By Elizabeth A. Murray, Mount St. Joseph University
The structure of a joint is interrelated with its specific functions. There are essentially six main types of joints, based on the shapes of articulating bones and—as a result of that anatomy—the range of motion they allow. These joint types and their motions vary from simple gliding movements of flat surfaces against each other, to angular movements.
Six Types of Joints
There are six main categories of freely movable synovial joints based on their structure—presented here, to some degree, from simple to complex in their movements: planar joints, pivot or rotational joints, hinge joints, condyloid or ellipsoidal joints, saddle joints, and ball-and-socket joints.
Plane or planar joints are articulations in which a pair of relatively flat bone surfaces simply slide against each other, like when using a sanding block against a wooden surface. Since the articulating surfaces never leave each other, they just slide back and forth.
These joints don’t allow as much movement as many other joint types, but they are still diarthrotic synovial joints. These planar joints can be found between the tarsal bones in the ankle and foot and between the carpal bones of the wrist.
Pivot or Rotational Joints
Pivot or rotational joints work like a trailer hitch. The surfaces don’t really leave each other so much as one surface rotates inside a circular or semicircular surface made by the other bone. For this reason, they are known as monoaxial joints, since movement is in a single plane.
This type of articulation at the part of the elbow joint is found where the radius joins the humerus, allowing us to rotate our forearm, palm up and palm down. A pivot joint is also seen between the first two vertebrae of the neck, allowing us to rotate our head left and right.
In a hinge joint, the articulating bones physically resemble a door or cabinet hinge. These allow movement in a single plane—so only in two directions, like back and forth—similar to the way a door moves.
Besides the hinge joint between the humerus and ulna at the elbow, the knees are hinge joints, as are the interphalangeal joints between bones in the fingers, which are called phalanges.
Condyloid or Ellipsoidal Joints
Condyloid or ellipsoidal joints allow a joystick-like movement between a concave oval surface and a matching convex oval surface. A good example of that is between the radius of the forearm and a couple of the carpal bones of the wrist, or between the metacarpals of the palm of the hand and the proximal phalanges of the fingers.
The corresponding oval ends of the bones nest in each other like spoons in a drawer. These condyloid or ellipsoidal joints are biaxial joints because the movement occurs in two planes.
Saddle joints are relatively rare articulations in which one bone resembles a saddle and the other a rider in that saddle. The best example of this is where the base of the thumb meets the wrist. This is where the metacarpal bone in the thumb side of the palm joins the lateral-most carpal of the wrist—called the trapezium, due to its shape.
Saddle joints are biaxial, as they allow movement in more than one direction. This is one reason the thumb is such a special feature of primates—this prehensile thumb allows the grasping motion characteristic of primate hands like ours.
These are what are known as multiaxial joints because they allow movement in all three dimensions—as in an x-axis, y-axis, and z-axis.
These joints allow the greatest range of motion—a complexity of movement that is only possible at our shoulder and hip joints, the ball-and-socket joints in the human body.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Simplified Model on the Workings of Joints
Hardware models are good schematic representations of the six main types of joints by structure, which can also be simplified to illustrate the main types of movement possible at a joint.
Take a pencil and put it on a flat surface—like a piece of blank paper, or alternatively use your index finger on one hand as a substitute for the pencil and use the palm of your other hand to represent the flat plane.
The spot where your pencil or finger is touching the plane represents the joint—which in the leverage system was the fulcrum—the place where the two bones meet. Gliding movements would be represented by sliding your pencil or finger on that flat surface—like making a little X or T—without altering the angle between the tip of the pencil, or your finger, and the flat surface.
Monoaxial Movements of Rotational Joints
To simulate rotational movement, spin a pencil, or your finger against a flat plane—this is how rotational joints work—one bone rotates against the other, but the angle between the bones doesn’t change; they stay in the same plane.
And the movement is said to be monoaxial, since the rotation is occurring along that single plane.
Angular motions work like a switch or a joystick—the angle between the two participating bones changes. So, keep the pencil or finger against the flat surface, but move it back and forth or right to left like flipping a switch or pulling a lever.
Multi-directional Angular Movement
Hinge joints work like this, but in either a simple forward-and-back pattern or right to left pattern, not in both of those planes, so they are monoaxial joints. However, condyloid joints have multiple directions for their angular movements, so are biaxial joints with two planes of movement—like a joystick that moves back and forth, as well as side to side.
Ball-and-socket joints move in multiple directions—and can rotate, as well. These types of joints move in all three dimensions. Sometimes the term ‘circumduction’ is used for movement in an arc—like standing with your shoulder toward a chalkboard, and then drawing a large circle on the board. But that’s just an ever-changing series of angular movements in a sequence.
Ball-and-socket joints can do even more than that. They combine these multidirectional angular movements with rotational movements as well, thus picking up all three axes/dimensions—so are called multiaxial joints.
Common Questions about the Different Types of Joints
There are six main categories of joints in our body.
Planar joints can be found between the tarsal bones in the ankle and foot and between the carpal bones of the wrist.
Ball-and-socket joints are multiaxial joints that allow movement in all three dimensions—as in an x-axis, y-axis, and z-axis.