Ligament and tendon prostheses of polyethylene terephthalate and method of preparing same

()2 ¦ BACKGROUND OF THE INVENTION ¦ The need for splints or artificial ligaments to replace . ~ or supplement natural ligaments and tendons where such ligaments and tendons have suffered damage, usually accidentaL, is sufficiently widespread so that conferences have been held on the subject and the problem has been discussed in reports by orthopedic surgeons. An example of a frequently-occurring injury ¦ requiring a device of this ki~d for satisfactory surgical repair ¦l is an acromioclavicular dislocation, in which the injury is 19 li produced by falling on the point of the shou der with the arm .. '1 ~,.

oz in the adducted position. By this actioQ one or more of the ligaments confining the acromioclavicular joint may become ` ruptured, and surfical repair utilizing an appropriate splinting device, to provide internal support for the damaged ligaments, ~1 is frequently indicated. Other ligaments such as ~he medial ¦¦ collateral and anterior cruciate may be slmilarly repaired.

! These constructions may also be useful in surgical reconstruction of damaged tendons including achilles and ¦! patellar tendons, and possibly flexor digital tendons. Tendons o ¦ possess a very poor capacity for self-regeneration, and thus ¦¦ require very long periods of time to effect their own repair ~! without the assistance of a prosthetic implant.

j ~ Surgeons who are experienced in the repair of ligament j¦ and tendon damage have recommended several desirable character- I !l istics for materials (or constructions) to be applied as internal ¦ splints:

I 1 1) The material must be capable of exerting ¦ mechanical strength equal to that of the damaged ligamen~, at ,I least under moderate stress activity.

20 1'1 2) It ~ust have suf~icient resistance to elongation under stress that it will retain its mechanical effectiveness.

3. The material should be acceptable for permanent ' implant in the human body, preferably without the necessity for ., ' i.

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~ - 2 - , ~ oZ removal by a second operation ~n important condi~ion for good acceptability is that the material be sufficiently porous so ', as to permit invasion by the host tissues.

Ii 4) The splint should permit early activity.

¦ Primarily on account of their desirable characteristics of strength, porosity, and flexibility, the attention of surgeons was directed to woven and knitted Dacron (polyethylene ~¦ terephthalate, Du Pont) tubular constructions used in vascular ,j surgery as potential materials of construction for ligament lo ~. I splints. However, it has been found that Dacron prostheses in the constructions conventionally used have inadequate I resistance to elongation under stress, the elongation reaching values as high as 150%. Further, it is highly desirable that the cross-section of the prostheses be such that it will be invaded by the host tissue and that an encasement be provided ¦ for formation of a living structure which will supplement the prosthesis.

! As is evident, then, a structure which provides ! for greater resistance to elongation and which is suf~iciently 1 rigid so that a tubular structure with an open lumen can be provided is highly to be desired.

! ! SUM~R~ OF THE INVE~TION j, , To prepare a prosthesis in accordance with the present invention, a fabric strip is restrained from shrinking ! * Trade Mark ; i I - 3 ~13~0~ in the lengthwise direction and is then treated with a shrinking agent under conditions su-h that the extensibility of the fabric strip is reducecl by at least about 50%. The strip may be flat or in tubular form, generally, in flattened tubular form.

To provide rigidity, the strip may be formed into a tubular form, slipped onto a mandrel and then heat-set, as ~y treatment at about 250F for about 3 minutes. In addition to providing rigidity, the heat-setting operation provides an open lumen for invasion by host tissue.

In a preferred form, at least one surface o~ the strip is of velour construction, the velour surface facilitating adhesion of host tissue thereto.

Also, the fabric may be of woven, circularly-knit or warp-knit construction.

Accordingly, the present invention provides a method of preparing a Dacron* prosthesis of reduced extensibility suitable for implantation in a patient for replacement or supplementation or repair of a damaged ligament or tendon.

The present invention can provide a method of preparing a prosthesis of increased rigidity and having an open lumen for repair, supplementation or replacement of a damaged ligament or tendon in a patient.

Thus the present invention provides a method o preparing a prosthesis for repair, supplement or replacement of a damaged ligament or tendon, comprising the step of treating an elongated strip of polyethylene terephthalate having two * Trade Mark 5~s~ ~ 02 surfaces, wi.th a shrinking agent under conditions such that only lengthwise shrinkage is prevented, said treatment being continued for a period long enough to effect a substantial reduction in the lengthwise extensibi'ity of said strip.

Also provided is a prosthesis suitable for repair of a damaged ligament or tendon, comprising a polyethylene terephthalate fabric strip of reduced extensibility in the longitudinal direction, the term "fabric" being taken to include woven, circularly-knit and warp-knit goods.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others in the methods taught, and the article possessing the features, properties, and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

BRIEF DE~SCRIPTION OF THE DR~WINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

~ c~ l ,. I Fig. 1 shows a Dacron strip under restraint in preparation for treatment with a shrinking agent;

~I Fig. 2 is a sectional view of a Dacron strip formed ¦l into a tube;

¦ Fig. 3 is a sectional view o~ an initiallyflattened tubular strip formed into a double-walled tube;

l Fig. 4 is a sectional view of a Dacron tube ~n il accordance with the present invention~ said tube having I, longitudinally-extending ridges on the surface thereo~; and lO ¦j Fig. 5 is a graph showing the elongation under stress of an artificial ligame~t prepared in accordance with the present invention and a vascular graft prepared by conv-entional methods. - DESCRIPTION OF THE PREDERRED EMBODIMENTS The Dacron abric to be used in the process o~ ¦ the present invention may be initially in the form of a 1at ! strip or may be a flattened tube prepared by weaving, circular! knitting or warp-knitting. Where the material is a flat strip, it may be woven or warp-knit. Where the material is clean, !, ;

~O l' as received~ it may be subJected to a shrinking or compacting treatment as received. Otherwise, the material is cleaned by conventional washing or scouring to remove sizing, oils, or . i any other foreign ma~ter. I * Trade Mark - 6 .

OZ i It is conventional to compac~ knl~ed Dacron products 'l by a process currently in use, preferred shrinking agents being , CH2C12 and CH2C12 in combination with N02. Conventionally~ ¦i the material is simply exposed to the shrinking agent to effect I the desired degree of compaction, the principal objective being " to reduce the siæe of the openings between the threads constituting the fabric. However, such fabrics, subsequent to !~ the shrinking operation, have a degree of ex~ensibility as shown Il in the lower curve of Fig. 5 which is so great that a splint l'i made from such a fabric fails to provide the required support.

j I have found that subjecting the fabric to compaction with the ¦I shrinking agent under restraint in the longitudinal direction Ij greatly reduces the extensibility of the compacted fabric. In ¦I general, the elongation at a given stress should be reduced by I¦ at least 50%~ Preferably, the elongation should be reduced ¦I by about 60%. Thus7 under a stress which in a conventionallyshrunk fabric which would produce an elongation o~ 150~/O~the elongation of a fabric treated in accordance with the present invention is ll~only about 60% as can be seen from the upper curve in Fig. 5.

,'' Fig. 1 shows schematically a fabric strip ll held 'i in a rigid framework 12 between clamps 13. The entire framework with the strip 11 held under restraint can be placed in a vessel, not shown, for treatment with the shrinking agent under the desired conditions of temperature and humidity. I * Trade Mark 1.

~ 7 The fabric strip can be either ~lat or tubular , in construction during the compaction process s~ep. Howe~er, I have found that it is desirable that the prosthesis to be implanted in a patient should be tubular, that is, should have an open lumen. The fabric strip, assuming that it is initially tubular in construction as when circularly-kni~ woven or ¦I warp-knit in tubular form, and whether or not held in open tub~lar form during the compaction process, will collapse when Il removed from restraint. Accordingly, the strip is placed on lo Ij a mandrel and is heat-set to provide the strip with some rigidity, the amount of rigidity provided being sufficient so ¦ that an open lumen will be maintained. Fig. 2 shows how a ' f-lat strip can be formed into a cylinder 16 by sewing the two edges 17 and 18 thereof together with ~acron thread 19. This l! tubular section can now be placed over a mandrel and heat-set in conventional fashion, as by heating for three minutes at Ii 250F. ll Another suitable construction is shown in Fig. 3, ¦I the strip in this case being a woven or knit tube in flattened 2~ 1I form which is then formed into a double-walled cylinder 21 , by sewing edges 22 and 23 together with Dacron thread 24. In Il this case, edges 22 and 23 are actually folds rather than i, true edges.

The range of tendons to be supplemented or repaired or replaced is from about 2 mm in diameter to about 10 mm in * Trade Mark ; ~ 8 1~3'14~Z diameter. For the smallest tendons, ~he construction of Fig. Z is generally adequate so far as rigidity îs concerned For somewhat larger ~endons say from about 3 mm to about 6 mm, the doublewalled construction of FigD 3 may give adequate rigidity For the largest tendons, the construction shown in the prosthesis of Fig 4 is preferred.

This construction starts with a flattened tube having a circumference, or rather, periphery7 in cross-section o between about 30 and about 70 mm.

Starting with the flattened tube , the material being indicated by the reference numeral 26, the two i layers comprising the flattened tube are se~n together longitudinally along lines about 2 mm in from each edge~ using Dacron thread 27. The tube ;s then refolded so that each of the original ridges 28 lies between new folds 29.

The new folds are similarly sewn together longitudinally using Dacron threads 30. The tubing, now having four ridges, is compacted by chemical treatment and is then heat-set on a mandrel as described above. Obviously the above procedure can be modiied to provide any number of ridges from 1 upward to the point where the entire circumference of the tubing consists of ridges with virtually no tubing therebetween. However, from 3 to about 6 ridges are generally p-referred, the la~ger number of ridges being used with larger tubing. Also, as can readily be seen, it is possible to start with the double-walled construction of Fig. 3 and then incorporate ridges thereon. Further, the hei~ht of the ridges is not limited ', .

, I ~ g I * Trade Mark ~;

,. I 3~0;~ , i to 2 mm, but this value has been found to be convenient or l~ the sewing s~ep and there is li~tle increase in rigidity provided~ by corresponding increase in the height of the ridges.

jj The purpose of the open lumen in the constructions ¦l of Figs. 2 - 4j as has already been noted, is to provide for ! ingrowth of body tissue. Such tissue must anchor to the Il Dacron strip as part of the process. The anchoring is !i facilitated if at least one surface is of ~he well-known velou structure. This structure is indicated in Fig. 4 by exterior o ~ loop 32 and interior loop 33. Tests have shown that the velour ~¦ construction accelerates ingrowth of body tissue and provides ¦i firm anchorage for same. Clinical results have been obtained ¦~ on twenty-five patients who sustained a Type III separation of ¦I the acromioclavicular joint. All of these patients were treated !

¦! by the method of internal fixation. The patients ranged in age from 17 to 67 years, with an average of 33 years. The patients were followed for periods ranging from 12 months to six years, the average period o follow-up being 35 months. The ,, mechanism of injury was similar in all patients in this series, I l~ namely, a fall on the point of the shoulder.

Twenty-three of the twenty-five patients were examined t and evaluated, whereas two of the patients were evaluated by telephone.

Of the patients evaluated~ more than one-half were * Trade Mark . i, - 10 - ( I! i 'noted to have no pain of any type The remainder, with one exception, have had occasional discomfort without compromise in activity. One patient w~.o had mild discomfort was a weight ' lifter who had pain only when actually lifting weights, but ~i otherwise suffered no limitations of activity. Function liwas normal in all patients and no deformity was noted. There !i was a reduction in internal rotation in three o~ the patients~ ~the internal rotation being reduced to seventy degrees as ' opposed to the normal internal rotation of nine~y degrees. As o ¦! can be seen from the above sample of results obtained withprostheses in accordance with the present invention, the li prostheses last for at least six years, cause only minimal ¦' discomfort, yield the subjects a good range of motion, and produce no deformity following surgery Many patients return , to relatively normal activities within two weeks. This return to early activity has decreased the morbidity associated with this type of injury.

¦ It will thus be seen that the advantages set ~orth above, among those made apparent from the preceding description, are 20 li efficiently attained and, since certain changes may be made Il, in carrying out the above method and in the article set forth without departing from the spirit and scope o~ the invention, , it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpre~ed , as illustrative and not in a limiting sense.

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- 11. - i ~ i 3~0Z 1'' i It îs also to be unders~ood that the following claims are intended to cover all of the generic and specific ~i , features of the invention herein desc,ribed, and all statements of the scope o the invention which, as a matter of language, might be said to fall therebetween, .. . .

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