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John J. Elias, PhD
Alfred F. Faust, MD
Yung-Hua Chu, MS Edmund
Y. Chao, PhD
Andrew J. Cosagrea, MD ABSTRACT Much attention has been focused on
the action of the quadriceps and the hamstrings in the mechanics of the
knee, especially how they participate as either agonists or antagonists
for the ACL. The
gastrocnemius muscle, which crosses both the ankle and the knee joint, has
also been studied. One in
vivo experiment suggested that the gastroc acts as an antagonist for the
ACL by providing an anterior translation force for the tibia.
Another study, done in vitro, suggests that the gastrocnemius
strained the PCL more than the ACL. No
significant research has been done on the soleus, which can affect tibial
rotation and therefore some degree of anterior translation.
The purpose of this study was to use cadaver knees to determine how
open chain forces placed through the knee to simulate quadriceps,
hamstring, and gastroc soleus contractions affected the tibial translation
in both intact ACL knees and those with the ACL transected. The knees in the test were all
cadaver knees, age range 67-77 years, and had most of the soft tissue
removed but the major muscle groups and patellar mechanism intact.
The knee was tested at 20, 50, and 80 degrees of extension in an
open chain fashion, while loads were applied to the major muscle groups to
simulate muscle contractions. The hamstring force used was 180N, based on previous
theoretical calculations showing the peak gastrocnemius muscle force is
approximately the same as the peak hamstring force during multiple
functional activities. Results show that the soleus acting
alone is capable of providing an agonist force to the ACL and provide
posterior tibial translation. The
range measured was 0.24-0.36mm, with the most significant translation
occurring at 50 degrees of knee flexion.
When acting alone, it was found that the gastrocnemius acts as an
antagonist to the ACL, providing anterior translation in a significant
fashion in most of the cases tested.
When the gastrocnemius and soleus underwent a simulated
co-contraction, the resultant motion was anterior tibial translation,
especially at 50 degrees of flexion. The soleus is capable, at least in
these experiments, of providing some agonist control for the ACL.
The degrees of force used in this study do not in anyway replicate
the high forces seen when athletes often tear the ACL, i.e. closed chain
pivoting activities. However,
it serves as a benchmark to provide further study that may help prevent
this type of injury. COMMENTS As the authors indicate, the
article is not able to provide the extreme and exact muscular
co-contractions and activity seen in a typical closed chain sporting move.
However, it serves as a platform to rethink how we treat the soleus
muscle. Using cadaver
specimens always takes out the human tissue response, and performing these
tests in an open chain condition makes transposition of the data into a
closed chain situation more difficult.
With closed chain mechanics, the mortise of the talus may prevent
any anterior tibial translation, as the position of slight knee flexion
often incorporates ankle dorsiflexion. Perhaps we should perform more
isolated soleus strengthening via a seated calf machine, or just have the
patient perform seated calf raises while a family member sits on their
lap. Do persons with weakness
to the soleus due to spinal disc disruption or nerve root compression have
greater rates of ACL tears in that leg?
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