From the arm we want to move into the forearm.
Remember the bone in the arm was the Humerus.
And we talked about the different features.
The trochlea, the capitulum, the medial and lateral epicondyles.
Then we move into the forearm.
In the forearm and there are two bones, the radius, and the ulna.
Again it is important to know on which side of the forearm.
Remember we always do everything from anatomical position.
So described in anatomical position, the radius is the lateral bone of the forearm.
The ulna is the medial bone of the forearm.
Both of them have articulations with the humerus in the elbow joint.
They also have articulations with each other in what is called the proximal and distal
radioulnar joints.
And the intermediate radioulnar joint.
But we will not talk about those joints in this class.
So let’s go from the arm into the forearm.
Let's first talk about the ulna.
The how do you remember which bone is medial and lateral.
Well there are some tricks that you can use to help you remember.
If I stray from anatomical position and I raise my arm laterally, if I look at my forearm
I know now that there are two bones, a radius and ulna.
And I can hold this up and we know a radius and ulna.
When we do pronation supination the radius is the bone that is revolving.
The ulna is the bone that is underneath.
So simply remember ulna underneath.
Bring it back down to anatomical position the ulna is more medial than the radius.
If we look at the ulna, the ulna we mentioned when we did the arm in the elbow, has a large
lump on the end called the olecranon process.
The olecranon process forms that lump on the back of your elbow.
Then there is, if we look at it from a medial view, kind of a C shaped depression that is
called the trochlear notch.
That will fit on the trochlea of the humerus.
As you can see in this articulated skeleton, the trochlear notch fits over the trochlea
of the humerus to make the hinge joint of the elbow.
Immediately in front of the trochlear notch we have a coronoid process.
Do not confuse this with the coracoid process of the scapula.
This is the coronoid process of the ulna.
And if we come down off of that coronoid process of the ulna about an inch there is a small
raised area here known as the ulnar tuberosity, the ulnar tuberosity.
The remainder of the shaft of the ulna is fairly round, fairly uneventful.
However there is a raised border that is a fairly sharp edge.
That border is known as the interosseous ridge.
Keep in mind, inter-means between, and osseous refers to bone, that ridge must be between
the bones of the forearm.
So if we look at this articulated skeleton again we can see the interosseous ridge here
pointing toward the radius.
So the ridge will be between the two bones.
The interosseous ridge.
Then when we get down to the distal end of the ulna we have a small area, a small rounded
area, known as the head of the ulna.
And off of the head of the ulna is a small fingerlike projection known as the styloid
process of the ulna.
The styloid process of the ulna.
Now there are other features on the ulna that help you determine whether it is left or right.
The ulna articulates with the other bone of the forearm, the radius.
So here we have the radius.
The radius has a rounded head near the elbow end, the proximal end.
That rounded head fits into a rounded notch on the ulna.
The notch on the ulna for the radius, is known as the radial notch.
The radial notch.
So if I want to tell if this ulna is a left or right ulna, what I need to do is first
decide which is the front, and which is the back.
Keep in mind this trochlear notch allows the ulna to articulate with the humerus in a hinge
like fashion.
And your elbow bends forward.
It does not bend backwards.
So we are going to have a hinge coming forward.
Keep in mind the olecranon process is a lump on the back of your forearm.
So now we know this is the front of the ulna.
The lump has to be the back of the ulna and the lump is at the elbow.
So we have a choice, this ulna could be here, or it could be here.
But now we know that it must articulate with the radius, the other bone of the forearm.
There are two clues as to which way we are going to face this bone.
One is the interosseous ridge.
The interosseous ridge, remember, between bone ridge, must be between the two bones.
So if I were to put the front of the ulna here and hold it this way, my interosseous
ridge is right here.
That would not be between the two bones.
If I hold it here so I have the front pointing anteriorly and I have the interosseous ridge
here, now that would be between the two bones.
Also, if we come to the proximal end of the interosseous ridge that is where we see the
radial notch.
The radio notch articulates with the radius.
So again, if I were try to put that in my right forearm the radius would not be here.
Because the radius is along the lateral side of the forearm.
If I put it in my left forearm with the radial notch here that would point toward the radius.
So that should be enough information for you determine how to tell a left ulnar from a
right ulna.
Let's recap quickly the features of this ulna.
The large lump on the posterior proximal shaft of the ulna is the olecranon process.
Immediately in front of that there's a fossa known as the trochlear notch.
In front of that trochlear notch is a raised area known as the coronoid process.
You come down from the coronoid process you see the ulna tuberosity.
Immediately lateral to the coronoid process you see the radial notch.
Remember, the radial notch is on the ulna.
Then we go down along the shaft as the interosseous ridge of the ulna.
At the distal end of the ulna we have a rounded head, with a little fingerlike projection
that sticks up, known as the styloid process.
If we look at the radius, again it helps us determine a left or a right radius by comparing
it to the ulna.
We already talked about the head of the radius.
The radius has a nice round head that articulates with the ulna and the capitulum of the humerus
at the elbow joint.
We have a head, and right below the head we have an area known as the neck.
Then there is a tubercle on the radius, known as the radial tuberosity.
Then again as we go down the shaft, the shaft is fairly rounded, but there is a sharp border
on that shaft.
That sharp border is known as the interosseous ridge of the radius.
That is a big hint.
That ridge needs to point toward the other bone.
At the distal end of the radius it kind of fans out a little bit like a spoon and it
has a notch, an ulna notch.
The ulna notch is on the radius, because it is a notch for the ulna.
Just as the radial launch was on the ulna.
And, although it is not as pronounced there is a projection on the distal end of the radius
known as the styloid process of the radius.
So we have almost all of the information we need now to determine whether this is a left
or a right radius.
We know the head goes toward the elbow end.
That could be here, or here, or here, or here.
or here, here, here, here.
So what have I done?
I flipped it anterior versus posterior and medial versus lateral.
Remember, the radius is the lateral bone of the forearm.
So it either must be here, or here.
Versus here or here.
Now all we need to determine is what is the front of this bone, versus what is the back
of this bone.
So we need to know anterior versus posterior.
The easiest way to do that is to use your imagination.
I don't want to throw anybody off on this but use your imagination.
If you cup your hand, your forearm comes down and ends as a cup in your hand, anteriorly.
If I flip it over I come down and I don't end as a cup.
I end as knuckles on the back of my hand.
No don't get confused, I am not implying that these bones go out into the hand.
I am just giving you a way to keep straight anterior versus posterior.
If you look at the front of the radius it comes down and forms a cup like structure
on the distal end, whereas the posterior end of the radius comes down and has some ridges
on the back, much like you would have knuckles on the back of your hand.
So just kind of use that little bit of imagination, the cup portion of this radius is the front.
Just like your palm forms a cup in the front.
The knuckles would be the back, just like you have knuckles on the back of your hand.
Now again don't get confused, I am not implying that the radius and ulna go out into the hand,
they don't.
I'm just trying to show you some tricks that you could use to keep this straight.
So now I know the elbow end.
I know the front.
And I know the interosseous ridge must point toward the other bone.
So let's try it.
If I put this in the right forearm I have the elbow and then I have the cup in the front,
but I have the interosseous ridge pointing lateral.
That can't be between the two bones.
So this can't be a right radius.
So let's try it on the left forearm.
The head near the elbow.
The cup toward the front and now the interosseous ridge pointing toward the other bone, so this
would be a left radius.
Now let's put that together with the left ulna that I had.
So we can see how the head of the radius fits into the radial launch of the ulna.
The head of the ulna fits and the ulna notch of the radius.
Now when we are flexing and extending at the elbow, that is movement only of the ulna.
When we are doing pronation supination, that is movement of the radius, but not the ulna.
The radius will revolve around between the heads of the radius in the head of the ulna.
In pronation supination we do not move the ulna.
We revolve the radius.
Much like we see here on this articulated skeleton.
Noticed that during flexion and extension at the elbow we are not moving the radius.
The radius is going along for the ride.
During pronation supination we are not moving the ulna.
The radius is doing the moving.