The present invention relates generally to body tissue fixation systems, including body tissue fixation hardware comprising biocompatible, bioabsorbable (resorbable) thermoplastic plates, and methods of using those systems and hardware.

FIELD OF THE INVENTION
 The present invention relates generally to body tissue fixation systems,
 including body tissue fixation hardware comprising biocompatible,
 bioabsorbable (resorbable) thermoplastic plates, and methods of using
 those systems and hardware.
 BACKGROUND OF THE INVENTION
 Traditional orthopedic and traumatological fixation systems to facilitate
 bone fracture healing (osteosynthesis) 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. Sequin and R.
 Texhammar, AO/ASIF Instrumentation, Springer-Verlag, Berlin, Heidelberg,
 1981, at p. 21-22, 55-79, 107-108, 117-122, the entire disclosure of which
 is incorporated herein by reference. 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 has
 been reported. See, e.g., L.-E. Moberg et al. Int. J. Oral. Maxillofac.
 Surg. 18 (1989) at pp. 311-314, the entire disclosure of which is
 incorporated herein by way of this reference. Other reported shortcomings
 include stress shielding, see P. Paavolainen et al., Clin Orthop. Rel.
 Res. 136 (1978) 287-293, the entire disclosure of which is incorporated
 herein by way of this reference, and growth restriction in young
 individuals, see K. Lin et al, Plast. Reconstr. Surg. 87 (1991) 229-235,
 the entire disclosure of which is likewise incorporated herein by way of
 this reference. In infants and young children, there is the risk that
 metallic plates and screws can sink into and below the cranial bone, as a
 consequence of skull bone growth, thereby threatening the brain. See,
 e.g., J. Fearon et al., Plast. Reconstr. Surg. 4 (1995) 634-637, the
 entire disclosure of which is incorporated herein by way of this
 reference. Therefore, it is generally recommended that non-functional
 implants should be eventually removed, at least in growing individuals.
 See C. Lindqvist, Brit. J. Oral Maxillofac. Surg. 33 (1995) p. 69-70, the
 entire disclosure of which is incorporated herein by way of this
 reference.
 Especially in maxillofacial and in cranial surgery, metallic mini plates
 are popular for use. 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; and 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 references
 therein, the discloures of which are incorporated herein by reference.
 Mini plates are small, thin, narrow plates, which have holes for screw
 fixation. They are typically located on bone, perpendicularly over the
 fracture to fix the bone mass on both sides of the fracture to each other.
 Typical geometries of mini plates are described e.g. in U.S. Pat. No.
 5,290,281 at FIGS. 6A-6F, the entire disclosure of which is incorporated
 herein by way of this reference.
 The main advantage of metallic plates (like titanium, stainless steel and
 cobalt chrome molybdenum plates), is that they are strong, tough and
 ductile so that they can be deformed or shaped (e.g., bended) at room
 temperature in the operation room, either by hand or with special
 instruments, to a form corresponding to the surface topography of bone to
 be fixed. In this way, the plate can be fixed flush on the bone surface to
 which the plate is applied.
 In light of the above shortcomings of metallic plates, however,
 bioabsorbable plates have been developed for fracture fixation.
 Longitudinal, six-hole plates were developed for orthopaedic animal
 studies. See Eitenmuller et al., European Congress on Biomaterials,
 Abstracts, Instituto Rizzoli, Bologna, 1986, p. 94, the entire disclosure
 of which is incorporated herein by this reference. However, because of
 their inadequate strength, some of the plates were broken in animal
 experiments involving fracture fixation.
 A special advantage of bioabsorbable plates is that they can be provided
 with openings for the insertion therethrough of surgical fasteners (like
 screws), while 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, the entire disclosure of which is
 incorporated herein by way of this reference.
 The main disadvantage of prior art bioabsorbable plates is that they can be
 deformed (bended) permanently and safely only at elevated temperatures
 above their glass transition temperature (T.sub.g), as has been described
 e.g. in EP 0 449 867 B1 and in U.S. Pat. No. 5,569,250, the entire
 disclosures of which are incorporated herein by way of this reference.
 Below their T.sub.g, the prior art bioabsorbable plates are brittle and
 break easily when deformed. Only at temperatures above the T.sub.g does
 the molecular structure of prior art plates have enough mobility to allow
 shaping (e.g., bending) without the risk of breaking. Accordingly, U.S.
 Pat. No. 5,569,250 describes a biocompatible osteosynthesis plate that is
 capable of being used in a secured relationship over a plurality of
 adjacent bone portions. That biocompatible osteosynthesis plate includes
 an elongated section having a top face and a bottom face, at least one
 fastener opening disposed between the top face and the bottom face, and
 means disposed upon the elongated section to permit the formation of
 additional fastener openings therethrough, during a surgical procedure.
 The osteosynthesis plate is in a first thermochemical state in a first
 configuration and is capable of being converted to a second thermochemical
 state so that it may be deformed prior to fixation. The first
 thermochemical state is typically room temperature (operation room
 conditions) and the second thermochemical state is typically an elevated
 temperature above the T.sub.g of the polymer material (e.g., for
 polylactides between 50-60.degree. C.). Accordingly, in order to shape the
 plates disclosed in U.S. Pat. No. 5,569,250, they must be changed from
 their first thermochemical state to the second thermochemical state by
 heating, and thereafter they must be changed again back to the first
 thermochemical state prior to fixation. Because the thermal conductivity
 of polymeric materials is poor, the conversion of material to a second
 temperature is a slow process. Therefore, the clinical use of plates of
 U.S. Pat. No. 5,569,250 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, the entire
 disclosure of which is incorporated herein by reference, described a
 bioabsorbable poly-L-lactide miniplate and screw system for osteosynthesis
 in oral and maxillofacial surgery. However, in order to shape the plates
 of that reference, they first 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 they be fitted to the surface
 of the bone.
 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
 at least with one fixation device, like a screw, rod, clamp or
 corresponding device, wherein the plate comprises at least two essentially
 superimposed plates to provide a multilayer plate construction. The
 individual plates of said multilayer plate construction are flexible, so
 as to permit a change of form of said multilayer plate construction to
 substantially assume the shape of the bone surface in the operation
 conditions by means of an external force, such as by hand and/or by
 bending instrument directed to said multilayer plate construction, whereby
 each individual plate assumes a position of its own with respect to other
 individual plates by differential motion along the respecitive surfaces of
 coinciding plates.
 Although the said multilayer plate fits even the curved bone surface
 without heating of individual plates, the clinical use of 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 disturbances and increased risks of foreign
 body reactions.
 U.S. Pat. No. 4,671,280, the entire disclosure of which is incorporated
 herein by reference, describes the manufacturing of a fastener member or
 staple, by the winding of an oriented bioabsorbable polymeric filament
 around a forming bar, which winding is carried out at a temperature below
 the glass transition temperature of the polymer. Ordinarily, winding will
 be done at ambient temperature. Because the oriented filament is quite
 stiff, the coils are bowed out slightly from the sides of the forming bar.
 Thus, the coils do not fully assume the desired fastener member (or
 staple) configuration until the filaments are heated, which will normally
 be done during the annealing step (see, e.g., U.S. Pat. No. 4,671,280;
 Column 5, first two paragraphs). Thus, while U.S. Pat. No. 4,671,280 may
 describe some bending of drawn filament at an ambient temperature, the
 bending does not give the desired configuration of the material until the
 filaments are additionally heated. The filaments are heated during the
 annealing step to a temperature above the glass transition temperature of
 the material (see also Example 1 of U.S. Pat. No. 4,617,280).
 A need, therefore, exists for a bioabsorbable (bioresorbable or
 biodegradable) osteosynthesis device, like a plate, which is thin and
 substantially rigid and substantially deformable at a first thermochemical
 state, being also dimensionally stable before and after deformation
 (shaping) in the said first thermochemical state. A need also exists for a
 bioabsorbable (bioresobable or biodegradable) osteosynthesis plate, which
 is strong, tough, does not produce a substantial inflammatory response,
 and which plate can be deformed, yet dimensionally stable at temperatures
 below the glass transition temperature (T.sub.g) of the material from
 which the device is made, to facilitate shaping. A need further exists for
 such a bioabsorbable (bioresorbable or biodegradable) osteosynthesis
 plate, which is strong, tough, does not produce a substantial inflammatory
 response, and which plate can be deformed, yet dimensionally stable at
 room temperature in operation room conditions, to facilitate the shaping
 of the plate. Likewise, a need exists for such a bioabsorbable
 (bioresorbable or biodegradable) osteosynthesis plate, which is strong,
 tough, does not produce a substantial inflammatory response, and which
 plate can be deformed, yet dimensionally stable in operation room
 conditions (in the first thermochemical state) to allow its fixation on
 bone without distortion of the configuration of the bone fragments to be
 fixed, and which shaped plate is also dimensionally stable at a second
 thermochemical state, in tissue conditions, when fixed on bone surface to
 facilitate non-problematic bone fracture healing.
 SUMMARY OF THE INVENTION
 Prior art, U.S. Pat. No. 5,569,250, teaches that bioabsorbable polymeric
 fixation implants, like plates, should be manufactured of non-oriented
 material and that the implants are relatively rigid at a first
 thermochemical state and are relatively deformable only at a second
 thermochemical state (at elevated temperature) to which the implant is
 temporarily brought prior to implantation.
 In this invention we have found, surprisingly, that brittle and/or
 relatively weak bioabsorbable thermoplastic polymers, copolymers, polymer
 alloys or composites with ceramic particulate fillers or fiber
 reinforcements, having T.sub.g of the material above human body
 temperature, which materials cannot be deformed at room temperature, can
 be transformed through uni- and/or biaxial orientation of the material in
 the solid state to materials which are deformable at room temperature.
 Accordingly, the present invention describes uni- and/or biaxially
 oriented, rigid and tough materials and implants, like plates, which can
 be deformed at a first thermochemical state, like at room temperature in
 operation room conditions, prior to implantation, and which implants
 retain their deformed (shaped) form well in the second thermochemical
 state at body temperature in tissue conditions, when implanted on bone, so
 that they keep the fixed bone fragments essentially in the desired
 position to facilitate bone fracture healing.
 It should be emphasized that the first thermochemical state can be any
 temperature below T.sub.g of the material down to the room temperature
 area, because the uni- and/or biaxially oriented materials retain their
 properties of being substantially deformable and substantially rigid at
 such temperatures. An advantage of the present invention is to provide a
 low profile uni- and/or biaxially oriented biocompatible implant of
 sufficient strength to be capable of effecting a secured relationship
 between a plurality of adjacent bone portions. Another advantage of the
 present invention is to provide an uni- and/or biaxially oriented
 biocompatible implant that is bioresorbable over a desired period of time
 while not generating a substantial inflammatory response. A further
 advantage of the present invention is to provide an uni- and/or biaxially
 oriented bioabsorbable and biocompatible implant, like a plate, that is
 relatively rigid at a first thermochemical state, but is also relatively
 deformable at said first thermochemical state prior to implantation.
 A further advantage of the present invention is to provide an uni- and/or
 biaxially oriented bioabsorbable implant that is capable of being
 repeatedly deformed at the said first thermochemical state prior to
 implantation. Another advantage of the present invention is to provide an
 uni- and/or biaxially oriented biocompatible implant that can be easily
 and inexpensively manufactured with reduced internal stresses. A further
 advantage of the present invention is that it provides an uni- and/or
 biaxially oriented biocompatible fixation device that is capable of
 securing another such uni- or biaxially oriented biocompatible implant
 device and one or more adjacent bone portions.
 The present invention, moreover, in one form thereof, provides a
 low-profile uni- and/or biaxially oriented biocompatible osteosynthesis
 plate that is capable of being shaped to secure a plurality of adjacent
 bone portions. The osteosynthesis plate of the present invention includes
 an elongated section having a top face and a bottom face, which elongated
 section is capable of being shaped to traverse a fracture site or
 osteotomy site for subsequent fixation to adjacent bone portions. The uni-
 and/or biaxially oriented osteosynthesis plate further includes a
 plurality of fastener openings disposed between the top face and bottom
 face to allow the traverse of a plurality of surgical fasteners
 therethrough. The osteosynthesis plate further includes means disposed
 upon the elongated section to permit the formation of additional fastener
 openings therethrough during a surgical procedure, at the discretion of
 the surgeon. The osteosynthesis plate is relatively rigid at a first
 temperature and is deformable in three dimensions, yet dimensionally
 stable, at said first temperature. The osteosynthesis plate retains a
 deformed position at said first temperature in operation conditions, but
 can be subsequently returned to its original configuration by
 redeformation at said first temperature and said first thermochemical
 state. As such, the uni- and/or biaxially oriented osteosynthesis plate of
 the present invention may be repeatedly deformed and returned to its
 original configuration at said first temperature (first thermochemical
 state), in order to contour the osteosynthesis plate precisely to a
 desired configuration through successive iterations.
 The present invention also includes bioresorbable fixation devices, or bone
 screws, that are capable of being inserted through fastener openings
 disposed within the uni- and/or biaxially oriented osteosynthesis plates
 of the present invention. As such, the present invention contemplates a
 bone stabilization device including an uni- and/or biaxially oriented
 bioresorbable osteosynthesis plate and bioresorbable surgical fastener.
 The present invention also provides a method for forming a low-profile,
 uni- and/or biaxially oriented biocompatible osteosynthesis plate,
 including the steps of formation of a sheet stock, polymer orientation
 uni- and/or biaxially, formation of an uni- and/or biaxially oriented,
 osteosynthesis plate from oriented sheet stock, finishing, surface
 cleaning, sterilization and packaging.
 The present invention is also directed to a method for enabling a secured
 relation between a plurality of adjacent bone portions, including the
 steps of providing a low-profile, uni- and/or biaxially oriented,
 biocompatible, osteosynthesis plate, positioning the uni- and/or biaxially
 oriented biocompatible osteosynthesis plate upon a plurality of adjacent
 bone portions, providing a plurality of surgical fasteners for enabling a
 fixed relation between the uni- and/or biaxially oriented osteosynthesis
 plate and at least one adjacent bone portion, positioning the plurality of
 surgical fasteners within a plurality of fastener openings upon the uni-
 and/or biaxially oriented osteosynthesis plate and securing the plurality
 of surgical fasteners into the adjacent bone portions.
 Uni- and/or biaxial orientation of polymers or polymer composites with
 solid state deformation is a well known process in polymer science and
 technology. During orientation, polymer molecules or their segments tend
 to align with their long axis in the orientation direction. A description
 of molecular background of orientation of polymeric materials and of its
 physical characterization is given, e.g., in U.S. Pat. No. 4,968,317, the
 entire disclosure of which is incorporated herein by reference. The
 effects of orientation are most pronounced in partially crystalline
 polymers, but it is also possible to orient non-crystalline (amorphous)
 polymers, as has been described in PCT/FI96/00511, the entire disclosure
 of which is also incorporated herein by way of this reference.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 For the purpose of promoting an understanding of the principles of the
 invention, reference will now be made to the preferred embodiments of the
 present invention. It will nevertheless be understood that no limitation
 of the scope of the invention is thereby intended, such alterations and
 further modifications, and such further applications of the principles of
 the invention therein being contemplated as would normally occur to one
 skilled in the art to which the invention relates.
 Referring to FIG. 1A, there are shown uni- or biaxially oriented
 biocompatible, bioabsorbable osteosynthesis plates 1-6, 6a and 6b,
 according to preferred embodiments of the present invention. The uni- or
 biaxially oriented biocompatible osteosynthesis plates 1-6 are shown as
 being disposed over bone fractures 7-10, while plates 6a and 6b are shown
 as being disposed in position for facial reconstruction. It will be
 appreciated that the uni- or biaxially oriented biocompatible,
 bioabsorbable osteosynthesis plates of this invention, like plates 1-6
 (and 6a & 6b), may be of any size or shape as will be hereinafter
 discussed. Further, the uni- or biaxially oriented biocompatible
 osteosynthesis plates 1-6 (and 6a & 6b) may also be deformable and rigid
 at a first thermochemical state, like in operation room conditions. "A
 thermochemical state" as used in describing the present invention is
 defined according to U.S. Pat. No. 5,569,250, as a combination of thermal
 and chemical conditions resulting from exposure to certain thermal and
 chemical environments like room temperature and operation room atmosphere,
 respectively. Although one type of change in thermochemical state occurs
 by a change of temperature alone, changes in thermochemical state of an
 uni- and/or biaxially oriented biocompatible implant of the present
 invention should be understood as not limited only to changes in
 temperature. Preferably, the uni- and/or biaxially oriented biocompatible,
 bioabsorbable osteosynthesis plates of this invention are relatively rigid
 at both room temperature and at human body temperature and they are
 deformable at temperatures (like at room temperature) below the T.sub.g of
 the material from which the uni- and/or biaxially oriented biocompatible
 osteosynthesis plates are made. Therefore, there is no need to heat the
 plates of this invention to temperatures above the T.sub.g of the
 material, as must be done with prior art plates. Because of the uni-
 and/or biaxial molecular orientation of the materials of the invention,
 they exhibit the substantial rigidity and substantial deformability in all
 temperatures between T.sub.g of the material and room temperature or even
 to temperatures below room temperature.
 Importantly, the uni- and/or biaxially oriented biocompatible,
 bioabsorbable osteosynthesis plates of this invention are formed by a
 method such that the uni- and/or biaxially oriented biocompatible
 osteosynthesis plates are dimensionally stable and deformable in operation
 conditions at room temperature and/or at any temperature above room
 temperature (first thermochemical state), but at or below body temperature
 (second thermochemical state). As used herein, the term "dimensionally
 stable" means that the uni- or biaxially oriented biocompatible,
 bioabsorbable osteosynthesis plates are able to retain substantially the
 same configuration at either of said two thermochemical states so that the
 uni- and/or biaxially oriented osteosynthesis plates facilitate bone
 fracture healing by keeping the fracture pieces in the proper position in
 relation to each other.
 The rigidity, deformability and the dimensional stability of the plates are
 due to the manufacturing process of uni- and/or biaxially oriented plates,
 which is also discussed below. The uni- and/or biaxially oriented
 biocompatible osteosynthesis plates, like those of FIG. 1, are typically
 formed from uni- and/or biaxially oriented bioabsorbable polymer,
 copolymer, polymer alloy or composite with particle filler or fiber
 reinforcement. An example of such materials is a lactide (80 mol-%) and
 glycolide (20 mol-%) copolymer composition which is oriented and has a
 glass transition temperature of between 50.degree. C. and 65.degree. C.
 Uni- and/or biaxially oriented osteosynthesis plates made using
 bioabsorbable oriented materials and in the manner discussed below will
 retain a substantial proportion of their strength after the first several
 weeks or months after implantation when this strength must be relatively
 high. Uni- and/or biaxially oriented osteosynthesis plates may be made of
 partially crystalline or non-crystalline (amorphous) materials. Uni-
 and/or biaxially oriented osteosynthesis plates of the invention are
 capable of stabilizing a plurality of bone portions for a period of from
 one to several months following implantation, and yet they will be
 completely resorbed after one year or several years following
 implantation, depending on such factors as chemical composition and molar
 mass of the bioabsorbable polymeric material, implant size and geometry or
 the position of the implant in the human body. Accordingly, the resorption
 time can be tailored to be fast or slow. Slow resorption is advantageous
 in the case of slow healing fractures and a relatively fast resorption of
 the bioabsorbable material reduces the unwanted cosmetic appearance as
 well as growth restriction in pediatric patients.
 It will be appreciated that the uni- and/or biaxially oriented
 biocompatible, bioabsorbable osteosynthesis plate of the invention may be
 of a variety of sizes and/or shapes, as hereinafter discussed, and may
 also be of a bioresorbable material of different origins. In addition, the
 uni- and/or biaxially oriented biocompatible osteosynthesis plates are
 preferably both rigid and deformable at room temperature (below T.sub.g of
 the material) and at human body temperature.
 Referring to FIGS. 2A-2D and 3, several uni- and/or biaxially oriented
 osteosynthesis plates according to the invention, are described. FIG. 2A
 shows a plate in the form of a flat plate 11. The flat plate 11 includes
 an elongated section 12 having a top face 13 and a bottom face 14. The
 flat plate 11 is further shown to include a plurality of fastener openings
 15 that are of substantially cylindrical shape and are disposed between
 the top face 13 and the bottom face 14. The fastener openings 15 are
 operable to allow the traverse of surgical fasteners for enabling a
 secured relationship between the flat plate 11 and a bone surface (not
 shown) to which the flat plate 11 may be applied. It will be appreciated
 however, that the fastener openings 15 do not have to be present if there
 are other means for securing the flat plate 11 to bone. Preferably, the
 flat plate 11 is applied to a bone surface such that the plane or contour
 formed by the bottom face 14 is substantially flush with the bone surface
 to which the flat plate 11 is applied.
 The flat plate 11 further includes means disposed upon the elongated
 section 12 to permit the formation of additional fastener openings
 therethrough at a plurality of different positions during a surgical
 procedure, as was described, e.g., in EP 0 449 867 B1. In a typical
 embodiment, this is provided by having the elongated section 12 include a
 mid-portion 12a which is disposed between the fastener openings 15 and
 having substantially the same width as the portion of the flat plate 11,
 which is adjacent to the fastener openings 15. Accordingly, the surgeon is
 able to drill through the mid-portion 12a to form additional fastener
 openings as the particular application may require. It will be noted that
 additional fastener openings may be formed as well on, e.g., o the axis of
 the elongated section 12. It is natural that the arrangement of fastener
 openings and additional fastener openings can have different embodiments
 depending on the bone quality, fracture type etc. Other types of fastener
 opening and additional fastener opening combinations known in the art are
 shown in, e.g., in EP 0 449 867 B1.
 The flat plate 11 is has a "low profile" construction, that is, of a
 preferably thin nature so as to cause a minimum protrusion above the bone
 surface to which it is applied. In this regard, the term "low profile"
 will be used to refer to a construction in which the width is greater than
 about four to six times the height of the plate 11. For example, the plate
 11 may typically have a width ("w") of 4-8 mm, a length ("l") of between
 about 10 mm to 80 mm and a height ("h") (thickness) of about 0.3 mm to 2
 mm, as shown in FIGS. 2 and 3. The flat plate 11 is further provided to be
 preferably of a bioresorbable material, such that the flat plate 11 may be
 resorbed into the body through processes well known to those skilled in
 the art over a desired period of time. In this regard, the flat plate 11
 may formed from one of the materials described in this invention.
 The flat plate 11 is also characterized by its ability to be deformed,
 without heating it above the T.sub.g of the plate material, during a
 surgical procedure where it will be conformed to the contour of the bone
 surface to which it is applied. This feature is especially useful in the
 surgical repair of bone surfaces having high curvatures, including the
 maxillofacial bones of the craniofacial skeleton. During such deformation,
 the flat plate 11 is deformed by manipulating the plate by hand or with
 manipulating device(s) in a first thermochemical state, i.e., in the
 operation room conditions during a surgical operation. Accordingly, there
 is no need, before its deformation, to elevate that plate to a higher
 temperature, using e.g., a heating device, as is needed in prior art U.S.
 Pat. No. 5,569,250. The deformed plate of the invention will then be
 placed into the second thermochemical state when fixed on bone in the body
 to secure the bone fracture. More preferably, because the flat uni- and/or
 biaxially oriented osteosynthesis plate 11 is formed by a method which
 causes the plate to be deformable, ductile, rigid and dimensionally stable
 during operation under the operation room conditions, in the first
 thermochemical state, the flat plate 11 is able to return to its original
 configuration upon deforming it again in operation room conditions. As
 such, it will be appreciated that this ability allows the flat plate 11 to
 be repetitively deformed and returned to its original configuration, thus
 allowing for successive attempts by a surgeon during a surgical procedure
 to conform the flat plate 11 in three dimensions to correspond as closely
 as possible to the contours of the bone surface to which the flat plate 11
 will be applied. These successive deformations can be done conveniently
 and rapidly in operation room by operation table without heating and
 cooling conversions, which are necessary for the bending of prior art
 plates, like those of U.S. Pat. No. 5,569,250.
 The formation of additional fastener openings through the flat plate 11 may
 be accomplished by simply drilling through the material from which the
 flat plate 11 is made as discussed above. Such drilling is performed
 through means well known to those skilled in the art. The flat plate 11 is
 then operable to accept a plurality of surgical fasteners, such as
 biocompatible and bioresorbable bone screws, which may be constructed of
 the same material as the flat plate 11, or may alternatively be made of
 another bioabsorbable material.
 The positioning of the flat plate 11 is preferred to be with its bottom
 face 14 in substantially flush contact with the bone surface to which it
 is applied, and with a plurality of fasteners (not shown) disposed
 therethrough for securing it into position, wherein the head of the
 surgical fastener is tightened against the top face 13 of the flat plate
 11. This arrangement results in a secured relationship between the flat
 plate 11 and the underlying bone surface. According to an advantageous
 embodiment, the fastener opening 15 (see FIGS. 2 and 3) is conically
 widened from its opening end on the top face 13 so that it forms a
 countersink 15a on the top face 13.
 In addition to a simple plate with a constant width w and one or several
 fastener openings (as is seen in FIGS. 2A and 2B) the uni- or biaxially
 oriented, bioabsorbable plates of the invention can have such a design
 that the width of the plate in the area of the isthmus between two
 fastener openings is smaller than the width of plate around the fastener
 openings (or the width of the area into which additional fastening
 openings can be drilled). FIGS. 2C-2D describe such plates. A special
 advantage of plates of FIGS. 2C-2D is that these plates can be deformed
 also in the flat plane of the plate (in the plane of figure), in addition
 to bending and torsional deformations, which are typical for constant
 width plates, like those of FIGS. 2A-2B.
 Referring now to FIGS. 4 and 5, there is shown a uni- or biaxially oriented
 biocompatible flat osteosynthesis plate 17 according to a preferred
 embodiment of the present invention. FIG. 4 illustrates a perspective view
 of the osteosynthesis plate 17, which includes an elongated section 18
 having a top face 19 and a bottom face 20. The flat, smooth-surfaced
 configuration of osteosynthesis plate is intended to render the plate 17
 in a "low-profile" configuration. This is accomplished by making the
 elongated section 18 to be as thin as possible to accomplish the desired
 result without any protrusions which disadvantageously increase the
 thickness of the plates according to the prior art U.S. Pat. No.
 5,569,250. Preferably, the width of the osteosynthesis plate 17 is greater
 than approximately four to six times the thickness of the plate. It has
 been determined that a minimum thickness of the plate is desirable for
 minimizing the amount of mass and the cross-section of the osteosynthesis
 plate 17, as well as providing the desired resorption time for a complete
 resorption of the osteosynthesis plate into the body. It has also been
 determined that this principle, which involves the spreading of the mass
 of an osteosynthesis plate over a larger surface area, provides improved
 results in both reducing the cosmetic effect of implantation of these
 devices, as well as providing a more favorable time for resorption of the
 material due to smaller cross-sectional area.
 The osteosynthesis plate 17 is also characterized by its ability to be
 deformed during a surgical procedure in the operation room conditions, to
 be conformed to the contour of the bone surface to which it is applied.
 This feature is especially useful in the surgical repair of bone surfaces
 having high curvatures, including the maxillofacial bones of the skull, as
 previously described.
 The osteosynthesis plate 17 also includes a plurality of fastener openings
 21 which are disposed between the top face 19 and the bottom face 20. As
 before, the fastener openings 21 are operable to allow the traverse of a
 plurality of surgical fasteners therethrough. The fastener openings 21 may
 each be further provided with a countersink 22 which is capable of
 acceping a preferably correspondingly shaped portion of a head of a
 surgical fastener. As such, the countersink 22 may be oriented in a
 substantially hemispherical configuration, a substantially frustoconical
 configuration, or in any other configuration suitable for the particular
 need.
 FIGS. 4 and 5 also illustrate a surgical fastener in the form of a bone
 screw 23 located above the surface of the osteosynthesis plate 17 in FIG.
 4, and located in its fully inserted position in FIG. 5. When fully
 inserted, the head 24 of the bone screw 23 may be mainly or substantially
 contained below the top face 19 of the plate 17 thereby complementing the
 low-profile configuration of the osteosynthesis plate 17. The bone screw
 23 may be made from the same or different biocompatible and bioabsorbable
 material as the osteosynthesis plate 17, thereby providing a fully
 bioresorbable bone stabilization device.
 As is illustrated in FIGS. 4 and 5, when the surgical fastener is provided
 in the form of a bioresorbable bone screw 23, head 24 of the bone screw 23
 includes a fastener socket 25 into which the tip of the installation tool,
 like a screwdriver 26, can be pushed. The screwdriver 26 is used for
 engaging the bone screw 23 for insertion within a fastener opening 21 and
 subsequent rotation of the bone screw 23 while threading into an
 underlying bone structure. The cross-section of the socket 25 can be,
 e.g., triangular, quadrangular (like in FIG. 4), hexagonal, etc. It will
 be appreciated that the socket 25 and the corresponding tip of a
 screwdriver 26 may be shaped in any suitable configuration to match each
 other.
 Referring to FIGS. 6A through 6J, there are shown a plurality of
 configurations of flat uni- or biaxially oriented osteosynthesis plates
 according to the present invention. FIGS. 6A and 6B show L-plates 27 and
 28 according to the present invention. The L-plates 27 and 28 are further
 shown to include a plurality of fastener openings 29 and 30 disposed upon
 the elongated sections 31 and 32 near the terminal portions and at the
 corner sections of the elongated sections. A typical L-plate 27 has a
 width w of about 12 mm, a length (l) of about 20 mm and a thickness of
 about 0.5-1.0 mm. FIGS. 6C-61 show other configurations of plates, like a
 T-plate (6C), Y-plate (6D), X-plates (6E and 6F), square plate (6G),
 triangle plate (6H) and H-plate (6I). All of such plates may include a
 plurality of holes for fasteners, depending on the size and use
 indications of the plate. FIG. 6J shows a mesh-plate 33 with a plurality
 of smaller holes 34 for fastener fixation and bigger holes 35 to
 facilitate tissue healing through the plate 33 and to reduce the mass of
 the plate 33. It will be appreciated that the examples set forth in FIGS.
 6A-6J are meant to be only illustrative, and not a limitation, of the
 varieties of osteosynthesis plate shapes which may be constructed
 according to the present invention. It will further be appreciated that
 these osteosynthesis plates may be constructed of any of the materials
 previously discussed, or may be constructed from other suitable materials.
 As before, it is preferred that any of the above osteosynthesis plates be
 constructed of a bioabsorbable (resorbable) material. Also as before, the
 bioabsorbable material may be combined in a bone stabilization device with
 bioabsorbable surgical fasteners, such as bone screws.
 It will also be appreciated that any of the above osteosynthesis plates may
 be constructed in a configuration, as shown in FIGS. 1-6. In addition, it
 will be appreciated that any of the above osteosynthesis plates may be
 constructed to include means disposed upon the elongated section to permit
 the formation of additional fastener openings therethrough during a
 surgical procedure, as provided in EP 0 449 867 B1, and in the description
 relating to FIGS. 2 and 3 herein. Further, all of the above-mentioned
 osteosynthesis plates are intended to be of a low-profile configuration,
 constructed in a flat configuration, such as in FIGS. 1-6.
 The osteosynthesis plates of the present invention can be manufactured of
 thermoplastic bioabsorbable (resorbable or biodegradable) polymers,
 copolymers, polymer alloys, or composites e.g. of poly-a-hydroxy acids and
 other aliphatic bioabsorbable polyesters, polyanhydrides, polyorthoesters,
 polyorganophosphatzenes, tyrosine polycarbonates and other bioabsorbable
 polymers disclosed in numerous publications, e.g. in S. Vainionpaa et al.,
 Prog. Polym. Sci., 14 (1989) 679-716, FI Patent No. 952884, FI Patent No.
 955547 and WO-90/04982, EP 0449867 B1, U.S. 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,
 the disclosures of all of which are incorporated herein by way of this
 reference.
 Implants in accordance with the invention 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 fibres
 manufactured of a resorbable polymer or of a polymer alloy, or with
 biodegradable glassfibres, such as P-tricalsiumphosphate fibres,
 bioglassfibres or CaM fibres (cf. e.g. EP146398, the entire disclosure of
 which is incorporated herein by way of this reference). Ceramic powders
 can also be used as additives (fillers) in implants to promote new bone
 formation.
 Implants according to the invention can also contain layered parts
 comprising a flexible outer layer, which is a surface layer improving the
 toughness of the implant and/or operating as a hydrolysis barrier, and a
 stiffer inner layer or core of the implant. To prepare such an embodiment,
 the implant can be coated with an outer layer having different chemical
 and mechanical properties (e.g., hydrolysis and strength retention) than
 the core of the implant. In such a case, an outer layer having greater
 resistance to hydrolysis than the implant's core can be used, enabling the
 implant (after insertion in a patient) to retain its strength and
 biodegrade in less time than it would have without such an outer coating.
 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
 fibres, such as carbon) or for facilitating its treatment (e.g.
 colorants). According to one advantageous embodiment the implant of the
 invention contains some bioactive agent or agents, such an 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.
 A typical manufacturing procedure to make plates of the present invention
 is as follows. First the polymer raw material (and optional additives
 and/or filler(s) and/or reinforcing fibers) in the form of a powder,
 flakes, pellets or granulate, etc., will be melted in a continuous
 process, like extrusion, or with a noncontinuous process, like injection
 molding or compression molding. The melted material will be cooled so that
 it solidifies to an amorphous or partially crystalline (crystallinity
 typically 5-50%) preform, like a cylindrical rod or bar, a flat balk with
 a rectangular cross-section, a plate or a sheet stock. Cooling can be done
 inside a special mold in injection molding and in compression molding
 techniques. In extrusion, the preform will be formed from material melt in
 a die and the preform will be led onto a special cooling belt or into a
 cooling solution to make a solid preform. Thereafter, the solid preform
 will be oriented with an uni- and/or biaxial solid state deformation
 process to create an oriented plate preform. The orientation transforms
 the sheet stock, which cannot be deformed without substantial damage or
 breaking at room temperature, into a form where the molecular orientation
 toughens the sheet stock, so that after orientation it can be deformed
 without substantial damage or breaking at room temperature or also at any
 higher temperature between room temperature and Tg of the polymeric raw
 material.
 The orientation is typically made at a temperature (T) above T.sub.g of the
 polymeric raw material, but below the melting temperature of the material,
 if it is partially crystalline. The orientation is typically made by
 drawing the unoriented plate preform in the solid state. The drawing can
 be done freely by fixing the ends of the plate preform into fixing clamps
 of a drawing machine, tempering the system to the desired drawing
 temperature and by increasing the distance between the fixing clamps so
 that the plate preform is stretched and oriented structurally. This type
 of orientation is mainly uniaxial. The drawing can be done also through a
 conical die, which can have, e.g., a circular, an ellipsoidal, a square or
 rectangular cross-section. When the cross-sectional area of the
 bioabsorbable polymer billet, which will be drawn through the die is
 bigger than the cross-sectional area of the die outlet, the billet will be
 deformed and uni- and/or biaxially oriented during the drawing, depending
 on the geometry of billet and die.
 The billet may be forced through the die also by pushing the billet
 mechanically with a piston through the die (ram extrusion) or by pushing
 the billet through the die with hydrostatic pressure (see e.g. N. Inoue,
 in Hydrostatic Extrusion, N. Inoue and M. Nishihara (eds.), Elsevier
 Applied Science Publishers, Barbing, England, 1985, p. 333-362, the entire
 disclosure of which is incorporated herein by way of this reference).
 It is also possible to create orientation by shearing the flat billet
 between two flat plates which glide in relation to each other and approach
 each other at the same time, as is seen schematically in cross-sectional
 FIGS. 7A and 7B, where 36 and 37 are shearing plates and 38 is a billet
 before shearing and 39 a billet after shearing. The arrows in FIG. 7A show
 the course of motion of shearing plates 36 and 37 in relation to each
 others.
 It is also possible to deform the billet in a compression molding device
 between flat plates which are pushed towards each other, so that the
 billet deforms biaxially between the plates and attains the desired final
 thickness. The deformation can be done also by rolling the rod-like or
 plate-like preform between rollers, which flatten the preform to the
 desired thickness orienting the material at the same time biaxially. It is
 natural that different deformation methods can be combined with each
 other. For example, hydrostatic deformation can be combined with die
 drawing, or rolling can be combined with drawing, e.g., by using two pairs
 of rollers, one set after the other, which rollers have different rolling
 speeds, etc. Optionally, the billet and/or die, compression plates or
 rolls can be heated to the desired deformation temperature with electrical
 heating or with a suitable heating medium, like a gas or heating liquid.
 The heating can be done also with microwaves or ultrasonically to
 accelerate the heating of the billet.
 Regardless of the deformation method, the purpose of the solid state
 deformation is the orientation of the material uni- and/or biaxially, so
 that the material is transformed to such material that is substantially
 rigid and substantially deformable at the conditions of surgical
 operation.
 Solid state deformation, to create oriented bioabsorbable fixation
 materials, has been described in several publications, like in U.S. Pat.
 No. 4,671,280, U.S. Pat. No. 4,968,317, U.S. Pat. No. 4,898,186, EP 0
 321176 B1, WO 97/11725, D. C. Tunc and B. Jadhav, in Progress in
 Biomedical Polymers, eds. C. G. Gebelein and R. L. Dunn, Plenum Press, New
 York 1992, p. 239-248, FI Patent No. 88111 and FI Patent No. 98136, the
 entire disclosures of each of which are incorporated herein by way of this
 reference. However, only in this invention have we found, surprisingly,
 that when the rigid bioabsorbable (resorbable) fixation plate material,
 which cannot be deformed substantially at temperatures below T.sub.g of
 the material, is oriented uni- and/or biaxially, it is transformed into a
 material which is substantially rigid but can be deformed substantially at
 temperatures below T.sub.g of the material, for use advantageously in bone
 fracture fixation.
 Following the orientation step, osteosynthesis plates, such as flat plates
 of FIGS. 1-6, can be formed from the oriented sheet stock by machining or
 stamping the plate and the fastener opening(s) and the countersink(s). The
 next step of the method of the present invention involves the finishing of
 the plates, to provide a smooth surface and an aesthetic appearance for
 the article. This is accomplished by trimming with suitable trimming
 devices, such as knives or cutting blades, or may also be accomplished by
 an additional stamping step. Once the removal of surface irregularities
 has occurred, the substantially completed product is subjected to cleaning
 with a suitable cleaning agent, like ethyl alcohol water mixture.
 Mechanical agitation and ultrasonic agitation can be used to facilitate
 the cleaning. In this step, the outer surface of the osteosynthesis plate
 is cleaned of fingerprints, soils and oils resulting from contact with
 human hands and other surfaces, as well as impurities which may collect on
 the surface.
 In the next step of the method of the present invention the plates are
 dried in high vacuum, optionally at an elevated temperature, and packed
 into a plastic foil and/or aluminum foil pouch(es) which is (are) sealed.
 Another drying step and filling of the pouch with an inert gas (like
 nitrogen or argon gas) before heat sealing of the pouch, may also be
 carried out. In the next step the plates closed into the packages, are
 sterilized with .gamma.-radiation, using a standard dose of radiation
 (e.g., 2.5-3.5 MRad). If gas sterilization will be used (like ethylene
 oxide), the plates must be sterilized before closing the package.
 It is natural that the above-mentioned steps of manufacturing an
 osteosynthesis plate of the present invention may further include
 additional steps, such as for quality control purposes. These additional
 steps may include visual or other types of inspections during or between
 the various enunciated steps, as well as final product inspection
 including chemical and/or physical testing and characterization steps and
 other quality control testing.
 The method for imparting a secured relationship between a plurality of
 adjacent bone portions according to the present invention will now be
 described. The first step of this method includes providing a sterile,
 low-profile uni- or biaxially oriented biocompatible osteosynthesis plate,
 such as any of the osteosynthesis plates of FIGS. 1-6. This is achieved by
 opening the plate package in an operation room by an operation table and
 supplying the sterile plate to the surgeon. Depending on the surface
 topography of the bone to be fixed, the surgeon then shapes (deforms), if
 necessary, the osteosynthesis plate to a first desired configuration by
 hands or with any manipulation instrument. The surgeon can then test the
 result of shaping conveniently, by pressing the plate gently against the
 bone to be fixed, and if the first desired configuration is not sufficient
 for completing the surgical requirements, the surgeon can reshape the
 osteosynthesis plate to a second desired configuration.
 In addition, it will be appreciated that the method of the present
 invention further includes the capability for repetitively reshaping, at
 constant operation room temperature, the osteosynthesis plate to
 successive desired configurations and ceasing reshaping the osteosynthesis
 plate when a desired final configuration of the osteosynthesis plate has
 been achieved.
 The osteosynthesis plate is then positioned upon a plurality of adjacent
 bone portions. A plurality of surgical fasteners are then provided for
 imparting a fixed relationship between the osteosynthesis plate and at
 least one adjacent bone portion. A plurality of surgical fasteners are
 then positioned within a plurality of fastener openings located upon the
 osteosynthesis plate. The plurality of surgical fasteners are then secured
 to the adjacent bone portions, thereby engaging the low-profile
 biocompatible osteosynthesis plate with each bone portion. This method may
 further include the additional steps of creating at least one additional
 fastener opening through the osteosynthesis plate at a location adjacent
 to at least one bone portion, positioning an additional surgical fastener
 within each additional fastener opening, and securing each additional
 surgical fastener into each bone portion, thereby enhancing an engagement
 of the osteosynthesis plate with each bone portion, as was described e.g.
 in EP 0 449 867 B1. This method may also include the step of engaging the
 osteosynthesis plate with at least one adjacent osteosynthesis plate.
 Alternatively, the method for imparting a secure relationship between a
 plurality of adjacent bone portions is similar to that described above,
 but the osteosynthesis plate is secured by means of an adhesive. In this
 regard, after the osteosynthesis plate is formed in the manner described
 above, the surgeon places an adhesive between the bone portions to be
 secured and the osteosynthesis plate. The adhesive may typically be a
 cyanoacrylate, though other suitable adhesives may be used. The surgeon
 then brings the osteosynthesis plate into contact with the bone portions,
 thereby securing the osteosynthesis plate to the bone portions.
 The principles of the present invention described broadly above will now be
 described with reference to the following specific examples, without
 intending to restrict the scope of the present invention.
 EXAMPLE 1
 Pellets of copolymer material comprising about 80 mol-% of L-lactide and
 about 20 mol-% of glycolide were supplied by PURAC biochem bv, of
 Gorinchem, Holland. The pellets were formed such that they had an inherent
 viscosity of about 5.9 dl/g and a molecular weight Mv of about 336,000.
 The inherent viscosity was measured at 25.degree. C. using 100 mg polymer
 per 100 ml of chloroform.
 The pellets were extruded into a form of a cylindrical bar with a diameter
 of 6.0 mm using a single screw extruder (Axon BX-15, Axon Plastmaskiner,
 Sweden) and allowed to cool to ambient room temperature (20.degree. C.).
 The extruded bar had an inherent viscosity of about 3.4 dl/g and a
 molecular weight Mv of about 158,000. The crystallinity of the extruded
 bar was about 1.5% and the glass transition temperature T.sub.g was about
 53.degree. C. (as measured with differential scanning calorimeter,
 Perkin-Elmer DSC-7). To induce crystallinity, the extruded bar was then
 annealed for 16 hours under vacuum (0.02 mbar) at 110.degree. C. After
 annealing, the inherent viscosity of the bar was unchanged (about 3.4
 dl/g) and the crystallinity was about 19%. The annealed bar was oriented
 uniaxially by drawing it through a heated tapered die (T=90.degree. C.) to
 produce an oriented rod with a diameter of 3.0 mm (draw ratio=4). After
 orientation, the crystallinity of the material was over 20%.
 The uniaxially oriented rod was oriented biaxially by compressing it
 between parallel stainless steel molding plates. A steel band of the
 thickness of 1.2 mm was placed between the molding plates on both sides of
 the rod (these bands determined the thickness of the plate after molding).
 The rod was preheated three minutes at 60.degree. C. under low compression
 force (.about.0.1 kN), which prevented shrinking while allowing the
 material to become rubbery. After preheating the temperature of the
 compression molding plates was elevated stepwise at 10.degree. C.
 increments (during 3 minutes) to 90.degree. C., while elevating also the
 compression force stepwise at 10 kN increments to 30 kN. The mold was then
 cooled rapidly (in 2 minutes) to room temperature (20.degree. C.) with
 cooling water led into cooling channels in the walls of the mold. The mold
 was opened and the plate-like biaxially oriented preform was removed from
 the mold. Such preforms were then processed further with drilling and
 grinding, producing plates having a configuration similar to the plate
 shown in FIG. 2B. The dimensions of the machined plates were
 1.2.times.5.5.times.40 mm. The holes had a diameter of 1.5 mm and they
 were located at 3 mm distance from each other. The plates were then gamma
 sterilized with a minimum dose of 2.5 MRad (25 kGy). After gamma
 irradiation the inherent viscosity of the plates was about 1.3 dl/g and
 the molecular weight Mv was about 42,000. The crystallinity of the plates
 was determined to be more than 20%. A flexural strength of 180 MPa was
 measured for the plates.
 When the plates were bent at room temperature (20.degree. C.) to angles of
 10.degree., 90.degree. and 145.degree. out of the plane of the plates (see
 FIGS. 8A, B and C, respectively) they showed ductile plastic deformation
 and retained the desired bending angle after the stress was relieved. It
 was shown that bending did not change the strength of the plates.
 Commercial straight 8 hole prior art plates measuring 1.0 mm.times.5.6
 mm.times.41 mm, part 915-2417, Lot 435600 according to 1.5 mm
 Lactosorb.RTM. System (manufacturer Walter Lorenz Surgical, Inc.,
 Jacksonville, Fla.) were tested for flexural and thermal properties. The
 flexural strength of 125 MPa was measured for the plates. The plates were
 amorphous and showed the glass transition temperature T.sub.g at about
 60.degree. C., as measured with DSC (differential scanning calorimetry).
 When the plates were bent at room temperature (20.degree. C.) to various
 angles out of the plane of the plates, like in FIG. 8, they showed crazing
 at relatively small bending angles and fractured in brittle mode when the
 bending angle exceeded about 10-15.degree..
 Some plates of the invention were placed in a phosphate buffer solution at
 0.13 M, pH 7.4, and 37.degree. C. to determine, in vitro, the change in
 strength over time as the plates degrade. After six weeks, the plates were
 shown to retain more than 80% of their original flexural strength, while
 the flexural strength was approximately zero at about 18 weeks. The plates
 were completely absorbed after about two years in vivo.
 Bending of prior art plates was also studied in the following way: Pellets
 of copolymer material comprising about 80 mol-% L-lactide and about 20
 mol-% glycolide as described above were placed in a rectangular stainless
 steel mold measuring 1.2.times.50.times.100 mm. The mold was then placed
 into a vacuum press and evacuated to about 0.02 mbar. The mold was heated
 to 165.degree. C. (about 10.degree. C. above Tm) and a closing force of 60
 kN was applied to the mold for five minutes. The mold was then cooled
 rapidly (in 2 minutes) to room temperature (20.degree. C.) with cooling
 water led into cooling channels in the walls of the mold. The mold was
 opened and the plate-like preform was removed from the mold. Such preforms
 were then further processed with drilling and grinding producing plates
 having a configuration similar to the plate shown in FIG. 2B. The
 dimensions of machined plates were 1.2.times.5.5.times.40 mm, and the
 drillholes were similar to those in the oriented plates. The crystallinity
 of the plates were determined to be about 5%. To induce crystallinity,
 some plates were annealed for 16 hours under vacuum (0.02 mbar) at
 110.degree. C. After annealing the crystallinity of those plates was about
 20%. The plates were then gamma sterilized with a minimum dose of 2.5 MRad
 (25 kGy). After gamma irradiation the inherent viscosity of the plates was
 about 1.4 dl/g and the molecular weight Mv was about 47,000. The flexural
 strength of 115 MPa and 106 MPa was measured for the nonannealed and
 annealed plates, respectively. When the plates were bent at room
 temperature (20.degree. C.) to various angles out of the plane of the
 plates they showed crazing already at small bending angles between
 10-20.degree. and fractured in brittle mode when the bending angle
 exceeded about 25.degree..
 EXAMPLE 2
 A cylindrical rod with a diameter of 6.1.+-.0.2 mm was made of P(L/DL)LA
 (70/30) (trademark Resomer.RTM. LR708 of Boehringer Ingelheim, Ingelheim
 am Rhein, Germany, with inherent viscosity 5.5 dl/g) by single screw
 extrusion (with the same extruder as in Example 1). Rods were cooled to
 the ambient temperature (20.degree. C.).
 Extruded rods were oriented (and self-reinforced) by die drawing method
 (with the draw ratio of 4). Diameter of the drawn rods was 3.0.+-.0.1 mm.
 Suitable drawing temperatures for the material were between 70-100.degree.
 C.
 About a 150 mm long piece of the oriented, self-reinforced rod was set
 between two parallel compression molding plates. The rod was preheated
 three minutes at 60.+-.5.degree. C. between the plates under gentle
 compression (&lt;1 kN). After preheating the temperature of the compression
 molding plates was elevated to 90.degree. C. At the same time, the
 compression force was elevated to 30 kN. The thus made plate (thickness
 1.2 mm) was cooled during 2 minutes to the temperature of 50.degree. C.
 under compression force of 30 kN and released from the mold. The total
 cycle time was 8 minutes. Such plates were machined mechanically to the
 final dimensions of 1.2 mm.times.3 mm.times.40 mm. The plates were then
 sterilized with .gamma.-radiation (25 kGy).
 Flexural strength of the sterilized, oriented, self-reinforced plates was
 measured at 150.+-.20 MPa. The crystalinity of the plates was 0%, as
 measured by differential scanning calorimetry (DSC). The amorphous plates
 were bent in situ (at room temperature) without any preheating to an angle
 of 90.degree. out of the plane of the plate (with the method illustrated
 in FIG. 8). The plates showed ductile plastic deformation and retained the
 desired bending angle after the bending stress was relieved.
 In the bending of prior art plates, the following occurred. Nonoriented
 corresponding plates with dimensions of 1.2 mm.times.3 mm.times.40 mm were
 manufactured of Resomer LR 708 by injection molding (molding machine:
 Battenfeld injection molding machine molded 230/45 Unilog 2000,
 Manufacturer: Battenfeld Kunststoffinaschinen Ges M.G.H., Austria). The
 plates were kept at room temperature (20.degree. C.) for 2 hours before
 bending them as above. DSC measurements showed that the plates were
 amorphous, and all plates broke before a bending angle of 90.degree. was
 achieved.
 EXAMPLE 3
 Thermoplastic, bioabsorbable pseudo-polyaminoacid poly (DTH carbonate)
 (PDTHC) (M.sub.w =200,000) was synthesized according to S. I. Ertel and J.
 Kohn, J. Biomed. Mater. Res. 28 (1994) 919-930 and F. H. Silver et al., J.
 Long-Term Effects Med. Implants 1 (1992) 329-346, the entire disclosure of
 which is incorporated herein by way of this reference.
 Thermoplastic, bioabsorbable polyorthoester (POE) (M.sub.w =80,000) was
 synthesized of diketene acetal and of diols trans- cyclohexane dimethanol
 and of 1,6-hexanediol (60//40 ratio of diols) according to Daniels, A. U.
 et al., Trans. Soc. Biomater. 12 (1989) 235 and Daniels, A. U. et al.
 Trans. Soc. Biomater. 12 (1989) 74, the entire disclosure of which is also
 incorporated herein by way of this reference.
 Thermoplastic, bioabsorbable polyanhydride (PAH) (M.sub.w =20,000) was
 synthesized of 1,3 bis (p-carboxyphenoxy) propane and sebacic acid
 according to U.S. Pat. No. 5,618,563, Example 1, the entire disclosure of
 which is also incorporated herein by way of this reference.
 Poly-L-lactide (PLLA) (M.sub.w =700,000) was supplied by PURAC biochem bv,
 Gorinchem, Holland.
 Each polymer, PDTHC, POE, PAH and PLLA was extruded to cylindrical bars
 according to Example 1 herein, and they were oriented uniaxially by
 drawing them through a heated die at a temperature (T) 20.degree. C. above
 T.sub.g of the corresponding polymer. The draw ratio was in each case 2.5.
 The uniaxially oriented rods were processed to biaxially oriented plates
 with the mold compression method of Example 1 herein. Heating was done in
 each case at T=T.sub.g +20.degree. C., where T.sub.g was the glass
 transition temperature of the corresponding polymer. The plate preforms
 were machined with grinding to plates with dimensions of 1.2 mm.times.5.5
 mm.times.40 mm.
 Corresponding non-oriented plates were prepared by melt extrusion from the
 same polymers to compare the bending behavior of oriented and non-oriented
 plates. Each polymer melt was extruded through a die with a rectangular
 outlet with dimensions 1.5 mm.times.20 mm. The melted polymer preform was
 led from the die outlet onto a cooling belt where it solidified forming a
 non-oriented plate-preform with the thickness of 1.2 mm. After the
 preforms were cooled to room temperature they were processed mechanically
 to plates with the same dimensions as the oriented plates.
 The oriented and non-oriented plates were bent at room temperature to an
 angle of 45.degree. C. by the method of Example 1 (FIG. 8) herein. All the
 oriented plates were bent without significant damage of the bending area
 and retained their bent form after the bending stress was released.
 Non-oriented PLLA, POE and PAH plates broke during bending and
 non-oriented PDTHC plates developed many cracks and crazes to the bending
 area. The oriented plates were redeformed without significant damage by
 bending them again at room temperature to their original configurations.
 The non-oriented, bended PDTHC plates either broke or damaged further when
 bent back to their original configurations at room temperature.
 The tensile strength of redeformed (straight) oriented plates was 80-95% of
 the tensile strength of oriented plates that had never been bent. The
 tensile strength of non-oriented, non-broken, redeformed PDTHC plates was
 ca. 20-40% of the tensile strength of corresponding plates that had never
 been bent. This experiment showed that oriented plates can be bent and
 rebent at room temperature, but non-oriented plates do not bear up to such
 a treatment.
 EXAMPLE 4
 A rectangular bar with the thickness of 2.4 mm and the width of 3 mm was
 made of P(L/DL)LA (70/30) by melt extrusion according to Example 2.
 The non-oriented billet was oriented uniaxially in hydrostatic extrusion
 according to FIG. 9. A 10 cm long billet 40 was located into the chamber
 41 of a hydrostatic extrusion device 42 which chamber 41 was filled with
 silicone oil 43. At the tip of the device 42 was a stainless steel die 44
 with the rectangular, conical inner channel 45 with the inlet dimensions
 of 2.4 mm.times.3 mm, outlet dimensions of 1.2 mm.times.3 mm and channel
 length of 10 mm. The tip 46 of the billet 40 was first cut conically and
 the tip 46 was pushed tightly into the channel 45 of the die before
 filling the chamber with silicone oil 43 and beginning with the
 hydrostatic extrusion.
 The chamber 41, die 44, oil 43 and billet 40 were heated to the hydrostatic
 extrusion temperature of 70.degree. C., and the system was kept at this
 temperature 30 min before starting the hydrostatic extrusion process. The
 process was started by increasing the hydrostatic pressure of silicone oil
 43 inside of the extrusion chamber 41 to 150 MPa with a hydraulic piston
 47. The hydrostatic pressure forced the billet through the die, so that
 the material was oriented uniaxially when the cross-section of the
 rectangular billet changed from 2.4 mm.times.3 mm (FIG. 9B) to 1.2
 mm.times.3 mm (FIG. 9C). The oriented preform was wiped clean with soft
 paper and cut to plates with dimensions of 1.2 mm.times.3 mm.times.40 mm.
 An in situ bending test of the plates was done at room temperature as in
 Example 2. The plates showed ductile plastic deformation at room
 temperature and retained the bending angle of 90.degree. after the bending
 stress was relieved.
 EXAMPLE 5
 Rectangular bars were manufactured of P(L/DL) LA (70/30) with melt
 extrusion according to Example 2, but this time mixing of the P(L/DL)LA
 (70/30) powder before extrusion was carried out with 20 wt-% of bioactive
 glass (BAG) particles. Composition of the bioactive glass was: Na.sub.2 O
 (6 wt-%), K.sub.2 O (12 wt-%), M.sub.g O (5 wt-%), CaO (20 wt-%), P.sub.2
 O.sub.5 (4 wt-%) and SiO.sub.2 (53 wt-%). The glass was manufactured
 according to WO 96/21638, the entire disclosure of which is incorporated
 herein by way of this reference. A particle fraction with sizes between 20
 .mu.m-60 .mu.m was sieved from crushed glass and this fraction was used as
 a bioactive particle filler in the P(L/DL)LA.
 The melt extruded P(L/DL)LA bars with 20 wt-% of BAG particle filler were
 oriented with hydrostatic extrusion according to Example 4, but using a
 processing temperature of 90.degree. C. and hydrostatic pressure of 200
 MPa. The oriented billets were processed to bending test plates as in
 Example 4. Also, these plates showed ductile plastic deformation without
 breaking at room temperature when bent to a bending angle of 90.degree.
 and the plates retained their blended configuration after the bending
 stress was relieved.
 Corresponding non-oriented plates were prepared by melt extrusion from
 P(L/DL)LA and 20 wt-% of BAG particles with the equipment and process
 described in Example 2. All the non-oriented plates broke during the
 bending experiment (which was done according to Example 4) before reaching
 the bending angle of 90.degree..
 EXAMPLE 6
 Similar bars as in Example 5 were manufactured from P(L/DL)LA, but using as
 filler, instead of bioactive glass particles, bioactive glass fibers which
 were melt spun from the same glass raw material. The fibers had diameters
 between 40-80 .mu.m and the fibers were cut to 6 mm long particles before
 mixing them with P(L/DL)LA powder.
 The mixture ratio 80 wt-% of P(L/DL)LA and 20 wt-% of bioactive glass
 fibers was used. The melt extrusion and orientation of the melt extruded
 billets with hydrostatic extrusion, and also the plate manufacturing and
 plate testing, were done as in Example 5. The oriented plates with
 bioactive glass fiber reinforcement also showed ductile plastic
 deformation without breaking at room temperature when bent to a bending
 angle of 90.degree., and the plates substantially retained their bent
 configuration after the bending stress was relieved.
 Corresponding non-oriented plates were prepared by melt extrusion from
 P(L/DL)LA and 20 wt-% of bioactive glass fibers with the equipment and the
 process described in Example 2. All the non-oriented plates broke during
 the bending experiment (which was done according to Example 4) before
 reaching the bending angle of 90.degree..
 EXAMPLE 7
 Non-oriented, rectangular bars with cross-sectional dimensions of 2
 mm.times.3 mm were prepared by melt-extrusion (with single screw extruder
 Axon) from polymers PDTHC, POE and PLLA described in Example 3. Each bar
 48 was deformed and oriented biaxially by drawing-rolling technique, by
 drawing each bar slowly (drawing speed 1 cm/min) through heated rollers
 (49 and 50) in a manner shown in the schematic side-view in FIG. 10A. As
 is shown in the frontal view in FIG. 10B, the minimum distance d between
 the rollers (49 and 50) determined the final thickness of the rolled-drawn
 billets. The value of d=1.1 mm was used in these experiments. The
 temperature of the rollers was T.sub.g +30.degree. C., where T.sub.g was
 the glass transition temperature of the corresponding polymer.
 The oriented rolled-drawn preforms were processed into plates with
 dimensions 1.1 mm.times.4 mm.times.40 mm by mechanical machining
 (grinding). The deformability of such plates was tested at room
 temperature with the bending experiment described in Example 2. All the
 plates could be bent to an angle of 90.degree. without significant damage.
 The plates also retained the bent configuration immediately after
 releasing the bending force.
 EXAMPLE 8
 The objective of the bioabsorbable cranial, facial, mandibular or maxillar
 plating system is to provide adequate fixation of the osteotomies made or
 fractures treated during the healing process. To fulfill this demand, the
 plates must be located in close contact with the attached bone throughout
 the surface of the plate to provide maximum fixation. Depending on the
 anatomical conditions, the demand for bending or twisting is variable as
 per the location of the plate and/or the physical characteristics of the
 bone surface of each individual patient.
 In the mandible, the angulus area requires twisting of the plates in a
 propeller form with axial torsion angles of up to 90 degrees; as in the
 apical region, the plate must be curved with a radius of 40 to 60 mm to
 follow the congruence of the bone surface. In the maxilla, the plates must
 be bent in a step-like or curved form of up to 90 degrees of angulation.
 In most cases, a combination of bending, curving and twisting is used to
 achieve exactness of contact.
 The following clinical experiments demonstrated, that changes in the form
 of the plates are stable for the purposes of surgical bone fracture
 fixation operations, once plates are bent at room temperature to be flush
 with the bone surfaces to be fixed.
 Mandibular symphysis fractures (like 10 in FIG. 1) of ten patients were
 treated with oriented six-hole P(L/DL)LA plates (see 6 in FIG. 1) with
 dimensions 1.2 mm.times.4 mm.times.40 mm (made according to Example 2),
 using P(L/DL)LA screws (diam. 2.0 mm, length 8 mm) for plate fixation. The
 straight plates were bent, in situ, during the operation to the curved
 form to be flush on the bone surface. An uneventful, good healing of all
 fractures was seen after one year's follow up.
 Mandibular angular fractures in 6 patients were treated with six hole
 plates made of oriented PDTHC of Example 3. The plates had dimensions of
 1.2 mm.times.5.5 mm.times.40 mm and they were twisted into a propeller
 form at room temperature to be flush with the bone surface. The twisted
 plates were fixed on bone over the fracture with PDTHC screws (2.0 mm
 diam., 8 mm length). All fixations retained their position with
 uneventful, good healing as was seen after 6 months' follow-up.