Mortality is increased in people with AS and circulatory disease is the most frequent cause of death. AS patients have an increased risk of 60% for cerebrovascular mortality, and an overall increased risk of 50% for vascular mortality. About one third of those with Ankylosing spondylitis have severe disease, which reduces life expectancy.

As increased mortality in ankylosing spondylitis is related to disease severity, factors negatively affecting outcomes include:

- Male sex

- Plus 3 of the following in the first 2 years of disease:

- Erythrocyte sedimentation rate (ESR) >30 mm/h

- Unresponsive to NSAIDs

- Limitation of lumbar spine range of motion

- Sausage-like fingers or toes

- Oligoarthritis

- Onset <16 years old

Arthritis mutilans' parent condition psoriatic arthritis leaves people with a mortality risk 60% higher than the general population, with premature death causes mirroring those of the general population, cardiovascular issues being most common. Life expectancy for people with psoriatic arthritis is estimated to be reduced by approximately 3 years.

The hunched position that often results from complete spinal fusion can have an effect on a person’s gait. Increased spinal kyphosis will lead to a forward and downward shift in center of mass (COM). This shift in COM has been shown to be compensated by increased knee flexion and ankle dorsiflexion. The gait of someone with ankylosing spondylitis often has a cautious pattern because they have decreased ability to absorb shock, and they cannot see the horizon.

It is not always certain why arthritis of the knee develops. Most physicians believe that it is a combination of factors that can include muscle weakness, obesity, heredity, joint injury or stress, constant exposure to the cold, and aging. Cartilage in the knee begins to break down and leaves the bones of the knee rubbing against each other as you walk. Persons who work in a place that applies repetitive stress on the knees are at a high risk of developing this condition. Bone deformities increase the risk for osteoarthritis of the knee since the joints are already malformed and may contain defective cartilage. Having gout, rheumatoid arthritis, Paget's disease of bone or septic arthritis can increase your risk of developing osteoarthritis.

Some physicians and most podiatrist believe that Pes Planus (flat feet) cause increased rates and earlier incidence of knee osteoarthritis. In a study of army recruits with moderate to severe flat feet, the results showed that they had almost double the rate of knee arthritis when compared to recruits with normal arches.

The cause of JIA remains a mystery. However, the disorder is autoimmune — meaning that the body's own immune system starts to attack and destroy cells and tissues (particularly in the joints) for no apparent reason. The immune system is thought to be provoked by changes in the environment, in combination with mutations in many associated genes and/or other causes of differential expression of genes. Experimental studies have shown that certain mutated viruses may be able to trigger JIA. The disease appears to be more common in girls, and the disease is most common in Caucasians.

Associated factors that may worsen or have been linked to rheumatoid arthritis include:

- Genetic predisposition; When one family member has been diagnosed with rheumatoid arthritis or another autoimmune disorder, the chances are higher that other family members or siblings may also develop arthritis.

- Females are more likely to develop rheumatoid arthritis than males at all ages.

- A strong belief is held that psychological stress may worsen the symptoms of rheumatoid arthritis. However, when the emotional stress is under control, the arthritis symptoms do not always disappear, suggesting that the association is not straightforward.

- Though no distinct immune factor has been isolated as a cause of arthritis, some experts believe that the triggering factor may be something like a virus which then disappears from the body after permanent damage is done.

- Because rheumatoid arthritis is more common in women, perhaps sex hormones may play a role in causing or modulating arthritis. Unfortunately, neither sex hormone deficiency nor replacement has been shown to improve or worsen arthritis.

The cause of JIA, as the word "idiopathic" suggests, is unknown and an area of active research. Current understanding of JIA suggests that it arises in a genetically susceptible individual due to environmental factors.

Worldwide prevalence of spondyloarthropathy is approximately 1.9%.

There are established epigenetic and environmental risk factors for RA. Smoking is an established risk factor for RA in Caucasian populations, increasing the risk three times compared to non-smokers, particularly in men, heavy smokers, and those who are rheumatoid factor positive. Modest alcohol consumption may be protective.

Silica exposure has been linked to RA.

RA reduces lifespan on average from three to twelve years. According to the UK's National Rheumatoid Arthritis Society, Young age at onset, long disease duration, the concurrent presence of other health problems (called co-morbidity), and characteristics of severe RA—such as poor functional ability or overall health status, a lot of joint damage on x-rays, the need for hospitalisation or involvement of organs other than the joints—have been shown to associate with higher mortality". Positive responses to treatment may indicate a better prognosis. A 2005 study by the Mayo Clinic noted that RA sufferers suffer a doubled risk of heart disease, independent of other risk factors such as diabetes, alcohol abuse, and elevated cholesterol, blood pressure and body mass index. The mechanism by which RA causes this increased risk remains unknown; the presence of chronic inflammation has been proposed as a contributing factor. It is possible that the use of new biologic drug therapies extend the lifespan of people with RA and reduce the risk and progression of atherosclerosis. This is based on cohort and registry studies, and still remains hypothetical. It is still uncertain whether biologics improve vascular function in RA or not. There was an increase in total cholesterol and HDLc levels and no improvement of the atherogenic index.

Arthritis mutilans occurs mainly in people who have pre-existing psoriatic arthritis, but can occur, if less often, in advanced rheumatoid arthritis; it can also occur independently. Psoriasis and psoriatic arthritis are interrelated heritable diseases, occurring with greater heritable frequency than rheumatoid arthritis, primary Sjogren's syndrome and thyroid disease. Psoriasis affects 2–3% of the Caucasian population, and psoriatic arthritis affects up to 30% of those. Arthritis mutilans presents in about 5–16% of psoriatic arthritis cases, involves osteolysis of the DIP and PIP joints, and can include bone edema, bone erosions, and new bone growth. Most often psoratic arthitis is seronegative for rheumatoid factor (occurring in only about 13% of cases), and has genetic risk factor overlap with ankylosing spondylitis with HLA-B27, IL-23R77, and IL-1, however, as of 2016, immunopathogenesis is unclear.

Arthritis is the most common cause of disability in the USA. More than 20 million individuals with arthritis have severe limitations in function on a daily basis. Absenteeism and frequent visits to the physician are common in individuals who have arthritis. Arthritis can make it very difficult for individuals to be physically active and some become home bound.

It is estimated that the total cost of arthritis cases is close to $100 billion of which almost 50% is from lost earnings. Each year, arthritis results in nearly 1 million hospitalizations and close to 45 million outpatient visits to health care centers.

Decreased mobility, in combination with the above symptoms, can make it difficult for an individual to remain physically active, contributing to an increased risk of obesity, high cholesterol or vulnerability to heart disease. People with arthritis are also at increased risk of depression, which may be a response to numerous factors, including fear of worsening symptoms.

JIA occurs in both sexes, but like other rheumatological diseases, is more common in females. Symptoms onset is frequently dependent on the subtype of JIA and is from the preschool years to the early teenaged years.

Sacroiliitis is a condition caused by inflammation within the sacroiliac joint. This joint is located where the base of the spine, known as the sacrum, and the pelvis, known as the ilium, intersect. "Itis" is a latin term denoting inflammation.

Since sacroiliitis can describe any type of inflammation found within the sacroiliac joint, there can be a number of issues that cause it. These include:

- Degenerative arthritis, or osteoarthritis of the spine, can cause degeneration within the sacroiliac joints and lead to inflammation and joint pain.

- Any form of spondyloarthropathies, which includes ankylosing spondylitis, psoriatic arthritis, reactive arthritis or arthritis related to inflammatory bowel diseases, including ulcerative colitis or Crohn's disease.

- Pregnancy can cause inflammation as a result of the widening and stretching of the sacroiliac joints to prepare for childbirth. Additionally, the added weight carried during childbearing can put an extra amount of stress on the SI joints, leading to abnormal wear.

- Traumatic injury such as a fall or car crash that affects the lower back, hips, buttocks or legs.

- Though rare, infection within the sacroiliac joints or another part of the body, such as a urinary tract infection, can cause inflammation.

There are several diseases where joint pain is primary, and is considered the main feature. Generally when a person has "arthritis" it means that they have one of these diseases, which include:

- Osteoarthritis

- Rheumatoid arthritis

- Gout and pseudo-gout

- Septic arthritis

- Ankylosing spondylitis

- Juvenile idiopathic arthritis

- Still's disease

Joint pain can also be a symptom of other diseases. In this case, the arthritis is considered to be secondary to the main disease; these include:

- Psoriasis (Psoriatic arthritis)

- Reactive arthritis

- Ehlers-Danlos Syndrome

- Haemochromatosis

- Hepatitis

- Lyme disease

- Sjogren's disease

- Hashimoto's thyroiditis

- Celiac disease

- Non-celiac gluten sensitivity

- Inflammatory bowel disease (including Crohn's disease and ulcerative colitis)

- Henoch–Schönlein purpura

- Hyperimmunoglobulinemia D with recurrent fever

- Sarcoidosis

- Whipple's disease

- TNF receptor associated periodic syndrome

- Granulomatosis with polyangiitis (and many other vasculitis syndromes)

- Familial Mediterranean fever

- Systemic lupus erythematosus

An "undifferentiated arthritis" is an arthritis that does not fit into well-known clinical disease categories, possibly being an early stage of a definite rheumatic disease.

Sacroiliitis (say-kroe-il-e-I-tus) is a medical condition caused by any inflammation within one, or both, of the sacroiliac joints. Sacroiliitis is a feature of spondyloarthropathies, such as axial spondyloarthritis (including ankylosing spondylitis), psoriatic arthritis, reactive arthritis or arthritis related to inflammatory bowel diseases, including ulcerative colitis or Crohn's disease. It is also the most common presentation of arthritis from brucellosis.

About 25% of people over the age of 50 experience knee pain from degenerative knee diseases.

Jaccoud arthropathy (JA), Jaccoud deformity or Jaccoud's arthopathy is a chronic non-erosive reversible joint disorder that may occur after repeated bouts of arthritis. It is caused by inflammation of the joint capsule and subsequent fibrotic retraction, causing ulnar deviation of the fingers, through metacarpophalangeal joint (MCP) subluxation, primarily of the ring and little-finger. Joints in the feet, knees and shoulders may also get affected. It is commonly associated with systemic lupus erythematosus (SLE), and occurs in roughly 5% of all cases.

When associated with rheumatic fever it is also called chronic post–RF arthropathy.

Originally thought to be associated only with rheumatic fever, it has since been shown to occur also in SLE, Sjögren syndrome, scleroderma, dermatomyositis, psoriatic arthritis, vasculitis, ankylosing spondylitis, mixed connective tissue disease, and pyrophosphate deposition disease. It is distinct from bone erosion which is commonly associated with rheumatic arthritis, and also distinct from mild deforming arthropathy which is associated with SLE. There have also been cases of non-rheumatic JA associated with Lyme disease, HIV-infection and a number of other conditions.

Treatment focuses toward alleviating pain and in maintaining functionality of the affected joints through use of nonsteroidal anti-inflammatory drugs, corticosteroids, antimalarial drugs and physiotherapy. Surgery is also a possibility, with osteotomy or stabilization with Kirschner intramedullary wire. Tendon relocation, however, has been shown to only work in 30% of cases. The condition is named after the French 19th century physician Sigismond Jaccoud.

Many rheumatic disorders of chronic, intermittent joint pain have historically been caused by infectious diseases. Their etiology was unknown until the 20th century and not treatable, like Lyme disease (in the Northern and Northeastern US), coccidiomycosis or Valley fever (in the Western US), and Chikungunya in India and a myriad of causes for postinfectious arthritis also known as reactive arthritis like, for example, the once very common rheumatic fever after Group A Streptococcus infection up to the rare Whipple's disease.

Major rheumatic disorders currently recognized include

- Back pain

- Bursitis/Tendinitis of the shoulder, wrist, biceps, leg, knee cap (patella), ankle, hip, and Achilles tendon

- Capsulitis

- Neck pain

- Osteoarthritis

- Palindromic rheumatism has been theorized to be a form of rheumatoid arthritis.

Although these disorders probably have little in common in terms of their epidemiology, they do share three characteristics: they cause chronic, often intermittent pain, they are difficult to treat and are collectively very common.

Rheumatic diseases caused by autoimmunity include:

- Ankylosing spondylitis

- relapsing polychondritis

- systemic lupus erythematosus

- rheumatoid arthritis

- gout, inflammatory arthritis, pseudogout

- juvenile arthritis

- Sjögren syndrome

- scleroderma

- Polymyositis

- Dermatomyositis

- Behçet's disease

- Psoriatic arthritis

Spondyloarthropathy or spondyloarthrosis refers to any joint disease of the vertebral column. As such, it is a class or category of diseases rather than a single, specific entity. It differs from spondylopathy, which is a disease of the vertebra itself. However, many conditions involve both spondylopathy and spondyloarthropathy.

Spondyloarthropathy with inflammation is called axial spondyloarthritis. In the broadest sense, the term spondyloarthropathy includes joint involvement of vertebral column from any type of joint disease, including rheumatoid arthritis and osteoarthritis, but the term is often used for a specific group of disorders with certain common features, the group often being termed specifically seronegative spondylarthropathies. They have an increased incidence of HLA-B27, as well as negative rheumatoid factor and ANA. Enthesopathy is also sometimes present in association with seronegative.

Non-vertebral signs and symptoms of degenerative or other not-directly-infected inflammation, in the manner of spondyloarthropathies, include asymmetric peripheral arthritis (which is distinct from rheumatoid arthritis), arthritis of the toe interphalangeal joints, sausage digits, Achilles tendinitis, plantar fasciitis, costochondritis, iritis, and mucocutaneous lesions. However, lower back pain is the most common clinical presentation of the causes of spondyloarthropoathies; this back pain is unique because it decreases with activity.

Because women may be underdiagnosed, the exact incidence of reactive arthritis is difficult to estimate. A few studies have been completed, though. In Norway between 1988 and 1990, the incidence was 563.3 cases per 100,000 for chlamydia-induced reactive arthritis and 5 cases per 100,000 for that induced by enteric bacteria. In 1978 in Finland, the annual incidence was found to be 5835.7 per 100,000.

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.

25% of cases progress to severe destructive arthritis. In the United States and Canada, mortality is estimated at about 4% and in Europe, mortality is estimated at 21.7%.

The exact cause is unknown. Mechanical factors, dietary and long term use of some antidepressants may be of significance. There is a correlation between these factors but not a cause or effect. The distinctive radiological feature of DISH is the continuous linear calcification along the antero-medial aspect of the thoracic spine. The disease is usually found in people in their 60s and above, and is extremely rare in people in their 40s and 30s. The disease can spread to any joint of the body, affecting the neck, shoulders, ribs, hips, pelvis, knees, ankles, and hands. The disease is not fatal, however some associated complications can lead to death. Complications include paralysis, dysphagia (the inability to swallow), and pulmonary infections. Although DISH manifests in a similar manner to ankylosing spondylitis, these two are totally separate diseases. Ankylosing spondylitis is a genetic disease with identifiable marks, and affects organs. DISH has no indication of a genetic link, and does not affect organs other than the lungs, which is only indirect due to the fusion of the rib cage.

Long term treatment of acne with vitamin derived retinoids, such as etretinate and acitretin, have been associated with "extraspinal" hyperostosis.

Reactive arthritis may be self-limiting, frequently recurring, chronic or progressive. Most patients have severe symptoms lasting a few weeks to six months. 15 to 50 percent of cases involve recurrent bouts of arthritis. Chronic arthritis or sacroiliitis occurs in 15–30 percent of cases. Repeated attacks over many years are common, and patients sometimes end up with chronic and disabling arthritis, heart disease, amyloid deposits, ankylosing spondylitis, immunoglobulin A nephropathy, cardiac conduction abnormalities, or aortitis with aortic regurgitation. However, most people with reactive arthritis can expect to live normal life spans and maintain a near-normal lifestyle with modest adaptations to protect the involved organs.

There has long been said to be a link between "rheumatic" pain and the weather. There appears to be no firm evidence in favour or against; a 1995 questionnaire given to 557 people by A. Naser and others at the Brigham and Women's Hospital's Pain Management Center concludes that "changes in barometric pressure are the main link between weather and pain. Low pressure is generally associated with cold, wet weather and an increase in pain. Clear, dry conditions signal high pressure and a decrease in pain."

Axial spondyloarthritis (also often referred to as axSpA) is a chronic, autoinflammatory disease predominantly affecting the axial skeleton (sacroiliac joints and spine). The most known member of the axial spondyloarthritis disease family is ankylosing spondylitis. Axial spondyloarthritis is an umbrella term that has been introduced in the year 2009 to characterize a diverse disease family that share clinical and genetic features, such as the involvement of the axial skeleton. The expression was introduced in order to unify (1) less severe forms of spondylitis, (2) the early phase of ankylosing spondylitis as well as (3) ankylosing spondylitis itself into one term.