 In this video I will describe the structural and functional classification of joints and provide examples of each category. So a synonym for the word joint is articulation. And we can categorize articulations or joints either functionally or structurally. Let's start looking at the functional categorization that is classification of articulations based on their movement. A synarthrosis is an example of a functional classification of articulations where there is no motion at that joint. It's an immobile articulation, a synarthrosis. And we see here a few examples of synarthrosis. The coronal suture between the frontal bone and the parietal bone is a synarthrosis. Similarly the squamous suture between the parietal bone and the temporal bone is another example of a synarthrosis. And then on the posterior the lambdoid suture between the occipital bone and the parietal bone is another example of a synarthrosis. And so all of the joints of the skull with the exception of the temporomandibular joint are immobile joints and therefore they are all synarthrosis. We'll see that the sutures of the skull are fibrous joints and so a fibrous synarthrosis is a subtype adding a structural classification on top of the functional classification. So all immobile joints are considered synarthrosis and if it's a immobile joint where dense fibrous connective tissue holds the two bones together, that's what we call a suture. And so another category of articulations based on function is amphiarthrosis. So amphiarthrosis are slightly mobile joints. They don't allow a large range of motion, they're not freely mobile joints, but they have some mobility. An example that we see here, the intervertebral disc, a pad of fibrocartilage between the bodies of adjacent vertebrae allows limited movement between the bodies of the vertebrae. And so functionally the intervertebral disc forms an amphiarthrosis and because this is a joint made out of cartilage, a cartilaginous joint that's a structural categorization, so this cartilaginous amphiarthrosis is also known as a synthesis. So a structural subcategory of amphiarthrosis, if it's an amphiarthrosis, a slightly mobile joint where the bones are held together by cartilage, we call that a synthesis. And so typically fibrocartilage is the type of connective tissue found at a synthesis to allow a slight amount of motion between the articulating bones. If a joint allows free motion, a wide range of motion or free mobility, not just a slight amount of motion but lots of motion, then this is what we call a diarthrosis. So diarthrosis is the functional category of freely mobile articulations. There are many familiar examples of diarthrosis. The one that we see in the illustration here is the temporomandibular joint. So the temporomandibular joint is an articulation between the condylar process of the mandible and the mandibular fossa of the temporal bone. This forms the joint commonly known as the jaw that enables opening of the mouth and enables chewing. And so this is a freely mobile joint categorized as a diarthrosis. Other examples of diarthrosis would include the familiar joints of the cromial region, the glenohumeral joint, or commonly known as the shoulder joint, or the joint that's located in the articulation between the ulna and the humerus. The humeral ulnar joint, commonly referred to as the elbow joint, is another example of a diarthrosis. All diarthrosis have the same structural category. So structurally, all diarthrosis are considered synovial joints. So the synovial joints have the same structure. What we can see here is an articular capsule, a fibrous connective tissue layer that surrounds a joint cavity which is filled with fluid called synovial fluid. And the inner layer of the articular capsule produces this synovial fluid from the synovial membrane. And so all diarthrosis are also synovial joints. Diarthrosis is just the functional category, and synovial joints is the structural category. Here we see three subtypes of fibrous joints. So a suture, in A we see, a suture is a fibrous synarthrosis. So it's an immobile joint held together by fibrous connective tissue, dense connective tissue. In B, the example we see here, the interosseous membrane forms a syndesmosis. So a syndesmosis, this is the category for fibrous amphiarthrosis. So an amphiarthrosis, remember, is slightly immobile. And the distal radio ulnar joint is stabilized by a broad band of fibrous connective tissue, the anti-brachial interosseous membrane. So this is structurally a fibrous joint, the bones are held together by fibrous connective tissue. And it's functionally an amphiarthrosis. So a fibrous amphiarthrosis is what we call a syndesmosis. Then see here the last example, we have a gonfosis. And gonfosis are the fibrous joints that anchor our teeth into the sockets, into the alveolar sockets, the dental alveoli, the sockets in the mandible and maxilla, where the teeth are located. And so there's a special type of fibrous connective tissue that anchors the teeth into the socket, into the dental alveolus, and that's known as the periodontal ligament. The periodontal ligament connects between the outer layer of the tooth, the cementum of the tooth, to the bone of the dental alveolus in the mandible or maxilla. Another type of fibrous joint is known as a synostosis. So a synostosis occurs when two bones fuse together. We have examples here of synostoses that are the joints holding the ilium, ischium, and pubis together to form the coxal bones. So there are two major subcategories of cartilaginous joints. Cartilaginous joints is a structural category of articulations. And if a cartilaginous joint is also a synarthrosis, meaning it's an immobile joint, that's what we call a synchondrosis. Typically, hyaline cartilage is the connective tissue holding two bones together to form a synchondrosis. The example we see here is the epiphyseal growth plate that is a synchondrosis between the diaphysis and the epiphysis of a long bone during adolescence that enables the interstitial growth mechanism to lengthen the bone. Then the example we see in B is a symphysis, which is a cartilaginous amphiarthrosis, a cartilaginous joint that has a slight amount of motion. Typically, fibrocartilage is the connective tissue joining two bones together at a symphysis. So the pubic symphysis is the example we see here, the articulation between the right and left pubic bones. This allows a slight amount of motion, but it's not a freely mobile joint like a diarthrosis, and so this is categorized as a symphysis, a cartilaginous amphiarthrosis. The other example of a symphysis that we saw is the intervertebral disc, another cartilaginous amphiarthrosis where two bones are stabilized by fibrocartilage. So synovial joints is a structural category, and the characteristics of a synovial joint are an articular capsule of fibrous connective tissue that surrounds a joint cavity filled with synovial fluid. The inner layer of the articular capsule is the synovial membrane that produces the synovial fluid. The function of synovial fluid is to help lubricate the joint, and the ends of the articulating bones are covered with articular cartilage to help protect the bone. So synovial joints are all freely mobile joints, they are all categorized functionally as diarthrosis, but structurally we call them synovial joints. There are many examples of synovial joints, the one that we're looking at now is the tibiofemoral joint, commonly known as the knee joint. So the articulation between the femoral condyles and the condyles of the tibia has a fluid filled synovial cavity, so it is a synovial joint with a capsule of connective tissue that contains the synovial fluid, and there's articular cartilage covering the femoral condyles and the condyles of the tibia. There are also some accessory structures commonly found in synovial joints, so the tibiofemoral joint has fat pads. We can see here an infrapatellar fat pad, a cushion of adipose tissue located inferior to the patella. The patella also helps to protect the anterior of the tibiofemoral joint, and the infrapatellar fat pad provides further cushioning between the patella and the tibiofemoral joint. And we can see there are also bursa. Bursa are fluid filled cushions. They're essentially little sacks of synovial fluid, so a bursa provides further cushioning to a synovial joint. We can see here the infrapatellar bursa is a bursa that helps to cushion the tibiofemoral joint that's located just inferior to the patella. There's also a pre-patella bursa that helps to cushion the anterior surface of the patella. There are also ligaments that help to stabilize synovial joints. Here we see the intracapsular ligaments that are found in the tibiofemoral joint. There's both a posterior cruciate ligament and an anterior cruciate ligament located deep within the tibiofemoral joint, helping to stabilize the tibiofemoral joint. Another accessory structure that we can see in the tibiofemoral joint is a meniscus. A meniscus is a pad of fibrocartilage that provides further cushioning and also can help to improve the fit to help stabilize synovial articulation. At the tibiofemoral joint, the medial and lateral menisci are C-shaped pads of fibrocartilage that help to improve the fit of the surface of the tibia to help stabilize the rounded femoral condyles that are articulating with a relatively flat surface of the condyles of the tibiofemoral joint. Thank you for watching.