The Thumb

Question 1

Classify the 1st carpometacarpal joint

Answer 1

synovial, multiaxial, simple, saddle joint

Question 2

Classify the 1st metacarpophalengeal joint

Answer 2

synovial, multiaxial, simple, condyloid joint

Question 3

Classify the 1st IP joint

Answer 3

synovial, uniaxial, simple, hinge joint

Question 4

What is the nerve supply to the 1st carpometacarpal joint?

Answer 4

Twigs from anterior and posterior interosseous nerve – C7, 8

Question 5

What is the nerve supply to the 1st MCP joint

Answer 5

Twigs from the median nerve – C7

Question 6

What is the nerve supply to the 1st IP joint

Answer 6

Twigs from the median nerve – C7

Question 7

Describe the articular surfaces of the 1st carpometacarpal joint

Answer 7

• Between trapezium and base of 1st metacarpal
• Reciprocally concavoconvex surfaces create saddle joint
• Coated in hyaline cartilage
• Trapezium is concave AP and convex transversely.
• Base of 1st metacarpal is concave transversely and convex AP.

Question 8

Describe the articular surfaces of the 1st metacarpophalengeal joint

Answer 8

• Rounded head of metacarpal
  o Biconvex
  o Wider anteriorly than posteriorly
  o Articular surface does not extend far posteriorly
  o Curvature is greater transversely than AP
• Shallow oval concavity of base of proximal phalanx
  o Small articular surface
  –> Increased anteriorly by palmar ligament
• Coated in hyaline cartilage

Question 9

Describe the articular surfaces of the 1st interphalengeal joint

Answer 9

• Pulley shaped head of the proximal phalanx
• Base of the distal phalanx
  o Median ridge separates two shallow facets
• Palmar ligament attaches to anterior margin of base of distal phalanx – increasing the articular surface

Question 10

Describe the joint capsule of the 1st carpometacarpal joint

Answer 10

• Loose but strong fibrous capsule
• Lined in synovial membrane
• Completely surrounds the joint
• Attaches to articular margins of trapezium and base of 1st metacarpal
• Thickened laterally by radial carpometacarpal ligament
• Thickened anteriorly and posteriorly by the anterior and posterior oblique ligaments.

Question 11

Describe the joint capsule of the 1st metacarpophalengal joint

Answer 11

• Loose fibrous capsule
• Surround the joint
• Attaches to articular margins (closer postieorly)
• Strengthened at sides by collateral ligaments
• Strengthened posteriorly by expansion of extensor pollucis longus
• Capsule replaced anteriorly by palmar ligament
• Synovial membrane lines all non-articular surfaces
  o Anterior and posterior recesses when the joint is extended

Question 12

Describe the joint capsule of the 1st interphalengeal joint

Answer 12

• Fibrous capsule completely surrounds the joint
• Replaced anteriorly by the palmar ligament
• Strengthened at the sides by collateral ligaments

Question 13

What are the attachments of the radial carpometacarpal ligament?

Answer 13

O: lateral surface of trapezium

I: lateral base of 1st metacarpal

Question 14

what is the function of the radial carpometacarpal ligament?

Answer 14

Strengthens the joint capsule

Question 15

What are the attachments of the anterior/posterior oblique ligaments?

Answer 15

O: anterior/posterior surface of trapezium

I: converge to insert on medial side of 1st MC

Question 16

What is the function of the anterior oblique ligament?

Answer 16

limit thumb extension

Question 17

what is the function of the posterior oblique ligament?

Answer 17

limits thumb flexion

Question 18

what are the main stabilisers of the 1st CMC joint?

Answer 18

Tendons crossing the joint line. E.g. abductor pollicis longus, extensor pollucis brevis

Question 19

What are the static stabilisers of the 1st CMC joint?

Answer 19

shape of articular surfaces and loose fibrous capsule means that large degree of mobility, little stability

Question 20

What are the stabilising factors of the 1st MCP joint?

Answer 20

tendons of the flexor pollucis longus and extensor pollucis longus & brevis, abductor pollicis brevis

Collateral ligiamente

Question 21

What is a power grip?

Answer 21

o Thumb flexed and opposed at CMC joint
o Extended at IP joint
o Used in function activity – holding screwdriver, hook type in carrying bags.

Question 22

What is a precision grip?

Answer 22

o Handle small objects between fingers and opposed thumb

o Finer control of digits

Question 23

What are the boundaries of the anatomical snuffbox?

Answer 23

Scaphoid (floor)

Abductor pollucis longus & Extensor pollucis brevis (laterally)

Extensor pollucis longus (medially)