Download Prof. Dr. Muhammad Imran Qureshi

The Wrist Joint
(Radio carpal Articulation)
By
Prof. Dr. Muhammad Imran Qureshi
Type Of the Joint: Compound
Variety Of the Joint: Biaxial of Ellipsoid Variety
Articular Surfaces: They are covered with Hyaline
Cartilage. They are:
Proximally, the concave socket, formed by the distal
surfaces of the radius and the triangular articular
disc.
Distally, the convex proximal surface of the carpus
(formed by the scaphoid, lunate, and triquetrum
bones along with their interosseous ligaments). The
disc joins the medial edge of the articular surface of
the radius to the styloid process of the ulna. It is
triangular in shape and separates the ulna from the
joint. In the resting position of hand only the
scaphoid and lateral part of the lunate articulate with
the two shallow fossae on the distal surface of the
radius. (The lateral Triangular facet is for the
Scaphoid and the medial Quadrangular facet for the Lunate). The remainder of the
lunate is in contact with the articular disc while the triquetrum is applied to the medial
part of the capsule of the joint.
Fibrous Capsule:
It passes from the margins of the
distal ends of the radius and ulna
and from the margins of the
articular disc to the proximal row of
carpal bones, excluding the
pisiform.
The anterior and posterior parts of
the fibrous capsule contain fibers
which pass obliquely downwards
and medially.
Synovial Capsule / Membrane:
The synovial membrane lines the fibrous capsule and covers the interosseous
ligaments of the carpus. Sometimes there is a defect in the triangular disc in which
case, it may become continuous with the synovial membrane of the distal radio-ulnar
joint.
Ligaments of the joint:
Only Extra capsular Ligaments are present in this joint.
They comprise of slightly thickened portions of the capsule attached to the styloid
processes of the radius and ulna and passing to the scaphoid and triquetrum
respectively. They are called the radial and ulnar collateral ligaments respectively.
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Blood Supply of the joint:
It is provided from branches from the arteries which anastomose around it.
These are the branches from Palmar and Dorsal carpal arches, Posterior interosseous
artery and recurrent branch from the deep palmar arch.
Nerve Supply of the joint:
It follows the Hilton’s Law.
This is through the anterior (deep branch of median) and posterior interosseous (deep
branch of radial) nerves and the dorsal branch of the ulnar nerve.
Movements of the joint:
Transversely, this ellipsoid joint has a long radius of
curvature which permits abduction and adduction while
anteroposteriorly it has a short radius which permits
flexion and extension.
All these movements are supplemented by similar
movements at the inter carpal joints, which are
principally responsible for abduction and greatly
increase the range of flexion.
At the radio carpal joint, extension and adduction have
the greatest range. In adduction, the carpal bones slide
laterally, the lunate passing further on to the radius
while the triquetrum comes into contact with the
triangular disc.
Because of the two different curvatures of the joint at
right angles to one another, rotation is not possible at
this joint. As a result, the carpal bones move with the
radius in pronation and supination at the radio ulnar
joints.
Thus the movement of adduction when the hand is
pronated the hand is deviated laterally but still
towards the ulna which is now lateral to the radius in
the distal forearm. For this reason, adduction is
commonly called 'ulnar deviation' and abduction
‘radial deviation'. The direction of the radio carpal
joint is oblique.
The flexion and extension at the radio carpal joint is
always accompanied by similar movement at the mid
carpal joint.
Of the total range of flexion (about 80o) a greater
proportion occurs at the mid carpal joint; in extension
(60o), there is a greater proportion at the wrist Joint itself.
These four movements are carried out by combinations of muscle groups.
Thus flexion is produced by flexor carpi radialis and flexor carpi ulnaris as prime
movers, assisted by palmaris longus and the flexors of fingers and thumb and abductor
pollicis longus.
Extension is produced by the radial extensors (longus and brevis) and the ulnar
extensor as prime movers assisted on occasion by the extensors of fingers and thumb.
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Abduction (limited to about 15o because of the more distal projection of the radial styloid
process) is carried out by abductor pollicis longus and, when the wrist is displaced from
the midline, by flexor carpi radialis and the two radial extensors acting together.
Similarly adduction (60°) is brought about by simultaneous contraction of flexor and
extensor carpi ulnaris.
The most usual movement of the wrist is one of extension combined with radial
abduction, and of flexion combined with ulnar adduction.
Hammering in a nail illustrates this movement, and exactly similar movements of the
wrist, in the working position of the forearm, occur in a variety of everyday acts like
eating and drinking, washing and dressing, writing, etc.
Indeed, pure flexion-extension and abduction-adduction are unusual movements. Since
extension-abduction is an antigravity movement in the normal working position, this may
explain the presence of two radial extensors where one serves on the ulnar side, and
there is only one flexor each for radial and ulnar sides.
Stability Of the joint:
Bony Factors:
The lateral and dorsal margins of the radius extend further distally than its other
margins. This reduces the likelihood of posterior dislocation of any of the carpal bones.
Ligamentous Factors:
Only the collateral ligaments are strong. The anterior and posterior ligaments are merely
thickened fibers of the capsule.
Muscular Factors:
The tendons of long flexors of the fingers and thumb stabilize the joint anteriorly
The tendons of long extensors of the fingers and thumb stabilize the joint posteriorly
Scaphoid fracture
It is the most frequently fractured carpal bone. The usual cause of fracture is falling on
outstretched hand. The patient feels pain over “snuff box”. It doesn’t always show up
on an x-ray for 2-3 weeks. Usually there is difficulty healing because of poor blood
supply.
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