Atlas of Anatomy

20 Elbow & Forearm

Radius & Ulna

Fig. 20.1   Radius and ulna
Right forearm.

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Elbow Joint

Fig. 20.2   Elbow (cubital) joint
Right limb. The elbow consists of three articulations between the humerus, ulna, and radius: the humeroulnar, humeroradial, and proximal radioulnar joints.

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Fig. 20.3   MRI of the elbow joint
Sagittal section.

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Fig. 20.4   Humeroulnar joint
Sagittal section through the humeroulnar joint, medial view.

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Assessing elbow injuries
The fat pads between the fibrous capsule and synovial membrane are part of the normal anatomy of the elbow joint. The anterior pad is most readily seen on a sagittal MRI while the posterior pad is often hidden within the bony fossa (Fig. 20.3). With an effusion of the joint space, the inferior edge of the anterior pad appears concave as it gets pushed superiorly by the intra-articular fluid. This causes the pad to resemble the shape of a ship's sail, thus creating a characteristic "sail sign." The alignment of the prominences in the elbow also aids in the identification of fractures and dislocations.

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Ligaments of the Elbow Joint

Fig. 20.5   Ligments of the elbow joint
Right elbow in flexion.

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Table 20.1 Joints and ligaments of the elbow

Joint

Articulating surfaces

Ligament

Humeroulnar joint

Trochlea

Ulna (trochlear notch)

Ulnar collateral l.

Humeroradial joint

Capitellum

Radius (articular fovea)

Radial collateral l.

Proximal radioulnar joint

Radius (articular circumference)

Ulna (radial notch)

Annular l.

Fig. 20.6   Joint capsule of the elbow
Right elbow in extension, anterior view.

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Radioulnar Joints

images The proximal and distal radioulnar joints function together to enable pronation and supination movements of the hand. The joints are functionally linked by the interosseous membrane. The axis for pronation and supination runs obliquely from the center of the humeral capitellum through the center of the radial articular fovea down to the styloid process of the ulna.

Fig. 20.7   Supination
Right forearm, anterior view.

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Fig. 20.8   Pronation
Right forearm, anterior view.

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Subluxation of the radial head ("nursemaid's elbow")
When small children are abruptly pulled up by their arm, the immature head of the radius can dislocate from the annular ligament, resulting in painful pronation.

Fig. 20.9   Proximal radioulnar joint
Right elbow, proximal (superior) view.

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Radius fracture
Falls onto the outstretched arm often result in fractures of the distal radius. In a "Colles' fracture," the distal fragment is tilted dorsally.

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Fig. 20.10   Distal radioulnar joint rotation
Right forearm, distal view of articular surfaces of radius and ulna. The dorsal and palmar radioulnar ligaments stabilize the distal radioulnar joint.

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Muscles of the Forearm (I)

Fig. 20.11   Anterior muscles
Right forearm, anterior view. Muscle origins (O) are shown in red, insertions (I) in blue.

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Muscles of the Forearm (II)

Fig. 20.12   Posterior muscles
Right forearm, posterior view. Muscle origins (O) are shown in red, insertions (I) in blue.

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Muscle Facts (I)

Fig. 20.13   Anterior compartment
Right forearm, anterior view.

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Fig. 20.14   Superficial and intermediate groups
Right forearm, anterior view.

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Fig. 20.15   Deep group
Right forearm, anterior view.

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Muscle Facts (II)

Fig. 20.16   Radialis group
Right forearm, posterior view.

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Table 20.3 Posterior compartment of the forearm: Radialis muscles

Muscle

Origin

Insertion

Innervation

Action

images Brachioradialis

Distal humerus (distal surface), lateral intermuscular septum

Styloid process of the radius

Radial n. (C5, C6)

Elbow: flexion Forearm: semipronation

images Extensor carpi radialis longus

Lateral supracondylar ridge of distal humerus, lateral intermuscular septum

2nd metacarpal (base)

Radial n. (C6, C7)

Elbow: weak flexion Wrist: extension and abduction

images Extensor carpi radialis brevis

Lateral epicondyle of humerus

3rd metacarpal (base)

Radial n. (C7, C8)

Fig. 20.17   Radialis muscles of the forearm
Right forearm.

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Muscle Facts (III)

Fig. 20.18   Superficial group
Right forearm, posterior view.

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Fig. 20.19   Deep group
Right forearm, posterior view.

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Fig. 20.20   Muscles of the posterior forearm
Right forearm, posterior view.

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