The joints are formed by the articulation of the heads of the metacarpal bones with the bases of the proximal phalanges. Both bones have oval articular surfaces.
A fibrous capsule encloses each metacarpophalangeal joint. The synovial membrane lines the capsule of each joint, attaching to the margins of the articular surfaces.
The metacarpophalangeal joints are capable of a number of movements:
Muscles acting at the joint
- Flexor digitorum profundus (major flexor)
- Flexor digitorum superficialis (major flexor)
- Flexor digiti minimi (major flexor of the little metacarpophalangeal joint)
- Abductor digiti minimi (little metacarpophalangeal joint)
- Dorsal interossei
- Palmar interossei
- Extensor digitorum (middle and ring metacarpophalangeal joints)
- Extensor digiti minimi (little metacarpophalangeal joint)
- Extensor indicis (index metacarpophlangeal joint)
- A triangular collateral ligament strengthens the joint capsule on each side
- Palmar ligaments are thick plates, strongly attached to the proximal phalanx but only loosely attached to the metacarpal
- Transverse metacarpal ligaments hold the heads of the index, middle, ring and little metacarpals together.