AssessmentsBones of the upper limb
Bones of the Upper Limb
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
Contributors:Ursula Florjanczyk, MScBMC, Elizabeth Nixon-Shapiro, MSMI, CMI, Tanner Marshall, MS, Jerry Ferro, Evode Iradufasha, MD
The upper limb is connected to the axial skeleton, which is the cranium, vertebral column, and associated thoracic cage, by the bony pectoral girdle at the sternoclavicular joint, which is the connection between the clavicle and sternum.
Each upper limb is made up of 32 bones, and has a number of different regions.
Then there’s the arm, which only has one bone, called the humerus.
OK, now let’s have a look at the shoulder girdle first.
The scapula helps to connect the rest of the upper limb to the trunk, while stabilizing and assisting the shoulder during movement while serving as an attachment point for numerous muscles and ligaments.
Now, like any respectable triangle, the scapula has three borders; the shortest and the thinnest of them is the superior border.
Then there’s the medial border, which runs parallel to the vertebral column, and finally, there’s the lateral border which is the thickest one.
The lateral border is also known as the axillary border because it points towards the axilla, or armpit region.
The point where the medial and lateral borders meet is the inferior angle, and we also have the superior angle which is the junction of the superior and medial borders.
Immediately lateral to the notch, the scapula has a bony projection called the coracoid process, which is this bony hook that first projects anteriorly, and then curves towards the lateral side similar to a bent finger.
The coracoid process serves as an attachment point for four structures including the coracoacromial ligament, the pectoralis minor muscle, the coracobrachialis muscle, and the short head of the biceps brachii.
If we flip the scapula over, we can see its posterior surface.
Below the superior border, there’s a prominent ridge of bone called the spine of the scapula, which becomes broader as it extends laterally and superiorly to give rise to the acromion process, or simply the acromion.
This is where a muscle called the infraspinatus attaches.
The space above the spine is called the supraspinous fossa, and as you might have guessed it… well, it is an attachment point for the supraspinatus muscle.
No surprises here!
And the coracoacromial ligament stabilizes this joint.
Ok, now the tip of the acromion articulates with the lateral end of an S-shaped bone called the clavicle, forming the acromioclavicular joint, which helps with stability and motion of the shoulder joint.
The medial two thirds of the clavicle are convex anteriorly, and the lateral third is flattened and concave anteriorly.
Medial to the trapezoid line, there’s the conoid tubercle, which is where the conoid ligament attaches.
Both the trapezoid and the conoid ligaments help stabilize the pectoral girdle.
When determining the orientation of the clavicle, it is good to remember that the lateral portion is flat, and the inferior surface is rough compared to the smooth superior surface.
The clavicle is also one of the bony boundaries of the cervico-axillary canal, which is a passageway that extends between the upper limb and the neck, so the clavicle also protects the neurovascular bundle supplying the upper limb.
Now that was a lot of info!
Feel free to take a second to pause the video and see if you can label these missing parts of the scapula from A to F?
OK, now let’s look at that single bone in the arm, the humerus.
Proximally, the humeral head articulates with the glenoid cavity to form the glenohumeral joint, while the distal end of the humerus articulates with the radius and ulna distally to form the elbow joint.
Towards its distal end, the humerus flattens a bit, giving rise to two bony projections known as the medial and lateral epicondyles.
Above the lateral epicondyle, there’s the lateral supracondylar ridge, which is a roughened ridge of bone where the extensor carpi radialis longus, the brachioradialis muscle, and the triceps brachii muscles attach.
Finally, the tip of the distal humerus, referred to as the condyle of the humerus, has two articular surfaces, which makes sense as it articulates with the two bones of the forearm; the radius and ulna.
Medially, there’s the trochlea, which literally translates to “pulley”; which is lucky, because it really looks like one!
It can be difficult to remember which fossa articulates with which bone, so you can try and remember the phrase ‘CRAzy TULips’.
The CRA in CRAzy represents the Capitulum articulating with the RAdius, and the TUL in TULips represents the Trochlea articulating with the ULna.
Lateral to the coronoid fossa there’s the radial fossa, which sits just proximally to the capitulum.
If we flip the bone and look on the posterior side just at the same level, there is a much larger depression called the olecranon fossa, which accommodates the olecranon process of the ulna when the forearm is fully extended.
Next up, there’s the forearm, which is made of two parallel bones; the ulna, medially, and the radius, laterally.
You can remember their position when you text your friends “UM, RLy?”!
The ulna is the main stabilizing bone of the forearm.
The upper limb starts from the pectoral girdle to hand. The pectoral girdle is made up of the clavicle and scapula. Next is the arm, which contains the humerus, the forearm containing the radius and the ulna; the wrist made up of the carpals; the hand made up of the metacarpals; and finally, digits contain phalanges. Each bone has a unique shape that helps it perform its specific function.