Fibrous, cartilage, and synovial joints

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Fibrous, cartilage, and synovial joints

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Your body is made of around 206 bones, which are connected together by about 360 joints.

These joints can be classified into three main groups based on their structure and how they move.

Fibrous joints which generally don’t move at all, cartilaginous joints which allow some movement, and synovial joints which are freely movable.

Let’s begin with the fibrous joints, which are also called synarthrosis or fixed joints.

In fibrous joints, bones are connected by ligaments and they fall into three main categories based on their location.

First, we have sutures, which are the joints between the bones of the skull.

Skull bones are supported by their interlocking design and short ligaments that connect adjacent bones together.

Adult sutures are stiff and completely fixed. But in the fetus and the babies, the sutures are more widely spaced and therefore partially movable.

During labor, there’s a process called molding where the baby’s skull bones slightly overlap, temporarily reducing the baby’s head diameter, so that it can pass through a mother’s pelvis.

Second, there’s the syndesmosis which is the joint between the radius and ulna in the forearm. Along their shafts, they are attached by long bands of ligaments called the interosseous membrane.

Unlike the interlocking sutures, syndesmoses are slightly mobile throughout life.

The third category of fibrous joints is a gomphosis, which is a joint between the roots of a tooth and its socket within the jawbone - either the maxilla or mandible.

A tooth is anchored in its socket by periodontal ligaments, which allow light movements to lessen the impact, like when you are chewing on corn nuts.

Next are the cartilaginous joints, which are joints surrounded by hyaline cartilage which can stretch to allow some movement.

One type of cartilaginous joint is a synchondrosis, and an example of a synchondrosis is the costochondral joint where a bit of cartilage attaches the rib to the sternum.

Summary

There are three types of joints in the human body: fibrous, cartilaginous, and synovial. Fibrous joints are held together by dense connective tissue, cartilaginous joints are held together by cartilage, and synovial joints are free-moving and enclosed in a capsule. Each type of joint has different features and performs different functions.

Fibrous joints include the sutures between the bones of the skull. These are very strong joints but with limited to no motion. Cartilaginous joints include the disks that separate the vertebrae. These joints allow for some movement but are mostly stable. Synovial joints are the most common type of joint in the body and include all joints that move, such as the shoulder, elbow, hip, and knee. Synovial joints are surrounded by a capsule filled with synovial fluid, which lubricates the joint and allows for smooth movement.

Sources

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Radiographic Evaluation of Arthritis: Degenerative Joint Disease and Variations" Radiology (2008)
  6. "Joint Space in Normal Gleno-Humeral Radiographs" Acta Orthopaedica Scandinavica (1983)
  7. "Radiographic Evaluation of Arthritis: Degenerative Joint Disease and Variations" Radiology (2008)