The carpometacarpal joint of the thumb, also known as trapeziometacarpal joint, plays a vital role in the normal activity of the thumb. It must be appreciated that most of the activity of human hand depends upon the movements of thumb and index finger. Thus it can be rightfully stated that this joint is vital for functioning of hand.
Type:
The carpometacarpal joint of the thumb is a sellar (saddle) joint, and thus it enjoys a wide range of mobility.
Saddle Joint (Joint of the Thumb)
Articulating surfaces:
The joint exists between the base of first metacarpal bone and the trapezium.
Joint of the Thumb
Ligaments and capsule:
The joint is held in place by three distinct ligaments: Lateral, Anterior (Palmar) and Posterior (Dorsal).
- Lateral Ligament: It runs from the lateral side of trapezium to the radial side of metacarpal base.
- Anterior and Posterior Ligaments: They are oblique bands converging to the ulnar side of metacarpal base from the palmar and dorsal surfaces of the trapezium respectively.
There is also a strong fibrous capsule, which adds to the stability of this joint.
Synovial Membrane:
The synovial membrane lines the joint capsule and is separate from it.
Blood Supply:
The joint receives its blood supply from the radial artery and its first dorsal metacarpal branch.
Nerve Supply:
The joint is innervated by articular twigs from the posterior interosseous nerve.
Movements:
The joint shows a wide range of movements including flexion, extention, adduction, abduction and some circumduction. It can also perform opposition.
Muscles producing movements:
- Flexion: Flexor pollicis brevis (Details = Muscles of Thenar Eminence), Opponens pollicis (Details = Muscles of Thenar Eminence), Flexor Pollicis Longus
- Extension: Abductor pollicis longus, Extensor pollicis longus, Extensor Pollicis Brevis
- Abduction: Abductor pollicis longus, Abductor pollicis brevis
- Adduction: Adductor pollicis
- Opposition: Opponens pollicis, flexor pollicis brevis
- Circumduction: The abductors, flexors, extensors and adductors all acting consecutively.