Wrist and Hand Biomechanics Flashcards
(34 cards)
3 Joints form the wrist complex
Distal Radio-Ulnar
Radio-Carpal
MidCarpal
Flexion & Extension Mechanics
- Primary axis for flex-ext is through the capitate
- Flexion primarily occurs at the midcarpal joint
- Extension primarily occurs at the radiocarpal joint
Closed Pack Position of Wrist
Supinatory Twist
There is slight supination in the wrist with extension.
This “screw home” movement is needed for the wrist to achieve full close pack position for intrinsic stability.
Closed pack (max stability) helps with performing functional activities involving force transmission from the hand to the forearm – walking on all fours, pushing a heavy object
The carpal bone responsible for this twist is scaphoid
Moving from Flexion to Extension
In flexion, the distal and proximal rows are in loose packed position.
Moving from flexion to extension, the carpals must glide anteriorly
As the wrist reaches neutral, the distal row stops moving
To allow continued movement of the proximal row, the scaphoid does a small supinatory twist, locking the scaphoid and distal row into CPP
Once the distal row and scaphoid are close-packed, movement continues at the prox row.
Movement b/w lunate and scaphoid during extension
Movement between the lunate and the scaphoid must occur to allow the final stage of Extension
The scaphoid creates an asymmetry, resulting in a supinatory twist – this causes a twist in the capsules and ligaments creating the close pack position on full extension
So if somebody is struggling with full wrist extension, scaphoid joint play is probably indicated
For athletes that spend time on their hands, scaphoid joint play is probably indicated
Closed Pack Position & Injury
m/c fractured/dislocated carpals
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Scaphoid = most commonly fractured carpal
Lunate = most commonly subluxed or dislocated (palmarly)
Radial & Ulnar Deviation Mechanics
Axis of movement is through the capitate
UD has greater range
Functional Arches
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All the arches work for a common purpose of improving the functional ability of
the hand
Structurally, the arches are
1 longitudinal (per finger)
1 transverse carpal
1 transverse metacarpal
The Transverse Carpal (Proximal transverse) arch
- formed by the distal row
- Each of the carpal bones move independently of each other.
- Proximal row is more mobile than distal
- The distal row centers around the capitate and provides less movement (due to its articulations with the metacarpals)
The Transverse Metacarpal (Distal transverse) arch
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- Formed by the heads of the metacarpals.
- The third metacarpal, the capitate, and lunate are the center point.
- It is relatively flat at rest; the curvature considerably increases with
- strong clenching of the fist or thumb to pinky opposition
Length-tension relationships
Length-tension relationships
The wrist provides a stable base for the hand, and its position controls the length of the extrinsic muscles to the digits
Muscles of the wrist movement serve 2 important functions:
1.) Provide fine adjustment of the hand into its functioning position
2.) And once this position has been achieved, they stabilize the wrist to provide a stable base for the hand
Length-Tension Relationships
Key point
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movements of the wrist are usually in reverse of the movements of the fingers and reinforce the action of the extrinsic muscles of the fingers
Greatest interphalangeal flexion force
Length tension relationships
ulnar deviation and neutral flexion-extension
Dorsal Digital Expansion aka Extensor Mechanism
A broad, flat aponeurotic band of tissue composed of extrinsic extensor tendon and sheath posteriorly, and by the tendons of the interosseous and lumbrical muscles anteriorly
Prehension - Power Grip
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- A forceful act with flexion at all fingers (D1-5)
- The thumb is the stabilizer to the object being held between the fingers and the palm – clamping action of the fingers pushing the object against the palm and countered by the thumb
- The 2 ulnar fingers flex across toward the thenar eminence
- The thenar and hypothenar act as buttresses as the fingers flex around the object to be grasped
- With all power grips the hand is kept stable and power movements are produced by either radial or ulnar deviation of the wrist (i.e. hammering), supination and pronation of the wrist, and elbow extension
Prehension - Precision Grip
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- Lacks a static phase
Is dynamic/isotonic - The object is picked up by the fingers and thumb but is not in contact with the palm
- Sensory surfaces of the digits are used for maximum sensory input to influence delicate adjustments
Prehension Comparison
Power
All 5 digits
Includes Ulnar side of hand
Object contacts palm
Isometric/Static
Precision Digits 1-3 only Does not include Ulnar side of hand Object in digits Isotonic/dynamic
Grip Innervation
- Precision grip activity is mainly performed by the median side of the hand
- Power grips rely on the interaction of the median and ulnar side of the hand.
Swan Neck Deformity
Deformity in the fingers
MCP Flexion
PIP Extension
DIP Flexion
Cause
contracture of the intrinsic muscles
tearing of the Volar plate
Usually seen with RA or post trauma
Boutonniere Deformity
Deformity in the fingers
MCP Extension
PIP Flexion
DIP Extension
Cause
Rupture central slip of DDE (aka dorsal hood aka extensor mechanism)
Usually seen with RA or post trauma
Dupuytren’s Contracture
Contracture of the palmar fascia
As a result there is a fixed flexion deformity of the MCP and PIP joints
Usually seen in digits 4 & 5 with skin also being adhered to the fascia
Note: this is connective tissue, it is not neuromuscular
DIP and PIP NODES
Heberden’s (DIP) and Bouchard’s (PIP) nodes – arthritic changes on the dorsal surfaces
Ulnar drift
due to the changes in the MCP
and resulting pull on the long tendons. Seen with RA
