Hand Complex

Carpometacarpal (CMC) Joints (2nd-5th)

Joints between carpals and metacarpals.

- Inconsistent classification: debate on plane vs. saddle joint

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

1st Carpometacarpal (CMC) joint

saddle joint

2 degrees of freedom:

- Flexion/extension

- Abduction/adduction

more mobile than 2nd & 3rd joint

allows opposition motion

Location: Articulation between 1st metacarpal and

trapezium

Biomechanics:

Most mobile and complex of the CMC joints owing to

its saddle-shaped design

Loose joint capsule to accommodate large motion

Relies on ligaments and tendons for stability

1lb of force at tip of the thumb = 12lbs at the base

Volar Anterior Oblique Ligament (AOL)

Variable anatomy; curtain-like structure covering the volar joint surface

Dorsal Deltoid Ligament

Primary stabilizers of the thumb CMC joint

- Consists of 3 stout bands (fan-shaped like the deltoid): dorsoradial, dorsal central and posterior oblique ligaments

- Originate from the dorsal tubercle of the triquetrum and insert onto the dorsal base of the 1st metacarpal

Thumb CMC Joint Osteoarthritis

Pathophysiology:

Degenerative attenuation of stabilizing ligaments followed by increased mechanical stress

of the CMC joint

- 40% and 25% of incidence in women and men over 75 years of age respectively

- Causes debilitating pain and weakness in pinching and loading activities

Considering that CMC OA comes from stress on ligaments and 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?

Close-packed position (most congruent): Full opposition

Open-packed position (least congruent): Mid-range

Loose packed position to minimize compression

1st Metacarpophalangeal (MCP) joint

Condyloid joint

- Functions more like a "hinge" joint with very limited side-

to-side motion

Metacarpophalangeal (MCP) joint

Joint between metacarpals and phalanges.

Condyloid joint

- 2 degrees of freedom:

- Flexion/extension and abduction/adduction

Proximal Interphalangeal (PIP) Joint

Joint between the proximal and middle phalanges

hinge joint: flexion/extension

Distal Interphalangeal (DIP) Joint

joint between middle and distal phalanges

hinge joint: flexion/extension

Interphalangeal (IP) Joint

joint between proximal and distal phalanges of the first digit

hinge joint

Volar plate

Prevents hyperextension

- Strong fibrocartilage located on volar aspect of the joint spanning across the joint space

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

- Forms the 'floor' of the finger joints

Distal wrist crease

crease that separates the distal and proximal rows of the carpal bones (pisiform to the tubercle of the trapezium)

Distal palmar crease

This crease lies at the base of the fingers and marks the location of the proximal pulley:

A. Distal palmar crease

B. Hypothenar crease

C. PIP crease

D. Thenar crease

D. Proximal palmar crease

1st dorsal interosseous muscle

fills posterior side of thumb space (space between 1st and 2nd metacarpal bones)

What are the movements of the thumb?

flexion, extension, abduction (radial & palmar), adduction, opposition

Collateral Ligaments (of the hand)

Shared ligamentous structures between MCP, PIP, DIP, IP joints of the fingers and thumb:

Located on radial and ulnar sides of the joint

to provide lateral (side-to-side) stability

2 components:

- Proper collateral ligament: 'cord' like

- Accessory collateral ligament: 'fan' shaped

Skier's Thumb

Tear of the ulnar collateral ligament (UCL) of the thumb MCP joint

Mechanism of injury: Fall or direct trauma to the thumb in valgus stress

Gamekeeper's thumb

injury to the thumb that results in tearing or stretching of the MP joint or rupture of the ulnar collateral ligament

Chronic tear of the thumb MCP UCL ligament

Deep transverse metacarpal ligaments

Strong bands connecting volar plates of adjacent

finger MCP joints

The Proper collateral ligament becomes taut in what motion?

flexion

The Accessory collateral ligament becomes taut in what motion?

extension

Closed pack position (of the finger joints)

Fully congruent joint surfaces held tightly together by maximal tension in joint ligaments.

MP joints: flexion

IP joints: extension

In IP joints, the proper collateral ligaments are taut in all motions. Volar

plates are taut in extension. Making extension what kind of position?

closed pack position

Fracture splinting

To prevent contracture formation, in this intervention:

- MCPs are positioned in 70° flexion

- PIP and DIP joints in full extension

- Also called "intrinsic plus/safe position"

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

Thumb is both power and precision whereas the fingers are moreso for power because its more important to be stable

Extrinsic hand muscles

Muscles in the forearm that cause movement in the hands or fingers

What extrinsic hand muscles are the flexors (anterior forearm)?

flexor digitorum profundus (FDP), flexor digitorum superficilis (FDS), and flexor pollicis longus (FPL)

What extrinsic hand muscles are the extensors (posterior forearm)?

Superficial layer:

- Extensor digitorum (ED)

- Extensor digiti minimi (EDM)

Deep layer:

- Abductor pollicis longus (APL)

- Extensor pollicis brevis (EPB)

- Extensor pollicis longus (EPL)

- Extensor indicis (EI)

Flexor retinaculum

Aka transverse carpal ligament

Forms the roof of the carpal tunnel enclosing 9 tendons:

- FPL (1 tendon)

- FDS (4 tendons)

- FDP (4 tendons)

Flexor digitorum superficialis (FDS)

Action: Digit 2-5 flexion at PIP joint

Origin:

- Humeroulnar head: medial epicondyle and

coronoid process of ulna

- Radial head: oblique line of radius

Insertion: Shaft of middle phalanges

Nerve innervation: Median nerve

Flexor digitorum profundus (FDP)

Action: Digit 2-5 flexion at DIP joint

Origin:

- Proximal three quarters of anteromedial surface of

ulna and interosseous membrane

Insertion: Base of distal phalanges

Nerve innervation:

Digits 2&3: AIN of median nerve

Digits 4&5: Ulnar nerve

Camper's chiasm

where the FDS 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

What type of joint flexion does the FDS handle?

PIP flexion

What type of joint flexion does the FDP handle?

DIP flexion

The _____ does not divide and continues to insert into the distal phalanx

FDP

How would you isolate the action of the FDS?

Flex the targeted digit while holding the rest of the

digits in extension

How would you isolate the action of the FDP?

Hold the targeted digit just proximal to the DIP joint

- Only allow the DIP to flex while keeping the PIP in extension

Flexor pollicis longus (FPL)

- Part of the deep layer of anterior forearm muscles

Thumb flexor

Action: thumb flexion at IP and MCP joints

Origin:

- Anterior surface of radius and adjust interosseous membrane

- Interosseous membrane

Insertion: Base of distal phalanx of the thumb

Nerve innervation: AIN of the median nerve

Flexor tendon pulleys

found on the flexor side to prevent bowstringing and consist of A1, A2, A3, and A4 and C1, C2, C3, and C4.

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

- Annular are much stronger than cruciate

- A2 pulley is the strongest

Thumb: 2 annular (A1, A2) and 1 oblique

- A1 located at MCP joint

- Oblique located in the middle of the proximal phalanx: most critical against bowstringing

Trigger finger/ thumb

Pathophysiology: Inflamed nodule forms on the

thickened flexor tendon sheath. Nodule becomes

trapped proximal to the A1 pulley structure when the

digit is trying to extend from full flexion.

Mechanism of injury: overuse/repetitive gripping

What are the finger extensors?

extensor digitorum, extensor indicis, extensor digiti minimi

Extensor Compartments

Thick fibrous band securing the extensor tendons

6 fibro-osseous tunnels form compartments:

- 1st compartment: APL and EBP

- 2nd compartment: ECRB/L

- 3rd compartment: EPL

- 4th compartment: EDC and EDI

- 5th compartment: EDM

- 6th compartment: ECU

Extensor indicis (EI)

Action: extension of wrist and digit 2

Origin: Distal third of ulna and interosseous membrane

Insertion: Digit 2 extensor expansion

Innervation: Posterior interosseous nerve (PIN): continuation of deep branch of the radial nerve

Dorsal extensor compartment: 4th compartment

Extensor digitorum (EDC)

Action: Digit 2-5 extension

Origin: Lateral epicondyle

Insertion: Digit 2-5 extensor expansion

Nerve innervation: Posterior interosseous nerve (PIN): continuation of deep branch of the radial nerve

Dorsal extensor compartment: 4th compartment

Unique feature: Tendons are linked to each other in dorsal hand with juncturae tendinae: connective tissue band

Extensor Digiti Minimi (EDM)

Action: Digit 5 extension

Origin: Lateral epicondyle

Insertion: Digit 5 extensor expansion

Nerve innervation: Posterior interosseous nerve (PIN): continuation of deep branch of the radial nerve

Dorsal extensor compartment: 5th compartment

Juncturae Tendinae (JT)

Connective tissue band linking adjacent

tendons of the EDC proximal to the

MCP joints

- Highly variable structure

- Assist in centralizing the extensor tendon