Surface anatomy

WRIST and HAND

Organization of the wrist & hand

Bones: 14 phalanges, 5 metacarpals, 8 carpals
  - Phalanges: 14 total
  - Metacarpals: 5 total
  - Carpals: 8 total
    - Proximal row: 4 carpals
      - Scaphoid (most frequently fractured)
      - Lunate (most frequently dislocated)
      - Triquetrum
      - Pisiform (small, pea-shaped bone)
    - Distal row: 4 carpals
      - Trapezium
      - Trapezoid
      - Capitate
      - Hamate (features a hook)
Clinical Tip: A mnemonic to remember the carpals is "Straight Line To Pinky, Here Comes The Thumb"

Wrist organization

Articulation: Notice how the scaphoid and the lunate articulate with the radius.
  - This arrangement explains why the scaphoid and lunate are injured most often during falls on an outstretched hand.
  - Scaphoid: Most frequently fractured.
  - Lunate: Most frequently dislocated.
FOOSH: Acronym for "Fall on Outstretched Hand"

Gap and cartilaginous disk

There is a large gap between the head of the ulna and the triquetrum & pisiform.
A cartilaginous disk exists in between these structures.

Metacarpals and Phalanges

Metacarpals: 5
- Structure: Base, shaft, head
Phalanges: 14 total; associated joints include:
  - Metacarpophalangeal (MCP)
  - Proximal interphalangeal (PIP)
  - Distal interphalangeal (DIP)
The thumb is rotated 90 degrees compared to the other fingers.

JOINTS

Wrist Joint Introduction

The wrist joint is crucial for the functioning of the upper limb, especially at its distal part, the hand.
Moving the hand in space is essential for advanced and precise hand functions.

Wrist Joint Actions

Flexion and Extension
Radial and Ulnar Deviation: Abduction/Adduction
Important Note: Always keep the hand in the anatomical position when observing joint actions.

Metacarpal and Interphalangeal Joint Motion

Interphalangeal joints (PIP & DIP):
- Flexion & Extension
Metacarpophalangeal joint (MCP):
- Flexion & Extension
- Abduction & Adduction (action is guided by the middle finger as the axis)

Thumb Motions

Interphalangeal (IP): Flexion & Extension
Metacarpophalangeal (MCP):
- Flexion & Extension
- Abduction & Adduction
As we develop, the thumb rotates, review its motions:
  - Flexion
  - Extension
  - Abduction
  - Adduction
  - Opposition

Wrist Ligaments & Cartilage

Ligaments of the Wrist

Palmar Radiocarpal Ligament:
  - Components:
    - Radioscapholunate part
    - Radiotriquetral part
    - Radiocapitate part
Dorsal Radioulnar Ligament
Palmar Radioulnar Ligament
Ulnar Collateral Ligament: Connects ulnar side structures
- Ulnolunate Part
Palmar Ulnocarpal Ligament:
- Ulnotriquetral part

Triangular Fibrocartilage Complex (TFCC)

The TFCC is a load-bearing structure located between the lunate, triquetrum, and ulnar head.
Function: Acts as a stabilizer for the ulnar aspect of the wrist.
The TFCC is susceptible to both acute and chronic degenerative injury.

Hand Ligaments

Ligaments of the Fingers

Each of the MCP & IP joints possess a joint capsule, reinforced by:
- Collateral Ligaments: Named ulnar or radial collateral.
- Volar Plate: Its rupture can cause acute forms of Swan Neck deformity.

UCL of the Thumb

The Ulnar Collateral Ligament (UCL) is critical for stabilizing the thumb during grasping activities.
Clinical Pearl: Injury to the UCL is known as "Gamekeeper's Thumb".

Wrist Retinaculum and Spaces

Guyon’s Canal

Known as Ulnar Tunnel, consists of ulnar nerve and artery; a notable site for compression injuries.
Anatomical Coverage: Covered by the pisohamate ligament.
Clinical Pearl: Compression of the ulnar nerve in this tunnel is referred to as "handlebar palsy".

Carpal Tunnel

Formed by:
- Proximal structures: Pisiform & scaphoid tubercle
- Distal structures: Hook of the hamate & tubercle of the trapezium
Covered by: Flexor retinaculum (transverse carpal ligament)
Contents:
  - Median Nerve
  - Flexor Digitorum Superficialis
  - Flexor Digitorum Profundus
  - Flexor Pollicis Longus
Clinical Correlation: Compression of the median nerve within the tunnel leads to Carpal Tunnel Syndrome.

Anatomical Snuffbox

Borders: Formed by the tendons of the:
  - Abductor Pollicis Longus
  - Extensor Pollicis Brevis (lateral border)
  - Extensor Pollicis Longus (medial border)
Contents: Scaphoid bone; radial artery traverses the floor along with the superficial branch of the radial nerve.
Clinical Use: Used to palpate the scaphoid if a fracture is suspected.

Flexor Forearm

Know Actions, Nerve, and Group

Groups: Muscles of the common flexor tendon; consist of:
- Superficial, Middle, and Deep layers of the forearm
Hint: The term 'Flexor' indicates that it produces flexion; 'Carpi' indicates the wrist; 'Radialis' indicates position on the radial side; 'Ulnaris' indicates position on the ulnar side.

Common Flexor Tendon

Attaches to the medial epicondyle of the humerus.
Muscles attaching here:
  - Pronator Teres
  - Flexor Carpi Radialis
  - Palmaris Longus
  - Flexor Carpi Ulnaris
  - Flexor Digitorum Superficialis

Three Layers of the Flexor Forearm Muscles

Superficial Layer:
   - Muscles:
     - Pronator Teres
     - Flexor Carpi Radialis
     - Palmaris Longus
     - Flexor Carpi Ulnaris
Intermediate Layer:
- Muscle:
- Flexor Digitorum Superficialis
Deep Layer:
   - Muscles:
     - Flexor Digitorum Profundus
     - Flexor Pollicis Longus
     - Pronator Quadratus

Detailed Actions of Layers

Superficial Layer:
  - Pronator Teres: Pronation, innervated by median nerve
  - Flexor Carpi Radialis: Flexion, radial deviation, median nerve
  - Palmaris Longus: Assists with flexion, median nerve (variable presence)
  - Flexor Carpi Ulnaris: Flexion, ulnar deviation, ulnar nerve
Intermediate Layer:
- Flexor Digitorum Superficialis: Attaches to the base of the middle phalanx; causes wrist flexion and finger flexion (2-5 at PIP and MCP), median nerve
Deep Layer:
  - Flexor Digitorum Profundus: Attaches to the base of distal phalanx; finger flexion (2-5 at IP and MCP); innervation:
    - Fingers 2 & 3 = median nerve
    - Fingers 4 & 5 = ulnar nerve
    - Note: Jersey Finger refers to a rupture of the FDP from its distal attachment at the distal phalanx.
  - Flexor Pollicis Longus: Thumb flexion, innervated by median nerve
  - Pronator Quadratus: Pronation, innervated by median nerve

Extensor Forearm

Know Action, Nerve Supply and Group

Muscles:
  - Extensor Carpi Radialis Longus
  - Extensor Carpi Radialis Brevis
  - Extensor Carpi Ulnaris
Hint: 'Extensor' indicates that the muscle produces extension.
  - The name elements include:
    - 'Pollicis' for thumb
    - 'Digitorum' for fingers
    - 'Radialis' for radial side
    - 'Ulnaris' for ulnar side
    - 'Indicis' for the index finger
    - 'Digiti Minimi' for the little finger

Groups of the Extensor Forearm

Muscles of the common extensor tendon
Muscles of the mobile wad of three (Extensor Carpi Radialis Longus, Extensor Carpi Radialis Brevis, Brachioradialis)
Muscles of the out-croppers (e.g., Abductor Pollicis Longus, Extensor Pollicis Brevis)

Common Extensor Tendon

Attachment: Lateral epicondyle of the humerus
Muscles:
  - Extensor Carpi Radialis Brevis
  - Extensor Digitorum
  - Extensor Carpi Ulnaris
  - Extensor Digiti Minimi
Clinical Pearl: "Tennis elbow" refers to lateral epicondylitis.

Muscles of the Extensor Forearm Innervation

All muscles in this group are innervated by the radial nerve.
Supinator: Works in conjunction with biceps brachii to supinate the forearm.
Actions:
  - Extensor Carpi Radialis Longus & Brevis: Extend and radially deviate the wrist; part of the mobile wad of three
  - Extensor Carpi Ulnaris: Extends and deviates wrist to the ulnar side.
  - Extensor Digitorum: Extends fingers and wrist; contributes to extensor expansion.
  - Extensor Indicis: Index finger extension.
  - Extensor Digiti Minimi: Fifth finger extension.
  - Extensor Pollicis Longus: Thumb extension.

Hand Muscles

Group: Thenar Eminence Muscles

Thenar Eminence:
  - Short muscles of the thumb include:
    - Opponens Pollicis
    - Abductor Pollicis
    - Flexor Pollicis Brevis (OAF)
Actions:
  - Opponens Pollicis: Opposition of the thumb at the carpometacarpal joint (bringing pads of thumb and fifth finger together).
  - Abductor Pollicis Brevis: Abduction of the thumb (at metacarpophalangeal joint), assists in opposition.
  - Flexor Pollicis Brevis: Flexes the thumb (at carpometacarpal and metacarpophalangeal joints), assists in opposition.
Innervation: All innervated by median nerve (C6, 7, 8, T1)

Palmer and Dorsal Interosseous Muscles (PAD & DAB)

Palmar Interossei:
  - Actions:
    - Adduction of the thumb, second, fourth, and fifth fingers towards the third finger.
    - Assists in flexion of these fingers at the metacarpophalangeal joints.
  - Innervation: Ulnar nerve (C8, T1)
Dorsal Interossei:
  - Actions:
    - Abduction of the second, third, and fourth fingers at the metacarpophalangeal joints.
    - Assists in flexion of these fingers at the metacarpophalangeal joints.
    - Assists in finger extension at interphalangeal joints.
  - Innervation: Ulnar nerve (C8, T1)

Adductor Pollicis & Lumbricals

Adductor Pollicis:
- Action: Adduction of the thumb (at carpometacarpal and metacarpophalangeal joints); assists in flexion of the thumb (at metacarpophalangeal joint).
- Innervation: Ulnar nerve (C8, T1)
Lumbricals:
  - Connect to flexor digitorum profundus tendons.
  - Actions:
    - Extend fingers (2-5) at the interphalangeal joints.
    - Flex fingers (2-5) at the metacarpophalangeal joints.
  - Innervation:
    - Second and third fingers: median nerve (C6, 7, 8, T1)
    - Fourth and fifth fingers: ulnar nerve (C7, 8, T1)

Hypothenar Eminence

Muscles:
  - Opponens Digiti Minimi
  - Abductor Digiti Minimi
  - Flexor Digiti Minimi
Actions:
  - Opponens Digiti Minimi: Opposition of the fifth finger at the carpometacarpal joint.
  - Abductor Digiti Minimi: Abduction of the fifth finger; assists in opposition.
  - Flexor Digiti Minimi Brevis: Flexion of the fifth finger at the metacarpophalangeal joint; assists in opposition.
  - Innervation: All innervated by ulnar nerve (C7, 8, T1).

Extensor Expansion

Definition and Function

The extensor expansion is the specialized anatomical structure through which muscles from the extensor and flexor compartments, along with hand intrinsic muscles, coordinate to achieve full finger extension.
Muscles Contributing:
  - Flexor Digitorum Profundus
  - Extensor Digitorum
  - Lumbricals
  - Palmar Interossei
  - Dorsal Interossei

Structure and Mechanics

On the dorsum of the finger, the Extensor Digitorum tendon separates into tendonous bands:
- Central Split: Inserting into the base of the middle phalanx.
- Lateral Bands: Inserting into the base of the distal phalanx.

Finger Injuries

Mallet Finger: Rupture of the distal insertion of the Extensor Digitorum at the distal phalanx.
Boutonniere: Rupture of the central slip at the base of the middle phalanx (PIP joint).
Swan Neck: Results from rupture of the volar plate or can occur due to rheumatoid arthritis or synovitis of the FDP tendon.
Jersey Finger: Rupture of the distal insertion of the flexor tendon.