Chapter #7 Joints of the Skeletal System

I. Introduction I. Introduction A. A joint is formed wherever two or more bones meet. B. Joints are the functional junctions between bones. II. Classification of Joints A.Joints can be classified according to the type of tissue that binds them together. 1) Fibrous Joints a) Fibrous joints are fastened tightly together by a layer of fibrous CT. b) Little or no movement occurs at a fibrous joint.

c) There are three types of fibrous joints. A syndesmosis is characterized by bones bound by relatively long fibers of connective tissue. Ex: Joint between tibia and fibulaA syndesmosis is characterized by bones bound by relatively long fibers of connective tissue. Ex: Joint between tibia and fibula A suture occurs where flat bones are united by a thin layer of connective tissue and become interlocked by a set of bony processes. Ex: skull bonesA suture occurs where flat bones are united by a thin layer of connective tissue and become interlocked by a set of bony processes. Ex: skull bones A gomphosis is formed by the union of a cone-shaped bony process in a bony socket. Ex: Joints between the teeth and the sockets in the mandibleA gomphosis is formed by the union of a cone-shaped bony process in a bony socket. Ex: Joints between the teeth and the sockets in the mandible

2) Cartilaginous Joints a) Bones of cartilaginous joints are held together by a layer of cartilage. b) There are two types of cartilaginous joints. A synchondrosis is characterized by bones united by hyaline cartilage that disappears as a result of growth. Ex: Joint between the sternum & first rib, and within a growth plate.A synchondrosis is characterized by bones united by hyaline cartilage that disappears as a result of growth. Ex: Joint between the sternum & first rib, and within a growth plate. A symphysis is a joint whose articular surfaces are covered by hyaline cartilage and attached to a pad of fibrocartilage. Ex: Pubic Symphysis in pelvic girdle and the intervertebral disks.A symphysis is a joint whose articular surfaces are covered by hyaline cartilage and attached to a pad of fibrocartilage. Ex: Pubic Symphysis in pelvic girdle and the intervertebral disks.

3) Synovial Joints a) Synovial joints have a more complex structure than other types of joints. b) These joints include articular cartilage, a joint capsule, and a synovial membrane.

. Joints can also be classified according to the amount of movement possible: 1)Synarthroses (synarthrotic joints): Immovable joints 2)Amphiarthroses (amphiarthrotic joints): Slightly movable joints 3)Diarthroses (diarthrotic joints): Freely movable joints

III. General Structure of a Synovial Joint A.The articular ends of bones are covered by a layer of cartilage called articular cartilage. B.The bones are held together by a joint capsule that is strengthened by ligaments. C.The inner layer of the joint capsule is lined by a synovial membrane that secretes synovial fluid. The synovial fluid moistens and lubricates the articular surfaces. D.Some synovial joints are divided into compartments by menisci.

E. Some synovial joints have fluid-filled bursae associated with them. 1)Bursae are usually located between the skin and underlying bony prominences. 2)Bursae act as cushions and aid the movement of tendons over bony parts. 3)Bursae are named according to their locations.

Section IV: Types of Synovial Joints

A. Ball-and-socket joints 1)In a ball-and-socket joint, the globular head of a bone fits into the cup-shaped cavity of another. 2)These joints permit a wide variety of movements. 3)The hip and shoulder are ball-and-socket joints. B. Condyloid joints 1)A condyloid joint consists of an ovoid condyle of one bone fitting into an elliptical cavity of another. 2)This joint permits a variety of movements. 3)The joints between the metacarpals and phalanges are condyloid.

C. Gliding joints 1)Articular surfaces of gliding joints are nearly flat. 2)These joints permit the articular surfaces to slide back and forth. 3)Most of the joints of the wrist and ankle are gliding joints. D. Hinge joints 1)In a hinge joint, the convex surface of one bone fits into the concave surface of another. 2)This joint permits movement in one plane only. 3)The elbow and the joints of the phalanges are the hinge type.

E. Pivot joints 1)In a pivot joint, a cylindrical surface of one bone rotates within a ring of bone or fibrous tissue. 2)This joint permits rotational movement. 3)The articulation between the proximal ends of the radius and the ulna is a pivot joint, so is the joint between the atlas & axis. F. Saddle joints 1)A saddle joint is formed between bones that have complementary surfaces with both concave and convex regions. 2)This joint permits a variety of movements. 3)The joint between the carpal and metacarpal of the thumb is a saddle joint.

Section V. Types of Joint Movements

V. Types of Joint Movements A.Muscles acting at freely movable joints produce movements in different directions and in different planes. B.Joint movements include: 1) Flexion: Bending parts at a joint so that the angle between them is decreased and the parts come closer together. Ex: Bending the knee. 2) Extension: Straightening parts at a joint so that the angle between them in increased and the parts move further apart. Ex: Straightening the knee.

3)Hyperextension: Excessive extension of the parts at a joint, beyond the anatomical position. Ex: Bending the head back beyond the upright position. 4)Dorsiflexion: Flexing the foot at the ankle. 5)Plantar Flexion: Extending the foot at the ankle. Ex: Pointing the toes. 6)Abduction: Moving a part away from the midline. Ex: Lifting the arm horizontally to form a right angle with the side of the body. 7)Adduction: Moving a part toward the midline. Ex: Returning the arm from the horizontal position to the side of the body.

8)Rotation: Moving a part around an axis. Ex: Twisting the head side to side. 9)Circumduction: Moving a part so that its end follows a circular path. Ex: Moving the finger in a circular motion without moving the hand. 10) Supination: Turning the hand so the palm is upward or turning the foot so that the medial margin is raised. (Carrying a bowl of soup = supination) 11) Pronation: Turning the hand so the palm is downward or turning the foot so that the medial margin is lowered.

12) Eversion: Turning the foot so the sole is outward. 13) Inversion: Turning the foot so the sole is inward. 14) Elevation: Raising a part. Ex: Shrugging the shoulders. 15) Depression: Lowering a part. Ex: Drooping the shoulders. 16) Protraction: Moving a part forward. Ex: Thrusting the chin forward. 17) Retraction: Moving a part backward. Ex: Pulling the chin backward.

Figure 7.8ef

Figure 7.8h

Section VI. Examples of Synovial Joints

D. Knee Joint 1) The knee joint includes two condyloid joints between the femur and the tibia, and a gliding joint between the femur and the patella. 2) The joint capsule is relatively thin, but is strengthened by ligaments and tendons 3) Several ligaments, some of which are within the joint capsule, help keep the articular surfaces together.

a)Patellar Ligament: Connects the patella to the tibia. The patellar ligament is sometimes called the patellar tendon because it connects the muscles of the thigh to the tibia. b) Oblique Popliteal Ligament: Connects the lateral condyle of the femur to the tibia. c) Arcuate Popliteal Ligament: Connects the lateral condyle of the femur to the head of the fibula.

d) Tibial Collateral Ligament (or medial collateral ligament/MCL) Connects the medial condyle of the femur to the medial condyle of the tibia. e) Fibular Collateral Ligament (or lateral collateral ligament/LCL) Connects the lateral condyle of the femur to the head of the fibula. f)Anterior Cruciate Ligament (ACL) Connects the anterior part of the tibia to the posterior part of the femur. g) Posterior Cruciate Ligament (PCL) Connects the posterior part of the tibia to the anterior part of the femur.

4) Two menisci (medial & lateral) separate the articulating surfaces of the femur and the tibia, and help compensate for differences in the shapes of these surfaces. 5) Several bursae are associated with the knee joint: a) Suprapatellar Bursa: Found superior to the patella b) Prepatellar Bursa: Found anterior to the patella, between it and the skin c) Infrapatellar Bursa: Found inferior to the patella 6) The knee joint permits flexion and extension; when the leg is flexed at the knee, some rotation is possible.

Aging and Joints I. With aging a person usually has a) Decrease production of synovial fluid b) Articular cartilage becomes thinner c)Ligaments become shorter and less flexible.

Effects on the joints are influenced by 1. genetic factors 2. wear and tear Some changes can begin as early as age 20, but most begin much later. By age 80, almost everyone develops some type of degeneration in the knees, elbow, hips, and shoulders. Stretching and aerobic exercises can help to maintain full range of motion and minimize the effects of aging by maintaining the function of ligaments, tendons, muscles, synovial fluid, and articular cartilage