Types of Force: 5 Scenarios
HIDEInteractive Transcript
0:00
Now let's talk about the manifestations of injury.
0:04
The first thing is a pop that is very, very common,
0:08
especially when there's no external force applied
0:11
to the knee, but rather a rotational movement of an athlete,
0:15
for example, involved in a sport.
0:17
And the reason we get a pop with the ACL is that
0:22
because of what's called a OID arrangement
0:26
of the collagen fibers in the LACL, they kind
0:29
of convulse when they tear.
0:31
And that can lead to a sensation of a pop
0:35
that the patient can, um, uh, feel.
0:40
This is uncommon, particularly with example
0:43
with the medial collateral ligament
0:45
and some of the other ligaments of the knee.
0:47
So that is the pop that you often get in the history
0:51
of patients who have complete tears
0:53
of the anterior cruciate ligament.
0:56
The second clinical manifestation is the joint effusion.
1:01
The artery to the anterior cruciate ligament is
1:04
relatively small.
1:06
So although you will get a joint effusion, it takes time
1:11
and typically the fluid starts accumulating hours,
1:14
sometimes even six hours after the injury
1:18
and increases during the first day.
1:21
So slow accumulation of joint fluid.
1:26
Now, failure to develop such an effusion over the first
1:29
or second day may indicate that there is a capsular injury
1:34
and with the posterior cruciate ligament
1:37
and sometimes the anterior cruciate ligament,
1:40
it is the posterior capsule that may be disrupted.
1:44
So here an example, the MR image showing you a complete tear
1:48
of the anterior cruciate ligament with a lot
1:51
of joint fluid now appearing posterior to the femur,
1:55
to the tibia, and to the joint itself.
1:58
So that may, uh, be seen.
2:01
And then a important point, if an immediate
2:05
and large effusion occurs, you ought to suspect
2:08
that there is a bone injury, often an osteochondral
2:12
fracture, and generally a he arthrosis or a lipo.
2:17
He arthrosis is present.
2:19
I'll talk more about those findings.
2:21
He arthrosis and lipo, he arthrosis on Friday.
2:25
The condition does have certain tests that can be utilized
2:29
and I would stress three of them.
2:32
I'm showing you pictures how they're performed.
2:34
We're not gonna talk about it.
2:35
I don't know how to perform them,
2:37
but there's an anterior jaw test, a lockman test,
2:41
and a pivot ship test.
2:43
In general, the anterior jaw test is the least effective
2:48
in diagnosing a tear of the anterior cruciate ligament.
2:53
A lockman test is particularly effective in
2:56
excluding complete tears
2:59
Of the anterior cruciate ligament.
3:01
And a pivot shift test is the most sensitive in the
3:05
diagnosis of ACL tearing.
3:07
Okay? It is, uh, I'm sorry,
3:09
the most specific I should have said
3:11
with a high specificity, but low sensitivity.
3:15
So three major tests, none of which is ideal.
Donald Resnick, MD
Professor Emeritus, Department of Radiology
University of California, San Diego
Mini N. Pathria, MD, FRCP(C)
Division Chief, Musculoskeletal Imaging
University of California San Diego
Eric Y. Chang, MD
Adjunct Professor, Radiology
University of California, San Diego
Brady K. Huang, MD
Clinical Professor of Radiology
UC San Diego Medical Center
© 2026 Medality. All Rights Reserved.
