Anatomy and Physiology of Joints
Table of Contents
- Defining Joints
- Classification of Joints
- Amphiarthroses Joints
- Diarthroses Joints
- Ginglymus or Hinge Joint
- Trochoid or Pivot Joint
- Condyloid Joint
- Saddle Joint
- Ball-and-Socket Joint
- Gliding Joints
- Gliding Movement
- Angular Movement
In human body, joints are defined as the junction where the bones of the skeleton are connected. Joints are also termed as ‘articulations’. The major function of the joints is to provide flexibility to the skeletal frame and allow growth. The movement of each joint depends on the following:
- Structure of the joint and interaction with the surfaces.
- Flexibility with surrounding tissues.
- Position of the ligament muscles and tendon.
Joints can be immovable, fixed or allow limited movement. Most joints allow considerable amount of motion. There are over 230 movable and slightly movable joints in the body.1
The internal structure of many joints is very complicated because joints are not only composed of ends of bones but also consist of:
- Ligaments—Ligaments are white fibers, which are hard and bind bones together.
- Cartilage—Cartilage are kind of connective tissue. They cover the bones and give a cushion effect to the bone ends.
- Articular capsule—It is a fibrous tissue and covers the ends of the bones.
- Synovial membrane—This lines the capsule and secretes a lubricating fluid called synovia.
Classification of Joints
Joints are classified based on structure and function. They are synarthroses joints, amphiarthroses joints and diarthroses joints.2
Synarthroses JointsThese are ‘immovable’ joints or articulations and include those joints whose bone surfaces are in direct contact with each other. These joints are fixed firmly by connective tissue or hyaline cartilage. Synarthroses joints are of four types as follows.
In this kind of joint, the margins of bone are uninterruptedly joined by a thin layer of fibrous tissue (see Fig. 1). This joint is found in the skull. Sutura can be true suture (bones are joined through a series of processes and ends interlocked together) and false suture (joints formed by roughened surfaces placed in closed proximity with one another).
True sutures are of four types.
- Sutura dentate: In this joint, the edges of the bones form tooth-like projections. For example, suture connecting the parietal bones.
- Sutura serrata: In this joint, the edges of the bones look like the teeth of a fine saw. For example, suture connecting the two portions of the frontal bone.
- Sutura limbosa: In such joints, the surface shows a degree of slant along with interlocking. For example, suture connecting the frontal and perietal bones.
The false sutures are of two varieties.
- Sutura squamosa: Overlapping of adjacent bones by broad sloping margins is seen in sutura squamosa. For example, present between the frontal and parietal bones.
- Sutura harmonia: This kind is seen in such joints where adjacent rough surface are in simple apposition or in close proximity. For example, joints connecting the maxillae or the joints present between the horizontal parts of the palatine bones.
This is a fibrous joint where the sharp edge of one bone goes into the cleft of another edge of the bone. It is also called as wedge and groove joint. For example, rostrum of the sphenoid.
In this kind of joint, a conical process is inserted into a socket. For example, tooth in its socket.
Synchondrosis is a temporary form of joint where the connecting medium is cartilage. Later, this cartilage is converted into bone. This is also called cartilage joint. This is ound in bodies of long bones, between the occipital and sphenoid after some years of birth.
These joints are slightly movable. They consist of adjacent bony surfaces connected by disks of fibrocartilage, which are broad and flattened. These joints are present between the tibia and fibula, the discs between vertebrae.
These joints or articulations can move about freely. This is also called as synovial joints (see Fig. 3). These joint consist of adjacent bony surfaces, which are as follows
- Covered by articular cartilage.
- Connected by ligaments.
- Lined by synovial membrane.
Articular discs completely or incompletely divide the diathroses joints. Following are the types of diathroses joints and is based on the kind of motion.
9.Ginglymus or Hinge Joint
In this kind, the surface of the joints is moulded or connected by strong collateral ligaments to allow motion in one plane that is, forward or backward. For example, interphalangeal joints, joint between the humerus and ulna.
10.Trochoid or Pivot Joint
The movement in this kind of joint is limited to rotation, as one bone pivots within a bony or an osseoligamentous ring. For example, the joint between the first and second cervical vertebrae (the atlas and axis).
This is also called as condylar joint. In this kind of joint, the ovoid head of one bone moves in an oval cavity of another. This permits all movements except axial rotation. For example, wrist joint.
The articulating surfaces are reciprocally saddle-shaped and permit movement of all kinds like flexion, extension, adduction, abduction, and circumduction. There is no axial rotation. For example, carpometacarpal joint of the thumb.
In this kind of joint, a rounded surface of one bone (ball) moves within a cup-shaped depression (socket) on another bone, allowing greater freedom of movement. This is also called as spheroidal joint. For example, joints of the hip and shoulder.
This kind of joint is formed by the opposed surfaces. The opposed surfaces are flat or curved so that the bones slide against each other. It is also called as arthrodial joint and plane joint. For example, small bones of the carpus and tarsus, intervertebral joints.
Movements of joints
In this kind of movement, one surface of the joint slides over the other without circular movements and seen in all movable kinds of joints. This is seen in flat surfaced joints and between two contiguous surfaces.
This kind of movement is seen in long bones. The angular movements may be,
- Forward and backward constituting flexion and extension.
- Toward and from the median plane of the body constituting adduction and abduction.
In this kind of movement, the head of the bone moves in the cavity of joints. This is seen in shoulder and hip joints.
In this kind of movement,
- The bone goes around a central axis without undergoing change from its axis.
- The axis of rotation may lie in a separate bone.
- A bone may rotate around its own longitudinal axis.
- The axis of rotation may not be quite parallel to the long axis of the bone.
Joints are very important for the movement of the skeletal frame, without which people would not be able to move at all. Owing to various movements of the joints, people are capable of doing different kinds of physical activities.
Hence, it is extremely important to maintain the health of joints with a balanced diet and adequate exercise.
1.Van De Graaff, Kent M. Human Anatomy. 5th edn. Boston, MA: WEB McGraw-Hill, 1998.
2.Henry G. Anatomy of the Human Body. 20th edn, 1918.
3.Edith JA. The Anatomy and Physiology Learning System: Textbook. Philadelphia, PA: W.B. Saunders Company 1995.