TBL6 - Bones of the Forearm and Hand

Question 1

Describe the structure of the ulna

Answer 1

The shaft of the ulna is thick proximally, tapers distally, and is enlarged by the ulnar head at the distal end

Question 2

What is noticeable about the large styloid process of the radius?

Answer 2

The large styloid process of the radius extends farther distally than the head of the ulnar; thus, only the radius contributes to the wrist joint

Question 3

What is the most common cause of Colles fracture (dinner fork) and what causes the resulting dinner fork deformity?

Answer 3

1) A complete transverse fracture of the distal 2 cm of the radius, called a Colles fracture, is the most common fracture of the forearm
2) The distal fragment is displaced dorsally and is often comminuted (broken into pieces)
3) The fracture results from forced extension of the hand, usually as the result of trying to ease a fall by outstretching the upper limb

Question 4

What is the function of the fibrous interosseous membrane?

Answer 4

The fibrous interosseous membrane interconnecting the radius and ulna distributes forces received by the radius from the hand to the ulna and humerus

Question 5

List the carpal bones from lateral to medial in each row. What two bones articulate with the radius at the wrist joint?

Answer 5

1) The wrist consists of eight small carpal bones arranged in articulated proximal and distal rows of four
2) Distal row (lateral to medial):
a) Trapezium
b) Trapezoid
c) Capitate
d) Hamate
3) Proximal row (lateral to medial):
a) Scaphoid
b) Lunate
c) Triquetrum
d) Pisiform
4) The scaphoid and lunate bones articulate with the radius at the wrist joint

Question 6

What does the distal row of carpal bones articulate with aside from the proximal row of carpal bones? What do the heads of the metacarpals articulate with?

Answer 6

1) The distal row of carpal bones articulate with the bases of the five metacarpal bones of the hand
2) The heads of the metacarpals articulate with the proximal phalanges of the five digits at the metacarpophalangeal (MCP) joints

Question 7

What is unique about the phalanx of the first digit (thumb)? What is common among the other four phalanges?

Answer 7

1) The phalanx of the first digit (thumb) articulates with the distal phalanx at a single interphalangeal (IP) joint
2) The proximal, middle, and distal phalanges of the other digits (fingers) employ two IP joints

Question 8

In anatomical position, describe the radius and ulna to be either medial or lateral

Answer 8

In the anatomical position, the radius and first digit are positioned laterally and the ulna and fifth digit are positioned medially

Question 9

Which artery is at risk when the scaphoid bone is fractured and what are clinical consequences when arterial injury occurs?

Answer 9

1) The radial artery is at risk of rupture when the scaphoid bone is fractured
2) Owing to the poor blood supply to the proximal part of the scaphoid, union of the fractured parts may take at least 3 months
3) Avascular necrosis of the proximal fragment of the scaphoid (pathological death of bone, resulting from inadequate blood supply) may occur, and produce degenerative joint disease of the wrist
4) In some cases, it is necessary to fuse the carpals surgically (arthrodesis)

Question 10

Why is fracture-separation of the distal radius common in children and what is the prognosis for normal bone growth?

Answer 10

1) Fracture–separation of the distal radial epiphysis is common in children because of frequent falls in which forces are transmitted from the hand to the radius
2) In a lateral radiograph of a child’s wrist, dorsal displacement of the distal radial epiphysis is obvious
3) When the epiphysis is placed in its normal position during reduction, the prognosis for normal bone growth is good

Question 11

How are brachydactyly and polydactyly distinguished and what causes syndactyly?

Answer 11

1) Brachydactyly - Shortened digits
2) Polydactyly - The presence of extra fingers or toes (The extra digits frequently lack proper muscle connections)
3) Syndactyly - If two or more fingers or toes are fused
4) Normally, mesenchyme between prospective digits in hand- and footplates is removed by cell death (apoptosis). However, in 1 per 2,000 births, this process fails, and the result is fusion between two or more digits (Syndactyly)