Hey everyone! This is Nicole from Kenhub, and in this tutorial, we'll be looking at some of the main joints in the human body.
Joints are classified according to the range of motion they exhibit and the type of tissue that holds neighboring bones together. When classifying joints according to the types of tissues holding the bones together, we can describe synovial joints which are usually covered by a capsule and contains synovial fluids allowing for large movements such as those of the hip joint on the right here; fibrous joints which, unlike synovial joints, do not have a joint cavity and therefore are connected by a fibrous tissue such as the syndesmosis of the radioulnar joints – fibrous joints don't allow for a lot of movement – and; cartilaginous joints which are joints that are connected entirely by cartilage either hyaline or fibrocartilage. They typically have less movement than synovial joints and more movement than fibrous joints and you can see an example of this on the right in the pubic symphysis. However, since most of the joints we're going to talk about today are major joints involving a large amount of movement, the joints we're mainly going to be focusing on will be synovial.
Synovial joints can be further classified according to its range of motion which is described in reference to the movement of the joint about three axes – the x axis, the y axis and the z axis. In this case, joints can be described as ball and socket joints where the spheroidal surface of one bone articulates with the depression or socket of another such as the glenohumeral joint; hinge joints where movement occurs in a single plane such as the elbow joint; ellipsoid joints where everything except axial movement is permitted between the ovoid head of one bone and the elliptical cavity of another such as the radiocarpal joint; plane joints or gliding joints where two bones glide over one another such as the acromioclavicular joint; pivot joints where movement occurs around a single axis usually within a bony ring such as the atlantodental joint which is the joint between the dens of the axis and the transverse ligament of the axis which is highlighted in green in this image; and saddle joints where the face of one bone is concave and the face of the contiguous bone is convex such as the distal carpometacarpal joint of the thumb. And throughout this tutorial when we look at the major joints of the body, we'll point out the various types of joints as we go along.
The first joint we're going to have a look at today is the temporomandibular joint otherwise known as the TMJ. This joint is the main connection between the skull and the lower jaw. It connects the head of the mandible to the squamous part of the temporal bone. The temporomandibular joint is a combined hinge and ellipsoid synovial joint with a synovial fluid-filled joint capsule that contains an articular disc. The ligaments that support this joint include the medial and lateral collateral ligaments, the temporomandibular ligament, the stylomandibular ligament, and the sphenomandibular ligament.
The zygapophyseal joints of the vertebral arches are formed between the superior and inferior articular processes of adjacent vertebrae and essentially operate as plane joints allowing superior-inferior movement of the vertebrae but limiting lateral movement. The zygapophyseal joints are also known as facet joints. Like the TMJ that we just saw, each facet joint is surrounded by a thin, loose capsule as you can see here highlighted in green.
The sternoclavicular joint is a joint of the shoulder girdle. This joint is formed by the sternal end of the clavicle articulating with the manubrium of the sternum at the clavicular notch of the manubrium. This joint is a double plane synovial joint and it is surrounded by an articular cartilage capsule. The sternoclavicular joint is an important joint because it anchors the clavicle and the sternum to the axial skeleton. This joint is stabilized on its anterior and posterior surfaces by the sternoclavicular ligaments but it is also reinforced by two accessory ligaments – the anterior interclavicular ligament and the posterior costoclavicular ligament.
The acromioclavicular joint is also a joint at the shoulder girdle and as the name suggests, it is formed between the acromion of the scapula and the lateral end of the clavicle. The acromioclavicular joint also known as the AC joint is a plane synovial joint. This joint can be easily palpated and it is stabilized by three ligaments namely the acromioclavicular ligament, the trapezoid ligament, and the conoid ligament. Note that the trapezoid and conoid ligaments are collectively known as the coracoclavicular ligament.
The glenohumeral joint which is also simply known as the shoulder joint is classified as a ball and socket synovial joint. This joint is formed between the head of the humerus and the glenoid fossa of the scapula and the shoulder joint is supported by the transverse humeral ligament, the coracoacromial ligament, the glenohumeral ligament, and its fibrous joint capsule. This joint permits a range of movements and, as a result of its extensive mobility, it is a relatively unstable joint.
The elbow joint is a compound hinge synovial joint and is formed by the articulation of the distal end of the humerus with the radius and the ulna of the antebrachial region of the upper limb. The reason the elbow joint is classified as a compound synovial joint is due to the facts that this joint is comprised of smaller separate articulations namely the humeroulnar joint formed between the humerus and the ulna, the humeroradial joint formed between the humerus and the radius, and the proximal radioulnar joint formed between the proximal part of the radius and the proximal part of the ulna, and these three joints together constitute the elbow joint. The elbow joint nevertheless is reinforced by several ligaments including the ulnar collateral ligament which extends between the medial epicondyle of the coronoid process and the olecranon of the ulna; the radial collateral ligament which courses between the lateral epicondyle, the annular ligament and the anterior and posterior margins of the radial notch of the ulna; and of course the annular ligament which runs from the major margins of the radial notch to the ulna encircling the head of the radius.
The wrist joint connects the carpal bones of the hand to the forearm. This joint which is comprised of a number of joint complexes is also known as the radiocarpal joint. It is an ellipsoid-type synovial joint and it is stabilized by several ligaments including the palmar radiocarpal ligament, the palmar ulnocarpal ligament, the ulnar collateral ligament and the radial collateral ligament. Flexion, extension, adduction and abduction are all movements that can be performed at this joint.
Now let's move from the wrist joint to the joints formed between the proximal bases of the metacarpal bones and the distal carpal bones. These joints are the carpometacarpal joints which are ellipsoid synovial joints. As you can see in the image, there are five carpometacarpal joins in the hand corresponding to the number of digits. Of these five joints, the carpometacarpal joint of the thumb which is also known as the trapeziometacarpal joint differs in that it is a saddle joint and this allows the thumb to oppose with the other fingers.
The metacarpophalangeal joints or the MCP joints of the hand are formed by the connection between the distal ends of the metacarpals of the hand and the proximal base of the first phalanges. These joints are what we refer to as the knuckles of the hand and they are ellipsoid-type synovial joints. They are stabilized by the collateral ligaments of the metacarpophalangeal joints and the palmar ligaments of the metacarpophalangeal joints also known as the palmar or volar plates. The MCP joints allow for flexion, extension, adduction and abduction movements about these joints.
Moving down to the lower half of the body, we can now see the sacroiliac joint formed here between the sacrum and the ilium. This joint of the pelvis is an atypical synovial joint and has a very limited range of motion. It is stabilized by the interosseus ligaments, the anterior sacral ligament and the posterior sacral ligament.
The hip joint is a ball and socket type synovial joint where the head of the femur articulates with the concavity of the acetabulum of the pelvis. This joint is stabilized by a number of ligaments. The transverse acetabular ligament and the ligament of the head of the femur are inner ligaments that stabilize this joint. The iliofemoral ligament, the ischiofemoral ligament and the pubofemoral ligaments are the outer ligaments that stabilize the hip joint. Movements that occur about this joint include flexion, extension, abduction, adduction, internal rotation and external rotation.
At the junction between the thigh and the lower leg is the knee joint which is a hinge type of synovial joint. This joint is a rather unstable joint that requires support from tendons and muscles. It is formed between the femur, the tibia and the patella. The ligaments that stabilize the knee joint are the patellar ligament, the tibial and fibular collateral ligaments, and the anterior and posterior cruciate ligaments. Movements of the knee joint include extension, flexion, lateral rotation and medial rotation.
At the distal end of the lower leg, we can see the ankle joint. This joint is formed between the distal ends of the tibia and fibula and the talus of the foot. The tibia and fibula form a socket at the ankle known as the ankle mortise into which the body of the talus fits. The ankle joint is a hinge type synovial joint and it allows for dorsiflexion and plantarflexion of the foot as well as both supination and pronation. There are two major ligaments that make up the ankle. Firstly, the deltoid ligament which is otherwise known as the medial collateral ligament of the ankle joint, and the medial collateral ligament is comprised of the tibiocalcaneal ligament, the tibionavicular ligament, and the tibiotalar ligaments. The second major ligament to support the ankle is the lateral collateral ligament of the ankle joint which is comprised of the anterior tibiofemoral ligament, posterior tibiofemoral ligament, and calcaneofibular ligament.
Just inferior to the ankle joint, we see the subtalar joint – a plane synovial joint which consists of anterior and posterior articulations. In this joint, the talus articulates with the navicular and the calcaneus effectively forming the talocalcaneonavicular joint and the talocalcaneal joint respectively. The talocalcaneonavicular joint which is also the anterior compartment at the joint is stabilized by the talonavicular ligament and the plantar calcaneonavicular ligament. The talocalcaneal joint which is the posterior compartment of this joint is stabilized by the medial and lateral talocalcaneal ligaments, the interosseus talocalcaneal ligament, and the cervical ligament.
Finally, the interphalangeal articulations of the foot are formed between the phalanges of the toes of the foot. The first digit – the big toe – forms only one interphalangeal joint while the second to fifth digits form two interphalangeal joints on each digit. This is due to the fact that the big toe only possesses a proximal and distal phalanx whereas the rest of the toes possess a proximal, middle and distal phalanx. The interphalangeal joints are hinge type synovial joints that is stabilized by an articular capsule and two collateral ligaments. These joints permit flexion and extension movements of the toes.