Postoperative
determination femoral position of ACL autograft
on the lateral radiograph
M. MILANKOV, M. STANKOVIC, V. KECOJEVIC, N. MILJKOVIC, S. NINKOVIC
Department
of Orthopedic Surgery and Traumatology, Institute of Surgery, Clinical
Center, Medical School, University of Novi Sad
ABSTRACT
The exact position of the autograft as well as its behavior during
knee motion can be checked by MRI, but this is an expensive method,
unfortunately not available in every hospital. A postoperative radiograph
indirectly shows the position of the graft according to the position
of the screws A simple method for radiographic determination of ACL
autograft position which uses tiny wire marker, is described.
Twenty tree bone-tendon-bone arthroscopic ACL reconstructions were
done. At the time of preparation of the autograft, a tiny wire marker
was put between junctions of bone and the tendon part of the autograft.
Postoperative lateral x-rays were scanned and measured.
Comparing the average values of the position of the anterior edge
of the screw and wire marker, first being located at 42% and second
being located at 32% of the total sagittal diameter of the lateral
condyle measured along Blumensaat's line, from the most posterior
contour of the lateral femoral condyle a statistically significant
difference was found (t=8,95, p<0,05).
The screw does not show precise position of the ACL autograft. This
fact has consecutive influence on the interpretation of the x-rays
after reconstruction of the ACL and estimation of the results. It
is also noticed that in the same cases, as a result of screwing, twisting
of bone part of the autograft in the femoral bone chanal occurs.
Key
words: ACL deficiency rupture, autograft and ACL reconstruction,
arthroscopic ACL reconstruction.
INTRODUCTION
For achieving knee stability, it is crucial to replace an injured
anterior cruciate ligament (ACL) with an optimally anatomically positioned
ACL autograft. The exact position of the autograft as well as its
behavior during knee motion can be checked by MRI[4,7,9,13,15], but
this is an expensive method, unfortunately not available in every
hospital. A postoperative radiograph indirectly shows the position
of the graft according to the position of the screws. Up till now,
several different methods have been described to determine and measure
ACL femoral graft position[2,8,16].
When we started performing arthroscopic reconstruction of ACL, we
couldn't clearly see the junction between bone and ligament part of
the graft, while putting the femoral part of bone-tendo-bone autograft.
Because of this, we had problems in putting and fixation of autograft
in the femoral canal. We had no special pencil for marking the autograft,
so we started to use a tiny wire to mark the junction between bone
and ligament part of the autograft. Postoperative x-rays have shown
significant difference between the position of screw and wire. In
the same cases, as a result of screwing, twisting of bone part of
the autograft in the femoral bone chanal occurs.
In this paper, a new simple method for radiographic control of ACL
autograft position which uses tiny wire marker, is described. Only
radiographic measurements were performed, for there were no possibilities
for other objective clinical measurements.
Picture 1.
Tiny wire marker was put between junctions of the bone and tendon
part of the autograft.
Figure 2. Graphic
presentation of the a/t % and b/t% ratio 23 patient. screw position
wire postion.
Picture 3.
Lateral radiograph of patient No 22. Autograft is posterior to the
sreew. a/t ratio is 38%; b/t ratio 25%. Screw is not showing the real
postion of the autograft.
Picture 4.
Lateral radiograph of patient No 12. At the time of inserteing an
intereference screw autograft has been twisted. Autograft is positioned
anterior to the sreew. a/t ratio is 28.23%; b/t ratio 37.32%. Screw
is not showing the real postion of the autograft.
MATERIALS
AND METHODS
Twenty three arthroscopic ACL reconstructions, using bone-tendon-bone
autograft, were done in a bloodless field. The average age of patient
was 19,7 years17-34. Mail to female ratio was 18 to 5, left to right
knee ratio was 14 to 9. At the same time, 6 patients had partial medial
meniscectomy, while only 1 patient had partial lateral menisectomy.
All patients had chronic isolated ACL injury which had occurred at
least 3 months prior to the reconstruction. Preoperatively, all operated
knees had positive Lachman and pivot shift tests. During the preparation
of the autograft, tiny wire markers were put between junctions of
the bone and tendon part of the autograft (picture 1).
Postoperative lateral x-rays of all operated knees were made. After
a careful examination of these x-rays femoral position of the autograft
was determined using a quadrant method described by Bernard et al[8].
Distance t represents the total saggital diameter of the lateral condyle
along the Blumensaat's line, a and b is defined as a distance from
posterior contour of the lateral femoral condyle to the postoperative
position of the anterior margin of the screw and wire. Ratio between
a/t, b/t, defines the femoral postion of the autograft with respect
to the screw and wire (table 1).
All x-rays were scanned and measurements were done using a Corel Draw
8 program package, while the statistic analysis was made using Microsoft
Excel. Central tendency (mean, median, mode) and dispersion (standard
deviation, variance, min-max values, standard eror - S.E.mean) are
presented. Student t test was used to test correlation between the
parameters and p value <0.05 was considered statistically significant.
RESULTS
Comparing the average values of the position of the anterior edge
of the screw (a/t ratio) which was located at 42% (28-47) and wire
marker (b/t ratio) 32% (25-39) of the total sagittal diameter of the
lateral condyle measured along Blumensaat's line from the most posterior
contour of the lateral femoral condyle, a statistically significant
difference was found (t=8,95, p<0,05, picture 2).
DISCUSSION
Unsatisfactory results after ACL reconstruction usually are concequences
of intraoperative technical errors[10]. Even when an ideal tunnel
positioning is achieved, success rate still do not exceed 88%[2].
A femoral placement more anterior than the anatomical insertion of
ACL is the most common error. This causes a relative shortening of
the graft comparing to the length of normal ACL and results in high
strain on the graft while the knee is flexed[3]. This may either restrict
flexion of the knee if the graft resists the increased loads or lead
to elongation of the graft and thus result in secondary knee instability.
On the other hand, femoral placement more posterior or distal to the
normal site of attachement may result in excessive tightening of the
graft while the knee is extended. This may either restrict extension
or overstretch the graft[12].
The exact position of the autograft after ACL reconstruction can be
determined by MRI, which is an expensive diagnostic tool not available
in every hospital. MRI provides very accurate information, at the
same time being noninvasive and safe imaging procedure, free of ionizing
radiation and well tolerated by patients. Recently there have been
significant advances in this technique, especially in the ability
to interpret images. Images obtained by MRI can provide useful information
in diagnosing tears, establishing normal anatomy of ACL and studying
the reconstructed graft[6,11].
On a postoperative lateral x-ray of the operated knee, the femoral
placement of ACL can be determined according to the anterior edge
of the femoral tunnel, with reference to the screw. This radiografic
determination of the ACL graft position which is based on the screw
position on a postoperative lateral x-ray, is not always a reliable
method. For this reason, a new radiographic method which uses wire
marker was developed for determination of femoral position of ACL
graft. By using this new method, it was showed that the position of
the screw does not show the precise position of ACL autograft. This
information had consecutive influence on the further interpretation
of the x-rays after ACL reconstruction and estimation of the results.
Failure of the reconstruction and further damage to the knee were
correlated with improper placement of the graft. It has been noticed
in some cases (pictures 3,4), that as a result of screwing in the
femoral canal , twisting of bone part of the autograft occurs and
this could be one of the causes for disparity between radiographic
and clinical finding. Graft translocation may occur as the interference
screw pushes the graft plug to the opposite peripheral portion of
the drill hole tunnel. This may affect the intended isometric or anatomic
placement of the graft[5]. The center of the tunnel do not coincide
with the centers of the graft and screw. Use of interference screws
introduces displacement of graft center in the tunnel. This usualy
implies a posterior shift in the femoral tunnel[14]. The surgeon must
keep in mind that the interference screw will translate and twist
the graft to the opposite side of the bone tunnel. Careful, thoughtful
screw placement, in conjunction with bone plug orientation, can avoid
malpositioning of the graft construct.
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Mailing address:
Department of Orthopedic Surgery and Traumatology
Institute of Surgery
Clinical Center, Medical School, University of Novi Sad
Hajduk Veljkova 1, 21 000 Novi Sad,
Yugoslavia
Tel.: +381 21 612 022
Fax: +381 21 29 929
E-mail: milankom@eunet.yu
