Hand Anatomy of Bones Muscles and Joints

The human hand generally has five digits - one thumb and four fingers in one hand, but the thumb is also included as fingers. Hands have hard tissues which give shape and stability. The hand is the grasping organ, forelimb of certain vertebrates that exhibits great flexibility in the digits and in the human body. 

Hands are made up of the phalanges, the carpal bones, the metacarpal bones and the wrist joint. The function of the hand is locomotion; a manipulative function. In the tip of fingers, the upper part is covered with fingernails, to improve that manipulation, whereas palms and undersides of the finger are marked by creases and ridges known as palm prints and fingerprints. The function of the palm is to improve the grip and sensitivity of the body. 

Bones of the Hand 

In the human hand, bones are divided into three distinct groups: 

• Carpals 

• Metacarpals 

• Phalanges 

Carpals 

The carpal bones have eight smalls that make the wrist of the human body, which connects the hand to the forearm. The word “carpel” is derived from “carpus”. The set of small irregular shaped bones, a total of eight are located in the wrist area. 

These bones are organised into two distinct rows proximal and distal. 

Proximal Row (Lateral to Medial) 

• Scaphoid 

• Lunate

• Triquetrum 

• Pisiform (a sesamoid bone, formed within the tendon of the flexor) 

Distal Row (Lateral to Medial) 

• Trapezium 

• Trapezoid 

• Capitate

• Hamate (projection on its palmar surface, called the hook of hamate) 

Basically, the carpal bones form an arch in the coronal plane. The flexor, retinaculum, a membranous band, spans between the medial and lateral edges of the arch, forming the carpal tunnel. Whereas the scaphoid and lunate articulate with the radius to form the wrist joint (also known as the radio carpel), distal rows have both the articulate with the metacarpals. 

Metacarpals 

These bones articulate with carpals, and distally with the proximal phalanges. 

They are in roman number and each associated with the counting.

Metacarpal IN - Thumb

Metacarpal II - index finger 

Metacarpal III - middle finger 

Metacarpal IV -  ring finger

Metacarpal V - little finger

Metacarpals consist of a shaft, a head and a base. The medial and lateral surfaces of the metacarpals are allowing attachment of the interossei muscles. 

Phalanges 

These are the bones of the fingers. The thumb has proximal and distal phalanx, while the rest of the digits have a middle, proximal and distal phalanges. 

Muscles of the Hand 

Muscles play a very important role in our body which can be divided into two groups 

• Extrinsic muscles 

• Intrinsic muscles 

Extrinsic Muscles 

The extrinsic muscles are located in the posterior and anterior compartments of the forearm. They control harsh movements and a powerful grip. 

Intrinsic Muscles 

These muscles of the hands are located within the hand itself. They are responsible for the fine motor function of the human hand. 

The muscles consist of five parts:

• Thenar muscles 

• Hypothenar muscles 

• Lumbricals 

• Palmar interossei 

• Dorsal interossei 

Thenar Muscles

There are four total thenar muscles in the human hand, they are easy and evident on the whiter side of the palmar surface of the hands, at the base of the thumb. These muscles form the ball and fleshy part of the thumb called the thenar eminence, 

These are named as follows 

Adductor pollicis, abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.

These muscles are responsible for various thumb movements, abduction, adduction, flexion, and opposition. 

Hypothenar Muscles 

The hypothenar muscles are the four small muscles of the medial compartment of the hand. The hypothenar muscles are palmaris, brevis, abductor digiti minimi, minimi muscles, opponens digiti. 

These muscles are intrinsic muscles of the hand located within the medial side of the palm. They span between the medial aspect of the carpal and metacarpal bones of the finger. These muscles form a fleshy prominence on the medial side of the palm the hypothenar eminence. 

The hypothenar muscles have great functions like little finger lateral rotation, abduction, flexion and opposition. 

Lumbrical Muscles

The lumbrical muscles, the word lumbrical comes from the Latin word ‘lumbricidae’, which means earthworm. There are four small intrinsic muscles of the hand located between the metacarpal bones, and the deep to the palmar fascia. 

The first lumbrical forms from the palmar surface and radial side of the tendon of the index finger. 

The second lumbrical forms from the radial side and palmar surface of the tendon of the middle finger.

The third lumbrical forms from the radial side of the ring and the ulnar side of the middle finger tendon.

The fourth lumbrical forms from the radial side of the little finger tendon and the ulnar side of the ring finger tendon. 

Palmar Interossei Muscles 

These muscles are small unipennate intrinsic muscles of the hand. These muscles lie on The palmar surface of the hand and along with the dorsal interossei muscles complete the space between metacarpal bones. 

Palmar interossei contain four muscles connected to the 1st, 2nd, 3rd, 4th, and 5th fingers. 

Sometimes, the 1st finger is rudimentary, the 3rd finger does not have palmar interosseous muscles. These muscles are strong adductors of the fingers, but also greatly contribute to flexion and the extension of the 2nd, 4th, and 5th finger. 

Dorsal Interossei Muscles 

In the hand anatomy, these are four muscles in the back of the hand that act to abduct ring fingers, index assists in the flexion.