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