GENERAL CONSIDERATIONS ON BONES & JOINTS Kaan Ycel M.D., Ph.D. 21. September 2011 Wednesday GENERAL CONSIDERATIONS ON BONES Osteology (Gk, osteon, bone, logos, science) is the branch of medicine concerned with the development and diseases of bone tissue. The human skeleton 270 bones in the newborn 222 bones in children 206 bones in adults Why Humans Have 270 Bones at Birth, but Only 206 Bones Once We are Adults Including the hyoid bone (os hyoideum) and the three auditory ossicles (malleus, incus and stapes) on each side, the head (caput) has 29 bones. The vertebral column (columna vertebralis) has 26 bones. Thorax (chest) is composed of 25 bones. The number of the upper limb/extremity bones (ossa membri superirois) is 64, whereas that of the lower limb/extremity is 62. The skeletal system may be divided into 2 functional parts: The axial skeleton head (cranium or skull) neck (hyoid bone and cervical vertebrae) trunk (ribs, sternum, vertebrae, and sacrum) The appendicular skeleton Limbs including those forming the shoulde & pelvic girdles 126 bones in the appendicular skeleton 80 bones in the axial skeleton Bone is a living tissue capable of changing its structure as the result of the stresses to which it is subjected. Like other connective tissues, bone consists of cells, fibers, and matrix. It is one of the hardest structures of the animal body, because of the calcification of its extracellular matrix. Living bones have some elasticity (results from the organic matter) and great rigidity (results from their lamellous structures and tubes of inorganic calcium phosphate). Its color, in a fresh state, is pinkish-white externally, and deep red within. Cartilage and Bones The skeleton is composed of cartilages and bones. Cartilage is a resilient, semirigid form of connective tissue that forms parts of the skeleton where more flexibility is required for example, where the costal cartilages attach the ribs to the sternum. Cartilage and Bones Also, the articulating surfaces (bearing surfaces) of bones participating in a synovial joint are capped with articular cartilage that provides smooth, low-friction, gliding surfaces for free movement. Cartilage and Bones Blood vessels do not enter cartilage (i.e., it is avascular); consequently, its cells obtain oxygen and nutrients by diffusion. The proportion of bone and cartilage in the skeleton changes as the body grows; the younger a person is, the more cartilage he or she has. The bones of a newborn are soft and flexible because they are mostly composed of cartilage. Bone has a protective function; the skull and vertebral column, for example, protect the brain and spinal cord from injury. periosteum perichondrium A fibrous connective tissue covering surrounds each skeletal element like a sleeve, except where articular cartilage occurs; that surrounding bones is periosteum, whereas that around cartilage is perichondrium. The periosteum and perichondrium nourish the external aspects of the skeletal tissue. They are capable of laying down more cartilage or bone (particularly during fracture healing) and provide the interface for attachment of tendons and ligaments. Classification of Bones Bones are classified according to their shape. 1)Long bones 2)Short bones 3)Flat bones 4)Irregular bones 5)Sesamoid bones Classification of Bones Long bones Long bones are tubular (e.g., the humerus in the arm). Classification of Bones Short bones Short bones are cuboidal and are found only in the tarsus (ankle) and carpus (wrist). Classification of Bones Flat bones Flat bones usually serve protective functions (e.g., the flat bones of the cranium protect the brain). Classification of Bones Irregular bones Irregular bones have various shapes other than long, short, or flat (e.g., bones of the face). Classification of Bones Sesamoid bones Sesamoid bones (e.g., the patella or knee cap) develop in certain tendons and are found where tendons cross the ends of long bones in the limbs; they protect the tendons from excessive wear and often change the angle of the tendons as they pass to their attachments. There are two types of bones according to histological features: compact bone and spongy (trabecular) bone. They are distinguished by the relative amount of solid matter and by the number and size of the spaces they contain. All bones have a superficial thin layer of compact bone around a central mass of spongy bone, except where the latter is replaced by a medullary (marrow) cavity. Spongy bone is found at the expanded heads of long bones and fills most irregular bones. Compact bone forms the outer shell of all bones and also the shafts in long bones. Spongy or cancellous bone consists of a lattice of thin threads of bone called trabeculae and is less dense than compact bone. The orientation of the trabeculae is modelled by the mechanical stress to which the bone is exposed (Wolff's law). The architecture and proportion of compact and spongy bone vary according to function. Compact bone provides strength for weight bearing. In long bones designed for rigidity and attachment of muscles and ligaments, the amount of compact bone is greatest near the middle of the shaft where the bones are liable to buckle. Bone Markings and Formations Bone markings appear wherever tendons, ligaments, and fascias are attached or where arteries lie adjacent to or enter bones. Other formations occur in relation to the passage of a tendon (often to direct the tendon or improve its leverage) or to control the type of movement occurring at a joint. Bone Markings and Formations Surfaces of the bones are not smooth. Bones display elevations, depressions and holes. The surface features on the bones are given names to distinguish and define them. Some of the various markings and features of bones Linear elevation line, crest Some of the various markings and features of bones Round elevation tubercule (small eminence), protuberance (swelling) External occipital CT scan Some of the various markings and features of bones Sharp elevation spine, process Some of the various markings and features of bones Rounded articular area head, condyle Vasculature and Innervation of Bones Bones are richly supplied with blood vessels. Most apparent are the nutrient arteries (one or more per bone) that arise as independent branches of adjacent arteries outside the periosteum. Vasculature of Bones Veins accompany arteries through the nutrient foramina. Many large veins also leave through foramina near the articular ends of the bones. Bones containing red bone marrow have numerous large veins. Lymphatic vessels are also abundant in the periosteum. Innervation of Bones Nerves accompany blood vessels supplying bones. The periosteum is richly supplied with sensory nervesperiosteal nervesthat carry pain fibers. The periosteum is especially sensitive to tearing or tension, which explains the acute pain from bone fractures. Innervation of Bones Bone itself is relatively sparsely supplied with sensory endings. Within bones, vasomotor nerves cause constriction or dilation of blood vessels, regulating blood flow through the bone marrow. Accessory Bones Accessory (supernumerary) bones develop when additional ossification centers appear and form extra bones. Many bones develop from several centers of ossification, and the separate parts normally fuse. Sometimes one of these centers fails to fuse with the main bone, giving the appearance of an extra bone. Careful study shows that the apparent extra bone is a missing part of the main bone. Heterotopic Bones Bones sometimes form in soft tissues where they are not normally present (e.g., in scars). Horse riders often develop heterotopic bones in their thighs (rider's bones), probably because of chronic muscle strain resulting in small hemorrhagic (bloody) areas that undergo calcification and eventual ossification. Changes in Bones Atrophy (decrease in size) might develop in unused bones, such as in a paralyzed limb. Bone may be absorbed, which occurs in the mandible when teeth are extracted. Bones hypertrophy (enlarge) when they support increased weight for a long period. Bone Fractures Trauma to a bone may break it. For the fracture to heal properly, the broken ends must be brought together, approximating their normal position. This is called reduction of a fracture Fractures are more common in children than in adults because of the combination of their slender, growing bones and carefree activities. Osteoporosis During the aging process, the organic and inorganic components of bone both decrease, often resulting in osteoporosis, a reduction in the quantity of bone, or atrophy of skeletal tissue. Hence, the bones become brittle, lose their elasticity, and fracture easily. Bone scanning is an imaging method used to assess normal and diminished bone mass. GENERAL CONSIDERATIONS ON JOINTS Joints (articulations) are unions or junctions between two or more bones or rigid parts of the skeleton. Joints exhibit a variety of forms and functions. It is the fact that, whether or not movement occurs between them, it is still called a joint. Some joints have no movement, others allow only slight movement, and some are freely movable. Classification of Joints Joints are classified according to the tissues that lie between the bones: 1)Fibrous joints 2)Cartilaginous joints 3)Synovial joints Fibrous joints The bones are united by fibrous tissue. The amount of movement occurring at a fibrous joint depends in most cases on the length of the fibers uniting the articulating bones. The sutures of the cranium are examples of fibrous joints. These bones are close together, either interlocking along a wavy line or overlapping. syndesmosis type of fibrous joint A syndesmosis type of fibrous joint unites the bones with a sheet of fibrous tissue, either a ligament or a fibrous membrane. Consequently, this type of joint is partially movable. The interosseous membrane in the forearm is a sheet of fibrous tissue that joins the radius and ulna in a syndesmosis. dentoalveolar syndesmosis (gomphosis or socket) A dentoalveolar syndesmosis (gomphosis or socket) is a fibrous joint in which a peglike process fits into a socket articulation between the root of the tooth and the alveolar process of the jaw. Mobility of this joint (a loose tooth) indicates a pathological state affecting the supporting tissues of the tooth. Cartilaginous joints The bones are united by hyaline cartilage or fibrocartilage. primary cartilaginous jointssynchondroses In primary cartilaginous joints, or synchondroses, the bones are united by hyaline cartilage, which permits slight bending during early life. Secondary cartilaginous jointssymphyses, Secondary cartilaginous joints, or symphyses, are strong, slightly movable joints united by fibrocartilage. The fibrocartilaginous intervertebral discs between the vertebrae consist of binding connective tissue that joins the vertebrae together. Synovial joints The bones are united by a joint (articular) capsule (composed of an outer fibrous layer lined by a serous synovial membrane) spanning and enclosing an articular cavity. Synovial joints are the most common type of joints and provide free movement between the bones they join. They are joints of locomotion, typical of nearly all limb joints. This type of joints has three common features: Joint cavity: The joint cavity of a synovial joint, like the knee, is a potential space that contains a small amount of lubricating synovial fluid, secreted by the synovial membrane. Articular cartilage: The articular surfaces are covered by hyaline cartilage Articular capsule : Articular capsule : This structure surrounds the joint and formed of two layers. Inside the capsule, articular cartilage covers the articulating surfaces of the bones; all other internal surfaces are covered by synovial membrane. 1.Fibrous capsule 2.Synovial membrane Some synovial joints have other distinguishing features, such as a fibrocartilaginous articular disc or meniscus, which are present when the articulating surfaces of the bones are incongruous. Ligaments A ligament is a cord or band of connective tissue uniting two structures. Articular capsules are usually strengthened by articular ligaments. These are from dense connective tissue and they connect the articulating bones to each other. Ligaments Articular ligaments limit the undesired and/or excessive movements of the joints. intrinsic extrinsic Articular ligaments are classified as intrinsic and extrinsic ligaments. Articular disc: Articular disc: Help to hold the bones together. Labrum: Labrum: A fibrocartilaginous ring which deepens the articular surface for one of the bones. Fatt Pads: Fatt Pads: A pad of fat lying within a joint, covered with synovial membrane and thought to assist in the spreading of synovial lubricant, e.g. infrapatellar fat pad of stifle joint. Bursa Bursae are flattened sacs that contain synovial fluid to reduce friction. Its walls are separated by a film of viscous fluid. Bursae are found wherever tendons rub against bones, ligaments, or other tendons. They are commonly found close to joints where the skin rubs against underlying bony structures, for example, the prepatellar bursa. Tendon Sheath A layer of the synovial membrane around a tendon. Permits the tendon to move. Types of synovial joints The six major types of synovial joints are classified according to the shape of the articulating surfaces and/or the type of movement they permit: 1.Plane joints 2.Hinge joints (ginglymus, trochlear joints) 3.Saddle joints 4.Condyloid (ellipsoid type) 5.Ball and socket joints 6. Pivot joints Plane joints (gliding joints) Plane joints (gliding joints) permit gliding or sliding movements in the plane of the articular surfaces. The articular surfaces of the plane joints are almost flat. uniaxial Most plane joints move in only one axis, hence they are called uniaxial joints. Examples for Plane joints Acromioclavicular joint between the acromion of the scapula and the clavicle Hinge joints (ginglymus, trochlear joints) Also uniaxial flexion and extension only, around the transverse axis. knee Bones are joined with strong collateral ligaments. e.g. elbow and knee joints. Cylindrical projections (condyles) fit into concave shapes. Saddle joints abduction adduction & flexion and extension biaxial joints that allow movement in two planes sagittal and frontal. The articular surfaces resemble a saddle shape and are concave and convex respectively. Examples for Saddle joints Carpometacarpal joint at the base of the 1st digit (thumb Carpometacarpal joint at the base of the 1st digit (thumb) Condyloid (ellipsoid type) joints Flexion and extension as well as abduction and adduction Biaxial Examples for Condyloid (ellipsoid type) joints Metacarpophalangeal joints (knuckle joints) Radiocarpal joint (wrist) Ball and socket joints (enarthrosis, spheroidal joint) Movement in multiple axes and planes: flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction multi-axial joints The spheroidal surface of a bone articulates with the socket shaped articular surface of another bone. Examples for Ball and socket joints Hip joint Shoulder joint Shoulder joint Pivot joints Rotation around a central axis uniaxial The rounded part of a bone rotates in a sleeve or ring like osteofibrous structure. The rounded end of one bone fits into the sleeve of bone or ligaments. Examples for Pivot joints Median atlantoaxial joint Atlas (C1 vertebra) rotates around a finger-like process, the dens of the axis (C2 vertebra), during rotation of the head. Proximal and distal radioulnar joints Stability of Joints depends on four main factors: 1)Negative pressure within the joint cavity 2)Shape, size, and arrangement of the articular surfaces 3)Ligaments 4)Tone of the muscles around the joint Articular Surfaces The ball-and-socket arrangement of the hip joint and the mortise arrangement of the ankle joint are good examples of how bone shape plays an important role in joint stability. Other examples of joints, however, in which the shape of the bones contributes little or nothing to the stability, include the acromioclavicular joint, the calcaneocuboid joint, and the knee joint. Ligaments then fibrous ligaments stretch Fibrous ligaments prevent excessive movement in a joint, but if the stress is continued for an excessively long period, then fibrous ligaments stretch. Should the tone of the muscles that normally support the arches become impaired by fatigue, then the ligaments will stretch and the arches will collapse, producing flat feet. Elastic ligamentsreturn to their original length after stretching Elastic ligaments, conversely, return to their original length after stretching. Muscle Tone In most joints, muscle tone is the major factor controlling stability. For example, the muscle tone of the short muscles around the shoulder joint keeps the hemispherical head of the humerus in the shallow glenoid cavity of the scapula. The knee joint is very unstable without the tonic activity of the quadriceps femoris muscle. Without the action of these muscles, very little force would be required to dislocate this joint. Joint vasculature and innvervation Joints receive blood from articular arteries that arise from the vessels around the joint. The arteries often anastomose (communicate) to form networks (periarticular arterial anastomoses) to ensure a blood supply to and across the joint in the various positions assumed by the joint. Articular veins are communicating veins that accompany arteries (L. venae comitantes) and, like the arteries, are located in the joint capsule, mostly in the synovial membrane. Joint innvervation Joints have a rich nerve supply provided by articular nerves with sensory nerve endings in the joint capsule. The capsule and ligaments receive an abundant sensory nerve supply. Hilton's law: Hilton's law: A sensory nerve supplying a joint also supplies the muscles moving the joint and the skin overlying the insertions of these muscles. Examination of Joints When examining a patient, the clinician should assess the normal range of movement of all joints. When the bones of a joint are no longer in their normal anatomic relationship with one another, then the joint is said to be dislocated. Examination of the shoulder joint Knee examination Dislocation of Joints Some joints are particularly susceptible to dislocation because of: a) lack of support by ligaments b) the poor shape of the articular surfaces, c) the absence of adequate muscular support. The shoulder joint, temporomandibular joint, & acromioclavicular joints are good examples. Dislocation of the acromioclavicular joint Anterior knee dislocation Dislocation of the hip is usually congenital, being caused by inadequate development of the socket that normally holds the head of the femur firmly in position. Damage to Ligaments Joint ligaments are very prone to excessive stretching and even tearing and rupture. If possible, the apposing damaged surfaces of the ligament are brought together by positioning and immobilizing the joint. In severe injuries, surgical approximation of the cut ends may be required. Trauma and Infection of Bursae and Tendon Sheaths Bursae and synovial sheaths are commonly the site of traumatic or infectious disease. For example, the extensor tendon sheaths of the hand may become inflamed after excessive or unaccustomed use. An inflammation of the prepatellar bursa may occur as the result of trauma from repeated kneeling on a hard surface. Osteoarthritis Synovial joints are well designed to withstand wear, but heavy use over several years can cause degenerative changes. Some destruction is inevitable during such activities as jogging, which wears away the articular cartilages and sometimes erodes the underlying articulating surfaces of the bones. Osteoarthritis The normal aging of articular cartilage begins early in adult life and progresses slowly thereafter, occurring on the ends of the articulating bones, particularly those of the hip, knee, vertebral column, and hands. osteoarthritis Degenerative joint disease or osteoarthritis is often accompanied by stiffness, discomfort, and pain. Osteoarthritis is common in older people Osteoarthritis is common in older people and usually affects joints that support the weight of their bodies (e.g., the hips and knees). Arthroscopy The cavity of a synovial joint can be examined by inserting a cannula and an arthroscope (a small telescope) into it. This surgical procedure enables orthopedic surgeons to examine joints for abnormalities, such as torn menisci (partial articular discs of the knee joint). Some surgical procedures can also be performed during arthroscopy (e.g., by inserting instruments through small puncture incisions).