Forearm Anatomy: Unveiling the Radialposterior Interosseous Nerve

Forearm Anatomy

distal to the tip
1. Biceps brachii inserts at ulnar margin radial tuberosity (long head proximal, short head distal); powerful supinator of forearm
2. Primary elbow extensor (triceps) inserts on olecranon process.
3. Mobile wad: brachioradialis, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB)
4. Flexor-pronator mass: pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS)
1. ### Osteology
1. Ulna
2. Radius
1. Proximally: two curved processes, the olecranon and the coronoid processes, with an intervening trochlear notch
2. Distally, the ulna tapers and ends in a lateral head and a medial styloid process.
3. Proximally: head with a central fovea, neck, and proximal medial radial tuberosity (for insertion of biceps tendon)
4. Gradual bend (convex laterally) and increase in size distally
1. Restoration of the radial bow (and length) is critical in the fixation of radial shaft fractures to maintain arc of pronation and supination.
5. Distally, the radius is composed of the carpal articular surface, an ulnar notch, a dorsal tubercle (Lister tubercle, which is at the level of the scapholunate joint), and a lateral styloid process.
1. ### Arthrology: proximally includes the elbow joint and distally includes the wrist joint
1. ### Radius and ulna connected by oblique interosseous membrane/ligament (disrupted in Essex-Lopresti injury), which transmits axial load from radius at wrist to ulna at elbow
2. Muscles (** Fig. 2.6 , Table 2.6): arranged according to both location and function
1. Volar flexors (superficial and deep) ( Fig. 2.7)
2. Dorsal extensors (superficial and deep) (see Fig. 2.7)
3. 4.




FIG. 2.6 Muscle attachments of the forearm (anterior and posterior views). From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone.




| --- FIG. 2.7 Volar flexors (superficial and deep). From Drake RL et al, editors: Gray’s atlas of anatomy, ed 2, Philadelphia, 2015, Churchill Livingstone. Muscles of Forearm Muscle | ** Origin | Insertion | Action | Innervation |
| --- | --- | --- | --- | --- |
| Superficial Flexors Pronator teres | Medial |
| epicondyle and coronoid | Midlateral |
| radius | Pronating, flexing forearm | Median nerve Flexor carpi radialis | Medial |
| epicondyle | Second and third metacarpal bases | Flexing wrist | Median nerve Palmaris longus | Medial |
| epicondyle | Palmar |
| aponeurosis | Flexing wrist | Median nerve Flexor carpi ulnaris | Medial |
| epicondyle and posterior ulna | Pisiform | Flexing wrist | Ulnar nerve Flexor digitorum superficialis | Medial |
| epicondyle, proximal anterior ulna, | Base of middle phalanges | Flexing PIP joint | Median nerve | and anterior radius | |
| --- | --- | --- | --- | --- |
| Deep Flexors Flexor digitorum profundus | Anterior and medial ulna | Base of distal phalanges | Flexing DIP joint | Median–anterior interosseous/ulnar nerves Flexor pollicis longus | Anterior and lateral radius | Base of distal phalanges | Flexing IP joint, thumb | Median–anterior interosseous nerve Pronator quadratus | Distal ulna | Volar radius | Pronating hand | Median–anterior interosseous nerve |
| Superficial Extensors Brachioradialis | Lateral |
| supracondylar humerus | Lateral distal radius | Flexing forearm | Radial nerve Extensor carpi radialis longus | Lateral |
| supracondylar humerus | Second |
| metacarpal base | Extending wrist | Radial nerve Extensor carpi radialis brevis | Lateral |
| epicondyle of humerus | Third |
| metacarpal base | Extending wrist | Radial nerve Anconeus | Lateral |
| epicondyle of humerus | Proximal |
| dorsal ulna | Extending forearm | Radial nerve Extensor digitorum | Lateral |
| epicondyle of humerus | Extensor |
| aponeurosis | Extending digits | Radial–posterior interosseous nerve Extensor digiti minimi | Common |
| extensor tendon | Small finger extensor expansion over proximal phalanx | Extending small finger | Radial–posterior interosseous nerve Extensor carpi ulnaris | Lateral |
| epicondyle of humerus | Fifth |
| metacarpal base | Extending/adducting hand | Radial–posterior interosseous nerve |
| Deep Extensors Supinator | Lateral |
| epicondyle of humerus, ulna | Dorsolateral radius | Supinating forearm | Radial–posterior interosseous nerve Abductor | Dorsal | First | Abducting/extending | Radial–posterior pollicis longus | ulna/radius | metacarpal base | thumb | interosseous nerve | --- | --- | --- | --- | --- | Extensor pollicis brevis | Dorsal radius | Thumb |
| proximal phalanx base | Extending thumb MCP joint | Radial–posterior interosseous nerve Extensor pollicis longus | Dorsolateral ulna | Thumb dorsal phalanx base | Extending thumb IP joint | Radial–posterior interosseous nerve Extensor indicis proprius | Dorsolateral ulna | Index finger extensor apparatus (ulnarly) | Extending index finger | Radial–posterior interosseous nerve |
5. Table 2.6