Joints

In order for the body to be cohesive and connected, it needs joints. A joint is where any two bones meet or articulate, regardless of its mobility or immobility. Joints are classified into four major categories, bony, fibrous, cartilaginous, and synovial. A bony joint, also known as syntosis, forms when the gap between two bones ossifies and becomes a single bone such as the joining of an epiphysis and diaphysis. A fibrous joint is present when collagenous fibers connect two bones together and can be classified as sutures, gomphosis, or syndesmosis. Cartilaginous joints are two bones connect through cartilage. These joints can be classified as synchdroses or symphyses. The last classification is the synovial joint which are two bones separated by an encapsulated space filled with synovial fluid.

Fibrous Joint

A fibrous joint are present when collagen fibers bound two bones together. It can be classified as sutures, gomphosis, or syndesmosis. Sutures have short collagen fibers and are immobile. These joints are only present in the skull and can be classified as serrate, lap, and plane sutures. Serrate sutures are joints that articulate through collagen fibers when the bones have wavy ends and fit each other like a puzzle. These joints are found in the coronal and lamboid sutures. Lap sutures are present when two bones have straight overlapping edges like two wedges that fit neatly together. Lap sutures can be seen in the temporal bone. Plane sutures occur when two bones have straight nonoverlapping edges. The intermaxillary suture is an example of a plane suture.

Cartilaginous Joints

A cartilaginous joint are when two bones are connected by cartilage. Cartilaginous joints are synchondrosis if the two bones are connected through hyaline cartilage. A synchondroses joint is present in the attachment of the first rib to the sternum. Cartilaginous joints are symphysis if two bones are joined by fibrocartilage. Pubic symphysis is an example of a symphysis.

Synovial Joints

Synovial Joints consists of two bones covered in articular cartilage and separated by an articular cavity that contains synovial fluid. It also has an outer membrane that is continuous with the periosteum called the fibrous capsule, and an inner membrane known as the synovial membrane. The synovial membrane contains fibroblasts cells that secrete fluid and macrophages to clear debris. Synovial joints are also made up of accessory structures such as tendons, ligaments, and bursa. A tendon is a strip of tissue that connects muscle to bone while a ligament connects bone to bone. A bursa is a fibrous sac that is filed with synovial fluid located between adjacent muscles, where a tendon passes over the bone.

Six Classes of Synovial Joint

Ball and socket joints: a ball and socket joint occurs when one bone has a smooth hemispherical head that fits into a cuplike socket of another bone. The shoulder is a ball and socket joint because the humerus forms the smooth head which fits into the cavity created by the scapula. Ball and socket joints are multiaxial because it has three ranges of freedom, flexion, internal rotation, and abduction. To get your ball and socket joint moving, try this fun exercise

Empty Can: Start the empty can exercise with light dumbbells on both hands and keeping the arms straight down your side. Lift your arms at a 45 degree angle, up to shoulder height and then bring back down to starting position. Repeat this exercise 10 times. This exercise abducts the arm and strengthens the rotators cuff, the muscle of the shoulder.
Condylar Joints: A condylar joint is present when the one bone is convex while the other bone contains a depression to fit the convex bone. Condylar joints are biaxial joints, able to move in two planes. The movement of the condylar joints can be seen in the radiocarpal joint of the wrist and the bases of the finger. To see how your wrist can move in two directions, try this short activity.
1. Hold your palm out in front of you. When you close your palm and flex, the joint flexes in the sagittal direction. Now, relax your palm and fan your fingers out. This movement occurs in the frontal plane.
Gliding Joints: Gliding joints are also known as the plane joints. These joints are usually made up of two flat bones that slide over each other. Although their movements are slight and complex, these joints are capable of moving in two planes. For example, the facets of the vertebrae slide anteriorly and posteriorly to tilt the head back and forth.
Hinge Joints: Hinge joints are monoaxial and can only move in one plane. The movement of a hinge joint is similar to that of a door, it opens and closes, flexes in one direction and relaxes in another. Hinge joints consist of a bone with a convex surface fitting in a depression in another bone. The elbow and knee are classic examples of a hinge joint. Read more to find out about fun exercises to move the elbow.
1. Bicep curls are a great way to move your elbow and see how a hinge joint works. Start with your arms to the side, the inside of the elbow facing the front. Hold a free weight on both hand, and while keeping your bicep close to your side, bring the weights up to your shoulders then back to the starting position.
Pivot Joints: Pivot joints are monoaxial joints that allow the bone to spin on its longitudinal axis. An example of a pivot joint is the radioulnar joint of the elbow. The anular ligament wraps around the neck of the radius, allowing the arm to pronate and supinate. Pronation occurs when the palm is facing down and supination occurs when the palm is facing up.

Movement of Synovial Joint

Anatomical position occurs when a person is standing straight, feet are shoulder width apart, palms facing out, and head facing forward. At this position, all joints are at zero position. Check out these different exercises to get your synovial joints moving.

Bicep Curls: Flexion is decreasing a joint’s angle while extension is increasing the angle of a joint. When you flex your bicep, the angle of the elbow is decreasing. As you relax your bicep, the muscles are extending since the angle of the elbow is increasing. Some exercises that promote flexion and extension are bicep curls and squats.

Hip Abduction and Hip Adduction: Abduction is movement away from the midline of the body while adduction is movement toward the midline. When your arms are at your side and you move them toward your head in the sagittal plane, you are abducting because you are moving away from the midline. As you bring your arms back down to side, you are moving closer to the midline, therefore you are adducting. Shoulders are not the only joint that can adduct and abduct. Next time you’re at the gym, try using the hip abduction and adduction. This machine exercises your adductor brevis, longus, and magnus. Both machines keep you in the sitting position while allowing you to use your hips to bring your legs closer together (adduction) or pushing your legs apart (abduction). This machine is a great way to shape the inner thighs.

Pushups: Protraction is the anterior movement of the body part in the horizontal plane and retraction is posterior movement. A common joint that can protract and retract is the shoulder. When doing pushups, the shoulder is protracted when the elbows are locked and the body is doing a plank. The shoulder retracts to bring the body closer to floor. Pushups are a great exercise to keep your shoulder joints moving while strengthening your arms and chest.

Shrugging: Although shrugging may seem effortless, it actually moves your shoulder joints through elevation and depression. As the shoulder moves up, it is elevating the scapula and as it moves down, it depresses the scapula.

Pitching a baseball: Pitching a baseball causes a joint to circumduct, one end moves in a circular motion while the other end remains stationary.