What is the role of intra-operative fluoroscopic measurements to determine tibial tunnel placement in anatomical anterior cruciate ligament reconstruction?

Abstract

The hypothesis for this study was that intra-operative fluoroscopic measurements can be used to determine tibial tunnel placement during anatomic anterior cruciate ligament (ACL) reconstruction. The anteromedial (AM) and posterolateral (PL) bundle insertion sites were marked with a thermal device and measured in a consecutive cohort of 67 patients undergoing anatomical ACL reconstruction. For double bundle reconstruction, guide pins were passed in the center of the AM and PL tibial footprints. For single bundle (SB) reconstruction a guide wire was placed between the center of AM and PL footprints. Subsequently, the position of the centers of the AM and PL insertion sites were measured on standardized lateral intra-operative fluoroscopic images. The center for the AM bundle was found to be at 31% (range 20-42%) of the AP distance on the medial joint line and at 35% (range 23-42%) of the AP distance on the Amis and Jakob line. The center of the PL bundle was at 48% (range 37-59%) of the AP distance on the medial joint line and 48% (range 39-58%) of the AP distance on the Amis and Jakob line. The center of the tibial tunnel in the SB group (n = 15) was at 42 and 41% in relation to the medial joint line and the Amis and Jakob line, respectively. Because a significant anatomic variation exists between patients, the decision with respect to tunnel placement should not be merely based on intra-operative fluoroscopic images.

Full text

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KNEE
What is the role of intra-operative fluoroscopic measurements
to determine tibial tunnel placement in anatomical anterior
cruciate ligament reconstruction?
Philip Kasten•Michal Szczodry•James Irrgang•
Eric Kropf•Joanna Costello•Freddie H. Fu
Received: 29 November 2009/Accepted: 2 February 2010/Published online: 9 March 2010
? Springer-Verlag 2010
Abstract
operative fluoroscopic measurements can be used to
determine tibial tunnel placement during anatomic anterior
cruciate ligament (ACL) reconstruction. The anteromedial
(AM) and posterolateral (PL) bundle insertion sites were
marked with a thermal device and measured in a consec-
utive cohort of 67 patients undergoing anatomical ACL
reconstruction. For double bundle reconstruction, guide
pins were passed in the center of the AM and PL tibial
footprints. For single bundle (SB) reconstruction a guide
wire was placed between the center of AM and PL foot-
prints. Subsequently, the position of the centers of the AM
and PL insertion sites were measured on standardized lat-
eral intra-operative fluoroscopic images. The center for the
AM bundle was found to be at 31% (range 20–42%) of the
AP distance on the medial joint line and at 35% (range 23–
The hypothesis for this study was that intra-
42%) of the AP distance on the Amis and Jakob line. The
center of the PL bundle was at 48% (range 37–59%) of the
AP distance on the medial joint line and 48% (range 39–
58%) of the AP distance on the Amis and Jakob line. The
center of the tibial tunnel in the SB group (n = 15) was at
42 and 41% in relation to the medial joint line and the
Amis and Jakob line, respectively. Because a significant
anatomic variation exists between patients, the decision
with respect to tunnel placement should not be merely
based on intra-operative fluoroscopic images.
Keywords
Reconstruction ? Fluoroscopy ? Tibial tunnel position ?
Tibial insertion, radiograph, X-ray image
Double bundle ? Anterior cruciate ligament ?
Introduction
The ACL is composed of two functional bundles, the
anterior-medial (AM) bundle and the posterior-lateral (PL)
bundle [4]. The two bundles of the ACL are initially seen
during fetal development, and persist as two distinct bun-
dles throughout life, although there is a high degree of
variability in the size of each bundle between individual
patients [4]. Cadaveric studies have demonstrated that the
AM bundle is approximately twice as long as the PL
bundle, and that the two bundles have a similar cross-
sectional diameter [5, 31]. The PL bundle plays a more
significant role in rotatory stability of the knee. Numerous
clinical and basic science studies have demonstrated single
bundle (SB) ACL reconstruction does not adequately
restore normal knee kinematics, particularly tibial rotation
[27]. Biomechanical studies have shown that anatomic
double bundle (DB) reconstruction better restores knee
kinematics compared to SB reconstruction alone [15, 16,
The work was performed at the Department of Orthopaedic Surgery,
University of Pittsburgh Medical Center (UPMC), USA.
M. Szczodry ? J. Irrgang ? E. Kropf ? F. H. Fu (&)
Department of Orthopaedic Surgery, University of Pittsburgh
Medical Center, Kaufmann Medical Building, Suite 1011,
3471 Fifth Avenue, Pittsburgh, PA 15213, USA
e-mail: ffu@upmc.edu
J. Costello
Department of Radiology, University of Pittsburgh
Medical Center, UPMC Presbyterian, Room 3950 CHP CMT,
200 Lothrop St., Pittsburgh, PA 15213, USA
P. Kasten
Department of Orthopaedic Surgery, University of Dresden,
Fetscherstr. 74, 01307 Dresden, Germany
P. Kasten
Department of Orthopaedic Surgery, University of Heidelberg,
Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany
123
Knee Surg Sports Traumatol Arthrosc (2010) 18:1169–1175
DOI 10.1007/s00167-010-1082-8

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28, 30]. Clinical studies comparing SB and DB ACL
reconstruction, however, have shown similar clinical
results, but improved rotational stability after DB recon-
struction [1, 16, 21, 25, 29].
Recommendations for tibial tunnel placement during SB
ACL reconstruction are often related to an anterior-pos-
terior distance on lateral radiographs [2, 7, 12, 18, 19, 26].
By use of intra-operative fluoroscopy, these images can be
obtained in the operating room and the use of these images
has been advocated by some to guide placement of the
tibial tunnel. However, to the best of our knowledge, no
prior studies have evaluated the use of intra-operative
fluoroscopy to assess tunnel placement during anatomic
DBACLreconstruction.
descriptive study was conducted with intra-operative
measurements and fluoroscopic documentation of the guide
wires that were used for tibial tunnel placement by a single
experienced senior surgeon. The hypothesis for this study
was that intra-operative fluoroscopic measurements can be
used to determine the tibial tunnel placement during ana-
tomic anterior cruciate ligament (ACL) reconstruction.
Therefore,a prospective
Materials and methods
A consecutive cohort of 78 individuals, who underwent
anatomic ACL reconstruction for acute injury, was ana-
lyzed. Seven patients were excluded because of inadequate
imaging. Furthermore, 3 chronic cases and 1 revision had
to be excluded due to the altered anatomy of the ACL
stumps. Surgery was performed on an average of 51.8 days
(SD 38.6, range 4–211) after injury but not before the full
range of knee motion was achieved. Only patients with a
clearly visible soft tissue stump of the ACL and adequate
fluoroscopic images were included to the study (n = 67).
There were 33 females and average age was 23.7 years
(range 14.8–55.3). Importantly, all individuals were skel-
etally mature and radiographs confirmed that all physes
were closed. The average height and weight of the 67
patients were 1.74 m (range 1.52–1.93 m) and 76.4 kg
(range 46.7–115.6 kg), respectively.
The antero-posterior and medial–lateral dimensions of
the tibial insertion sites were measured in all patients.
Fifteen patients ultimately did not undergo DB recon-
struction because the tibial insertion sites measured less
than 14 mm, and were thus considered to be too small for a
DB reconstruction. The subset of patients who underwent
SB reconstruction (5 male, 10 female, 24.2 ± 11 years
old) on average were shorter (1.68 m, range 1.54–1.84 m),
and lighter (64.7 kg, range 46.7–88.5) than the patients that
underwent DB ACL reconstruction. The rupture pattern of
the ACL is shown in Table 1. An intermediate bundle was
found in 2 patients (3%).
Looking from the lateral parapatellar viewing portal
with a 30? arthroscope the anatomic insertion sites of the
native AM and PL bundles were marked on the tibia with a
thermal device (Fig. 1a–c). Meticulous dissection was
performed with care taken to preserve the borders of the
AM and PL bundles for later reference. Next, the anterior-
posterior and medio-lateral diameter of the insertion sites
of each bundle and both bundles combined were measured
arthroscopically with an arthroscopic ruler (Smith and
Nephew Andover, MA, USA) (Fig. 2). If the dimension of
the tibial insertion was sufficient for DB reconstruction
(i.e. C14 mm in antero-posterior length; n = 52), a
3.2 mm guidewire for the PL tibial tunnel was then inserted
with a 45? drill guide with the tip of the guidewire exiting
the center of the insertion site of the previously defined PL
bundle (Fig. 2). The position of the drill guide was con-
firmed by use of the ruler to ensure that subsequent drilling
would result in a tunnel in the center of the PL bundle. As a
secondary guide, we confirmed that the center of the PL
tibial tunnel was within an anatomic triangle created by the
posterior root of the lateral meniscus, the PCL, and the AM
bundle tibial footprint. The center of the AM tibial tunnel
was then separately marked with another 3.2 mm guide-
wire placed anteromedial to the PL tunnel with an ACL tip
guide set at 55? in the center of the AM footprint. A ruler
was used to ensure that the location of the tip of the
guidewire was within the center of AM insertion site
(Fig. 2). For SB ACL reconstruction cases (n = 15) a
guidewire was placed between the center of AM and PL
footprints, using a 45? drill guide. Extension of the knee
under arthroscopic visualization was used to rule out an
impingement with the guide wires in place and after
implantation of the grafts. In no case there was an intra-
operative extension deficit.
Exact lateral fluoroscopic images were then taken in
full knee extension (Fig. 3). Overlap of the posterior
aspect of the medial and lateral femoral condyles was
utilized as a guide to ensure that exact lateral images
were obtained in all cases. The bony outlines of the
fluoroscopic images were transferred to tracing paper.
Reference lines for fluoroscopic measurements in the
sagittal plane included the medial joint line [5, 26] which
connects the anterior and posterior edges of the tibial
articular surface, and Amis and Jakob line [2, 5, 7]
passing through the posterior corner of the medial tibial
Table 1 The rupture patterns of the ACL
n = 67Rupture patterns
IntactElongatedProximalMid-substance Distal
AM18 36166
PL093915 4
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plateau and parallel to the medial joint line (Fig. 3). Both
referencing methods were used for better comparison with
previous studies [2, 5, 7]. The pin position, representing
the center of the AM and PL bundle for DB ACL
reconstruction or SB tibial tunnels, was normalized by
dividing the distance from the anterior edge of the tibia to
the pins intersection along the length of the medial joint
line or Amis and Jakob line [2] and then multiplying by
100 (with 0% being the most anterior point and 100%
being most posterior point).
Results
The dimensions of the insertion sites are shown in Table 2.
The distance between the two guide wires averaged
8.4 mm (SD 1.5, range 6–12 mm).
The centers for the AM and PL bundles with reference
to the medial joint line and Amis and Jakob line are dis-
played in Table 3. The center of the tibial tunnel in the
subjects that underwent anatomic SB ACL reconstruction
was 42% (SD 6.7%; range 32–56%) and 41% (SD 4.4%;
Fig. 1 a In order to
anatomically reconstruct the
tibial insertion sites the
anteromedial (AM) and the
posterolateral (PL) bundles are
carefully dissected using a
thermal device. This view from
the lateral portal shows the
length of the tibial insertion to
be 18 mm in a left knee. A wide
range of measurements from 12
b to 20 mm c were noted (both
lateral view in left knees)
Fig. 2 Intraoperative
measurements of the AM
insertion site width (a) and
length (b) and of the PL
insertion site width (c) and
length (d). Pins are placed in the
center of the insertions sites
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range 37–52%) of the AP distance in relation to the medial
joint line and the Amis and Jakob line, respectively.
Discussion
The most important finding in the present study is the
substantial anatomic variation between patients with
regards to the position of the ACL and individual bundle
insertions on the tibia. In the past, there were numerous
recommendations for tibial tunnel placement during ACL
reconstruction: in the late 1980’s Good et al. [10] and in the
mid 1990’s Goble et al. [9] preferred a more anterior
placementof the tibialtunnel duringSBACL
reconstruction recommending that the tunnel be placed in
the first third of the antero-posterior diameter of the tibia.
Romano et al. [24] found an extension deficit of more than
10? when the tibial tunnel was placed at 23% on the Amis
and Jakob line in a clinical study. For this reason, several
authors favor a more posterior position of the tibial tunnel.
Based on clinical outcome, Howell and Taylor [13] and
Howell [11] have shown that the ideal placement of the
tibial tunnel to avoid impingement with the inter-condylar
notch is 44% of the antero-posterior diameter of the joint
line [11, 13]. Using magnetic resonance arthrography,
Staubli and Rauschning determined the center of the tibial
tunnel should be 44% of the mid-sagittal intercondylar line
passing through the maximum diameter of the proximal
tibia. However, their recommendations depend on whether
an anatomic, cross-sectional anatomic or a magnetic reso-
nance arthogrpahy was chosen as a measurement method
[26]. Mauch et al. [19] determined that the tibial tunnel was
placed at 38% with a manual arthroscopic technique and
anatomic referencing and at 41% of Amis and Jakob line
by use of computer navigation. The anatomic referencing
of the study by Mauch et al. [19] aimed for the center of the
tibial tunnel being 7 mm anterior to the PCL, with this
point located along an imaginary line between the anterior
horn of the lateral meniscus and the medial tibial spine.
According to the concept in which the tunnel for SB
reconstruction should be placed in the average position
between the placement of the pins for the AM and PL
tunnels, placement for theoretical SB tunnel in our patients
corresponds to 42% of AP distance on the Amis and Jakob
line and 40% of the AP distance on the medial joint line.
The center of the tibial tunnel in our subjects that actually
underwent anatomic SB ACL reconstruction was close to
these theoretical values with 41% and 42% of the AP
distance in relation to the Amis and Jakob line and the
medial joint line, respectively. This suggests that previous
recommendations [3, 11, 23, 26] for SB ACL reconstruc-
tion may represent a tunnel that is placed in the postero-
lateral area of the ACL insertion that corresponds to the
insertion of the PL bundle. The authors placement of
the AM bundle on the tibial side is more anterior than the
recommendation of some authors [3, 11, 23, 26] for
placement of the tunnel during SB ACL reconstruction.
One of the most common technical causes of graft
failure in ACL reconstruction is non–anatomic placement
of the bone tunnels. Non-anatomic placement of the tunnels
can result in abnormal tension in the graft, loss of motion
and recurrent instability [8, 15, 19, 30]. For correct
placement both basic knowledge of the dimensions and the
natural position of the ACL insertion sites and knowledge
of anatomic landmarks during surgery are essential [12,
18]. According to Hutchinson et al. [14] the most repro-
ducible anatomic landmark for SB ACL reconstruction is
Fig. 3 Calculation of the anteroposterior position of the AM guide
wire (a) in relation of the total length (c) of the joint line and the
Amis/Jakob line
Table 2 Anatomic measurements of the insertion sites
n = 67Tibial insertion
Mean ± SD (range, mm)
Width Length
AM bundle9.3 ± 1 (7–11)9.3 ± 1.2 (6–11)
PL bundle 6.8 ± 1.1 (4–10)8.0 ± 1.1 (5–10)
Total insertion 17.4 ± 1.8 (12–20)
Table 3 Fluoroscopic measurements of the center of the AM and PL
bundle
Center of AM bundle
MV (SD, range)
Center of PL bundle
MV (SD, range)
Medial joint line31% (5%; 20–42%)48% (5%; 37–59%)
Amis and Jacob line35% (4%; 23–42%)48% (4%; 39–58%)
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the posterior cruciate ligament (PCL). They found that the
anterior border of the PCL was consistently 10.9 mm
posterior to the central sagittal insertion point of the
anterior cruciate ligament [14]. A non-cadaveric anatomic
dissection study found the center of the ACL in the sagittal
plane was on average 7 mm (range 7–8 mm) anterior to the
anterior margin of the PCL [20]. This relationship was
found to be consistent independent of knee size [20]. In
addition, the tibial insertion should lie on an imaginary line
between the anterior horn of the lateral meniscus and the
spine of the medial tubercle [19]. Because a high vari-
ability of the tibial insertion dimensions has been descri-
bed, we believe that absolute specifications in millimeters
from defined anatomic landmarks should not be used to
judge the placement of the tibial tunnels.
With increasing knowledge about the two functional
bundles of the ACL, different recommendations for place-
ment of the tibial tunnels for DB ACL reconstruction have
been proposed. Muneta et al. placed their guide wire for the
AM tunnel ‘‘in the center of the ACL’’ attachment and the
guide wire for the PL tunnels was placed 3 mm posterior to
the AM guide wire as it emerged into the joint [22]. It is
therefore unlikely that this resulted in separate tibial tunnels
as the tunnels emerged into the joint with the use of bundles
that ‘‘usually measured 6 or 7 mm in diameter’’ [22]. Simi-
larly, Adachi et al. [1] used average sizes of 6.8 mm and
5.9 mm for PL and AM bundles, respectively, with the
centers of their tunnels lying only 3 mm apart. However,
others have described performing anatomic ACL recon-
struction while leaving a 2-mmbonybridge betweenPLand
AM tunnels (of average diameters of 5 and 7 mm) as they
entered the joint [6]. This, it has been suggested, may facil-
itate graft healing and improve biomechanical function [6].
To further improve the reproducibility of graft place-
ment, intra-operative fluoroscopic visualization for place-
ment of the tunnel has been proposed. In a study by Klos
et al. [17] the variability in graft placement was reduced
significantly with the use of fluoroscopy. In the current
study guide wires were placed in the anatomic centers of
the AM and PL bundles by direct visualization under
arthroscopy and the position was verified by measurement
of the dimensions of the insertion site with a ruler. Then,
the positioning of the wires was recorded by intra-operative
fluoroscopy to clarify the question whether the wires had a
consistent position in relation to the tibial plateau, and
therefore could be used as a guideline for tibial tunnel
placement. However, fluoroscopic imaging revealed a
considerable variation of the position of the guide wires in
relation to the AP distance of the tibial plateau: standard
deviation ranged from 4 to 5% with the minimum and
maximum values differing up to 19%. Therefore, we
believe that placement of the tibial tunnels should not be
merely basedonfluoroscopicimages. Fluoroscopic
guidelines may help to avoid placement of tunnels well
outside an acceptable range, but do not accurately define
the true anatomic insertion sites.
Other studies also examined the position of the AM and
PL bundle and the variability of the tibial insertions. With
reference to Amis and Jakob line, Colombet et al. [5] found
the center of the AM bundle was at 36% and the center of
the PL bundle was at 52% in a cadaveric study of 7 knees.
Zantop et al. [32] examined 20 cadaveric knees and found
the center of the AM bundle was at 30% and the center of
the PL bundle was at 44% along a line similar to Amis and
Jakob line. A recent cadaveric study from Doi et al. [7]
performed on 31 specimens, described the center of AM
footprint at 34% and the center of PL at 38% of Amis and
Jakob’s line. Interestingly, minimum and maximum values
in their data differed as much as 19% and 20% for AM and
PL, respectively, which supports finding in the current
study. We present for the first time an intra-operative
evaluation of the tibial ACL footprint position using fluo-
roscopy with a large sample size. The center for the AM
bundle was located at 35% along Amis and Jakob’s line,
which is between the results described by Colombet et al.
[5] and Doi et al. [7]. The center of the tunnel for the PL
bundle was at 48% of the antero-posterior distance on
Amis and Jakob line, which is between the positions
described by Colombet et al. [5] and Zantop et al. [32].
Theuseofdifferentlinesforreferencingaddstodivergent
recommendations for SB ACL reconstruction: some authors
use the medial joint line [11, 13, 23], while others use the
AmisandJakobline[2,3,19,24]forreferencingtheposition
ofthetibialtunnelwhenperformingSBACLreconstruction.
Ourdata showsthattheuseofdifferent lines toreferencethe
antero-posterior diameter of the tibia can have an important
effect on the description oftunnel location. Forexample, the
center for the AM bundle was found to be at 31% of the AP
distance on the medial joint line and at 35% of the AP dis-
tance on the Amis and Jakob line.
There are some limitations to this study. The position of
the tibial insertion site of the ACL was described in only
one plane, but the readers should keep in mind that the
ACL is a 3 dimensional structure. A potential inconsistency
exists with the acquisition of lateral fluoroscopic images, as
the images were captured intraoperatively using bony
landmarks to best-approximate the exact lateral view.
Therefore, a small amount of error in measurements may
have occurred in the current study, even if the authors took
great care to standardize the images.
Conclusion
The center for the AM bundle was found to be at 31% of
the AP distance on the medial joint line and at 35% of the
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AP distance on the Amis and Jakob line. The center of the
PL bundle was at 48% of the AP distance on the medial
joint line and 48% of the AP distance on the Amis and
Jakob line. The center of the tibial tunnel in SB group was
at 42 and 41% in relation to the medial joint line and the
Amis and Jakob line, respectively. However, substantial
anatomic variation between patients was found. Therefore,
tibial tunnel placement should not be merely based on
intra-operative fluoroscopic images.
Acknowledgments
funding or grant. None of the researchers has received (or agreed to
receive) from a commercial entity something of value (exceeding the
equivalent of US$500) related in any way to this manuscript or
research.
This study was not supported by an outside
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