0:00

Let's focus on muscle strain.

0:02

So this is something that we are commonly called upon

0:05

to image, particularly in our elite athletes.

0:08

And again, this is an injury

0:10

that takes place at the myo tendonous junction.

0:14

Now, when we use that word, we need to understand

0:16

that there are a number of different myo tendonous junctions

0:20

that we have, uh, in our muscle.

0:22

There's one at the surface of the muscle

0:24

where tendon fibers contribute to this epimysium,

0:28

which is the surface layer.

0:30

There's a bio tendonous junction

0:32

where the free tendon meets the bone,

0:34

and then within the muscle itself,

0:36

there are frequently tendon slips

0:38

that extend into the muscle

0:40

that have their own myo tendonous junction running

0:43

for variable length.

0:45

This is a, a beautiful, um, specimen

0:49

of a myo tendonous junction showing the finger-like

0:52

expressives by how this, uh, junction takes place.

0:56

And it's quite broad

0:58

and this allows for loading to dissipate

1:02

between the muscle and the tendon.

1:04

But this is the vulnerable area

1:06

where we're gonna be seeing the majority

1:08

of our muscle strain injuries.

1:10

These happen after a single discreet trauma.

1:14

The patient knows exactly

1:16

when the injury happens. Now why do

1:20

We see these and where do we see these?

1:22

Well, we know that all

1:23

Of our muscles, Uh, at least our skeletal muscles,

1:26

are gonna perform some sort of eccentric work.

1:28

The muscles that tend to experience strain most frequently.

1:32

The list taken here from an article by Palmer many years ago

1:37

emphasized muscles that have type two

1:39

Fibers, long muscles that

1:42

Cross two joints, and those that have penate architecture.

1:47

And of these, I can tell you

1:48

that the architecture is really the most important.

1:52

When we look at muscle strains, we see

1:55

that these generally occur in the large muscles

1:58

of our lower extremity, particularly the hamstrings, all

2:02

of which have this penate type of architecture,

2:05

which I will go over, uh, with you,

2:07

where the tendon is not actually centrally located

2:10

Within the muscle, But lies on the

2:13

surface of the muscle.

2:14

In fact, switching sides between the proximal end

2:17

of the muscle and the distal end

2:19

of the muscle very, very frequently.

2:22

So not the typical appearance that you might think of, of

2:25

where the tendon is located.

2:26

Now, in terms of fiber types,

2:28

this has been mentioned were the type one fibers,

2:31

which are a slow twitch on the type two fibers,

2:34

which are fast twitch shown here on, uh, this h

2:37

and e stain, uh, uh, play a role.

2:39

But I can tell you that this is really a minor factor.

2:43

Uh, we're basically born with a particular fiber type.

2:45

It's been said that athletes can increase their proportion

2:49

of type two, but this is really, really minuscule

2:52

and I don't think this is really an important finding when

2:56

it comes to, uh, muscle injury.

2:58

We really shouldn't emphasize this.

3:00

We should emphasize length.

3:02

And it makes sense that muscles that are long,

3:04

that are exposed to two moment arms, one for example,

3:08

if we look at the hamstrings, a moment, arm at the hips

3:11

where they're stretched as the hip is extended,

3:13

another moment arm, uh, sorry, as the hip is flexed

3:17

and another at the knee where they're stretched,

3:19

as the knee is extended, you can see

3:21

that the stretch combines across the two joints,

3:24

and that makes sense that long muscles

3:26

that cross two joints are more predisposed to straight.

3:29

But I'll tell you, it's really not that simple.

3:33

I show you here the sartorious.

3:35

This is the longest muscle in our body.

3:37

It is a parallel muscle,

3:39

and we almost never see a strain involving this.

3:42

So the length of it is a factor,

3:45

but again, it's the penetration

3:47

of the muscle that's important.

3:49

This is parallel, whereas the hamstring fibers are penate

3:53

and that pation is what leads to strain.