9: Skeletal Joints (Articulations)
- Page ID
- 169032
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Chapter Overview
Structural and Functional Classification of Joints
The adult body has 206 bones; except for the hyoid, each connects to at least one other bone. Joints (articulations) are where bones (or bone and cartilage) meet to connect the skeleton, transmit forces, and permit movement. Several joints are designed for stability and provide for little or no movement. Importantly, joint stability and movement are related to each other. This means that stable joints allow for little or no mobility between the adjacent bones. Conversely, joints that provide the most movement between bones are the least stable.
Structural classification of joints is based on the type of connecting tissue and presence or absence of a joint cavity (fibrous, cartilaginous, synovial), while functional classification describes the degree of movement permitted (synarthrosis, amphiarthrosis, diarthrosis).
Fibrous Joints: Sutures, Gomphoses, and Syndesmoses
Fibrous joints unite bones with fibrous connective tissue and lack a joint cavity; they include immobile sutures between skull bones, gomphoses anchoring teeth in their sockets, and slightly movable syndesmoses linking parallel bones via ligaments or an interosseous membrane.
Cartilaginous Joints: Synchondroses and Symphyses
Cartilaginous joints join bones with cartilage and have no joint cavity; synchondroses use hyaline cartilage and are typically immobile, whereas symphyses use fibrocartilage to allow limited movement, as seen in the pubic symphysis and intvertebral discs.
Functional Joint Types: Synarthrosis, Amphiarthrosis, Diarthrosis
Functionally, joints are classified as synarthroses (essentially immovable), amphiarthroses (slightly movable), or diarthroses (freely movable), with all synovial joints falling into the diarthrotic category and varying by the number of movement axes (uniaxial, biaxial, multiaxial).
Core Structural Features of Synovial Joints
Synovial joints share key components—articular hyaline cartilage, a fluid-filled joint cavity, and a multi-layered articular capsule—and are stabilized by ligaments, muscles, tendons, and sometimes articular discs or menisci, while bursae and tendon sheaths reduce friction.
Types of Synovial Joints and Their Motions
Synovial joints are categorized by shape and permitted movements into pivot, hinge, condyloid, saddle, plane, and ball-and-socket types, each allowing specific patterns of motion such as rotation, flexion–extension, abduction–adduction, circumduction, and multiaxial movement.
Region-Specific Joint Movements
Named movements at particular joints and regions include head and neck flexion, extension, and rotation; forearm pronation and supination; ankle and foot dorsiflexion, plantarflexion, inversion, and eversion; and combined flexion, extension, lateral flexion, and rotation across the vertebral column.
Temporomandibular Joint Structure and Movements
The temporomandibular joint, between the mandibular condyle and temporal bone, contains an articular disc and functions as a combined hinge and gliding joint, allowing elevation, depression, protraction, retraction, and lateral excursion of the mandible.
Shoulder and Elbow Synovial Joints
The shoulder (glenohumeral) joint is a multiaxial ball-and-socket joint with a shallow glenoid cavity deepened by a labrum and stabilized mainly by rotator cuff muscles and supporting ligaments and bursae, while the elbow combines hinge and pivot components stabilized by collateral and annular ligaments.
Hip and Knee Synovial Joints
The hip is a deep, stable ball-and-socket joint with strong capsular ligaments and an acetabular labrum, whereas the knee is a modified hinge joint with cruciate and collateral ligaments, menisci, and a locking mechanism that together guide and stabilize its complex rolling and gliding motions.
Ankle Joint and Ligamentous Support
The ankle (talocrural) joint operates as a hinge between the tibia–fibula mortise and the talus, with medial (deltoid) and lateral ligament complexes providing stability and limiting excessive eversion and inversion, common sites of ankle sprain.
Embryonic Development of Joints and Epiphyseal Plates
Joints develop from mesenchyme that differentiates into bone, cartilage, and fibrous tissue; limb joints arise from cartilage models separated by a joint interzone that cavitates to form synovial cavities, while temporary synchondroses at epiphyseal plates later ossify into synostoses at skeletal maturity
To achieve the chapter objectives, you are expected to actively engage with the material. Learning the tissues is not a passive process - your understanding will grow as you interact with the content, peers, and instructor, regularly checking your thinking against feedback and revisiting concepts until you can explain and apply them on your own.
By the end of this chapter, students should be able to:
- Define a skeletal joint (articulation) and distinguish structural versus functional classifications.
- Classify any joint by structure (fibrous, cartilaginous—synchondroses/symphyses, synovial) and by function (synarthrosis, amphiarthrosis, diarthrosis), citing representative examples of each.
- Describe and identify the hallmark tissues and features of fibrous joints (sutures, gomphoses, syndesmoses) and cartilaginous joints, with locations in the body.
- Describe core components of synovial joints—articular cartilage, joint cavity, synovial fluid, articular capsule (fibrous layer and synovial membrane)—and friction-reducing/support structures (ligaments: extrinsic/intrinsic/intracapsular; bursae; tendon sheaths; articular discs/menisci).
- Distinguish the six synovial joint types by surface shape and axes of motion (pivot, hinge, condyloid, saddle, plane, ball-and-socket) and match each to key examples.
- Define and recognize named body movements, including flexion/extension, abduction/adduction, circumduction, medial/lateral rotation, pronation/supination, dorsiflexion/plantarflexion, inversion/eversion, elevation/depression, protraction/retraction, opposition/reposition, and lateral flexion.
- Describe the anatomy, stabilizers, and motions of selected joints: temporomandibular; atlanto-occipital and atlanto-axial; shoulder (glenohumeral); elbow and proximal radioulnar; wrist; hip; knee; ankle (talocrural) and subtalar; vertebral facet and intervertebral symphysis joints.
- Explain how specific ligaments and soft tissues contribute to stability and motion (example: rotator cuff; ACL, PCL, MCL, LCL, and menisci at the knee; annular ligament at the proximal radioulnar joint; deltoid and lateral collateral ligaments at the ankle; acetabular and glenoid labra).
- Compare motion capabilities across cervical, thoracic, and lumbar regions and relate them to joint orientation and type.
- Apply anatomical terminology to communicate joint structure, function, movement, and common clinical correlations (example: ankle sprain, ACL injury, rotator cuff pathology, TMJ dysfunction
- 9.1: Classification of Joints
- This page discusses the classification of joints, or articulations, that connect bones or cartilage. Joints are structurally divided into fibrous (immobile), cartilaginous (slightly mobile), and synovial (freely movable) types. Functionally, they are classified as synarthrosis (immobile), amphiarthrosis (slightly movable), and diarthrosis (freely movable).
- 9.2: Fibrous Joints
- This page details fibrous joints that connect bones through connective tissue without a joint cavity, including sutures, syndesmoses, and gomphoses. Sutures provide skull stability and brain protection, while infant fontanelles allow flexibility. Syndesmoses connect parallel bones with limited movement, essential for leg stability and forearm mobility. Gomphoses secure teeth in sockets as immovable joints.
- 9.3: Cartilaginous Joints
- This page covers cartilaginous joints, which connect bones through cartilage without joint cavities. It explains two types: synchondroses, linked by hyaline cartilage (e.g., epiphyseal plates), and symphyses, connected by fibrocartilage (e.g., pubic symphysis). Synchondroses can be temporary or permanent, while symphyses allow limited movement. These joints are functionally classified as synarthroses (immovable) and amphiarthroses (slightly movable).
- 9.4: Synovial Joints
- This page provides an overview of synovial joints, detailing their structure, function, and the role of synovial fluid in facilitating movement. It describes various types of synovial joints, the anatomy and function of bursae in the knee, and the conditions affecting joints, such as arthritis. Osteoarthritis, the most common type linked to aging, is discussed, along with symptoms and treatments.
- 9.5: Types of Body Movements
- This page explores essential body movements involving the foot, scapula, and mandible, including inversion, eversion, protraction, retraction, elevation, and depression. It emphasizes the importance of these movements for balance, posture, and daily activities. Additionally, it discusses lateral excursion of the mandible and rotation of the scapula key for arm abduction, along with thumb movements like opposition and reposition.
- 9.6: Anatomy of Selected Synovial Joints
- This page covers the articulations of the vertebral column, focusing on the anatomy and functionality of key synovial joints, including those in the neck, shoulder, elbow, hip, knee, and ankle. It discusses joint mobility influenced by structural orientation, common injuries like dislocations and sprains, and specific conditions such as bursitis and arthritis.
Thumbnail: Structure of a synovial joint. (CC BY 4.0; via Synovial Joints).