HAND

Important Structures of the Hand

The important structures of the hand can be categorized into several categories:

  • Bones and Joints

  • Ligaments and Tendons

  • Muscles, Nerves, Blood Vessels

    The front, or palm-side, of the hand is referred to as the palmar side. The back of the hand is called the dorsal side.

Bones and Joints

Overview of Hand Bones

  • The hand consists of various types of bones that each contribute to its functionality:
      - Phalanges: 14 bones in total found in the fingers and toes. Each finger contains three phalanges (distal, middle, proximal), but the thumb contains only two.
      - Metacarpals: Five bones that form the middle part of the hand.
      - Carpals: Eight bones that constitute the wrist. These bones are connected to the forearm bones, the ulna and the radius.

  • Proximal Row of Carpals:
      - Scaphoid
      - Lunate
      - Triquetrum
      - Pisiform

  • Distal Row of Carpals:
      - Trapezium
      - Trapezoid
      - Capitate
      - Hamate

Joints of the Hand

  • MCP Joints: Metacarpophalangeal joints are formed by the connections of the phalanges to the metacarpals and function like hinges when bending or straightening fingers and thumb.
      - IP Joints: Interphalangeal joints are of two types:
        - Proximal IP Joint (PIP Joint): Located between the proximal and middle phalanges.
        - Distal IP Joint (DIP Joint): Located between the distal and middle phalanges. The thumb has one IP joint due to its unique structure.

Ligaments

Overview of Ligaments

  • Ligaments are tough bands of fibrous tissues that connect bones together.

  • Collateral Ligaments:
      - Located on either side of each finger and thumb joint.
      - Function: Prevent abnormal lateral bending of the joints.

  • Volar Plate:
      - The strongest ligament in the PIP joint, connects proximal phalanx to the middle phalanx on the palm side.
      - Function: Prevent hyperextension of the PIP joint.
      - Loosening due to disease or injury can lead to finger deformities.

Tendons

Overview of Tendons

  • Extensor Tendons:
      - These tendons are responsible for the straightening of fingers. They originate from muscles located on the backside of the forearm.
      - Tendons pass over the wrist and divide to form the extensor hood covering the top of each finger, with branches connecting to the bones of the middle and end fingers.
      - The connection point to the middle phalanx is termed the central slip. The function is to help straighten fingers when extensor muscles contract.
      - Damage to the central slip can cause significant problems such as tears.

Muscles

Overview of Muscles

  • Hand muscles can be categorized into extrinsic and intrinsic muscles:
      - Extrinsic Muscles: Originate from the elbow or forearm, control gross movements, and provide force for grip.
      - Intrinsic Muscles: Located directly within the hand; their primary role is fine motor control.

  • Intrinsic Muscles:
      - Small muscles that guide fine finger movements, ensuring fingers are positioned correctly during activities.

  • Thumb Opposition:
      - Two muscles allow the thumb to move across the palm, vital for grasping objects.

Nerves

Overview of Nerves

  • Nerves traveling to the hand include the radial nerve, median nerve, and ulnar nerve:
      - Radial Nerve:
        - Location: Thumb-side edge of the forearm, extending toward the back of the hand.
        - Supplies sensation primarily to the back of the thumb, from thumb to the third finger.
      - Median Nerve:
        - Travels through the carpal tunnel, providing sensation to the thumb, index finger, long finger, and half of the ring finger. Controls the thenar muscles, involved in thumb opposition.
      - Ulnar Nerve:
        - Passes through Guyon's canal, providing sensation to the little finger and half of the ring finger, while supplying small muscles in the palm and thumb.

  • Issues such as pain or numbness in the hand can arise from nerve irritation due to constant bending or wrist positions.

Blood Vessels

Overview of Blood Flow

  • The Radial Artery:
      - Located at the front of the wrist near the thumb; common site for pulse measurement.

  • The Ulnar Artery:
      - Runs alongside the ulnar nerve through Guyon's canal.
      - Provides blood to the hand, with both the radial and ulnar arteries arching within the palm to supply blood to the fingers.

Muscle Groups in the Hand

Extrinsic vs. Intrinsic Muscles

  • Extrinsic Muscles:
      - Primarily located in the anterior and posterior compartments of the forearm.
      - Control gross movements and provide a strong grip.

  • Intrinsic Muscles:
      - Located within the hand, responsible for fine motor functions.

Thenar Muscles

  • Three muscles located at the base of the thumb, collectively known as the thenar eminence:
      - Opponens Pollicis:
        - Largest thenar muscle, responsible for opposition of the thumb.
        - Attachments: Tubercle of trapezium to the first metacarpal.
        - Innervation: Median nerve.
      - Abductor Pollicis Brevis:
        - On the lateral aspect of thenar eminence.
        - Innervation: Median nerve (recurrent branch).
      - Flexor Pollicis Brevis:
        - Comprising superficial and deep parts; innervated by median nerve (superficial) and ulnar nerve (deep part).

Hypothenar Muscles

  • Form the hypothenar eminence at the base of the little finger:
      - Opponens Digiti Minimi:
        - Lies below other hypothenar muscles; responsible for opposition of the little finger.
        - Innervation: Ulnar nerve.
      - Abductor Digiti Minimi:
        - Most superficial hypothenar muscle.
        - Innervation: Ulnar nerve.
      - Flexor Digiti Minimi Brevis:
        - Lateral to abductor digiti minimi.
        - Innervation: Ulnar nerve.

Lumbricals

  • Four lumbricals, crucial for finger movement, link extensor and flexor tendons:
      - Attachments: Originate from flexor digitorum profundus and insert into the extensor hood.
      - Innervation: Lateral two by median nerve, medial two by ulnar nerve.

Interossei

  • Located between metacarpal bones, divided into dorsal and palmar groups.
      - Dorsal Interossei: Four muscles responsible for abduction of fingers.
      - Palmar Interossei: Three (sometimes four) muscles responsible for adduction of fingers.

Wrist Anatomy

Major Articulations

  • The wrist consists of two major joints:
      - Radiocarpal Joint
      - Midcarpal Joint

Osteology of the Wrist

  • Ten bones comprise the wrist’s anatomy:
      - Distal radius
      - Distal ulna
      - Eight carpal bones

Ligaments of the Wrist

Overview of Wrist Ligaments

Ligament

Function

Comments

Dorsal radiocarpal ligament

Resists extremes of flexion

Attaches between the radius and dorsal carpal bones

Radial collateral ligament

Resists extremes of ulnar deviation

Strengthened by specific muscles

Palmar radiocarpal ligament

Resists extremes of wrist extension

Thickest ligament, consisting of three parts

Ulnar collateral ligament

Resists extremes of radial deviation

Stabilizes distal radioulnar joint

Carpal Tunnel

  • The transverse carpal ligament forms the carpal tunnel through which the median nerve and tendons pass.

  • Conditions such as Carpal Tunnel Syndrome can occur due to swelling in the tunnel, causing pain or paresthesia and leading to muscular weakness in the intrinsic muscles around the thumb.

Functionality and Kinesiology of the Wrist

  • The wrist can flex, extend, and move side to side (radial and ulnar deviation).

Mention of Conditions

  • The wrist is essential for the proper functioning and positioning of the hand.

  • Pain or weakness in the wrist significantly affects grip and motor control of the hand.