0:00

So here are the different muscle

0:01

architectures I've just selected.

0:03

The most common types that we deal with,

0:06

these are considered parallel muscles, the strap

0:09

and fusiform types.

0:10

Whereas this group here with varying types

0:13

of tendon arrangement are the penate ones.

0:16

You'll notice that in the parallel

0:19

that the tendon fibers insert in parallel

0:22

with the orientation of the tendon, whereas in the penate,

0:26

they insert on the tendon as an angle,

0:29

as illustrated on this ultrasound here,

0:32

showing you the gastroc anemia, soleus confluence,

0:35

showing you the angulation

0:37

as the structures insert on their respective tendons,

0:41

there is a strap type that is segmented.

0:44

For example, the abdominal musculature,

0:47

which is a bit more predisposed

0:49

to strain than a standard strap.

0:51

But again, in general, we do rarely see

0:54

some strains in these uh, muscles,

0:57

but they're far less common than in the penate types

1:01

that we will be focusing on.

1:03

In terms of these parallel muscles, they have the capacity

1:07

to shorten quite significantly.

1:09

So the biceps, which is a classic parallel muscle

1:12

with tendons at each end, can shorten up to 50%.

1:16

Uh, nicely illustrated here by Arnold, uh, showing you

1:20

how short he can get his biceps.

1:22

Because of this, when we get injuries, the muscle

1:25

and tendon tend to retract,

1:27

and I can tell you that we see tendon damage far more

1:31

frequently than muscle damage than in this fusiform, uh,

1:35

type of, uh, architecture.

1:37

As you see in this patient

1:38

where there is a biceps tendon tear,

1:41

looks like there's some tendinosis,

1:43

and you get a great degree

1:44

of retraction in this type of muscle.

1:47

Now, the word penate comes from the word feather,

1:51

and it's a beautiful description for the architecture

1:54

of the Penn eight muscles.

1:55

And if you look at this semi menos in an elderly patient

2:00

who has quite a bit of muscle atrophy from low activity

2:03

level, that, uh, architecture becomes very, very clear.

2:07

And I think the best way to understand why this creates

2:11

so much force and why it's so powerful is to use the analogy

2:15

of a rope tug.

2:17

And if you're tugging just at the end of the rope,

2:20

you can't generate the force that you can

2:23

with multiple hands working in series.

2:26

So with this type of architecture,

2:28

we really are generating a great deal of force on the tendon

2:31

by muscle fibers that act in series.

2:35

Now, these can't shorten as much as the parallel muscles,

2:38

but they are much more powerful and generate more force.

2:42

So let's take a look at the, uh, architecture here

2:47

on a unipennate, you can see that the tendon tends

2:51

to be on the surface, uh, of the muscle.

2:54

Sorry, I don't know what happened to my picture there.

2:56

Let me go back to that. Um, so

2:59

This image taken from the visible human project

3:02

and a corresponding, uh, uh, image from one

3:05

of our patients in a unipennate architecture,

3:08

the tendon is on the surface.

3:10

This is quite common.

3:12

And here we can see, uh, for example, in the hamstrings

3:16

as well as in all of the quadriceps,

3:18

the tendon is lying on the surface.

3:21

And again, as I mentioned,

3:22

it will vary on side depending upon whether your

3:26

proximal or distal.

3:27

For example, in the rectus, when you're near the hip,

3:30

the tendon is gonna be anterior,

3:32

and then as you move down lower, it can move

3:36

to the posterior margin.

3:37

And then this will go on

3:39

and, uh, form the, uh, confluence to form the quadriceps,

3:43

uh, tendon, uh, further distally.

3:45

So with unipennate, again,

3:48

where you are imaging is gonna change

3:50

where the tendon is located,

3:52

and I think it's a really good idea for everybody

3:55

to keep one good set of normal anatomy handy, uh, so

4:00

that when you do have an injury

4:01

and you can't remember exactly

4:03

where the tendons are located, then you can use

4:06

that as a reference.

4:07

But because the tendon switches from side to side,

4:11

your injury may be located on just one side of the muscle.

4:15

It may travel across the muscle fibers over

4:18

to the other side

4:20

or be located on the opposite side, uh, more distally.

4:24

And that's not at all unusual

4:25

because the myo tendonous junctions are switching sides

4:29

as you go up and down the muscle.