The human body can be seen as a machine made up of several different parts that enable movement. These movements occur in the many joints formed by the specific components of the body’s musculoskeletal system. The joints in the human body, connect various segments together and often allow for movement between the two pieces. The design of the joint shall represent their demands. Joints are designed to allow various degrees and types of movement and are classified by both structural design and functionality. Some joints, like that of the shoulder, elbow, and knee, are self-lubrication, almost frictionless, and are capable of resisting compression and maintaining heavy loads while still performing smooth and precise movements. Other joints, such as stitching between bones Enable very little movement of the skull (only during birth) to protect the brain and the sense organs The bond between the tooth and the jawbone is often called a joint and is defined as a fibrous joint known as gomphosis. Arthrology is the study of joint structure, function, and dysfunction.

The joint is a bond /articular surface between two bones that link the skeletal system into a functional whole. However, joints have a number of functions, perhaps the most essential is to help in motion. Joints are also able to bear the Weight of the body and provide stability. Joints are designed in variations from simple to complex. Simple human joints tend to have stability as a main function; more complicated joints typically have mobility as a main function. Moreover, most of the joints in the human body have a dual mobility-stability feature and it must bring dynamic stability to life. The stability joints in the design are similar to the table joints in that the ends of the bones can be contoured to fit into the bones or choose to lie flat against each other. Capsules (The outer layer of the capsule is made up of a strong fibrous tissue that holds the joint together and the inner layer is lined with a synovial membrane that secretes the synovial fluid), articulator surface which is very smooth and covered with cartilage called hyaline, Synovial cavity filled with Synovial fluid, ligaments and tendons, these are all components of synovial joints, which are designed primarily for mobile joints. Synovial joints are constructed in such a way that the ends of the bone components are covered by hyalin cartilage and enclosed in a synovial sheath and a fibrous layer that together constitute the joint capsule. The basis of the type is divided into two broad categories, on the basis of the type of materials and the methods of uniting the bony components. Subdivisions of these specific categories are based on materials that form and contours of the articulations used and the form of motion that is permitted. The two categories of joints are synarthroses (non-synovial) and diarthroses (synovial joints).

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In fibrous joints, bone is bound to another bone directly by fibrous tissues. There are three different types of fibrous joints in the human body: sutures, gomphosis, and syndesmoses. Sutures are fibrous joints in which short collagen fibers connect the bones of the skull together making them immobile or slightly mobile. Sutures can be listed as Serrate which is an interlocking of wavy lines as that of the coronal, sagittal, and lambdoid sutures. Lap which are overlapping beveled edges as that of the temporal and parietal bones. Plane (butt) which is straight, non-overlapping edges as that of the maxillary and palatine processes. Gomphoses are the attachment of the tooth to its socket, held in place by a fibrous periodontal ligament composed of collagen fibers, connecting the tooth to the jawbone, and allowing the tooth to move slightly under the tension of chewing. Syndesmoses are fibrous joints, where two bones are connected by long collagen fibers, the gap between the bones and the length of the fibers gives these joints more mobility than the sutures and gomphosis. Syndesmoses joints are like that of the interosseus membrane connecting the radius to the ulna allowing supination and pronation which is very mobile and the joint between the tibia to the fibula which is less mobile. The cartilaginous joint has either fibrocartilage or hyaline fibrocartilage. As an example of the cartilaginous joint, Vertebral joints are joints in which disks of fibrocartilage are directly linked to the bones. The first sternocostal joint is an example that is constructed of hyaline cartilage. Cartilaginous joints are sometimes referred to as amphiarthrodial joints, Because they permit a small amount of motion, such as twisting or bending and some compression. These joints provide a great deal of stability. There are two types of cartilaginous joints: Synchondroses which is a plate of hyalin cartilage that connects bones to synchondrosis. Examples of synchondrosis are temporary joints in epiphyseal plates in children who connect epiphysis to diaphysis and sternum to first rib but other costal cartilages are connected to the sternum by synovial joints and Symphyses The articular surfaces of the bones are covered by the hyaline cartilage which is fused to the intermediate pad or plate of the fibrocartilage, which is the main connecting material. It acts as a shock absorber and allows a limited amount of joint movement. Symphyses are amphiarthrotic joints built to be flexible and strong. Examples: the Pubic symphysis linking the right and left pubic bones to the interpubic disk and the vertebral body to the intervertebral disk.

The shoulder complex is composed of the clavicle, the scapula, and the humerus. It is an intricate combination of three joints that link the thorax to the upper extremity. It provides mobility so that we can place our hand over a wide range of space. It includes the sternoclavicular articulation which is the joint between the sternum manubrium and clavicle bone. It is structurally classified as a synovial saddle joint and functionally classified as a diarthrosis and multiaxial joint. The acromioclavicular joint is a joint at the top of the shoulder. It is the junction between the acromion and the clavicle. It is a plane synovial joint. The scapulothoracic joint is not a true anatomical joint, but it binds the sternoclavicular and acromioclavicular joints and the junction between the anterior surface of the scapula and the thoracic cage. The shoulder joint (glenohumeral joint) is the joint of the ball and socket between the scapula and the humerus. It is the joint that connects the upper limb to the trunk. The elbow complex consists of three bones, three ligaments, two joints, and one capsule. The articulation of the humerus with ulna and radius is commonly known as the Joint elbow.

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And the raradioulnardial joints. The joint of the elbow is considered to be a loose joint of the hinge. Allowing for flexion and extension movements that occur in the sagittal plane around the coronal axis. A slight bit of axial rotation and side-to-side motion of the ulna occurs during flexion and extension. Proximal and distal radioulnar joints are interlinked and function as a single joint. The two joints acting together produce a rotation of the forearm. Radioulnar joints are diarthrodial uniaxial joints of the pivot type that allow supination and pronation to occur in the transverse plane around the longitudinal axis. The wrist complex as a whole is biaxial, with extension/flexion movements around the coronal axis and ulnar deviation / radial deviation of the anteroposterior axis.

The complex as a whole is variable, it arises from factors such as ligamentous laxity, the shape of the articular surfaces, and restricting the effects of muscles. The ranges shall be contributed in different proportions of radiocarpal and midcarpal joints.

The hand consists of five digits: four fingers and one thumb. Each digit has a carpometacarpal joint and a metacarpophalangeal Joint. The digits of each of them have two interphalangeal joints, a proximal interphalangeal joint and a distal interphalangeal and the thumb just has one. There are 19 bones and 19 joints distal to the carpals that make up the hand complex. The temporomandibular joints are the two joints that link up the jawbone to the skull. This is a bilateral synovial articulation. It is used during chewing, swallowing, talking, yawning… Superiorly, it’s made up of the articular fossa of the temporal bone but the articulation with the condyle of the mandible is inferior. It is a pure hinge joint synovial joint as it makes some gliding, too. The sacroiliac joint is a synovial, nonaxial joint between the sacrum and the Ilium. It is defined as a plane joint, but the articular surfaces are very irregular. The role of the sacroiliac joint is to transmit weight from the upper body through the vertebral column to the bones of the hip. It is designed for great stability and has very little mobility. The role of the sacroiliac joint is to transmit weight from the upper body through the vertebral column To the bones of the hip. like other synovial joints, it is articular surface is covered with hyaline cartilage. Synovial has a fibrous capsule reinforced by ligaments. the membrane forms the non-articular parts of the joint. It is widely agreed, that the motions that do occur when the SI joint is nutation and counternutation. The hip joint (coxofemoral joint), where the acetabulum of the pelvis and the head of the femur. These two parts make up the diarthrodial ball-and-socket joint with three degrees of freedom: flexion/ extension in the sagittal plane, abduction/adduction in the frontal plane, and medial/lateral rotation in the transverse plane. The hip joint is built to bear the weight of the shoulder, arms, and trunk both of them in upright posture The hip joint is used for weight-bearing tasks. The joint of the hip, the tibiofemoral is one of the most complex joints in the body. The knee is completely protected and preserved by muscles and ligaments with no bone support, and it is often exposed to strains and stresses. It’s a synovial hinge joint with three degrees of freedom of rotation. Flexion and extension occur in the sagittal plane around the coronal axis via the epicondyles of the distal femur, medial/lateral (internal/external) rotation occurs in the transverse plane about a longitudinal axis through the lateral side of the medial tibial condyle, and abduction and adduction occur in the frontal plane around an anteroposterior axis. Unlike the elbow, the knee joint is not a true hinge, because it has a rotational component. The ankle joint or talocrural joint is a synovial hinge joint found in the lower limb. It is shaped by the bones of the hip (tibia and fibula) and the abdomen (talus). Functionally, the joint performs dorsiflexion and plantarflexion of the foot. The ankle/foot complex meets these requirements through the movements of its 28 bones that form 25 component joints. These joints include the proximal and distal tibiofibular joints, talocrural (ankle) joint, talocalcaneal (subtalar) joint, talonavicular and calcaneocuboid joints (transverse tarsal joints), five tarsometatarsal joints, metatarsophalangeal joints, and nine interphalangeal joints.

References:

1. Joint Structure and Function by Levangie, Pamela K.
2. Clinical Kinesiology and Anatomy (Clinical Kinesiology for Physical Therapist Assistants) 5th Edition by Lynn S. Lippert PT MS (Author)
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