Note: Descriptions are shown in the official language in which they were submitted.
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PERFORATED METALLIC PANELS AND STRIPS FOR INTERNAL FIXATION
OF 90NE FRACTURES AND FOR RECONSTRUCTIVE SURGERY
This is a continuation-in-part of my co-pending
application Ser. No. 07/860,029 filed March 30, 1992.
FIELD OF THE INVENTION
The present invention relates to perforated metallic
panels and strips for use in orthognathic and reconstructive
surgery and for rigid internal fixation of fractures in trauma
surgery.
BACKGROUND OF THE INVENTION
A bone fracture is a traumatic disruption of the
continuity of a bone. If there is relative motion of the bone
fragments at the fracture site irritation of the surrounding
tissues and heavy pain ensue and the time of fracture healing is
usually extended. Proper rejoinder of bone fragments is thus
dependent upon the immobilization of the fracture site.
Classically, bone fragment reduction (bone fragments properly
aligned and abutted along the fracture line) and immobilization
for fractured limb bones has been accomplished by external limb
casts. Such casts must be worn for long periods of time, are
heavy and unbalancing to the body skeletal structure and
muscular system, inhibit bone vascularity (pramotes fast and
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effective bone healing), and may result in bone resorption
because of the total absence of tensile and compressive
functional force loading throughout the fractured bone
structure. fractures in bones other than the arms and legs
are more difficult to immobilize and the use of exterior casts
may not be possible.
aver the past twenty-five years the use of compression
plate techniques for internal fixation of fractures have been
developed and widely appl;ed. With internal fixation, by
means of bone screws and compression plates, particularly plates
made of b;ocompatible metals and metal alloys (such as titanium
and stainless steel), immediate and absolute immobilization is
achieved through lnterfragmentary compression. .Other
materials and devices such as wires, intramedullary nails or
externally fixed p;ns are used mainly to reduce bone fracture
mobility and improve the position of the fracture segments.
The basic aim of tnternal bone fracture fixation is to allow
early, pain-free movement of the injured limb, mandible, etc.,
thus avoiding the consequences of long lasting immobilization,
i.e., bone fracture disease, bone resorption, etc.
In addition to the use of bone screws and compression
plates to effectively accomplish internal bone fracture
fixation, implantable biocompatible metallic plates are being
increasingly used in oral and maxillofacial surgery to effect
the surgical correction of craniofacial anomalies.
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Craniofacial surgery requires the use of both compression and
non-compression plates. Thus, in orthognathic proced~res, it
may not be desirable to compress an osteotomy. Also,
midfacial trauma injuries are frequently treated through the use
of non-compression bone fixation plates.
With internal bone fixation it is important that the
application of the implanted plate or fracture reduction device
result in relative immobility of the bone fragments (fracture
situations) or surgically prepared bone parts (reconstruction
situations) and tight closure of the bone interfaces. Without
such immobility and tight closure, changing tension and
compression loads tend to produce relative motion at the bone
interfaces w~th resultant undesirable bone fragment or bone part
shortening due to bone resorption. Through the proper use of
a biocompatible metallic bone stabilization plate or fracture
reduction device (a surgically applied implant), static forces
applied by the plate or device prevent relative motion between
the bone interface surfaces. Thus, complete immobilization
and stabilization of the bone fragments or bone parts (through
the plate or device) prevents relative motion at the bone
interfaces in spite of functional use of the limb, mandible,
etc., without external immobilization or splinting. With
mechanical stimuli (forces and motion~ permitted via internal
bone fixation techniqu0s, rapid and healthy healing of a
fracture or sur~ical reconstruction is promoted and bone
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vascularity is maintained and restored. Vascularity of bone
is interrupted by the fracture trauma and by surgical
intervention but r~vascularization is restored and enhanced by
the rigid immobilization of the bone fragment or bone part
interfaces through internal fixation techniques.
Further developments in compression and non-compression
bone fixation plate designs and attachment screws (also formed
of biocompatible metals and metal alloys) have related to screw
head and screw hole geometry, i.e., conical geometry of the
screw shoulder and oval screw holes in the fixation plate for
promoting bone fragment compression during screw application.
Attempts to obtain optimal stability of fixation have most
recently resulted in the use of congruent fitment between the
underside of the head of bone screws and the screw holes in the
fixation plate including both counter-sunk holes (conical
geometry) and hemicylinderical holes. Also, the development
of low head profiles for bone screws has permitted the use of
implantable bone plates in fixation situations directly below
soft tissue body surfaces without causins cosmetic appearance
abnormalities or creating an uneven and irritating surface
characteristic of such plates otherwise caused by screw heads.
Over the past ten years there has been an increasing
interest in~ and use of, perforated biocompatible metallic
strips and panels as a means for rigid internal fixation of
fractures in trauma surgery and as a plate material for bone
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part immobilization and stabilization and bone graft support
material in orthognathic and reconstructive surgery. of
particular interest has been the use of perforated strips and
panels fabricated of titanium as an unequaled implant material
in use clinically for over 30 years with no documented cases of
allergic reactions. Pure titanium is the material of choice
in craniofacial reconstructive surgery when non-removal of the
implant is indicated. As an implant material, pure titanium
is preferred because its low density (weight) and elastic
modulus (stiffness) are approximately one-half that of stainless
steel or cobalt-chromium alloys and the materlal is corrosion
resistant and pliable. Bone plates made from perforated
titanium strips and perforated titanium panels can be cut to
appropriate configuration and contoured at the time of surgery
and, when affixed to bone fragments or bone parts with bone
screws, provide solid, stable fixation means during trauma
surgery and planned reconstructive surgery.
A preferred form of perforated titanium strips and
panels (titanium mesh) includes rows of substantially square
perforations which are formed in titanium sheet material by
mechanical means (stamping and machining), by electrical arc
cutting, and by milllng means which preserve the stress free
condition of the sheet material. The use of titanium mesh
with square holes for internal fixation of bone fractures and
for reconstructive surgery provides the surgeon with an
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implantable plate material which can be easily cut to desired
contour and shaped or bent to conform to bone fracture and
reconstruction sites without inducing mechanical stresses into
the material because the formabil1ty of such mesh is equal along
each of the legs defining each of the square holes. Also, as
a perforated sheet material the plate structure provides the
surgeon with a multlplicity of ready-made holes through which
bone screws can be seated and applied to fasten the plate
structure to bone fragments and parts. Bending of the
perforated sheet material does not distort the square holes to
the extent that bone screws can not be applied. This is not
the case with mesh implant structures wherein the perforations
are round holes. While perforated titanium implant
strips and panels of the type described (square holes) provide
the trauma and reconstructive surgeon with a highly desirable
bone fixation plate structure~ such panels and strips have in
the past required that the screws applied through the plate
structure have their head portions extend above the outer plate
surface. Although in many internal bone fixation and
reconstructive situations screw head protrusion is not an
objectionable factor and causes no problem with respect to the
healing process following surgery, where the implanted plate
structure is at or near the body surface the protrusion of screw
heads may be noticeable and irritating.
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It is a principal object of the present invention to
provide a unique perforated metallic plate structure for the
internal fixation of fractures and for use in orthognathic and
reconstructive surgery.
It is a further object of the invention to provide a
unique metallic plate structure, including a multiplicity of
chamfered square perforations for receiving bone screws, for use
in orthognathic and reconstructive surgery and for rigid
internal fixation of bone fractures in trauma surgery.
It is still a further object of the invention to provide
unique perforated metallic panels and strips for use in
orthognathic and reconstructive surgery and for r1gid internal
fixation of bone fractures with the panel and strip perforations
comprising a multiplicity of substantially square chamfered
holes arranged in rows and lines.
It is yet another object of the ~resent invention to
provide a unique perforated metallic plate structure, including
arcuately chamfered s~uare screw holes, for use in orthognathic
and reconstructive surgery and for rigid internal fixation of
bone fractures without the significant protrusion of the head
portion of bone screws applied through such screw holes into the
bone fragments or parts to which the plate structure is
attached.
It is still another object of the invention to provide
unique perforated metallic paneis and strips for use in
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orthognathic and reconstructive surgery and for rigid internal
fixation of bone fractures with the panel and strip perforations
comprising a multiplicity of substantially square holes which
are arcuately chamfered for receiving the hemispherical
underside of low profile bone screws.
Other objects and advantages of the invention will be
apparent from the following summary and detailed description of
the bone fracture and bone reconstruction fixation plate
structure of the invention taken together with the accompanying
drawing figures.
SUMMARY OF THE INVENTION
The present invention relates to improved perforated
strips and panels of biocompatible metallic sheet material for
use in the internal fixation of bone fractures and for use in
orthognathic and reconstructive surgery. The implantable
metallic strips and panels of the invention are fabricated of
biocompatible metals and metal alloys selected from the group
consisting of titanium, titanium alloys, cobalt-chrome alloys
and stainless steel (preferably fabricated from pure titanium)
and include uniform rows and lines of arcuately chamFered square
holes for receiving, in congruent fitment, the hemispherical
underside of bone screws having low profile heads. The square
hole perforations, with inward arcuate chamfered entry configur-
ation, are created by milling techniques that result in the
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finished perforated strips and panels being free of mechanically
induced stresses as are normally created by metal stamping,
forging and mechanical machining procedures. The inward
arcuate chamfer of each square hole is substantially uniform in
arc configuration abGut the entire periphery of the hole.
Thus, the chamfer i9 not merely the chamfer that would be
created by a spherical mechanical burr or chamfer tool applied
to a square hole resulting in a partial hemispherical chamfer
only along the middle areas of each of the legs defining the
1~ square hole and no chamfer at the corners of the hole.
The use of perforated titanium strips and panels with
square holes for the internal fixation of bone fractures and for
reconstructive surgery provides the surgeon with an implantable
plate material which can be easily cut to desired contour and
shaped or bent to conform to bone fracture and bone recon-
struction sites without inducing mechanical stresses into the
material. Also, as a pliable perforated sheet material, the
strip and panel structures of the invention provide the surgeon
with a plate material having a multiplicity of ready-made holes
through which bone screws having a low profile head
(with a hemispherical underside) can be seated and applied to
fasten the plate structure to bone fragments and parts without
the protrusion of screw heads.
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BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is an oversized top plan view of a perforated
metallic strip of implantable bone fracture reduction and bone
reconstruction plate material in accordance with the present
invention; and
FIG. 2 is an enlarged cross-sectional view of the
perforated metallic strip of FIG. 1 taken along line 2-2 of FIG.
1 showing the inward arcuate chamfer contour of the square screw
holes of the strip and the congruent seating ir) one of such
holes of a low profile bone screw.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2 of the drawing sheet, there
is illustrated an improved perforated strip of biocompatible
metall~c sheet material 10, in accordance with the invention,
for use in the internal fixation of bone fractures and for use
in orthognathic and reconstructive surgery. The implantable
perforated strip 10 is fabricated from a sheet of rslatively
thin (stress freo) metal or metal alloy (preferably titanium,
titanium alloy~, cobalt-chrome alloys or stainless steel).
The strip perforations 12 comprise substantially square holes
arranged in rows and lines to form a uniform mesh of bone plate
material. The square perforations 12 of the strip 10 are
chamfered in substantially uniform arcuate configuration about
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their entire periphery inwardly from the upper opening edge 14
of each perforation to the lower opening edge 16 thereof.
The square perforations 12 of the implantable strip 10
are created by milling procedures which preserve the stress free
condition of the original metallic sheet material from which the
strip is fabricated and such perforations are configured to
receive in congruent fitment low profile head bone screws. An
example of such a screw is shown in FIGS. l and 2 as self-
tapping screw 18 which includes a threaded shank 20 and a screw
head 22 having a hemispherical underside portion, a low profile
upper head portion and cruciform slots 24 for receiving an
appropriate screwdriver tlp (not shown). Congruent fitment of
the hemispherical underside of the screw head 22 of the screw 18
is shown with respect to the arcuate chamfer of the square
perforation 12 of the strip 10. The self-tapping screw 18
also includes a fluted tip portion 26 which improves the bone
cutting action of the screw during its insertion into bone.
Implantable perforated strips of the type described
above ~particularly suitable for orthognathic and reconstructive
surgery) may be preferably fabricated, in accordance with the
invention, in five inch lengths with 1 to 4 lines of
perforations in widths of from 3/16 inch (one line of square
holes) to 11/16 inch (four lines of square holes). Such
strips, preferably formed from unalloyed commercially pure
titanium sheet material with a yield strength in the range of
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30,000 to 40,000 psi, have a ~inished thickness of from about 1
mm to about 1.5 mm. Perforated panels may be preferably
fabricated from like sheet titanium material in a size of 3 and
1/4 inch width and 5 and 1/4 inch length.
Examcle: A perforated metallic strip for use in
orthognathic and reconstructive surgery and for rigid internal
fixation of fractures in trauma surgery, of the type illustrated
in FIGS. 1 and 2, has been fabricated from unalloyed
commercially pure titanium with a yield strength in the range of
30,000 to 40,000 psi. The strip (having a thickness of 1 mm,
a width of 1/2 inch and length of 5 inches, and including 3
lines of arcuately chamfered square perfarations arranged
uniformly in 30 rows~ was utilized after appropriate contouring
and shaping to reduce and immobilize (with low profile head bone
screws and hemispherical head underside) a bone fracture in the
maxilla of a patient. Because the square holes of the strip
are chamfered in arcuate uniform inward configuration about the
entire periphery of the holes, bending and shaping of the strip
does not adversely affect the desired congruent fitment of the
bone screws (seated through the strip) to the strip holes to
effect affixation of the strip to the underlying bone structure.
While the invention has been described in connection
with a particular structural embodiment of a perforated metallic
strip, with perforations comprising a multiplicity of
substantially square chamfered holes arranged in rows and lines,
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for internal fixation of bone fractures and for reconstructive
surgery, many modifications of the invention will be apparent to
those skilled in the art. Accordingly, such modifications are
to be inc1uded within the spirit and scope of the invention as
defined by the following claims.
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