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Harukazu Tohyama, MD et al There are approximately 23,000
ankle injuries in the US each day, with anterior talofibular ligament
(ATF) sprains being the most common ligamentous injury. One of the tests to aid with diagnosis is the anterior drawer
test, which assesses the integrity of the ATF to restrain anterior talar
movement. There have been
conflicting reports in the literature regarding the efficacy of this test,
and one problem that arises is the fact that there is no definitive
consensus on the amount of force needed to effectively produce the test.
These authors wanted to use in-vitro and ex-vitro models to
determine how many Newton’s of force is required to provide accurate
data. In the typical ortho
clinic, placing the patient under anesthesia is not realistic, yet muscle
guarding and swelling can alter the results.
Having a good understanding of the amount of force to use could
provide better screening data. There were 9 cadaver ankles used
for the study, mean age 52.3 years. Ankles
were tested using an experimental fixture device that placed the ankle in
either the neutral position, or 10-20 degrees of plantarflexion.
The ankles underwent test forces that ranged from 10-60N, with the
ATF intact and then transected. The live humans used for this
presented to the ortho clinic with an acute ankle sprain, average time
from injury to presentation 4.9 days, and mean age 23.2 years.
There were a total of 14 subjects, who underwent a surgical
exploration of the ATF and other lateral ligaments to determine the degree
of the sprain. While under
anesthesia, their ankle laxity was tested using a custom designed ankle
laxity-testing device using the same forces as used on the cadavers.
The person was also tested awake, to determine if a difference was
seen. The results indicate that while
under anesthesia, a force of 30N was more sensitive at detecting laxity
than 60N was. This may occur
because forces at 60N may cause involuntary muscle contraction, which
stiffens the joint. This may
go along with another study that found no significant increase in laxity
between injured ankles and normal ankles when 150N was used.
Further testing found that with the cadavers, a lower load of
anterior force was more sensitive for detecting motion after the
transection than a higher load. Also,
the 10 and 20-degree plantarflexion positions were more apt to give an
accurate reading than the neutral position.
There did not appear to be any differences between the amounts of
laxity found and age, so the differences between the groups ages is not a
significant variable. The authors conclude that lower
grade forces, around 30N, are the best option when performing anterior
drawer testing. Any greater
force may result in muscle contraction and joint stiffening, which could
alter results. Also, a device
such as the Telos stress gauge, used to apply a 150N force during stress
radiographs, may end up with false negative results. COMMENTS The study poses a significant
question, which is “how much force to use during a ligament test”.
Obviously, more is not better.
I have never cranked on an ankle, knee or any other joint, because
as this study indicates, the early motion is what provides the data.
When performing valgus or varus stress testing of the knee, we
usually just perform the test to determine if there is laxity and
approximately how much gapping occurs.
We rarely try to push it to the extreme end range, and should
probably do the same for the ankle as well. When I perform the anterior drawer,
I do it a little different than most.
I have the patient put the metatarsal heads on a rolled up towel,
while lying supine with the knees bent.
This puts the ankle in the 10-20 degrees of plantar flexion.
Instead of pulling the talus forward, I stabilize the talus and
push the distal tibia and fibula posterior, which I feel gives me more
control and sensitivity. There
will always be a rotational component to this, with the lateral ankle
usually moving more. Always
grade side to side, and realize that when the other ankle has suffered
sprains in the past, you may no longer have a “normal” for which to
compare, and will need to use your own judgment and experience as the
baseline. It would be nice if someone made a
small device that PT’s could use to train themselves to have a good feel
for how much force to apply, either pushing or pulling. How many of us know how much force 30N is, and can we
reproduce this efficiently? I
doubt it!
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