transversely across the diaphysis of an isolated long bone such that a bone plug having a longitudinal axis is thereby produced having a canal running through the bone plug perpendicular t:o the longitudinal axis of the plug> wherein said canal is defined by the natural infra-medullary canal of said long bone, and wherein said plug retains tire natural architecture surrounding the intra-medullary canal.

23. A diaphysial cortical bone dowel comprising a transverse bone plug obtained from a transverse cut in the diaphysis of a long bone having an infra-medullary canal, said plug comprising a canal running therethrough, wherein said canal is defined by a portion of the natural intra-medullary canal of said long bone.