Elbow Resources

Elbow functional anatomy (R)(M) Elbow functional anatomy (R)(M)


Function of the elbow
The elbow functions to position the hand in space. It allows the hand to operate at different distances from the body.

Medial collateral ligament and valgus stability.
The MCL has an anterior and posterior bundle joined by a transverse ligament. The anterior bundle is taut in all positions of the elbow but the posterior bundle is taut only during flexion.
The anterior bundle inserts into the medial coronoid process. It is the primary valgus stabilizer of the elbow and the radial head is a secondary stabilizer. If the anterior bundle is intact loss of the radial head doesn't lead to valgus instability.
If the anterior bundle is cut but the posterior bundle is retained instability results; if the anterior bundle is retained but the posterior bundle cut the elbow is still stable.

Lateral collateral ligament and varus stability
The lateral collateral ligament complex is made up of:
• Radial collateral ligament
• Lateral ulnar collateral ligament (LUCL)
• Annular ligament
The RCL and LUCL arise from the lateral epicondyle (axis of rotation).
The RCL inserts into the annular ligament.
The LUCL inserts into the tubercle of the supinator crest, distal to the annular ligament. It is an important lateral stabilizer of the humeroulnar joint and if deficient, posterolateral rotatory instability of the elbow results.
The most important stabilizer against varus forces is the ulnohumeral joint, providing 55% of resistance to varus stress in full extension, and 75% of resistance to varus stress in full flexion.

Annular ligament
This is attached at the margins of the radial notch and encircles the radial head. It is not attached to the radial head. It provides no stability to proximal migration of the radius.

Longitudinal stability
The radial head normally transmits 50% of the axial load to the distal humerus. Maximal force occurs in full extension of the elbow, with the forearm pronated and the wrist clenched. If the radial head is excised, the central band of the interosseous membrane transmits 75-85% of the axial load from the radius to the ulna.
The elbow can transmit up to 3 times body weight.

Carrying angle
The normal carrying angle is 10 degrees in males and 13 degrees in females. This is measured in full extension. If there is any flexion deformity this can give a spurious valgus deformity.

Strength
Normally flexion strength exceeds extension strength. Flexion should be tested with the elbow at 90 degrees and neutral rotation. Men are about 50% stronger than women. The dominant arm is around 10% stronger. Flexion force is greatest at angles between 90 and 100 degrees.
Normally supination is stronger than pronation.
Haemarthrosis and joint effusion
The position of maximal joint volume is 80 degrees of flexion. If a tense effusion is present, the elbow will assume this position, to minimize pressure.
A small joint effusion can be identified by loss of the infra-condylar recess (soft spot), which is located distal to the lateral condyle, adjacent to the lateral aspect of the olecranon and radial head. This is also the best spot to aspirate the elbow.

Range of motion
Normal flexion extension is from 0-145 degrees. The functional flexion arc is from 30 to 130 degrees.
Normal supination is 85 degrees; pronation is 75 degrees. Functional range is 50-50 degrees.
The axis of the radial head moves 2mm laterally in full pronation, due to the ovoid shape of the radial head. This allows some extra room for the radial tuberosity in pronation.

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