Anatomy of Distal Humerus and Ulna

Distal Humerus

• The medial lip of the distal humerus is prominent and projects farther distally than the lateral lip.
• The trochlear groove is located midway between the medial and lateral lips.
• Muscles originate from the anterior and posterior aspects of the distal humerus.
• Muscles that originate on the shaft: Brachialis, brachioradialis, extensor carpi radialis longus, triceps brachii medial and lateral head
• Muscles that originate on the medial epicondyle: Pronator teres, flexor carpi radialis, palmaris longus, superficial flexor digitorum, and flexor carpi ulnaris
• Muscles that originate on the lateral epicondyle: Supinator, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus

Distal Ulna

• The ulna has a thick proximal end.
• The concave trochlear notch of the ulna is the large jawlike process located between the anterior tips of the olecranon and coronoid processes.
• The coronoid process projects sharply from the anterior proximal ulna.
• The radial notch of the ulna is an articular depression just lateral to the inferior aspect of the trochlear notch.

Elbow Joint Capsule and Ligaments

• The capsule is large, loose, and weak anteriorly and posteriorly.
• The capsule blends with the proximal border of the annular ligament except posteriorly.
• The capsule is reinforced anteriorly by oblique and vertical bands of fibrous tissue, posteriorly by the posterior ligament, and laterally/medially by the collateral ligaments.
• The medial collateral ligament arises from the medial epicondyle and consists of three sets of fibers: the anterior set, the intermediate set, and the posterior set.
• The lateral collateral ligament arises from the lateral epicondyle and consists of two (or three) sets of fibers: the anterior or radial set, the thicker intermediate or lateral set, and the posterior set.

Elbow Flexion

• Passive flexion is limited by the impact of the radial head against the radial fossa, the coronoid process against the coronoid fossa, the tension in the posterior part of the capsule, and the passive tension developed in the triceps.

Humero-Ulnar Joint

• The distal humerus resembles a bicycle fork, with the axis of the articular surfaces running through the middle portion.
• This midsection contains two fossae: the coronoid fossa (anteriorly) and the olecranon fossa (posteriorly).
• The humeral end angulates anteriorly at 45° with the shaft.
• The articular surface of the ulna is rotated 45° posteriorly to its long axis.

Elbow Flexion and Extension

• Combining active elbow flexion from extension with shoulder extension is an effective way for producing biceps-generated elbow flexor torque.
• In an open kinematic chain, extension of the elbow is performed by gravity when the arm is unloaded, but the biceps controls extension by isotonic eccentric action when weight is held.
• In a closed kinematic chain, the triceps is eccentrically controlled during elbow flexion as the body is lowered to the ground in a push-up and concentrically to extend the elbow.

Clinical Examples of Reverse Concentric Isotonic Contraction

• A person with complete paralysis of the trunk and lower extremity can use near-normal shoulder, elbow flexor, and wrist extensor muscle strength to move up to a sitting position from supine.
• A person with C6 tetraplegia can use the innervated clavicular portion of the pectoralis major and anterior deltoid to pull the humerus toward the midline, rotating the elbow into extension.

Elbow Flexor Muscles

• Brachialis:
  • One-joint muscle
  • Works in flexion of the elbow in all positions of the forearm
  • Active in all types of contractions
  • Active during slow and fast motions
• Biceps Brachii:
  • Two-joint muscle
  • Functioning is affected by the position of the shoulder
  • Mobility muscle due to its insertion close to the elbow joint axis
  • It is less effective in the beginning of the range of motion (ROM) as an elbow flexor rather than a stabilizer

Elbow Flexor Muscle Function

• Biceps Brachii:

  • Has its largest mechanical advantage (MA) between 80° and 100° of elbow flexion.
  • Produces its greatest torque in this range.
  • Has a small MA when the elbow is in full extension.
  • Is active during unresisted elbow flexion with the forearm supinated and when the forearm is midway between supination and pronation in both concentric and eccentric contractions, but it tends not to be active when the forearm is pronated.
  • Is active during rapid extension.

• Brachioradialis:

  • It is inserted at a distance from the joint axis, so the largest component of muscle force goes toward joint compression and stability
  • Shows no activity during eccentric flexor activity when the motion is slow with the forearm supinated
  • Shows no activity during slow, unresisted, concentric elbow flexion

Explore the anatomy of the distal humerus and ulna in this quiz. Learn about the prominent features of the medial and lateral lips, as well as the muscles that originate from various aspects of these bones. Test your knowledge on the key points related to their structure and function.