Download - Bio Mechanics and Pa Tho Mechanics of Hand
BIOMECHANICS AND PATHOMECHANICS OF HAND
PRIYANKA SOOD
Hand complex
Carpometacarpal (CMC) Joints of 2-5
• Composition• Carpal Arch• Ligament Support– Transverse Carpal
Ligament– Dorsal and Palmar CMC
Ligaments– Dorsal and Palmar
Metacarpal Ligaments– Metacarpal Interosseous
Ligaments
Metacarpophalangeal (MCP) Joints of 2-5 Fingers
• Ligament Support– Capsule– Volar Plate– Collateral Ligaments– Motions
Interphalangeal Joints of 2-5 Fingers
• Hinge Joints• Motions
CMC of Thumb
• Saddle Joint• Ligament Support– Capsule– Intermetacarpal
Ligament
MCP of Thumb
• Ligament Support
• IP Joint of Thumb
OUTLINE OF BIOMECHANICS
Types of grasp • Arches of the hand • Functional position of the hand • Joints of the hand • Mechanism for finger flexion • Mechanism for finger extension; the extensor mechanism
• Clinical appearance of peripheral nerve injuries in the hand
Types of grasp • Two types of grasp are differentiated according to the position and mobility of
the thumb's CMC and MP joints. • POWER grasp (The terms grasp, grip, and prehension are interchangeable.)
(The adductor pollicis stabilizes an object against the palm; the hand's position is static.) – cylindrical grip (fist grasp is a small diameter cylindrical grasp) – spherical grip – hook grip (MP extended with flattening of transverse arch; the person may or may
include the thumb in this grasp) – lateral prehension (this can be a power grip if the thumb is adducted, a precision grip if
the thumb is abducted). • PRECISION (Muscles are active that abduct or oppose the thumb; the hand's
position is dynamic.) – palmar prehension (pulp to pulp), includes 'chuck' or tripod grips – tip-to-tip (with FDP active to maintain DIP flex) – lateral prehension (pad-to-side; key grip)
Arches
ARCHES• Three arches balance stability and mobility in the hand. The proximal
transverse arch is rigid, but the other two arches are flexible, and are maintained by activity in the hand's intrinsic muscles.
• PROXIMAL TRANSVERSE ARCH describe this arch as a composite of two arches, the proximal and distal carpal arches.
• a stable bony arch that forms the posterior border of the carpal tunnel.
• The arch's integrity is maintained by a soft tissue "strut" formed by the flexor retinaculum or transverse carpal ligament (also called the volar carpal ligament). This ligamentous strut connects the scaphoid and trapezium on the arch's radial side with the hamate on its ulnar side, and forms the anterior border of the carpal tunnel.
• DISTAL TRANSVERSE ARCH • this the metacarpal arch, because it is formed
by the metacarpal heads; metacarpals 2 and 3 are stable while 4 and 5 are relatively mobile. You can observe the arch's combination of "radial" stability and "ulnar" mobility by loosely closing your fist, then squeezing more tightly, when you will observe movement in the more mobile fourth and fifth metacarpals.
• LONGITUDINAL ARCH Observe this arch's behaviour as you loosely close your fist. Tighten the fist and watch the fourth and fifth metacarpals.
• The arches provide a balance between stability and mobility for grasping. For instance, we produce the so-called "chuck grasp" by using the more stable second and third metacarpals, instead of the more mobile fourth and fifth metacarpals.
Functional position of the hand
• Wrist – extended 20 degrees – ulnarly deviated 10 degrees
• Digits 2 through 5 – MP joints flexed 45degrees – PIP joints flexed 30-45 degrees – DIP joints flexed 10-20 degrees
• Thumb – first CMC joint partially abducted and opposed – MP joint flexed 10 degrees – IP joint flexed 5 degrees
Functional position of hand
JOINT STRUCTURE AXIS MOTION CLOSE-PACKED POSITION
Metacarpo-phalangeal (MP)
biaxial(condylar)
lateralA-P
flexion/extensionabduction/adduction
first: extension2nd-5th: flexion
Proximal Interphalangeal (PIP)
uniaxial lateral flexion/extension extension
Distal Interphalangeal (DIP)
uniaxial lateral flexion/extension extension
Metacarpophalangeal (MP) condyloid, biaxial joints
• joint's palmar aspect is palpable at level of distal palmar crease
• proximal joint surface is convex and distal surface is concave roll and glide occur in same direction – anterior with flexion – posterior with extension. Joint capsule supported by two collateral ligaments
• close-packed position: – MP joints of digits 2 through 5: close-packed in flexion; you
cannot abduct or adduct these joints when they are flexed. – MP joint of thumb: close-packed in extension
Interphalangeal (IP) uniaxial hinge joints
• supported by two collateral ligaments, and by
smaller versions of a volar plate. • Like MP joint, proximal joint surface is
convex and distal surface is concave roll and glide occur in same direction – anterior with flexion – posterior with extension
• close-packed in extension
Mechanism for finger flexion
• Mechanism for finger flexion FDP: flexor digitorum profundus (the deeper of the two)
• FDS: flexor digitorum superficialis (the more superficial muscle)
Biomechanics of Finger Flexion
• Gliding mechanisms – Ligaments– Bursa– Digital tendon sheaths
• Annular Pulleys– A1-A5
• Cruciate Ligaments– C1-C3
• Function of Pulleys
Biomechanics of Finger Extension
• Extensor Hood– EDC tendons– DI and PI tendons– Lumbricales– Central tendon– Oblique Retinacular
Ligaments– Sagittal Bands
• Effects on MCP joints• Effects on IP Joints
Mechanism for finger extension
• The extensor mechanism is an elaboration of the extensor digitorum comunis (EDC) tendon on the dorsum of each phalanx. The extensor indicis (EI) and the extensor digiti minimi (EDM) insert into the extensor mechanisms of the second and fifth digits, respectively.
Tendons helping extensor mechanism
Muscles that transmit force to the otherwise non-contractile extensor
mechanism:
• Dorsal interossei (DI)• PALMAR INTEROSSEI• LUMBRICALS
CLINICAL APPEARANCE OF PERIPHERAL NERVE INJURIES IN THE HAND
1.Median: • Often due to carpal tunnel sd. • Wasting of thenar eminence • Decreased thumb function, especially
opposition
2. Ulnar:• Damage to ulnar nerve can occur with trauma
to elbow region. Ulnar neuropathy is a frequent complication of diabetes mellitus
• Wasting of web space and interosseous spaces.
• Affects adductor pollicis and ulnar head of FPB. A person who lacks strength in these muscles cannot grasp with the thumb .
3. Radial:• Associated with gunshot or stab wounds,
fracture of humerus, "Saturday night palsy." • person demonstrates a "dropped wrist," and
cannot reposition thumb. • lack of wrist extension may cause hand grip
to be weak.
Boutonniere Deformity
• Tear or stretch of the central extensor tendon at PIP
• Note: unopposed flexion at PIP
• Extension at DIP• Trauma or
inflammatory arthritis
Swan Neck Deformity
• Contraction of intrinsic muscles (trauma, RA)
• NOTE: Extension at PIP
Osteoarthritis
• Heberden’s nodes: DIP
• Bouchard’s nodes: PIP
Rheumatoid Arthritis
• MCP swelling• Swan neck
deformities• Ulnar deviation at
MCP joints• Nodules along
tendon sheaths
Mallet Finger
• Hyperflexion injury• Ruptured terminal
extensor mechanism at DIP
• Incomplete extension of DIP joint or extensor lag
• Treatment: – stack splint
Dupuytren’s Contractures
• Palmar or digital fibromatosis
• Flexion contracture• Painless nodules near
palmar crease• Male> Female• Epilepsy, diabetes,
pulmonary dz, alcoholism
Thank you