Cartilage is the tough but flexible tissue that covers the ends of your bones at a joint. It also gives shape and support to other parts of your body, such as your ears, nose and windpipe. Healthy cartilage helps you move by allowing your bones to glide over each other. It also protects bones by preventing them from rubbing against each other.

Injured, inflamed, or damaged cartilage can cause symptoms such as pain and limited movement. It can also lead to joint damage and deformity. Causes of cartilage problems include

• Tears and injuries, such as sports injuries
• Genetic factors
• Other disorders, such as some types of arthritis

Osteoarthritis results from breakdown of cartilage.

This is a supportive connective tissue with a flexible rubbery matrix. The cells that secrete the matrix are called chondroblasts. The chondroblasts surround themselves with the matrix until they become trapped in little cavities called lacunae. Then they are called chondrocytes.

Cartilages do not have blood vessels except when transforming into bone. Nutrition and waste removal therefore depend on slow diffusion through the matrix from/to blood vessels in the dense irregular connective tissue membrane (perichondrium) surrounding it. Chondrocytes thus have slow rates of metabolism and cell division. Injured cartilages therefore heal slowly.

The matrix contains collagen fibres which give cartilages their flexibility and strength.

Cartilages are divided into three types: hyaline cartilage, elastic cartilage and fibrocartilage.

HYALINE CARTILAGE

Hyaline cartilage has a clear glassy blue-white appearance, arising from the invisible fineness of its collagen fibres. It is the most abundant type of cartilage. It covers the ends of bones where bones form joints (articular surfaces) and forms the cartilage rings of the respiratory tract (larynx, trachea and bronchi). It also forms the costal cartilages which attach the ribs to the sternum and the epiphyseal plates (growth plates) of bones and the embryonic skeleton. The tip of the nose is also supported by hyaline cartilage.

Hyaline cartilage provides support and some flexibility.

ELASTIC CARTILAGE

Elastic cartilage contains conspicuous elastic fibres among bundles of collagen fibres. It provides rigidity with even more flexibility than hyaline cartilage. It is found in the external ear, epiglottis and auditory tube.

FIBROCARTILAGE

Fibrocartilage contains coarse, readily visible bundles of collagen. It has more collagen fibres than hyaline cartilage. It is found in the discs between vertebrae, the symphysis pubis (joint between the public bones). It is somewhat flexible and capable of withstanding considerable pressure. There is no perichondrium around the fibrocartilage.

Cartilage Templates

Bone is a replacement tissue; that is, it uses a model tissue on which to lay down its mineral matrix. For skeletal development, the most common template is cartilage. During fetal development, a framework is laid down that determines where bones will form. This framework is a flexible, semi-solid matrix produced by chondroblasts and consists of hyaluronic acid, chondroitin sulfate, collagen fibers, and water. As the matrix surrounds and isolates chondroblasts, they are called chondrocytes. Unlike most connective tissues, cartilage is avascular, meaning that it has no blood vessels supplying nutrients and removing metabolic wastes. All of these functions are carried on by diffusion through the matrix. This is why damaged cartilage does not repair itself as readily as most tissues do.

Throughout fetal development and into childhood growth and development, bone forms on the cartilaginous matrix. By the time a fetus is born, most of the cartilage has been replaced with bone. Some additional cartilage will be replaced throughout childhood, and some cartilage remains in the adult skeleton.

Intramembranous Ossification

During intramembranous ossification, compact and spongy bone develops directly from sheets of mesenchymal (undifferentiated) connective tissue. The flat bones of the face, most of the cranial bones, and the clavicles (collarbones) are formed via intramembranous ossification.

The process begins when mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells (Figure 6.16a). Some of these cells will differentiate into capillaries, while others will become osteogenic cells and then osteoblasts. Although they will ultimately be spread out by the formation of bone tissue, early osteoblasts appear in a cluster called an ossification center.

The osteoblasts secrete osteoid, uncalcified matrix, which calcifies (hardens) within a few days as mineral salts are deposited on it, thereby entrapping the osteoblasts within. Once entrapped, the osteoblasts become osteocytes (Figure 6.16b). As osteoblasts transform into osteocytes, osteogenic cells in the surrounding connective tissue differentiate into new osteoblasts.

Osteoid (unmineralized bone matrix) secreted around the capillaries results in a trabecular matrix, while osteoblasts on the surface of the spongy bone become the periosteum (Figure 6.16c). The periosteum then creates a protective layer of compact bone superficial to the trabecular bone. The trabecular bone crowds nearby blood vessels, which eventually condense into red marrow (Figure 6.16d).

Figure 6.16 Intramembranous Ossification Intramembranous ossification follows four steps. (a) Mesenchymal cells group into clusters, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form. (d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow.

Intramembranous ossification begins in utero during fetal development and continues on into adolescence. At birth, the skull and clavicles are not fully ossified nor are the sutures of the skull closed. This allows the skull and shoulders to deform during passage through the birth canal. The last bones to ossify via intramembranous ossification are the flat bones of the face, which reach their adult size at the end of the adolescent growth spurt.

Endochondral Ossification

In endochondral ossification, bone develops by replacing hyaline cartilage. Cartilage does not become bone. Instead, cartilage serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than intramembranous ossification. Bones at the base of the skull and long bones form via endochondral ossification.

In a long bone, for example, at about 6 to 8 weeks after conception, some of the mesenchymal cells differentiate into chondrocytes (cartilage cells) that form the cartilaginous skeletal precursor of the bones (Figure 6.17a). Soon after, the perichondrium, a membrane that covers the cartilage, appears Figure 6.17b).

Figure 6.17 Endochondral Ossification Endochondral ossification follows five steps. (a) Mesenchymal cells differentiate into chondrocytes. (b) The cartilage model of the future bony skeleton and the perichondrium form. (c) Capillaries penetrate cartilage. Perichondrium transforms into periosteum. Periosteal collar develops. Primary ossification center develops. (d) Cartilage and chondrocytes continue to grow at ends of the bone. (e) Secondary ossification centers develop. (f) Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.

As more matrix is produced, the chondrocytes in the center of the cartilaginous model grow in size. As the matrix calcifies, nutrients can no longer reach the chondrocytes. This results in their death and the disintegration of the surrounding cartilage. Blood vessels invade the resulting spaces, not only enlarging the cavities but also carrying osteogenic cells with them, many of which will become osteoblasts. These enlarging spaces eventually combine to become the medullary cavity.

As the cartilage grows, capillaries penetrate it. This penetration initiates the transformation of the perichondrium into the bone-producing periosteum. Here, the osteoblasts form a periosteal collar of compact bone around the cartilage of the diaphysis. By the second or third month of fetal life, bone cell development and ossification ramps up and creates the primary ossification center, a region deep in the periosteal collar where ossification begins (Figure 6.17c).

While these deep changes are occurring, chondrocytes and cartilage continue to grow at the ends of the bone (the future epiphyses), which increases the bone’s length at the same time bone is replacing cartilage in the diaphyses. By the time the fetal skeleton is fully formed, cartilage only remains at the joint surface as articular cartilage and between the diaphysis and epiphysis as the epiphyseal plate, the latter of which is responsible for the longitudinal growth of bones. After birth, this same sequence of events (matrix mineralization, death of chondrocytes, invasion of blood vessels from the periosteum, and seeding with osteogenic cells that become osteoblasts) occurs in the epiphyseal regions, and each of these centers of activity is referred to as a secondary ossification center (Figure 6.17e).

How Bones Grow in Length

The epiphyseal plate is the area of growth in a long bone. It is a layer of hyaline cartilage where ossification occurs in immature bones. On the epiphyseal side of the epiphyseal plate, cartilage is formed. On the diaphyseal side, cartilage is ossified, and the diaphysis grows in length. The epiphyseal plate is composed of four zones of cells and activity (Figure 6.18). The reserve zone is the region closest to the epiphyseal end of the plate and contains small chondrocytes within the matrix. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the osseous tissue of the epiphysis.

Figure 6.18 Longitudinal Bone Growth The epiphyseal plate is responsible for longitudinal bone growth.

The proliferative zone is the next layer toward the diaphysis and contains stacks of slightly larger chondrocytes. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. Chondrocytes in the next layer, the zone of maturation and hypertrophy, are older and larger than those in the proliferative zone. The more mature cells are situated closer to the diaphyseal end of the plate. The longitudinal growth of bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy.

Most of the chondrocytes in the zone of calcified matrix, the zone closest to the diaphysis, are dead because the matrix around them has calcified. Capillaries and osteoblasts from the diaphysis penetrate this zone, and the osteoblasts secrete bone tissue on the remaining calcified cartilage. Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.

Bones continue to grow in length until early adulthood. The rate of growth is controlled by hormones, which will be discussed later. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the epiphyseal line (Figure 6.19).

Figure 6.19 Progression from Epiphyseal Plate to Epiphyseal Line As a bone matures, the epiphyseal plate progresses to an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone.

How Bones Grow in Diameter

While bones are increasing in length, they are also increasing in diameter; growth in diameter can continue even after longitudinal growth ceases. This is called appositional growth. Osteoclasts resorb old bone that lines the medullary cavity, while osteoblasts, via intramembranous ossification, produce new bone tissue beneath the periosteum. The erosion of old bone along the medullary cavity and the deposition of new bone beneath the periosteum not only increase the diameter of the diaphysis but also increase the diameter of the medullary cavity. This process is called modeling.

Bone Remodeling

The process in which matrix is resorbed on one surface of a bone and deposited on another is known as bone modeling. Modeling primarily takes place during a bone’s growth. However, in adult life, bone undergoes remodeling, in which resorption of old or damaged bone takes place on the same surface where osteoblasts lay new bone to replace that which is resorbed. Injury, exercise, and other activities lead to remodeling. Those influences are discussed later in the chapter, but even without injury or exercise, about 5 to 10 percent of the skeleton is remodeled annually just by destroying old bone and renewing it with fresh bone.

What’s the Bottom Line?

How much do we know about glucosamine and chondroitin supplements?

• We have some information about the safety and usefulness of glucosamine and chondroitin from large, high-quality studies in people.

What do we know about the effectiveness of glucosamine and chondroitin supplements?

• Research results suggest that chondroitin isn’t helpful for pain from osteoarthritis of the knee or hip.
• It’s unclear whether glucosamine helps with osteoarthritis knee pain or whether either supplement lessens osteoarthritis pain in other joints.

What do we know about the safety of glucosamine and chondroitin supplements?

• Studies have found that glucosamine and chondroitin supplements may interact with the anticoagulant (blood-thinning) drug warfarin (Coumadin). Overall, studies have not shown any other serious side effects.
• If you take glucosamine or chondroitin supplements, tell your health care providers. They can do a better job caring for you if they know what dietary supplements you use.

What Are Glucosamine and Chondroitin?

Glucosamine and chondroitin are structural components of cartilage, the tissue that cushions the joints. Both are produced naturally in the body. They are also available as dietary supplements. Researchers have studied the effects of these supplements, individually or in combination, on osteoarthritis, a common type of arthritis that destroys cartilage in the joints.

Cartilage is the connective tissue that cushions the ends of bones within the joints. In osteoarthritis, the surface layer of cartilage between the bones of a joint wears down. This allows the bones to rub together, which can cause pain and swelling and make it difficult to move the joint. The knees, hips, spine, and hands are the parts of the body most likely to be affected by osteoarthritis.

What the Science Says About Glucosamine and Chondroitin for Osteoarthritis

For the Knee or Hip

Glucosamine

Major studies of glucosamine for osteoarthritis of the knee have had conflicting results.

• A large National Institutes of Health (NIH) study, called the Glucosamine/chondroitin Arthritis Intervention Trial (GAIT), compared glucosamine hydrochloride, chondroitin, both supplements together, celecoxib (a prescription drug used to manage osteoarthritis pain), or a placebo (an inactive substance) in patients with knee osteoarthritis. Most participants in the study had mild knee pain.
  • Those who received the prescription drug had better short-term pain relief (at 6 months) than those who received a placebo.
  • Overall, those who received the supplements had no significant improvement in knee pain or function, although the investigators saw evidence of improvement in a small subgroup of patients with moderate-to-severe pain who took glucosamine and chondroitin together.
• In several European studies, participants reported that their knees felt and functioned better after taking glucosamine. The study participants took a large, once-a-day dose of a preparation of glucosamine sulfate sold as a prescription drug in Europe.
• Researchers don’t know why the results of these large, well-done studies differ. It may be because of differences in the types of glucosamine used (glucosamine hydrochloride in the NIH study vs. glucosamine sulfate in the European studies), differences in the way they were administered (one large daily dose in the European studies vs. three smaller ones in the NIH study), other differences in the way the studies were done, or chance.

Chondroitin

In general, research on chondroitin has not shown it to be helpful for pain from knee or hip osteoarthritis.

• More than 20 studies have looked at the effect of chondroitin on pain from knee or hip osteoarthritis. The quality of the studies varied and so did the results. However, the largest and best studies (including the NIH study discussed under the heading “Glucosamine” above) showed that chondroitin doesn’t lessen osteoarthritis pain.

Joint Structure

A few studies have looked at whether glucosamine or chondroitin can have beneficial effects on joint structure. Some but not all studies found evidence that chondroitin might help, but the improvements may be too small to make a difference to patients. There is little evidence that glucosamine has beneficial effects on joint structure.

Experts’ Recommendations

Experts disagree on whether glucosamine and chondroitin may help knee and hip osteoarthritis. The American College of Rheumatology (ACR) has recommended that people with knee or hip osteoarthritis not use glucosamine or chondroitin. But the recommendation was not a strong one, and the ACR acknowledged that it was controversial.

For Other Parts of the Body

Only a small amount of research has been done on glucosamine and chondroitin for osteoarthritis of joints other than the knee and hip. Because there have been only a few relatively small studies, no definite conclusions can be reached.

• Chondroitin for osteoarthritis of the hand
  A 6-month trial of chondroitin in 162 patients with severe osteoarthritis of the hand showed that it may improve pain and function.
• Glucosamine for osteoarthritis of the jaw
  One study of 45 patients with osteoarthritis of the jaw showed that those given glucosamine had less pain than those given ibuprofen. But another study, which included 59 patients with osteoarthritis of the jaw, found that those taking glucosamine did no better than those taking a placebo (pills that don’t contain the active ingredient).
• Glucosamine for chronic low-back pain and osteoarthritis of the spine
  A Norwegian trial involving 250 people with chronic low-back pain and osteoarthritis of the lower spine found that participants who received glucosamine fared the same at 6 months as those who received placebo.

What the Science Says About Safety and Side Effects

• No serious side effects have been reported in large, well-conducted studies of people taking glucosamine, chondroitin, or both for up to 3 years.
• However, glucosamine or chondroitin may interact with the anticoagulant (blood-thinning) drug warfarin (Coumadin).
• A study in rats showed that long-term use of moderately large doses of glucosamine might damage the kidneys. Although results from animal studies don’t always apply to people, this study does raise concern.
• Glucosamine might affect the way your body handles sugar, especially if you have diabetes or other blood sugar problems, such as insulin resistance or impaired glucose tolerance.

If you use dietary supplements, such as glucosamine and chondroitin, read and follow the label instructions, and recognize that “natural” does not always mean “safe.”

The U.S. Food and Drug Administration regulates dietary supplements, but the regulations for dietary supplements are different and less strict than those for prescription or over-the-counter drugs.

Some dietary supplements may interact with medications or pose risks if you have medical problems or are going to have surgery. Most dietary supplements have not been tested in pregnant women, nursing mothers, or children.

More To Consider

• If your joints hurt, see your health care provider. It’s important to find out what’s causing your joint pain. Some diseases that cause joint pain—such as rheumatoid arthritis—may need immediate treatment.
• If you take warfarin or have blood sugar problems, make sure you talk to your doctor about potential side effects if you are considering or taking glucosamine or chondroitin supplements.
• If you’re pregnant or nursing a child, it’s especially important to see your health care provider before taking any medication or supplement, including glucosamine or chondroitin.
• Help your health care providers give you better coordinated and safe care by telling them about all the health approaches you use. Give them a full picture of what you do to manage your health.

Chondromalacia, also called chondromalacia patellae, refers to softening and breakdown of the articular cartilage of the kneecap. This disorder happens most often in young adults and can be caused by:

• Injury.
• Overuse.
• Misalignment of the patella.
• Muscle weakness.

Instead of gliding smoothly across the lower end of the thigh bone, the kneecap rubs against it, roughening the cartilage underneath the kneecap. The damage may range from a slightly abnormal surface of the cartilage to a surface that has been worn away to the bone. Chondromalacia injury happens when a blow to the kneecap tears off either a small piece of cartilage or a large fragment containing a piece of bone, known as osteochondral fracture.

Your connective tissue supports many different parts of your body, such as your skin, eyes, and heart. It is like a "cellular glue" that gives your body parts their shape and helps keep them strong. It also helps some of your tissues do their work. It is made of many kinds of proteins. Cartilage and fat are types of connective tissue.

Over 200 disorders that impact connective tissue. There are different types:

• Genetic disorders, such as Ehlers-Danlos syndrome, Marfan syndrome, and osteogenesis imperfecta
• Autoimmune disorders, such as lupus and scleroderma
• Cancers, like some types of soft tissue sarcoma

Each disorder has its own symptoms and needs different treatment.

Your elbow joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the elbow joint move. When any of these structures is hurt or diseased, you have elbow problems.

Many things can make your elbow hurt. A common cause is tendinitis, an inflammation or injury to the tendons that attach muscle to bone. Tendinitis of the elbow is a sports injury, often from playing tennis or golf. You may also get tendinitis from overuse of the elbow.

Other causes of elbow pain include sprains, strains, fractures, dislocations, bursitis and arthritis. Treatment depends on the cause.

Elbow Joint

The elbow joint is a uniaxial hinge joint formed by the humeroulnar joint, the articulation between the trochlea of the humerus and the trochlear notch of the ulna. Also associated with the elbow are the humeroradial joint and the proximal radioulnar joint. All three of these joints are enclosed within a single articular capsule (image).

The articular capsule of the elbow is thin on its anterior and posterior aspects, but is thickened along its outside margins by strong intrinsic ligaments. These ligaments prevent side-to-side movements and hyperextension. On the medial side is the triangular ulnar collateral ligament. This arises from the medial epicondyle of the humerus and attaches to the medial side of the proximal ulna. The strongest part of this ligament is the anterior portion, which resists hyperextension of the elbow. The ulnar collateral ligament may be injured by frequent, forceful extensions of the forearm, as is seen in baseball pitchers. Reconstructive surgical repair of this ligament is referred to as Tommy John surgery, named for the former major league pitcher who was the first person to have this treatment.

The lateral side of the elbow is supported by the radial collateral ligament. This arises from the lateral epicondyle of the humerus and then blends into the lateral side of the annular ligament. The annular ligament encircles the head of the radius. This ligament supports the head of the radius as it articulates with the radial notch of the ulna at the proximal radioulnar joint. This is a pivot joint that allows for rotation of the radius during supination and pronation of the forearm.

Joint disorders are diseases or injuries that affect your joints. Injuries can happen because of overuse of a joint. Or you could have a sudden injury, such as an accident or a sports injury.

Your ankle bone and the ends of your two lower leg bones make up the ankle joint. Your ligaments, which connect bones to one another, stabilize and support it. Your muscles and tendons move it.

The most common ankle problems are sprains and fractures. A sprain is an injury to the ligaments. It may take a few weeks to many months to heal completely. A fracture is a break in a bone. You can also injure other parts of the ankle such as tendons, which join muscles to bone, and cartilage, which cushions your joints. Ankle sprains and fractures are common sports injuries.

If you feel pain and stiffness in your body or have trouble moving around, you might have arthritis. Most kinds of arthritis cause pain and swelling in your joints. Joints are places where two bones meet, such as your elbow or knee. Over time, a swollen joint can become severely damaged. Some kinds of arthritis can also cause problems in your organs, such as your eyes or skin.

Types of arthritis include

• Osteoarthritis is the most common type of arthritis. It's often related to aging or to an injury.
• Autoimmune arthritis happens when your body's immune system attacks healthy cells in your body by mistake. Rheumatoid arthritis is the most common form of this kind of arthritis.
• Juvenile arthritis is a type of arthritis that happens in children.
• Infectious arthritis is an infection that has spread from another part of the body to the joint.
• Psoriatic arthritis affects people with psoriasis.
• Gout is a painful type of arthritis that happens when too much uric acid builds up in the body. It often starts in the big toe.

A bursa is a small, fluid-filled sac that acts as a cushion between a bone and other moving parts, such as muscles, tendons, or skin. Bursitis occurs when a bursa becomes inflamed. People get bursitis by overusing a joint. It can also be caused by an injury. It usually occurs at the knee or elbow. Kneeling or leaning your elbows on a hard surface for a long time can make bursitis start. Doing the same kinds of movements every day or putting stress on joints increases your risk.

Symptoms of bursitis include pain and swelling. Your doctor will diagnose bursitis with a physical exam and tests such as x-rays and MRIs. He or she may also take fluid from the swollen area to be sure the problem isn't an infection.

Treatment of bursitis includes rest, pain medicines, or ice. If there is no improvement, your doctor may inject a drug into the area around the swollen bursa. If the joint still does not improve after 6 to 12 months, you may need surgery to repair damage and relieve pressure on the bursa.

Dislocations are joint injuries that force the ends of your bones out of position. The cause is often a fall or a blow, sometimes from playing a contact sport. You can dislocate your ankles, knees, shoulders, hips, elbows and jaw. You can also dislocate your finger and toe joints. Dislocated joints often are swollen, very painful and visibly out of place. You may not be able to move it.

A dislocated joint is an emergency. If you have one, seek medical attention. Treatment depends on which joint you dislocate and the severity of the injury. It might include manipulations to reposition your bones, medicine, a splint or sling, and rehabilitation. When properly repositioned, a joint will usually function and move normally again in a few weeks. Once you dislocate a shoulder or kneecap, you are more likely to dislocate it again. Wearing protective gear during sports may help prevent dislocations.

Your hip is the joint where your femur (thigh bone) meets your pelvis (hip bone). There are two main parts: a ball at the end of the femur, which fits in a socket in the pelvis. Your hip is known as a ball-and-socket joint. This is because you have a ball at the end of your femur, and it fits into a socket in your pelvis. This makes your hips very stable and allows for a wide range of motion. When they are healthy, it takes great force to hurt them. However, playing sports, running, overuse, or falling can sometimes lead to hip injuries such as:

• Strains
• Bursitis
• Dislocations
• Fractures (broken bones)

Certain diseases also lead to hip injuries or problems. Osteoarthritis can cause pain and limited motion. Osteoporosis of the hip causes weak bones that break easily. Both of these are common in older people.

Another problem is hip dysplasia, where the ball at the end of the femur is loose in the hip socket. It can cause hip dislocation. Babies who have hip dysplasia are usually born with it, but sometimes they develop it later.

Treatment for hip disorders may include rest, medicines, physical therapy, or surgery, including hip replacement.

Most kinds of arthritis cause pain and swelling in your joints. Joints are places where two bones meet, such as your elbow or knee. Infectious arthritis is an infection in the joint. The infection comes from a bacterial, viral, or fungal infection that spreads from another part of the body. Symptoms of infectious arthritis include

• Intense pain in the joint
• Joint redness and swelling
• Chills and fever
• Inability to move the area with the infected joint

One type of infectious arthritis is reactive arthritis. The reaction is to an infection somewhere else in your body. The joint is usually the knee, ankle, or toe. Sometimes, reactive arthritis is set off by an infection in the bladder, or in the urethra, which carries urine out of the body. In women, an infection in the vagina can cause the reaction. For both men and women, it can start with bacteria passed on during sex. Another form of reactive arthritis starts with eating food or handling something that has bacteria on it.

To diagnose infectious arthritis, your health care provider may do tests of your blood, urine, and joint fluid. Treatment includes medicines and sometimes surgery.

Juvenile arthritis (JA) is arthritis that happens in children. It causes joint swelling, pain, stiffness, and loss of motion. It can affect any joint, but is more common in the knees, hands, and feet. In some cases it can affect internal organs as well.

The most common type of JA that children get is juvenile idiopathic arthritis. There are several other forms of arthritis affecting children.

One early sign of JA may be limping in the morning. Symptoms can come and go. Some children have just one or two flare-ups. Others have symptoms that never go away. JA can cause growth problems and eye inflammation in some children.

No one knows exactly what causes JA. Most types are autoimmune disorders. This means that your immune system, which normally helps your body fight infection, attacks your body's own tissues.

JA can be hard to diagnose. Your health care provider may do a physical exam, lab tests, and x-rays. A team of providers usually treats JA. Medicines and physical therapy can help maintain movement and reduce swelling and pain. They may also help prevent and treat complications.

Your knee joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the knee joint move. When any of these structures is hurt or diseased, you have knee problems. Knee problems can cause pain and difficulty walking.

Knee problems are very common, and they occur in people of all ages. Knee problems can interfere with many things, from participation in sports to simply getting up from a chair and walking. This can have a big impact on your life.

The most common disease affecting the knee is osteoarthritis. The cartilage in the knee gradually wears away, causing pain and swelling.

Injuries to ligaments and tendons also cause knee problems. A common injury is to the anterior cruciate ligament (ACL). You usually injure your ACL by a sudden twisting motion. ACL and other knee injuries are common sports injuries.

Treatment of knee problems depends on the cause. In some cases your doctor may recommend knee replacement.