Book - Buchanan's Manual of Anatomy including Embryology 8

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A personal message from Dr Mark Hill (May 2020)  
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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Frazer JE. Buchanan's Manual of Anatomy, including Embryology. (1937) 6th Edition. Bailliere, Tindall And Cox, London.

Buchanan's Manual of Anatomy: I. Terminology and Relative Positions | II. General Embryology | III. Osteology | IV. Bones of Trunk | V. Bones of Head | VI. Bones of Upper Limb | VII. Bones of Lower Limb | VIII. Joints | IX. The Upper Limb | X. Lower Limb | XI. The Abdomen | XII. The Thorax | XIII. Development of Vascular Systems | XIV. The Head and Neck | XV. The Nervous System | XVI. The Eye | XVII. The Ear | Glossary
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Chapter VIII Joints

Joints may be regarded as gaps in the skeleton where movemen may take place, and it is not surprising to find that, speaking generally those joints have the simplest structure in which least movement is allowed.

If one of the sutures on the vault ot the skull be examined, it wil be found that there is very little movement between the two bone: bounding it, and that they are separated and at the same time helc together by a very thin film of fibrous tissue, which is, of course, th( original membrane in which the cranial bones were ossified. On th< surface the periosteum, covering the bones, is continued from one tc the other, but is firmly blended with the interstitial fibrous tissue.

A joint of this class, formed by a stoppage in the ossification—£ stoppage, indeed, which may be only temporary—and composed o: the original tissue in which the ossification had taken place, is knowr ts a fibrous joint, and this class includes all joints in which parts ol the skeleton are bound together by material more flexible than themselves without the intervention, at any time, of a joint cavity.

Sometimes, when greater freedom of movement is needed, the fibrous interval between the bones may be greater, and the joint, instead of being a suture, is then known as a syndesmosis.

Sometimes, as in the base of the skull, where chondrification has preceded ossification, the gap between the two bones is filled with uninvaded hyaline cartilage, and in that case the articulation becomes a primary cartilaginous joint.

It has been seen, therefore, that a fibrous joint is a very primitive orm of articulation, depending on a part of the original precursor of the one, whether it be fibrous tissue or cartilage, remaining in its original flexible condition. When two bones connected by cartilage—that is to say, primary cartilaginous joint—have to provide for a large amount o movement, the central part of the cartilage disappears and a joint cavi y is formed, leaving a layer of articular or encrusting cartilage on tne end of each bone, and converting the original fibrous peric ondrium into a true capsule, which may be reinforced afterwards y extracapsular connective tissue whenever special strain has to


iwn CC ? ^ even existing tendons may acquire attachments t ? , i e cjnes, and be converted into ligaments of the accessor

mnc+ U e> i 01 ! g 1 i 1 ls ^ ar from necessary to assume that all, or evei most, such structures are formed in this way.


After the joint cavity has been formed, the connective tissue cells surrounding it arrange themselves into a pavement epithelium or synovial membrane, and secrete a lubricating fluid called synovia.

At first, it is said, the synovial membrane lines the whole joint cavity, but later on, when active movement begins, that part which covers the articular cartilage is worn away, and the synovial membrane now ceases wherever the cartilage begins.

A joint in which there is a constant synovial cavity is known as a synovial joint, and different subdivisions of this class are recognized according to the kind of movement needed and the shape which the bony ends take to adapt themselves to it.

Sometimes, when more than one perfectly distinct kind of movement is required at one joint, intracapsular fibro-cartilages or menisci are formed, and these partly or completely divide the joint into two, so that each part may be specialized for its own particular movement. These menisci are always fibrous or fibro-cartilaginous, are always thickest where they are attached to the capsule, and thinnest where they are farthest away from it. When these facts are harmonized with the teachings of comparative anatomy, which shows them appearing in certain animals as the need for them arises, and disappearing in others in which the need no longer exists, they suggest that menisci are originally ingrowths from the true capsule into the joint.

Where the movement of a synovial joint is not very pronounced, and is chiefly of a gliding nature, the joint ends are similar, and the articulation is spoken of as a plane joint. The clavicular and carpal joints are examples of this.

Movements round two axes, to a limited extent, combined with great strength, may be obtained by two saddle-shaped joint surfaces . . another reciprocally, and forming what is known as a saddle

joint. The only example of this subdivision in man is the carpometacarpal joint of the thumb.

A ball-and-socket joint, allowing movement in any direction is found in the shoulder and hip.

When a joint with ball-and-socket ends has its capsule so disposed hat movement can only take place round two axes, it is spoken of as a condyloid. Examples of this are seen in the carpo-metacarpal joints of the fingers, which may be flexed or abducted, but cannot be twisted round, so that the nails look towards the palm.

Some anatomists, recognizing only form as a basis of classification, regard the knee as a double condyloid, though the function is different rom that of a single one, because the second condyle plays the part of e outrigger of a native canoe, and prevents lateral movement, thus, roi E a physiological point of view, making the joint a hinge.

the hinge or ginglymus is well represented in the human body, the est examples being the elbow and interphalangeal joints. In the -rue hinge the axis is horizontal, as in the hinge of a box. When it is

rertical, as in the hinge of a door, the articulation is spoken of as a

hvot joint.


There are still a few joints for which it is difficult to find a place in either of these two main divisions, owing to the fact that they sometimes have synovial cavities of small extent, and sometimes none. For these a third main division, called cartilaginous joints, has been provided to include the symphysis pubis and the intervertebral discs, which, in the lumbar region, have a synovial cavity in the nucleus pulposus.

Having cleared the way by these remarks, a formal classification of joints may now be attempted; it is the one which is most in harmony with the views of the writers at the present time, though it must in fairness be stated that no classification has yet been produced which could stand careful destructive criticism.


Classification of Joints.


Fibrous

Joints


Synovial

Joints


Cartilaginous

Joints


True sutures


False sutures


Serrate.

Denticulate.

Limbous. r Squamous.

) Harmonic.

1 Wedge-and-groove (schindylesis). (Peg-and-socket (gomphosis).

Syndesmoses.

With uni-axial movement: Hinge-joint (ginglymus).

With bi-axial movement (g^vtoid i oint v (Saddle joint.

With poly-axial movement: Ball-and-socket joint.

With gliding movement: Plane joint.

(Primary cartilaginous joint.

(Secondary cartilaginous joint.


The explanatory notes which follow will make this classification more intelligible.

Suture. — There are two forms of suture, called true and false. When the margins of the bones present a number of projections with intervening depressions, so that they become closely interlocked, the suture is called true. When the opposed margins are more or less flat, so that there is merely apposition without interlocking, the suture is spoken of as false.

True sutures are of three kinds—serrated, denticulate, and limbous. In the serrate suture the margins of the bones are saw-like, as in the frontal suture; in the denticulate suture the margins present projections like teeth, as in the interparietal suture; and in the limbous suture the margins of the bones are so ridged and bevelled that they overlap, as m the lower and medial parts of the fronto-parietal suture.

False sutures are of two kinds—squamous and harmonic. In the sqiiamous suture the margins are so bevelled that one overlaps the other, as in the squamo-parietal suture. In the harmonic suture the surfaces, which are rough, are in direct apposition, as between the maxillae. In the wedge-and-groove suture a ridge on one bone is received into a cleft on another. Such a suture is also known as schindylesis , and it is exemplified in the articulation between the rostrum of the sphenoid and the vomer.

The peg-and-socket suture or gomphosis is only represented by the sockets of the teeth.

Ligaments. —These are composed of white fibrous tissue, and, as their name implies, they bind the bones together. At a synovial joint their chief use is to control movement, the bones being maintained in position by the muscles and atmospheric pressure. At their attachments they are intimately associated with the periosteum. When the fibrous tissue is arranged continuously round the joint the ligament is called a capsular ligament. In other cases the tissue is disposed as round cords, and in a third variety it forms flattened bands.

Synovial Membranes. —These membranes are associated with movable structures, such as joints, gliding tendons, and the skin covering bony projections. Accordingly there are three kinds of synovial membrane—namely, articular, tendon or vaginal, and bursal.

The articular synovial membranes line the interior of synovial joints, except where there is articular cartilage, and they stop at the margin of this cartilage. In some joints they give rise to folds, some of which contain adipose tissue. Such folds are known as synovial fringes.

It is usually taught that everything inside the capsule, except articular hyaline cartilage, is lined by synovial membrane, but there seems reason to doubt whether this really persists over the menisci.

The tendon or vaginal synovial membranes, also known as synovial sheaths, invest those tendons which glide freely within fibrous sheaths. They are met with around the ankle, particularly behind the lateral and medial malleoli, and upon the palmar aspect of the fingers.

The bursal synovial membranes, commonly called synovial bursae, are synovial sacs which are situated between the integument or a muscle and some bony projection. They may be deep-seated or subcutaneous. The deep-seated hursce are situated between a muscle, or its tendon, and the contiguous bone— e.g., the tendon of the biceps brachii and the anterior part of the tuberosity of the radius. The subcutaneous hursce are placed beneath the integument, which they separate from some bony projection— e.g., the prepatellar bursa.

Movements. —The different kinds of movement at synovial joints are angular, circumduction, rotation, and gliding.

Angular Movement. —This increases or diminishes the angle between two or more bones. When it takes place in a forward and backward direction, so as to bend or straighten a joint, it is spoken of as flexion and extension. When it takes place laterally, away from or towards the median plane of the body, it is called abduction and adduction. In the case of the hand the median line from or towards which abduction and adduction take place is a line passing through the centre of the middle finger, and in the case of the foot, through the centre of the second toe.

Circumduction. —This consists of the four forms of angular movement, occurring successively in such sequence as flexion, abduction, extension, and adduction. It occurs at ball-and-socket and condyloid joints, and during the movement a part of the limb describes a cone, the apex of which is formed by the proximal end at the moving joint, whilst the base is described by the distal end.

Rotation. —This is movement of a bone round its axis without much disturbance of its position. It occurs at ball-and-socket and pivot joints, and also at the knee, which is a hinge-joint.

Gliding Movement. —This consists of a simple to-and-fro or sliding movement of two articular surfaces, as between the articular surfaces of vertebrae, and at the carpal and tarsal joints. When the gliding is combined with a certain amount of turning or rolling, so as to bring different parts of the articular surfaces successively into contact in different positions of the joint, the movement is known as coaptation, as at the femoro-patellar joint.

A description of the different articulations will be found with that of the regions to which they belong.