Musculoskeletal: Anatomy - Elbow and forearm

Question 1

In what direction do the fibres of the interosseous membranes run?

Answer 1

Inferiorly from radius to ulna, to transmit forces to the humerus (e.g. in FOOSH)

Question 2

Which is the longer of the two forearm bones?

Answer 2

Ulna

Question 3

What palpable aspect of the forearm delineates the medial boundary between the flexor and extensor compartments?

Answer 3

Posterior border of ulna

Question 4

With what movement of the thumb is the radial styloid process most easily palpated?

Answer 4

Abduction of thumb

Question 5

Which is more distal: radial or ulna styloid?

Answer 5

Radial ~1cm more distal (also larger)

Question 6

What is the clinical significant of isolated radial or ulna fractures?

Answer 6

Likely to be associated with dislocation of nearest joint (due to shafts being bound together by interosseous membrane)

Question 7

What is a Colles fracture?

Answer 7

Complete transverse fracture of distal 2cm of the radius
Often there is an avulsion fracture of the ulnar styloid

Question 8

What is the most common fracture of the forearm?

Answer 8

Colles fracture

Question 9

Describe dinner-fork deformity

Answer 9

Seen in Colles fracture
Posterior angulation just proximal to wrist and normal anterior curvature of hand
Due to dorsal displacement of distal fragment of radius

Question 10

What is the common flexor attachment of the muscles of the forearm?

Answer 10

Medial epicondyle and supra-epicondylar ridge

Question 11

What is the common extensor attachment of the muscles of the forearm?

Answer 11

Lateral epicondyle and supra-epicondylar ridge

Question 12

What are the subcut borders of the anterior and posterior compartments of the forearm?

Answer 12

Medial: subcut border of ulna palpable posteriorly in proximal forearm and medially in distal forearm
Lateral: radial artery palpable in anterior forearm distally and laterally in proximal forearm

Question 13

Describe the functional division of anterior and posterior compartments of the forearm

Answer 13

Anterior: flexor-pronator muscles, supplied by median n. except for 1.5 exceptions supplied by ulnar n.
Posterior: extensor-supinator muscles, supplied by radial n. (directly or via deep branch)

Question 14

What does the anterior compartment of the forearm communicate with?

Answer 14

Central compartment of the palm via the carpal tunnel

Question 15

How many muscles cross the elbow joint? What is the breakdown by part/compartment?

Answer 15

17
2x arm flexors (biceps brachii, brachialis)
2x arm extensors (triceps brachii, anconeus)
5x superficial and intermediate muscles of anterior compartment of forearm (pronator teres, FCR, palmaris longus, FCU, FDS)
6x superficial muscles of posterior compartment of forearm
1x deep muscle of posterior compartment of forearm

Question 16

What is the difference in bulk and strength between flexor and extensor muscles of forearm?

Answer 16

Flexors twice the bulk and strength of extensors

Question 17

Which muscles are in what layers of the anterior compartment of the forearm?

Answer 17

Superficial (from lateral to medial attachment/course): pronator teres, FCR, palmaris longus (present in 17% of population), FCU
Intermediate: FDS
Deep: pronator quadratus, FDP, FPL

Question 18

How many muscles are in each layer of the anterior compartment of the forearm?

Answer 18

Superficial: 4
Intermediate: 1
Deep: 3

Question 19

Which muscles attach via the common flexor tendon?

Answer 19

Muscles of the superficial layer of the anterior compartment: pronator teres, FCU, FCR, palmaris longus

Question 20

Which muscles of the superficial layer of the anterior compartment of the forearm have both ulnar and humeral heads?

Answer 20

Pronator teres
FCU

Question 21

What is the proximal and distal attachment, innervation, and main action of pronator teres?

Answer 21

Proximal: humeral head to common flexor attachment, ulnar head to coronoid process
Distal: lateral aspect mid-radial shaft
Innervation: median n. (C6-7)
Action: forearm pronation, elbow flexion

Question 22

What is the proximal and distal attachment, innervation, and main action of FCR?

Answer 22

Proximal: common flexor attachment
Distal: base of 2nd metacarpal
Innervation: median n. (C6-7)
Action: wrist flexion and abduction

Question 23

What is the proximal and distal attachment, innervation, and main action of FCU?

Answer 23

Proximal: humeral head to common flexor attachment, ulnar head to olecranon and posterior ulna (via aponeurosis)
Distal: pisiform, hook of hamate, 5th metacarpal
Innervation: ulnar n. (C8)
Action: wrist flexion and adduction

Question 24

What is the proximal and distal attachment, innervation, and main action of palmaris longus?

Answer 24

Proximal: common flexor attachment
Distal: distal half flexor retinaculum and apex of palmar aponeurosis
Innervation: median n. (C7-8)
Action: wrist flexion, tenses palmar aponeurosis

Question 25

What is the proximal and distal attachment, innervation, and main action of FDS?

Answer 25

Proximal: humero-ulnar head to common flexor attachment and coronoid process, radial head to superior half of anterior radial border
Distal: shafts of middle phalanges of fingers (not thumb)
Innervation: median n. (C7-T1)
Action: flexion at PIPJ and MCPJ of fingers (not thumb)

Question 26

What is the proximal and distal attachment, innervation, and main action of FDP?

Answer 26

Proximal: proximal 3/4 of anteromedial ulna and interosseous membrane
Distal: medial part to base of distal phalanges of digits 4-5, lateral part to base of distal phalanges of digits 2-3
Innervation: medial part by ulnar n. (C8-T1), lateral part by anterior interosseous n. from median n. (C8-T1)
Actions: flexion at DIPJ

Question 27

What is the proximal and distal attachment, innervation, and main action of FPL?

Answer 27

Proximal: anterior radius and adjacent interosseous membrane
Distal: base of distal phalanx of thumb
Innervation: anterior interosseous n. from median n. (C8-T1)
Action: flexion of phalanges of thumb

Question 28

What is the proximal and distal attachment, innervation, and main action of pronator quadratus?

Answer 28

Proximal: distal 1/4 anterior ulna
Distal: distal 1/4 anterior radius
Innervation: anterior interosseous n. from median n. (C8-T1)
Action: forearm pronation, deep fibres bind radius and ulna together