Kinesiology Lecture 4.1: Wrist and Hand

What is the axis of forearm pronation and supination?

A longitudinal axis running through the radius and ulna

During pronation and supination, which bone primarily moves?

The radius moves around the ulna

At the proximal radioulnar joint, what are the joint surfaces?

Convex radius on concave ulna

At the distal radioulnar joint (DRUJ), what are the joint surfaces?

Concave radius on convex ulna

According to the concave-convex rule, how does the radius glide at the DRUJ during pronation?

Ventrally (volarly)

According to the concave-convex rule, how does the radius glide at the DRUJ during spination?

Dorsally

Clinical Application: A patient has restricted dorsal glide of the radius at the DRUJ. Which motion is likely limited?

Supination

Clinical Application: A patient has restricted ventral glide of the radius at the DRUJ. Which motion is likely limited?

Pronation

What are the origins of pronator teres?

Medial epicondyle and pronator ridge of the ulna

Where does the pronator teres insert?

Anterior surface of the radius

Besides pronation, what additional action may pronator teres assist with?

Elbow flexion

Which muscle is located near the wrist and acts as a pronator?

Pronator quadratus

What is the origin of pronator quadratus?

Pronator ridge

What is the insertion of pronator quadratus

Anterior radius

Which muscle is the strongest supinator of the forearm?

Biceps brachii

Where does biceps brachii insert?

Radial tuberosity

What is the origin of the supinator muscle?

Lateral epicondyle

Where does the supinator insert?

Proximal radius

Where does brachioradialis insert?

Radial styloid process

Clinical Application: Which muscle would be most important for forceful supination, such as turning a screwdriver?

Biceps brachiiWrist, radioscaphoid, scapholunate, capitolunate, capitoscaphoid, DRUJ, MCPs

What joints are included in this wrist and hand lecture?

Wrist, radioscaphoid, scapholunate, capitolunate, capitoscaphoid, DRUJ, MCPs, IPs, thumb, and CMC

What structure forms part of the DRUJ capsule?

Fibrocartilage disc (TFCC)

What does TFCC stand for?

Triangular fibrocartilage complex

What structure helps stabilize the distal radioulnar joint?

TFCC

List the anterior forearm muscles shown in lecture

Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and FDS

What does FDS stand for?

Flexor digitorum superficialis

What are the two layers of dorsal fascia?

Superficial and deep

What are the two layers associated with the extensor retinaculum?

Supratendinous and infratendinous

What does “supratendinous” mean?

Above the tendons

What does “infratendinous” mean?

Between the tendons

How many compartments are formed by the extensor retinaculum?

Six

How many vertical septa does the extensor retinaculum?

Six septa

What is the function of the extensor retinaculum?

Creates fibro-osseous tunnels for extensor tendons and their sheaths

Distally, the extensor retinaculum continues as what structure?

Deep fascia of the hand

WHat happens when the finger pulley mechanism is removed?

Tendon excursion doubles for same ROM

What defeormity can occur when pulleys fail?

Bowstringing

Why are finger pulleys important biomechanically?

They maintain tendon proximity to bone and optimize force transmission

Clinical application: A patient demonstrates bowstringing after pulley injury. What biomechanical problem is occurring?

Tendons are pulling away from the bone, reducing efficiency

Approximately what percentage of wrist flexion/extension occurs at the midcarpal joint?

About 60%

Which carpal bones move into a closed-packed position during further wrist extension?

Scaphoid and lunate

Wrist extension is completed with movement of which carpal row on the radius?

Proximal row

What is the axis for radial deviation and ulnar deviation?

Through the capitate

Which tendon is the primary PIP extensor?

Central tendon

Why are the lateral bands weak extensors when the PIP is flexed?

They descend during PIP flexion

Why can’t the DIP be extended if the PIP is flexed?

PIP flexion relaxes the lateral bands and terminal tendon

Which muscles are more effective as MP flexors?

Interossei

Which muscles are more effective as IP extensors?

Lumbricals

Why is resting tension in the FDP important for lumbrical function?

Without it, the FDP migrates distally and the lumbrical becomes actively insufficient

Clinical application: A patient cannot extend the DIP while the PIP remains flexed. What structure's mechanics explain this?

Relaxation of the lateral bands and terminal tendon

What is a swan-neck deformity?

Hyperextension of the PIP with flexion of the DIP

A swan-neck deformity may develop after what injury?

Mallet fingers

What tendon loss can contribute to swan-neck deformity?

FDS tendon loss

What structures make up the extensor mechanism (dorsal aponeurosis)?

EDC, extensor hood/connective tissue expansion, dorsal and volar interossei, and lumbricals

Where do the interossei originate?

Metacarpals

From where do the lumbricals originate?

FDP

Where do the lumbricals insert?

Radial extensor expansion

Why are the intrinsic muscles necessary for normal finger extension?

They place tension on the extensor mechanism to extend the PIP and DIP joints

What deformity results from absence of intrinsic muscle function?

Claw deformity (MCP extension with IP flexion)

Clinical application: A patient demonstrates MCP hyperextension with IP flexion. What muscle group is likely deficient?

Intrinsic muscles

How can IP extension be assisted in the absence of intrinsic function?

By passively flexing the MCPs to place tension on the extensor mechanism

Which structure is the primary extensor of the PIP joint?

Central tendon

Why are the lateral bands weak extensors from a flexed position?

They descend when the PIP is flexed

How does extension strength of the lateral bands change as the PIP extends?

Strength increases as extension increases

What happens to the lateral bands when the PIP flexes via FDS contraction?

They relax

Why can the DIP not extend if the PIP is flexed?

PIP flexion relaxes the lateral bands and terminal tendon

Clinical application: A patient is unable to actively extend the DIP while maintaining PIP flexion. What biomechanical principle explains this?

Relaxation of the lateral bands and terminal tendon with PIP flexion

What action do the vertical fibers of the interossei perform?

Flex the MCP joint

What action do the oblique fibers of the interossei perform?

Extend the PIP and DIP joints

As the MCP joint flexes, what happens to the ability of the interossei to flex the MCP?

Their ability increases

In MCP extension, the interossei function more as what?

Abductors

What structure prevents excessive volar excursion of the oblique intrinsic fibers?

Transverse metacarpal ligament

Why is the transverse metacarpal ligament important?

It keeps the intrinsic muscles effective as IP extensors

What is unique about the lumbricals’ origin and insertion?

Both are tendinous

Where do the lumbricals insert?

Radially on the lateral band

Which are more effective IP extensors: lumbricals or interossei?

Lumbricals

Which are more effective MCP flexors: lumbricals or interossei?

Interossei

What prevents dorsal migration of the lumbricals during MCP extension?

Transverse metacarpal ligament

Why is resting tension in the FDP important for lumbrical function?

Without it, the FDP migrates distally and the lumbrical becomes actively insufficient

Clinical application: A patient loses normal FDP tension. What effect may this have on the lumbricals?

Active insufficiency and impaired IP extension

What produces passive extensor forces distally at the DIP?

Intrinsic contraction and force at the PIP

PIP extension creates passive tension in what structure?

ORL

What role does EDC tension play in IP extension?

EDC tension is needed for IP extension

Under what condition can EDC extend the IP joints?

When the MCP joints are held in flexion

What structures contribute fibers to the dorsal hood (extensor expansion)?

Juncturae, sagittal bands, extensor tendon, interossei, and lumbricals

What is the function of the juncturae tendinum?

Assist extension of adjacent connected fingers

Why may a proximal extensor tendon lacteration be missed clinically?

Juncturae tendinum can maintain extension via adjacent fingers

What effect does thumb IP flexion have on index finger extension?

It restrains index extension via EDC/EPL juncturae

What is the flexor digital sheath?

A synovial-lined fibro-osseous tunnel

What is the purpose of the synovial sheath?

Provides a low-friction gliding system

What two types of pulleys are present in the flexor sheath?

Annular and cruciate pulleys

How many pulleys does the thumb contain?

Two annular and one oblique pulley

Which pulleys are biomechanically most important in the fingers?

A2 and A4

What happens biomechanically when A2 or A4 is disrupted?

The moment arm of the flexor tendon changes significantly

Loss of the retinaculum leads to what phenomenon?

Bowstringing

Which pulley is most important in the thumb?

The oblique pulley

Loss of the thumb oblique pulley results in what functional deficit?

Loss of IP joint motion

Loss of the A1 pulley may result in approximately how much motion loss?

Up to 30% loss of motion

Clinical application: A climber ruptures the A2 pulley. What biomechanical problem is expected?

Bowstringing and altered flexor tendon moment arm