Biomechanics Week 8 Wrist and Hand

Distal forearm joint

Concave distal radius in medial lateral and anterior posterior directions

ulnar tilt

Lateral radius (styloid) is longer than ulna (~25 degrees)

Allows increased ROM for ulnar deviation

Ulnar tilt of distal radius

25 degrees

radial styloid process contatcs

carpus bones which allows for more UD than RD

Palmar tilt of radius

10 degrees

Palmar tilt allows for

more flexion

1 multiple choice option

Fracture of the Distal radius disrupts

ulnar and palmar tilts

Radiocarpal joint

concave radius and convex scaphoid, lunate and triquetrum

Distal radius takes what percentage of compression forces on the wrist

80%

Triangular Fibrocartilage takes the other __ and passes it to ulna

20%

Most contact area of the radiocarpal joint occurs

when the slightly extended and UD

mid carpal joint

Joint between proximal and distal carpal rows.

Proximal row of carpals at the Midcarpal joint

Concave distal surface that connects to distal row

distal row of carpals at the Midcarpal joint

Convex proximal surface that connects to proximal row

Wrist ligaments

radial collateral, ulnar collateral, palmar radiocarpal, dorsal radiocarpal

dorsal radiocarpal connects

radius to scaphoid, lunate, and triquetrum;

the dorsal radiocarpal reinforces

posterior radiocarpal joint

Which ligament guides the natural roll and slide of the proximal row of carpals

dorsal radiocarpal

dorsal radiocarpal Fibers that attach to lunate prevent

anterior dislocation of the bone

dorsal radiocarpal has lots of

mechanoreceptors

Radial collateral ligament provides

lateral support to the wrist

What muscles provide lateral stability to the wrist

APL and EPB

Palmar collateral ligament

Made of 3 ligaments

Palmar/Volar Collateral Ligament runs

from radius to ulnar carpals

Palmar collateral ligament is taut during

extension of the wrist

Palmar collateral ligament limits

impingement between dorsal radius and carpal bones

TFCC

triangular fibrocartilage complex

Intrinsic wrist ligaments are classified by

lengths

intrinsic wrist ligaments

short, intermediate, long

short wrist ligaments

Stabilize and unite distal carpals

intermediate wrist ligaments

Scapholunate ligament

Scapholunate ligament

Primary stabilizer of the lunate

Long wrist ligament

Inverted Vs

inverted V ligaments

Taut with radial and ulnar ligaments

Dorsal intercarpal ligament provides

transverse stability

If the ligaments are injured the mechanoreceptors lose

their proprioception

Triangular Fibrocartilage

ulna is separated from the distal row of carpals by fibrocartilaginous disc

Triangular Fibrocartilage attaches

palmar and dorsal capsular ligaments of DRUJ

Proximal disc connects to

ulnar head

distal disc attaches to

lunate and triquetrum

central 80% of TFCC is

Avascular and can't heal well

TFCC function

•Stabilizes the distal radioulnar joint

•Stabilizes the ulnar side of the carpus itself

Cushions the ulna on the carpus

•Allows axial loading of the ulnar aspect of the forearm

•Increases the articular surface for the carpus

Palmar ulnocarpal ligament shares an attachments with the

palmar radioulnar capsular ligament to secure the position of the TFC

Tendon of ECU runs through 6th compartment and adheres to

dorsal capsular ligament of the DRUJ

degeneration of TFCC

can lead to instability

One of first clinical signs of RA

TFCC Degeneration

TFCC Degeneration symptoms

weak grip, crepitus, and reduced ROM

Wrist osteokinematics

flexion, extension, radial deviation, ulnar deviation

Dart throwers motion

A pattern of wrist extension/radial deviation to wrist flexion/ulnar deviation that places very little strain on the SL ligament and also requires less motion of the scaphoid or lunate.

Dart throwers Extension also has

RD

Dart throwers flexion

UD

AoR of the wrist passes through the

Capitate

Wrist flexion functional ROM

40 degrees

Wrist extension Functional ROM

40 degrees

Wrist RD functional ROM

10 degrees

Wrist UD functional ROM

30

Wrist functional ROM is about the

50-80% of max wrist ROM

Wrist central column

Radius-Lunate-Capitate-Third Metacarpal

Radio carpal and midcarpal joint shapes

Concave proximal partner and convex distal partner

Wrist flexion arthrokinematics

palmar roll, dorsal slide

Wrist extension arthrokinematics

dorsal roll, palmar slide

Wrist extension elongates

all the muscles and palmar radiocarpal ligaments

Wrist Radial deviation arthrokinematics

radial roll, ulnar glide

Wrist Ulnar deviation arthrokinematics

ulnar roll, radial glide

Double V ligaments

Wrist intercarpal and ulno/radiocarpal ligaments

Distal inverted V is formed by

proximal intercarpal ligament

Proximal inverted v is formed by

lunate attachments of palmar ulnocarpal and radiocarpal ligaments

Primary cause of wrist laxity

rupture of ligaments

Ulnar deviation stretches

Palmar ulnocarpal ligament

Radial deviation stretches

Palmar Radiocarpal ligament

Rotational Collapse of Wrist

Proximal carpals get compressed on both sides

Most mobile carpals

Proximal row

Compression of the proximal carpals

causes zigzag collapse if ligaments not intact

-zigzag collapse

As one carpal bone or row moves out of place, other bones compensate by moving in the opposite direction

most frequently dislocated carpal

lunate

Scaphoid forms the link between the lunate and

distal carpal row between it's two poles

If scaphoid fractures or ligament ruptures we can have

scapholunate dissociation

scapholunate dissociation

Ligaments between scaphoid and lunate are disrupted

DISI

Dorsal intercalated segmental instability

Dorsal intercalated segmental instability

Distal lunate dislocates faces dorsally

DISI causes an

Excessive gap to form between scaphoid and lunate

Active gripping with a DISI can

force the capitate between the scaphoid and lunate

VISI

Volar intercalated segmental instability

Volar intercalated segmental instability

Distal lunate dislocation and faces volarly

VISI occurs with

lunotriquetral ligament injury

ulnar translocation of the carpus

-Ulnar tilt of radius creates a tendency for the carpus to translate in an ulnar direction

-Excessive translocation can alter the biomechanics

Ulnar Translocation of the Carpus is resisted by

Extrinsic ligaments

If the extrinsic ligaments are weakened overtime

The carpus migrate ulnarly

What kind of treatment is necessary for a DISI or VISI

Surgery, pot-op therapy

Why is the scaphoid susceptible to avascular necrosis?

Because it's located directly in line of the compression forces of the distal forearm and the distal carpals

What happens neurologically if the ligaments of the wrist are damaged?

A loss of proprioception occurs because the mechanoreceptors are injured

Which ligaments play a role in ScaphoLunate stability at the wrist?

Dorsal intercarpal, radioscaphocapitate, Long radiolunate, Scaphotrapeziotrapezoid ligament, dorsal radiocarpal ligament and (Dorsal, palmar and proximal scapholunate ligaments, all make up the Scapholunate interosseous ligament)

scapholunate ligament

Most commonly injured ligament in the wrist

Active structures limiting wrist extension

Wrist and finger flexor muscles

Passive structures limiting wrist extension

Palmar ligaments

Active structures limiting wrist flexion

Wrist and finger extensors

Passiv structures limiting wrist flexion

Dorsal ligaments

What is the Dart Thrower's motion?

Movement in both the frontal and sagittal planes

Midcarpal wrist flexion arthrokinematics

Distal carpals rolls anterior and slide posterior

Midcarpal wrist extension

Distal carpals roll posterior and slide anterior