0363-5465/102/3030-0498$02.00/0
THE AMERICAN JOURNAL OF SPORTS MEDICINE, Vol. 30, No. 4
© 2002 American Orthopaedic Society for Sports Medicine
The Effect of Graft-Tunnel Diameter
Disparity on Intraosseous Healing of the
Flexor Tendon Graft in Anterior Cruciate
Ligament Reconstruction*
Shuji Yamazaki,† MD, Kazunori Yasuda,‡§ MD, PhD, Fumihisa Tomita,† MD,
Akio Minami,† MD, PhD, and Harukazu Tohyama,‡ MD, PhD
From the †Department of Orthopaedic Surgery and the ‡Department of Medical
Bioengineering and Sports Medicine, Hokkaido University School of Medicine,
Sapporo, Japan
Background: Graft-to-tunnel healing is a significant factor in anterior cruciate ligament reconstruction, but there have been few
studies on the effect of graft-tunnel diameter disparity on intraosseous healing of the flexor tendon graft.
Hypothesis: Graft-tunnel diameter disparity of 2 mm has no effect on the pull-out strength of the graft from the bone tunnel.
Study Design: Controlled laboratory study.
Methods: Forty-two beagle dogs were divided into three groups. In each animal, reconstruction was performed in the left knee
by using a 4-mm diameter autogenous flexor tendon for groups 1 and 2 and by using a 4-mm wide bone-patellar tendon-bone
graft in group 3. A 4-mm diameter tunnel was drilled in the tibia of groups 1 and 3 and a 6-mm diameter tunnel, in group 2. In
each group, seven animals were sacrificed at 3 and 6 weeks.
Results: The perpendicular fibers connecting the graft to the bone were generated in groups 1 and 2, and the number appeared
to be higher in group 2, where the space was greater. There was no significant difference in the ultimate failure load between
groups 1 and 2 at each period.
Conclusion: Graft-tunnel diameter disparity of up to 2 mm may not adversely affect intraosseous healing of the flexor tendon
graft.
Clinical Relevance: Surgeons need not be overly concerned about minor graft-tunnel diameter disparities.
© 2002 American Orthopaedic Society for Sports Medicine
in a bone tunnel is correlated with collagen-fiber continuity between the bone and the tendon. In a rabbit ACL
reconstruction model using the flexor tendon, Grana et
al.7 found that at 3 weeks after surgery the graft is rigidly
fixed in the bone tunnel so that the graft cannot be pulled
out from it. We have previously reported that the pull-out
strength of the canine flexor tendon graft in a bone tunnel
is equivalent to that of the bone-patellar tendon-bone
graft at 6 weeks.17 In the previous studies, the bone tunnel was drilled so that the diameter was equivalent to that
of the grafted tendon,17 or the tunnel was drilled without
quantitative measurement.2, 7, 15
In clinical ACL reconstruction, there is a possibility that
the diameter of the bone tunnel is drilled to a greater
diameter than that of the autograft. In addition, grafttunnel diameter disparity occasionally occurs in revision
ACL reconstruction. Orthopaedic surgeons have been con-
A firm attachment of graft tissue to bone is important for
the success of ACL reconstruction. However, much remains unclear about healing of the flexor tendon graft
within the bone tunnel. Results of previous histologic
studies have suggested that collagen fiber continuity between the bone and the grafted flexor or extensor tendon
is progressively reestablished.2, 4, 6, 10, 11, 18 Rodeo et al.,15
using an extraarticular graft model with the canine extensor tendon, showed that the pull-out strength of the graft
* Presented at the 25th annual meeting of the AOSSM, Traverse City,
Michigan, June 1999.
§ Address correspondence and reprint requests to Kazunori Yasuda, MD,
PhD, Department of Medical Bioengineering and Sports Medicine, Hokkaido
University School of Medicine, Kita-15 Nishi-7, Sapporo, 060-8638, Japan.
No author or related institution has received any financial benefit from
research in this study. See “Acknowledgment” for funding information.
498
Vol. 30, No. 4, 2002
Graft-Tunnel Diameter Disparity in ACL Reconstruction
cerned that the graft-tunnel diameter disparity may have
adverse effects on healing of the flexor tendon graft within
the bone tunnel. However, few experimental studies have
been conducted to quantitatively document the effects of
the disparity on the flexor tendon graft in ACL reconstruction. The purpose of this study was to clarify biomechanically and histologically the effect of graft-tunnel diameter
disparity on intraosseous healing of the flexor tendon
graft within the bone tunnel in ACL reconstruction.
tubated endotracheally and was fixed in a supine position
on an operating table. A median skin incision was made in
the left knee by using a sterile technique, and the ACL
was exposed and resected through a medial parapatellar
approach. The transverse ligament was incised from the
infrapatellar fat pad to allow for full visualization of the
tibial attachment of the ACL.
In groups 1 and 2, a 10-cm length of the flexor digitorum
superficialis tendon was harvested from the left hindlimb
through a longitudinal incision made at the posteromedial
aspect of the distal lower leg. The tendon was then sharply
trimmed parallel to the fiber orientation so that the doubled tendon could be passed through a 4-mm diameter
sheath. At the looped end of the doubled tendon, a No. 1
Ti-Cron suture (Sherwood, Davis & Geck, Danbury, Connecticut) was passed through the loop. At the free end, the
same suture was firmly attached in a whipstitch fashion.
In group 3 the bone-patellar tendon-bone preparation with
a width of 4 mm and a bone plug length of 10 mm was
harvested from the extensor apparatus of the left knee,
and the bone plugs were then trimmed so that they could
be passed through a 4-mm diameter sheath. A drill hole
with a diameter of 1 mm was made in each bone plug, and
a No. 1 Ti-Cron suture was passed through each hole.
After the preparation, the cross-sectional area of the
middle portion of each graft was measured with an area
micrometer, as described in previous studies.8, 9 In brief,
the middle portion was placed in the micrometer slot and
the plunger was placed on the specimen in the slot. The
thickness of the specimen was measured with a constant
compressive stress of 0.12 MPa applied for a 2-minute
period.3 The cross-sectional area of the middle portion was
calculated by multiplying the slot width by the measured
thickness. The cross-sectional area of the graft in groups 1
and 2 was 10.1 ⫾ 1.1 mm2 and 10.7 ⫾ 0.6 mm2, respectively; there were no significant differences between the
groups (P ⫽ 0.160, power, 1- ␤ ⫽ 0.271).
The anteromedial surface of the tibia was exposed, and
the periosteum was elevated. In groups 1 and 3, a bone
tunnel with a diameter of 4 mm was drilled into the tibia
through the tibial insertion of the resected ACL to the
exposed anteromedial surface of the tibia (Fig. 1). In group
2, a bone tunnel with a diameter of 6 mm was drilled in
the same manner. A small incision was then made in the
proximal posterolateral part of the joint capsule. A sharp
curette was inserted from the incision over the top of the
lateral femoral condyle. The cortical bone at this point was
then curetted so that a bony trough was created along
the over-the-top route to enhance the adhesion between
the graft and the bone and to position the graft close to the
original femoral insertion. For each graft, the distal-most
15 mm was placed in the tibial bone tunnel, and the
proximal end of each graft was routed through the trough
in the lateral femoral condyle. A mark was placed 15 mm
proximal to the distal end of the graft, which was pulled
into the tibial tunnel until the mark reached the edge of
the tunnel. The suture attached to the distal end of the
graft was then tied over a screw inserted into the tibia.
The suture attached to the proximal end of the graft was
tensioned until the surgeon felt that the Lachman sign
MATERIALS AND METHODS
Study Design
Animal experimentation was performed under the guidelines of the Rules and Regulations of Animal Care and Use
Committee, Hokkaido University, School of Medicine. Forty-two healthy adult beagle dogs weighing 10.9 ⫾ 0.6 kg
(mean ⫾ standard deviation) were divided into three
study groups of 14 animals each. In each group, anatomic
ACL reconstructions were performed in the left knee after
the ACL was resected. In groups 1 and 2, a doubled flexor
tendon with a diameter of 4 mm was grafted to reconstruct
the ACL. In group 1, a bone tunnel with a diameter of 4
mm was drilled in the tibia, so that the graft fit tightly
within the bone tunnel (Fig. 1A). In group 2, a bone tunnel
with a diameter of 6 mm was drilled in the tibia, so that
the graft fit loosely within the tunnel (Fig. 1B). In group 3,
a bone-patellar tendon-bone preparation with a width of 4
mm and a 10 mm-long bone plug at each end was grafted
into a 4-mm tibial tunnel (Fig. 1C). Group 3 served as a
control to represent bone-to-bone healing as opposed to
tendon-to-bone healing.21 In each group, seven animals
were sacrificed at both 3 and 6 weeks after the operation.
At each period, five of the seven animals were used for
biomechanical testing and the remaining two were used
for histologic examination.
Surgical Procedure and Postoperative Treatment
Surgery was performed with the animal under anesthesia
induced by the intramuscular administration of ketamine
hydrochloride (10 mg/kg) followed by the intravenous injection of pentobarbital (25 mg/kg). Each animal was in-
Figure 1. Surgical procedures in groups 1 (A), 2 (B), and 3
(C). The diameter of the graft and of the tibial bone tunnel are
shown in each picture.
499
500
Yamazaki et al.
was obliterated. The suture was then tied over a screw
inserted into the bone with the knee at 45° of flexion (Fig.
2). The surgical wound was irrigated with a physiologic
saline solution containing antibiotics and closed with 3– 0
nylon sutures.
None of the animals were immobilized postoperatively,
and all were allowed unrestricted daily activities in their
cages (cage dimensions: 70 cm in width, 68 cm in height,
and 70 cm in depth). Each animal was sacrificed by a
lethal injection of thiamylal sodium at the predetermined
period.
Biomechanical Testing
The knee specimen, with a femur length of 45 mm and a
tibia length of 60 mm, was removed from the animal
immediately after sacrifice. Each specimen for biomechanical testing was wrapped in gauze moistened with
physiologic saline solution and then wrapped in an airtight polychlorovinylidene film. The specimens were
stored at –32°C until the time of testing. Before mechanical testing, each knee was thawed overnight at 4°C. All
Figure 2. Graft fixation procedure. Each end of the graft was
tethered with polyester sutures to a screw inserted into the
bone. The 15-mm long distal end was placed in the tibial
tunnel, and the proximal end was routed over the top of the
femoral condyle.
American Journal of Sports Medicine
soft tissues other than the graft were carefully dissected.
Then the cross-sectional area of the graft was measured
with the area micrometer in the manner described earlier.3, 8, 9 The femur and the tibia were separately cast in
rectangular aluminum tubes of 20 ⫻ 20 ⫻ 50 mm3 by
using polymethyl methacrylate resin.
The prepared femur-graft-tibia specimen was attached
to a conventional tensile tester with a set of specially
designed grips (PMT-250W, Orientec, Tokyo, Japan). The
tibia was positioned to allow for tensile loading aligned
with the long axis of the bone tunnel with the knee at 45°
of flexion (Fig. 3). The anchoring strength of the graft
within the tibial bone tunnel was determined with the
following procedure. The suture tethering the graft to the
tibia was cut, but the suture fixing the graft to the femur
was not resected. Before the tensile test, the specimen was
preconditioned with a static preload of 0.5 N for 5 minutes,
followed by 10 cycles of loading and unloading with a
strain of 0.5% at a cross-head speed of 20 mm/min.8, 9, 17
After the preconditioning, pull-out tests were performed
at the same rate, and load-deformation curves were drawn
on a recorder (X-Y-T Recorder 3023, Yokogawa, Tokyo,
Japan). We selected this strain rate value on the basis of
the results of our previous studies in a canine model.8, 9, 17
Figure 3. For pull-out testing, the femur-graft-tibia complex was mounted on a tensile tester to allow for tensile
loading aligned with the long axis of the bone tunnel. The
test was performed after sutures tethering the graft to the
tibia were cut.
Vol. 30, No. 4, 2002
Graft-Tunnel Diameter Disparity in ACL Reconstruction
501
The specimen was kept moistened throughout the test
period with a physiologic saline solution spray. From the
load-deformation relationship, the ultimate load and the
linear stiffness were obtained. During the pull-out tests,
failure modes were observed.
ulation tissue at 3 weeks in each animal. The granulation
tissue was grossly thicker on the anterior aspect than on
the posterior aspect. At 6 weeks, the volume of the granulation tissue decreased in each knee.
Histologic Observations
Histologic Observation
In each group, two specimens were used for histologic
examination at both 3 and 6 weeks after the operation.
Each graft-tibia specimen intended for histologic observation was fixed in a 10% buffered formalin solution immediately after harvesting. After the specimen was decalcified, it was cast in paraffin blocks. The specimens were
sectioned parallel to the longitudinal axis of the bone
tunnel and were stained with hematoxylin and eosin, safranin O, and toluidine blue. For all specimens, the tendon-bone interface and the intraosseous tendon substance
were evaluated with light and polarized light microscopy.
In addition, the graft-tibia complexes that had been
used for the pull-out tests were fixed in a 10% buffered
formalin solution. They were then decalcified, cast in paraffin blocks, sectioned in the same manner as described
previously, and stained with hematoxylin and eosin. In
these specimens, the failure modes were microscopically
determined.
Statistical Analysis
All data are reported as the mean and standard deviation
of measured values. For assessment of the influence of
treatment on the ultimate load and the linear stiffness, a
one-way analysis of variance was performed at each time
period. A Fisher’s protected-least-significant-difference
test was applied for post hoc multiple comparisons. The
significance limit was set at P ⫽ 0.05 for each test.
RESULTS
All 42 animals had no postoperative complications and
were used for the analysis. At the time of sacrifice, we did
not find tears in any graft or any apparent degenerative
changes on the articular cartilage and the menisci. The
intraarticular portion of the graft was enveloped by gran-
Figure 4. Orientation of histologic specimens for groups 1
and 2 (A) and for group 3 (B).
The diameter of the bone tunnel appeared to be greater in
group 2 than in group 1 at both 3 and 6 weeks after the
operation, whereas it appeared that the diameter of the
bone tunnel in group 2 decreased at 6 weeks (Figs. 4 and
5, A through D). The space between the flexor tendon and
the bone (tendon-bone gap) seemed to be greater in group
2 than in group 1 at both 3 and 6 weeks, whereas the
grafted tendon within the bone tunnel appeared to be
thicker in group 2 than in group 1. The tendon-bone gap
was filled with highly cellular granulation tissue in the
specimens from groups 1 and 2 (Fig. 5, A through D). At 3
weeks, perpendicular fibers (resembling Sharpey fibers)
connecting the tendon to the bone were observed in the
granulation tissue in both groups 1 and 2 (Figs. 6 and 7, A
and B). At 6 weeks, it appeared that the number of the
perpendicular fibers in the granulation tissues increased
in comparison with the 3-week specimens of each group
(Fig. 7, C and D). The number of perpendicular fibers at
each period appeared to be higher in group 2 than in group
1, although we did not make any quantitative comparison.
In group 3, new bone formed from the tunnel wall was
partly attached to the surface of the bone plug at 3 weeks,
and empty lacunae were observed in the trabeculae of the
bone plug except near the tendon insertion and in the
superficial portion (Figs. 4 and 5, E and F). At 6 weeks,
new bone completely surrounded the necrotic bone plug
(Fig. 5, E and F).
Mechanical Evaluations
All flexor tendon grafts in groups 1 and 2 were pulled out
from the tunnel at 3 weeks (Table 1). At 6 weeks, two of
the five grafts had failed in the tendon substance in group
1 and three of the five had failed in group 2; the remaining
specimens were pulled out from the tunnel. No grafts
failed at the femoral insertion at either period. In group 3
at 3 weeks, three patellar tendon-bone grafts were pulled
out from the tunnel with the bone plug whole and one with
a small fragment peeled off from the bone plug. The remaining graft failed in its midsubstance. At 6 weeks, the
tendon portion was pulled out from the tunnel with a
small bony fragment in two knees, and the remaining
three specimens failed in the midsubstance. No grafts
failed at the femoral insertion at either period.
A one-way analysis of variance for the effects on the
ultimate load to failure of the graft-tibia complex demonstrated that there were significant differences among
groups at 3 weeks (P ⫽ 0.037; power, 1- ␤ ⫽ 0.641) but no
significant differences among groups at 6 weeks (P ⫽
0.625, power, 1- ␤ ⫽ 0.111). At 3 weeks, the ultimate load
of group 1 was significantly lower than that in group 3
(P ⫽ 0.012), and there were no significant differences
between groups 2 and 3 (P ⫽ 0.123) (Fig. 8A). The average
502
Yamazaki et al.
American Journal of Sports Medicine
Figure 5. Low-magnification histologic specimens of the flexor digitorum superficialis tendon graft (groups 1 and 2) and
bone-patellar tendon-bone graft (group 3) within the bone tunnel at 3 and 6 weeks. A, group 1 at 3 weeks. B, group 2 at 3 weeks.
C, group 1 at 6 weeks. D, group 2 at 6 weeks. E, group 3 at 3 weeks. F, group 3 at 6 weeks. (hematoxylin and eosin stain, original
magnification ⫻ 5)
lower than those of specimens that failed in midsubstance
(group 1, 238 ⫾ 17 N; group 2, 253 ⫾ 59 N). We did not
attempt any statistical comparison because of the small
sample size (Table 1). In group 3, we did not find any
relationship between the ultimate load and the site of
failure.
Analysis of variance demonstrated that there were significant differences in the linear stiffness of the graft-tibia
complex among groups at 3 weeks (P ⫽ 0.01; power, 1- ␤ ⫽
0.851), but there were no significant differences at 6 weeks
(P ⫽ 0.457; power, 1- ␤ ⫽ 0.157). The stiffness of group 1
was significantly lower than that of group 3 at 3 weeks
(P ⫽ 0.003), whereas there were no significant differences
between groups 2 and 3 (P ⫽ 0.136) (Fig. 7B). There were
no significant differences between groups 1 and 2 (P ⫽
0.055).
DISCUSSION
Figure 6. Location and orientation of sections for the anterior part of the tendon graft-bone interface in groups 1 and 2.
ultimate load at 3 weeks in group 1 (87 N) was lower than
that in group 2 (132 N); there were no significant differences between groups 1 and 2 (P ⫽ 0.217). At 6 weeks,
there were no significant differences in the ultimate load
between groups 1 and 2 (P ⫽ 0.539). The average ultimate
load values of the specimens that failed by tibial pullout at
6 weeks (group 1, 183 ⫾ 25 N; group 2, 191 ⫾ 69 N) were
The results of this study of ACL reconstruction with flexor
tendon graft showed that the perpendicular fibers connecting the graft to the bone were generated in the loosely
fit group as well as in the tightly fit group. The number of
perpendicular fibers at each period appeared to be higher
in the loosely fit group than in the tightly fit group, although the space between the flexor tendon and the bone
seemed to be greater in the loosely fit group than in the
tightly fit group. Therefore, the graft-tunnel diameter disparity does not appear to have an adverse histologic effect
and may have a positive effect on the formation of perpendicular fibers connecting the graft to the bone. We found
that average values of ultimate load and stiffness of the
flexor tendon graft in the large-diameter tunnel were
Vol. 30, No. 4, 2002
Graft-Tunnel Diameter Disparity in ACL Reconstruction
503
Figure 7. The anterior part of the tendon graft (G)-bone (B) interface in groups 1 and 2. A, group 1 at 3 weeks. B, group 2 at
3 weeks. C, group 1 at 6 weeks. D, group 2 at 6 weeks. (hematoxylin and eosin stain).
greater than those in the smaller one, although this difference was not statistically significant. The biomechanical results suggest that the graft-tunnel diameter disparity does not have an adverse effect on mechanical strength
of the graft in the bone tunnel.
There were some limitations to this study. Because it
was performed using a canine model, we did not completely mimic the standard ACL reconstruction performed
in human patients. For example, we used the flexor digitorum superficialis tendon instead of the hamstring tendon because the canine hamstring tendons are too thin to
use as a single-strand graft in ACL reconstruction and too
short to use as a doubled graft. The femoral side of the
tendon was placed in the trough created along the overthe-top route, whereas the over-the-top technique is not
commonly used for the bone-patellar tendon-bone graft. In
the canine model, the over-the-top route has commonly
been used for the femoral side to minimize variability of
the graft position at the femoral site.1, 12, 13, 20 We adjusted
only the maximum diameter of the graft in this study.
Therefore, the graft diameter variability may be one of the
limitations in this study. However, the difference in the
average graft cross-sectional area between groups 1 and 2
was less than 1 mm2, although the difference in the crosssectional area of the bone tunnel between groups 1 (12.5
mm2) and 2 (28.3 mm2) was larger than 15 mm2. We
believe that this graft cross-sectional area variability was
acceptable.
The tunnel orientation variability was also one of the
limitations in this study, because we did not control tibial
tunnel orientation as well as had previous animal studies
of ACL reconstruction.1, 7, 12, 13, 16, 20, 21 We adjusted the
initial graft tension until the positive Lachman test was
obliterated. This tensioning technique was not quantitative, but it has been used in previous animal investigations of ACL reconstruction and in clinical practice.1, 7, 12, 13, 16 We have to recognize that these factors
may have affected the results in this study. In addition,
well-controlled rehabilitation could not be applied postoperatively in this study.
Another limitation of this study was that we selected
the relatively low cross-head speed of 20 mm/min for the
loading of the grafts, based on the results of our previous
studies in a canine model.8, 9, 17 Woo et al.19 and Danto and
Woo5 showed that there was little effect of strain rate on
the failure mode or the mechanical properties of the liga-
504
Yamazaki et al.
American Journal of Sports Medicine
TABLE 1
Results of Mechanical Evaluations
Time
period
3 Weeks
Group 1
Group 2
Group 3
6 Weeks
Group 1
Group 2
Group 3
Ultimate
load
(N)
Linear
stiffness
(N/mm)
Failure mode
66
62
78
72
159
162
176
88
167
69
216
162
299
145
127
37
23
28
29
48
54
62
49
63
25
73
61
78
59
46
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Tibial pullout
Midsubstance tear
Small fragment avulsion
162
176
211
250
225
142
240
299
274
186
191
338
250
270
157
73
74
61
96
98
47
77
77
65
72
74
103
55
65
48
Tibial pullout
Tibial pullout
Tibial pullout
Midsubstance tear
Midsubstance tear
Tibial pullout
Tibial pullout
Midsubstance tear
Midsubstance tear
Midsubstance tear
Midsubstance tear
Midsubstance tear
Midsubstance tear
Small fragment avulsion
Small fragment avulsion
ment. In contrast, Noyes et al.14 reported that the rate of
loading had a significant effect on the type of failure.
Therefore, the strain rate for mechanical tests may
slightly influence our biomechanical results. In this study,
the graft was not always pulled out from the tunnel in
pull-out testing at 6 weeks. Therefore, we could not determine the pull-out strength of the graft from the bone
tunnel at 6 weeks. From a clinical viewpoint, however, it is
important to determine where the weakest site is in the
graft-bone complex, the graft-bone tunnel interface or the
intraarticular tendon site, because the lowest strength
holds the key to success in ACL reconstruction. We focused on graft healing within the tibial bone tunnel. That
is, there were no graft failures at the femoral insertion.
This phenomenon may be affected by the following facts.
First, during pull-out testing, we did not cut the sutures
tethering the graft to the femur. Second, the femoral end
of the graft was flexed approximately 90° to the direction
of the tensile load at the over-the-top portion of the femoral condyle. Therefore, we cannot directly refer to graft
healing within the femoral tunnel.
Another limitation of this study is related to study design. We analyzed the data from only two specimens for
histologic observation and from five for mechanical testing
from each group at each time point. Because of the small
sample size for histologic evaluation, we did not attempt
Figure 8. The ultimate load (A) and the linear stiffness (B) of
the graft-tibia complex in pull-out testing.
quantitative assessment of histologic observations. Therefore, histologic findings in this study were based on subjective assessment. In addition, we did not obtain sufficient power for statistical comparisons on biomechanical
parameters because of the small sample size. Also, we only
chose two tunnel diameters. Therefore, we were not able
to clarify the effect of a greater disparity or to determine
the degree of disparity that might become deleterious.
Rodeo et al.15 found that the pull-out strength of the
tendon from the bone tunnel progressively increased with
obliteration of the space between the tendon and the bone.
Their finding suggests that closer opposition of the tendon
to the bone correlates with higher pull-out strength of the
tendon in the bone tunnel. In contrast, we observed that
the space between the tendon and the bone at 3 weeks was
greater in the loosely fit group than in the tightly fit group
and that the average pull-out strength at 3 weeks was
higher in the loosely fit group than in the tightly fit group.
Therefore, our findings seem to be in contrast to their
results. However, they also showed that the progressive
increase in pull-out strength of the tendon was correlated
with the degree of fiber continuity between the tendon and
the bone. In our study, abundant perpendicular fibers that
attached the graft to the bone were observed histologically
in the loosely fit group. These findings suggest that the
perpendicular fibers that attached the graft to the bone in
Vol. 30, No. 4, 2002
Graft-Tunnel Diameter Disparity in ACL Reconstruction
the loosely fit group may have increased pull-out strength
of the graft in the bone tunnel.
A graft-tunnel diameter disparity of approximately 2
mm (roughly 50% of the graft diameter) may be acceptable
in ACL reconstructions using the flexor tendon graft. This
statement does not mean that the bone tunnel should be
drilled too loosely. We believe that an excessively large
bone tunnel should be avoided from the viewpoint of graft
isometry and preservation of the bone tissue. During actual reconstruction surgery, however, orthopaedic surgeons sometimes have a dilemma when they choose one of
two drills with different diameters. When a drill with a
smaller diameter is chosen to make a press-fit tunnel,
there is the possibility that the graft cannot be pulled into
the tunnel because of high friction. However, if they
choose a drill with a greater diameter, a loosely fit tunnel
may present adverse effects to intraosseous graft healing
within the tunnel. The results of the present study suggest
that, in such cases, surgeons can safely choose the drill
with a greater diameter. In addition, the flexor tendon
graft is not completely cylindrical, because the graft is
compressed by the tensile force and by the bony edge of the
tunnel outlet. In actual ACL reconstruction, graft-tunnel
diameter disparity commonly exists at a localized portion
within the cylindrical bone tunnel, specifically at the intraarticular outlet portion of the tunnel.
The results of this study suggest that a graft-tunnel
diameter disparity of 2 mm may not have adverse effects
on intraosseous healing of the flexor tendon graft in ACL
reconstruction. Therefore, orthopaedic surgeons need not
be overly concerned in cases with minor graft-tunnel diameter disparities.
2. Blickenstaff KR, Grana WA, Egle D: Analysis of a semitendinosus autograft in a rabbit model. Am J Sports Med 25: 554 –559, 1997
3. Butler DL, Grood ES, Noyes FR, et al: Effects of structure and strain
measurement technique on the material properties of young human tendons and fascia. J Biomech 17: 579 –596, 1984
4. Chiroff RT: Experimental replacement of the anterior cruciate ligament: A
histological and microradiographic study. J Bone Joint Surg 57A: 1124 –
1127, 1975
5. Danto MI, Woo SL: The mechanical properties of skeletally mature rabbit
anterior cruciate ligament and patellar tendon over a range of strain rates.
J Orthop Res 11: 58 – 67, 1993
6. Forward AD, Cowan RJ: Tendon suture to bone. An experimental investigation in rabbits. J Bone Joint Surg 45A: 807– 823, 1963
7. Grana WA, Egle DM, Mahnken R, et al: An analysis of autograft fixation
after anterior cruciate ligament reconstruction in a rabbit model.
Am J Sports Med 22: 344 –351, 1994
8. Katsuragi R, Yasuda K, Tsujino J, et al: The effect of nonphysiologically
high initial tension on the mechanical properties of in situ frozen anterior
cruciate ligament in a canine model. Am J Sports Med 28: 47–56, 2000
9. Keira M, Yasuda K, Kaneda K, et al: Mechanical properties of the anterior
cruciate ligament chronically relaxed by elevation of the tibial insertion.
J Orthop Res 14: 157–166, 1996
10. Kernwein GA: A study of tendon implantations into bone. Surg Gynecol
Obstet 75: 794 –796, 1942
11. Kernwein G, Fahey J, Garrison M: The fate of tendon, fascia and elastic
connective tissue transplanted into bone. Ann Surg 108: 285–290, 1938
12. McFarland EG, Morrey BF, An KN, et al: The relationship of vascularity
and water content to tensile strength in a patellar tendon replacement of
the anterior cruciate in dogs. Am J Sports Med 14: 436 – 448, 1986
13. McPherson GK, Mendenhall HV, Gibbons DF, et al: Experimental mechanical and histologic evaluation of the Kennedy ligament augmentation
device. Clin Orthop 196: 186 –195, 1985
14. Noyes FR, DeLucas JL, Torvik PJ: Biomechanics of anterior cruciate
ligament failure. An analysis of strain-rate sensitivity and mechanism of
failure in primates. J Bone Joint Surg 56A: 236 –253, 1974
15. Rodeo SA, Arnoczky SP, Torzilli PA, et al: Tendon-healing in a bone
tunnel. A biomechanical and histological study in the dog. J Bone Joint
Surg 75A: 1795–1803, 1993
16. Tohyama H, Beynnon BD, Johnson RJ, et al: The effect of anterior
cruciate ligament graft elongation at the time of implantation on the
biomechanical behavior of the graft and knee. Am J Sports Med 24:
608 – 614, 1996
17. Tomita F, Yasuda K, Mikami S, et al: Comparisons of intraosseous graft
healing between the doubled flexor tendon graft and the bone-patellar
tendon-bone graft in anterior cruciate ligament reconstruction. Arthroscopy 17: 461– 476, 2001
18. Whiston TB, Walmsley R: Some observations on the reaction of bone and
tendon after tunnelling of bone and insertion of tendon. J Bone Joint Surg
42B: 377–386, 1960
19. Woo SL, Peterson RH, Ohland KJ, et al: The effects of strain rate on the
properties of the medial collateral ligament in skeletally immature and
mature rabbits: A biomechanical and histological study. J Orthop Res 8:
712–721, 1990
20. Yoshiya S, Andrish JT, Manley MT, et al: Graft tension in anterior cruciate
ligament reconstruction. An in vivo study in dogs. Am J Sports Med 15:
464 – 470, 1987
21. Yoshiya S, Nagano M, Kurosaka M, et al: Graft healing in the bone tunnel
in anterior cruciate ligament reconstruction. Clin Orthop 376: 278 –286,
2000
ACKNOWLEDGMENT
This work was supported by grants-in-aid (Nos. 10558124,
12470299, 12671389, and 13671480) for Scientific Research
from the Ministry of Education and Culture, Japan.
REFERENCES
1. Arnoczky SP, Tarvin GB, Marshall JL: Anterior cruciate ligament replacement using patellar tendon. An evaluation of graft revascularization in the
dog. J Bone Joint Surg 64A: 217–224, 1982
505