Chapter 8: Joints PDF

Preview

Summary

Marieb and Cohen ed. 11...

Description

CHAPTER 8 Joints 8.1 – JOINTS ARE CLASSIFIED INTO STRUCTURAL AND 3 FUNCTIONAL CATEGORIES 

Joints are classified by structure and function o Structural Classification: Focuses on the material binding the bones together and whether a joint cavity is present.  3 structural classifications:  Fibrous Joints  Cartilaginous Joints  Synovial Joints o Functional Classification: Based on the amount of movement allowed at the joint  3 functional classifications:  Synarthroses: Immovable joints o Largely restricted to axial skeleton  Amphiarthroses: Slightly movable joints  Diarthroses: Freely moveable joints o Predominate appendicular skeleton

STRUCTURE DICTATES FUNCTION!!!! 

In general, fibrous joints are immovable and synovial joints are freely movable

8.2 – IN FIBROUS JOINTS, THE BONES ARE CONNECTED BY FIBROUS TISSUE 



Fibrous Joints: Bones are joined together by the collagen fibers in connective tissue o No joint cavity o Amount of movement allowed depends on length of connective tissue fibers o Most are immovable or slightly moveable 3 types of Fibrous Joints: 1. Sutures (“Seams”)   



Only between bones of skull; wavy articulating bone edges interlock and junction is completely filled by minimal amount of very short CT fibers Bones are knit together but sutures allow the skull to expand and brain grows during youth During middle age, the fibrous tissue ossifies and the skull bones fuse into a single unit o Once sutures are closed they are called Synostoses Sutures serve as a protective function to create an immovable joint

2. Syndesmosis   

Bones connected EXCULISVELY to ligaments, cords or bands of fibrous tissues Short fibers = less movement Long fibers = more movement

3. Gomphosis  

A peg-in-socket fibrous joint Only example is articulation is a tooth with its bony alveolar socket o They have a short ligament (no movement)

8.3 – IN CARTILAGINOUS JOINTS, THE BONES ARE CONNECTED BY CARTILAGE  

In cartilaginous joints the articulating are united by cartilage o Like fibrous joints, they lack a joint cavity and are not highly moveable 2 types of cartilaginous joints: 1. Synchondroses  A bar or plate of hyaline cartilage unites bones at the synchondrosis  Synarthrotic  Most common examples: o Epiphyseal plates of long bones in kids o Costal cartilage of 1st rib o Manubrium is sternum

2. Symphyses  A joint where fibrocartilage unites bones is a symphysis  Fibrocartilage is compressible and resilient; this acts as a shock absorber and allows minimal movement at the joint  Hyaline cartilage is also present on bony surfaces  Amphiarthrotic joints designed for strength with flexibility  Common examples: o Intervertebral joints o

Pubic symphysis of pelvis

8.4 – SYNOVIAL JOINTS HAVE A FLUID-FILLED JOINT CAVITY 

Synovial Joint: Are those articulating bones are separated by a fluid-containing joint cavity O Permits substantial amount of movement; therefore all synovial joints are freely-moveable diarthroses O Nearly all joints of the limbs are synovial joints

General Structures 



6 distinguishing features: 1. Articular Cartilage: Hyaline cartilage that is a spongy cushion absorbs compression on a joint A. Keeps bones from being crushed 2. Articular Capsule: A joint cavity is enclosed by a twolayered articular capsule. A. Dense irregular CT that is continuous with articulating bones B. Strengthens the joint so that the bones are not pulled apart C. Synovial membrane: Inner layer of joint capsule consist of loose CT I. Covers all surfaces that are not covered by hyaline cartilage 3. Synovial Fluid: A small amount of synovial fluid occupies all free spaces within the joint capsule A. Fluid is derived largely by filtration from blood flowing in capillaries B. Secreted by cells in synovial membrane, but it thins and becomes less viscous during joint activity C. Weight-bearing, reduces friction between cartilages 4. Reinforcing Ligaments: Synovial joints are reinforced and strengthened by several bandlike ligaments (Connect bone to bone) A. Most often these are capsular ligaments (thickened parts of fibrous layer) B. Double Jointed: When joint capsules and ligaments are stretcher and looser than average 5. Nerves and Blood Vessels: Synovial joints are richly supplied with sensory nerve fibers that innervate the capsule A. Most fibers monitor joint position and stretch but some detect pain B. Richly supplied with BV; extensive capillary beds produce blood filtrate that is the basis for synovial fluid Besides the 6 basic components certain synovial joints have other features O Hips and knee joints have cushioning fatty pads between fibrous layer and the synovial O

membrane or bone Others have discs or wedges of fibrocartilage separating the articular surfaces  When present these are called articular discs or menisci  They extend inward from the articular capsule and partially or completely divide the synovial cavity  Articular discs improve the fit between articulating bone ends

Bursae and Tendon Sheaths  Bursae and tendon sheaths are not strictly part of the synovial joint  Bags of lubricant to reduce friction between adjacent structures during joint activity  Bursae: A flattened fibrous sac lined with a synovial membrane and contains a small amount of synovial fluid  Tendon Sheath: An elongated bursa that wraps completely around a tendon subjected to friction

Factors Influencing the Stability of Synovial Joints 

The stability of a joint depends chiefly on 3 factors: 1. Shape of Articular Surfaces: a. Determines what movements are possible b. Minor role in stability; many joints have shallow sockets or noncomplementary articulating surfaces that hinder joint stability c. Large articulating surfaces fit snug; ball and socket of hip 2. Ligaments: a. Capsules and ligaments unite bones and prevent undesired motion b. More ligaments = more stable c. Ligaments easily snap which hinders durability of joint 3. Muscle Tone: a. The muscle tendons that cross the joint are most important stabilizing factor b. Muscle tone is extremely important in reinforcing the shoulder and knee joints, as well as the arches of the foot

Movements Allowed By Synovial Joints

Special Movements

8.5 – FIVE EXAMPLES ILLUSTRATE THE DIVERSITY OF SYNOVIAL JOINTS Temporomandibular Joint (TMJ)      



Modified hinge joint; lies just anterior to the ear At this joint, the condylar process of mandible articulates with the inferior surface of the squamous part of the temporal bone Posteriorly, it forms the concave mandibular fossa; anteriorly it forms a dense knob called the articular tubercle The lateral aspect of the loose articular capsule that encloses the joint is thickened into a lateral ligament Within the capsule, an articular disc divides the synovial cavity into superior and inferior compartments 2 types of movement occur at TMJ: (i) The concave inferior disc surface receives the condylar process of the mandible and allows the familiar hinge-like movement of depressing and elevating the mandible while opening and closing the mouth (ii) The superior disc surface glides anteriorly along with the condylar process when the mouth is opened wide. This anterior movement braces the condylar process against the articular tubercle, so that the mandible is not forced through the thin roof of the mandibular fossa when one bites on hard food The superior compartment also allows for joint to glide from side to side o Called lateral excursion

Shoulder (Glenohumeral) Joint   



 



Stability is sacrificed for mobility Ball and socket joint; the large hemisphere of humerus head fits in the shallow glenoid cavity The articular capsule enclosing the joint activity (from the margin of the glenoid cavity to the anatomical neck of the humerus) is remarkably loose and thin o Contributes to joints freedom There are few ligaments reinforcing the shoulder joint; located primarily on the anterior aspect: o The superiorly located coracohumeral ligament provides the only strong thickening of the capsule and helps support the weight of the upper limb o 3 glenohumeral ligaments strengthen the front of capsule somewhat but are weak Muscle tendons that cross the shoulder joint is the main stabilizers The “superstabilizer” is the long head of biceps brachii o The tendon attaches to the superior margin of the glenoid labrum, travels through the joint cavity, and then runs within the intertubercular sulcus of the humerus. It secures the head of the humerus to the glenoid cavity 4 other tendons (and associated muscles) make up the rotator cuf o This cuff encircles the shoulder joint and blends with articular capsule o o

The four muscles of the rotator cuff are the subscapularis, infraspinatus, supraspinatus, and teres minor The rotator cuff can be severely stretched when the arm is vigorously circumducted; common injury for baseball players

Elbow Joint   

 



Elbow joint provides a stable and smoothly operating hinge that allows flexion and extension only Within the joint, both the radius and the ulna articulates with the condyles of the humerus A relatively lax articular capsule exetnds inferiorly from the humerus to the ulna and radius, and to the anular ligament encircling the head of the radius Anteriorly and posteriorly, the articular capsule is thin and allow for substantial freedom for flexion and extension Side to side movements are restricted by two strong capsualr ligaments: (i) Ulnar Collateral Ligament (medially) (ii) Radial Collateral Ligament (triangular ligament on the lateal side) Supination: Radius twists over ulna

Hip (Coxal) Joint   



Ball and socket; good range of motion Movement occurs in all planes but all limited due to the deep socket and strong ligaments Hip joint is formed by the articulation of the spherical head of the femur with the deeply cupped acetabulum of the hip bone o Depth of the acetabulum is reinforced by a circular rim of fibrocartilage called the acetabular labrum The thick articular capsule extends from the rim of the acetabulum to the neck if the femur and completely enclose the joint



Several of these strong ligaments reinforce the capsule of the hip joint. These include: o Iliofemoral Ligament: A strong V-shaped ligament anteriorly o Pubofemoral Ligament: A triangular thickening of the inferior part of the capsule o Ischiofemoral Ligament: A spiraling posterior ligament



These ligaments are arranged in such a way that they “screw” the femur head into the acetabulum when a person stands up straight, thereby giving stability The ligament of the head of the femur (ligamentum teres) is a flat intracapsular bands that runs from the femur to the head of the lower lip of the acetabulum o This ligament is slack during most movements



Knee Joint  

Largest and most complex joint in the body Knee consists of 3 joints in 1: o Femoropatellar Joint: An intermediate one between the patella and the lower end of the femur o Tibiofemoral Joint: Medial joints o Menisci (Semi-Lunar Cartilage): C-shaped cartilage between the femoral condyles Prevent side-to-side gliding of the femur on the tibia and absorb shock transmitted to the knee joint The tibiofemoral joint acts primarily as a hinge, permitting flexion and extension o Bicondylar joint with some rotation is possible when the knee is partially flexed and when knee is extending o When the knee is fully extended, side-to-side movements, and rotation are strongly resisted by ligaments and menisci The femoropatellar joint is a plane joint; patella glides across the distal end of femur during knee flexion The knee joint is only partially encapsulated o Thin articular capsule is present only on the sides and posterior aspects of the knee, where it covers the bulk of the femoral and tibial condyles. Anteriorly, where the capsule is absent there are 3 broad ligaments run from the patella to the tibia below: 



 



o o  







Patellar Ligament Medial Patellar Retinacula

o Lateral Patellar Retinacula These ligaments merge imperceptibly into the articular capsule on each side The patellar ligament and retinacula are continuations of the quadriceps muscle tendons on the anterior thigh o Physicians tap the patellar ligament to test knee-jerk reflex The synovial cavity of the knee joint has a complicated shape, with several extensions that lead to “dead ends” o At least a dozen of bursae is associated with the joint All 3 types of joint ligaments (extracapsular, capsular, and intracapsular) stabilize and strengthen the capsule of the knee joint o All capsular and extracapsular ligaments act to prevent hyperextension of the knee and are stretched tight when the knee is extended Main Ligaments: 1. Fibular & Tibial Collateral Ligaments o Critical in preventing lateral or medial rotation when the knee is extended o The broad, flat tibial collateral ligament runs from the medial epicondyle of the tibial shaft below and is fused to the medial meniscus 2. Oblique Popliteal Ligament  Actually, part of the tendon of the semimembranosus muscle that fuses with joint capsule  Helps stabilize the posterior aspect of knee joint 3. Arcuate Popliteal Ligament  Arcs superiorly from the head of the fibula over the popliteus muscle and reinforces joint capsule posteriorly

(a) Cruciate Ligaments 

The knee’s intracapsular ligaments are called cruciate ligaments o They cross each other forming an X in a notch between the femoral condyles o Act as restraining straps to help prevent anterior-posterior displacement of the articular surfaces o They are outside the synovial cavity

NOTE: Two cruciate ligaments both run superiorly to the femur and are named for their tibial attachment site 

There are 2 cruciate ligaments: (i) Anterior Cruciate Ligament: o Attaches to the anterior intercondylar area of tibia → passes posteriorly, laterally, and upward to attach to the femur on the medial side of the lateral condyle o Prevents forward sliding of the tibia on the femur and checks hyperextension o

Somewhat lax when knee is flexed and taut when knee is extended

(ii) Posterior Cruciate Ligament:

o

Stronger ligament; attached to the anterior intercondylar area of tibia

o

Passes posteriorly, laterally, and upward to attach to the femur on the medial side of the medial condyle Prevents backwards displacement of the tibia or forward sliding of the femur

o



Quadriceps is the most important musculature reinforcing the knee joint o Anterior thigh and tendon of semimembranosus muscle posteriorly



Knee has a built-in locking device...