CA1296256C - Osteosynthetic implant - Google Patents

Abstract

Abstract of the Disclosure Two bone fragments may be connected by means of an osteosynthetic implant including connecting devices and connecting bands comprising reabsorbable, biocompatible material, such as, for example, polygluconate or polylactate, the bands preferably in woven or knit form, and connected to the bone fragments by means of connecting elements. Different types of connecting elements are suitable for use with different types of bone fragments to be connected, and may comprise either tamping liners with tamping counterpieces or hollow screws. The connecting elements have an internal hollow bore, and may be implanted with a special tool to present any breakage of the connecting elements.
The osteosynthetic implant comprising reabsorbable material is particularly suitable for osteosynthesis in children, since growth disturbances are eliminated.

Description

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BACJGROUND OF ~HE INVE.~rION
_ield of_ tke_ Inierlt on The present invention relates to an osteosynthetic implant for the fi~ation and/or support of flat and tubular bone fradments, particularly in chlldren.
Description of the Prior Art Osteosynthetic implantation is currently practiced primarily in adults. Only in a ~ery limited number of cases, such as, for e~ample, in multiple fractures, is osteosynthetic implantation practiced T~7ith children during their growth years. The use of synthetic implants in children may result, it is l;not~n, in growth disturballces which require corresponding surgical corrections. Preliminary e~periments with osteosynthetic connecting elements t~ere performed, although not specifically with reference to pediatric surgery, using screws made f`rom reabsorbable material. The results of these experiments were not encouraging, particularly as re~gards implantat1on o~f the osteosynthetic connecting elements. The range of application was limited, but the screws generally did not : : :: :: : :
withstand stresse~s produced during the process of implantation. The screw heads eenera1ly broke because the reabsorbable materlal had nsufficient strength. Also, the problem of ; f1~ation t~as not solved for those cases in which : :: :
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the irldividl1al bone fragmen-ts had to be supported b~ additional elements sueh as plates or cerclage Ull its.
Wor~ proceeded from eonsiderations and e~periences gained from osteosynthetic implantation in adults. In the use of metal i~lplants, a level of microstability must be attained, that is to sa.y, a level of stability which permits only the srnallest mo-enlents between the fra~Jments. Microstable connections permit stresses of appro~imately 60-80 Icp over the area of the fractllre, Wit}lOUt perceptible movements be;llg noted.
rhe consi.derable elasticity of bones of children al~d adolescents in -t.heir grc)~th years perlnits, however, a l.evel of macrostability.
~acrostable eonnections, subjected to a stress of 10-20 kp o~er the area of the fracture, still perlnit slight, pereeptible movements. The fracture is tbereby stable as to support and movement. A microstable osteos~nthetie implantation such as is achievable, for e.~ample, in adult surgery, is not interlded for c.hildren and adolescents.
This Icnowledge is conseiously utilized :~ by the inventor to provide a new osteosynthetie implant ~hich is suitable for use in pediatrie surgery.

' ~L~96~S6 SU~I~IAR~' OF THE INVENTION
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It is an object of the present in~ention to proYide a synthetic implant for pediatric surgery which provides osteosynthetic contacts causing no growth disturbances, or onl~-very slight levels of growth disturbances, The osteosynthetic implant described herein comprlses a band of reabsorbable material which i~s attachable to bone fragments b~ means of connecting elements of reabsorbable material penetrating the band and the bone fragments. The use of connecting ele~ents colllprising reabsorbable material with the bands, l~hich function lii~e tension belts, enables osteosynthetic implantation even in children during their growth ye,trs without cau~ing growth disturbances, and ach.ieves the necessary macrostability.
In fractures of hollow cylindrical bones, hollow screws having a head, a central bore with a regular cross-sectional configuration, such as a cYlindrical bore with e~tended portions directed radially -out~ardly in a cruoiform~fash1on, and an a~ial penetratlng aperture provided at the tip of the screw are preferred. S~ch screws require the use:of a special tool for~ implantation, by means of which the distribution of rorce during insertion of the scret~s is even over approximately the entire .

F-1~4 4 ~L2~ 5~i length of the screw, so that the screw does not break during insertion.
The e~tended portions of the cylindrical bore rna~- be constructed as channel groo~-es to avoid any outwardly directed force to prevent the screw from breaking.
The penetration of the screws and the reabsorption of the reabsorbable material of the screws and bands is i.mpro~ed when the hollow screws are provided with radially penetrating hol.es.
The tool which is disclosed for use during osteosynthetic implant,ation using the ho]low screws described above comprises a screwdriver havi.rl~ an ext.ernal contour corresponding ~o the cross-sectional configuration of the internal bore of the scre~i, and an a.~ial centering pin. The centering pin serves to guide the screw in an allgning ~lanner with respect to the bore hole in the bone.
In order, on the one hand, to penetrate the bands, and, on the other hand, to center the screw in the bore of the bone fragment, it is :
preferred that:the centering pin is supported in an axially displaceable manner against spring pressure in the screwdriver.

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In accordance with the invention, there is provided an osteosynthetic implan~ for the fixation and support of flat and tuhular bone fragments comprising: at least one connecting band attachable to join said bone fragments by means of at least two connecting elements penetrating said connecting band and said bone fragments, said connecting band and said connecting elements both comprising biocompatible material which is reabsorbable.
Embodiments of the invention will now be described with reference to the accompanying drawings in which;
Fig. 1 shows an example of craniofacial application of the osteosynthetic implant embodying the present invention;
Fig. 2 shows a top view of a band with a connecting element comprising reabsorbable material;
Figs. 3a and 3b show a perspective view of a tamping liner and a tamping counterpiece in cross section;
Fig. 4 shows a cross-sectional view illustrating the use of the osteosynthetic implant with hollow screws for a hollow cylindrical bone fracture;
Fig. Sa shows a side view of the hollow screw used in the osteosynthetic implant shown in Fig. 4;
Fig. 5b shows an end view of the head of the hollow screw shown in Fig. Sa;
Fig. 5c shows an end view of ~he tip of the hollow screw shown in Fig. 5a;
Fig. 6 shows a perspective view of a screwdriver for use in implanting the hollow screw shown in Fig. 5a;

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Eig. 7 shot;s an enlarged cross-sectional ~-iew of the terminal end of the screwdri~er in the shaft of a hollot~ screw; and Fig. 8 shows a graphical representation of the strength of the connection bett~-een the bone fragments in relation to the healing time.
DESCRIPTION OF PREFERRED EMBODIMENTS

The osteosynthetic-implant embodying the present i:nvention utilizes:
connecting elements and bands, the bands ser~-ing as tension belts which evenly transfer forces from one ?.~one fragment to the other to fi~ both fragnlents in place. The connecting elements ~enetrate the band or bands and the corresponding bone fraglnellts. The borle fragments are designated by reference letter (F) in the fig~lres. Connecting elements (1), which, in practice, are only a few millimeters in diameter, are shown in the diagram as points. The bands are designated by reference numeral (2). The distanee between the bone fragments is, for the sake of claritv, depicted on a larger scale than life-size.
An enlarged ~ieu of one embodiment of ~the osteosynthetic implant 1S shown in Fig. 2.
Band (2) is knit or wo~en from filaments of reabsorbable biocompatible materials. The mesh uidth, the f1lament distance, and the shape are selected so that the tissue or wea~e is easily :

~-154 7 i2~

penetrated by the connecting elements It i5 essential that the elastic defornlation of the band in the ~ongitudinal direction be relati~~ely slight. Longitudinal elastic deformation is influenced b~ the corresponding filament shape and ~.-eave. As Fig. 2 shows, filaments (21) are preferably only displaced in the area where connecting elements pene1rate the band (2).
Depending upon the type of bone fragn1ents to be cGnnected, different connecting elements may be used. Connecting elements may be fabricated fro1n l;nown materials, such as, for e~ample, polygluconate, polylactate, and the like, 1~hich are biodegradable and biocompatible.
In Figs. 3a and 3b, connectin~ elements suitable for connecting flat bone fragments are shown in a perspective, cross-sectional view. A
tamping liner is designated by reference numeral (10), comprising tubular part (ll) with an ann~ular collar unit (12) at one end. According to a preferred embodiment, the wall thichness of annular collar unit (12) may be, for e~;ample, about 0.5 mm~ with a total length of ~ppro~;mately 2 mm. The diameter of collar unit (12) may be appr~ximately 5 mm, while the internal diameter of the tubular part (ll) may be appro~imately 2 mm. Tamping counterpiece (13) is graduated in diameter and is formed like a peg or tamping unit. External serrations ~l4) ensure a .

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good press fit during imp1antation and pre~-ent tamping liner (10) or counterpiece (13) from brealcing during assembly. Central cylir)drical blind ho~e (1~) provides a mounting support for the counterpiece on a surgical instru~le-nt, for e~ample, a specialized pair of parallel tongs, which facilitates lmplantation. The length of the tamping counterpiece is preferably greater than the length of tamping liner (10), because the liner should generally be shorter than the thichness of the flat bone. It is, however, also possible to l~ork with screws and nuts, wherever t,his is advallta~eous due to considerations of accessibilit~.
I~'hile in khe case of flat bone connectiorls, the bands used for joining bone fragments often are only .applied on one side of the bone, it is both possible and desirable in the case of tubular bone fragments ~o apply bands (2) to two opposing sides of the bone.
Connecting elements penetrate both bands and have an effect cornparable to that of a tension belt.

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For a connection of tubular bone fra~ments, hollow soreus ~(3) sre preferably used as connecting elemsnts.~ A suitable hollow screw :

(3),is shown in Figs. 5a-c, Hollow screh~ l3) comprises shaft ~30) provided on its entire ` - length with external screw threading (31) h~ith :: : : :
~ relatively great thread course distances. Head ::

~: ' . ` 1299~2~;6 (32) of the screw is preferably flat, and fGrms a collar. The hollow screw is penetrated b~- a central bore (33) preferably over its entire length. This may be formed in various ~ays. It is important in a preferred embodiment that the central bore has e~tended portions which are directed radially outwardly. In the embodiment shown in Figs. ~b and 5c, the central bore is generally circular with four radial grooves spaced e~uidistantl~ from one another in a cruciform arrangement. The end of the screw is penetrated by an a~ial passa~e hole (34), the purpose of which will be further described below.
Several radial bores (35), which penetrate to centrAl internal bore (33) serve to promote tissue-lil;e interminglin~ and facilitate the biolo~ical decomposition of the screw.
To implant the hollow screw, a special screwdriver tool is necessary. This tool resembles an I~nbuss key wrench having a cross-sectional configuration corresponding to the :
configuration of central bore (33) of the screw.
Tool (4) is shown in its entirety in a perspective view and shown partially~and in an enlar~ed cross-sectional view in Figs. 6 and 7, respectively. Tool (4) comprises hollow shaft (41), which is cruciform in cross-sectional conflguration corresponding to central bore l33) of the scre~, and has an enlarged end which F-154 ~o 1~36ZS~i serves as handle (42). Handle (42) ma,~ be attached to the shaft b~- screhing. At the tip of the shaft, a bore (44), is pro~ided, through which a centering tip (46) projects, the centering ti.p being axially adjust~ble i~ the internal bore (4~) of shaft (41). Centering tip (46~ is enlarged at one end to form a guide piece (47)J which is retained in internal bore (4~).
He1.ic~l, cGmpression spring (48) with pressure plates (49) displaces the centering tip to its initial end position. Compression spring ~48) has its c.at.ching stud on handle (42), T~hich may be removed by scre~ lg.
Centerillg tip (46) serves, during the osteos~nthetic implantation, a.s a guide n~eans.
Screw (3) is mounted on screwdri~er tool (4)~
with centering tip (46) projecting through screw (3) and t.hrough axial passage hole (34) at the tip of screw (3).
It is possible, by means of centering tip (46), to penetrate band (2) and the already prepared bore in the bone fragment, and thus ~prepare the ;d~ for the screh~ implant. On the opposin~g side of the band, the filaments of the band (2) are penetrated and the bore provided in the bone fragment is also penetrated by the centering tip (46). Since the tip is axiall~
adjustable by means of the spring, the dan~er of .

F-1~4 11 12g62~6 centering tip ( Ll 6) causing injuries ~ay be avoided.
The cruciform e~ternal contour of scre~driver tool shaft (41), which precisel~-corresponds to the cross-sectional configur-ation of central internal bore (33) of screw (3), conveys, even with a relatively high level of torque, ver~ slight surface pressure to screw (3), and avoids radial forces, which may cause bursting and destruction of the screw. rhe force therefore need no longer be transferred to the shaft of the scre~ (30~ through the head of the scre~ (32). The danger of a disturbance and material failure is thereby considerably reduced.
If such a breal;age should nonetheless occur, then the oontact between the remaining parts and the screwdriver is still preserved, and the parts can be screwed out again later.
Finall~, the sequence of the healing process using the new osteosynthetic implant will be briefly described.
In th1s regard, reference is made to the graphic representation shown in Fig. 8. Time is marked on the abscissa of the coordinate system, while the ordinate represents the strength of the connection bet~een the bone fragments connected. The cur~es merely represent quaIitative and not quantitative relationships.
Initiation of the operative contact is considered :

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to be at time point "O". The strength of the connection initially corresponds to the strength of the implant used. This is represented as a li~htl~r dr~wrl unbro~en line. The biological deco~position of the reabsorbable material of the osteosynthetic implant, which causes a decrease in its strength, begins after about four weeks.
Ho~ever, the oonnective ticsue-like intergrowth and penetration of the implant begins after only two ~eeks. The strength during the intergrolith period is depicted by dotted lines. Ossification begins at about the fourth to the si~th ~eek, appro~imately, ~hen the strength of the intergro~th then increases over the stren~th of the implant connection. Tile overall strength of the conrlec-tion does not correspond to the sull)lrlation of both strength values, but is rather represented by the curve which is shown as a thick, unbro~en line.
During the relatively short time which elapses until biodegradation of the reabsorbable material occurs~ the osteosynthetic implant does not give rise to growth disturbances~
A second surgical procedure for re~oving the implant is eliminated by the practice of the present invention. Through this, particularly in the case of the infantile s~eletal structures, an additional detriment to '162S~i growt;h caused b~ the operation and the e~posure of the bolle is pre~ent,ed.
O~erall, the length of incapacitatiGn, as well as tlle~total costs of the clinical treatmellt are thus considerabl~ reduced.
In Fig. 2, band (2) is depicted in a woven form. The relativel~ loose weave facilitates penetration of the connecting elements through band (2). To prevent the bands from ripping during penetration, it is important that t,he warp threads be heat molded with the longitudinal filaments.

Claims (7)

1. An osteosynthetic implant for the fixation and support of flat and tubular bone fragments comprising: at least one connecting band attachable to join said bone fragments by means of at least two connecting elements penetrating said connecting band and said bone fragments, said connecting band and said connecting elements both comprising biocompatible material which is reabsorbable.

2. An osteosynthetic implant for tubular bones in accordance with claim 1, wherein said connecting elements comprise hollow screws having a flat head and a central bore having a cylindrical cross-sectional configuration with radially directed extensions and an axially penetrating aperture at the tip of said screw.

3. An osteosynthetic implant in accordance with claim 2, wherein said radially directed extensions of said central bore are equidistantly spaced hollow grooves.

4. An osteosynthetic implant in accordance with claim 2, wherein said hollow screws are provided with a plurality of radial bores which penetrate central bore.

5. An implant in accordance with claim 1, wherein said connecting element comprises a tamping liner having a central bore and a tamping counterpiece mountable in said central bore of said tamping liner and having an enlarged head limiting its insertion into said tamping liner.

6. An implant in accordance with claim 1, wherein said band comprises woven filaments, and the warp filaments are heat sealed with the longitudinal filaments at regular distances.

7. An implant in accordance with claim 1, wherein said band comprises woven filaments, and said filaments cross one another at an angle of approximately 60°.