Hand pt 2

Other names of extensor hood mechanism

Other names of extensor hood mechanism

Extensor expansion, extensor apparatus, aponeurosis, retinaculum, dorsal hood

These tendons terminate in the extensor hood mechanism

Extrinsic extensors, lumbricals, and interossei

Role of the extensor hood mechanism

• extend the digits in different positions of finger flexion

• to provide shortcuts for the extensor tendons and to permit the digits in full flexion.

Two Systems of the extensor assembly

1. Tendinous System

2. Retinacular System

This tendon will attach to the base of the proximal phalanx and then will give off 3 bands

Extensor digitorum communis

Direct continuation of the extensor digitorum tendon; attaches to the dorsal side of the base of the middle phalanx

Central Band

The central band attaches to?

dorsal side of the base of the middle phalanx

course on either side to the PIP joint and continue over mid phalanx and insert to the base of DIP joint

Lateral Band

The lateral bands insert to?

base of DIP joint

This muscle originates from the FDP tendon then inserts to the lateral band

Lumbricals

This muscle originates from the sides of the MCP → Proximal phalanx → Dorsal hood expansion

Interossei

Has a separate muscle belly in the forearm

Extensor indicis

Triangular sheet of aponeurosis located at the proximal end of the extensor mechanism

Dorsal expansion / Extensor Hood

Types of fibers of the Dorsal Expansion

1. Transverse Fibers

2. Oblique fibers

The dorsal expansion attaches to the _______ forming a _____

volar plates forming a sling

Function of the Transverse fibers of the extensor hood

connects the extensor tendon with either side of the palmar plate at the MCP joint

Function of the oblique fibers of the extensor hood

course distally and medially to fuse with the lateral and central bands

provide stability and support act as check-rein structures, helping to prevent bowstringing of the extensor tendons during finger extension

Oblique retinacular ligaments

Attachments of the ORLs

sides of proximal phalanx and annular + cruciate pulleys volarly → Lateral bands

Anatomic Snuffbox is AKA

Fovea Radialis

Triangular depression located immediately distal and slightly dorsal to the radial styloid process

Fovea Radialis / Anatomic Snuffbox

Lateral border of the Anatomic Snuffbox

Tendon of Abductor pollicis Longus (most lateral) → Extensor Pollicis Brevis

Medial border of the Anatomic Snuffbox

Extensor pollicis longus tendon

What artery can be felt in the Fovea Radialis

Radial Artery

The anatomic snuffbox is used to identify this type of fracture

Scaphoid fracture

formed anteriorly at the wrist by a deep arch formed by the carpal bones and flexor retinaculum

Carpal Tunnel

Medial Attachment of the Carpal Tunnel

Pisiform + hook of hamate

Lateral attachment of the Carpal Tunnel

Distal End of Radius

Contents of the Carpal Tunnel

1. 4 tendons of FDS

2. 4 tendons of FDP

3. Median nerve

4. FPL tendon

Functional Position of the hand

1. Slight wrist extension (20 deg)

2. Slight wrist ulnar deviation (10 deg)

3. Fingers moderately flexed at the MCP joints (45 deg)

4. Fingers moderately flexed at the PIP joint (30 deg)

5. Fingers slightly flexed at the DIP joint

Grip used primarily to support or carry an object

Hook Grip

Finger Contribution to Hook Grip

Primary - FDS

Secondary - FDP

Thumb Contribution to Hook Grip

Does not contribute to this grip. It is held in extension, away from the hand

Grasp objects that are cylindrical in shape and large enough that the thumb does not touch the fingers

Cylinder Grip

Finger Contribution to Cylinder Grip

Primary - FDP → FDP (increased force)

Interossei flex the MCP and ulnar deviate

Thumb Contribution to Cylinder Grip

• Flexes and Adducts

• Rotation occurs depending on the width of the grip

Which grip has the fingers more spread apart, Spherical or Cylinder?

Spherical

Due to the more spread out nature of the spherical grip, this muscle works more

Interossei

The Fist Grip is AKA

Digital palmar prehension pattern

The Lateral Pinch Grip is AKA

Key grip

AKA pad-to-pad prehension grip

Three prong chuck

Which digits are involved in the Three prong chuck grip

Pads of Distal #2-3 digits contact the pad of the distal thumb

Least precise of the precision grips

Lateral pinch grip

Tip-to-Tip Grip is AKA

Tip prehension grip

in tip-to-tip grip, this finger is most often used

Index finger