GB2081585A - Surgical sutures - Google Patents

Abstract

A surgical suture of improved knottability is obtained without adversely affecting the knot breaking strength by providing a polymeric monofilament 5 with a hole 2 extending therethrough from one end to the other. The volume percent of the hole is preferably between ten and thirty five percent.

Description

SPECIFICATION Surgical sutures This invention relates to polymeric surgical sutures. Such sutures are classified either as absorbable or non-absorbable and may be monofilamentous or poly-filamentous in construction.

Poly-filamentous sutures are preferred by surgeons because they have superior knotting characteristics relative to monofilament materials. On the other hand, monofilament sutures are preferable for the patient as they are less likely to potentiate infection.

It is generally accepted that monofilaments, such as monofilament stainless steel, monofilament nylon, monofilament polyethylene and monofilament polypropylene are the most inert of the nonabsorbable sutures. When implanted in areas where infection occurs, as a rule, they are not "spit" spontaneously by the wound, nor do they require surgical removal. In cross section, all of these monofilaments have one thing in common. They are solid with no "dead spaces" or interstices.

On the other hand, all braided and all twisted sutures when implanted where infection occurs, will, as a rule, be "spit" spontaneously by the wound or require surgical removal in order for healing to occur. All of these braided and twisted materials have one thing in common. In cross section they consist of many filaments and dead spaces. For example, in cross section, braided silk has forty to fifty percent dead space.

On the basis of the above facts, it seems possible that there is a direct relationship between dead spaces in a suture and the incidence of spontaneous spitting or the necessity for surgical removal of the suture when infection occurs. If this hypothesis is correct, monofilaments should be the sutrues of choice for the patient undergoing surgery. However, surgeons have a great deal of difficulty in their use of monofilament sutures. All of them are stiff, difficult to knot, and have a tendency to open spontaneously.

Some in addition have sharp ends, kink or are too elastic. All monofilament sutures apparently pose difficulties in surgical techniques. Many surgeons continue to use monofilament sutures despite the problems they create because of the excellent patient response. However, monofilaments obviously cannot be used if a surgical knotting technique is deemed inadequate by the surgeon. For this reason, many attempts have been made in the prior art to improve the knottability of monofilament sutures.

A surgical suture according to the present invention consists essentially of at least one sterile, polymeric monofilament having at least one hole extending between the ends thereof, the total volume percent of the hole or holes in the monofilament being sufficient to improve the knottability of the monofilament without substantially adversely affecting the knot-breaking strength of the suture. In this way it is possible to provide a monofilament surgical suture which has the knottability attributes of a braided poly-filamentous suture.

By the term "improved knottability" as used herein is meant not only increasing the security of a knot against slippage but also increasing the flexibility of pliability of the monofilament which enhances the ease with which the monofilament can be knotted.

The reason by which the hole-containing surgical suture of the invention provides improved knot security is not known for certain. It is theorised, however, that upon knotting the suture collapses slightly at the points of contact or knotting so as to create a "hill and dale" effect. As a result, the force necessary to have the thread at the knotting point climb out of the distorted or collapsed area, i.e. out of the "dale" and over the "hill", is substantially increased. In other words, while the co-efficient of friction of the monofilament suture of the invention remains the same, the distortion of the surface at the knotting point increases the contact area which in turn increases the total friction.

It has also been found that the hole-containing surgical sutures of the invention are characterised by an increased flexibility or pliability, a property important to the surgeon who must tie off the sutures. The stiffness or relatively high restoration force that characterises conventional monofilament sutures, as aforementioned, makes monofilament sutures difficult to knot, a universal complaint.

Lastly, a serendipitous advantage gained from the improved knot security exhibited by the novel sutures of the invention is that it is not necessary for the surgeon to leave long ears in the knot as is normally done with conventional monofilament sutures so as to allow for possible slippage of the knot. Since knots made with the monofilament sutures of the present invention are secure, the surgeon can leave significantly shorter ears in the knot thereby reducing the amount of suture material left in the wound.

It has now been conclusively established that sutures are potentiators of infection and the less suture material that need be present in the wound the better.

The invention will now be described in more detail with reference to the accompanying drawings, in which :- Figure 1 is a perspective view of a monofilament suture formed with a single hole therethrough; Figure 2 is a perspective view of a monofilament suture containing three holes therethrough.

Figure 3 is a cross section of a spinnerette modified for hollow fibre production; and Figure 4 is a top view along lines A-A' of Figure 3.

Monofilament sutures according to the invention can be of any fibre-forming polymeric material which when drawn into a fibre and heat treated for stabilisation of physical properties results in fibre which is physiologically acceptable and which as the tensile strength and knot breaking strength required for acceptable use as a suture. Among such suitable polymeric materials can be listed fibre-forming polyolefins such as polyethylene and polypropylene, preferably isotactic polypropylene, co-polymers of ethylene and propylene and the like, polytetrafluoroethylene, nylon, polyesters, etc. The polymeric materials may also be constructed from the synthetic polymeric materials hydrolyzable by the body and from which synthetic absorbable sutures can be formed.Examples of such materials are disclosed in U.S. patents nos: 3,736,646,3,636,956, 3,463,159, 3,225,776,3,792,766 and re-issute patent no: 30,170.

The hole or holes passing through the monofilaments of the invention can take any desried shape or form. Thus, the hole or holes can be circular, rectan gular,triangular, oval and so forth. Nor need the hole or holes be centrally located. As shown in Figure 1, the hold 2 is centrally located in suture 5 and extends axially therethrough. However, orientation of the hole within the suture can be other than axial, if desired. As shown in Figure 2, more than one hole 2' can be provided in the monofilament suture 5.

Advantageously, the cross sectional area of the hole is substantially uniform throughout its length.

The total volume percent of the hole 2 or holes 2' in the sutures must be sufficient to provide the desired improvement in knottability but should not be so high as to substantially adversely affect the knot breaking strength of the suture and in most instances the tensile strength of the suture. (By knot breaking strength is meant the force required to effect a break at the knot.) The hole size selected will vary depending primarily upon the particular polymeric material from which the monofilament is constructed and the suture size but in general a total volume percent of up to thirty five volume percent is satisfactory. Hole sizes of about five to twelve volume percent are ordinarily preferred.

Monofilament sutures according to the invention can be constructed by any suitable means. One convenient method comprises spinning the polymer from a melt using a fibre-forming spinnerette whose orifice is modified to include a centrally located solid element or insert containing a tubular extension which forces extrusion about the tube to enable formation of the hollow filament.

Referring to Figure 3 and Figure 4 a spinnerette 7 having orifice 9 whose size generally ranges from about 0.005 inch or largerto say about 0.150 inch is suitable for spinning monofilaments. To adapt the spinnerette for hollow filament production a tight fitting insert 11 having a tubular extension 13 is provided in the orifice opening 9 of the spinnerette 7. Tubularextension l3communi- cates with a passageway 15 which extends perpendicularly through spinnerette 7 into the insert 11. Thus, passageway 15 is composed of a passageway 17 in spinnerette7 and passageway 19 in insert 11. A second passageway 21 communicates with passageway 15, extends perpendicularly from passageway 17 and opens at the face side of the spin nerette. The entrance to passageway 15 is sealed when the insert is positioned within the orifice 9.The orifice 9 is comprised of an elongate section 22 and a funnel section 24 containing an exit stem portion 23 of substantially narrower diameter into which pro jects tubular extension 13. The external diameter of the tubular extension 13 is less than that of the stem portion 23 and the extension is positioned axially within orifice 9 so as to form an annular space 25 between the outside wall oftubularextension 13 and the wall of stem portion 23. Thus, the external diameter of tubular extension 13 determines the size of the hole to be formed in the filament before hot drawing and hot stretching, if any. Polymer is extruded as by a straight bore piston extruder through orifice 9 and the annular space 25.

The passages 15 and 21 are provided in the insert and spinnerette because the hole 2 formed during fibre formation will tend to close very soon after the polymer stream leaves the spinnerette 7 unless gas is supplied through tubular extension 13. Gas such as air may be forced through the insert under slight applied pressure or air may be aspirated through the tubular extension simply by the motion of the polymer stream. It has been found that the aspiration system is quite satisfactory, provided that the polymer stream is started out at a very high velocity and then cut back to the desired velocity for fibre extrusion. Typically once a hole is opened up in the polymer stream by this procedure it tends to open during the entire extrusion operation.In spinning from solution, the solution may be extruded either into an atmosphere heated up to or above the boiling point of the solvent or into a non-solvent for the polymer.

After spinning, the polymer monofilament is drawn to effect orientation and to improve tensile strength. This is accomplished by drawing the monofilament at elevated temperatures which will vary depending upon the polymer being spun. The draw temperatures are conventional ranging from 130'Cto 160C as are the draw ratios which ordinar ily range from 3:1 to 11:1.The drawing step may be conducted in one or more steps, in air or in a bath containing a liquid non-solvent for the polymer. This drawing brings about a significant increase in tensile strength and molecular orientation as measured by the x-ray orientation angle.

After drawing of the holecontaining monofilaments, the monofilaments may be subjected to a hot stretching treatment. This may be carried out by running the drawn monofilament from a feed roll to a take-up roll and heating the monofilament between the rolls at a temperature above its glass transition temperature with the take-up roll rotating at a speed faster than the feed roll. Any means which applies tension to the heated monofilament such that the monofilarnent is stretched, for example, up to its breaking point, can be employed. Elongations over ten percentand particularly from twenty percent up to, but not including the breaking point, are s normally suitable.

The following examples are included to further illustrate the present invention.

EXAMPLE I A hollow 40 monofilament suture of isotactic polypropylene was prepared in the following manner.

The spinnerette of a conventional fibre forming straight bore extruder (not shown) was modified as shown in Figure 3 and Figure 4 using the insert 11 with its tubular extension seated within the orifice 9 of the spinnerette as shown in the figures. The inter nal diameter of the orifice portion 23 in spinnerette 7 was approximately 1.6 mm. The tubular extension had an outer diameter of approximately 0.6 mm and an internal diameter of 0.35 mm. 25 grams of polyp ropylene (wt. average mol. wt = 375,000 to 450,000) in the form of polymer pellets were loaded into the straight bore extruder at a temperature of 260 C.

Extrusion began one hour later, at 260 C. The throughput was started out at approximately 19.6 g/mm and then cut back to approximately 1.4 g/mm.

This created an aspiration system which draws air through respectively passageways 21 and 17 tubular extension 13 and hole 2 formed by the extrusion.

The monofilamentwas wound by a wind-up (not shown) at 10 m/min.

The extruded fibre had an outside diameter of about 0.54 mm and an eleven percent hole. After the extrusion the extruded fibre was hot drawn to eight times its length through a one foot long tube at 1400 to 1450C. The final drawn fibre had: Denier 196 Tenacity 6.1 widen Elongation (rupture) 43% O.D. .19 mm % hole * 10% * Definition of "% hole" for hollow fibre Area l.D. of the hole x 100=%hole Area O.D. of the monofilament The drawn fibre was compared for knot security with a commercial polypropylene solid monofilament suture of the 4-0 size (U.S.P. size designation), using the knot security test of Thacker et al in The America I Journal of Surgery, (1975).

With a two-throw square knot, with .75 ears and a knot tying force of 283 g, the commercial suture knot held securely in only one out of ten tries, while the hollow fibre knot held securely in nine out of ten tries.

EXAMPLE 11 Knotting monofilaments Polypropylene hollow monofilaments with about ten percent hole prepared according to the general procedure described in Example I, had a knot security about equal to other polypropylene monofilaments with twenty to thirty five percent hole (see Table I). Thus by decreasing the amount of hole in the cross section there is no apparent sacrifice in knot security, while knot break strength approaches that of solid fibre.

An indication of the knot security advantage conferred by ten percent hole can be seen by comparison with "Prolene" when both were tied with just two throws. The Hollow polypropylene monofilament broke nine out of ten times while Prolene broke only once in ten tries (see Table II) Table I-Small Hole vs. Large Hole Knot Security Tying Break Breaks Tying Fiber Throws Ears Force Force Tries Method M1-140-5 (denier 196, 10% hole) 2 .75 cm 10 oz. 801 g 9/10 Instron 3 .25 10 oz. 936 g 10/10 Instron M1-93-3 (denier 117, 25% hole) 2 .75 10 or. 408, 5111, Instron 392 7/10 3 .25 10 oz. 605 10/10 Instron Table 11~Small Hole Fiber vs. Prolene 40 Sutures Tying Break Breaks Tying Fiber Throws Ears Force Force Tries Method "Prolene" 4-0 2 .75 cm 10 oz. 805 g. 1/10 Instron M1-140-5 (4-0 range, 10% 1/hole) 2 .75 cm 10 oz. 801 g. 9/10 Instron 2 .75 cm cm' 818 g. 5/5 Hand While the above description has focussed on the production of monofilament sutures it should be understood that the invention contemplates polyfilamentous sutures made up of a plurality of the hollow monofilaments braided or twisted together or with one or more non-hollow filaments. Furthermore, other modifications and changes will readily occur to those skilled in the art and thus it is not desired to limit the invention to the exact construction shown and described.

Claims (11)

1. A surgical suture consisting essentially of at least one sterile polymeric monofilament having at least one hole extending between the ends thereof, the total volume percent of the hole or holes in the monofilament being sufficient to improve the knottability of the monofilament without substantially adversely affecting the knot breaking strength of the suture.

2. A surgical suture according to claim 1 wherein the inert polymeric monofilament is a polyolefin.

3. A surgical suture according to claim 2 wherein the polyolefin is polyethylene.

4. A surgical suture according to claim 2 wherein the polyolefin is polypropylene.

5. A surgical suture according to claim 2 wherein the polyolefin is a co-polymer of ethylene and propylene.

6. A surgical suture according to claim 1 wherein the inert polymeric monofilament is a polyester.

7. A surgical suture according to claim 1 wherein the polymeric monofilament is a nylon monofilament.

8. A surgical suture according to any one of the preceding claims wherein the total volume percent of the hole or holes in the monofilament is up to thirty five volume percent.

9. A surgical suture according to any one of claims 1 to 7 wherein the total volume percent of the hole or holes in the monofilament is about ten volume percent

10. A surgical suture according to any one of the preceding claims wherein the hole or holes is or are cylindrical in shape.

11. A surgical suture according to claim 10 wherein the polymeric monofilament has a single, cylindrical hole axially positioned therein.