The hands, wrists, and fingers are the most distal (near the end) part of the upper extremities or upper limbs. The hand’s complex anatomy gives it excellent flexibility and allows the hand to perform essential functions for everyday life. The basic parts of the hands may be divided into three sections: the wrist or carpus, the metacarpus or the palm, and the digits or the fingers(1).
Anatomy of the Wrist
The wrist allows the hand to move in different directions. The wrist is where the hands attach to the bones of the forearm (radius and ulna)(2).
Bones of the Wrist
The wrist is made up of eight small and irregularly shaped bones. These bones are collectively known as the carpal bones and divided into two groups, based on their location(3). On the upper side or proximal row of the wrist are the following bones(4):
- Triquetrum, a pyramid-shaped bone
- Pisiform, the smallest of all carpal bones
- Scaphoid, the largest of the proximal row carpal bones
- Lunate, a crescent-shaped bone
Meanwhile, on the lower side or distal row of the wrist are(5):
- Trapezium, the first distal carpal bone found under the thumb
- Trapezoid, the bone to the side of the thumb
- Hamate, the bone under the pinky finger
- Capitate, the largest of all carpal bones and is found in the center of the wrist
Ligaments of the Wrist
Together with the carpal bones, the wrist joint is made up of soft tissues, such as nerves, blood vessels, tendons, and ligaments. There are four notable ligaments in the wrist joint(6):
- Palmar radiocarpal, the ligament on the palmar side (near the front) of the wrist, which helps ensure that the wrist joint does not overextend
- Dorsal radiocarpal, the ligament found on the dorsal side (near the back) of the wrist, which helps limit the wrist joint’s full flexion or bend
- Ulnar collateral, the ligament that allows the hands to move with the radius
- Radial collateral, the ligament that stretches from the trapezium to the forearm’s radius bone
Additionally, the wrist joint contains a two-layered joint capsule, which offers additional structural support to the joint(7). This joint capsule’s inner layer produces synovial fluid, a liquid that ensures the joint is well lubricated(8).
Anatomy of the Palm
The palm is also known as the metacarpus. The palm is where the muscles that balance finger movements are found(9). The metacarpus also contains the bones that connect the fingers to the wrist.
Bones of the Hand
The metacarpus consists of five bones(10). Each metacarpal bone features a base, shaft, and head. The base of the metacarpal bones connects to the carpal bones(11). The rounded head of the metacarpals makes up the knuckles prominently seen on the back of the hand. The metacarpal heads are also where the bones of the fingers are attached. The bones are named metacarpal bones 1- 5, starting from the thumb and going to the pinky finger(12).
- Metacarpal bone 1 connects to the thumb and is the thickest and shortest metacarpal bone.
- Metacarpal bone 2 is the base of the pointer finger and is the bone with the largest base and longest shaft.
- Metacarpal bone 3 is the base of the middle finger.
- Metacarpal bone 4 connects to the ring finger.
- Metacarpal bone 5 connects to the pinky finger and is the smallest of the five metacarpals.
Muscles of the Hand
The hand muscles are divided into two categories: intrinsic and extrinsic muscles(13).
The intrinsic muscles help with motor balance and control. A study noted that intrinsic muscle function may be required for a stronger and more functional grasp or hand closing(14). The intrinsic muscles are made up of five muscle groups(15):
- Lumbrical, which originate from two tendons (extensor digitorum communis and flexor digitorum profundus)
- Thenar, which controls the thumb movements
- Hypothenar, which moves the little finger
- Palmar interossei, which allows finger adduction (moving away from the midline or spreading the fingers)(16)
- Dorsal interossei, which allows finger abduction (moving towards the midline or bringing the fingers together)(17)
The extrinsic muscles originate from the forearm and stretch into the hand. The extrinsic muscles include the flexor carpi ulnaris, flexor digitorum profundus, and flexor digitorum superficialis(18).
Anatomy of the Fingers
In medical settings, the fingers are also referred to as digits. The fingers are named digits 1-5, starting from the thumb and ending at the little finger.
Bones of the Fingers
One hand has 14 finger bones or phalanges(19). These bones are divided into three parts: the head, base, and shaft or body. The types of bones in the fingers are(20):
- Proximal phalanges, which are the largest bones in the fingers
- Middle phalanges, which are capable of flexing and extending the joint between the distal phalanges, though at a limited capacity
- Distal phalanges, which are shorter than the other phalanges
The structure of the thumb differs from that of the other fingers(21). The proximal phalanx of the thumb is shorter and thicker than other phalanges. Moreover, the thumb does not have a middle phalanx(22). Instead, the proximal phalanx of the thumb connects directly to the distal phalanx. Reliable knowledge of the hand’s anatomy is crucial for diagnosing acquired and congenital hand conditions. A small traumatic hand injury may cause significant hand stiffness and eventual loss of function, especially if it is not treated immediately or properly(23).