The only bone found in the arm, and remember that anatomically the arm is from the shoulder
to the elbow, the only bone found in the arm is the humerus.
Now the humerus articulates with the scapula, and we've seen on the articulated skeleton
already, but here I have my left scapula, this is a left humerus, at the glenohumeral
joint, also known as the shoulder joint.
So the head of the humerus will fit into the glenoid cavity, or the glenoid fossa, of the
scapula.
How can we tell a left humerus from a right humerus?
Well again first of all you need to know that the humerus is a bone in the arm.
Not the forearm.
In the arm.
The humerus has a rounded head.
Not a full ball, but only about half of a ball.
Very smooth surface.
That smooth surface has to fit into the glenoid fossa on the scapula.
So you would not want to put the smooth surface away from the scapula.
It has to face toward the scapula.
There are many features of the humerus that will help you determine left from right.
Near the head of the humerus there are two lumps.
One is a fairly large projection called the greater tubercle, and a small one which is
anterior, known as the lesser tubercle.
So a greater tubercle, very large.
And a lesser tubercle, fairly small.
The lesser tubercle is on the anterior portion of the humerus.
Between those two tubercles is a groove known as the intertubercular groove.
Remember inter means in between.
So intertubercular groove means the groove between the two tubercles.
Now because the long head of the biceps brachii runs through this groove it is often also
referred to as the bicipital groove.
For the biceps muscle, the bicipital groove.
So on the proximal end of the humerus, the end closest to the torso, we have the head
of the humerus.
We have the greater tubercle and the lesser tubercle and the intertubercular groove.
Where the head of the humerus attaches to the rest of the humerus at a line approximately
here we have what is known as the anatomical neck of the humerus, where the head attaches
to the remainder of the shift.
Just below the greater tubercle we have an area here known as the surgical neck of the
humerus.
The surgical neck of the humerus is where the humerus is often a fractured during a
fall.
As we follow the shaft of the humerus down, approximately halfway down, not quite halfway
down, on the lateral aspect of the humerus there is a small raised triangular area.
This area is known as the deltoid tuberosity.
It is the insertion point for the deltoideus muscle.
The deltoid tuberosity.
And if you look carefully along this humerus right at that deltoid tuberosity, and if you
hold it on edge and sight down on the bone it appears that the shaft of the humorous
twists just a little bit right below the deltoid tuberosity, sort of like the twisting of a
drill bit.
That structure is known as the radial groove or the spiral groove.
Spiral groove from the name of the twisting or spiraling around.
Radial groove because the radial nerve can be found in that groove.
Then as we continue down the remainder of the shaft of the humerus we get to the features
of the humerus that are involved in helping form the elbow joint.
To tell the front of the humerus from the back of the humerus by looking at the distal
end of the humerus there are two fossas that are of some anatomical importance.
Easy to see, there's actually three fossas but there are two that are easy to see.
In the front there's a small somewhat medially located fossa.
And in the back there is a large fossa.
So small fossa to the front.
Large fossa to the back.
The fossa in the back is known as the olecranon fossa.
So you want to put the large fossa in the back.
The olecranon fossa.
How do we remember that?
Well if we look at our elbow, there's a large lump on our elbow.
When we flex at the elbow we can see a large lump.
That lump is actually the olecranon process of our ulna.
When I extend at the elbow the lump appears to disappear.
Well where did it go?
During extension that lump went into the olecranon fossa so that we have a smooth area.
So the olecranon fossa on the posterior aspect of the humerus.
The smaller fossa in the front is the coronoid fossa.
And we will see that it accommodates the coronoid process of the ulna.
Now on the medial side of this humerus at the elbow we have a medial epicondyle.
And on the lateral side we have a smaller projection known as the lateral epicondyle.
Immediately medial to the lateral epicondyle there's an area that looks as though somebody
maybe took a small ball or a marble and drove it into the bone here.
That is called the capitulum.
Medial to the capitulum, just inferior to the olecranon fossa is a rolled area known
as the trochlea.
So you can easily tell a humorous, left versus right, simply by knowing where the humerus
is located in the body and then knowing two of the features at the proximal end or two
of the features at the distal end.
You don't need the whole humerus to tell the difference.
We will recap quickly.
The head of the humerus plugs into the glenoid cavity or glenoid fossa.
We have a greater and lesser tubercle with an intertubercular groove.
The lesser tubercle and intertubercular groove are anterior.
So you can already tell if this is anterior and this is medial just that alone tells you
this is a left humerus.
If we go to the distal end of the humerus we know that there is a capitulum and a trochlea.
The capitulum is more lateral.
The trochlea is more medial.
And the large olecranon fossa is in the back.
So we know that this, from just looking at the distal end of the bone has to be a left
humerus.
Now the absolute most easiest way is to look at the whole bone.