MINIREVIEW SERIES FOR THE 50TH
VOLUME
Leeds-Keio arti®cial ligament: a new concept for the anterior
cruciate ligament reconstruction of the knee
Hideo Matsumoto and Kyosuke Fujikawa1
Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo and 1 Department of Orthopaedic
Surgery, National Defense Medical College, Saitama, Japan(Received for publication on June 21, 2001)

Abstract. The features of the Leeds-Keio arti®cial ligament, which was developed as a collaborative
project between the University of Leeds in the UK and Keio University, are introduced. The ligament
is made of polyester, and has a mesh structure. The diameter of the polyester ®bers is 22 mm. The ligament has a tensile strength suf®cient for anterior cruciate ligament (ACL) reconstruction, and fatigue
tests have shown satisfactory durability of the ligament. The stiffness of the Leeds-Keio arti®cial ligament is about 200 N/mm, which is similar to the natural ACL. A combination of a bone plug and stapling is used for the bone ®xation, taking into consideration the strength in both the initial mechanical®xation and the long term ®xation. From an animal study, it was shown that ®brous tissue was induced
around the arti®cial ligament, and the collagen ®bers became aligned in the longitudinal direction of
the ligament. For the clinical experience, one-hundred and thirty ®ve cases were reviewed. The
Lachaman sign disappeared in 87.4%, and the pivot shift sign disappeared in 88.1%. Side-to-side difference of anterior displacement of the knee, measured with a KT-2000 knee arthrometer at 30 degreesof ¯exion, was less than 3 mm in 85.9%. More than 90% of the patients experienced full range of
motion. Thus, from the clinical results, it can be concluded that reasonable stability was obtained withthe operation. If the Leeds-Keio arti®cial ligament may not be the perfect substitute for the ACL, bothexperimental and clinical studies indicate that it represents a major forward step in the history of knee
ligament surgery. (Keio J Med 50 (3): 161±166, September 2001)
Key words: knee, ligament, reconstruction, anterior cruciate ligament, arti®cial ligament

Introduction
Knee ligament injury often impedes the sports activities of athletes. Injury of the anterior cruciate ligament(ACL), in particular, may sometimes even terminate
their participation in sports. Therefore, an accurate diagnosis and prompt treatment are essential to allow
athletes to resume their sports activities. Primary sutureof the ligament in the acute phase used to be the standard treatment for ACL injury, but several reports
concluded that this method failed to obtain satisfactory
results. Primary reconstruction is now usually recommended for injuries to the ACL, even in the acutephase. Several materials have been developed for ACL
reconstruction, including autogenous tissues, allografts

and arti®cial materials, but each material has several
weak points and the perfect substitute has not yet beendeveloped.
The Leeds-Keio arti®cial ligament was developed in1982 as a collaborative project between the Rheumatism Research Unit, University of Leeds in the United
Kingdom and the Department of Orthopaedic Surgery,
Keio University in Japan (Fig. 1).1 It has been usedclinically for knee ligament reconstruction, particularly
for ACL reconstruction, and in the other types of reconstructive surgery for more than 19 years. In general,satisfactory results have been reported with this arti®cial ligament, although there are still some points ofcontroversy.2,3 In this paper, the features of the LeedsKeio arti®cial ligament are introduced and the ex-

Reprint requests to: Dr. Hideo Matsumoto, Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan, e-mail: mhideo@med.keio.ac.jp
161

162

Matsumoto H and Fujikawa K: Leeds-Keio Arti®cial LigamentFig. 1

The Leeds-Keio arti®cial ligament.

perimental and clinical studies on this ligament are
reviewed.
Historical Background and Concept of theLeeds-Keio Arti®cial Ligament
The development of arti®cial ligaments has a long
history, started in the ®eld of veterinary surgery in the
beginning of the 20th century and followed by the
medical ®eld. Silver wire, stainless wire, silk string,nylon string, polyethylene and other synthetic ®bers
were initially tried as the material for the arti®cial ligaments. However, most of these were abandoned at thestage of animal experiments and were not used clinically at all, since the implants tended to rupture at avery early stage after the operation. After these earlyexperiments, there has been a long pause in the development of arti®cial ligaments.
The second wave in the development of arti®cial
ligaments was started in the late 1970's. An arti®cial
ligament using carbon ®ber was developed by Jenkins
in 1978,4 and an arti®cial ligament made from GoreTex (polytetra¯uoroethylene) was also developed in
1985.5 Both were called arti®cial ligaments, but theydiffer in concept from each other. The Gore-Tex one isa so called prosthetic type, which means that the ligament is expected to work as a ligament by itself semipermanently. On the other hand, the carbon ®ber one
is a so called scaffold-type, and is expected to work as
a ligament until biological tissue is induced aroundthe implant, which subsequently becomes ligamentous
tissue and ®nally assumes the role of the original arti®cial ligament.
A knee ligament receives not only a tensile force but
also a substantial bending force at its bone attachment
when the knee is ¯exed or extended. In physiologicalknee ligaments, the tensile force is carried by the mid-dle ®brous portion aligned in its longitudinal direction,and the bending force is carried by the cartilage portion
at its bone attachments. Therefore, it is important for
an arti®cial ligament to have suf®cient strength against
both the tensile and the bending forces. Since most of
the arti®cial ligaments are made of synthetic ®bers, it
is relatively easy to provide the tensile strength, but it
may be dif®cult to cope with the bending force. Breakage at the bone attachment had thus been a weak pointof arti®cial ligaments. This weak point however can beovercome if the growth of a biological tissue (ideallycartiligenous tissue) is induced around the arti®cial ligament. Hence, the scaffold-type arti®cial ligament has agreat advantage in that it can cope with the bending
force exerted on it.
In fact, the Gore-Tex arti®cial ligament had an extremely high tensile strength, and, therefore, excellent
stability was achieved immediately after the operation.5
With these favorable short term results, this ligament
was at one time widely used clinically. However, it was
gradually recognized that this ligament was often ruptured within a certain period after the operation, possibly because the arti®cial ligament could not tolerate thebending force, in spite of its suf®cient strength against
the tensile force. Thus, the Gore-Tex arti®cial ligament
has been completely abandoned in the ®eld of knee
surgery.
On the other hand, it was proved both experimentally and clinically that good tissue induction was observed around the carbon ®ber arti®cial ligament.4 It
was widely used clinically all over the world, and it wasthought that an ideal arti®cial ligament had been developed. However, the weak point of the carbon ®ber,that is fragility, was gradually recognized after the ligament was ®rst used clinically. It was reported that the
carbon ®ber arti®cial ligament tended to break up into
many fragments which induced severe synovitis in theknee joint. The search for and development of an ideal
arti®cial ligament was therefore restarted.
Material and Structure of theLeeds-Keio Arti®cial Ligament
There are several conditions imposed on the material from which an arti®cial ligament is constructed: 1)
no toxicity; 2) biocompatibility; 3) mechanical strength;4) easy handling; 5) low cost/bene®t ratio, and 6) theability to induce tissue (in case of the scaffold type).
The Leeds-Keio arti®cial ligament is made of polyester,which has a long history in its use as material for arti®cial vessels in the human body, and has been proved
to be successfully biocompatible in a number of studies.
In addition, it has excellent mechanical properties(strength and stiffness) and the ability to induce tissue
growth around it.1

Keio J Med 2001; 50 (3): 161±166

As far as the structure of arti®cial ligaments is concerned, most of them are woven with bundles of synthetic ®bers, and the method of weaving is also one of
the important factors in a successful arti®cial ligament.
There are some arti®cial ligaments which are woven
like a shoe-lace, in which most of the ®bers run obliquely to the long axis of the ligament, and repeatedloading along the ligament may cause a longitudinal
realignment of the ®bers thus leading to a loosening of
the ligament structure. The Leeds-Keio arti®cial ligament has a mesh structure woven with longitudinal
bundles of polyester ®bers and transverse bundles atright angles arranged at intervals of 2.5 mm. The advantage of this arrangement is that the load along theligament can be transferred by only the longitudinal
bundles, and structural loosening does not occur withthis arrangement.
The diameter of the polyester ®bers in the LeedsKeio arti®cial ligament is 22 mm. The thickness of the®bers is also an important factor. Tissue induction is
expected to occur around the scaffold type of arti®cial
ligament which is initiated by the foreign body reaction
to the arti®cial ®bers. Therefore, the smaller the diameter of the arti®cial ®bers is, the more tissue induction
occurs. The surface area of the ®bers is in an inverse
proportion to the diameter, and, therefore, is one of themost important factors for the foreign body reaction. In
addition, the smaller diameter has the mechanical advantage of reducing the bending deformity at the bone
attachment when a bending torque is applied to each®ber.
There are different types of arti®cial ligaments fordifferent purposes; the tubular type with a diameter of
10 mm (LKDT) which is usually used for the ACL reconstruction, and several tape-type ligaments from 10
mm to 60 mm in width (LK10±LK60) for other ligament reconstructions.
Mechanical Properties of theLeeds-Keio Arti®cial Ligament
Suf®cient tensile strength is an important factor for
an arti®cial ligament, but the ability to maintain thestrength after implantation should be also considered.
The tensile strength of the normal ACL is about 630 N
in older persons, according to an experimental study by
Kennedy,6 and about 1730 N in the young according
to a study by Noyes.7 Therefore, arti®cial ligaments
for ACL reconstruction should have a tensile strength
equal to or greater than these ®gures. The mechanicalproperties (tensile strength and stiffness) of the LeedsKeio arti®cial ligament were tested under the following
conditions (n  170):1 LKDT (used for the ACL reconstruction) was used as ligament whose gauge length
was 40 mm. Strain rate was 1%, 50% or 100% per sec-

163

ond, and the media were room air at 20  C or physiological saline at 37  C.
The maximum tensile strength ranged from 2061 G
31 N (preconditioned for 3 hours at 25 cycles underload of 50±500 N) to 2350 G 28 N (non-preconditioned). The average stiffness ranged from 151 G 91 N/
mm (non-preconditioned) to 294 G 26 N/mm (preconditioned for 3 hours at 25 cycles under load of 50±500
N). A fatigue test was also carried out under the following conditions (n  18):1 sinusoidal 500 N was
loaded at a frequency of 25 cycles in room air at 20  C
or in saline at 37  C.
None of the ligaments tested in these series ruptured.
The average value of the residual strength was about
1700 N (77% of the original strength) after 10  10 6
cycles.
The Leeds-Keio arti®cial ligament was demonstrated
to have suf®cient tensile strength for ACL reconstruction, and the fatigue test showed satisfactory durabilityof the ligament.
The stiffness of the substitute material is also an important factor, particularly for the scaffold-type arti®cial ligament. If the stiffness is too low, the substitutecannot work as a constraint, and if it is too high, tissue
induction around the arti®cial ligament is hindered by
the stress shielding. Amis, et al. reconstructed sheep
Achilles tendons, having an average stiffness of 46 N/
mm, with polyester (40 N/mm in stiffness) or carbon®ber (600 N/mm in stiffness), and compared the pathological ®ndings at 15 to 18 months after the operation.8
The authors found that the biological reaction wasstronger with carbon ®ber but that the amount of collagen ®bers induced was much higher with polyester®ber. In other words, tissue induction occurred as a reaction to the material but tissue maturation occurred
when the induced tissue was under tension with less stiff
material. Therefore, an arti®cial ligament with a stiffness similar to the natural ligament may offer great
advantages for the tissue induction. The stiffness of theLeeds-Keio arti®cial ligament is about 200 N/mm,
which is similar to the natural ACL, but further experimental studies are required to determine the ideal stiffness of the substitute.
Bone Fixation System ofLeeds-Keio Arti®cial Ligament
There is no point in achieving the correct mechanicalstrength of an arti®cial ligament without also considering the strength of its ®xation to the bone. Therefore, the mechanical strength of the bone ®xation is anequally important factor for a good operative outcome.
In the Leeds-Keio arti®cial ligament, a combination ofa bone plug and stapling is used for the bone ®xation(Fig. 2). The initial mechanical strength of the ®xation is164Matsumoto H and Fujikawa K: Leeds-Keio Arti®cial Ligamentmechanically and biologically when bone union occurs
between the tunnel and the plug after the operation.
Tissue Induction of the Leeds-Keio Arti®cial LigamentFig. 2 Bone ®xation system. A combination of a bone plug and stapling is used for the bone ®xation.

expected to be carried out by the stapling and the longterm ®xation is expected to be performed by the biological osseointegration between the plug and the tunnel.
A double stapling method is used for the tibial ®xation,
and Fastlok stapling, which is a staple with buckle, forthe femoral ®xation. It was revealed from an experimental study that the double stapling method has morethan double the tensile strength (647 G 25 N) comparedwith that of the single stapling method (253 G 68 N).9
Fastlok stapling works by pinching the arti®cial ligament between the staple and the buckle when the tension is applied to the arti®cial ligament. The mechanicalstrength of the Fastlok stapling is twice compared tothat of the double stapling (1035±1223 N, 1113 N on
average). In addition, fatigue testing, in which the mechanical strength of the Fastlok stapling was examined
after 1.5 million cycles of loading (between 50 and 400
N), revealed that the residual strength of the stapling
was suf®cient (852 N on average).1
The bone plug ®xation is a method of ®xing the arti®cial ligament both mechanically and biologically and isachieved by making a double bone tunnel with different
diameters (11 mm and 6 mm). A bone plug with diameter of 11 mm is taken from the extra-articular exit of
the bone tunnel using a special reamer. The tunnel
is then continued on through to the intra-articularside (the original site of the ligament attachment) withanother reamer of 6 mm in diameter. After the arti®cial
ligament is passed through this double bone tunnel, thebone plug is replaced in the tunnel. With this method,
the arti®cial ligament is ®xed to the bone tunnel both

As previously described, it is important for thescaffold-type arti®cial ligament to induce biologicaltissue. Tissue induction and remodeling around theLeeds-Keio arti®cial ligament were examined experimentally using 16 dogs.10,11 The ACL was replacedwith the arti®cial ligament under tension in 13 of the 16
dogs and without tension in the remaining 3 dogs inorder to examine the effect of tension on tissue remodeling. Fixation of the arti®cial ligament was achieved by
the use of bone screws and washers, taking the size ofthe animal into consideration. The animals were sacri®ced at different postoperative intervals between 8 and
36 weeks. After macroscopic observation, microangiography was carried out using a blue acrylic dye and thevascularization of the induced tissue was observed
through a binocular microscope. Histological samples
were then prepared from the materials and were also
examined microscopically.
From the macroscopic observation, proliferation ofthe ®brous tissue with a rich blood supply was observed
around the arti®cial ligament at 8 weeks after the operation (Fig. 3). The ®brous tissue occupied the wholeintercondylar space in some cases. This proliferation ofthe ®brous tissue was similar to the foreign body reaction. The proliferated ®brous tissue was, however,found only in a limited area around the arti®cial ligament at 12 to 16 weeks after the operation, and thevascularity was also reduced. The induced ®brous tissue
resembled the natural ACL at 24 to 36 weeks after theoperation, and vessels were observed only at the femoral and tibial insertions of the induced ACL (Fig. 4).

Fig. 3 Macroscopic ®ndings at 8 weeks after the ACL reconstruction(from the canine experiment). Proliferation of ®brous tissue wasfound around the arti®cial ligament.

Keio J Med 2001; 50 (3): 161±166

Fig. 4 Macroscopic ®ndings at 24 weeks after the ACL reconstruction (from the canine experiment). The induced ®brous tissue resembled to the natural ACL and the vessels were observed only at the
femoral and tibial insertion of the ACL.

165

Fig. 6 Histological ®ndings at 36 weeks after the ACL reconstruction(from the canine experiment). The ®brocytes became spindle shaped
and their number was much reduced, with dense collagen ®bersaligned in the direction of the longitudinal ®bers of the arti®cial ligament.

stage. In addition, cells similar to chondrocytes wereobserved at the bone insertion of the ligament.
From these results, it was found that the tissue induction around the arti®cial ligament was initialized by
the foreign body reaction, which subsequently brought
about proli®c neocollagenesis. The proliferation subsided once the arti®cial ligament was covered with tissue, and then remodeling occurred, in which the collagen ®bers gradually became aligned in the longitudinal
direction of the arti®cial ligament, if the repeated tension was applied to the induced tissue by ®rst replacing
the ligament under tension.
Fig. 5 Histological ®ndings at 8 weeks after the ACL reconstruction(from the canine experiment). Proliferation of immature round ®brocytes is combined with the appearance of foreign body giant cells, withcoarse and randomly oriented collagen ®bers.

Histological examination showed proliferation of immature round ®brocytes combined with the appearanceof foreign body giant cells at 8 weeks after the operation, and the collagen ®bers were rough with a randomorientation (Fig. 5). The number of the ®brocytes was
reduced at 12 to 16 weeks after the operation, although
the foreign body giant cells were still observed. The
collagen ®bers became denser than those observed at 8
weeks post-operatively. The ®brocytes became spindleshaped and the number of the cells was much reduced
at 24 to 36 weeks after the operation. The dense collagen ®bers were aligned in the direction of the longitudinal ®bers of the arti®cial ligament (Fig. 6), although
the foreign body giant cells were still observed at thisOperative Procedures
The operation is usually carried out arthroscopically.
Intra-articular conditions are examined carefully, andcombined meniscal or cartilaginous injuries, if any, aretreated before starting the ACL reconstruction. A skinincision (about 30 mm in length) is made at the anterior
surface of the tibia and the tibial bone surface is exposed. The reamer guide is ®xed from the center of thephysiological ACL insertion of the tibia intra-articularly to the exposed tibial anterior surface. The distal
half of the bone tunnel is made by taking a bone plugwith a diameter of 11 mm from the tibial surface using areamer. The tunnel is then continued on through into
the intra-articular side with another reamer of 6 mm indiameter. Another skin incision is made at the lateralside of the femur, the iliotibial tract is split, and the
distal part of the femoral shaft is exposed. The reamer
guide is ®xed from the postero-lateral corner of thephysiological ACL insertion of the femur to the
exposed femoral shaft, and the same procedure as for166

Matsumoto H and Fujikawa K: Leeds-Keio Arti®cial Ligament

the tibial bone tunnel is repeated on the femur. The
Leeds-Keio arti®cial ligament (LKDT-LK30) is passed
through the tunnels as far as possible under the remnant of the ACL. The arti®cial ligament at the tibial
side is ®xed to the tibia with the double stapling
method, and at the femoral side it is ®xed with Fastlok
stapling after the ligament has been manually tightened. A notchplasty is carried out if narrowing of thenotch exists. After con®rming full range of motion, suf®cient stability and no notch impingement, the joint iswashed with saline, a suction drainage is left in the joint
and the wound is closed.2,3Clinical Experiences
More than 1000 cases have been operated on since1982. However, since the operative procedure waschanged several times, this paper reviews 135 cases inwhich the above-described procedure of the ACL reconstruction was carried out, and those have been followed up for ®ve years or more.12 Preoperatively, allcases showed remarkable giving way subjectively and at
least 1 Lachman sign and pivot shift sign. The Lachman sign disappeared in 87.4%, scored a trace in 4.4%,
was mildly positive in 5.2% and was gross positive in
3.0%. Pivot shift sign disappeared in 88.1%, scored a
trace in 5.2%, was mildly positive in 3.0% and wasgross positive in 3.7%. Side-to-side difference of anterior displacement of the knee, measured with a KT2000 knee arthrometer at 30 degrees of ¯exion, was lessthan 3 mm in 85.9%. No signi®cant difference in anterior terminal stiffness between the operated side andthe contralateral side was found in 77.0%. More than
90% of the patients experienced a full range of motion.
Thus, from these clinical results, it can be concluded
that reasonable stability was obtained by the operation
with the Leeds-Keio arti®cial ligament.

Although it may not be the perfect substitute for the
ACL, this ligament represents a forward step in thehistory of knee ligament surgery.
References
1.

2.

3.
4.

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Conclusion
The Leeds-Keio arti®cial ligament was developed asa new device for the ACL reconstruction, and reasonable clinical results have been obtained with it.

12.

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