Download Carpal Bones

Wrist
Introduction
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The wrist contains eight small carpal bones, which as a group act
as a flexible “spacer” between the forearm and hand.
Distal forearm
Distal forearm
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Distal end of the radius
A. anterior view of the distal radius showing an ulnar tilt of
about 25 degrees.
B. a medial view of the distal radius showing a palmar tilt of
about 10 degrees.
Carpal Bones
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From a radial(lateral)to ulnar direction, the proximal row of
carpal bones includes the scaphoid, lunate, triquetrum, and
pisiform.
The distal row includes the trapezium, trapezoid, capitate,
and hamate.
Carpal Bones
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The proximal row of carpal bones is joined in a relatively
loose fashion.
The distal row of carpal bones is bound tightly by strong
ligaments, providing a rigid and stable base for articulation
with the metacarpal bones.
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Carpal Bones
Scaphoid
•The scaphoid has two convex surfaces called poles.
•The proximal pole articulates with the scaphoid facet of the
radius.
•The distal pole has a slightly rounded surface, which articulates
with the trapezium and trapezoid.
Lunate
•The lunate is the most inherently unstable of the carpal bones,
in part because of its shape, but primarily because of its lack of
firm ligamentous attachments to the relatively rigid capitate
bone.
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Carpal Bones
Triquetrum
•The triquetrum is the third most frequently fractured bone of
the wrist, after the scaphoid and lunate.
Pisiform
•The pisiform, meaning “shaped like a pea”, articulates loosely
with the palmar surface of the triquetrum.
Capitate
•The capitate is the largest of all carpal bones.
•The large head articulates with the deep concavity provided by
the scaphoid and lunate.
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Carpal Bones
Trapezium
•The trapezium has an asymmetric shape.
•The proximal surface is slightly concave for articulation with
the scaphoid.
•Particular importance is the distal saddle-shaped surface, which
articulates with the base of the first metacarpal.
Hamate
•The hamate base, or distal surface, articulates with the bases
of the fourth and fifth metacarpals.
•This articulation provides important functional mobility to the
ulnar aspect of hand, most noticeably when the hand is cupped.
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What is Carpal Tunnel?

The tunnel serves as a passageway for the median nerve
and the tendons of extrinsic flexor muscles of the digits.
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Arthrology
Joints of the Wrist
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Radiocarpal joint
Midcarpal joint
•Medial compartment
•Lateral compartment
Intercarpal joints.
Intercarpal joints contribute to wrist motion through small
gliding and rotary.
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Radiocarpal joint
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The proximal components of the radiocarpal joint are the
concave surfaces of the radius and an adjacent articular
disc.
The distal components of the radiocarpal joint are the
convex proximal surfaces of the scaphoid and the lunate.
The thick articular surface of the distal radius and the
articular disc accept and disperse the forces that cross the
wrist.
Approximately 20% of the total compression force that
crosses the radiocarpal joint passes through the articular
disc.
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Radiocarpal joint
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The remaining 80% passes directly through the scaphoid
and lunate to the radius.
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The contact areas at the radiocarpal joint tend to be greatest
when the wrist is partially extended and ulnarly deviated.
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This is also the wrist position at which maximal grip strength
is obtained.
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Midcarpal joint
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The midcarpal joint is the articulation between the proximal
and distal rows of carpal bones.
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The midcarpal joint can be divided descriptively into medial
and lateral joint compartments.
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The lager medial compartment is formed by the convex head
of the capitate and apex of the hamate, fitting into the
concave recess formed by the distal surfaces of the
scaphoid, lunate, and triquetrum.
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Midcarpal joint
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The lateral compartment of the midcarpal joint is formed by
the junction of the slightly convex distal pole of the scaphoid
with the slightly concave oroximal surfaces of the trapezium
and the trapezoid
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Wrist ligaments
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Wrist ligaments are essential to maintaining the natural
intercarpal alignment and for transferring forces within and
across the carpus.
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Extrinsic ligaments have their proximal attachments on the
forearm but attach distally within the wrist.
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Intrinsic ligaments have both their proximal and distal
attachments within the wrist.
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Extrinsic ligaments
The
dorsal radiocarpal ligament courses distally in an ulnarly direction,
attaching primarily between the distal radius and the dorsal surfaces of
the lunate and triquetrum.
The fibers that attach to the lunate provide an especially important
restraint against anterior(volar)dislocation of this inherently.
Extrinsic ligaments
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The palmar radiocarpal ligaments become maximally taut at full
wrist extension.
The primary global function of the TFCC is to securely bind the
distal ends of the radius and ulna while simultaneously permitting
the radius, with attached carpus, to freely rotate(pronate and
supinate) around a fixed ulna.
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Intrinsic ligaments
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Thin dorsal intercarpal ligament provides transverse stability
to the wrist by interconnecting the trapezium, scaphoid,
lunate, and triquetrum.
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Kinematics of wrist motion
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The osteokinematics of the wrist are defined for 2 degrees of
the freedom.
Flexion-extension and ulnar-radial deviation.
Osteokinematics
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The wrist rotates in the sagittal plane about 130 to 160
degrees.
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On average, the wrist flexes from 0 degrees to about 70 to
85 degrees and extends from 0 degrees to about 60 to 75
degrees.
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Total flexion normally exceeds extension by about 10 to 15
degrees.
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End-range extension can be limited by stiffness in the thick
palmar radiocarpal ligaments.
Osteokinematics
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The wrist rotates in the frontal plane approximately 50 to 60
degrees.
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Radial and ulnar deviation is measured as the angle between
the radius and the shaft of the third metacarpal.
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Ulnar deviation of the wrist occurs from 0 degrees to about
35 to 40 degrees.
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Radial deviation occurs from 0 degrees to about 15 to 20
degrees.
Because of the ulnar tilt of the distal radius, maximum ulnar
deviation normally is double that of radial deviation.
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Arthrokinematics
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The axis of rotation for wrist movement is assumed to pass
through the head of the capitate.
The axis runs in a medial-lateral direction for flexion and
extension.
Anterior-posterior direction for radial and ulnar deviation.
Wrist extension and flexion
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Radiocarpal joint is represented by the articulation between
the radius and lunate.
Midcarpal joint is represented by the articulation between
the lunate and capitate.
Dynamic interaction within the joints of the
central column of the wrist
Ulnar and radial deviation of the wrist
Carpal instability
Two common types of carpal instability
1. rotational collapse of wrist: the “zig-zag” deformity
2. Translocation of the carpus
Rotational collapse of the wrist
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The lunate is the most frequently dislocated carpal bone.
Scaphoid forms an important mechanical link between the
lunate and the more stable, distal row of carpal bones.
Volar intercalated segment instability(VISI)
Dorsal intercalated segment instability(DISI)