Arm Anatomy

• • • Arm

• Osteology

  • Humerus

    • Posterior spiral groove (for radial nerve) adjacent to the deltoid tuberosity that runs obliquely from proximal medial to distal lateral

    • Trochlea: medial spool-shaped structure; articulates with olecranon of the ulna

    • Capitellum: lateral globe-shaped structure; opposes radial head

Articular surface of distal humerus has 7-degree valgus tilt relative to shaft (carrying angle of elbow).

 

FIG. 2.5 Elbow joint including fibrous membranes of joint capsule and ligaments.

From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.

 

Table 2.4

 

Elbow Ligaments

 

 

Ligament Components Comment(S)
Medial or ulnar collateral	Anterior band	Anteroinferior portion of the medial humeral epicondyle to sublime tubercle (18 mm distal to coronoid tip) Strongest elbow ligament and primary restraint to valgus stress Taut from 60 degrees of flexion to full extension Reconstructed in UCL reconstruction (Tommy John surgery)
	Posterior band	Taut from 60 to 120 degrees of flexion Greatest change in length from flexion to extension
	Transverse band	Cooper ligament
Lateral collateral	Lateral ulnar collateral ligament	Lateral humeral epicondyle to supinator crest Deficiency results in posterolateral rotator instability
	Anular ligament, quadrate (anular ligament to radial neck), and oblique cord

Arthrology

 

 

Table 2.5

 

Muscles of the Arm/Elbow

 

 

Muscle	Origin	Insertion	Action	Innervation
Coracobrachialis	Coracoid	Midhumerus (medial)	Flexion, adduction	Musculocutaneous
Biceps brachii	Coracoid (short head) Supraglenoid (long head)	Radial tuberosity	Supination, flexion	Musculocutaneous
Brachialis	Anterior humerus	Ulnar tuberosity (anterior)	Flexing forearm	Musculocutaneous radial
Triceps brachii	Infraglenoid (long head) Posterior humerus (lateral head) Posterior humerus (medial head)	Olecranon	Extending forearm	Radial

• Elbow: hinge (ulnohumeral articulation) and pivot joint (radiocapitellar articulation)

  • Radial head should line up with capitellum at all arm positions on all radiographic views.

  • Tensile forces at medial elbow, compressive forces at lateral elbow

Capsuloligamentous structures of elbow are a key source of testable material (Fig. 2.5).

• Capsule allows maximum distension at approximately 70 to 80 degrees of flexion (patients with effusion most comfortable in this position).

• Anterior capsule attaches at a point approximately 6 mm distal to the tip of the

  coronoid.

  • Coronoid tip is an intraarticular structure that is visualized during elbow arthroscopy.

• Elbow ligaments (Table 2.4)

  • Medial or ulnar collateral ligament primary valgus stabilizer

  • Lateral ulnar collateral ligament posterolateral stabilizer

  • Osborne’s ligament stabilizes ulnar nerve in cubital tunnel.

Ligament of Struthers: variant anatomy arising from supracondylar process to attach to medial epicondyle; potential site of median nerve compression

• Muscles of the arm/elbow ( Table 2.5)

• Brachialis strongest elbow flexor and attaches to the coronoid 11 mm