wrist acadimya 1.4

8/3/2019 Wrist Acadimya 1.4

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Dr Youssef Masharawi1


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Palmar flexion Begins at midcarpal joint with tightening of

dorsal extrinsic ligaments Triquetrum moves proximally and dorsaly on

hamate

Lunate shifts dorsally with triquetrum

palmar rotation of the lunate

Via the SLL the scaphoid also palmar rotates

Dorsal ligaments lock the triquetrum on hamateand TFC


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Dorsal flexion

Begins at midcarpal joint, initiated by wristextensors

Triquetrum moves proximally and dorsallyon hamate - RLTL tightens

Capitate and lunate remain coaxial

With RCL tightening, dorsiflexes scaphoidand capitate. This sling across scaphoid

prevents palmar flexion of the lunate whichwould occur due to elevation of triquetrumon hamate. Movement occurs primarily at

the radiocarpal joint


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Radial deviation

Proximal carpal row flexes and moves ulnarly.Distal row is displaced radially

Scaphoid rotates into palmar flexion, clears theradial styloid process and allows greatermovement - drops into gap

Triquetrum moves proximally and distally onhamate

Lunate shifts dorsally with triquetrum, makingthe lunate axis now dorsal to the capitate axis

and any force though capitate now causespalmar rotation of the lunate Via the SLL, the scaphoid also forced into further

palmar flexion/rotation


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Ulnar deviation Proximal row slides radially, whilst distal row

moves ulnarly Triquetrum moves distally and palmarly on

hamate

Lunate shifts palmarly with triquetrum, makingthe lunate axis now palmar to the capitate axisand any force though capitate now causesdorsal rotation of the lunate

Via the SLL, the scaphoid also forced into furtherdorsal flexion/rotation creating a lengthenedappearance of scaphoid


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KINEMATICS OF WRIST

FUNCTION

Several columnar theories eg : Weber

(1984 Three columns:

1. Force bearing column2. Control column

3. Thumb axis column


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2. Control column

distal ulna

ulnar carpal complex: TFC, triquetrum,

hamate, base of 4th and 5th MC * Function: longitudinal force

transmission deflected to force-bearing

column via hamate-capitate articulation,

which allows rotational control of proximal

carpal row


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3. Thumb axis column

distal third of scaphoid

trapeziotrapezoid joint

base of first metacarpal * Function: supports base of the thumb,

allowing its independent function


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POINTS TO NOTE: no direct motor control of wrist as all motor

units controlling wrist arise from forearmand insert distal to wrist (except FCU).


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POINTS TO NOTE: Wrist accomplishes functions of stability

and mobility by making use of a dualarticular system.

Motion in stable range of one joint(proximal/radiocarpal) is amplified at

second joint (distal/midcarpal) without loss

of stability.


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POINTS TO NOTE: Most important volar intrinsic ligaments for

stability are scapholunate andlunotriquetral.

Biomechanically extrinsic ligaments are

stiffer while intrinsic ligaments capable of

greater elongation before permanentdeformation occurs.


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Loose packed position

slight extension and ulnar deviation Closed packed position

RD and extension combined

Capsular patternflexion = extension in restriction

Innervations

-abundant, note close proximity to numerousnerve


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CLASSIFICATION OF CARPAL

INSTABILITY

Intracarpal instability generally classifiedin one of three ways:

anatomically - radial or ulnar

ability to be radiographicallydemonstrated - static or dynamic

orientation of the lunate - VISI or DISI


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CLASSIFICATION OF CARPAL

INSTABILITY Wrist instability results from either an

incompetent ligamentous support system or achange in the joint contact surface configurationor both

Ligament incompetence may be result ofcongenital laxity, stretching or traumatic rupture(partial/complete)

Changes in joint contact surface configurationusually secondary result of fracture


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Four major types of carpal

instabilities

dorsiflexion instability (most common) palmar flexion instability

ulnar translocation dorsal subluxation


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Dorsal intercalated segement

instability (DISI)

Often associated with radial instabilitiesinvolving scaphoid and lunate

Capitate displaces dorsal to long axis of

radius producing Zig-Zag radius-lunate-

capitate alignment


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Volar intercalated segment

instability (VISI)

often associated with ulnar instabilitiesinvolving lunotriquetral or midcarpal joints

lunate palmar flexes


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Ulnar translocation occurs if carpus has shifted in an ulnar

direction


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Dorsal subluxation Carpus subluxed dorsally in its normal

relationship to radius.


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Mechanism of injury:Carpal injuries represent a spectrum of bony and

ligamentous damage.

Final injury determined by:

- type of 3 dimensional loading

- magnitude and duration of forcesinvolved

- position of hand at time of impact - biomechanical properities of bones and

ligaments


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Also remember radiocapitate ligament maximally taut in

maximum extension and ulnar deviation radioscaphoid ligament is maximally taut

in maximum extension

proximal carpal row stabilized to distalforearm by five ligaments, whereas distalrow by only one ligament (radiocapitate)

weakest ligaments are on radial side(radial collateral and radiocapitate)


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most susceptible position of wrist is maximal

extension where dorsal articular surfaces areunder marked compression and volar ligamentstructures are under marked tensile stress

most wrist injuries occur via a fall on theoutstretched hand and with the impact on thethenar aspect of the wrist wrist extension,

ulnar deviation and intercarpal supination,causing reproducible pattern of ligament failure

wrist acadimya 1.4

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