BIO 004 · Human Anatomy
Articulations and Joints
Block 2 · Module 6: Articulations and Joints
A reference for the joints video and lab. A joint is where bones meet. This page covers how joints are classified, the fibrous and cartilaginous joints, the full structure of a synovial joint, the movements joints allow, the six synovial joint types, the shoulder and knee joints, and the common joint disorders.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the synovial joint structure, the six joint types, the shoulder and knee joints, and the joint disorders.
- Classify joints by structure and by function, and state the criteria for each.
- Describe the three types of fibrous joints and the two types of cartilaginous joints.
- Identify the structures of a synovial joint, its accessory structures, and its nerve and blood supply.
- Name the six types of synovial joints with their axes, and describe the movements at synovial joints.
- List the factors that affect range of motion and the common joint disorders.
- Describe the structure and supporting ligaments of the shoulder joint and the knee joint.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
Joint classification
Add a chart of fibrous, cartilaginous, and synovial joints.
A synovial joint
Add a labeled cross-section of a synovial joint.
The six synovial joints
Add a figure of the six synovial joint types with examples.
Classifying Joints
A joint, or articulation, is where two or more bones meet. Joints are classified two ways: by structure and by function. Learn both classifications.
Structural classification
The structural classification uses two criteria: whether a synovial cavity is present, and the type of connective tissue holding the bones.
| Structural class | Synovial cavity | Connective tissue holding the bones |
|---|---|---|
| Fibrous joint | none | dense connective tissue rich in collagen fibers |
| Cartilaginous joint | none | cartilage, hyaline or fibrocartilage |
| Synovial joint | present | the dense irregular connective tissue of an articular capsule |
Functional classification
The functional classification uses one criterion: the degree of movement the joint permits.
| Functional class | Degree of movement | Examples |
|---|---|---|
| Synarthrosis | immovable | sutures of the skull, gomphoses |
| Amphiarthrosis | slightly movable | syndesmoses, symphyses |
| Diarthrosis | freely movable | all synovial joints |
Fibrous Joints
Fibrous joints lack a synovial cavity, the bones are held closely by dense connective tissue, and they permit little or no movement. Compare the types by structure, mobility, and example.
| Type | Structure | Mobility | Examples |
|---|---|---|---|
| Suture | thin layers of dense irregular connective tissue, with interlocking edges that add strength and absorb shock | immovable in adults, a synarthrosis; slightly movable in infants and children, an amphiarthrosis | only between the bones of the skull; the metopic suture is a frontal suture that persists past about age six |
| Syndesmosis | more dense connective tissue and more space than a suture, the bones united by a ligament | slightly movable, an amphiarthrosis | the distal tibiofibular joint, united by the anterior tibiofibular ligament |
| Gomphosis | a cone-shaped peg held in a socket by the periodontal ligament | immovable, a synarthrosis | a tooth in its bony socket |
| Interosseous membrane | a substantial sheet of dense connective tissue binding neighboring long bones | slightly movable, an amphiarthrosis | between the radius and ulna; between the tibia and fibula |
- Synostosisa joint where two separate bones fuse completely into one, for example a suture that ossifies in adulthood
Cartilaginous Joints
Cartilaginous joints lack a synovial cavity and allow little or no movement. Compare the two types by the cartilage that connects the bones.
| Type | Connecting cartilage | Mobility | Examples |
|---|---|---|---|
| Synchondrosis | hyaline cartilage | immovable, a synarthrosis | the epiphyseal growth plate, which becomes a synostosis when bone replaces the cartilage; the joint between the first rib and the manubrium |
| Symphysis | a broad, flat disc of fibrocartilage | slightly movable, an amphiarthrosis | the pubic symphysis, the manubriosternal joint, the intervertebral joints between vertebral bodies; all symphyses lie in the midline |
Synovial Joint Structure
A synovial joint has a synovial cavity between the articulating bones and allows considerable movement. All synovial joints are freely movable, diarthroses.
Articular cartilage and capsule
- Articular cartilagehyaline cartilage covering the articulating bone surfaces, smooth and slippery, it reduces friction and absorbs shock but does not bind the bones
- Articular capsulea sleeve-like capsule that surrounds the joint, encloses the synovial cavity, and unites the bones
- Fibrous membranethe outer layer of the capsule, dense irregular connective tissue attached to the periosteum, strong and flexible
- Ligamentsthickened fibrous bundles of the fibrous membrane that resist strain and prevent dislocation
- Synovial membranethe inner layer of the capsule, areolar connective tissue with elastic fibers
- Articular fat padsaccumulations of adipose tissue that may cushion the joint
Synovial fluid
- Synovial fluida viscous, clear, pale-yellow fluid of hyaluronic acid and interstitial fluid, secreted by the synovial membrane
- Lubricationforms a thin film that reduces friction between the joint surfaces
- Nourishmentsupplies oxygen and nutrients to, and removes wastes from, the avascular articular cartilage
- Defensecontains phagocytic cells that clear microbes and debris from normal wear
- Warm-up effectgel-like at rest, it thins with movement, which is why warming up before exercise eases the joints
Accessory Structures of Synovial Joints
Accessory ligaments and discs
- Extracapsular ligamentsligaments that lie outside the articular capsule, as the collateral ligaments of the knee
- Intracapsular ligamentsligaments inside the capsule but kept out of the synovial cavity by synovial folds, as the cruciate ligaments of the knee
- Articular discs (menisci)crescent-shaped fibrocartilage pads between the bone surfaces, they improve fit, absorb shock, distribute weight, and spread synovial fluid
- Labruma fibrocartilage rim around the socket of a ball-and-socket joint that deepens it, found at the shoulder and hip
Bursae and tendon sheaths
- Bursaesmall sac-like structures filled with fluid, placed to reduce friction between skin, bone, muscle, tendon, or ligament
- Tendon sheathstube-shaped bursae that wrap a tendon where it passes through a tight space, as at the wrist and ankle
Nerve and blood supply
- Nerve supplythe same nerves that supply the muscles moving the joint, they carry pain information and help adjust movement
- Blood supplyarteries near the joint branch into the capsule and ligaments, veins carry wastes away, the articular cartilage is fed instead by the synovial fluid
Movements at Synovial Joints
Gliding and angular movements
- Glidingsimple back-and-forth or side-to-side movement, no change in the angle between bones
- Flexiondecreases the angle between bones, usually in the sagittal plane
- Extensionincreases the angle between bones, the reverse of flexion
- Lateral flexionbending the trunk or head sideways, in the frontal plane
- Hyperextensionextension that continues past the anatomical position
- Abductionmovement away from the midline of the body
- Adductionmovement toward the midline of the body
- Circumductionmovement of the distal end of a part in a circle
Rotation and special movements
- Rotationa bone turns around its own long axis, medial rotation toward the midline, lateral rotation away
- Elevation, depressionlifting a body part upward, then lowering it
- Protraction, retractionmoving a body part forward, then back to position
- Inversion, eversionturning the sole of the foot inward, then outward
- Dorsiflexion, plantar flexionbending the foot up at the ankle, then pointing the toes down
- Supination, pronationturning the palm to face anteriorly, then posteriorly
- Oppositionmoving the thumb across the palm to touch the fingertips
The Six Types of Synovial Joints
Synovial joints are sorted by the shape of their surfaces, which sets the axes of movement: uniaxial moves around one axis, biaxial around two, triaxial around three. Compare the six.
| Joint type | Shape of the surfaces | Axes of movement | Examples |
|---|---|---|---|
| Plane joint | flat or slightly curved surfaces that glide | biaxial or triaxial gliding | the intercarpal and intertarsal joints |
| Hinge joint | a convex surface fits a concave one | uniaxial, flexion and extension | the elbow, ankle, and interphalangeal joints |
| Pivot joint | a rounded surface fits a ring of bone and ligament | uniaxial, rotation | the atlantoaxial and radioulnar joints |
| Condyloid joint | an oval projection fits an oval depression | biaxial | the radiocarpal and metacarpophalangeal joints |
| Saddle joint | each surface is both concave and convex | biaxial | the carpometacarpal joint of the thumb |
| Ball-and-socket joint | a ball fits a cup | triaxial | the shoulder and hip joints |
Factors Affecting Range of Motion
Range of motion is the arc, measured in degrees, through which the bones of a joint can move. Several factors set its limits.
- Bone shapethe structure and fit of the articulating bones
- Ligament tensiontaut ligaments restrict movement and direct the bones
- Muscle arrangementmuscle tension reinforces the restraint set by the ligaments
- Contact of soft partsone body surface meeting another can limit movement
- Hormonesrelaxin loosens the pubic symphysis and pelvic ligaments late in pregnancy
- Disusea joint unused for a long time loses range as fluid, ligament flexibility, and muscle decline
The Shoulder Joint
The glenohumeral joint, a ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula. It is the most freely movable joint in the body, and the price of that mobility is instability.
Structure
- Typea ball-and-socket joint, also called the glenohumeral or humeroscapular joint
- Articulating bonesthe head of the humerus and the glenoid cavity of the scapula
- Why it moves so freelythe articular capsule is loose and the glenoid cavity is shallow relative to the large humeral head
Ligaments and supporting structures
- Articular capsulea thin, loose sac that envelops the joint, from the glenoid cavity to the anatomical neck of the humerus
- Coracohumeral ligamentruns from the coracoid process to the greater tubercle, strengthens the superior part of the capsule
- Glenohumeral ligamentsthree thickenings of the anterior capsule, from the glenoid cavity to the lesser tubercle and anatomical neck, stabilize the joint near the limits of motion
- Transverse humeral ligamenta narrow band between the greater and lesser tubercles that holds the long head of the biceps tendon in place
- Glenoid labruma rim of fibrocartilage around the glenoid cavity that slightly deepens and enlarges it
- Bursaefour are associated with the joint: the subscapular, subdeltoid, subacromial, and subcoracoid bursae
Movement and the rotator cuff
- Movementsflexion, extension, hyperextension, abduction, adduction, medial and lateral rotation, and circumduction
- Source of stabilitythe ligaments add little strength, most stability comes from the rotator cuff muscles
- Rotator cuff (SITS)the supraspinatus, infraspinatus, teres minor, and subscapularis, which hold the humeral head in the glenoid cavity
The Knee Joint
The tibiofemoral joint, the largest and most complex joint in the body. It is a modified hinge joint, and the joint most often injured.
Structure
- Typea modified hinge joint, the largest and most complex joint in the body
- Three joints, one cavitya medial and a lateral tibiofemoral joint between the femoral and tibial condyles, and a patellofemoral joint between the patella and the femur
Ligaments, anterior and posterior
- Articular capsulethe capsule that encloses the joint
- Patellar retinaculathe medial and lateral retinacula, fused quadriceps tendon and fascia, strengthen the anterior surface
- Patellar ligamentthe continuation of the quadriceps tendon from the patella to the tibial tuberosity, strengthens the anterior surface
- Oblique popliteal ligamenta broad ligament that strengthens the posterior surface of the joint
- Arcuate popliteal ligamentstrengthens the lower lateral part of the posterior surface
The collateral and cruciate ligaments
Four ligaments are the heart of knee stability. Compare them by where they sit and what each one resists.
| Ligament | Location | What it resists |
|---|---|---|
| Tibial collateral ligament | the broad ligament on the medial side, from the medial epicondyle of the femur to the medial condyle of the tibia | forces that would open the knee on the medial side |
| Fibular collateral ligament | the round ligament on the lateral side, from the lateral epicondyle of the femur to the head of the fibula | forces that would open the knee on the lateral side |
| Anterior cruciate ligament | an intracapsular ligament, crossing within the joint | limits hyperextension and stops the tibia from sliding forward; torn in roughly 70 percent of serious knee injuries |
| Posterior cruciate ligament | an intracapsular ligament, crossing within the joint | stops the tibia from sliding backward; important on stairs and inclines |
The menisci
- Medial meniscusthe C-shaped fibrocartilage disc on the medial side of the joint
- Lateral meniscusthe more circular, O-shaped disc on the lateral side
- Transverse ligamentthe band that joins the two menisci to each other
Knee injuries
- Unhappy triada lateral blow to a planted knee that tears three structures at once: the tibial collateral ligament, the medial meniscus, and the anterior cruciate ligament
- ACL and womenthe anterior cruciate ligament is torn three to six times more often in women, from a narrower intercondylar space, a wider pelvis and greater knee angle, ligament-loosening hormones, and less protective muscle strength
- Swollen kneeimmediate swelling is blood from torn vessels, delayed swelling is excess synovial fluid
- Dislocated kneedisplacement of the tibia relative to the femur, most often anterior, it can damage the popliteal artery
- PRICEthe first-aid approach to a knee injury: protection, rest, ice, compression, elevation
Common Joint Disorders
- Double-jointedgreater ligament flexibility and range of motion, the joints are less stable and dislocate more easily
- Bursitisinflammation of a bursa, from repeated overuse, infection, or rheumatoid arthritis, with pain, swelling, and limited movement
- Torn meniscusa tear of the knee cartilage, common in athletes, repaired by arthroscopy with a fiber-optic camera
- Rheumatismany painful disorder of the supporting structures, bones, ligaments, tendons, or muscles, not caused by infection or injury
- Arthritisa form of rheumatism with swollen, stiff, painful joints, the leading cause of physical disability in adults over 65
- Osteoarthritisa progressive, degenerative loss of joint cartilage from aging and wear, in the large weight-bearing joints
- Rheumatoid arthritisan autoimmune disease that attacks the cartilage and joint linings, usually on both sides, inflaming the synovial membrane
- Gouty arthritissodium urate crystals deposit in joints, often the base of the big toe, eroding the cartilage with inflammation and pain
See also: Bone Histology for the cartilage that lines and cushions joints.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Classify joints by structure into fibrous, cartilaginous, and synovial, and give one example of each.
- Name the six types of synovial joint and give a body example of each.
- Use the parts of a synovial joint to explain how it allows movement with little friction.
- Compare a suture and a synovial joint by how much movement each allows and why.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.