Arthritis is a form of joint disorder that involves inflammation in one or more joints.There are over 100 different forms of arthritis.The most common form of arthritis is osteoarthritis (degenerative joint disease), a result of trauma to the joint, infection of the joint, or age. Other arthritis forms are rheumatoid arthritis, psoriatic arthritis, and related autoimmune diseases. Septic arthritis is caused by joint infection.

The major complaint by individuals who have arthritis is joint pain. Pain is often constant, and may be localized to the joint affected. The pain from arthritis is from inflammation around the joint, damage to the joint from disease, daily wear and tear of the joint, muscle strains caused by forceful movements against stiff and painful joints, and from fatigue.

Prevalence of arthritis

There are 52.5 million adults in the US, equating to 22.7% of the population, reported to have a form of arthritis, rheumatoid arthritis, gout, lupus or fibromyalgia. With people living longer in the US, the prevalence of doctor-diagnosed arthritis is expected to increase. It has been estimated that by the year 2030, 67 million, 25% of the projected total adult population aged 18 years and older, will have doctor-diagnosed arthritis. Arthritis has a significantly higher age-adjusted prevalence in women (23.9%) than men (18.6%), with the prevalence increasing with age and higher among women than men in every age group. According to the CDC, 60% of people with arthritis are women, and most forms of arthritis are more common in women, with the exception of gout, which is more common in men.

In primates,including humans, the elbow joint is the synovial hinge joint between the humerus in the upper arm and the radius and ulna in the forearm which allows the hand to be moved towards and away from the body.The superior radioulnar joint shares joint capsule with the elbow joint but plays no functional role at the elbow.The elbow region includes prominent landmarks such as the olecranon (the bony prominence at the very tip of the elbow), the elbow pit, and the lateral and medial epicondyles. The name for the elbow in Latin is cubitus, and so the word cubital is used in some elbow related terms, as in cubital nodes for example.

The elbow joint is a complex hinge joint formed between the distal end of the humerus in the upper arm and the proximal ends of the ulna and radius in the forearm. The elbow allows for the flexion and extension of the forearm relative to the upper arm, as well as rotation of the forearm and wrist.

Like all other synovial joints, a thin layer of smooth articular cartilage covers the ends of the bones that form the elbow joint. The joint capsule of the elbow surrounds the joint to provide strength and lubrication to the elbow. Slick synovial fluid produced by the synovial membrane of the joint capsule fills the hollow space between the bones and lubricates the joint to reduce friction and wear.

An extensive network of ligaments surrounding the joint capsule helps the elbow joint maintain its stability and resist mechanical stresses. The radial and ulnar collateral ligaments connect and maintain the position of the radius and ulna relative to the epicondyles of the humerus. The annular ligament of the elbow extends from the ulna around the head of the radius to hold the bones of the lower arm together. These ligaments allow for movement and stretching of the elbow while resisting dislocation of the bones.

Being a hinge joint, the only movements allowed by the elbow are flexion and extension of the joint and rotation of the radius. The range of motion of the elbow is limited by the olecranon of the ulna, so that the elbow can only extend to around 180 degrees. Flexion of the elbow is limited only by the compression soft tissues surrounding the joint.

Because so many muscles originate or insert near the elbow, it is a common site for injury. One common injury is lateral epicondylitis, also known as tennis elbow, which is an inflammation surrounding the lateral epicondyle of the humerus. Six muscles that control backward movement (extension) of the hand and fingers originate on the lateral epicondyle. Repeated strenuous striking while the muscles are contracted and against force – such as that occurring with the backhand stroke in tennis – causes strain on the tendinous muscle attachments and can produce pain around the epicondyle. Rest for these muscles will usually bring about recovery.

The femur or thighbone, is the most proximal (closest to the hip joint) bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in the hindlimbs. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap forming the knee joint. By most measures the femur is the strongest bone in the body. The femur is also the longest bone in the body.

Structure

The femur is the only bone in the thigh. The two femurs converge medially toward the knees, where they articulate with the proximal ends of the tibiae. The angle of convergence of the femora is a major factor in determining the femoral-tibial angle. In females the femora converge more than in males because the pelvic bone is wider in females. In the condition genu valgum (knock knee) the femurs converge so much that the knees touch one another. The opposite extreme is genu varum (bow-leggedness). In the general population of people without either genu valgum or genu varum, the femoral-tibial angle is about 175 degrees.

The femur is the longest and, by most measures, the strongest bone in the human body. Its length on average is 26.74% of a person's height,[4] a ratio found in both men and women and most ethnic groups with only restricted variation, and is useful in anthropology because it offers a basis for a reasonable estimate of a subject's height from an incomplete skeleton.The femur is categorised as a long bone and comprises a diaphysis (shaft or body) and two epiphyses (extremities) that articulate with adjacent bones in the hip and knee.

The foot (plural feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws or nails.

Structure

The human foot is a strong and complex mechanical structure containing 26 bones, 33 joints (20 of which are actively articulated), and more than a hundred muscles, tendons, and ligaments. The joints of the foot are the ankle and subtalar joint and the interphalangeal articulations of the foot.

An anthropometric study of 1197 North American adult Caucasian males (mean age 35.5 years) found that a man's foot length was 26.3 cm with a standard deviation of 1.2 cm.

The foot can be subdivided into the hindfoot, the midfoot, and the forefoot:The hindfoot is composed of the talus (or ankle bone) and the calcaneus (or heel bone). The two long bones of the lower leg, the tibia and fibula, are connected to the top of the talus to form the ankle. Connected to the talus at the subtalar joint, the calcaneus, the largest bone of the foot, is cushioned underneath by a layer of fat.

The five irregular bones of the midfoot, the cuboid, navicular, and three cuneiform bones, form the arches of the foot which serves as a shock absorber. The midfoot is connected to the hind- and fore-foot by muscles and the plantar fascia.The forefoot is composed of five toes and the corresponding five proximal long bones forming the metatarsus. Similar to the fingers of the hand, the bones of the toes are called phalanges and the big toe has two phalanges while the other four toes have three phalanges. The joints between the phalanges are called interphalangeal and those between the metatarsus and phalanges are called metatarsophalangeal (MTP).

Both the midfoot and forefoot constitute the dorsum (the area facing upwards while standing) and the planum (the area facing downwards while standing).The instep is the arched part of the foot between the toes and the ankle.

A hand (Latin manus) is a prehensile, multi-fingered organ located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "hand" and fingerprints remarkably similar to human fingerprints) are often described as having "hands" instead of paws on their front limbs. The raccoon is usually described as having "hands" though opposable thumbs are lacking.

Fingers contain some of the densest areas of nerve endings on the body, and are the richest source of tactile feedback. They also have the greatest positioning capability of the body, thus the sense of touch is intimately associated with hands. Like other paired organs (eyes, feet, legs) each hand is dominantly controlled by the opposing brain hemisphere, so that handedness—the preferred hand choice for single-handed activities such as writing with a pencil, reflects individual brain functioning.

Some evolutionary anatomists use the term hand to refer to the appendage of digits on the forelimb more generally — for example, in the context of whether the three digits of the bird hand involved the same homologous loss of two digits as in the dinosaur hand.

The human hand has five fingers and 27 bones, not including the sesamoid bone, the number of which varies between people, 14 of which are the phalanges (proximal, intermediate and distal) of the fingers. The metacarpal bones connect the fingers and the carpal bones of the wrist. Each human hand has five metacarpals and eight carpal bones. Among humans, the hands play an important function in body language and sign language.

Structure

Many mammals and other animals have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The scientific use of the term hand in this sense to distinguish the terminations of the front paws from the hind ones is an example of anthropomorphism. The only true grasping hands appear in the mammalian order of primates. Hands must also have opposable thumbs, as described later in the text.

The hand is located at the distal end of each arm. Apes and monkeys are sometimes described as having four hands, because the toes are long and the hallux is opposable and looks more like a thumb, thus enabling the feet to be used as hands.

The word "hand" is sometimes used by evolutionary anatomists to refer to the appendage of digits on the forelimb such as when researching the homology between the three digits of the bird hand and the dinosaur hand.

The hip joint is one of the most important joints in the human body. It allows us to walk, run, and jump. It bears our body’s weight and the force of the strong muscles of the hip and leg. Yet the hip joint is also one of our most flexible joints and allows a greater range of motion than all other joints in the body except for the shoulder.

The hip joint is a ball-and-socket synovial joint formed between the os coxa (hip bone) and the femur. A round, cup-shaped structure on the os coax, known as the acetabulum, forms the socket for the hip joint.

Hyaline cartilage lines both the acetabulum and the head of the femur, providing a smooth surface for the moving bones to glide past each other. Hyaline cartilage also acts as a flexible shock absorber to prevent the collision of the bones during movement. Between the layers of hyaline cartilage, synovial membranes secrete watery synovial fluid to lubricate the joint capsule.

Surrounding the hip joint are many tough ligaments that prevent the dislocation of the joint. The strong muscles of the hip region also help to hold the hip joint together and prevent dislocation.Functionally, the hip joint enjoys a very high range of motion. The ball-and-socket structure of the joint allows the femur to circumduct freely through a 360-degree circle. The femur may also rotate around its axis about 90 degrees at the hip joint. Only the shoulder joint provides as high of a level of mobility as the hip joint. In addition to being flexible, each hip joint must be capable of supporting half of the body’s weight along with any other forces acting upon the body. During running and jumping, for example, the force of the body’s movements multiplies the force on the hip joint to many times the force exerted by the body’s weight. The hip joint must be able to accommodate these extreme forces repeatedly during intense physical activities.

If a knee or hip joint breaks in an accident or wears out in old age, a surgeon can replace it with a ball-and-socket joint made from metal and plastic and engineered in such a way that it will duplicate the motions of a human joint. Hip replacement was once impossible because, although joints could easily be produced in a laboratory, the human body rejected the materials. Sometimes the pins that held the artificial joint to other bones worked loose and required further surgery. Some joints, especially the artificial knee, didn't work very well because they were designed like hinges that just opened one way. Later, when the designers realized the knee needed to rotate slightly, they produced a joint that would fulfill these movements as well.

Medical pioneers finally overcame bodily rejection by making the joints out of non-irritating, man-made materials. Surgeons have now perfected hip and knee replacement surgeries so that recipients are relieved of pain and can walk at a smoother pace.

The knee is one of the largest and most complex joints in the body. The knee joins the thigh bone (femur) to the shin bone (tibia). The smaller bone that runs alongside the tibia (fibula) and the kneecap (patella) are the other bones that make the knee joint.

Tendons connect the knee bones to the leg muscles that move the knee joint. Ligaments join the knee bones and provide stability to the knee:

• The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).
• The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur).
• The medial and lateral collateral ligaments prevent the femur from sliding side to side.

Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia.Numerous bursae, or fluid-filled sacs, help the knee move smoothly.

The bones of the leg and foot form part of the appendicular skeleton that supports the many muscles of the lower limbs. These muscles work together to produce movements such as standing, walking, running, and jumping. At the same time, the bones and joints of the leg and foot must be strong enough to support the body’s weight while remaining flexible enough for movement and balance.

At the proximal end of the femur is a rounded prominence known as the head of the femur. The head of the femur forms the ball and socket hip joint with the acetabulum of the hip bone. The hip joint gives the leg an incredible range of motion while still providing support to the body’s weight.

At the distal end of the femur, two rounded condyles meet the tibia and fibula bones of the lower leg to form the knee joint. The knee is a strong but flexible hinge joint that uses muscles and ligaments to withstand the torques and strains of powerful leg movements. Between the femur and tibia is the meniscus, a layer of tough fibrocartilage that acts as a shock absorber.

In the lower leg, the tibia bears most of the body’s weight while the fibula supports the muscles of balance in the lower leg and ankle. The tibia forms the flexible ankle joint with the tarsal bones of the foot. Body weight is distributed among the seven tarsals, which can shift slightly to provide minute adjustments to the position of the ankle and foot. The calcaneus, or heel bone, is the largest tarsal bone and rests on the ground when the body is standing.

The tarsal bones and the five long metatarsal bones together form the arches of the foot. Body weight supported by the foot is spread across the arches from the tarsal and metatarsal bones, which make contact with the ground while standing. Like the tarsal bones, the position of the metatarsals can be adjusted to change the shape of the foot and affect balance and posture of the body.

Extending from the distal end of the metatarsals are the tiny phalanges of the toes. The phalanges connect to several muscles in the leg via long tendons. The phalanges can flex or extend to change the shape of the foot for balance, and provide added leverage to the foot during walking.

The pelvic region is the area between the trunk — or main body — and the lower extremities, or legs.The female pelvis is morphologically different (different in form) from a male’s but most of the differences are not apparent until puberty. The pelvic bones are larger and broader as they have evolved to create a larger space for childbirth.

The most noticeable differences are the width of the pubic outlet, the circular hole in the middle of the pelvic bones, and the width of the pubic arch, or the space under the base of the pelvis. The bones of the pelvis are the hip bones, sacrum, and coccyx. Each hip bone contains three bones — the ilium, ischium, and pubis — that fuse together as we grow older. The sacrum, five fused vertebral bones, joins the pelvis between the crests of the ilium. Below the sacrum is the coccyx, or tailbone, a section of fused bone that is the end of the vertebral column. The pelvis forms the base of the spine as well as the socket of the hip joint.

The hip joint is a ball-and-socket joint created by the femur and a part of the pelvis called the acetabulum. This joint and its ability to rotate in many angles is one of many pieces of anatomy that allows humans to walk. The external female genitals include the vaginal opening, clitoris, urethra, labia minora, and labia majora. Collectively, these parts are called the vulva.

The vaginal opening is also home to the urethra, the tube through which the body expels urine. It is an extension of the ureters, or tubes that deliver urine from the bladder. The bladder is situated below the uterus. The uterus is a pear-shaped, hollow organ where a fetus would develop prior to being born. Eggs, the female reproductive cells, are produced in the ovaries. A tube leads from each ovary to the uterus. These tubes are called the oviducts, or fallopian tubes. The pelvic region also holds several digestive organs. These include the large intestine and small intestine. Both are vital to digesting food and expelling solid waste. The large intestine ends in the rear of the pelvis at the anus, a sphincter muscle that controls the disposal of solid waste. The intestines are supported by a series of muscles known as the pelvic floor. These muscles also help the anus function and help push a baby through the vaginal opening during childbirth.

The shoulder is one of the largest and most complex joints in the body. The shoulder joint is formed where the humerus (upper arm bone) fits into the scapula (shoulder blade), like a ball and socket. Other important bones in the shoulder include:

• The acromion is a bony projection off the scapula.
• The clavicle (collarbone) meets the acromion in the acromioclavicular joint.
• The coracoid process is a hook-like bony projection from the scapula.

The shoulder has several other important structures:

• The rotator cuff is a collection of muscles and tendons that surround the shoulder, giving it support and allowing a wide range of motion.
• The bursa is a small sac of fluid that cushions and protects the tendons of the rotator cuff.
• A cuff of cartilage called the labrum forms a cup for the ball-like head of the humerus to fit into.

The humerus fits relatively loosely into the shoulder joint. This gives the shoulder a wide range of motion, but also makes it vulnerable to injury.

The spine is made of 33 individual bones stacked one on top of the other. This spinal column provides the main support for your body, allowing you to stand upright, bend, and twist, while protecting the spinal cord from injury. Strong muscles and bones, flexible tendons and ligaments, and sensitive nerves contribute to a healthy spine. Yet, any of these structures affected by strain, injury, or disease can cause pain.

When viewed from the side, an adult spine has a natural S-shaped curve. The neck (cervical) and low back (lumbar) regions have a slight concave curve, and the thoracic and sacral regions have a gentle convex curve (Fig. 1). The curves work like a coiled spring to absorb shock, maintain balance, and allow range of motion throughout the spinal column.

The muscles and correct posture maintain the natural spinal curves. Good posture involves training your body to stand, walk, sit, and lie so that the least amount of strain is placed on the spine during movement or weight-bearing activities (see Posture). Excess body weight, weak muscles, and other forces can pull at the spine's alignment:

• An abnormal curve of the lumbar spine is lordosis, also called sway back.
• An abnormal curve of the thoracic spine is kyphosis, also called hunchback.
• An abnormal curve from side-to-side is called scoliosis.

The two main muscle groups that affect the spine are extensors and flexors. The extensor muscles enable us to stand up and lift objects. The extensors are attached to the back of the spine. The flexor muscles are in the front and include the abdominal muscles. These muscles enable us to flex, or bend forward, and are important in lifting and controlling the arch in the lower back. The back muscles stabilize your spine. Something as common as poor muscle tone or a large belly can pull your entire body out of alignment. Misalignment puts incredible strain on the spine (see Exercise for a Healthy Back).

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate, in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bones—vertebrae separated by intervertebral discs.The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

There are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples.

Structure

In the human vertebral column there are normally thirty-three vertebrae;the upper twenty-four are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx or tailbone. The articulating vertebrae are named according to their region of the spine. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region however is only rarely changed.

There are ligaments extending the length of the column at the front and the back, and in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.

The hand and wrist are made up of many different bones, muscles and ligaments that enable a wide range of movements.

Bones

The wrist is formed where the two bones of the forearm – the radius (the larger bone on the thumb side of the arm) and the ulna (the smaller bone on the pinky side) – meet the carpus. Rather than a single joint, the wrist is actually made up of multiple joints where the bones of the arm and hand meet to allow movement.

The carpus is formed from eight small bones collectively referred to as the carpal bones. The carpal bones are bound in two groups of four bones:

• The pisiform, triquetrum, lunate and scaphoid on the upper end of the wrist
• The hamate, capitate, trapezoid and trapezium on the lower side of the hand.

Other bones of the hand are:

• The metacarpals – the five bones that comprise the middle part of the hand
• the phalanges (singular phalanx) – the 14 narrow bones that make up the fingers of each hand. Each finger has three phalanges (the distal, middle, and proximal); the thumb has two.

Joints are formed wherever two or more of these bones meet. Each of the fingers has three joints:

• Metacarpophalangeal joint (MCP) – the joint at the base of the finger
• proximal interphalangeal joint (PIP) – the joint in the middle of the finger
• distal interphalangeal joint (DIP) – the joint closest to the fingertip.

Each thumb has two joints. The surfaces of the bones where they meet to form joints are covered with a layer of cartilage, which allows them to glide smoothly against one another as they move. The joints are enclosed by a fibrous capsule that is lined with a thin membrane called the synovium, which secretes a fluid to lubricate the joints.