Joints Development And Classification Anatomy Question And Answers

Joints

Question 1. Define joints and describe their classification.
Answer.

The joints are the junctions/meeting points between two or more bones. However, they can also be formed between bone and cartilage or between bone and tooth.

Joints Classification Joints are classified in two ways:

1. On the basis of the type of tissue (fibres or cartilage) binding the articulating bones or the presence or absence of a synovial cavity between the articular bones (structural classification).
2. On the basis of range and type of movement, they permit (i.e. functional classification).

Joints Structural classification

• Fibrous joint: It lacks the joint cavity and the articular bones are joined by the fibrous tissue. These joints are immovable or permit only slight movement.
• Cartilaginous joint: It also lacks the joint cavity and the articular bones are joined by the cartilage. These joints are immovable or permit only slight movement.
• Synovial joint: It has a joint cavity. The articular surfaces of the bones are covered by the articular (hyaline) cartilage. The articular bones are enclosed by a fibrous capsule. The joint cavity between the articular surfaces contains viscous synovial fluid. These joints are freely movable and permit a maximum degree of movement.

Joints Functional classification

• Immovable joints (synarthrosis), for example, fibrous joints (vide supra)
• Slightly movable joints (amphiarthrosis), for example, cartilaginous joints (vide supra)
• Movable joints (diarthrosis), for example, synovial joints (vide supra)

Question 2. What are the different types of Fibrous Joints?
Answer.

• Fibrous Joints Sutures: These joints are found in the skull and are immovable (i.e. synarthrosis). The articulating bones are connected by sutural ligaments or thin membranes of fibrous tissue.
• Fibrous Joints Syndesmosis: The articulating bones are connected to each other by interosseous ligaments, and the bones involved lie at some distance apart, for example, the inferior (distal) tibiofibular joint. A slight movement is permitted at these joints; hence, functionally it is classified as amphiarthrosis.
• Fibrous Joints Gomphosis/peg and socket joint (dentoalveolar joint): Here, the cone-shaped root of the tooth fits into the alveolar socket of the jaw. The tooth is attached to the alveolar socket by the fibrous tissue (periodontal ligaments).

This type of joint is immovable, hence functionally classified as synarthrosis.

Question 3. Define a synovial joint and mention the characteristic features of a Typical Synovial Joint.
Answer.

A synovial joint is a joint with a cavity between two or more articulating bones. The cavity is lined by a synovial membrane and is filled with a synovial fluid. The synovial joints permit free movement, hence functionally classified as diarthrosis.

Typical Synovial Joint Characteristic features The characteristic features of a typical synovial joint:

• Articular surfaces are covered with hyaline (articular) cartilage, which provides a smooth, slippery surface to reduce friction between the articular surfaces of the bones during movement.
• Articular ends of bones are enclosed by a fibrous capsule; hence, it has a joint cavity.

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• The inner surface of the capsule and all intra-articular structures, except articular cartilages, are covered by a synovial membrane, which secretes synovial fluid.
• They are freely movable joints, hence functionally classified as diarthroses.
• The joint cavity is filled with synovial fluid.

Question 4. What are the differences between atypical, complex and compound synovial joints?
Answer.

• If the articular surfaces of a synovial joint are covered by a fibrocartilage, it is termed atypical synovial joint, e.g. temporomandibular joint.
• If the cavity of a synovial joint is divided completely or incompletely into two compartments by an intra-articular disc, it is called complex synovial joint, e.g. temporomandibular joint and sternoclavicular joint.
• If more than two articular surfaces are enclosed in a single fibrous capsule, it is called a compound synovial joint, e.g. elbow joint.

Question 5. Classify various types of synovial joints.
Answer.

• Plane joints: These are the joints in which the articular surfaces are flat and in contact. Only gliding movements are possible at these joints. Examples: Intercarpal joints and intertarsal joints.
• Hinge joints: These are the joints in which one articular surface is convex and the other is reciprocally concave. The movements take place around a transverse axis. Examples: Humeroulnar joint, interphalangeal joints, knee joints and ankle joints.
• Pivot joints: These are joints in which a bony pivot-like process rotates within an osseofibrous ring or an osseofibrous ring rotates around the bony pivot. Thus, the movements are possible only around a longitudinal axis through the centre of the pivot. Examples: Superior radioulnar joint, inferior radioulnar joint and median atlantoaxial joint.
• Condylar joints: In such joints, the convex condyle or condyles (articular surfaces) of one bone articulate with concave articular surfaces or surfaces of other bone. Movements occur not only mainly in the transverse axis but also partly in the vertical axis (rotation). Examples: Knee joint and temporomandibular joint.
• Ellipsoid joints: These joints are formed by an oval convex surface of one bone and an elliptical concave surface of the other bone. Examples: Radiocarpal joint (wrist joint) and metacarpophalangeal joints. Movements that are possible at such joints are flexion, extension, abduction, adduction and circumduction. No rotation occurs around a central axis.
• Saddle joints: In such joints, the articular surfaces are reciprocally concavoconvex (saddle-shaped). Movements permitted at these joints are the same as in the condylar type with some rotational movement. Examples: Carpometacarpal joint of thumb, sternoclavicular joint, calcaneocuboid joint and incudomalleolar joint.
• Ball and socket joints: In such joints, the rounded articular surface of one bone (the ball) fits into a cup-shaped cavity (the socket) of the other bone. In these joints, the movements are possible in every direction around a common centre. Examples: Hip joint and shoulder joint.

Question 6. What are the types of cartilaginous joints?
Answer.

There are two types of cartilaginous joints: primary and secondary.

• Primary cartilaginous joints (synchondroses): The bones forming these joints are united by a hyaline cartilage. They are immovable (synarthroses). After a certain age, the hyaline cartilage is slowly replaced by bone (synostosis). Examples: Joints between epiphysis and diaphysis of a growing long bone, costochondral joints, spheno-occipital joint (joint between basiocciput and basisphenoid at the base of skull) and 1st costosternal joint. These are temporary joints.
• Secondary cartilaginous joints (symphyses): These joints occur in the median plane of the body. The articular surfaces are covered by a plate of hyaline cartilage, which is then connected by a broad, flat fibrocartilaginous disc. Examples: Manubriosternal joint, pubic symphysis and intervertebral discs. These are permanent joints and do not disappear with age. A slight movement is possible (amphiarthrosis) at these joints.

Question 7. Compare and contrast the primary and secondary cartilaginous joints.
Answer.

Question 8. What are the closed-packed and loose-packed positions of a joint?
Answer.

Closed-packed position

It is the position of a joint in which fibrous capsule and ligaments are taut and articular surfaces are fully congruent, i.e. have a maximum area of contact with each other. This is the most stable position of joint and therefore dislocations are rare in this position.

Loose-packed position

It is the position of a joint in which articular surfaces are not congruent. The capsule and ligaments are lax. This is an unstable position of the joint; therefore, dislocations commonly occur in this position.

Question 9. Enumerate the intra-articular structures found within the synovial joint.
Answer.

• Cartilaginous structures:
  • Articular discs of temporomandibular and sternoclavicular joints
  • Articular menisci (semilunar cartilages) of the knee joint
  • Labrum: Glenoid labrum of the shoulder joint and the acetabular labrum of the hip joint
• Ligament-traversing joint: They bind articular surfaces, for example, ligamentum teres of the hip joint and cruciate ligaments of the knee joint
• Tendons traversing the joint cavity: These arise inside the capsule of the joint and transverse the joint cavity, for example, tendon of the long head of the biceps traversing the cavity of shoulder joint and the tendon of the popliteus traversing the cavity of the knee joint

Question 10. List the nerve supply of a synovial joint.
Answer.

The synovial joint is supplied by three types of nerves:

• Sensory nerves carrying pain from the articular fibrous capsule, ligaments and synovial membrane.
• Sensory nerves carry proprioceptive sensations from articular fibrous capsules and ligaments.
• Autonomic nerves supplying blood vessels. They regulate the flow of blood in an articular fibrous capsule.

Question 11. What is Hilton’s law?
Answer.

This law enunciates that the nerves supplying sensory fibres to the capsule of the joint also supply the muscles crossing the joint and skin over the joint. Therefore, when the joint is diseased, the irritation of these nerves causes

1. Reflex spasm of muscles to bring the joint in the position of maximum comfort and
2. The pain of the joint is referred to as the overlying skin.

Question 12. What are the types of movements that commonly occur in the synovial joints?
Answer.

Four types of movements commonly occur in the synovial joints:

• Gliding
• Angular
• Circumduction
• Rotation

Question 13. Write a short note on adjunct and conjunct rotation.
Answer.

• The rotation around a longitudinal axis is called rotation proper. It may be adjunct or conjunct.
• The adjunct rotation takes place actively by some muscles, while the conjunct rotation takes place passively due to the configuration of the articular surfaces or tension of some ligaments.

The differences between the adjunct and conjunct rotation are summarized in the following table:

Question 14. Enumerate the factors maintaining the stability of the joints.
Answer.

• Configuration of articular surfaces
• Ligaments
• Muscles
• Atmospheric pressure