The synovial joints have a synovial cavity between the bones of the joint.
This cavity is filled with synovial fluid that reduces friction in the joint, allowing the articulated bones to move freely.
Functional classes of joints:
- Synarthroses (joints with little or no movement)
- Amphiarthroses (slightly mobile joints), and
- Diarthroses (mobile joints or “freely mobile joints”)
Synovial joints are freely mobile joints. A formal medical term is “diarthrosis,” but synovial joints are commonly described as simply “mobile” or “freely mobile.”
The main joints of the appendicular skeleton (including the arms, hands, legs, and feet) are synovial.
Therefore, this articulation is essential in many health sciences, medicine, nursing, physiotherapy, sports science, occupational therapy, massage therapies, etc.
Some synovial joints are more complicated than others—for example, a metacarpophalangeal joint (finger) above the right.
More complicated synovial joints may involve two or more bones, including sesamoid bones such as the kneecap in the knee joint, bursas, and accessory ligaments.
At least two bones form each joint. A simple synovial joint is a metacarpophalangeal joint (MCP) 3, consisting of two articulated bones, the third metacarpal, and the third proximal phalanx.
The periosteum is a rigid white fibrous membrane that covers the outer surface of bones wherever its surface is not covered by cartilage. The periosteum is sometimes labeled in synovial joint diagrams to distinguish areas of bone covered by articular cartilage from the other characters of the bone.
The articular cartilage is hyaline cartilage (a bluish-white elastic material). The functions of articular cartilage in synovial joints include:
Reduces friction: aided by its layer of synovial fluid: as the load on the joint increases, the spongy cartilage absorbs water, increasing the proportion of hyaluronic acid in the lubricating film.
Absorbs shocks: cushioning effect helped by the bone’s contribution immediately behind the articular cartilage layer.
Three types of joints
- Joint capsule
- Fibrous capsule
The fibrous capsule is formed by dense irregular connective tissue. It joins the periosteum (layer) of the bones of the joint. The functions of the fibrous capsule in synovial joints include:
- Flexibility (of the fibrous capsule) allows movement in the joint
- Tensile strength (collagen fibers in the capsule) resists dislocation of the joint
- Synovial cavity
- Synovial membrane
- The synovial membrane is a layer of loose connective tissue that includes elastin and adipose tissue fibers.
The functions of the synovial membrane in synovial joints include:
- Synovial fluid discharge
- Synovial fluid
Synovial fluid functions in synovial joints include:
- Lubricate and reduce friction in the joint.
- Nutrient supply
- Elimination of metabolic waste.
- Phagocytic cells eliminate microbes and debris due to mechanical damage using the common.
- Meniscal cartilage = articular disc, meniscus or meniscus
Keep in mind that several different names/terms refer to meniscal cartilage. Mexico and Medicus are the singular forms, so medicine and meniscus are the corresponding plurals.
Intracapsular ligaments: s “Intracapsular” ignifies located inside the joint capsule. Intracapsular ligaments are, however, surrounded by folds of the synovial membrane. An example of an intracapsular ligament is one of the cruciate ligaments of the knee.
It means “Extracapsular” outside the joint capsule, although an extracapsular ligament can be fused with the joint capsule. An example of an extracapsular ligament is the fibular collateral ligament of the knee joint.
Bursa or bursas (plural)
Bursas are present in some synovial joints. They currently lie between muscle and bone, tendon and bone, or ligament and bone. The function of the bursas within synovial joints is to reduce the mechanical friction between a structure, for example, a bone, and another one, for instance, an extracapsular ligament, during the movement of the systems about the others.
Types of synovial joints
Synovial joints are classified into six different categories based on the shape and structure of the joint. The joint condition affects the type of movement allowed by the common. These joints can be described as planar, hinge, pivot, condylar, saddle, or ball-articulated joints.
The six types of synovial joints allow the body to move in various ways.
- Pivot joints allow rotation about an axis, such as between the first and second cervical of the vertebra, which allows the course of the head from side to side.
- The hinge joint of the elbow works like a door hinge.
- The joint between the trapezius carpus bone and the first metacarpal bone at the base of the thumb is a saddle joint.
- Planar (or flat), like those between the tarsal bones of the foot, allows the sliding movements between the bones.
- The radiocarpal joint of the wrist is condylar.
- The hip and shoulder joints are the only ball-articulated joints of the body.
Flat joints have bones with the articulation of flat or slightly curved surfaces. These joints allow you to plan movements; therefore, joints are sometimes called slip joints.
The range of movement is limited and does not involve rotation. The flat joints are found in the bones of the carpus in the hand and the tarsal bones of the foot, as well as between the vertebrae.
In the hinge joints, the end is slightly rounded or fits into the slightly-hollow end of another bone. In this way, one bone moves while the other remains motionless, similar to the door’s hinge. The elbow is an example of a hinge joint. Sometimes the knee is classified as a modified hinge joint.
Pivot joints consist of the rounded end of a bone that fits into a ring formed by the other bone. This structure allows rotary movement as the round bone moves around its axis.
An example of a pivot joint is the articulation of the first and second vertebrae of the neck that allows the head to move forward and backward. The wrist joint that allows the palm to rotate up and down is also a pivot joint.
Condylar joints consist of one end of a bone that fits into a hollow of another similarly oval bone.
This is sometimes called an ellipsoidal joint. This type of articulation allows angular movement along two axes, as seen in the joints of the wrist and fingers, which enables the movement of both, side by side and up and down.
Each bone in a saddle joint resembles a chair, with concave and convex portions that fit together. They allow similar angular movements to condylar joints but with a more excellent range of motion.
An example of a saddle joint is the thumb joint, which can move forward and backward, up and down; It can move more freely from the wrist or fingers.