The Elbow Complex: Part I

As I tell my PT students at Franklin Pierce University, “The elbow is as simple as it is complex.
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What I really mean by this is that the elbow is often thought of as this simple hinge joint, when in actuality there is a symphony of musculotendinous activation, neuromuscular input, static and dynamic stabilization, and complex joint kinematics that go into human motion at this area.  The elbow is not a simple hinge joint, but rather is made up of three complex joints, with the primary function of providing mobility to the wrist-hand complex.  Without the elbow, we would walk around like a T-Rex, with no ability to get our hand in functional positions.Below, you will find Part 1 of a 4 part series on the elbow.  These parts include considerations in:

1.) Anatomy,
2.) Kinesiology,
3.) Common Injuries
4.) Different treatment approaches to simple elbow pain and dysfunction.

ELBOW ANATOMY

BONY CONGRUENCY

The elbow complex is an innately stable joint.   It is comprised of three joint articulations between the humerus, ulna, and radius.  There are numerous muscular attachments, a majority of which are involved in the mobility of the wrist and hand for functional mobility.

elbow-bony-anatomy

Bony anatomy of the elbow

elbow-ligamentous-anatomy

Ligamentous anatomy of the elbow.

     As you can see from the the pictures listed, both the bony congruency and ligamentouselbow-anatomy-joint-capsule attachments make the elbow one of the most stable joints in the body.  If we take a closer look at the proximal portion of the ulna, you will notice the deep socket that is created to form the trochlear notch (aka, semi-lunar notch).  This semi-circular notch allows the trochlea of the humerus to be surround by approximately 200 degrees of bony coverage, (see picture on right) creating amazing amount of stability.

In contrast, the radial head is much more mobile, as it encompasses two joints in the elbow complex (Humeroradial and Proximal Radioulnar joints).  This is where articulation occurs to allow us to turn over our wrist to grab our pen, or grasp a spoon to bring food to our mouths.  This is where the complexity of the elbow joint comes into play, which will be discussed in Part 2 – Kinesiology of the Elbow.



LIGAMENTOUS SUPPORT

     Not only does the elbow have great bony congruency, it is surrounded by a network of ligaments, joint capsule, and fascia, which all reinforce its stability.  Of most importance, arguably, is the Ulnar Collateral Ligament (UCL), which is the primary structure that limits valgus stress (lateral angulation of the forearm in relation to the humerus).  The UCL is comprised of three bundles (anterior, posterior, and transverse), of which the anterior band is most injured in throwers.  This is the primary passive restraint to valgus force during elbow flexion from 20 to 120 degrees, which is why this bundle is the most injured during throwing  and oft repaired or reconstructed in the (in)famous “Tommy John” surgery.

lateral-elbow

medial-elbow

     On the lateral side of the elbow, there are several structures that provide stability, termed the Lateral Collateral Ligament Complex.  This includes the lateral collateral ligament (LCL), lateral ulnar collateral ligament (LUCL), and the annular ligament.   Of most importance is likely the annular ligament, which provides stability to the proximal radioulnar joint, maintaining congruency of the joint.  When this structure is injured (usually through falling on out-stretched arm with forearm in supination), the elbow lacks posterolateral stability and the radial head dislocates posteriorly.

The joint capsule is a fairly large, loose structure at rest.  I like to think of it as an accordion, where as the elbow reaches the limits of extension the anterior joint capsule tightens, and with flexion it becomes more lax.   The joint capsule surrounds the three joints of the elbow, providing one extra layer of stability.


rondo-dislocation

Falling on out-stretched arm, with forearm in supination, may lead to posterolateral instability and elbow dislocation.

MUSCULOSKELETAL CONSIDERATIONS

     The muscular attachments at or around the elbow joint serve for the function of assisting the hand and wrist.  So much so, that with repetitive work and motions of the hand/wrist, we see this present as elbow pain because of the proximal anatomical connection.  These injuries will be presented in Part 3 – Common Injuries of the Elbow.

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  • Elbow Flexors:
    • Biceps Brachii
    • Brachioradialis
    • Brachialis
  • Elbow Extensors:
    • Triceps Brachii
    • Anconeus
  • Forearm Rotators:
    • Supinator
    • Pronator teres
    • Pronator quadratus
  • Wrist Flexors:
    • Flexor carpi radialis
    • Flexor carpi ulnaris
    • Flexor carpi digitorum superficialis
    • Flexor carpi digitorum profundus
    • Palmaris longus
  • Wrist Extensors:
    • Extensor carpi radialis longus
    • Extensor carpi radialis brevis
    • Extensor digitorum communis
    • Extensor carpi ulnaris
    • Extensor digiti minimi

SUMMARY

     As mentioned, the anatomy of the elbow is as simple as it is complex.  We have only scratched the surface with the anatomy in this post.  What is not mentioned in this article is the importance of the fascial connections, peripheral nerves, and neuromuscular connections.  Part II will focus on Kinesiology, where we will touch on some of these topics.
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