Chapter 7 The Skeletal System Functions of Bone

Chapter 7 The Skeletal System

Functions of Bone • Support and Protection • It provides a framework for the body and gives it shape. • It supports and protects organs from injury. • Leverage • It provides a place for muscles, tendons, ligaments and tendons of the body to attach. • It helps make movement possible. • Storage • It stores minerals (Calcium) • Blood Cell Formation • It provides a place for hemotpoeisis

Bone Structure • Two main types of bone: • Cancellous Bone • Light and spongy inner layer of bone. • Consists of tiny spicules with bone marrow between. • Provides strength but prevents damage. • Compact Bone • Heavy and dense layer of outer bone • Found in shafts of long bones • Composed of haversian systems around a haversian canal

Bone Structure continued • Osteocytes- bone cells. • Periosteum- covering of bone • Inner layer contains osteoblasts. • Endosteum- membrane that lines the hollow interior surface of bones.

Haversian Systems • Concentric layers of ossified bone matrix arranged around a central Haversian canal • Layers of ossified bone matrix

Bone Cells • Osteoblasts • Cells that form bone. • Osteocytes • Once osteoblasts are trapped inside matrix of osseous material. • Can revert back to osteoblasts (remember this from last chapter? ) • Osteoclasts • Eat bone away. • Are the remodelers of bone • Withdraw calcium when needed from bone • Why is this important?

Blood Supply to Bone • Tiny vessels penetrate the periosteum. • Volkmann’s canals- tiny channels in the bone matrix that vessels pass through. • Are at right angles to Haversian canals that run lengthwise in the bone. • Nutrient Foramina- Where large vessels enter the bone. • Carry blood into and out of bone marrow. • Can be mistaken for fracture on radiographs.

Bone Formation • Bone is formed in 2 ways: • Endochondral Bone formation • Intramembranous Bone formation • Bone formation and growth is stimulated by Growth Hormone (GH) from the anterior pituitary (adenohypophysis) gland in the brain.

Endochondral Bone Formation • Endochondral Bone formation • Cartilage bone formation • Cartilage first, then bone • How most bones develop • Start as cartilage rods in long bones in diaphysis (shaft). • Contains primary growth center • Cartilage is removed gradually as bone is created and growth center expands. • Secondary growth center • Develop in epiphysis (ends) of bones

Growth plates • Located between diaphysis and epiphysis. • May be called epiphyseal growth plates. • Sites of creation of new bone that allows bone to lengthen as animal grows. • Cartilage is created on epiphyseal side while bone is created on diaphyseal side. • When bone reaches full length, all cartilage is replaced by bone and plates “Close”. • Remodeling may take place but bone will not get any longer. • Young animals may have epiphyseal fractures because this area is weaker than rest of bone.

Panosteitis • “Growing Pains” in dogs. • Inflammation of various bone layers • Seen prevalently in young giant breed dogs. • Basically, body can not keep up as bones are growing very quickly. • Can be confirmed through Radiographs. • May cause “Shifting Leg Lameness” • Treated with rest and anti-inflammatories • Usually occurs in the center of the bone.

Intramembranous Bone Formation • Occurs only in certain skull bones • Bone forms in the fibrous membranes that cover the brain in fetus. • Bone forms directly from osteoblasts with no cartilage intermediary.

Bone Shapes • • Long Bones Short Bones Flat Bones Irregular Bones

Long Bones • Longer than they are wide. • Has a proximal and distal epiphysis consisting of cancellous bone. • Main part of bone is diaphysis which composed of compact bone. • Found in digits and limbs.

Short Bones • Shaped like cubes. • Have core of cancellous bone covered by compact bone. • Carpal and tarsal bones.

Flat Bones • Thin and flat bones • Consists of two layers of compact bone separated by cancellous bone. • Bones in skull, pelvis, and scapula are examples.

Irregular Bones • Miscellaneous bones that do not fit into another category. • May have characteristics of more than one category. • Include vertebrae and sesamoid bones. • Patella is largest sesamoid bone in body.

Bone Marrow • Fills the spaces within bones • Has two types: • Red bone marrow • Hematopoietic tissue forms new blood cells. • Majority of bone marrow in young animals but less of older animals • Yellow bone marrow • Consists primarily of adipose connective tissue. • Common type of marrow in adult animals • Does not produce blood cells but can revert to red marrow if needed.

Common Bone Features • Articular Surfaces • Joint surfaces where bones come in contact with each other to form joints. • Consists of: • Condyles • Head • Facet • Covered by articular cartilage • Composed of what type of cartilage?

Condyle • Large, round articular surface. • Major condyle is located on end of humerus and femur. • Also located in skull.

Head • Somewhat spherical articular surface on the proximal end of a long bone. • Found on humerus, femur and rib. • Head is usually joined with rest of bone by a neck.

Femoral Head Osteotomy (FHO) • Head of femur is removed in cases of trauma or severe arthritis. • A “false joint” forms which gives more comfort to the patient.

Facet • A flat articular surface. • Found in carpal and tarsal bones as well as in vertebrae, radius and ulna.

Processes • All projections of a bone. • Heads and condyles are considered to be processes. • Tendons may attach to processes

Holes and Depressed Areas • Foramen: A hole in bone. • Usually allow the passage of nerve or blood vessel. • May exist simply to lighten structure (pelvis-obturator foramen) • Fossa: A depressed of sunken area on the surface of a bone. • Usually occupied by muscles or tendons.

Types of Skeletons • Bones of head and trunk are Axial Skeleton • Bones of limbs and appendages are Appendicular Skeleton. • Some animals may have Visceral Skeleton - bones formed in the viscera or soft organs.

Axial Skeleton bones of head & trunk • • • Skull Hyoid bone Spinal column Ribs Sternum

Skull • Usually consists of 37 or 38 separate bones • Most skull bones joined by sutures (fibrous joint) • Mandible is connected to skull by a synovial joint (TMJ)

Skull External bones: Frontal bones (2) Occipital bones (1) Parietal bones (2) Temporal bones (2) Incisive (2 ) Nasal (2) Maxillary (2) Zygomatic (2) Mandible (2) Palatine (2) Turbinates (2)

Skull Bones Continued • Categorized by: • Bones of Cranium • Bones of the ear • Bones of the face

Bones of the Cranium • Cranium-portion of skull that surrounds the brain. • External Bones of Cranium: • Frontal Bones (2) • Interparietal Bones (2) • Occipital Bone (1) • Parietal Bones (2) • Temporal Bones (2) • Internal Bones of Cranium: • Ethmoid Bone (1) • Sphenoid Bone (1)

External Bones of Cranium

Occipital Bone • Forms caudoventral portion or base of skull, most caudal skull bone. • Important because: • Where spinal cord exits skull • Skull bone that articulates with first cervical (neck) vertebrae. • Foramen Magnum is in center of occipital bone. • Occipital Condyles are on either side of foramen magnum

Interparietal Bones • Small bones located on dorsal midline between occipital and parietal bones • Clearly visible in young animals, may fuse together in older animals.

Parietal Bones • Form the lateral walls of the cranium • Well developed in dogs, cats and humans, but relatively small in horses and cattle.

Temporal Bones • • Located ventral to the Parietal bones Form walls of the cranium Contain middle and inner ear structures Form Temporamandibular Joints (TMJ’s) with the mandible (Lower jaw)

Frontal Bones • Form forehead region of skull. • Located rostral to parietal bone. • Frontal sinus is contained within frontal bone. • Horns are extension of frontal bone.

Internal Bones of the Cranium • Sphenoid Bone • Forms ventral portion of the cranium and contains the pituitary fossa. • This contains the pituitary gland. • Contains the sphenoidal sinus in most animals. • Ethmoid Bone • Located rostral to sphenoid bone. • Contains cribriform plate which has branches of olfactory nerve passing through. • In horses and humans also have ethmoidal sinus in the ethmoid bone.

Bones of the Ear • Hidden in the middle ear from the outside in: • The Malleus- hammer • The incus- anvil • The stapes- stirrup • Function is to transmit vibrations from the tympanic membrane (eardrum) to cochlea where vibrations are changed into nerve impulses.

External Bones of the Face • Incisive Bones: • Also called premaxillary bones • In common domestic animals house upper incisor teeth. (Ruminants have a dental pad instead) • Nasal Bones: • Form the bridge of the nose. • Size depends on length of nose of animal.

External Bones of the Face continued… • Maxillary Bones: • Make up upper jaw. • House upper canine teeth, premolars and molars. • Houses maxillary sinuses. • Forms hard palate with palatine bones. • Lacrimal Bones: • Form medial portion of the orbit of the eye. • Contain lacrimal sac which is part of tear system.

External Bones of the Face continued… • Zygomatic Bones: • Also known as the malar bones. • Join process from temporal bones to form zygomatic arch. • Mandible: • The lower jaw. • Houses all lower teeth and is the only moveable part of the skull. • Forms TMJ with the temporal bone on each side. • Unite at mandibular symphysis at rostral end. • Composed of shaft (horizontal portion) and ramus (vertical portion).

Internal Bones of the Face • Palatine Bones: • Make up part of hard palate • Pterygoid Bones: • Support part of the lateral walls of the pharynx (throat). • Vomer Bone: • Forms part of nasal septum (wall between left and right nasal passages). • Turbinates: • Also called nasal conchae. • Thin and scroll-like that fill most of nasal cavity space.

Hyoid Bone • Also called hyoid apparatus. • Supports base of tongue, the pharynx, and the larynx and assists in swallowing. • Composed of several parts that are united by cartilage.

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Spinal Column • • • Also called the vertebral column Made up of vertebrae that extends from skull to tip of tail. Vertebrae are divided into 5 portions: • Cervical (neck) • Abbreviated C • Contain 7 vertebrae in dogs and cats • Thoracic (chest) • Abbreviated T • Contain 13 vertebrae in dogs and cats • Lumbar (abdomen) • Abbreviated L. • Contain 7 vertebrae in dogs and cats. • Sacral (pelvis) • Abbreviated S. • Contain 3 vertebrae in dogs and cats. • Coccygeal (tail) • Abbreviated Cy. • Number is variable. • Refer to vertebrae by letter designation and number designation.

Vertebrae Characteristics • Consists of: • Body • The main, ventral portion of the bone. • Separated from other vertebrae by intervertebral disks of cartilage. • What type of cartilage makes this up? • Arch (neural arch) • Arch helps to make up vertebral foramen which allows passage of the spinal cord. • Processes • Transverse Processes • Laterally projecting • Site of muscle attachement. • Articular Processes • Found on cranial and caudal ends of vertebrae, help to join adjacent vertebrae. • Spinous Processes • Single and projects dorsally

Intervetebral Disk Disease (IVDD) • When disks “slip” • More predominant in long-backed breeds (dachsunds, Bassets). • Can confirm with radiographs. • Usually once it occurs, animal is predisposed. • Curative procedure is surgery to fuse spinal column together. • Animals may become paralyzed (dragging rear legs).

Cervical Vertebrae • Atlas is C 1 • Holds up head. • Has “wings of the atlas” • Has no vertebral body, just is a ring which spinal cord passes through. • Axis is C 2 • Has large spinous processes.

Thoracic Vertebrae • Have tall spinous processes. • Have articular facets which communicate with the ribs.

Lumbar Vertebrae • Dorsal to abdominal region. • Most massive-looking bones in spinal column.

Sacral Vertebrae • Fuse together to form one single, solid structure. • Called the sacrum. • Joins pelvis via sacroiliac joint.

Coccygeal Vertebrae • Bones of the tail. • Appearance changes as bones progress down the tail. • In humans fuse into coccyx.

Ribs • Flat bones that form the lateral walls of the thorax. • Usually rib number is equal to the number of thoracic vertebrae. • Have more of a moveable joints which is allows lungs to expand. • Term for rib is costal. • Sternal ribs attach to sternum • Asternal ribs make up caudal part of thorax. • Unattached ribs are called floating ribs.

Sternum • • Breastbone Made up of sternebrae. Most cranial sternebrae is manubrium Most caudal sternebrae is called xiphoid process. • May be broken during CPR.

Appendicular Skeleton • Made up of bones of limbs. • Thoracic limbs (front leg) • Scapula • Humerus • Radius • Ulna • Carpal bones • Metacarpal bones • Phalanges • Pelvic Limbs (back leg) • Pelvis • Ilium • Ischium • pubis • Femur • Tibia • Fibula • Tarsal bones • Metatarsal bones • Phalanges

Appendicular Skeleton (limb bones) Thoracic Limb • • • Scapula Humerus Radius Ulna Carpal bones (carpus) Metacarpal bones • Phalanges

Scapula • Most proximal bone of the thoracic limb. • Flat and triangular. • Has prominent ridge on lateral surface referred to as “spine of the scapula” • Glenoid cavity at distal end forms portion of ball and socket shoulder joint.

Humerus • Long bone of upper arm (brachium) • Has head at proximal end with tubercles (processes) where muscles attach. • Condyle at distal end is composed of trochlea, capitulum, medial and lateral epicondyles, and olecranon fossa. • Is not “funny bone” (actually is a nerve not a bone).

Ulna • One of two bones that form antebrachium (forearm). • Forms major portion of elbow joint with distal end of the humerus. • Has large olecranon process at proximal end which forms the point of the elbow. • Trochlear notch makes elbow tight. • End of trochlear notch forms anconeal process. • Where triceps brachii muscle attaches. • Coronoid process articulates with the radius.

Radius • Main weight bearing bone of the antebrachium. • Articulates with humerus and ulna. • Styloid process articulates with carpus.

Carpal Bones • Carpus has two rows of bones. • Is the “wrist” of the animals • Proximal row bones have names (radial carpal bone, ulnar carpal bone, accessory carpal bone) • Distal row bones numbered medial to lateral (1 st carpal, 2 nd carpal, etc)

Metacarpal Bones • Extend distally from distal row of carpal bones to proximal phalanges of the digits. • Numbered from medial to lateral (dewclaw being number 1 in dogs and cats). • Horses have one large metacarpal bone (cannon bone) and two non-weight bearing splint bones. • Cattle have fused metacarpal bones with sesamoid bones (proximal and distal).

Phalanges • Each digit is made up of two or three phalanges (single bones are phalanx) • In horses phalanges are the long and short pastern bone and coffin bone. • Also have 2 proximal and 1 distal (navicular bone) sesamoid bones. • Dogs and cats have a ungual process that surrounds the claw.

Appendicular Skeleton- Hind Limb • Connected to the axial skeleton at sacroiliac joint Pelvic Limb: • Pelvis • • • Ilium Pubis Ischium Femur Tibia Fibula Tarsal bones (tarsus) Metatarsal bones Phalanges

Pelvis • May be referred to as the os coxae • Develops as three separate bones on each side that fuse into a solid structure. • Joined at pelvic symphysis. • Bones are: • Ilium • Cranial most bone of pelvis • “Wings of the ilium” or hips. • Ischium • Most caudal pelvic bone • Tailbone is ischial tuberosity. • Pubis • Smallest of the pelvic bones

Pelvic landmarks • Acetabulum- portion of hip bone that forms ball and socket joint with femur. • We look at this area in cases of hip dysplasia. • Obturator foramen- large holes in pelvis that help to lighten weight of pelvis. • We look at this as landmark if radiograph is straight or not.

Femur • Long Bone of thigh • Proximal end is the ball portion is called head. • Proximal end also contains the trochanters where muscles attach. • Distal end forms stifle joint (knee) with condyles.

Patella • Kneecap is largest sesamoid bone in the body. • Formed in the distal tendon of the quadriceps femoris muscle on the cranial aspect of the stifle joint. • Helps to protect tendon as it passes down over the trochlea of the femur.

Patellar Luxation • When trochlear groove is not deep enough to contain patella so it slips in and out of place. • Usually will cause brief episodes of lameness which can correct. • May hear or feel “popping” in and out of place. • Found in small, toy breeds most prevalently. • Can be surgically corrected.

Fabellae • Two small sesamoid bones located in the proximal gastrocnemius or calf muscles. • Not present in cattle or horses.

Tibia • Main weight bearing bone of the lower leg (shinbone). • Forms stifle joint with femur. • Forms hock (ankle) with tarsus. • Medial malleolus- medial to distal articular surface, knob of ankle. • Tibial tuberosity of proximal end forms the tibial crest. • Where patellar tendon attaches.

Fibula • Thin but complete bone in dogs and cats. • Consists of proximal extremity, shaft, and distal extremity. • Serves as a muscle attachment site. • Horses and cattle do not have shaft of fibula. • Forms lateral malleolus at distal end.

Tarsal Bones • Ankle but in four legged animals is termed the “hock” • Consists of two rows of tarsal bones (similar to carpal bones in wrist). • Proximal row is named and distal row is numbered. • Contains calacaneal tuberosity which forms the point of the hock. Site of attachment for tendon of the gastrocnemius muscle.

Metatarsal Bones • Dogs and cats: four metatarsal bones (II to V) • Horses: 1 large metatarsal bone (cannon bone) and 2 small metatarsal bones (splint bones)

Pelvic Limb Phalanges • Similar to thoracic limb phalanges • Exceptions: dogs and cats • Usually only 4 digits (II to V)

Visceral Skeleton • Bones that form in organs • Examples • os cordis: in heart of cattle and sheep • os penis: in penis of dogs, beaver, raccoons, and walruses • os rostri: in nose of swine

Joints • • Junctions between bones Can be moveable or immovable. Arthro and articular refer to joints. 3 Types of joints: • Fibrous Joints (synarthroses) • Immovable • Found in sutures of skull bones • Cartilaginous Joints (amphiarthroses) • Slightly moveable • Vertebral disks between vertebrae • Pelvic and mandibular symphisis • Synovial Joints (diarthroses) • Freely moveable

Characteristics of Synovial Joints • Have Articular surfaces on bones • Articular cartilag covering articular surfaces • Fluid-filled joint cavity • Enclosed by a joint capsule • Synovial membrane- outer membrane • Synovial fluid- lubricates joint surfaces • Ligaments - fibrous Connective tissue that join bones to other bones.

Synovial Joint Movements • Flexion and Extension • Opposite movements • Increase (extension) or decrease (flexion) angle between two bones • Adduction and Abduction • Opposite movements • Move an extremity toward (Adduction) or away from (Abduction) medial plane • Rotation • Twisting movement of a part on its own axis • Circumduction • Movement of an extremity so that the distal end moves in a circle

Types of Synovial Joints • • Hinge Joints • One joint surface swivels around another • Only capable of flexion and extension Gliding Joints • Rocking motion of one joint surface on another • Primarily capable of flexion and extension • Abduction and adduction possible in humans not dogs/cats • Pivot Joints • One bone pivots (rotates) on another • Only capable of rotation • Ball-and-socket joints • Allow for all joint movements

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