The present invention relates generally to surgical tissue fixation
equipment and systems and, more particularly, to bioabsorbable fixation systems
including bodily tissue fixation hardware comprising biocompatible, bioabsorbable
(resorbable) polymeric or composite plates and fasteners for securing the plates
to bodily tissue for fixation thereof, and an installation instrument which triggers
(strikes) fasteners one after one into through-bores (holes) made through the plate
and into the underlying bodily tissue.
BACKGROUND OF THE INVENTION
Traditional orthopedic and traumatological and cranio-maxillo-facial
fixation systems to facilitate bone fracture healing (osteosynthesis) or soft tissue-to-bone
healing typically employ metallic hardware, e.g., plates, screws, rods and the like,
formed of biocompatible, corrosion resistant metals such as titanium and stainless
steel. Typical metallic plates are described, e.g., in the book F. Séquin and R.
Texhammar, AO/ASIF Instrumentation, Springer-Verlag, Berlin, Heidelberg, 1981, p.
21-22, 55-79, 107-108, 117-122. While such systems are generally effective for their
intended purposes, they possess a number of inherent shortcomings. For example,
metal release to the surrounding tissues (see, e.g., L.-E. Moberget al. Int.
J. Oral. Maxillofac. Surg. 18 (1989) p. 311-314) has been reported. Other
reported shortcomings are stress shielding (e.g., P. Paavolainen et al.,
Clin Orthop. Rel. Res. 136 (1978) 287-293) and growth restriction in young
individuals (e.g., K. Lin et al., Plast. Reconstr. Surg. 87 (1991)
229-235). In infants and young children there is the risk that metallic plates and
screws sink, as a consequence of skull bone growth, into and below the cranial bone
threatening brain (J. Fearon et al., Plast. Reconstr. Surg. 4 (1995)
634-637). Therefore, it is recommended generally that non-functional implants should
be removed, at least in growing individuals (see, e.g., C. Lindqvist, Brit. J. Oral
Maxillofac. Surg. 33 (1995) p. 69-70).
Especially in maxillofacial and in cranial surgery metallic mini plates
are popular (see, e.g., W. Muhlbauer et al., Clin. Plast. Surg.
14 (1987) 101-111 ; A. Sadove and B. Eppleg, Ann. Plast. Surg.
27 (1991) 36-43 ; R. Suuronen, Biodegradable Self-reinforced Polylactide
Plates and Screws in the Fixation of Osteotomies in the Mandible, Doctoral Thesis,
Helsinki University, Helsinki, 1992, p. 16; and see the references cited in the
previous references). Mini plates are small, thin, narrow plates, which have holes
for screw fixation. They are located typically on bone perpendicularly over the
fracture to fix the bone mass on both sides of the fracture to each others. Typical
geometries of mini plates are described, e.g., in US Pat. 5,290,281, in FIG. 6A-6F.
The main advantage of metallic plates, screws, etc. (like titanium,
stainless steel and cobalt chrome molybdenum plates or screws), is that they are
strong, and tough. Ductile metal plates can be deformed or shaped (bent) at room
temperature in an operation room by hand or with special instruments to the shape
of a form that corresponds to the surface topography of the bone to be fixed, so
that the plate can be fixed flush on the bone surface to which the plate is applied.
Because of the shortcomings of metallic plates, bioabsorbable plates
have been developed for fracture fixation. Longitudinal, six-hole plates were developed
by Eitenmülleret al. for orthopaedic animal studies (European Congress on
Biomaterials, Abstracts, Instituto Rizzoli, Bologna, 1986, p. 94). However, because
of inadequate strength, some of the plates were broken in animal experiments involving
A particular advantage of bioabsorbable plates is that they can be
provided with openings for the insertion of surgical fasteners (like screws) therethrough,
while also allowing means to permit the formation of additional fastener openings
therethrough during a surgical procedure at the surgeon's discretion, as has been
described in European Patent specification EP 0 449 867 B1.
However, the main disadvantage of most prior art bioabsorbable plates
is that they can be deformed (bent) permanently and safely only at elevated temperatures
above the glass transition temperature (Tg) of the bioabsorbable polymer,
as has been described, e.g., in EP 0 449 867 B1, US Pat. No. 5,569,250 and US Pat.
No. 5,607,427. Below the respective glass transition temperatures of the bioabsorbable
polymers from which they are made, most prior art bioabsorbable plates are brittle
and break easily when deformed. Only at temperatures above the Tg of
the bioabsorbable polymer from which a given plate is made does the molecular structure
of most prior art plates have enough mobility to allow shaping and bending of the
plate, without the risk of breaking.
Because the thermal conductivity of most polymeric materials is generally
poor, both heating and cooling of bioabsorbable plates are slow processes. Therefore,
the clinical use of such prior art plates is tedious, slow and complex, especially
if the surgeon must shape the plate several times to make it fit exactly to the
form of the bone to be fixed.
K. Bessho et al., J. Oral. Maxillofac. Surg. 55 (1997) 941-945,
describe a bioabsorbable poly-L-lactide miniplate and screw system for osteosynthesis
in oral and maxillofacial surgery. The plates of that reference also must be heated
by immersion in a hot sterilized physiologic salt solution, or by the application
of hot air, until they become plastic, and only then can those plates be fitted
to the surface of the bone being repaired.
EP 0 449 867 B1, describes a plate for fixation of a bone fracture,
osteotomy, arthrodesis, etc., said plate being intended to be fixed on bone with
at least one fixation device, like a screw, rod, clamp or some other corresponding
device. The plates of that reference comprise at least two essentially superimposed
plates, so as to provide a multilayer plate construction, so that the individual
plates of said multilayer plate construction are flexible to provide a change of
form of said multilayer plate construction to substantially assume the shape of
the bone surface under the operation conditions. That change of form is accomplished
by means of an external force, such as by hand and/or by a bending instrument directed
to said multilayer plate construction, whereby each individual plate assumes the
position of its own with respect to other individual plates by differential motion
along the surfaces of the coinciding plates.
Although the above multilayer plate can fit the curved bone surface
without heating of the individual plates, the clinical use of such multilayer plates
is tedious, because the single plates easily slip in relation to each other before
fixation. Additionally the thickness of multilayer plate system easily becomes too
thick for cranio maxillofacial applications, causing cosmetic disturbance and increased
risks of foreign body reaction.
To avoid the above mentioned shortcomings in the prior art devices,
US Pat. Appl. Serial No. 09/036,259, describes strong and tough, uni- and/or biaxially
oriented and/or self-reinforced bioabsorbable plates, which are deformable at room
temperature, like in operation room conditions, prior to implantation in a patient.
The plates described in that application retain their deformed (bent or shaped)
form so well at body temperature in tissue conditions (e.g., when implanted on a
patient's bone) that they keep the fixed bone fragments in the desired position
to facilitate bone fracture healing. When using such plates surgically, the surgeon
can bend (and rebend) the plate easily in operation conditions, without needing
the slow and tedious heating - bending - cooling procedure of the prior art plates.
While the clinical use of the bioabsorbable plates described in US
Pat. Appl. Serial No. 09/036,259 significantly reduces operation time in comparison
to the clinical use of other prior art bioabsorbable plates, the fixation of plates
on tissue or bone is still a slow and tedious process. Prior art fixation techniques
mainly use screws or screw-type fasteners for plate fixation. However, turning of
screws or screw-type fasteners into drill holes is a slow process. For example,
in a single maxillo-cranio-facial operation, tens of screws may be used for plate
fixation and such an operation may demand hours to complete. On the other hand,
manual use of other types of fasteners, like expansion bolts (pins), or plugs or
rivets is also a slow and risky process. For example, manual hammering of fasteners,
like those described in US Pat. No 5,261,914 or US Pat. No 5,607,427 can easily
be done too strongly, so that the head of the fastener and/or plate and/or underlying
tissue(s) is (are) damaged.
Two-component fasteners, like expansion bolts or plugs (such as those
described in H. Pihlajamäki et al.,: A biodegradable expansion plug for the
fixation of fractures of the medial malleolus, Ann Chir Gyn 83: 47-52, 1994) or
pop rivet-type fasteners can be complicated and risky to use because strong expansion
of a part of such a fastener can cause extensive compression to the surrounding
bone, leading to bone necrosis.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a surgical
tissue fixation system, including a bioabsorbable plate and a bioabsorbable fastener
to secure the plate to underlying bodily tissue and an installation tool which triggers
the fasteners one after another through drill holes made through the plate and into
the underlying bodily tissue. The plate and fastener equipment is particularly adapted
for fixating fractured or severed bones, or for affixing a ligament, tendon or connective
tissue on a bone or into a drillhole in a bone, to promote rapid and beneficial
healing of the treated bones and/or tissues.
In a preferred embodiment of the invention, the installation instrument
cooperates as part of a surgical system with one or more specially configured plates,
fabricated from bioabsorbable polymeric or composite material, wherein the plates
can be secured by a surgeon via a plurality of fasteners to a bone, cartilage, tendon,
connective tissue or other bodily tissue being repaired. Other details, objects
and advantages of the present invention will become apparent from the following
description of the presently preferred embodiments and presently preferred methods
of practicing the invention.
The invention provides for a surgical tissue fixation system according
to the features of claim 1.
Preferably it is provided for a surgical tissue fixation system comprising
a bioabsorbable plate, bioabsorbable fasteners and an installation instrument, which
triggers the fasteners one after another into the drill holes made through the plate
and optionally also into the underlying bodily tissue, with a single strike or with
several consecutive strikes, without the need of turning the fastener around its
long axis during installation.
It is preferably provided for a surgical tissue fixation system comprising
a bioabsorbable plate, bioabsorbable fasteners and an installation instrument, which
triggers the fasteners one after another precisely into the drill holes in plates,
so that the lower surface of the fastener head mates exactly with the upper surface
of the plate (or with the countersink surface in the upper part of the drill hole
in the plate).
It is preferably provided for a curved cannula for attaching to the
above fixation instrument, to allow application of the fasteners onto bone in areas,
e.g., such as the posterior mandible or subcutaneous spaces, where there is no access
with straight upright instrumentation.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become more readily apparent from the following
description of preferred embodiments, which are shown, by way of example only, in
the accompanying drawings.
DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1 is a schematic representation of a typical fastener, for securing a bodily
tissue fixation plate to underlying bodily tissue, as seen as perspective figures
from different directions.
- FIG. 2 is a perspective view illustrating a bioabsorbable fixation (osteosynthesis)
plate in combination with a fixation fastener, positioned in a relatively elevated
position inside of an installation cannula of an installation instrument, for insertion
of the fastener within a fastener opening of a fixation plate.
- FIG. 3 is a schematic cross-sectional representation of a fixation system (a
plate + fastener) according to a preferred embodiment of the present invention,
a fastener being applied into a drillhole in a plate and into a drillhole in the
underlying bone tissue.
- FIG. 4. is a schematic representation of a fastener being applied to a drillhole
with a curved cannula in an area where no direct access could be achieved.
- FIG. 5A-B show cross-sections of fasteners, showing different protuberance geometries.
- FIG. 6A-C show schematically, in a cross-section, elastic bending of a ridge
of a fastener during insertion into a drill hole.
- FIG. 7A-B show a surface of a fastener body with a ridge, which has been cut
with longitudinal grooves, including a side view (FIG. 7A) and an upper view (FIG.
7B) of the stem and ridge.
- FIG. 8 shows typical geometries of the head of the fastener when seen from the
upper side of the fastener in the direction of the longitudinal axis of the fastener.
- FIG. 9 shows schematically the tip of a cannula whose diameter has been decreased
by splitting it and pressing the split parts to each other.
The fastener(s) and plate(s) are manufactured of bioabsorbable polymer,
polymer alloy or composite material, which is strong and tough and retains its strength
in vivo several weeks or months.
FIG. 1 shows a typical fastener 1 comprising a proximal head 2, a
stem 3, from which one or more protuberances 4 emerge. Typical protuberances are
ridges, reaching at least partially around the stem 3, threads, pyramid-like or
half ball-shaped papillae, barbs, scales, etc. The geometry of protuberances 4 is
such, that it allows easy gliding of the fastener into the drill hole in the plate
6 in FIG. 2 and into the bone 7 in FIG. 2 or into an optional drillhole in the bone
10 in FIG. 3, while still locking the fastener effectively into its place, preventing
its movements backwards after installation. Finally, according to FIG. 1 the fastener
comprises the distal tip 5, which can be conical with a sharp or blunt or rounded
end 5a to facilitate its installation into the drillhole in the plate (and optionally
into the drillhole in bone).
The presently preferred bioabsorbable polymeric or composite materials
forming the fixation plates (the compositions of which will be later described in
greater detail) can be bent and shaped, in operation room conditions or at an elevated
temperature, typically at temperatures ranging from about 15°C to 120°C.
A number of geometries are useful for the plate, such as those described
in US Pat. Appl. Serial No. 09/036,259. The plate is desirably of a thickness of
less than about 2 mm and may include a plurality of spaced apart through-bores adapted
to accommodate fasteners. Fasteners also can be formed from any suitable biocompatible
and bioabsorbable polymeric or composite material from the classes used for forming
the plates or from other acceptable materials of similar properties and characteristics.
Such materials have been described extensively in prior art, e.g. in US Pat. Appl.
Serial No. 09/036,259.
FIG. 2 is a perspective view illustrating a fastener 1 used for fastening
of the plate 6 to underlying bodily tissue, like bone 7 during a surgical operation.
As suggested herein above, fastener 1 may be formed of any suitable bioabsorbable
and biocompatible polymeric or composite material; however, the material must be
chosen from those materials having sufficient strength and toughness and hardness
whereby the fastener head 2, stem 3 and fastener protuberances 4 and tip 5 (see
FIG. 1) do not fail upon the application of pressure to the fastener head 2, which
occurs when fastening the bodily tissue fixation plate 6 to underlying bodily tissue
7. Such pressure is applied by triggering the fastener 1 with the installation instrument
8, whose cannula 8a and piston or tool 8b are seen in FIG. 2, into a through-bore
9 in the plate and into an optional drillhole 10 in FIG. 3 in tissue 7 under the
plate. In the perspective of FIG. 2, a fastener 1 is positioned in a relatively
elevated position inside of an installation cannula 8a (the cross-section of the
cannula shows the fastener 1 inside of the cannula) of an installation instrument
8 (not seen totally in this Figure). The fastener 1 can be triggered (shot) into
a drillhole (bore) 9 in the plate 6 by pushing it rapidly with the piston 8b into
the drillhole 9.
FIG. 3 shows a cross-sectional view of a fastener 1 after having been
triggered into a drillhole 9 in the plate 6 and further into a drillhole 10 in the
bone 7. The head 2 of fastener 1 may optionally contain a tool receiving notch or
recess 11, which may be cylindrical or angular of its cross-section. The notch or
recess 11 is configured for receiving the tip of the piston (tool) 8b and for securing
the grip of the tip of the tool inside of the notch or recess with a frictional
grip. It is also possible, that the head of fastener 1 is smooth and there is no
frictional grip between the head 2 and the tip of the piston 8b.
While the tool-receiving portion of fastener head may assume any conventional
socket configuration, it is preferred that the head includes a socket shape adapted
to minimize the likelihood of inadvertent slippage of the tip of the triggering
tool during fastener installation. Moreover, the underside of the fastener head
2 is desirably contoured as conical to mate (conform) to the shape of a fastener
head seat 12 in FIG. 3 formed at the upper ends of through-bores 9 of plate 6, thus
minimizing the height of the fastener plate profile. It is preferred that the distal
end 5 of the stem 3 portion (with protuberances 4) of the fastener 1 be formed into
a generally pointed configuration 5a , as illustrated, so as to facilitate guidance
and insertion of the fastener into both its corresponding through-bore 9 and the
preformed receiving hole 10 that may be provided in the underlying bodily tissue
7 being repaired.
The maximum outer diameter D1 between the protuberances
(see FIGS. 5A-B) of the fastener 1 of the present invention is desirably less than
about 3.0 mm. Indeed, according to presently preferred embodiments of the invention,
the outer diameter is typically approximately 2.0 mm or less for normal service
requirements in surgery and up to about 2.5 mm for emergency requirements, and the
corresponding nominal bore diameter of through-bores 9 and 10 is preferably about
1.8-1.9 mm or less. Because of the very small diameters of the fasteners 1, they
are particularly well-suited for fixation of small and/or non-weight bearing bones
or other bodily tissues.
According to an advantageous embodiment of the invention, the protuberances
(e.g., scales, ridges or threads) on the fastener have such a structure that they
can deform at least partially elastically during insertion of the fastener. FIG.
5A and FIG. 5B show schematically in a cross-section such protuberances, (like horizontal
ridges), which can deform (bend) elastically during insertion. As shown in FIGS.
6A-C, when the maximum outer diameter D1 of the fastener (D1
= the maximum distance between protuberances on opposite sides of the fastener)
is bigger than the diameter D2 of the drillhole in the plate 6 and in
the compact bone 7 below (see FIG. 6 A), the protuberances can bend temporarily
inside the drillhole in the plate and in the compact bone below the plate (see FIG.
6B), but widen again to almost their original width when they have slipped into
the soft tissue or void space 13 below the compact bone. In such a case, the fixation
of the fastener is especially strong because the widened protuberances effectively
prevent the slippage of the fastener back from the drillhole.
According to FIG. 7A and 7 B, the protuberance (ridge) 4 on the surface
of the fastener stem 3, has been split to several parts having longitudinal grooves
4a. Such separate ridge parts bend elastically more easily than an intact ridge
on insertion of the fastener.
The head of the fastener also can have different geometries. FIGS.
8A-E show different types of fastener heads, as seen from above. FIG. 8A shows a
rounded head. FIG. 8B shows such a head equipped with a quadrangular tool-receiving
notch 14. FIG. 8C shows a flat head with a groove-like notch 15. FIG. 8D shows a
cross-like head and FIG. 8E a triangular head. It is evident that the form of the
head of the fastener is not limited to those forms expressly described here.
According to an advantageous embodiment, the fastener of the invention
can be cannulated, which means that inside of the fastener there is a longitudinal
hole which traverses the fastener. Such a cannulated fastener can be pushed along
a metallic guide-wire into the tissue. The guide-wire can facilitate the installation
operation in certain cases, e.g. guide-wire(s) can be used to keep the plate and/or
damaged tissue in a proper place before the installation of the fastener.
The installation instrument can be any instrument which triggers (strikes
or shoots) the fastener through a cannula by means of a piston through the drillhole
in a plate into the underlying bodily tissue. Such instruments have been described,
e.g., in US Pat. Appl. Serial Nos. 08/887,130 and 08/979,872. Accordingly, the installation
instrument has a conduit, such as a cannula, that may be easily inserted into the
patient and through which the fastener is delivered to the patient. This conduit
is aligned with a seat for holding a fastener and a means for pushing a fastener,
such as a piston, so that the pushing means is capable of pushing a fastener from
its seat, through the conduit and into the patient. In a preferred embodiment of
the invention, the shape of the conduit relatively exactly matches the shape of
the cross-section of the fastener so that the surgeon may more accurately direct
the angle and location at which the fastener enters the patient. In another preferred
embodiment, the pushing means may be made to slowly push the fastener from its seat
and through the conduit until the distal end of the fastener contacts the drillhole
of the plate at the end of the conduit. At that time, the pushing means may be made
to accelerate rapidly, thereby inserting the fastener into the drillhole of the
plate and into the tissue being treated. An advantage of this embodiment is that
the fastener is less likely to become jammed in the conduit while being pushed slowly
through it. Further, the conduit, piston, and fastener are subject to less wear,
which helps to ensure proper functioning of the instrument during an operation.
The seat for holding fasteners is capable of holding a magazine containing
one or more fasteners. When inserted into the seat, the magazine may be positioned
so that a fastener is aligned with the pushing means and the conduit leading to
the patient. Once a fastener has been inserted into the patient, the magazine may
be manually positioned so that another fastener is shifted into position to be inserted.
In one embodiment of this invention, the magazine may have means, such as a spring,
for automatically moving a fastener into position for insertion once a first fastener
has been inserted.
The magazine may be easily removed from the seat during an operation,
so that it may be replaced with a magazine containing one or more fasteners, without
requiring the conduit to be removed from the patient. Alternatively, the same magazine
could be removed, refilled with one or more additional fasteners, and reinserted
into the seat, without requiring the removal of the conduit from the patient. In
yet another preferred embodiment of the invention, when the magazine is positioned
to allow the insertion of one fastener into the patient, a portion of the magazine
is accessible to allow the insertion of one or more additional fasteners into the
magazine. In this fashion, additional fasteners may be added to the magazine without
requiring its removal from the device or the removal of the conduit of the device
from the patient.
In a preferred embodiment of the invention, the conduit or cannula
of the instrument is easily removable from the rest of the device. This allows the
same instrument to be used during an operation with differently shaped conduits,
depending upon the location and condition of the plate being fixed and tissue being
treated. Thus, for instance, during the same operation, the surgeon could insert
fasteners through a straight conduit (cannula), then easily replace the straight
conduit with a curved conduit and continue the operation without the need for an
entirely new device.
In yet another preferred embodiment of this invention, the device
has a safety mechanism that helps prevent the surgeon from inadvertently shooting
the fastener into the patient until the proper moment. This mechanism works in conjunction
with the triggering mechanism so that the means for propelling the fastener into
the patient cannot be actuated until both the triggering means and the safety mechanism
are actuated simultaneously.
FIG. 4 describes an installation device 8 with a curved cannula 8c,
inside of which is a fastener 1, which can be triggered from the cannula with a
flexible piston 8d into a tissue area where no direct access could be achieved.
Special attention must be directed to the relationship between the
fastener and the cannula and piston of the installation instrument. The fastener
must glide inside of the cannula easily but it should not be allowed to drop out
of the cannula end by its own weight. The fastener should be capable of moving completely
out of the cannula only when the piston pushes (strikes) it out into the drillhole
in the plate and in the bodily tissue. Such behavior is attained, e.g., when the
head of the fastener has a notch (as is described e.g. in FIG. 3 and in FIG. 8 B
and C) into which the tip of the piston can be pushed. When the geometries of the
notch and of the tip of the piston have been designed properly, a good frictional
grip between the fastener and the piston can be achieved.
Another option is to make the dimensions of the fastener head and/or
protuberances in relation to the inner diameters of the cannula such that a substantial
friction exists between the fastener head and/or protuberances and the inner surface
of the cannula, so that the fastener glides inside of the cannula only when it is
pushed forward by means of the piston.
According to an advantageous embodiment of the invention, the diameter
of the distal end of the instrument cannula is smaller than the diameter of its
proximal end. In such a case, the fastener glides easily inside of the cannula,
but cannot glide totally out of the cannula without a substantial push of the piston.
FIG. 9 shows such an embodiment, where the distal part of the cannula has been split,
e.g., by sawing to make grooves 16 which split the distal part of cannula into two
or several (in this case, four) parts. These parts have been bent slightly so that
the inner diameter of the distal part of the cannula is smaller than the diameter
of the other parts of the cannula. The fastener can be pushed easily to the end
(tip) of the cannula, but the reduced end of the cannula prevents the premature
drop of the fastener out of cannula. The tip of the fastener, which can protrude
out of the cannula, can be then located easily into the drillhole in the plate,
until the strike of the piston pushes the fastener totally out of the cannula and
into the drillhole.
The fixation fasteners and/or plates can be manufactured by known
techniques from known materials, such as thermoplastic bioabsorbable (resorbable
or biodegradable) polymers, copolymers, polymer alloys, or composites, e.g., of
poly-α-hydroxy acids and of other aliphatic bioabsorbable polyesters, polyanhydrides,
polyorthoesters, polyorganophosphatzenes, tyrosine polymers and other bioabsorbable
polymers disclosed in numerous publications, e.g., in S. Vainionpää et al.,
Prog. Polym. Sci., 14 (1989) 679-716, FI Pat. No. 952884, FI Pat. No. 955547
and WO-90/04982, EP 0449867 B1, US Pat. No. 5,569,250, S. I. Ertel et al., J. Biomed.
Mater. Res., 29 (1995) 1337-1348, as well as in the reference publications
mentioned in the aforementioned publications.
Implants (plates and/or fasteners) can be manufactured of biodegradable
polymers by using one polymer or a polymer alloy. The implants can also be reinforced
by reinforcing the material by fibers manufactured of a bioabsorbable polymer or
of a polymer alloy, or with biodegradable glassfibers, such as β-tricalsiumphosphate
fibers, bioactive glassfibres or CaM fibers (as described in, e.g., EP146398). Ceramic
powders can also be used as additives (fillers) in implants to promote new bone
Implants can also contain layered parts comprising, e.g., (a) a flexible
outer layer as a surface layer improving the toughness and/or operating as a hydrolysis
barrier and (b) a stiff inner layer. It is natural that the materials and implants
of the invention can also contain various additives for facilitating the processability
of the material (e.g. stabilizers, antioxidants or plasticizers) or for changing
its properties (e.g. plasticizers or ceramic powder materials or biostable fibers,
such as carbon) or for facilitating its treatment (e.g. colorants).
According to one advantageous embodiment, the implant contains some
bioactive agent or agents, such as antibiotics, chemotherapeutic agents, agents
activating healing of wounds, growth factor(s), bone morphogenic protein(s), anticoagulant
(such as heparin) etc. Such bioactive implants are particularly advantageous in
clinical use, because they have, in addition to their mechanical effect, also biochemical,
medical and other effects to facilitate tissue healing and/or regeneration.
Because the plates contemplated can be shaped (bent or twisted, etc.)
in situ rapidly and at room temperature, either manually or with special
bending tools (like forceps), the plates can be brought effectively into virtual
conformance with the underlying bodily tissue being repaired, including damaged
tissue having small radii of curvature, such as cranial and facial bones, even those
of a small child. Thereafter, the plate can be fixed on bone rapidly and safely
with fasteners, using the installation system. As a result, the bodily tissue on
opposite sides of the severance or fracture is rapidly and effectively restrained
against relative movement, whereby rapid, sturdy and non-disfiguring consolidation
and/or healing of the bodily tissue is achieved.
Because, according to an advantageous embodiment, the plate shaping
and fastener fixation procedures are done at room temperature, there is no risk
of heat-related damage to biological tissue in the immediate vicinity of the treatment
area, even in rather deep biological incisions, while such risk is a reality when
using prior art plates which are shaped in situ by using heat.
Because the whole tissue fixation operation by using the system is
done much more rapidly than when using prior art systems, surprising advantages
are obtained: a shorter operation time results in smaller risks of operation complications
and infections to the patient and considerable economic savings and/or increases
of efficacy of operation room facilities.
The principles of the present invention described broadly above will
now be described with reference to the following specific example, without intending
to restrict the scope of the present invention.
A side of a fresh cadaver swine mandible was prepared by removing
soft tissue from the testing surface of the bone. A bioresorbable bone fixation
plate was then fixed to the bone with 4 bioabsorbable monocortical screws or fasteners
of the invention.
Fixation plates, screws and fasteners were made from self-reinforced
70L/30DL PLA (Draw ration 3.5 to 5.5) (Manufacturer of Polymer is Boehringer Ingelheim
Pharma KG, BU Fine Chemicals, PM Resomer, D-55216 Ingelheim, Germany, tel +49-(0)6132-77
2633, fax +49(0)6132-77 4330, Mw = i.v. 5.5 to 7.0 dl/g). The plates
were made with the method described in PCT/EP99/01438, and the screws and tacks
were made according to PCT/FI 96/00511. The tack geometry was that of FIG. I of
this invention. The Principal dimensions of the 6-hole fixation plate were 5.5 x
39 x 1.2 mm. The screws had a diameter of 2.0 mm and a length of 6 mm. The tack
diameter was also 2.0 mm and length 6 mm.
Plate and screw fixation:
The fixation plate was laid on the bone. A screw hole of 1.5mm diameter
was drilled with an electric drilling machine into the bone through the screw hole
of the plate. The drilled hole was then tapped with a tapping instrument of 2.0
mm diameter. The screw was driven through the screw hole of the plate and into the
tapped screw hole with the manual screwdriver. The procedure was then repeated for
4 screws, leaving the innermost 2 screwholes of the 6-hole plate intact. That space
was left free for a pullout testing jig.
Plate and tack fixation.
A fixation plate was laid on the bone as above. A hole of 2.0mm diameter
was drilled for the tack with the electric drilling machine into the bone through
the screw hole of the plate. A tack was shot through the hole of the plate into
the drillhole with the tack insertion instrument. This procedure was repeated for
4 tacks, leaving the innermost 2 holes of the 6-hole plate intact. That space was
left free for a pullout testing jig.
The total time used for each of the above fixations was measured with
a stopwatch. The stopwatch was started before drilling the first drillhole and ended
when all four screws or fasteners were inserted. Five parallel tests were performed
for both fixation methods, and an assistant was serving instruments and implants
to the operating surgeon. Results
The total time used for inserting and fixing 4 screws in the above
plate varied from 124 to 178 seconds, with an average of 156 seconds. The total
time used for inserting and fixing 4 tacks in the above plate varied from 58 to
102 seconds, with an average of 76 seconds. This test showed that the time for fixation
with the method of this invention took only about 50 % of the time for fixation
using the prior art method.