Wrist Joint

Question 1

What type of joint is the wrist joint/radiocarpal?

Answer 1

It is a biaxial synovial joint of ellipsoid variety between lower end of radius and carpus.

Further notes:
The term “carpus” refers to the group of eight small bones that form the wrist in humans.

Question 2

List the 8 carpals.

Answer 2

1. Scaphoid (radius proximally, trapezium and trapezoid distally)
2. Trapezium (scaphoid proximally, 1st metacarpal distally)
3. Trapezoid (2nd metacarpal distally)
4. Lunate (medial to scaphoid on radius, capitate distally)
5. Capitate (3rd metacarpal distally)
6. Triquetrum (pisiform is attached to it, hamate distally)
7. Pisiform (hamate distally)
8. Hamate (4th and 5th metacarpal distally)

Posterior: same arrangement but pisiform won’t be seen posteriorly …
[Diagram]

Question 3

Describe the clinical significance of the pattern of blood supply to the lunate.

Answer 3

Kienböck’s disease: avascular necrosis of the lunate
NB: Lunate receives its blood supply from dorsal radiocarpal and intercarpal arch branches, via its palmar and dorsal surfaces.
[Radiograph]: Kienböck’s disease

Question 4

Describe the clinical significance of the pattern of blood supply to the scaphoid.

Answer 4

The blood supply to the scaphoid from branches of the radial artery is retrograde in nature. Scaphoid fractures are likely to lead to avascular necrosis, delaying the healing process and leading to non-union of the fracture.
[Video: 1 min 3 seconds]

Question 5

State the pattern of blood supply to the scaphoid.

Answer 5

Retrograde.

Dorsal carpal branch of the radial artery enters the scaphoid on the dorsal surface and supplies the proximal 80% of the scaphoid via retrograde blood supply.

Superficial palmar arch, a branch of the volar radial artery, supplies distal 20% of the scaphoid.

Question 6

Describe the clinical significance of the pattern of blood supply to the capitate bone.

Answer 6

Risk of avascular necrosis since the blood supply to the capitate is poor. However most capitate fractures do not progress to proximal pole avascular necrosis due to retrograde blood supply and direct supply to the proximal pole.

NB: it receives blood supply primarily from the dorsal intercarpal and dorsal basal metacarpal arches

Question 7

State the articular surfaces of the wrist joint.

Answer 7

Proximal articular surface: formed by inferior surface of the lower end of radius and inferior surface of the triangular articular disc of inferior radio-ulnar joint (concave ellipsoid surface)
Distal articular surface: formed by proximal surfaces of scaphoid, lunate and triquetral bones (smooth convex surface)

[Diagram]

Question 8

Why is the ulna not considered part of the wrist joint articulation?

Answer 8

It is excluded from the articulation by an articular disc. [Diagram]

Question 9

Why doesn’t the pisiform bone participate in the wrist joint articulation?

Answer 9

It acts primarily as a sesamoid bone to increase the leverage of the flexor carpi ulnaris and lies in a plane anterior to the other carpal bones.

Question 10

State the ligaments of the wrist joint and their extents.

Answer 10

1. Radial collateral ligament: from the tip of styloid process of radius to lateral aspects of the scaphoid and trapezium
2. Ulnar collateral ligament: from the tip of styloid process of ulna to the medial aspects of the triquetrum and pisiform bones
3. Palmar radiocarpal ligament: from anterior margin of the lower end of radius to the anterior surfaces of the scaphoid, lunate and triquetrum bones
4. Palmar ulnocarpal ligament: from the base of styloid process and adjoining part of articular disc to the anterior surface of the lunate and triquetrum
5. Dorsal radiocarpal ligament: from the posterior margin of the lower end of radius to the dorsal surface of the scaphoid, lunate and triquetrum bones.
6. [Diagram 1]

Question 11

State the relations of the wrist joint.

Answer 11

Anterior:
1. Tendons of FDS, FDP and ulnar bursa
2. Tendons of FPL and radial bursa
3. Median nerve
4. Tendon of FCR and associated synovial bursa
5. Ulnar nerve and vessels

Posterior:
1. Extensor tendons of wrist and fingers, and associated synovial sheaths
2. Anterior interosseous artery
3. Anterior interosseous nerve* check if Anterior or Posterior

Lateral:
1. Radial artery (across the radial collateral ligament)
2. Tendon of Ab.P.L.
3. Tendon of EPB

Medial: Dorsal cutaneous branch of ulnar nerve

Question 12

innervation of the wrist joint

Answer 12

posterior interosseous nerve (branch of radial nerve) and anterior interosseous nerve (branch of median nerve)

Question 13

What movements do the wrist joint permit?

Answer 13

1. Flexion and extension along the transverse axis.
2. Abduction and adduction occur along the anteroposterior axis.
3. Circumduction

Question 14

For each movement, state the muscles responsible.

Answer 14

Flexion: flexor carpi radialis, flexor carpi ulnaris, palmaris longus
Extension: extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris
Abduction: flexor carpi radialis, extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus
Adduction: flexor carpi ulnaris, extensor carpi ulnaris
Circumduction: all

Question 15

Give the range of movements of the wrist joint

Answer 15

Flexion - 60°
Extension - 50°
Abduction - 15°
Adduction - 50°

Question 16

State the boundaries of the carpal tunnel.

Answer 16

Floor (deep carpal arch): bounded medially by the pisiform bone and hook of hamate and laterally by the tubercles of scaphoid and trapezium bones [pr simply: the carpal bones]

Roof (flexor retinaculum): turns the carpal arch into the tunnel by bridging the space between the medial and lateral parts of the arch

Question 17

List the structures passing superficial to the flexor retinaculum from medial to lateral side.

Answer 17

1. Ulnar nerve
2. Ulnar artery
3. Palmar cutaneous branch of ulnar nerve
4. Tendon of palmaris longus
5. Palmar cutaneous branch of median nerve
6. Superficial palmar branch of radial artery
7. [Diagram]: the flexor retinaculum [Diagram]: structures passing superficially

Question 18

State the contents of the carpal tunnel.

Answer 18

1. Tendon of flexor pollicis longus
2. Median nerve
3. Tendons of flexor digitorum profundus
4. Tendons of flexor digitorum superficialis

Question 19

The ulnar artery and ulnar nerve lie within the canal of ____(1)____, whose roof is the ____(2)____, and whose floor is the ____(3)____.

Answer 19

(1) Guyon
(2) volar/palmar carpal ligament
(3) flexor retinaculum and pisohamate ligament
[Diagram 1] [Diagram 2]

Question 20

State the clinical relevance of the carpal tunnel.

Answer 20

Carpal tunnel syndrome: entrapment syndrome caused by entrapment of the median nerve within the carpal tunnel

Symptoms:
1. burning pain (pins and needles) along sensory distribution of median nerve (palmar aspect of lateral 3 and 1/2 digits)
2. weakness of thenar muscles
3. ape-thumb deformity may occur [a condition in which the thumb is permanently adducted, resulting in a loss of its opposable function]
4. positive Tinel’s sign and Phalen’s test

Question 21

Name one potential site of entrapment of the ulnar nerve at the wrist.

Answer 21

Guyon’s canal

Question 22

State two symptoms of ulnar canal syndrome/Guyon’s tunnel syndrome.

Answer 22

1. hyposthesia of medial 1 and 1/2 fingers
2. weakness of intrinsic muscles of the hand