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Joints and Articulations Arthrology Joints And Their Classification A joint, or articulation, is any point at which two bones meet, regardless of whether they are movable at that point The science of joint structure, function, and dysfunction is called arthrology The study of musculoskeletal movement is kinesiology Joints And Their Classification Kinesiology is a branch of biomechanics, which deals with a broad range of motions and mechanical processes in the body, including the physics of blood circulation, respiration, and hearing. About Joints Tendons Ligaments bind a muscle to bone bind bone to bone Both are dense regular connective tissue Muscles act at a joint, and have: Origin (the part that does not move) Insertion (the part that moves) action Characterizing Joints Joints can be characterized two different ways: 1) What type of movement does the joint allow? No movement, limited movement, free movement 2) What tissue joins the bones? Fibrous Joints Fibrous connective tissue (eg. suture, ligament, tooth) Cartilaginous Joints Hyaline cartilage (eg. epiphyseal plate, costal cartilage) Fibrocartilage (eg. pubic symphysis) Synovial Joints (Hyaline cartilage plus a capsule) Characterizing Joints by the Types of Movement Synarthrotic Amphiarthrotic immoveable, allows no movement allows only limited movement Diarthrotic freely moveable Warning: Don’t go any further until you memorize these three types of movements, or you will get lost! Characterizing Joints by the Types of Tissue Between Bones Fibrous Joints Fibrous connective tissue (eg. suture, ligament, tooth) Cartilaginous Joints Hyaline cartilage (eg. epiphyseal plate, costal cartilage) Fibrocartilage (eg. pubic symphysis) Synovial Joints (Hyaline cartilage plus a capsule) Warning: Don’t get fibrous connective tissue mixed up with fibrocartilage. Connective tissue is mostly collagen secreted by fibroblast cells. Connective tissue is not made of cells, unlike fibrocartilage. There are no nuclei seen in connective tissue. Characterizing Joints by the Types of Tissue Between Bones Fibrous Joints These are made of dense regular fibrous connective tissue Examples are sutures, ligaments, tooth sockets) Suture (dense fibrous C. T. between bony plates) Syndesmosis (these are the ligaments, which are also dense fibrous connective tissue ) Gomphosis (tooth socket; a type of ligament) Movement Allowed by the Different Types of Fibrous Joints Sutures (immoveable = synarthrotic) Gomphoses (immoveable = synarthrotic) Syndesmoses (slightly moveable = amphiarthrotic) Summary of Fibrous Joints A fibrous joint is two bones joined by dense fibrous connective tissue. No joint cavity Some fibrous joints are immoveable (sutures and gomphoses) and some are slightly moveable (syndesmoses, which are the ligaments) Suture •In sutures and gomphoses, the fibers are very short and allow for little or no movement Syndesmosis (ligaments) •In syndesmoses, the fibers are longer and the attached bones are more movable: ligament attaches! Gomphosis (special ligament) The periodontal ligament is the only example of a gomphosis That’s enough on fibrous joints. Now we will go on to cartilaginous joints. Cartilaginous Joints A cartilaginous joint is two bones joined by cartilage. The cartilage is either fibrocartilage (a symphysis joint) or hyaline cartilage (a synchondrosis). Hyaline cartilage joints (synchondroses) are synarthrotic (immovable). Examples are epiphyseal plates and costal cartilages Fibrocartilage joints (symphyses) are amphiarthrotic (slightly moveable). Examples are the pubic symphysis and intervertebral discs. Hyaline Cartilage Joints Hyaline cartilage joints (synchondroses) are synarthrotic (immovable). Examples are epiphyseal plates and costal cartilages Synchondrosis Epiphyseal plate Costal cartilages A synchondrosis is a joint in which the bones are bound by hyaline cartilage (A synchondrosis is synarthrotic: not moveable) A synchondrosis is a synarthrosis Fibrocartilage Joints Fibrocartilage joints (symphyses) are amphiarthrotic (slightly moveable). Examples are the pubic symphysis and intervertebral discs. Fibrocartilage Joints Symphysis In a symphysis, two bones are joined by fibrocartilage (A symphysis is amphiarthrotic: slightly moveable) Warning Remember, don’t confuse fibrous connective tissue with fibrocartilage! Joints are classified as being either fibrous (fibrous connective tissue) or cartilaginous (hyaline or fibrocartilage). Also, don’t confuse hyaline joints (which have no capsule and are not moveable) with synovial joints, which have hyaline cartilage, but also have a synovial capsule and are very moveable). Before we go on to synovial joints, let’s stop and talk about intervertebral discs. INTERVERTEBRAL DISCS Function is for shock absorption and a little movement. Made up of outer ring of fibrocartilage called the ANNULUS FIBROSIS, and the middle section is elastic cartilage called the NUCLEUS PULPOSIS, which provides the cushion. Why do we need an annular fibrosis ring? The nucleus pulposis is like a rubber ball. When you compress it, it can be flattened. The ring keeps it from compressing all the way. Intervertebral Disc Herniated Disc • • • • HERNIATED intervertebral disc happens when stress is put on it the wrong way. When you bend over, the disc compresses anteriorly. If there’s a weakness there, the annulus fibrosis tears, and the nucleus pulposis herniates (pokes out). It can press on the spinal nerves and cause a lot of pain or some paralysis. Improper lifting and pushing with the back can cause this. One treatment is to put a metal rod in to maintain the distance between the discs. Herniated Disc Review: Characterizing Joints by the Types of Tissue Between Bones Fibrous Joints Fibrous connective tissue (eg. suture, ligament, tooth) Cartilaginous Joints Hyaline cartilage (eg. epiphyseal plate, costal cartilage) Fibrocartilage (eg. pubic symphysis) Synovial Joints (Hyaline cartilage plus a capsule) We have covered fibrous and cartilaginous joints. Now we will discuss synovial joints. Synovial Joints Synovial joints also have hyaline cartilage connecting two bones, so they are sometimes classified as a type of cartilaginous joint, but because they are very different in structure and function, they usually have their own classification: Synovial Joints. Cartilaginous joints (the hyaline type) are not moveable. Synovial joints also have hyaline cartilage, but they have a capsule and are moveable. Synovial Joints This is the most familiar type of joint and the most common. It allows a wide range of motion so it is functionally classified as a diarthrotic joint (a diarthrosis) Examples include the elbow, knee, knuckles, the joints between the wrist and ankle bones Synovial joints are the most structurally complex type of joint, (having a joint cavity) and are the most likely to develop uncomfortable and crippling dysfunctions Synovial Joints Characteristics Enclosed chamber, flexible fibrous capsule A cavity filled with fluid, synovial fluid An inner membrane that produces lubricating fluid, synovial membrane Articular cartilages covering ends of bones Reinforcing ligaments to stabilize Innervated and vascular Structures Associated With Synovial Joints Articular Cartilage Capsule Synovial Fluid Menisci (articular discs) Ligaments Bursae Tendons Synovial Joint Structure In synovial joints, the facing surfaces of the two bones are covered with articular cartilage, a layer of hyaline cartilage about 2 mm thick These surfaces are separated by a narrow space, the joint (articular) cavity, containing a slippery lubricant called synovial fluid. This fluid is rich in albumin and hyaluronic acid, which give it a viscous, slippery texture. It nourishes the articular cartilages, removes their wastes, and makes movements at synovial joints almost friction-free Capsule A connective tissue membrane (articular capsule) encloses the cavity and retains the fluid. It has an outer fibrous capsule, which acts like a sleeve; it is continuous with the periosteum of the adjoining bones, and an inner, cellular synovial membrane, which makes the synovial fluid. SYNOVIAL fLUID • Lubricates the joint, allows smooth movement. Its viscosity (thickness) changes with pressure, so bones will never touch, even when you jump up and down. • Nourishes articular cartilage (which is Avascular). Every movement puts pressure on joint, forcing fluid into cartilage. Therefore, you need pressure on joints to feed the cartilage. Synovial Joint Structure In several synovial joints, fibrocartilage grows inward from the joint capsule and forms a pad between the articulating bones. When the pad crosses the entire joint capsule it is called an articular disc, or a MENISCUS. Some joints (such as the knee) use these MENISCI to act as a guide for movement of the bones to prevent unwanted movement such as lateral movement in the knee (Common injury). LIGAMENTS • • The joint capsule alone is not strong enough, so there are reinforcing LIGAMENTS, which provide most of the strength of holding the bones to bones. They are dense regular connective tissue. In the knee joint, the collateral ligaments are the main ligaments that keep the knee from moving medially to laterally. LIGAMENTS Ligaments take a long time to heal if torn because they do not have blood vessels of their own, like bones do. They already have enough fibroblasts and collagen, though, so they eventually can heal. It is better to break a bone than tear a ligament because bones have a better blood supply and heal faster. SPRAINS: are tears in a ligament, and are fairly serious. When a tendon or ligament is sprained, it can take 6 months to heal, and may even need surgery. Even a partial tear, you have to be careful. STRAIN: is a tear in a muscle, and is not as bad because it has good circulation and heals faster. If you can walk on it and it heals in a couple of days, it’s a strain. BURSAE A BURSA is a sack of synovial fluid that is involved in lubrication by serving as a cushion between a muscle/ligament or tendon/bone, etc. It does not need to be attached to any bone; it is like a pillow between the muscle and bone. Bursae cushion muscles, help tendons slide more easily over the joints, and sometimes enhance the mechanical effect of a muscle by modifying the direction in which its tendon pulls. It is lined by a synovial membrane which makes its synovial fluid. This fluid can become excessive during overuse, and pinches nerves in the area. What’s an inflamed bursa called? Bursitis. Crackling sounds in joints are from the release of gas bubbles in the synovial fluid. It does not lead to arthritis. Synovial Joint The knee joint has at least 13 bursae! Bursitis is inflammation of a bursa, usually due to overexertion of a joint. Tendinitis is a form of bursitis in which a tendon sheath is inflamed Bursae and Tendon Sheaths Tendon sheaths are also filled with synovial fluid, and can become inflamed with overuse. Types of Synovial Joints There are six types of synovial joints, characterized by the motion allowed by the shapes of the bones. 1. Plane 2. Hinge 3. Pivot 4. Condyloid 5. Saddle 6. Ball and socket Plane Joints Allows motion in one plane only (transverse or frontal plane). Examples are the carpal and tarsal bones, between the articular processes of the vertebrae, and at the sternoclavicular joint Hinge Joints Allows motion in the sagittal plane only. Examples are the elbow, knee, and IPJ = interphalangeal joints of the fingers and toes Pivot Joints Allows for pivot motion (transverse plane). Examples are the atlantoaxial joint between the first two vertebrae (shake head “no”) and proximal radioulnar joint, where the annular ligament on the ulna encircles the head of the radius Condyloid Joints Their shape is like a knob in a cup, so they are called “condylar”. Condylar joints allow for motion in TWO planes. Therefore, they are “biaxial”. Examples are the Metacarpal-phalangeal joints (MPJ’s) Saddle Joints Examples are at the base of the thumb (between the trapezium and metacarpal I) and sternoclavicular joint between the clavicle and sternum. Saddle joints are biaxial joints (two planes of movement); in primate anatomy, allows for the opposable thumb Ball and Socket Joints This type of joint allows for all three planes of movement, so they are multiaxial. Examples are the shoulder and hip joints. Three Important Synovial Joints Knee Joint Hip Joint Shoulder Joint The Knee Joint Tibiofemoral joint and patellofemoral joint The largest and most complex diarthrosis of the body Hinge joint, but has movements of gliding, rolling and rotation 3 articulations: lateral and medial articulations of femur and tibia; intermediate articulation of patella and femur. Note: Fibula does not articulate with the femur, only with the tibia. Extracapsular ligaments Patellar ligament (patellar tendon) Passes from the apex and margins of the patella distally to the tibial tuberosity Medial collateral ligament Extends from the medial epicondyle of the femur to the medial condyle of the tibia At its midpoint, its fibers are attached to the medial meniscus, Lateral collateral ligament Extends inferiorly from lateral epicondyle of femur to lateral surface of the fibular head Two ligaments lie outside the joint capsule: • tibial (medial) collateral ligament. •fibular (lateral) collateral ligament The two collateral ligaments prevent the knee from rotating when the joint is extended. Intracapsular ligaments of the knee There are two ligaments that lie inside the joint capsule. They are deep within the joint cavity, but they are not inside the fluid-filled synovial cavity. These ligaments cross each other in the form of an X: anterior cruciate ligament (ACL) posterior cruciate ligament (PCL) Intracapsular ligaments Anterior cruciate ligament (ACL) • Weaker of the two cruciates • Slack when knee is flexed, taut when fully extended • Prevents posterior displacement of femur and hyperextension of knee joint Posterior cruciate ligament (PCL) • Taut during flexion, prevents anterior displacement of femur on the tibia • Is the main stabilizing factor when weight-bearing during flexed knee position (ie. Walking downhill.) The ACL and PCL are named according to whether they attach to the anterior or posterior side of the tibia, (not for their attachments to the femur.) When the knee is extended, the ACL is pulled tight and prevents hyperextension. The PCL prevents the femur from sliding off the front of the tibia and prevents the tibia from being displaced backward. Menisci Medial and Lateral Menisci Crescent (C-) shaped plates of fibrocartilage located over the medial and lateral tibial condyles Thicker laterally, thinner inside the joint capsule Act like shock absorbers Thicker laterally, taper to thin unattached edges at interior of the joint. In the knee, two fibrocartilages extend inward from the left and right but do not entirely cross the joint Each is called a meniscus Menisci absorb the shock of the body weight jostling up and down on the knee and prevent the femur from rocking from side to side on the tibia. Anterior View of Flexed Knee Figure 9.14e, f Knee Joint On the final lecture exam (in class at the end of the semester), be able to label the drawing with the names of all of the structures of the knee joint, including the bones, ligaments, cartilage, membranes, capsule, menisci, etc. Know the movements allowed and the movements prevented by the anatomy of the knee. 10 pt Essay Question: Label this (1/2 point each) Essay Answer (a) Essay Answer (b) Quadriceps tendon Lateral Collateral ligament Lateral Meniscus Medial Collateral ligament Medial Meniscus Patellar ligament (patellar tendon) Medial Collateral ligament Lateral Collateral ligament Lateral Meniscus Medial Meniscus Posterior Cruciate ligament Hip Joint Strong, stable ball and socket joint, most moveable of all joints Transverse acetabular ligament (which bridges the acetabular notch) holds head in beyond its equator. Hip Joint The main factor responsible for stabilizing the hip joint is not the ligament at the fovea capitis inside the articular capsule. It is also not stabilized by the deep socket. The ligaments around the head of the femur give it stability. Hip Joint Ligaments Iliofemoral ligament Y shaped; Attaches to ant infer iliac spine and acetabular rim proximally and inferior intertrochanteric line distally Prevents hyperextension of the hip during standing Pubofemoral ligament Runs from the superior ramus of the pubis and passes laterally and to the intertrochanteric line (passing deep to the iliofemoral ligament.) Prevents overabduction of the hip joint Ischiofemoral ligament Runs from ischial part of acetabular rim, to the neck of femur (best seen from posterior view.) Prevents hyperextension of the hip by screwing the femoral head deeper into the acetabulum Ligament of the head of the femur (ligamentum teres) Weak, little importance in strengthening hip joint Runs from the transverse acetabular ligament and attaches to the pit (fovea capitis) of head. Hip Joint Figure 9.13a, b Posterior View of the Hip Joint Figure 9.13c, d Hip Ligaments On the final lecture exam (in class at the end of the semester), be able to label the drawing with the names of the ligaments that attach to the hip. 10 pt Essay Question: Label this Essay Answer: 1 pt each Anterior Posterior The Shoulder Joint Diarthrotic, ball and socket joint: Humeral head in glenoid cavity Shoulder Joint (Glenohumeral Joint) Ligaments: Glenohumeral ligaments : 3 fibrous bands From the anterior glenoid labrum to the anatomical neck of humerus Reinforce the anterior part of the articular capsule (and are inside the capsule, not visible from outside.) Coracohumeral ligament From base of coracoid process to anterior aspect of greater tubercle of humerus Transverse humeral ligament Runs from greater to lesser tubercle of humerus Creates a channel , bridging over the intertubercular groove Site for tendon of long head of biceps brachii Coracoacromial ligament From inferior aspect of acromion to coracoid process Forms a protective “arch” preventing superior displacement of the head Supraspinatus muscle passes under this arch. Shoulder Ligaments Shoulder:Glenohumeral Joint Shoulder Ligaments On the final lecture exam (in class at the end of the semester), be able to label the drawing with the names of the ligaments that attach the clavicle to the scapula and to the head of the humerus. 10 pt Essay Question: Label this Essay Answer: ½ pt each Ligaments of the Ankle Joint Anterior talofibular ligament Posterior talofibular ligament Calcaneofibular ligament Deltoid ligament Ligaments of the Ankle Joint Figure 9.17c Ligaments of the Ankle Joint Figure 9.17d