Tommelfingeren

Tommelfingeren refers to the thumb, the first digit of the hand. In human anatomy, the thumb is highly opposable and enables a wide range of grip and manipulation tasks that distinguish human hand function. The thumb’s base articulates with the wrist at the first carpometacarpal joint (CMC I), a saddle-shaped joint that allows opposition. It also has a metacarpophalangeal joint (MCP I) and an interphalangeal joint (IP) for bending and straightening.

The thumb’s movement is produced by several muscles, most notably the thenar group—abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis—forming the thenar eminence. The adductor pollicis strengthens grip but is not part of the thenar group. Innervation is primarily by the median nerve to the thenar muscles, with the deep branch of the ulnar nerve supplying the adductor pollicis. Sensation on the thumb’s skin is largely provided by branches of the median nerve.

Functionally, the thumb enables precision grip through opposition to the index finger and various power grips. Its ability to oppose, rotate across the palm, and participate in pinching and manipulating objects underpins many daily tasks, tool use, and fine motor activities.

Common clinical issues involve the thumb’s carpometacarpal joint (basal joint arthritis), De Quervain’s tenosynovitis affecting the thumb tendons, and ligament injuries such as gamekeeper’s (skier’s) thumb at the MCP joint. Fractures at the base of the first metacarpal, known as Bennet fractures, can also occur.

Etymology: tommelfingeren is a term used in several Nordic languages to denote the thumb.