Biomech Webinar 3

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Biomechanics wrist/hand:

Biomechanics wrist/hand Dr. Adrian VanIngen Webinar 3.

PowerPoint Presentation:

Osteokinematic movement at the wrist. Palmar flexion: 0-85/90 degrees. Dorsiflexion: 0-75/80 degrees. Radial deviation: 0-15/20 degrees. Ulnar deviation 0-35/37 degrees. Pronation: 0-80/80 degrees. Supination: 0-80/90 degrees.

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How much ROM is needed for functional movement of the wrist? 10 degrees of palmar flexion. 35 degrees of dorsiflexion. Intrinsic/extrinsic ligaments of the wrist provide stability for the radiocarpal , ulnocarpal , midcarpal , and intercarpal joints. They resist movement by tightening and allowing it by loosening.

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Sequential movement of the wrist during extension. * the distal carpal row moves dorsally and the proximal row moves palmarly until about 60 degrees ofextension * at about 60 degrees of extension, the hamate, capitate , trapezoid and scaphoid lie in a close pack position and form a rigid mass; this position of these four carpal bones also produces radial deviation which occurs with the wrist in this extended position. * this ridge mass moves dorsally as a unit on the triquetrum and lunate * the triquetrum and lunate move palmarly on the radius at the radiocarpal joint as the ridge mass moves dorsally until full extension is reached * at full extension, the wrist is in a close packed position with the exception of the pisiform and trapezium * during extension, the pisiform moves distally (inferiorly) and the radius moves proximally (superiorly) on the ulna

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sequential movements during wrist flexion from neutral * the distal carpal row moves palmarly and the proximal row moves dorsally * the scaphoid does not come to a close packed position with the distal row during flexion but both rows move until about 60 degrees of flexion * during about the last 30 degrees of wrist flexion, movement occurs mainly at the midcarpal joint with the distal row moving palmarly * during wrist flexion, there is a considerable distal shift of the radius on the ulna

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sequential movements during radial deviation movement mainly at mid-carpal joint with little movement at radiocarpal joint distal carpal row moves radially most say that the proximal row moves ulnarly but some say there is no or very little ulnar movement of the proximal row during radial deviation scaphoid and lunate move palmarly (flex) to make room for the trapezium which moves between radial styloid process and scaphoid radial deviation is limited when the wrist is fully flexed wrist flexion moves the scaphoid and lunate dorsally which blocks palmar movement of these carpals this blockage prevents a space from opening between the styloid process of the radius and scaphoid, blocking the movement of the trapezium and limiting radial deviation radial deviation is limited when the wrist is fully extended close pack position of the carpals at full wrist extension decreases intercarpal movement at the midcarpal joint decreased midcarpal movement blocks radial movement of the distal carpal row which decreases deviation

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LOADING OF WRIST the wrist is designed to withstand compression compression is transmitted mainly through the lunate/scaphoid to the radius and less so through fibrocartilage disc to ulna * about 80% of the compression forces at the wrist are transmitted to the large distal radius * about 20% of the compression forces by disc in a fall where a person breaks the fall with the arm, wrist and hand extended, force transmission occurs as follows * ground force is transmitted via third metacarpal to capitate * from capitate , force transmits to the lunate and scaphoid * from the lunate and scaphoid force is transmitted to the radius * if the forces are high, the distal radius or scaphoid can be fractured or the lunate dislocated

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MUSCLES MOVING WRIST muscles crossing the wrist joint generate movement and provide DYNAMIC STABILITY. wrist extensors: ext . carpi radialis longus ext . carpi radialis brevis ext . carpi ulnaris other muscles that may assist in wrist extension ext . digitorum ext . indicis ext . digiti minimi extensor carpi ulnaris , extensor carpi longus and brevis lie at periphery of wrist and away from the axis of motion so that they have a longer force arm and thus a mechanical advantage over the other muscles that can assist in wrist extension

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wrist flexors flexor carpi radialis flexor carpi ulnaris other muscles that may assist in wrist flexion flexor digitorum superficialis (the flexor digitorum profundus is so close to axis of movement that its position is mechanically too poor to produce wrist flexion) palmaris longus flexor carpi ulnaris and flexor carpi radialis lie at periphery of the wrist and away from the axis of motion, so that they have a longer force arm and thus a mechanical advantage over those muscles that can assist in wrist flexion

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  ulnar deviation *extensor carpi ulnaris with the wrist in neutral or extension *flexor carpi ulnaris with the wrist neutral and flexion radial deviation *extensor carpi radialis longus with the wrist in neutral or extension *extensor carpi radialis brevis produces only slight radial deviation with the wrist in neutral or extension because its distal attachment is so centrally located that the muscle can move the wrist only slightly in a radial direction *flexor carpi radialis with the wrist in neutral or flexion *other muscles that may assist in radial deviation -abductor pollicis longus -extensor pollicis brevis

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ARCHES OF THE HAND proximal transverse arch is at level of the distal carpal row and carpometacarpal joints distal transverse arch is through the heads of the metacarpals at the metacarpophalangeal joints longitudinal arch extends through the center of the hand from the proximal carpal row through the four fingers arches are maintained by the intrinsic muscles of the hand a flat hand results from a collapse of these arches because of paralysis of the intrinsic hand muscles

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Joint Type of movement Degrees of movement CMC of thumb Flexion/Extension Abduction/Adduction 0 - 45 / 0 – 15 0 – 70/ 0 - 80 CMC index, middle fingers Flexion/Extension Abduction/Adduction Slight to none Slight to none CMC ring finger Flexion/Extension 0 - 15 CMC little finger Flexion/ Extension Abduction/Adduction 0 - 30 0 – 10 /0 - 20 MCP of thumb Flexion/ Extension Abduction/ Adduction 0 – 50 Slight MCP Index, Middle, Ring, Little fingers Flexion/ Extension Abduction/ Adduction 0 – 90 0 – 45/ 0 - 45 IP thumb Flexion/ Extension 0 – 90 PIP Index, Middle, Ring, Little fingers Flexion/ Extension 0 - 100 DIP Index, Middle, Ring, Little fingers Flexion/ Extension 0 – 90 / 0 - 10 OSTEOKINEMATIC MOVEMENTS OF THE HAND

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CMC joint of the thumb *flexion : palmar rotation & palmar translation *extension : dorsal rotation & dorsal translation *abduction (palmar abduction): ulnar rotation & ulnar translation *adduction (palmar adduction): radial rotation & radial translation

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RANKING OF EXTRINSIC MUSCLES BY FORCE PRODUCTION 1. flexor digitorum superficialis (FDS) flexor digitorum profundus (slightly less than flexor digitorum superficialis ) extensor digitorum ( 1/3 of FDS) flexor pollicis longus ( 1/4 of FDS) extensor indicis ( 1/10 of FDS) 5. abductor pollicis longus ( 1/10 of FDS ) 6. extensor pollicis longus ( 1/50 of FDS) extensor pollicis brevis ( 1/50 of FDS) *notice that the force output of the flexor digitorum superficialis and profundus is much greater then that of the extensor digitorum

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HAND GRIPS AND FINGER PINCHES GRIPS * Power grip such as hammer grip, fist. * Precision grip such as holding a cup, screwing a light bulb. PINCHES *Dynamic tripod such as holding a pen. *Tip pinch, picking up button/coin. *Palmar pinch, holding a sheet of paper. *Lateral pinch, holding a key while inserting it in a lock.

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FORCES DURING GRIP AND PINCH compressive forces on finger joints *forces are least at the DIP * forces at the PIP and MCP vary with function + tip pinch forces are greater at the PIP than the MCP + lateral pinch forces are greater at the MCP than the PIP + the forces when opening big jars are greater at the MCP than the PIP + the forces when holding a glass are greater at the PIP than the MCP compressive forces at thumb * forces at IP = 2 - 3 X the applied force * forces at MCP = 5 - 6 X the applied force * forces at CMC = 6 - 12 X the applied force during normal pinch and grip actions, the tensile forces on the tendons of the extrinsic muscles are 4 - 5 X the applied force during normal pinch and grip actions, the tensile forces on the tendons of the intrinsic muscles are 1.5 - 3 X the applied

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