Articulations or Joints are specialized anatomical structures at
which the ends of certain bones are joined or the borders of other bones
are juxtaposed. These osseous junctions are secured by ligaments,
fibrous capsule and other binding tissues which restrict movements or
permit varying degrees of movements. Joints vary widely in their
structure, frequently presenting unique morphological features, adapted to
specific functional requirements.
Depending on the morphological characteristics of the joints, they
are classified into,
1. Fibrous Joints – Many of which are immovable and are
united by fibrous tissue (synarthroses).
2. Cartilaginous Joints – Slightly movable, the union between
the bones occurs via cartilage
3. Synovial Joints – Freely movable (diarthroses)
Synovial Joints are highly evolved articulations which permit free
movements. Because the human lower limbs are concerned with
locomotion and the upper limbs provide a great versatility of movements,
it is not surprising that most of the joints are of the synovial type. The
integrity of a synovial joint results from its ligaments and capsule which
bind the articulation externally and to some extent from the surrounding
muscles. The contiguous bony surfaces are covered with hyaline
cartilage and the joint cavity is surrounded by a fibrous capsule, the inner
surface of which is lined by a synovial layer containing cells that are
thought to secrete the viscous lubricating synovial fluid.
1. Articular Cartilage: Firmly adherent to the articular surfaces of
majority of bones. They are neither innervated nor supplied with
2. Ligaments: are composed mainly of bundles of collagenous fibres.
They are pliant and flexible to allow perfect freedom of movement.
3. Articular Capsule: Forms a complete envelope for a freely
movable joint and consists of external fibrous layer and internal
synovial layer. The fibrous layer gets attached to the periosteum
along the entire circumferance of the articular end of each bone.
Its flexibility permits movements, yet its strength protects joint
4. Synovial Membrane: Covers the inner surface of the fibrous
capsule, forming a closed sac called the synovial cavity. It is
composed of loose connective tissue and it has a free surface of
finger like projection called the Synovial Villi. The synovial cavity
contains only enough synovial fluid to moisten and lubricate the
synovial surfaces, but in an injured or inflammed joint, the fluid
may accumulate in painful amounts.