Increased risk of developing knee and hip osteoarthritis was found in those who:

- work with manual handling (e.g. lifting)

- have physically demanding work

- walk at work

- have climbing tasks at work (e.g. climb stairs or ladders)

Increased risk of developing hip osteoarthritis over time was found among those who work in bent or twisted positions.

Increased risk of knee osteoarthritis was found in those who:

- work in a kneeling or squatting position

- experience heavy lifting in combination with a kneeling or squatting posture

- work standing up

A number of studies have shown that there is a greater prevalence of the disease among siblings and especially identical twins, indicating a hereditary basis. Although a single factor is not generally sufficient to cause the disease, about half of the variation in susceptibility has been assigned to genetic factors.

As early human ancestors evolved into bipeds, changes occurred in the pelvis, hip joint and spine which increased the risk of osteoarthritis. Additionally genetic variations that increase the risk were likely not selected against because usually problems only occur after reproductive success.

The development of osteoarthritis is correlated with a history of previous joint injury and with obesity, especially with respect to knees. Since the correlation with obesity has been observed not only for knees but also for non-weight bearing joints and the loss of body fat is more closely related to symptom relief than the loss of body weight, it has been suggested that there may be a metabolic link to body fat as opposed to just mechanical loading.

Changes in sex hormone levels may play a role in the development of osteoarthritis as it is more prevalent among post-menopausal women than among men of the same age. A study of mice found natural female hormones to be protective while injections of the male hormone dihydrotestosterone reduced protection.

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.

55% of facet syndrome cases occur in cervical vertebrae, and 31% in lumbar. Facet syndrome can progress to spinal osteoarthritis, which is known as spondylosis. Pathology of the C1-C2 (atlantoaxial) joint, the most mobile of all vertebral segments, accounts for 4% of all spondylosis.

Like many other joints throughout the human body, facets can experience natural degeneration from constant use. Over time, the cartilage within the joints can naturally begin to wear out, allowing it to become thin or disappear entirely which, in turn, allows the conjoining vertebrae to rub directly against one another with little or no lubricant or separation. A result of this rubbing is often swelling, inflammation or other painful symptoms.

Over time, the body will naturally respond to the instability within the spine by developing bone spurs, thickened ligaments or even cysts that can press up against or pinch the sensitive nerve roots exiting the spinal column.

While primarily caused through natural wear and tear, advanced facet syndrome can also occur as a result of injury to the spine, degenerative disease or lifestyle choices. These causes can include:

- An unexpected, traumatic event such as a car accident, significant fall or high impact sports injury.

- Osteoarthritis

- Spondylolisthesis

- Obesity

- Smoking

- Malnutrition

- Lack of physical exercise or daily activity

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

Spondylitis is an inflammation of the vertebra. It is a form of spondylopathy. In many cases spondylitis involves one or more vertebral joints as well, which itself is called spondylarthritis.

Pott's disease is a tuberculous disease of the vertebrae marked by stiffness of the vertebral column, pain on motion, tenderness on pressure, prominence of certain vertebral spines, and occasionally abdominal pain, abscess formation, and paralysis.

Ankylosing spondylitis is an inflammatory disease involving the spine and sacroiliac joints, and is therefore also a form of spondylarthritis.

A combination of spondylitis and inflammation of the intervertebral disc space is termed a spondylodiscitis.

Spondylitis is one of the most common causes of back and neck pain, and results from inflammation of the vertebral joints. The condition is often not detected until it has fully developed and is causing pain. The pain is usually concentrated around the cervical region of the neck, shoulder and lower spine, with downward-moving stinging pain. Types of spondylitis include: cervical spondylitis – which affects the cervical spine, causing pain to spread the back of the neck; lumbar spondylitis – which causes pain in the lumbar region; and ankylosing spondylitis- which is primarily a disease that affects the sacroiliac joints, causing stiffness in the neck, jaw, shoulders, hips and knees.

Some of the diseases of cause of knee pain include the following:

- Knee osteoarthritis

- Chondromalacia patella

- Baker's cyst

- Meniscal cyst

- Discoid meniscus

- Osgood-Schlatter disease

- Larsen-Johansson disease

- Knee rheumatoid arthritis

- Osteochondritis dissecans disease

- Synovial chondromatosis disease

- Tumors

- Ankylosing spondylitis

- Reactive arthritis

- Tuberculosis arthritis

- Septic arthritis ("Pyogenic arthritis")

- Osteomyelitis

- Hemophilic arthritis

- Gout (Gouty arthritis)

- Neuroma

Causes of the swelling can include arthritis, injury to the ligaments of the knee, or an accident after which the body's natural reaction is to surround the knee with a protective fluid. There could also be an underlying disease or condition. The type of fluid that accumulates around the knee depends on the underlying disease, condition or type of traumatic injury that caused the excess fluid. The swelling can, in most cases, be easily cured.

Underlying diseases may include

- Knee osteoarthritis

- Rheumatoid arthritis

- Infection

- Gout

- Pseudogout

- Prepatellar bursitis (kneecap bursitis)

- Cysts

- Tumours

- Repetitive strain injury

Having osteoarthritis or engaging in high-risk sports that involve rapid cut-and-run movements of the knee — football or tennis, for example — means an individual is more likely to develop water on the knee.

In overweight or obese individuals the body places more weight on the knee joint. This causes more wear in the joint. Over time, the body may produce excess joint fluid.

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.

Shoulder arthritis is a clinical condition in which the joint that connects the ball of the arm bone (humeral head) to the shoulder blade socket (glenoid) has damaged or worn out cartilage. Normally the ends of the bone are covered with hyaline articular cartilage, a surface so smooth that the friction at the joint is less than that of an ice skate on ice. In arthritis, this cartilage is progressively lost, exposing the bone beneath. Shoulder arthritis is characterized by pain, stiffness, and loss of function and often by a grinding on shoulder motion.

One of the three forms of shoulder arthritis is osteoarthritis. Osteoarthritis is the gradual wearing down of the joint cartilage that occurs predominantly in elderly people, and sometimes as the result of overuse in athletes. Post-traumatic arthritis happens after a significant trauma is sustained by the joint, ruining the cartilage. This could be the result of a car accident or after repeated trauma. Rheumatoid arthritis is a disease where the body attacks its own cartilage and destroys it. In each of these cases, cartilage is being destroyed.

The main symptom of shoulder arthritis is pain; this is due to the grinding of the bones against each other because of the lack of cartilage. Pain usually occurs in the front of the shoulder and is worse with motion. People with shoulder arthritis will also experience moderate to severe weakness, stiffness developing over many years, and the inability to sleep on the affected shoulder.

Hip dysplasia may be caused by a femur that does not fit correctly into the pelvic socket, or poorly developed muscles in the pelvic area. Large and giant breeds are most susceptible to hip dysplasia (possibly due to the body mass index (BMI) of the individual animal, though, many other breeds can suffer from it. The Orthopedic Foundation for Animals maintains a list of top 100 breeds affected.

To reduce pain, the animal will typically reduce its movement of that hip. This may be visible as "bunny hopping", where both legs move together, or less dynamic movement (running, jumping), or stiffness. Since the hip cannot move fully, the body compensates by adapting its use of the spine, often causing spinal, stifle (a dog's knee joint), or soft tissue problems to arise.

The causes of hip dysplasia are considered heritable, but new research conclusively suggests that environment also plays a role. To what degree the causality is genetic and what portion environmental is a topic of current debate. Neutering a dog, especially before the dog has reached an age of full developmental maturity, has been proven to almost double the chance he or she will develop hip dysplasia versus intact dogs or dogs that were neutered after reaching adulthood Other environmental influences include overweight condition, injury at a young age, overexertion on the hip joint at a young age, ligament tear at a young age, repetitive motion on forming joint (i.e. jogging with puppy under the age of 1 year). As current studies progress, greater information may help provide procedures to effectively reduce the occurrence of this condition.

The problem almost always appears by the time the dog is 18 months old. The defect can be anywhere from mild to severely crippling, and can eventually cause severe osteoarthritis.

It is most common in medium-large pure bred dogs, such as Newfoundlands, German Shepherd Dogs, retrievers (such as Labradors, Tollers, or Goldens), rottweilers and Mastiff, but also occurs in some smaller breeds such as spaniels and pugs.

Arthritis is predominantly a disease of the elderly, but children can also be affected by the disease. More than 70% of individuals in North America affected by arthritis are over the age of 65. Arthritis is more common in women than men at all ages and affects all races, ethnic groups and cultures. In the United States a CDC survey based on data from 2007–2009 showed 22.2% (49.9 million) of adults aged ≥18 years had self-reported doctor-diagnosed arthritis, and 9.4% (21.1 million or 42.4% of those with arthritis) had arthritis-attributable activity limitation (AAAL). With an aging population, this number is expected to increase.

Disability due to musculoskeletal disorders increased by 45% from 1990 to 2010. Of these, osteoarthritis is the fastest increasing major health condition. Among the many reports on the increased prevalence of musculoskeletal conditions, data from Africa are lacking and underestimated. A systematic review assessed the prevalence of arthritis in Africa and included twenty population-based and seven hospital-based studies. The majority of studies, twelve, were from South Africa. Nine studies were well-conducted, eleven studies were of moderate quality, and seven studies were conducted poorly. The results of the systematic review were as follows:

- Rheumatoid arthritis: 0.1% in Algeria (urban setting); 0.6% in Democratic Republic of Congo (urban setting); 2.5% and 0.07% in urban and rural settings in South Africa respectively; 0.3% in Egypt (rural setting), 0.4% in Lesotho (rural setting)

- Osteoarthritis: 55.1% in South Africa (urban setting); ranged from 29.5 to 82.7% in South Africans aged 65 years and older

- Knee osteoarthritis has the highest prevalence from all types of osteoarthritis, with 33.1% in rural South Africa

- Ankylosing spondylitis: 0.1% in South Africa (rural setting)

- Psoriatic arthritis: 4.4% in South Africa (urban setting)

- Gout: 0.7% in South Africa (urban setting)

- Juvenile idiopathic arthritis: 0.3% in Egypt (urban setting)

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.

Eburnation describes a degenerative process of bone commonly found in patients with osteoarthritis or non-union of fractures. It is an ivory-like reaction of bone occurring at the site of cartilage erosion. Osteoarthritis is a degenerative disease of the joints characterized largely by central loss of cartilage and compensatory peripheral bone formation (osteophytes). Over time, as the cartilage wears away, bare, subchondral bone is revealed. Eburnation describes the bony sclerosis which occurs at the areas of cartilage loss.

There are several conditions and syndromes that can affect the cervical spine and they all vary due to the difference in place and type of injury.

- Rheumatoid arthritis Those infected with rheumatoid arthritis in their cervical spine are known to have neurological deficits. It results in occipital pain and myelopathy.

- Occipito-cervical junction This disorder may result from rheumatoid arthritis, causing the hyper-mobility of the connection between the neck and head, resulting in paralysis or pain.

- Cerebrovascular disease Cerebrovascular disease is a type of cervical spine disorder that can cause tetraplegia.

- Subaxial cervical spine

- Atlanto-axial joint

If an individual has injured his or her knee, he or she may note bruising on the front, sides or rear of the knee. Bearing weight on the knee joint may be impossible and the pain unbearable.bruising may be seen as bluish lesion.

SLAC and SNAC are both caused by injury, for example a fall on an extended hand. SLAC is caused by rupture of the scapholunate ligament, SNAC is caused by a scaphoid fracture which does not heal and because of that will develop in a non-union fracture. SLAC is more common than SNAC; 55% of the patients with wrist osteoarthritis has a SLAC wrist. Although they have a different underlying pathology, they both lead to abnormal wrist kinematics which will eventually lead to osteoarthritis of the wrist.

Spondylosis is caused from years of constant abnormal pressure, from joint subluxation, sports, or poor posture, being placed on the vertebrae, and the discs between them. The abnormal stress causes the body to form new bone in order to compensate for the new weight distribution. This abnormal weight bearing from bone displacement will cause spondylosis to occur. Poor postures and loss of the normal spinal curves can lead to spondylosis as well. Spondylosis can affect a person at any age; however, older people are more susceptible.

Monoarthritis is inflammation ("arthritis") of one joint at a time. It is usually caused by trauma, infection, or crystalline arthritis.

The hip could have major contractions or seizures from dysplasias. The caput is not deeply and tightly held by the acetabulum. Instead of being a snug fit, it is a loose fit, or a partial fit. Secondly, the caput or acetabulum are not smooth and round, but are misshapen, causing abnormal wear and tear or friction within the joint as it moves.

The body reacts to this in several ways. First, the joint itself is continually repairing itself and laying down new cartilage. However, cartilage repair is a relatively slow process, the tissue being avascular, so the joint may suffer degradation due to the abnormal wear and tear, or may not support the body weight as intended. The joint becomes inflamed and a cycle of cartilage damage, inflammation and pain commences. This is a self-fueling process, in that the more the joint becomes damaged, the less able it is to resist further damage. The inflammation causes further damage. The bones of the joint may also develop osteoarthritis, visible on an X-ray as small outcrops of bone, which further degrade the joint. Osteoarthritis is a degenerative disease marked by the breakdown of cartilage between joints resulting in painful bone-to-bone contact.

The underlying deformity of the joint may get worse over time, or may remain static. A dog may have good X-rays and yet be in pain, or may have very poor X-rays and have no apparent pain issues. The hip condition is only one factor to determine the extent to which dysplasia is causing pain or affecting the quality of life. In mild to moderate dysplasia it is often the secondary effects of abnormal wear and tear or arthritis, rather than dysplasia itself, which is the direct causes of visible problems.

Septic arthritis is due to a bacterial infection to the joint. It requires urgent joint washout in the operating room followed by intravenous antibiotic therapy for large joints. Small joints or children can be treated with repeated aspirations and intravenous antibiotics.

CPPD affects people of all cultures and ethnic origins, and, in the United States, around 50% of the population over 85 years of age are affected. It may cause considerable pain, but it is never fatal. Women are at a slightly higher risk than men, with an estimated ratio of occurrence of 1.4:1.