Rheumatoid arthritis (RA), is a chronic inflammatory disorder that most typically begins in the small joints in your hands and feet. However, the course can begin with other nonspecific symptoms, such as tiredness. After attacking the smaller joints of the body, RA often progresses into larger joints, such as the shoulders, elbows, hips, and knees. Symptoms include joint pain, swelling, red and puffy hands, and fatigue. RA degrades the lining of the joints and causes swelling that is painful and can lead to joint deformity in the affected joints. Rheumatoid arthritis tends to worsen over time. Though there is no permanent cure, the course of the disease can be modified so that the damage is less, the patient is more comfortable and the patient can continue to engage in and enjoy daily activities. Treatment is most effective when it is begun as early as possible, before the process of deformity is far progressed, but some relief can be offered by treatment at any stage.

Osteoarthritis is a joint disease that causes the cushion layer between one's bones, or cartilage to wear away. It is also called degenerative joint disease. Symptoms are similar to RA and develop in the same slow manner. They include pain, tenderness in the knee, stiffness when standing or walking, loss of flexibility, and grating sensations that can be heard when the knee joint is used.

Osteoarthritis in the knee begins with the gradual deterioration of cartilage. Without the protective cartilage, the bones begin to rub together, causing pain, loss of mobility, and deformity. It affects approximately 16 million people. The majority of arthritis cases involving the knee are osteoarthritic cases.

One knee may appear larger than the other. Puffiness around the bony parts of the knee appear prominent when compared with the other knee.

Osteoarthritis knee pain usually occurs while the joint is bearing weight, so the pain typically subsides with rest; some patients suffer severe pain, while others report no discomfort. Even if one knee is much larger than the other, pain is not guaranteed.

Transient synovitis causes pain in the hip, thigh, groin or knee on the affected side. There may be a limp (or abnormal crawling in infants) with or without pain. In small infants, the presenting complaint can be unexplained crying (for example, when changing a diaper). The condition is nearly always limited to one side. The pain and limp can range from mild to severe.

Some children may have a slightly raised temperature; high fever and general malaise point to other, more serious conditions. On clinical examination, the child typically holds the hip slightly bent, turned outwards and away from the middle line (flexion, external rotation and abduction). Active and passive movements may be limited because of pain, especially abduction and internal rotation. The hip can be tender to palpation. The log roll test involves gently rotating the entire lower limb inwards and outwards with the patient on his back, to check when muscle guarding occurs. The unaffected hip and the knees, ankles, feet and spine are found to be normal.

The main symptom is pain, causing loss of ability and often stiffness. "Pain" is generally described as a sharp ache or a burning sensation in the associated muscles and tendons, and is typically made worse by prolonged activity and relieved by rest. Stiffness is most common in the morning, and typically lasts less than thirty minutes after beginning daily activities, but may return after periods of inactivity. Osteoarthritis can cause a crackling noise (called "crepitus") when the affected joint is moved or touched and people may experience muscle spasms and contractions in the tendons. Occasionally, the joints may also be filled with fluid. Some people report increased pain associated with cold temperature, high humidity, or a drop in barometric pressure, but studies have had mixed results.

Osteoarthritis commonly affects the hands, feet, spine, and the large weight-bearing joints, such as the hips and knees, although in theory, any joint in the body can be affected. As osteoarthritis progresses, movement patterns (such as gait), are typically affected. Osteoarthritis is the most common cause of a joint effusion of the knee.

In smaller joints, such as at the fingers, hard bony enlargements, called Heberden's nodes (on the distal interphalangeal joints) or Bouchard's nodes (on the proximal interphalangeal joints), may form, and though they are not necessarily painful, they do limit the movement of the fingers significantly. Osteoarthritis of the toes may be a factor causing formation of bunions, rendering them red or swollen.

Juvenile rheumatoid arthritis presents gradually with early morning stiffness, fatigue, and weight loss.

Transient synovitis is a reactive arthritis of the hip of unknown cause. People are usually able to walk and may have a low grade fever. They usually look clinically nontoxic or otherwise healthy. It may only be diagnosed once all other potential serious causes are excluded. With symptomatic care it usually resolves over one week.

Those with hypermobile joints are more likely to have fibromyalgia, mitral valve prolapse, and anxiety disorders such as panic disorder.

Transient synovitis of the hip (also called toxic synovitis; see below for more synonyms) is a self-limiting condition in which there is an inflammation of the inner lining (the synovium) of the capsule of the hip joint. The term irritable hip refers to the syndrome of acute hip pain, joint stiffness, limp or non-weightbearing, indicative of an underlying condition such as transient synovitis or orthopedic infections (like septic arthritis or osteomyelitis). In everyday clinical practice however, irritable hip is commonly used as a synonym for transient synovitis. It should not be confused with sciatica, a condition describing hip and lower back pain much more common to adults than transient synovitis but with similar signs and symptoms.

Transient synovitis usually affects children between three and ten years old (but it has been reported in a 3-month-old infant and in some adults). It is the most common cause of sudden hip pain and limp in young children. Boys are affected two to four times as often as girls. The exact cause is unknown. A recent viral infection (most commonly an upper respiratory tract infection) or a trauma have been postulated as precipitating events, although these are reported only in 30% and 5% of cases, respectively.

Transient synovitis is a diagnosis of exclusion. The diagnosis can be made in the typical setting of pain or limp in a young child who is not generally unwell and has no recent trauma. There is a limited range of motion of the hip joint. Blood tests may show mild inflammation. An ultrasound scan of the hip joint can show a fluid collection (effusion). Treatment is with nonsteroidal anti-inflammatory drugs and limited weight-bearing. The condition usually clears by itself within seven to ten days, but a small group of patients will continue to have symptoms for several weeks. The recurrence rate is 4–17%, most of which is in the first six months.

In general, pigmented villonodular synovitis often manifests initially as sudden onset, unexplained joint swelling and pain; the joint swelling is disproportionate to the amount of pain the patient feels at first. Decreased motion and increased pain occur as the disorder progresses as well as locking of the joint. The localized form often manifests initially as a painless, slow-growing mass and progresses to the other common symptoms of PVNS. The swelling often feels warm to the touch. Diffuse PVNS symptoms are often confused with those of Rheumatoid arthritis. While pigmented villonodular synovitis can occur in both pediatric and geriatric patients, it is more common with ages 20–50.

Osteoarthritis (OA) is a type of joint disease that results from breakdown of joint cartilage and underlying bone. The most common symptoms are joint pain and stiffness. Initially, symptoms may occur only following exercise, but over time may become constant. Other symptoms may include joint swelling, decreased range of motion, and when the back is affected weakness or numbness of the arms and legs. The most commonly involved joints are those near the ends of the fingers, at the base of the thumb, neck, lower back, knee, and hips. Joints on one side of the body are often more affected than those on the other. Usually the symptoms come on over years. It can affect work and normal daily activities. Unlike other types of arthritis, only the joints are typically affected.

Causes include previous joint injury, abnormal joint or limb development, and inherited factors. Risk is greater in those who are overweight, have one leg of a different length, and have jobs that result in high levels of joint stress. Osteoarthritis is believed to be caused by mechanical stress on the joint and low grade inflammatory processes. It develops as cartilage is lost and the underlying bone becomes affected. As pain may make it difficult to exercise, muscle loss may occur. Diagnosis is typically based on signs and symptoms, with medical imaging and other tests occasionally used to either support or rule out other problems. In contrast to rheumatoid arthritis, which is primarily an inflammatory condition, in osteoarthritis, the joints do not typically become hot or red.

Treatment includes exercise, efforts to decrease joint stress, support groups, and pain medications. Efforts to decrease joint stress include resting and the use of a cane. Weight loss may help in those who are overweight. Pain medications may include paracetamol (acetaminophen) as well as NSAIDs such as naproxen or ibuprofen. Long-term opioid use is generally discouraged due to lack of information on benefits as well as risks of addiction and other side effects. If pain interferes with normal life despite other treatments, joint replacement surgery may help. An artificial joint typically lasts 10 to 15 years.

Osteoarthritis is the most common form of arthritis affecting about 237 million (3.3%) of the population. Among those over 60 years old, about 10% of males and 18% of females are affected. It is the cause of about 2% of years lived with disability. In Australia, about 1.9 million people are affected, and in the United States, 30 to 52.5 million people are affected. It becomes more common in both sexes as people become older.

Hypermobility generally results from one or more of the following:

- Abnormally shaped ends of one or more bones at a joint

- A Type 1 collagen or other connective tissue defect (as found in Ehlers-Danlos syndrome, Loeys-Dietz syndrome and Marfan syndrome) resulting in weakened ligaments/ligamentous laxity, muscles and tendons. This same defect also results in weakened bones, which may result in osteoporosis and fractures.

- Abnormal joint proprioception (an impaired ability to locate body parts in space and/or monitor an extended joint)

These abnormalities cause abnormal joint stress, meaning that the joints can wear out, leading to osteoarthritis.

The condition tends to run in families, suggesting a genetic basis for at least some forms of hypermobility. The term "double jointed" is often used to describe hypermobility; however, the name is a misnomer and should not be taken literally, as hypermobile joints are not doubled/extra in any sense.

Most people have hypermobility with no other symptoms. Approximately 5% of the healthy population have one or more hypermobile joints. However, people with "joint hypermobility syndrome" are subject to many difficulties. For example, their joints may be easily injured, be more prone to complete dislocation due to the weakly stabilized joint and they may develop problems from muscle fatigue (as muscles must work harder to compensate for weakness in the ligaments that support the joints). Hypermobility syndrome can lead to chronic pain or even disability in severe cases. Musical instrumentalists with hypermobile fingers may have difficulties when fingers collapse into the finger locking position. Or, conversely, they may display superior abilities due to their increased range of motion for fingering, such as in playing a violin or cello.

Hypermobility may be symptomatic of a serious medical condition, such as Stickler Syndrome, Ehlers-Danlos syndrome, Marfan syndrome, Loeys-Dietz syndrome, rheumatoid arthritis, osteogenesis imperfecta, lupus, polio, Down syndrome, morquio syndrome, cleidocranial dysostosis or myotonia congenita.

Hypermobility has been associated with chronic fatigue syndrome and fibromyalgia. Hypermobility causes physical trauma (in the form of joint dislocations, joint subluxations, joint instability, sprains, etc.). These conditions often, in turn, cause physical and/or emotional trauma and are possible triggers for conditions such as fibromyalgia.

Women with hypermobility may experience particular difficulties when pregnant. During pregnancy, the body releases certain hormones that alter ligament physiology, easing the stretching needed to accommodate fetal growth as well as the birthing process. The combination of hypermobility and pregnancy-related pelvic girdle during pregnancy can be debilitating. The pregnant woman with hypermobile joints will often be in significant pain as muscles and joints adapt to the pregnancy. Pain often inhibits such women from standing or walking during pregnancy. The pregnant patient may be forced to use a bedpan and/or a wheelchair during pregnancy and may experience permanent disability.

Symptoms of hypermobility include a dull but intense pain around the knee and ankle joints and the soles of the feet. The pain and discomfort affecting these body parts can be alleviated by using custom orthoses.

Common deformities of the knee include:

- Genu varum

- Genu valgum

- Genu recurvatum (Knee hyperextension)

- Knee flexion deformity

- Bipartite patella

Referred pain is that pain perceived at a site different from its point of origin but innervated by the same spinal segment. Sometimes knee pain may be related to another area from body. For example, knee pain can come from ankle, foot, hip joints or lumbar spine.

Repeated, periodic joint effusions of the knee. Usually one knee is affected but sometimes both knees. Other joints may also be involved along with the knee. Effusions are large, restricting range of motion but significant pain is not a feature. There is usually stiffness. Tenderness of the joint may or may not be present. Aspirated synovial fluid is usually sterile but will sometimes show elevated cell count (>100 cells/mL) with 50% being polymorphonuclear leukocytes.

Onset of effusions are sudden with no particular trigger or stimulus. Each episode lasts for a few days to about a week and recurs in cycles of 7 to 11 days with extremes of 3 days to 30 days also reported. Sometimes the joint may begin to swell again as soon as the fluid has subsided. Where both knees are affected concurrently, as one joint ceases to swell the other may become involved.

The cycle of joints swellings have been reported as being very regular, even predictable. This has been a characteristic feature of IH in many case reports. However, over the longer-term especially, these cycles of effusion and recovery may not be as constant as first reported.

In women, many cases seem to begin at puberty. Episodes of knee swelling may coincide the menstrual cycle. In nearly all case reports, pregnancy seems to suppress the condition but after birth, during lactation, it returns.

In the main, patients are mostly free of other symptoms. Fever is rare. There no signs of local inflammation or lymphatic involvement. Laboratory tests are generally normal or within reference limits.

Bursitis commonly affects superficial bursae. These include the subacromial, prepatellar, retrocalcaneal, and pes anserinus bursae of the shoulder, knee, heel and shin, etc. (see below). Symptoms vary from localized warmth and erythema to joint pain and stiffness, to stinging pain that surrounds the joint around the inflamed bursa. In this condition, the pain usually is worse during and after activity, and then the bursa and the surrounding joint becomes stiff the next morning.

The onset of the condition is usually gradual, although some cases may appear suddenly following trauma.

- Knee pain - the most common symptom is diffuse peripatellar pain (vague pain around the kneecap) and localized retropatellar pain (pain focused behind the kneecap). Affected individuals typically have difficulty describing the location of the pain, and may place their hands over the anterior patella or describe a circle around the patella (the "circle sign"). Pain is usually initiated when load is put on the knee extensor mechanism, e.g. ascending or descending stairs or slopes, squatting, kneeling, cycling, running or prolonged sitting with flexed (bent) knees. The latter feature is sometimes termed the "movie sign" or "theatre sign" because individuals might experience pain while sitting to watch a film or similar activity. The pain is typically aching with occasional sharp pains.

- Crepitus (joint noises) may be present

- Giving-way of the knee may be reported

The primary symptom of prepatellar bursitis is the swelling of the area around the kneecap. It generally does not produce a significant amount of pain unless pressure is applied directly to the swelling. The area of swelling may be red (erythema), warm to the touch, or surrounded by cellulitis, particularly if the area has become infected. In such cases, the bursitis is often accompanied by fever. Unlike arthritis, prepatellar bursitis generally does not affect the range of motion of the knee, though it may cause some discomfort when the knee is completely flexed. Flexion and extension of the knee may cause crepitus.

PVNS is locally aggressive and can spread to surrounding tissues, causing bone erosion and tissue damage. If not treated early, it can spread to areas outside the joint, and potentially cause permanent loss of range as well as intense pain. The disorder also has, on average, a 45% rate of recurrence.

The condition is usually characterized by a sudden onset of knee pain, worse at night. Examination reveals tenderness of the medial femoral condyle, joint effusion, and occasional locking of the knee joint.

Chondromalacia patellae (also known as CMP) is inflammation of the underside of the patella and softening of the cartilage.

The cartilage under the kneecap is a natural shock absorber, and overuse, injury, and many other factors can cause increased deterioration and breakdown of the cartilage. The cartilage is no longer smooth and therefore movement and use is painful. While it often affects young individuals engaged in active sports, it also afflicts older adults who overwork their knees.

"Chondromalacia patellae" is sometimes used synonymously with patellofemoral pain syndrome. However, there is general consensus that "patellofemoral pain syndrome" applies only to individuals without cartilage damage.

Chondromalacia patellae is a term sometimes treated synonymously with PFPS. However, there is general consensus that PFPS applies only to individuals without cartilage damage, thereby distinguishing it from chondromalacia patellae, a condition characterized by softening of the patellar articular cartilage. Despite this academic distinction, the diagnosis of PFPS is typically made clinically, based only on the history and physical examination rather than on the results of any medical imaging. Therefore, it is unknown whether most persons with a diagnosis of PFPS have cartilage damage or not, making the difference between PFPS and chondromalacia theoretical rather than practical. It is thought that only some individuals with anterior knee pain will have true chondromalacia patellae.

Trauma from ligamentous, osseous or meniscal injuries can result in an effusion. These are often hemarthrosis or bloody effusions.

Bursitis is the inflammation of one or more bursae (small sacs) of synovial fluid in the body. They are lined with a synovial membrane that secretes a lubricating synovial fluid. There are more than 150 bursae in the human body. The bursae rest at the points where internal functionaries, such as muscles and tendons, slide across bone. Healthy bursae create a smooth, almost frictionless functional gliding surface making normal movement painless. When bursitis occurs, however, movement relying on the inflamed bursa becomes difficult and painful. Moreover, movement of tendons and muscles over the inflamed bursa aggravates its inflammation, perpetuating the problem. Muscle can also be stiffened.