Exam 4: Hand Complex

Extrinsic and intrinsic hand muscles

The hand complex enables us to?

grasp, pinch, manipulate objects

What are the bones of the hand?

• 5 metacarpals: Fingers/Digits 1-5 (named by digit; ex: 1st metacarpal = thumb metacarpal)

• 5 proximal phalanx (P1)

• 4 middle phalanx (P2): absent in thumb

• 5 distal phalanx (P3)

What are the joints of the hand?

1. Carpometacarpal (CMC) joints

2. Metacarpophalangeal (MCP)

3. Proximal interphalangeal (PIP)

4. Distal interphalangeal (DIP)

5. Thumb only: Interphalangeal (IP)

Primary Stabilizers

1. Collateral ligaments

   1. True ligament: cord-strong ligament

   2. Accessory component: fan-like weaker ligament

2. Volar plate: strong fibrocartilage plate

Palmar surface anatomy: Identify the…

1. Distal wrist & palmar crease

2. Thenar muscle mass

3. Joint creases for MCP, PIP, DIP, thumb IP joints

Dorsal surface anatomy: Identify the…

1. Extensor digitorum (EDC) tendons

2. 1st, 2nd, 3rd extensor compartments

3. Metacarpophalangeal (MCP) joints

4. Proximal interphalangeal (PIP) joints

5. Distal interphalangeal (DIP) joints

6. 1st dorsal interosseous muscle

What are the 4 movements of the fingers?

1. Flexion

2. Extension

3. Abduction

4. Adduction

What are the 6 movements of the thumb?

1. Flexion (composite flexion = full flexion of all thumb joints)

2. Extension

3. Radial & palmar abduction

4. Adduction

5. Opposition

How does joint stability demands in the thumb joints differ from the finger joints?

• Thumb: power & precision (mobility)

• Fingers: stability more important to grasp

Finger joint: 2nd - 5th Carpometacarpal (CMC) joints

• Inconsistent classification, so debate on plane VS saddle joint

• 4th/5th CMC joints more mobile than 2nd/3rd CMC joints

Finger joint: Metacarpophalangeal (MCP) joint

• Condyloid joint (lacks axial rotation)

• 2 degrees of freedom: Flexion/extension & abduction/adduction

Finger joint: Proximal interphalangeal (PIP) & Distal interphalangeal (DIP) joint

Hinge joint: Flexion/extension

Thumb joint: 1st Carpometacarpal (CMC) joint - Saddle joint

2 degrees of freedom

• Flexion/extension

• Abduction/adduction

Thumb joint: 1st Metacarpophalangeal (MCP) joint - Condyloid joint

Functions more like “hinge” joint w/ very limited side-to-side motion

Interphalangeal (IP) thumb joint is what kind of joint?

Hinge joint

Carpometacarpal (CMC) joints

• 1st/4th/5th CMC joints more mobile than 2nd/3rd CMC joints

• Allows opposition motion

The thumb CMC joint is a special joint located at the…

Articulation between 1st metacarpal & trapezium

Biomechanics:

• Most mobile, complex of the CMC joints due to saddle-shape

• Loose joint capsule to accommodate large motion

• Relies on ligaments & tendons for stability

• 1 lb force @ tip of thumb = 12 lbs at base

(2) Ligaments of the unstable thumb CMC joint

• Volar Anterior Oblique Ligament (AOL): Variable anatomy; curtain-like structure covering volar joint surface

• Dorsal Deltoid Ligament: Primary stabilizers of thumb CMC joint

  • Has 3 stout bands (fan-shaped like deltoid): dorsoradial, dorsal central, posterior oblique ligaments

  • Originate from dorsal tubercle of triquetrum & insert onto the dorsal base of 1st metacarpal

Thumb CMC joint osteoarthritis: Pathophysiology

Degenerative attenuation of stabilizing ligaments, followed by increased mechanical stress of the CMC joint

• 40% & 25% of incidence in women & men 75+

• Causes debilitating pain & weakness in pinching & loading activities

Thumb ergonomics: Since CMC OA comes from stress on ligaments & mechanical load on the joint surface, should patients with CMC OA be positioned in its close-packed (maximizing congruency/ligament tautness) or loose-packed (minimizing compression) joint position?

• Loose-packed position to minimize further compression/not stretch out ligament any further. At mid-range; least congruent

• EX: natural resting position of thumb (not fully abducted in either direction is the position of comfort), using ergonomic scissors w/ larger grips ✂

Hand Joint Stabilizer: Collateral ligaments

Located on radial & ulnar sides of the joint to provide lateral (side-to-side) stability

2 components

1. Proper collateral ligament: “cord” like

2. Accessory collateral ligament: “fan” shaped

Hand joint stabilizers are shared ligamentous structures between the…?

MCP, PIP, DIP, IP joints of the fingers & thumb

Hand Joint Stabilizer: Volar plate

• Prevents hyperextension

• Strong fibrocartilage on volar aspect of joint, spanning across joint space

• Proximally reinforced by check-rein ligaments on either (lateral) side

• Forms “floor” of finger joints

Skier’s thumb is a tear of the…?

Ulnar collateral ligament (UCL) of thumb MCP joint

• MOI: Fall/direct trauma to thumb in valgus stress

• Chronic tear of thumb MCP UCL ligament = Gamekeeper’s thumb

  

Finger MCP Joints (2nd - 5th MCP joints)

Collateral ligaments

• Proper collateral ligament: taut in flexion

• Accessory collateral ligament: taut in extension

Deep transverse metacarpal ligaments: Strong bands connecting volar plates of adjacent finger MCP joints

Closed & open pack finger joint positions

Closed-pack position: Fully congruent joint surfaces held tightly together by max tension in joint ligaments.

• MP joints: flexion

• IP joints: extension

*IMPORTANT DISTINCTION: In IP joints, proper collateral ligaments are taut in all motions. Volar plates are taut in extension, making extension the closed-pack position.

To prevent contracture fraction in fracture splinting, the…

• MCPs positioned in 70* flexion

• PIP & DIP joints in full extension

• also called “Intrinsic plus/safe position”

  

Extrinsic hand muscles are finger & thumb muscles that originate in the forearm…

OUTSIDE of the hand

Extrinsic hand muscles: Flexors of Anterior forearm

• Intermediate layer: Flexor digitorum superficialis (FDS)

• Deep layer: FDP + Flexor pollicis longus (FPL)

Extrinsic hand muscles: Extensors (Posterior forearm)

• Superficial layer: ED, EDM

• Deep layer: APL, EPB/L, EI

The flexor retinaculum (transverse carpal ligament) forms the roof of the carpal tunnel, enclosing 9 tendons:

• FPL: 1 tendon

• FDS & FDP: 4 tendons each

Finger flexors (digits 2-5): Flexor digitorum superficialis (FDS)

Action: Digit 2-5 flexion at PIP joint

Origins:

• Humeroulnar head: medial epicondyle and coronoid process of ulna

• Radial head: oblique line of radius

Insertion: Shaft of middle phalanges

Nerve innervation: Median nerve

Finger flexors (digits 2-5): Flexor digitorum profundus (FDS)

Action: Digit 2-5 flexion at DIP joint

Origin: proximal ¾ of anteromedial surface of ulna & interosseous membrane

Insertion: Base of distal phalanges

Nerve innervation:

• Digits 2&3: AIN of Median nerve

• Digits 4&5: Ulnar nerve

Flexor digitorum superficialis (FDS) vs. Flexor digitorum profundus (FDP) Anatomy

Runs superficial to the FDP: at its insertion, the FDS splits into two tendon slips wrapping itself around the FDP to allow the FDP to pass through = Camper’s chiasm

• FDP doesn’t divide & cont. to insert into distal phalanx

• FDS = PIP flexion

• FDP = DIP flexion

Isolate the actions of FDS by flexing the targeted digit…

• while holding rest of digits in extension

• FDS has common muscle belly

Isolate the actions of FDP by holding the targeted digit…

• just proximal to DIP joint

• only allow DIP to flex, while keeping PIP in extension

Thumb flexor - Flexor pollicis longus (FPL) Overview

• Part of deep layer of anterior forearm muscles

• Action: thumb flexion @ IP & MCP joints

• Origin: Anterior surface of radius & adjust interosseous membrane + interosseous membrane

• Insertion: base of distal phalanx of thumb

• AIN nerve innervation (median n.)

Flexor Tendon Pulleys

Function: Prevent bowstringing of the flexors

Fingers: 5 annular pulleys (A1-A5) and 3 cruciate pulleys

• Annular pulleys much stronger than cruciate pulleys

• A2 pulley = strongest

Thumb: 2 annular pulleys (A1, A2) & 1 oblique pulley

• A1 pulley at MCP joint

• Oblique pulley in middle of proximal phalanx: most critical against bowstringing

Trigger finger/thumb

• Pathophysiology: Inflamed nodule forms on thickened flexor tendon sheath. Nodule becomes trapped proximal to A1 pulley structure when the digit’s trying to extend from full flexion.

• MOI: overuse/repetitive gripping

Finger Extensors: Superficial VS Deep Layers

• Superficial layer: EDC, EDM

• Deep layer: Extensor indicis (EI)

6 fibro-osseous tunnels form compartments, a thick fibrous band securing the extensor tendons

• 1st compartment: APL & EBP

• 2nd compartment: ECRB/L

• 3rd compartment: EPL

• 4th compartment: EDC & EDI

• 5th compartment: EDM

• 6th compartment: ECU

Finger Extensor: Extensor indicis (EI)

• Action: Digit 2 extension (index/pointer finger)

• Origin: Distal 3rd of ulna & interosseous membrane

• Insertion: Digit 2 extensor expansion

• Nerve: PIN - cont. of deep branch of radial n.

• Dorsal extensor compartment: 4th

• Unique: Tendons linked to each other in dorsal hand, w/ juncturae tendinae: CT band

Finger Extensor: Extensor digitorum communis (EDC)

• Action: Digit 2-5 extension

• Origin: Lateral epicondyle

• Insertion: Digit 2-5 extensor expansion

• Nerve: PIN - cont. of deep branch of radial n.

• Dorsal extensor compartment: 4th

• Unique: Tendons linked to each other in dorsal hand, w/ juncturae tendinae: CT band

Finger Extensor: Extensor digiti minimi (EDM)

• Action: Digit 5 extension

• Origin: Lateral epicondyle

• Insertion: Digit 5 extensor expansion

• Nerve: PIN (cont. of deep branch of radial n.)

• Dorsal extensor compartment: 5th

• Unique: Tendons linked to each other in dorsal hand, w/ juncturae tendinae: CT band

Finger Extensor: Juncturae tendinae (JT)

CT band linking adjacent tendons of EDC proximal to MCP joints

• highly variable in structure

• assist in centralizing extensor tendon

Finger extension: Why are we able to independently extend the index and small fingers but not the middle and ring fingers?

Because they each have their own individual extensor!

Extensor expansion is a…?

Complex web of CT structure that EDC tendon & intrinsic hand muscles insert into

• Facilitates finger extension!

Deep layer of Thumb Extensors are the…?

• APL, EPB/L (3)

• Assist w/ wrist radial deviation

• Form border of anatomical snuffbox

• In dorsal forearm

Anatomical Snuffbox 📐

1. Radial border: 1st dorsal compartment (triangle) - Shared compartment between APL & EPB

2. Ulnar border: EPL

3. Floor: Scaphoid - Pain w/ pressure in this location = scaphoid fracture

Thumb Extensor: Abductor Pollicis Longus (APL)

• Action: Thumb abduction & extension @ CMC

• Origin: Posterior proximal halves of ulnar, radius, interosseous membrane

• Insertion: base of 1st metacarpal

• Nerve: PIN - cont. of deep branch of radial n.

• 1st Compartment

Thumb Extensor: Extensor pollicis brevis (EPB)

• Action: Thumb extension @ CMC & MCP

• Origin: Posterior distal third of radius & interosseous membrane

• Insertion: base of thumb proximal phalanx

• Nerve: PIN - cont. of deep branch of radial n.

• 1st Compartment

Thumb Extensor: Extensor pollicis longus (EPL)

• Action: Thumb extension at ALL thumb joints

• Origin: Posterior middle third of ulna & interosseous membrane

• Insertion: base of thumb distal phalanx

• Nerve: PIN (cont. of deep branch of radial n.)

• Compartment: 3rd

Thumb extensor isolated function, from proximal to distal:

• APL: thumb CMC abduction/extension

• EPB: thumb MP extension

• EPL: thumb IP extension

De Quervain’s Tenosynovitis is Stenosing tenosynovitis = Degenerative thickening of the tendon sheath & retinaculum of tendons in 1st dorsal extensor compartment (APL + EPB)

Which motions would become painful for the patient?

Grasping, lifting, or twisting; due to pain at the radial side of the wrist, triggered by thumb movement & wrist deviation.

Intrinsic hand muscles: Vital for fine-motor hand control, divided into 4 groups (within the hand)

Perform fine motor skills

1. Muscles of thenar eminence (meaty part of thumb): ABP, flexor pollicis brevis, opponens pollicis

2. Muscles of hypothenar eminence (bulk on pinky side): Flexor digiti minimi, abductor digit minimi, opponens digiti minimi

3. Adductor pollicis (thumb adductor)

4. Lumbricals & interossei

These fill the space between our thumb metacarpals

Thenar & hypothenar “AFO” muscles function to…

synergically to perform opposition

What are the thenar muscles? “AFO”

1. Abductor pollicis brevis

2. Flexor pollicis brevis

3. Opponens pollicis (deeper to other 2 thenar muscles)

What are the hypothenar muscles? “AFO”

1. Abductor digiti minimi

2. Flexor digiti minimi brevis

3. Opponens digiti minimi (deeper to other 2 hypothenar muscles)

Thenar Muscles: Abductor pollicis brevis (APB)

• Action: Thumb abduction

• Origin: Flexor retinaculum & tubercles of scaphoid & trapezium

• Insertion: Lateral side of base of thumb proximal phalanx

• Nerve: Recurrent branch of median n. (pass thru carpal tunnel)

• MOST powerful muscle of thenar muscle

• Crosses thumb MCP joint

Thenar Muscles: Flexor pollicis brevis (FPB)

• Action: Thumb MP & CMC flexion

• Origin: Flexor retinaculum & tubercles of scaphoid & trapezium (same as OP)

• Insertion: Lateral side of base of thumb proximal phalanx

• Nerve: Recurrent branch of median n. (pass thru carpal tunnel)

• Has 2 heads: superficial & deep

• Crosses thumb MCP joint

Thenar Muscles: Opponens pollicis (OP)

• Action: Thumb opposition

• Origin: Flexor retinaculum & tubercles of scaphoid & trapezium (same as FPB)

• Insertion: Lateral side of 1st metacarpal (Doesn’t cross thumb MCP joint b/c it ends here)

• Nerve: Recurrent branch of median n. (pass thru carpal tunnel)

Hypothenar Muscles: Abductor digiti minimi

• Action: 5th digit abduction

• Origin: Pisiform

• Insertion: Medial side of base of 5th digit proximal phalanx

• Nerve: Deep branch of ulnar n.

Hypothenar Muscles: Flexor digiti minimi brevis

• Action: 5th digit proximal phalanx flexion

• Origin: Flexor retinaculum & hook of hamate

• Insertion: Medial side of base of 5th digit proximal phalanx

• Nerve: Deep branch of ulnar n.

Hypothenar Muscles: Opponens digiti minimi

• Action: 5th digit opposition

• Origin: Flexor retinaculum & hook of hamate

• Insertion: Medial border of 5th metacarpal

• Nerve: Deep branch of ulnar n.

Combined action of the thenar & hypothenar muscles is?

• Thenar muscles: Position thumb in varying amounts of opposition to facilitate grasping. Combines CMC abduction, flexion, medial rotation

• Hypothenar muscles: Raise & “cup” ulnar border of hand

Adductor pollicis: Overview

• Action: Thumb adduction

• 2 Origins

  • Oblique head: base of 2nd & 3rd metacarpal, capitate, adjacent carpals

  • Transverse head: anterior surface of 3rd metacarpal shaft

• Insertion: Medial base of thumb proximal phalanx

• Nerve: Deep branch of ulnar n. (like hypothenar muscles)

Ape Hand deformity in Carpal Tunnel Syndrome: Median n. compression @ carpal tunnel → atrophy of thenar muscles

What do you notice about the resting hand posture of the patient w/ this deformity?

• Atrophy in thenar muscles, thumb is completely flat in same plane as palm. Can’t bring thumb into palmar abduction

What accounts for this posture? Which muscles are working & overcompensating?

• Lack of participation from thumb thenar muscles

• Thumb adductor pollicis muscle overworked, keeping thumb close to palm (APM deformity)

Palmar & dorsal interossei

• Palmar: Unipennate, palmar surface of 2nd, 4th, 5th metacarpals

• Dorsal: Bipennate, adjacent sides of 2 metacarpals

• ALL insert into bases of proximal phalanges & extensor expansion

• Deep branch of ulnar n. innervated

Actions of the interossei are?

1. PAD: Palmar interossei ADduct

2. DAB: Dorsal interossei ABduct

4 Lumbricals “earth worm” numbered from radial to ulnar:

• Lumbricals 1-2 = unipennate (median n. innervation)

• Lumbricals 3-4 = bipennate (deep branch of ulnar n.)

Lumbricals 1-2

• Action: Digits 2-3, MCP flexion & IP extension

• Origins: lateral 2 FDP tendons

• Insertion: Extensor expansion (lateral side)

• Nerve: Median n. (same as FDP origin)

• Structure: Unipennate

Lumbricals 3-4

• Action: Digits 4-5, MCP flexion & IP extension

• Origins: Medial 3 FDP tendons

• Insertion: Extensor expansion (lateral side)

• Nerve: Deep branch of ulnar n. (same as FDP origin)

• Structure: Bipennate

Lumbricals & interossei work together to perform?

Finger MCP flexion & IP extension

Intrinsic plus position is what combined action of the intrinsic muscles:

MP flexion + IP extension

Intrinsic minus position is the combined action of the extrinsic muscles WITHOUT action of the intrinsics

• MP extension + IP flexion

• MCPs are hyperextended instead of being in neutral extension because EDC muscle acts unopposed on the MCP joints

Clinical: Ulnar Claw

• Intrinsic muscles affected by ulnar n. lesion @ wrist level

• Affected hand can’t extend digits 4+5 b/c paralyzed lumbricals/interossei = extensor digitorum cause hyperextension @ MCP joints, while intact FDP pulls IP joints into flexion

If you had carpal tunnel syndrome, would the hypothenar or thenar muscles be intact?

Hypothenar muscles since they’re innervated by the ulnar nerve, not median nerve (thenar muscles).