The musculoskeletal system (MSK) is an organ system that gives animals the ability to physically move, by using the muscles and skeletal system. Apart from locomotion, the skeleton also lends support and protects internal organs. In many organisms the skeleton is also used to store fat and minerals, and to produce blood cells.

The human musculoskeletal system consists of the human skeleton, made by bones attached to other bones with joints, and skeletal muscle attached to the skeleton by tendons. In most animals with solid skeletons, yellow bone marrow is used to store energy for the muscles and the red marrow produces blood cells and that produces oxygen for the body.

Muscular System

The muscular system is the biological system of humans that allows them to move. The muscular system in vertebrates is controlled through the nervous system, although some muscles (such as the cardiac muscle) can be completely autonomous.

There are about 650 skeletal muscles in the human body.

Muscle

Muscle is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Its function is to produce force and cause motion, either locomotion or movement within internal organs. Much of muscle contraction occurs without conscious thought and is necessary for survival, like the contraction of the heart or peristalsis, which pushes food through the digestive system. Voluntary muscle contraction is used to move the body and can be finely controlled, such as movements of the finger or gross movements like the quadriceps muscle of the thigh.

Types

There are three types of muscle:

Smooth muscle or "involuntary muscle" is found within the walls of organs and structures such as the oesophagus, stomach, intestines, bronchi, uterus, ureters, bladder, and blood vessels.
Cardiac muscle is also an "involuntary muscle" but it's a specialized kind of muscle found only within the heart.
Skeletal muscle or "voluntary muscle" is anchored by tendons to the bone and is used to affect skeletal movement such as locomotion.

Cardiac and skeletal muscle are "striated" in that they contain sarcomere and are packed into highly-regular arrangements of bundles; smooth muscle has neither. Striated muscle is often used in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions.

Muscle Anatomy

Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; myofibrils contain sarcomeres, which are composed of actin and myosin. Individual muscle cells are lined with endomysium. Muscle cells are bound together by perimysium into bundles called fascicles; the bundles are then grouped together to form muscle, which is lined by epimysium. Muscle spindles are distributed throughout the muscles and provide sensory feedback information to the central nervous system.

Skeletal muscle, which involves muscles from the skeletal tissue, is arranged in discrete groups, examples of which include the biceps brachii. It is connected by tendons to processes of the skeleton. In contrast, smooth muscle occurs at various scales in almost every organ, from the skin (in which it controls erection of body hair) to the blood vessels and digestive tract (in which it controls the caliber of a lumen and peristalsis).

There are approximately 650 skeletal muscles in the human body (see list of muscles of the human body). Contrary to popular belief, the number of muscle fibers cannot be increased through exercise; instead the muscle cells simply get bigger. It is however believed that myofibrils have a limited capacity for growth through hypertrophy and will split if subject to increased demand.

Physiology

The ten types of muscle have significant differences. However, all but three use the movement of actin against myosin to create contraction and relaxation. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the nerves, the motor nerves and motoneurons in particular. All skeletal muscle and many smooth muscle contractions are facilitated by the neurotransmitter acetylcholine.

Muscular activity accounts for most of the body's energy consumption. Muscles store energy for their own use in the form of glycogen, which represents about 1% of their mass. This can be rapidly converted to glucose when more energy is necessary.

Nervous control

Efferent leg

Vertebrates move muscles in response to voluntary and autonomic signals from the brain. Deep muscles, superficial muscles, muscles of the face and internal muscles all correspond with dedicated regions in the brain.

In addition, muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain, but most muscle activity is the result of complex interactions between various areas of the brain.

Nerves that control skeletal muscles in mammals correspond with neuron groups along the primary motor cortex of the brain's cerebral cortex. Commands are routed though the basal ganglia and are modified by input from the cerebellum before being relayed through the pyramidal tract to the spinal cord and from there to the motor end plate at the muscles. Along the way, feedback loops such as that of the extrapyramidal system contribute signals to influence muscle tone and response.

Deeper muscles such as those involved in posture often are controlled from nuclei in the brain stem and basal ganglia.

Afferent leg

Sometimes known as muscle memory, the sense of where our bodies are in space is called proprioception, the perception of body awareness. More easily demonstrated than explained, proprioception is the "unconscious" awareness of where the various regions of the body are located at any one time. This can be demonstrated by anyone closing their eyes and waving their hand around. Assuming proper proprioceptive function, at no time will the person lose awareness of where the hand actually is, even though it is not being detected by any of the other senses.

Several areas in the brain coordinate movement and position with the feedback information gained from proprioception.

The cerebellum and nucleus ruber in particular continuously sample position against movement and make minor corrections to assure a smooth projection.

Muscle Diseases

There are many diseases and conditions, which cause a decrease in muscle mass, known as atrophy. For example diseases such as cancer and AIDS induce a body-wasting syndrome called "cachexia", which is notable for the severe muscle atrophy seen. Other syndromes or conditions, which can induce skeletal muscle atrophy, are congestive heart disease and liver disease.

During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass. This condition is called "sarcopenia". The exact cause of sarcopenia is unknown, but it may be due to a combination of the gradual failure in the "satellite cells" which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival.

In addition to the simple loss of muscle mass (atrophy), or the age-related decrease in muscle function (sarcopenia), there are other diseases which may be caused by structural defects in the muscle (the dystrophies), or by inflammatory reactions in the body directed against muscle (the myopathies).

Symptoms of muscle disease may include weakness or spasticity/rigidity, myoclonus (twitching) and myalgia (muscle pain). Diagnostic procedures that may reveal muscular disorders include testing creatine kinase levels in the blood and electromyography (measuring electrical activity in muscles). In some cases, muscle biopsy may be done to identify a myopathy, as well as genetic testing to identify DNA abnormalities associated with specific myopathies.

Neuromuscular diseases are those that affect the muscles and/or their nervous control. In general, problems with nervous control can cause spasticity or paralysis, depending on the location and nature of the problem. A large proportion of neurological disorders leads to problems with movement, ranging from cerebrovascular accident (stroke) and Parkinson's disease to Creutzfeldt-Jakob disease.

Smooth Muscle

Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs; such as blood vessels, the bladder, the uterus, and the gastrointestinal tract. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure and function.

Structure

Smooth muscle can, like any muscle, contract and relax. In order to do this it contains intracellular contractile proteins called actin and myosin. While the fibers are essentially the same in smooth muscle as they are in skeletal and cardiac muscle, the way they are arranged is different. As non-striated muscle, the actin and myosin is not arranged into distinct sarcomeres that form orderly bands throughout the muscle cell. The cells themselves are generally arranged in sheets or bundles and connected by gap junctions. In relaxed state, each cell is spindle-shaped, 25-50 µm long and 5 µm wide.

The cells that compose smooth muscle have single nuclei.

Function

The contractile function of this muscle, to a large extent, determines function of the organ. For example, contractile function of vascular smooth muscle contributes to setting the level of blood pressure. Smooth muscle tissue serves to guide medium transport, such as blood, urine, sperm, bile by means of controlled contractions inducing peristaltic movements.

Control

Smooth muscle cells can be stimulated to contract or relax in many different ways. They may be directly stimulated by the autonomic nervous system ("involuntarily" control), but can also react on stimuli from neighboring cells and on hormones (vasodilators or vasoconstrictor) within the medium that it carries.

Cardiac Muscle

Cardiac muscle is a type of striated muscle found within the heart. Its function is to "pump" blood through the circulatory system by contracting.

Unlike skeletal muscle, which contracts in response to nerve stimulation, and like smooth muscle, cardiac muscle is myogenic, meaning that it stimulates its own contraction without a requisite electrical impulse. A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on. This transmission of impulses makes cardiac muscle tissue similar to nerve tissue, although the cells are connected by intercalated discs, which conduct electrical potentials directly, rather than the chemical synapses used by neurons.

Specialized pacemaker cells normally determine the overall rate of contractions. The nervous system does contact the heart, but only sends signals to speed up or slow down the heart rate, rather than controlling each beat. Since cardiac muscle is myogenic, the pacemaker serves only to modulate the cells; the cardiac muscles would still fire in the absence of a pacemaker, albeit randomly, and the heart would go into fibrillation.

Skeletal Muscle

Skeletal muscle is a type of striated muscle, attached to the skeleton. Skeletal muscles are used to facilitate movement, by applying force to bones and joints; via contraction. They generally contract voluntarily (via nerve stimulation), although they can contract involuntarily.

Muscles have an elongated, cylindrical shape, and are multinucleated (in mammals). The nuclei of these muscles are located in the peripheral aspect of the cell, just under the plasma membrane, which vacates the central part of the muscle fiber for myofibrils. This unique arrangement of the nuclei allows for higher efficiency. (Conversely, when the nucleus is located in the center it is considered a pathologic condition known as centronuclear myopathy.)

Skeletal muscles usually have one end (the "origin") attached to a relatively stationary bone, (such as the scapula) and the other end (the "insertion") is attached across a joint, to another bone (such as the humerus).

There are two types of fibers for skeletal muscles: Type I and Type II. Type I fibers appear reddish. They are good for endurance and are slow to tire because they use oxidative metabolism. Type II fibers are whitish; they are used for short bursts of speed and power, use anaerobic metabolism, and are therefore quicker to tire.

Human Skeleton

The human skeleton is made of individual or joined bones (such as the skull), supported and supplemented by a structure of ligaments, tendons, muscles, cartilage and other organs.

The skeleton is not unchanging; it changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton — bones form gradually during nine months in the womb. At birth, all bones will have formed, but a newborn baby has more bones than an adult. On average, an adult human has 206 bones (according to Gray's Anatomy, but the number can vary slightly from individual to individual), but a baby is born with approximately 270. The difference comes from a number of small bones that fuse together during growth. An infant is born with pockets of cartilage between particular bones to allow further growth. The sacrum (the bone at the base of the spine) consists of six bones, which are separated at birth but fuse together into a solid structure in later years. Growing is usually completed between ages 12 and 14, at which point the bones have no pockets of cartilage left to allow more growth.

Not all bones are interconnected directly. There are 6 bones (three on each side) in the middle ear that articulate only with each other. Another bone, the hyoid bone in the neck, does not touch any other bones in the body, and is supported by muscles.

The longest and heaviest bone in the body is the femur and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises 20% of the total body weight.

Function

The most obvious function of bone is to support the body. It also the site of hematopoiesis, the manufacture of blood cells, that takes place in bone marrow (which is why bone marrow cancer is very often a terminal disease). It is also necessary for protection of vital organs. Movement in vertebrates is dependent on the skeletal muscles, which are attached to the skeleton by tendons. Without the skeleton to give leverage, movement would be greatly restricted. Bone also serves as a mineral storage deposit in which nutrients can be stored and retrieved.

One way to group the bones of the human skeleton is to divide them into the axial skeleton and the appendicular skeleton. The axial skeleton consists of bones in the midline and includes all the bones of the head and neck, the vertebrae, ribs and sternum. The appendicular skeleton consists of the clavicles, scapulae, the arm bones, the bones of the pelvis and the leg bones.

A more systematic division of the bones of the human skeleton divides them into the:

Skull
Middle er
Shoulder girdle
Ribcage
Vertebra
Arms
Hands
Pelvis
Legs
Feet

List of bones of the human skeleton

A typical adult human skeleton consists of the following 206 bones, though a small portion of the human population have an extra bone, occurring in the form of an extra rib.

In the skull (22):

Cranial bones:

1. Frontal bone

2. Parietal bone (2)

3. Temporal bone (2)

4. Occipital bone

Sphenoid bone (2)

Ethmoid bone

Facial bones:

5. Zygomatic bone (2)

6. Superior and inferior maxilla

9. Nasal bone (2)

7. Mandible

Palatine bone (2)

Lacrimal bone (2)

Vomer bone

Inferior nasal conchae (2)

In the middle ears (6):

malleus (2)

incus (2)

stapes (2)

In the throat (1):

hyoid bone

In the shoulder girdle (4):

25. clavicle or collarbone (2)

29. scapula or shoulder blade (2)

In the thorax (25):

10. sternum

28. ribs (2 x 12)

In the vertebral column (24):

8. cervical vertebrae (7) incl. atlas & axis

14. lumbar vertebrae (5)

thoracic vertebrae (12)

In the arms (6):

11. humerus (2)

26. condyles of humerus

12. ulna (2)

13. radius (2)

27. head of radius

In the hands (54):

Wrist (carpal) bones:

scaphoid bone (2)

lunate bone (2)

triquetrum bone (2)

pisiform bone (2)

Trapezium (bone) (2)

trapezoid bone (2)

capitate bone (2)

hamate bone (2)

Palm or metacarpal bones:

metacarpal bones (5 × 2)

Finger bones or phalanges:

proximal phalanges (5 × 2)

intermediate phalanges (4 × 2)

distal phalanges (5 × 2)

In the pelvis (4):

15. ilium

16. sacrum

coccyx

In the legs (8):

18. femur (2)

17. hip joint (joint, not bone) (2)

22. greater trochanter of femur

23. condyles of femur

19. patella (2)

20. tibia (2)

21. fibula (2)

In the feet (52):

Ankle (tarsal) bones:

calcaneus (heel bone) (2)

talus (2)

navicular bone (2)

medial cuneiform bone (2)

intermediate cuneiform bone (2)

lateral cuneiform bone (2)

cuboidal bone (2)

Instep bones:

metatarsal bone (5 × 2)

Toe bones:

proximal phalanges (5 × 2)

intermediate phalanges (4 × 2)

distal phalanges (5 × 2)

The infant skeleton has the following bones in addition to those above:

sacral vertebrae (4 or 5), which fuse in adults to form the sacrum

coccygeal vertebrae (3 to 5), which fuse in adults to form the coccyx

ilium, ischium and pubis, which fuse in adults to form the pelvic girdle

Joint

A joint (articulation) is the location at which two bones make contact (articulate). Joints are constructed to both allow movement and provide mechanical support.

Classification

Structure and function of a joint are closely related.

Structural classification

Structurally, joints are classified as:

· fibrous - bones are connected by fibrous connective tissue.

· cartilaginous - bones are connected by cartilage.

· synovial - there is a space (synovial cavity) between the articulating bones.

Functional classification

Functionally, they can be classified as:

· synarthrosis - permit no movement.

· amphiarthrosis - permit little movement.

· diarthrosis - permit a variety of movements · (e.g. flexion, adduction, pronation). Only synovial joints are diarthrosis.

Fibrous joints

In fibrous joints bones are joined by tight and inflexible layers of dense connective tissue, consisting mainly of collagen fibers. In adults, these are not designed to allow any movement; however, in children, fibrous joints have not solidified and are movable. Examples of fibrous joints are:

· Cranial sutures, joining the bones of the cranium.

· Gomphoses, the joints between the roots of the teeth and their sockets (or alveoli) in maxilla and mandible.

Cartilaginous joints

In cartilaginous joints (also known as synchondroses) bones are connected entirely by cartilage. In comparison to synovial joints, cartilaginous joints allow only slight movement. Examples of cartilaginous joints are the pubic symphysis, the joints between the ribs and the sternum, and the cartilage connecting the growth regions of immature long bones. Another example is in the spinal column - the cartilaginous region between adjacent vertebrae.

Synovial joints

Synovial joints (or diarthroses, or diarthroidal joints) are the most common and most moveable type of joints in the body.

Structure

The whole of a diarthrosis is contained by a ligamentous sac, the joint capsule or articular capsule.

The surfaces of the two bones at the joint are covered in cartilage. The thickness of the cartilage varies with each joint, and sometimes may be of uneven thickness. Articular cartilage is multi-layered. A thin superficial layer provides a smooth surface for the two bones to slide against each other. Of all the layers, it has the highest concentration of collagen and the lowest concentration of proteoglycans, making it very resistant to shear stresses. Deeper than that is an intermediate layer, which is mechanically designed to absorb shocks and distribute the load efficiently. The deepest layer is highly calcified, and anchors the articular cartilage to the bone.

In joints where the two surfaces do not fit snugly together, a meniscus or multiple folds of fibro-cartilage within the joint correct the fit, ensuring stability and the optimal distribution of load forces.

The synovium is a membrane that covers all the non-cartilaginous surfaces within the joint capsule. It secretes synovial fluid into the joint, which nourishes and lubricates the articular cartilage. The synovium is separated from the capsule by a layer of cellular tissue that contains blood vessels and nerves.

Types of Joints

Synovial joints can be further grouped by their shape, which controls the movement they allow.

1. Ball and socket joints, such as the shoulder and hip joints. These allow a wide range of movement.

2. Condyloid joints (or ellipsoid), such as the knee. When the knee is extended there is no rotation, when it is flexed some rotation is possible. A condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. Some classifications make a distinction between condyloid and ellipsoid joints.

3. Saddle joints, such as at the thumb (between the metacarpal and carpal). Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints.

4. Hinge joints, such as the elbow (between the humerus and the ulna). These joints act like a door hinge, allowing flexion and extension in just one plane.

5. Pivot joints, such as the elbow (between the radius and the ulna). This is where one bone rotates about another.

6. Gliding joints, such as in the carpals of the wrist. These joints allow a wide variety of movement, but not much distance.

Ligament

A ligament is a short band of tough fibrous connective tissue composed mainly of long, stringy collagen fibers. Ligaments connect bones to other bones to form a joint. (They do not connect muscles to bones; that is the function of tendons.) Some ligaments limit the mobility of articulations, or prevent certain movements altogether.

Capsular ligaments are part of the articular capsule that surrounds synovial joints. They act as mechanical reinforcements. Extra-capsular ligaments join bones together and provide joint stability.

Ligaments are slightly elastic; when under tension, they gradually lengthen. This is one reason why dislocated joints must be set as quickly as possible: if the ligaments lengthen too much, then the joint will be weakened, becoming prone to future dislocations. Athletes, gymnasts, dancers, and martial artists perform stretching exercises to lengthen their ligaments, making their joints more supple. The term double-jointed refers to people who have more elastic ligaments, allowing their joints to stretch and contort further.

The study of ligaments is known as Desmology.

List of major ligaments

Knee

Anterior cruciate ligament (ACL)
Lateral collateral ligament (LCL)
Posterior cruciate ligament (PCL)
Medial collateral ligament (MCL)

Wrist Ligaments

Volar radiocarpal ligament
Dorsal radiocarpal ligament
Ulnar collateral ligament
Radial collateral ligament

Other

Periodontal ligament
Suspensory ligament
Cricothyroid ligament

Cartilage

Cartilage is a type of dense connective tissue. It is composed of cells called chondrocytes which are dispersed in a firm gel-like ground substance, called the matrix. Cartilage is avascular (contains no blood vessels) and nutrients are diffused through the matrix. Cartilage is found in the joints, the rib cage, the ear, the nose, in the throat and between intervertebral disks. There are three main types of cartilage: hyaline, elastic and fibrocartilage. The main purpose of cartilage is to provide a framework upon which bone deposition could begin. Another important purpose of cartilage is to provide smooth surfaces for the movement of articulating bones.

Much like other connective tissue, cartilage is composed of cells, fibers and a matrix.

Types of Cartilage

There are three different types of cartilage, each with special characteristics adapted to local needs.

Hyaline cartilage

This is the most abundant type of cartilage. The name hyaline is derived from the Greek word hyalos, meaning glass. This refers to the translucent matrix or ground substance. Hyaline cartilage is found lining bones in joints (articular cartilage.) It is also present inside bones, serving as a center of ossification or bone growth.

Elastic cartilage

Elastic cartilage (also called yellow cartilage) is found in the pinna of the ear and several tubes, such as the walls of the auditory and eustachian canals and larynx. Cartilage is present to keep the tubes permanently open. Elastic cartilage is similar to hyaline cartilage but contains elastic bundles (elastin) scattered throughout the matrix. This provides a tissue which is stiff yet elastic.

Fibrocartilage

Fibrocartilage (also called white cartilage) is a specialized type of cartilage found in areas requiring tough support or great tensile strength, such as between intervertebral disks, the pubic and other symphyses, and at sites connecting tendons or ligaments to bones. There is rarely any clear line of demarcation between fibrocartilage and the neighboring hyaline cartilage or connective tissue. The fibrocartilage found in intervertebral disks contains more collagen compared to hyaline. Fibrocartilage lacks a perichondrium.

Diseases / Medicine

There are several diseases, which can affect the cartilage. Chondrodystrophies are a group of diseases characterized by disturbance of growth and subsequent ossification of cartilage. Some common diseases affecting/involving the cartilage are listed below.

Arthritis: The cartilage covering bones in joints (articular cartilage) is degraded, resulting in limitation of movement and pain.

Achondroplasia: Reduced proliferation of chondrocytes in the epiphyseal plate of long bones results in a form of dwarfism.

Costochondritis: Inflammation of cartilage in the ribs which causes chest pain.

Herniated disk: Asymmetrical compression of a disk ruptures the cartilage ring, causing tissue to herniate into the spinal canal.

Tendon

A tendon (or sinew) is a tough band of fibrous connective tissue that connects muscle to bone. They are similar to ligaments except that ligaments join one bone to another. Tendons are designed to withstand tension. Typically tendons connect muscles to bones; together a combination of tendons and muscles can only exert a pulling force.

Composition

Tendons are composed mainly of water, type-I collagen and cells called tenocytes. Minor fibrillar collagens, fibril-associated collagens and proteoglycans are present in small quantities and are critical for tendon structure. Most of the strength of tendon is due to the parallel, hierarchical arrangement of densely-packed collagen fibrils. Tenocytes are specialized fibroblasts responsible for the maintenance of collagen structure.

Other information

Tendonitis refers to inflammation of a tendon.
The Achilles tendon is a particularly large tendon connecting the heel to the muscles of the calf. It is so named because the mythic hero Achilles was said to have been killed due to an injury at this spot.
Sinew was also widely used in the medieval times as a form of ancient elastic. Some specific uses include using sinew as thread for sewing, attaching feathers to arrows (see fletch), lashing tool blades to hafts, etc.
Tendon (particularly beef tendon) is used as a food in some cuisine.

Bone

Bone, also called osseous tissue, (Latin: "os") is a type of hard endoskeletal connective tissue found in many vertebrate animals. Bones support body structures, protect internal organs, and (in conjunction with muscles) facilitate movement; are also involved with cell formation, calcium metabolism, and mineral storage. The bones of an animal are, collectively, known as the skeleton. Bone has a different composition than cartilage, and both are derived from mesoderm.

Functions

Long bones can be connected to skeletal muscles via tendons. Bones connect at joints by ligaments. The interaction between bone and muscle is studied in biomechanics.

Structure

Bone is a relatively hard and lightweight composite material, formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxyapatite. It has relatively high compressive strength but poor tensile strength. While bone is essentially brittle, it does have a degree of significant elasticity contributed by its organic components (chiefly collagen). Bone has an internal mesh-like structure, the density of which may vary at different points.

Bone can be either compact or cancellous (spongy).

Bone can also be either woven or lamellar. Woven bone is put down rapidly during growth or repair.

Long bonesare tubular in structure (e.g. the tibia). The central shaft of a long bone is called the diaphysis, and has a hollow middle—the medullar cavity filled with bone marrow. Surrounding the medullar cavity is a thin layer of cancellous bone that also contains marrow. The extremities of the bone are called the epiphyses and are mostly cancellous bone covered by a relatively thin layer of compact bone. In children, long bones are filled with red marrow, which is gradually replaced with yellow marrow as the child ages.

Short bones (e.g. finger bones) have a similar structure to long bones, except that they have no medullar cavity.

Flat bones (e.g. the skull and ribs) consist of two layers of compact bone with a zone of cancellous bone sandwiched between them.

Irregular bones are bones, which do not conform to any of the previous forms (e.g. vertebrae).

All bones consist of living cells embedded in a mineralized organic matrix that makes up the main bone material.

Cells

Bone cells include osteoblasts, so called Bone Lining Cells, osteocytes and osteoclasts. Osteoblasts are typically viewed as bone forming cells. They are located near to the surface of bone and their functions are to make osteoid and manufacture hormones such as prostaglandin which act on bone itself.

If osteoblasts can be described as bone forming cells, the osteoclasts can be described as bone destroying cells. Osteoclasts are large, multinucleated cells located on bone surfaces in what are called Howship's lacunae.

Matrix

The matrix comprises the other major constituent of bone. It has inorganic and organic parts. The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of hydroxyapatite. The matrix is initially laid down as unmineralized osteoid (manufactured by osteoblasts). Mineralization involves osteoblasts secreting vesicles containing alkaline phosphatase.

Bone pathologies

One of the most common bone illnesses is a bone fracture. Bones heal by natural processes, but untended and unsupported can lead to misgrown bone.

Other illnesses are for example osteoporosis and bone cancer (osteosarcoma). The joints can be affected by arthritis.

Terminology

Process	A relatively large projection or prominent bump.
Articulation	The region where adjacent bones contact each other—a joint.
Articular process	A projection that contacts an adjacent bone.
eminence	A relatively small projection or bump.
tuberosity	A projection or bump with a roughened surface.
tubercle	A projection or bump with a roughened surface, generally smaller than a tuberosity.
trochanter	One of two specific tuberosities located on the femur.
spine	A relatively long, thin projection or bump.
suture	Articulation between cranial bones.
malleolus	One of two specific protuberances of bones in the ankle.
condyle	A large, rounded articular process.
epicondyle	A projection near to a condyle but not part of the joint.
line, ridge	A long, thin projection, often with a rough surface.
crest	A prominent ridge.
facet	A small, smooth articular surface.
foramen	An opening through a bone.
fossa	A broad, shallow depressed area.
canal	A long, tunnel-like foramen, usually a passage for notable nerves or blood vessels.
meatus	A short canal.
sinus	A cavity within a cranial bone.

There are also names for specific parts of long bones.

diaphysis, shaft	The long, relatively straight main body of the bone; region of primary ossification.
epiphyses	The end regions of the bone; regions of secondary ossification.
epiphyseal plate	The thin sheet of bone marking the fusion of epiphyses to the diaphysis (adults only).
head	The proximal articular end of the bone.
neck	The region of bone between the head and the shaft.

There are also names for different side of the bones:

Medial: Side of the bone towards the centre line of the body.

Lateral: Side of bone towards the outside line of the body.

So for example, using your right foot as an example, the left side of your big toe is called the medial side; whilst the right side of your little toe would be on the lateral side.

Also:

Proximal: Towards the top of your skull.

Distal: Towards the bottom of your feet.

Thus, the proximal end of the femur would be the head which joins at the hip, whilst the distal end of the femur would be the end which joins with the tibia.

Osteoporosis

Osteoporosis is a disease of bone in which bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is changed. Osteoporotic bones are more susceptible to fracture. Osteoporosis is defined by the World Health Organization (WHO) as either a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old person standard) as measured by DEXA or any fragility fracture. While treatment modalities are becoming available, prevention is still the most important way to reduce fracture. Due to its hormonal component, more women, particularly after menopause, suffer from osteoporosis than men.

Osteosarcoma

Osteosarcoma is the most common type of malignant bone cancer, accounting for 35% of primary bone malignancies. There is a preference for the metaphyseal region of tubular long bones. 50% of cases occur around the knee. It is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone.

Arthritis

Arthritis (from Greek arthro-, joint + -itis, inflammation; plural: arthritides) is a group of conditions that affect the health of the bone joints in the body. One in three adult Americans suffers from some form of arthritis, and the disease affects about twice as many women as men.

Arthritic diseases include rheumatoid arthritis and psoriatic arthritis, which are autoimmune diseases; septic arthritis, caused by joint infection; and the more common osteoarthritis, or degenerative joint disease. Arthritis can be caused from strains and injuries from repetitive motion, sports, overexertion and falls. Unlike the autoimmune diseases, osteoarthritis largely affects older people, and results from the degeneration of joint cartilage. Other forms are discussed below.

Arthritic joints can be sensitive to weather changes. The increased sensitivity is thought to be caused by the affected joints developing extra nerve endings in an attempt to protect the joint from further damage.

Types of Arthritis

Primary forms of arthritis:

Septic arthritis
Rheumatoid arthritis
Osteoarthritis
Gout and pseudogout
Juvenile arthritis
Still's disease
Ankylosing spondylitis

Secondary to other diseases:

Systemic lupus erythematosus (SLE)
Henoch-Schönlein purpura
Psoriatic arthritis
Reactive arthritis (Reiter's syndrome
Hemochromatosis
Hepatitis
Wegener's granulomatosis (and many other vasculitis syndromes)
Familial Mediterranean fever (FMF), HIDS (hyperimmunoglobulinemia D and periodic fever syndrome) and TRAPS (TNF-alpha receptor associated periodic fever syndrome).

Orthopedic Surgery

Orthopedic surgery or orthopedics (also spelled orthopaedics, see below) is the branch of surgery concerned with acute, chronic, traumatic, and overuse injuries and other disorders of the musculoskeletal system. Orthopaedic surgeons address most musculoskeletal aliments including arthritis, trauma and congenital deformities using both surgical and non-surgical means.

Practice

Orthopaedic surgeons address most musculoskeletal aliments including arthritis, trauma and congenital deformities using both surgical and non-surgical means. According to applications for board certification from 1999 to 2003, the top 25 most common procedures (in order) performed by orthopaedic surgeons are as follows:

1. Knee arthroscopy and meniscectomy

2. Shoulder arthroscopy and decompression

3. Carpal tunnel release

4. Knee arthroscopy and chondroplasty

5. Removal of support implant

6. Knee arthroscopy and anterior cruciate ligament reconstruction

7. Knee replacement

8. Repair of femoral neck fracture

9. Repair of trochanteric fracture

10.Débridement of skin/muscle/bone/fracture

11.Knee arthroscopy repair of both menisci

12.Hip replacement

13.Shoulder arthroscopy/distal clavicle excision

14.Repair of rotator cuff tendon

15.Repair fracture of radius (bone)/ulna

16.Laminectomy

17.Repair of ankle fracture (bimalleolar type)

18.Shoulder arthroscopy and débridement

19.Lumbar spinal fusion

20.Repair fracture of the distal part of radius

21.Low back intervertebral disc surgery

22.Incise finger tendon sheath

23.Repair of ankle fracture (fibula)

24.Repair of femoral shaft fracture

25.Repair of trochanteric fracture

Bone Grafting

Bone grafting

is a surgical procedure where bone is taken from a donor site and implanted into the patient. A common use of bone grafting is dental implants.

Autologous bone is typically harvested from the iliac crest of the pelvis.

Banked bone from cadavers may also be used.

Bone fracture

A bone fracture is a medical condition in which a bone becomes cracked, splintered, or bisected as a result of physical trauma. A bone fracture can also occur as a result of certain medical conditions that weaken the bones, such as osteoporosis or certain types of cancer.

Closed vs. open

In orthopaedic medicine, fractures are classified as closed or open (compound) and simple or multi-fragmentary (formerly comminuted).

· Closed fractures are those in which the skin is intact, while open (compound) fractures involve wounds that communicate with the fracture and may expose bone to contamination. Open injuries carry an elevated · risk of infection; they require antibiotic treatment and usually urgent surgical treatment (debridement). This involves removal of all dirt, contamination, and dead tissue.

· Simple fractures are fractures that occur along one line, splitting the bone into two pieces, while multi-fragmentary fractures involve the bone splitting into multiple pieces. A simple, closed fracture is much easier to treat and has a much better prognosis than an open, contaminated fracture. Other considerations in fracture care are displacement (fracture gap) and angulation. If angulation or displacement is large, reduction (manipulation) of the bone may be required and, in adults, frequently requires surgical care. These injuries may take longer to heal than injuries without displacement or angulation.

Another type of bone fracture is a compression fracture. An example of a compression fracture is when the front portion of a vertebra in the spine collapses due to osteoporosis, a medical condition which causes bones to become brittle and susceptible to fracture (with or without trauma).

Special considerations for children

In children, whose bones are still developing, there are risks of either a growth plate injury or a greenstick fracture.

A greenstick fracture occurs because the bone is not as brittle as it would be in an adult, and thus does not completely fracture, but rather exhibits bowing without complete disruption of the bone's cortex.
Growth plate injuries require careful treatment and accurate reduction to make sure that the bone continues to grow normally.
Plastic deformation of the bone, in which the bone permanently bends but does not break, is also possible in children. These injuries may require an osteotomy (bone cut) to realign the bone if it is fixed and cannot be realigned by closed methods.

Stress Fracture

A stress fracture is one type of incomplete fractures in bones. It could be described as a very small sliver or crack in the bone; this is why it is sometimes dubbed "hairline fracture". It typically occurs in weight-bearing bones, such as the tibia/fibula and metatarsals, which are all long bones of the leg.

Symptoms

Stress fractures usually have a narrow list of symptoms. It could present as a generalized area of pain, tenderness, and pain with weight-bearing. Usually when running, a stress fracture has severe pain in the beginning of the run, moderate pain in the middle of the run, and severe pain at the end and after the run.

Treatment

If a stress fracture occurs in a weightbearing bone, healing will be delayed or prevented by continuing to put weight on that limb.

Rest is the only way to completely heal a stress fracture. The average time of complete rest from the activity that caused the stress fracture is one week. A fracture requires 4 to 8 weeks of recuperation, however, which may include no more than light use of the injured body part, as long as activity does not cause pain. After the recuperative period, another 2 weeks of mild activity without any pain may be recommended before the bone may be safely considered healed and activity may gradually increase.

Rehabilitation usually consists of muscle strength training to help dissipate the excessive forces transmitted to the bones.

Bracing or casting the limb with a hard plastic boot or air cast may also prove beneficial by taking some stress off the stress fracture. An air cast has pre-inflated cells that put light pressure on the bone, which promotes healing by increasing blood flow to the area and takes away a lot of the pain because of the pressure it applies to the bone. If the stress fracture is severe enough, crutches also help to take all stress off the bone.

Hip fracture

A hip fracture is a fracture in the proximal end of the femur (the long bone running through the thigh), near the hip joint.

The term "hip fracture" sometimes includes the complex consequences of osteoporosis; in the vast majority of cases, a hip fracture is a fragility fracture due to a fall or minor trauma in someone with weakened osteoporotic bone. Most at risk are Caucasian, post-menopausal women. Most hip fractures outside of this group are the result of high-trauma injuries such as car accidents.

The death rate for a hip fracture is between 20% and 35% in the first year.

Synonyms

Most of the synonyms actually describe different types of hip fracture. All of these variations are important because each are treated differently.

· Fractured Neck of Femur (sometimes Neck of Femur Fracture or NOF) denotes a fracture adjacent to the femoral head. This acronym (NOF) is sometimes loosely used for Hip Fracture.

· Intertrochanteric or pertrochanteric fracture denotes a fracture which is a few centimeters lower and involves the greater trochanter.

· Fractured Head of Femur or Head Splitting Fracture denotes a fracture involving the head itself. This is rarer and usually the result of high energy trauma and a dislocation of the hip joint.

· Subtrochanteric fracture involves the shaft of the · femur immediately below the Greater Trochanter and may extend down the shaft of the femur.

Distal radius fracture; Colles' fracture; Smith's fracture; Barton's Fracture; Chauffeur's Fracture

Distal radius fractures are a very common injury of the that occur at the distal end, where the wrist joint lies.

Definition

A fracture affecting the distal end of the radius and often the ulnar styloid. Because of its close proximity to the wrist joint this injury is often called a wrist fracture.

Synonyms

Wrist fracture; fractured wrist; Colles' fracture; Smith's fracture; Barton's Fracture; Chauffeur's Fracture (so called because the crank used to start old cars often kicked back and broke the chauffeurs' wrists with a particular pattern).

Clavicle fracture

A clavicle fracture is a bone fracture in the clavicle, or collarbone.

Frequency

Clavicle fractures involve approximately 5% of all fractures in seen in ED. It is most commonly fractured between the proximal 2/3 and distal 1/3 of its length. Children and infants are particularly prone to it. Clavicle fractures can be present in the newborn period, especially following a difficult delivery.

Treatment

Treatment frequently involves resting affected extremity. Often a sling or figure 8 brace is used. In rare cases (2-5%) surgery may be required when skin is broken or if the fracture is extremely displaced (disunion). Surgical procedure will often call for a plate to be affixed along the bone on either side of the fracture and screwed into the clavicle. For adults, healing time is longer than in children.

Segond Fracture

The Segond fracture is a type of avulsion fracture, in which soft tissue structures tear off bits of their bony attachment, in this case the lateral tibial plateau of the knee, immediately beyond the surface which articulates with the femur.

Mechanism

Segond fracture is typically the result of abnormal varus, or "bowing", stress to the knee, combined with internal rotation of the tibia. Reverse Segond fracture, as its name suggests, is caused by abnormal valgus, or "knock-knee", stress and external rotation.

Originally thought to be a result of avulsion of the medial third of the lateral collateral ligament, the Segond fracture has been shown by more recent research to relate also to the insertion of the iliotibial tract (ITT) and the anterior oblique band (AOB), a ligamentous attachment of the fibular collateral ligament (FCL), to the midportion of the lateral tibia.

ANA	Antinuclear antibody test (see also FANA).
C1 - C7	Cervical vertebrae.
Ca	Calcium.
CPK	Creatine phosphokinase.
CTS	Carpal tunnel syndrome (carpal tunnel release: sample operative report).
DTR	Deep tendon reflex/es.
EMG	Electromyogram, electromyography.
ESR	Erythrocyte sedimentation rate.
IM	Intramuscular.
L1 - L5	Lumbar vertebrae 1 - 5 (spine e.g. L1 = 1st lumbar vertebra).
P	Phosphorus, pressure, pulse, para.
RF	Rheumatic fever, rheumatoid factor.
ROM	Range of motion (of joint).
SLE	Systemic lupus erythematosus.
T1 - T12	Thoracic vertebrae 1 - 12 (spine e.g. T1 = 1st thoracic vertebra).
TMJ	(Temporalist mandibulae junctio) temporomandibular joint.