To The Editor:
We read with great interest Anderson's article "Transepiphyseal
Replacement of the Anterior Cruciate Ligament in Skeletally Immature Patients.
A Preliminary Report" (2003;85:1255-63). Anterior cruciate ligament
injury is being recognized more frequently in children and adolescents, and
development of an operative protocol for treating this injury is needed. As
Anderson discussed, nonoperative treatment is likely to result in a poor
outcome, especially for athletes. We compliment Dr. Anderson on the quality of
his work and the detailed follow-up information.
In the past fifteen years, extensive work has been done, most notably by
Stephen Howell, on the optimum placement of the tibial tunnel during anterior
cruciate reconstruction. Howell and others have shown that impingement of the
graft may occur if it is placed too far anteriorly, leading to anterior knee
pain, impaired extension, and graft failure. In order to avoid impingement of
the graft on the roof of the intercondylar notch, the graft should emerge on
the tibial plateau in the posterior aspect of the footprint of the anterior
cruciate ligament1
and be placed such that it is posterior to the intercondylar
roof2.
The location of the tibial footprint of the anterior cruciate ligament in
children has been documented. It can be found in children by measuring
posteriorly from the anterior margin of the tibial tubercle along the tibial
plateau. The midpoint of the anterior cruciate ligament footprint in children
is at approximately 44% of the total antero-posterior dimension of the
tibia3. Although
Anderson reported, in his Materials and Methods section, that the graft was
placed in the posterior part of the footprint of the anterior cruciate
ligament, the fluoroscopic images of Figure 2 are inconsistent with this
statement. The guide wire shown in Figure 2 appears to be at approximately 30%
of the anteroposterior dimension of the tibia, a placement that could result
in a tibial tunnel that is too anterior and may impinge on the intercondylar
roof. Although problems with anterior graft placement on the tibia can be
addressed with a notchplasty, a large notchplasty in a child may encroach upon
the distal femoral physis.
We appreciate the complexity of the tibial tubercle and appreciate Dr.
Anderson's efforts to avoid physeal damage. The anatomy of the tibial tubercle
may dictate a more anterior placement of the tibial tunnel if the physis is to
be avoided completely. However, we think that the tibial tunnel should emerge
more posteriorly and that the use of notchplasty of the intercondylar roof
should be minimized or avoided altogether in skeletally immature patients.
I am impressed by Mr. Apel's and Dr. Shea's astute observation and
insightful comments. I also agree with their opinions about avoiding graft
impingement and minimizing the use of notchplasty of the intercondylar roof.
The most common technical mistake in the performance of anterior cruciate
ligament reconstruction is anterior placement of either the tibial or the
femoral drill hole. Tibial tunnel position has less effect on isometry than
femoral tunnel position does, but it is critical to the prevention of graft
impingement on the intercondylar notch. Complications associated with
impingement of an anterior cruciate ligament graft include limitation of
extension and mechanical trauma to the graft, resulting in failure.
Although I agree with Mr. Apel's and Dr. Shea's comments, there are several
extenuating factors associated with transepiphyseal reconstruction that should
be considered. First, although tibial tunnel position has a greater effect on
graft impingement, the location of the femoral tunnel also has an influence.
Graft impingement was studied with the femoral tunnel placed at the eleven
o'clock position in the right knee and the one o'clock position in the left
knee. In transepiphyseal anterior cruciate reconstruction, the femoral tunnel
is more inferior in the intercondylar notch (the nine-thirty position in the
right knee and the two-thirty position in the left knee). This position moves
the anterior cruciate graft down and away from the roof of the intercondylar
notch. Consequently, the tibial tunnel does not have to be as far posterior to
prevent impingement. Even so, it is technically possible to drill a more
posterior hole in the tibial epiphysis, if the surgeon deems that to be
necessary. However, greater obliquity of the tibial tunnel increases the
anteroposterior diameter of the hole as it enters the joint, diminishing the
effect of more posterior placement.
Second, Figure 2 was not a true lateral view and therefore may not
accurately reflect the tibial pin position. The c-arm image intensifier was
rotated 30° externally to demonstrate the physis extending into the tibial
tubercle. Figure 7, a lateral radiograph, allows a more accurate assessment of
the tibial tunnel position. In this figure, the tibial hole enters the joint
at approximately 35% of the anteroposterior diameter of the tibia.
Third, although I agree with the concept of avoiding notchplasty in
skeletally immature patients, I doubt that a small notchplasty will cause a
clinically relevant problem. In children, I usually perform a minimal
notchplasty, removing the soft tissue and only enough bone to see the
footprint of the anterior cruciate ligament on the femur, although, in one
patient, no adverse effects were associated with a notchplasty in which 3 mm
of the anterior outlet was removed. I respectfully disagree with the statement
that notchplasty may encroach on the distal femoral physis. It is proximal to
the anterior cruciate ligament insertion and therefore should not be in
jeopardy from reasonable enlargement of the anterior outlet of the
intercondylar notch.
Finally, if anterior tibial tunnel placement had been a substantial
problem, complications associated with anterior cruciate graft impingement
should have been evident. All of the patients in this series had extension of
the index knee that was equal to that of the normal, contralateral knee; the
mean side-to-side difference in anterior displacement was 1.5 mm as measured
with the KT-1000 arthrometer at 134 N; and the mean IKDC (International Knee
Documentation Committee) subjective score was 96.5 of 100 points. These
results did not demonstrate limitation of extension or graft failure, which
are complications associated with impingement. Therefore, it may be reasonable
to assume that anterior tibial tunnel placement and graft impingement was not
a clinically important problem in this series.