Learning Outcomes

• Identify the six types of synovial joints

Synovial joints are further classified into six different categories on the basis of the shape and structure of the joint. The shape of the joint affects the type of movement permitted by the joint (Figure 1). These joints can be described as planar, hinge, pivot, condyloid, saddle, or ball-and-socket joints.

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Planar Joints

Planar joints have bones with articulating surfaces that are flat or slightly curved faces. These joints allow for gliding movements, and so the joints are sometimes referred to as gliding joints. The range of motion is limited in these joints and does not involve rotation. Planar joints are found in the carpal bones in the hand and the tarsal bones of the foot, as well as between vertebrae (Figure 2).

Hinge Joints

In hinge joints, the slightly rounded end of one bone fits into the slightly hollow end of the other bone. In this way, one bone moves while the other remains stationary, like the hinge of a door. The elbow is an example of a hinge joint. The knee is sometimes classified as a modified hinge joint (Figure 3).

Pivot Joints

Pivot joints consist of the rounded end of one bone fitting into a ring formed by the other bone. This structure allows rotational movement, as the rounded bone moves around its own axis. An example of a pivot joint is the joint of the first and second vertebrae of the neck that allows the head to move back and forth (Figure 4). The joint of the wrist that allows the palm of the hand to be turned up and down is also a pivot joint.

Condyloid Joints

Condyloid joints consist of an oval-shaped end of one bone fitting into a similarly oval-shaped hollow of another bone (Figure 5). This is also sometimes called an ellipsoidal joint. This type of joint allows angular movement along two axes, as seen in the joints of the wrist and fingers, which can move both side to side and up and down.

Saddle Joints

Saddle joints are so named because the ends of each bone resemble a saddle, with concave and convex portions that fit together. Saddle joints allow angular movements similar to condyloid joints but with a greater range of motion. An example of a saddle joint is the thumb joint, which can move back and forth and up and down, but more freely than the wrist or fingers (Figure 6).

Ball-and-Socket Joints

Ball-and-socket joints possess a rounded, ball-like end of one bone fitting into a cuplike socket of another bone. This organization allows the greatest range of motion, as all movement types are possible in all directions. Examples of ball-and-socket joints are the shoulder and hip joints (Figure 7).

Watch this animation showing the six types of synovial joints.

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Pivot Joint Definition

Pivot joints are joints that permit rotatory movement of bones, around a single axis. Pivot joint is a synovial joint in which the ends of two bones connect. In this joint, a cylinder-shaped bone rotates inside another ligament that forms a ring around the joint. The joint between the atlas and the axis which is right under the skull, allows the turning of the head from side to side. The rotation of the skull is possible because of pivot joints. The twisting movement of the bones of the forearm, against the upper arm is due to pivot joints.

Implications of Pivot Joints

• The pivot joint located near the elbow, holds the two forearm bones, radius and ulna, together.
• The two bones, radius and ulna, are also connected to each other near the wrist by another pivot joint. These two bones twist around each other by using a pivot joint.
• The pivot joint situated at the base of the skull, connects the first vertebrae of the spine to the second vertebrae. Thereby, allowing the side-to-side rotation of the head.
• A pivot joint permits movement of the bones in one plane, such as rotation around a single axis.
• In the human body, the joint of the wrist that lets the palm of the hand move up and down is possible because of pivot joints.
• Without pivot joints, the skeleton of the human body would lack flexibility and freedom of movement thus, making the movement of the skeleton quite stiff and rigid.

Common disorders

The pivot joint can be affected by the following disorders

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1. Ankylosis: It is the fusion of bones across a joint and is a complication of arthritis
2. Ankylosing spondylitis: This is an inflammatory disease that causes some of the bones in the spine to fuse.
3. Capsulitis: Improper foot mechanics, where the ball of the foot might experience excess pressure causes the disorder capsulitis.
4. Dislocation: The displacement of the bone from its normal position.
5. Neoplasms: It is an abnormal growth of tissue which can be classified as characteristics of cancer
6. Rheumatoid arthritis: This is an autoimmune condition, which is caused by the immune system attacking healthy body tissue. This causes inflammation of joints, leading to immobility.

Conclusion

So far we have learnt how pivot joints help in flexibility and freedom of movement to the skeleton of the body. It allows movement of the head from side-to-side, the movement of wrists in up and down direction and twisting of the forearm bones against the upper arm. Therefore, the functioning of pivot joints is essential for smooth movement of joints.

Frequently Asked Questions on Pivot joints

Q1

What movements do pivot joints allow?

Pivot joints allow rotation for both internal and external. External rotation is when we rotate an arm outward and internal rotation is when we rotate an arm inward.

Q2

Give two examples of pivot joints.

Two examples of pivot joints are the pivot joints in the neck, that allows the head to rotate and the pivot joints between radius and ulna help in rotating the forearm.

Q3

What is the function of a pivot joint?

The pivot joint allows rotational movement as the rounded bones move across its own axis.

Q4

Is the wrist a pivot joint?

Yes, the wrist is a pivot joint that moves in relation to the forearm bones namely, radius and ulna.

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