2_Basic Structure and Function of Joints_2024.pdf

Basic Structure and Function of Joints PT 63 3 Overview of Lecture Classification Systems 1. Anatomic Structure and Movement Potential 2. Mechanical Analogy (synovial joints) Biological Materials that comprise Connective Tissues in Joints Types of Connective Tissues that form Structu...

Basic Structure and Function of Joints PT 63 3 Overview of Lecture Classification Systems 1. Anatomic Structure and Movement Potential 2. Mechanical Analogy (synovial joints) Biological Materials that comprise Connective Tissues in Joints Types of Connective Tissues that form Structure of Joints Classifying Joints based on Anatomic Structure and Movement Potential Reference: Table 2-1 in Neumann 1. Synarthrosis 2. Amphiarthrosis 3. Diarthrosis Synarthrosis A junction between bones that is held together by dense irregular connective tissue Allows little to no movement Function Bind bones together Transmit force from one bone to another with minimal joint motion Force shared across larger surface area → reduces risk of injury Synarthrosis Examples Sutures of skull Distal tibio-fibular joint Interosseous membranes of the forearm and leg Amphiarthrosis A junction between bones that is formed primarily by fibrocartilage and/or hyaline cartilage Allow relatively restrained movements Function Transmit and disperse forces between bones  Why is having some Amphiarthrosis movement at these joints important? Examples Interbody joint of spine: intervertebral disc with nucleus pulposus Pubic symphysis Manubriosternal joint Diarthrosis The Synovial Joint! An articulation that contains a fluid-filled joint cavity between the bones – a synovial membrane Specialized for movement Major joints of the upper and lower extremities All diarthrodial/synovial joints have 7 key features 1. Synovial fluid 2. Articular cartilage 3. Articular capsule 4. Synovial membrane 5. Capsular ligaments 6. Blood vessels 7. Sensory nerves Feature Function Synovial fluid Nutrition and lubrication Articular cartilage Covers end of bones, shock absorption Articular capsule Peripheral curtain of connective tissue (2 layers); protection Synovial membrane Inner layer of capsule, barrier to adjacent capillaries; make hyaluronate and lubricating glyco-proteins (lubricin) to the joint fluid Capsular ligaments Outer layer of capsule, dense irregular connective tissue; supper between bones and contents of joint; helps resist or control motion Blood vessels Capillary beds go as deep as junction between fibrous and synovial membranes; nutrition Sensory nerves Supply fibrous capsule; receptors for pain and proprioception SOME synovial joints have extra features Intraarticular discs / menisci Pads of fibrocartilage between articular surfaces Function: increase joint congruency, dissipate force Labrum Fibrocartilage Located in glenoid cavity and acetabulum Function: Deepen concave surface of the articulation  SOME synovial joints have extra features Fat Pad Within the joint capsule between fibrous and synovial membranes Most notable in knee and elbow Function: thicken joint capsule, reducing needed volume of synovial fluid for proper joint motion If enlarged / inflamed = bad news (pain and mechanical issue) --> MORE TO COME! Synovial Plicae Slack, overlapped pleats of tissue in innermost layer of joint capsule Function: increase synovial surface area, allow full joint motion without too much tension on synovial lining If enlarged / inflamed = bad news (pain and mechanical issue) Classifying Synovial Joints by Mechanical Analogy We need to understand synovial joints well to understand/assess joint movement Reference: Neumann Table 2-2 Seven Classifications Hinge Pivot Ellipsoid Ball-and-Socket Plane Saddle Condyloid Hinge Joint Angular motion occurs primarily in a plane perpendicular to the axis of rotation Slight translation allowed (but not much) Examples Humeroulnar joint Interphalangeal joints of digits Pivot Joint Angular motion of the mobile side of the joint is parallel to the axis of rotation Produces SPIN motion Think doorknob Examples Humeroradial joint Atlanto-axial joint in cranio-cervical region Ellipsoid Joint One side convex, elongated in 1 dimension One side concave, elongated in 1 dimension Because ”elliptic”, notable restriction in spin but allows bi-planar motion (flexion/extension & abduction/adduction) Example Radiocarpal joint Ball-and-Socket Joint 1 Spherical convex surface 1 Cup-like socket Motion allowed in all 3 planes Including spin Examples Glenohumeral joint Hip joint Plane Joint Pairing of 2 relatively flat or slightly curved surfaces Movements: slide & slight rotation Movement between bones created by tension in muscle or ligaments Lack definitive axis of rotation → motion not typically described in terms of degrees of freedom Examples Carpometacarpal joints (digits II-V) Intercarpal joints Intertarsal joints Saddle Joint Each “partner” bone of this joint has both a concave and convex surface Oriented approximately perpendicular to one another Reciprocally curved Think horse saddle and rider Function: allows bi-planar motion but limited spin Example Carpometacarpal joint of thumb Condyloid Joint Like a ball-and-socket joint, but concave member is relatively shallow Usually allows 2 degrees of freedom The 3rd DOF restricted by bony incongruency or ligaments, but may still be present in small degrees Often occur in pairs Examples Tibiofemoral joint Atlanto-occipital joint Metacarpophalangeal joint of finger  A little more about the axis of rotation Axis FIXED Axis NOT FIXED All points on the door undergo equal arcs “Moves” based on orientation of bones of rotation relative to one another during joint motion Instantaneous axis of rotation Location of the axis holds true only for a specific angle of motion i.e. it changes through the arc of motion Path of motion of the instantaneous axis of rotation = THE EVOLUTE The evolute is longer when the joint surfaces are less congruent